import and export of routes, ref #192

refactoring and tests
remove unused fields
2026-10-09 23:26:31 +00:00 · 2026-10-09 09:26:38 +02:00 · 2026-10-09 08:58:00 +02:00 · 2026-10-08 21:19:53 +02:00 · 2026-10-08 21:13:44 +02:00 · 2026-10-08 21:04:29 +02:00
324 changed files with 34407 additions and 13084 deletions
@@ -27,17 +27,16 @@ Any help is greatly appreciated!

 The code is split into two parts:

- `gpx`: a Typescript library for parsing and manipulating GPX files,
+- `gpx-rs`: a Rust library, compiled to WebAssembly, for parsing and manipulating GPX files,
 - `website`: the website itself, which is a [SvelteKit](https://kit.svelte.dev/) application.

-You will need [Node.js](https://nodejs.org/) to build and run these two parts.
+You will need [Node.js](https://nodejs.org/), [Rust](https://rustup.rs/) and [wasm-pack](https://rustwasm.github.io/wasm-pack/) to build and run these two parts.

-### Building the `gpx` library
+### Building the `gpx-rs` library

 ```bash
-cd gpx
-npm install
-npm run build
+cd gpx-rs
+wasm-pack build wasm --target bundler --out-dir ../pkg
 ```

 ### Running the website
@@ -64,9 +63,6 @@ This project has been made possible thanks to the following open source projects
    - [tailwindcss](https://github.com/tailwindlabs/tailwindcss) — easy styling
    - [Chart.js](https://github.com/chartjs/Chart.js) — beautiful and fast charts
 - Logic:
-    - [immer](https://github.com/immerjs/immer) — complex state management
-    - [Dexie.js](https://github.com/dexie/Dexie.js) — IndexedDB wrapper
-    - [fast-xml-parser](https://github.com/NaturalIntelligence/fast-xml-parser) — fast GPX file parsing
    - [SortableJS](https://github.com/SortableJS/Sortable) — creating a sortable file tree
 - Mapping:
    - [MapLibre GL JS](https://github.com/maplibre/maplibre-gl-js) — beautiful and fast interactive map rendering
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+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
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+ "thiserror-impl",
+]
+
+[[package]]
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+ "quote",
+ "syn 3.0.6",
+]
+
+[[package]]
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+checksum = "e95f91fcc7a621e8b030f6aa23c71fe9838ae2fb4d8118b75602a328f5144044"
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+ "pin-project-lite",
+]
+
+[[package]]
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+[[package]]
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+ "getrandom",
+ "js-sys",
+ "serde_core",
+ "wasm-bindgen",
+]
+
+[[package]]
+name = "walkdir"
+version = "2.5.0"
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+ "same-file",
+ "winapi-util",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9bb54f33acc68fd454578d9820b0bde1a1a3d17aa17bb7b6595806d02886d409"
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+ "cfg-if",
+ "once_cell",
+ "rustversion",
+ "wasm-bindgen-macro",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
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+ "tokio",
+ "wasm-bindgen",
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+[[package]]
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+ "quote",
+ "wasm-bindgen-macro-support",
+]
+
+[[package]]
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+ "bumpalo",
+ "proc-macro2",
+ "quote",
+ "syn 3.0.6",
+ "wasm-bindgen-shared",
+]
+
+[[package]]
+name = "wasm-bindgen-shared"
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+[[package]]
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+ "async-trait",
+ "cast",
+ "js-sys",
+ "libm",
+ "minicov",
+ "nu-ansi-term",
+ "num-traits",
+ "oorandom",
+ "serde",
+ "serde_json",
+ "wasm-bindgen",
+ "wasm-bindgen-futures",
+ "wasm-bindgen-test-macro",
+ "wasm-bindgen-test-shared",
+]
+
+[[package]]
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+ "proc-macro2",
+ "quote",
+ "syn 3.0.6",
+]
+
+[[package]]
+name = "wasm-bindgen-test-shared"
+version = "0.2.129"
+source = "registry+https://github.com/rust-lang/crates.io-index"
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+
+[[package]]
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+checksum = "88261b9deccee56594c11a3460c462c41f58d148598fe70ad77070126a68aba4"
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+ "js-sys",
+ "wasm-bindgen",
+]
+
+[[package]]
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+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c2a7b1c03c876122aa43f3020e6c3c3ee5c05081c9a00739faf7503aeba10d22"
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+ "windows-sys",
+]
+
+[[package]]
+name = "windows-core"
+version = "0.62.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b8e83a14d34d0623b51dce9581199302a221863196a1dde71a7663a4c2be9deb"
+dependencies = [
+ "windows-implement",
+ "windows-interface",
+ "windows-link",
+ "windows-result",
+ "windows-strings",
+]
+
+[[package]]
+name = "windows-implement"
+version = "0.60.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "053e2e040ab57b9dc951b72c264860db7eb3b0200ba345b4e4c3b14f67855ddf"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.118",
+]
+
+[[package]]
+name = "windows-interface"
+version = "0.59.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3f316c4a2570ba26bbec722032c4099d8c8bc095efccdc15688708623367e358"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn 2.0.118",
+]
+
+[[package]]
+name = "windows-link"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f0805222e57f7521d6a62e36fa9163bc891acd422f971defe97d64e70d0a4fe5"
+
+[[package]]
+name = "windows-result"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7781fa89eaf60850ac3d2da7af8e5242a5ea78d1a11c49bf2910bb5a73853eb5"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
+name = "windows-strings"
+version = "0.5.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7837d08f69c77cf6b07689544538e017c1bfcf57e34b4c0ff58e6c2cd3b37091"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
+name = "windows-sys"
+version = "0.61.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ae137229bcbd6cdf0f7b80a31df61766145077ddf49416a728b02cb3921ff3fc"
+dependencies = [
+ "windows-link",
+]
+
+[[package]]
+name = "zmij"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "29666d0abbfad1e3dc4dcf6144730dd3a3ab225bbbdac83319345b1b44ccfc1b"
@@ -0,0 +1,6 @@
+[workspace]
+members = ["engine", "wasm"]
+resolver = "3"
+
+[profile.release]
+debug = true
@@ -0,0 +1,14 @@
+# gpx-rs
+
+- `engine`: the GPX engine, plain Rust. Tested natively: `cargo test`.
+- `wasm`: the interface to the web page, compiled to WebAssembly.
+
+```
+wasm-pack build wasm --target bundler --out-dir ../pkg
+```
+
+The interface is tested in Node (it needs `wasm-pack`, which fetches the test runner the first time):
+
+```
+wasm-pack test --node wasm
+```
@@ -0,0 +1,11 @@
+[package]
+name = "gpx-engine"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+chrono = "0.4.45"
+postcard = { version = "1.1.3", features = ["use-std"] }
+quick-xml = "0.42.0"
+serde = { version = "1.0.229", features = ["derive"] }
+uuid = { version = "1.26.1", features = ["serde", "v4"] }
@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<gpx version="1.1" creator="gpx.studio" xmlns="http://www.topografix.com/GPX/1/1"
+     xmlns:ext="https://example.com/ext/0.1">
+    <metadata>
+        <name>self closing points</name>
+        <desc>Points without children are self-closing elements.</desc>
+        <extensions>
+            <ext:version>2.0</ext:version>
+            <ext:paths/>
+        </extensions>
+    </metadata>
+    <wpt lat="50.0" lon="4.0"/>
+    <wpt lat="50.1" lon="4.1"><name>with children</name></wpt>
+    <wpt lat="50.2" lon="4.2"/>
+    <trk>
+        <name>track</name>
+        <trkseg>
+            <trkpt lat="50.00" lon="4.00"/>
+            <trkpt lat="50.01" lon="4.01"><ele>12.5</ele></trkpt>
+            <trkpt lat="50.02" lon="4.02"/>
+        </trkseg>
+        <trkseg>
+            <trkpt lat="51.00" lon="5.00"/>
+        </trkseg>
+    </trk>
+</gpx>
@@ -1,18 +1,32 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <gpx xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xmlns="http://www.topografix.com/GPX/1/1" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd http://www.garmin.com/xmlschemas/TrackPointExtension/v1 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd http://www.topografix.com/GPX/gpx_style/0/2 http://www.topografix.com/GPX/gpx_style/0/2/gpx_style.xsd"
+    xmlns="http://www.topografix.com/GPX/1/1"
+    xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd
+                        http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd
+                        http://www.garmin.com/xmlschemas/TrackPointExtension/v1 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd
+                        http://www.topografix.com/GPX/gpx_style/0/2 http://www.topografix.com/GPX/gpx_style/0/2/gpx_style.xsd"
    xmlns:gpxtpx="http://www.garmin.com/xmlschemas/TrackPointExtension/v1"
    xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3"
-    xmlns:gpx_style="http://www.topografix.com/GPX/gpx_style/0/2" version="1.1" creator="https://gpx.studio">
+    xmlns:gpx_style="http://www.topografix.com/GPX/gpx_style/0/2" version="1.1"
+    creator="https://gpx.studio">
    <metadata>
        <name>simple</name>
+        <desc>description</desc>
        <author>
            <name>gpx.studio</name>
-            <link href="https://gpx.studio"></link>
+            <link href="https://gpx.studio">
+                <text>link text</text>
+            </link>
        </author>
    </metadata>
    <trk>
-        <name>simple</name>
+        <name>track name</name>
+        <cmt>track comment</cmt>
+        <desc>track description</desc>
+        <src>track source</src>
+        <link href="https://gpx.studio">
+            <text>track link text</text>
+        </link>
        <type>Cycling</type>
        <trkseg>
            <trkpt lat="50.790867" lon="4.404968">
@@ -0,0 +1,62 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<gpx xmlns="http://www.topografix.com/GPX/1/1"
+    xmlns:gpxtpx="http://www.garmin.com/xmlschemas/TrackPointExtension/v1" version="1.1" creator="https://gpx.studio">
+    <metadata>
+        <name>with_highway</name>
+    </metadata>
+    <trk>
+        <name>with_highway</name>
+        <trkseg>
+            <trkpt lat="50.790867" lon="4.404968">
+                <ele>109.0</ele>
+                <extensions>
+                    <gpxtpx:TrackPointExtension>
+                        <gpxtpx:Extensions>
+                            <surface>asphalt</surface>
+                            <highway>residential</highway>
+                        </gpxtpx:Extensions>
+                    </gpxtpx:TrackPointExtension>
+                </extensions>
+            </trkpt>
+            <trkpt lat="50.791000" lon="4.405100">
+                <ele>110.0</ele>
+                <extensions>
+                    <gpxtpx:TrackPointExtension>
+                        <gpxtpx:Extensions>
+                            <surface>asphalt</surface>
+                            <highway>residential</highway>
+                        </gpxtpx:Extensions>
+                    </gpxtpx:TrackPointExtension>
+                </extensions>
+            </trkpt>
+            <trkpt lat="50.791200" lon="4.405300">
+                <ele>111.0</ele>
+            </trkpt>
+            <trkpt lat="50.791400" lon="4.405500">
+                <ele>112.0</ele>
+                <extensions>
+                    <gpxtpx:TrackPointExtension>
+                        <gpxtpx:Extensions>
+                            <surface>gravel</surface>
+                            <highway>track</highway>
+                            <sac_scale>mountain_hiking</sac_scale>
+                            <mtb_scale>1</mtb_scale>
+                        </gpxtpx:Extensions>
+                    </gpxtpx:TrackPointExtension>
+                </extensions>
+            </trkpt>
+            <trkpt lat="50.791600" lon="4.405700">
+                <ele>113.0</ele>
+                <extensions>
+                    <gpxtpx:TrackPointExtension>
+                        <gpxtpx:Extensions>
+                            <surface>gravel</surface>
+                            <sac_scale>hiking</sac_scale>
+                            <mtb_scale>1</mtb_scale>
+                        </gpxtpx:Extensions>
+                    </gpxtpx:TrackPointExtension>
+                </extensions>
+            </trkpt>
+        </trkseg>
+    </trk>
+</gpx>
@@ -0,0 +1,38 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<gpx xmlns="http://www.topografix.com/GPX/1/1" version="1.1" creator="test">
+    <metadata>
+        <name>with links</name>
+        <author>
+            <name>someone</name>
+            <email id="someone" domain="example.com"/>
+            <link href="https://example.com/author"><text>author</text></link>
+        </author>
+        <link href="https://example.com/file-1"><text>first</text></link>
+        <link href="https://example.com/file-2"/>
+    </metadata>
+    <wpt lat="50" lon="4">
+        <name>summit</name>
+        <link href="https://example.com/wpt-1"><text>one</text></link>
+        <link href="https://example.com/wpt-2"/>
+        <link href="https://example.com/wpt-3"><text>three</text></link>
+    </wpt>
+    <trk>
+        <name>track</name>
+        <link href="https://example.com/trk-1"/>
+        <link href="https://example.com/trk-2"><text>two</text></link>
+        <trkseg>
+            <trkpt lat="50" lon="4"/>
+            <trkpt lat="50.1" lon="4.1"/>
+        </trkseg>
+    </trk>
+    <rte>
+        <name>route</name>
+        <link href="https://example.com/rte-1"/>
+        <link href="https://example.com/rte-2"/>
+        <rtept lat="51" lon="5"/>
+        <rtept lat="51.1" lon="5.1"/>
+    </rte>
+    <wpt lat="51" lon="5">
+        <name>email variants</name>
+    </wpt>
+</gpx>
@@ -1,9 +1,14 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <gpx xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xmlns="http://www.topografix.com/GPX/1/1" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd http://www.garmin.com/xmlschemas/TrackPointExtension/v1 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd http://www.topografix.com/GPX/gpx_style/0/2 http://www.topografix.com/GPX/gpx_style/0/2/gpx_style.xsd"
+    xmlns="http://www.topografix.com/GPX/1/1"
+    xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd
+                        http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd
+                        http://www.garmin.com/xmlschemas/TrackPointExtension/v1 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd
+                        http://www.topografix.com/GPX/gpx_style/0/2 http://www.topografix.com/GPX/gpx_style/0/2/gpx_style.xsd"
    xmlns:gpxtpx="http://www.garmin.com/xmlschemas/TrackPointExtension/v1"
-    xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3"
-    xmlns:gpx_style="http://www.topografix.com/GPX/gpx_style/0/2" version="1.1" creator="https://gpx.studio">
+    xmlns:gpxpx="http://www.garmin.com/xmlschemas/GpxExtensions/v3"
+    xmlns:gpx_style="http://www.topografix.com/GPX/gpx_style/0/2" version="1.1"
+    creator="https://gpx.studio">
    <metadata>
        <name>with_power</name>
        <author>
@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<gpx xmlns="http://www.topografix.com/GPX/1/1" xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3" version="1.1" creator="test">
+    <rte>
+        <name>with extensions</name>
+        <rtept lat="1" lon="1">
+            <ele>10</ele>
+            <extensions>
+                <gpxx:RoutePointExtension>
+                    <gpxx:rpt lat="1.1" lon="1.1"/>
+                    <gpxx:rpt lat="1.2" lon="1.2"></gpxx:rpt>
+                </gpxx:RoutePointExtension>
+            </extensions>
+        </rtept>
+        <rtept lat="2" lon="2">
+            <ele>20</ele>
+            <time>2024-01-01T00:00:00Z</time>
+        </rtept>
+        <rtept lat="3" lon="3"/>
+    </rte>
+    <rte>
+        <name>empty</name>
+    </rte>
+</gpx>
@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<gpx xmlns="http://www.topografix.com/GPX/1/1" xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3" version="1.1" creator="test">
+    <rte>
+        <name>Lausanne</name>
+        <cmt>comment</cmt>
+        <desc>description</desc>
+        <type>Cycling</type>
+        <rtept lat="46.544628096744418" lon="6.658079791814089">
+            <ele>500</ele>
+            <extensions>
+                <gpxx:RoutePointExtension>
+                    <gpxx:rpt lat="46.544483928009868" lon="6.658018603920937"/>
+                    <gpxx:rpt lat="46.544415950775146" lon="6.658358573913574"/>
+                    <gpxx:rpt lat="46.544415950775146" lon="6.658358573913574"/>
+                </gpxx:RoutePointExtension>
+            </extensions>
+        </rtept>
+        <rtept lat="46.544100000000000" lon="6.659000000000000">
+            <ele>510</ele>
+            <extensions>
+                <gpxx:RoutePointExtension>
+                    <gpxx:rpt lat="46.543900000000000" lon="6.659500000000000"/>
+                </gpxx:RoutePointExtension>
+            </extensions>
+        </rtept>
+        <rtept lat="46.543000000000000" lon="6.660000000000000">
+            <ele>505</ele>
+        </rtept>
+    </rte>
+</gpx>
@@ -1,9 +1,14 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <gpx xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xmlns="http://www.topografix.com/GPX/1/1" xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd http://www.garmin.com/xmlschemas/TrackPointExtension/v1 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd http://www.topografix.com/GPX/gpx_style/0/2 http://www.topografix.com/GPX/gpx_style/0/2/gpx_style.xsd"
+    xmlns="http://www.topografix.com/GPX/1/1"
+    xsi:schemaLocation="http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd
+                        http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd
+                        http://www.garmin.com/xmlschemas/TrackPointExtension/v1 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd
+                        http://www.topografix.com/GPX/gpx_style/0/2 http://www.topografix.com/GPX/gpx_style/0/2/gpx_style.xsd"
    xmlns:gpxtpx="http://www.garmin.com/xmlschemas/TrackPointExtension/v1"
    xmlns:gpxx="http://www.garmin.com/xmlschemas/GpxExtensions/v3"
-    xmlns:gpx_style="http://www.topografix.com/GPX/gpx_style/0/2" version="1.1" creator="https://gpx.studio">
+    xmlns:gpx_style="http://www.topografix.com/GPX/gpx_style/0/2" version="1.1"
+    creator="https://gpx.studio">
    <metadata>
        <name>with_waypoint</name>
        <author>
@@ -13,10 +18,14 @@
    </metadata>
    <wpt lat="50.7836710064975" lon="4.410764082658738">
        <ele>122.0</ele>
-        <name>Waypoint</name>
-        <cmt>Comment</cmt>
-        <desc>Description</desc>
+        <name>waypoint name</name>
+        <cmt>waypoint comment</cmt>
+        <desc>waypoint description</desc>
+        <link href="https://gpx.studio">
+            <text>waypoint link text</text>
+        </link>
        <sym>Bike Trail</sym>
+        <type>Bike Trail</type>
    </wpt>
    <trk>
        <name>with_waypoint</name>
@@ -0,0 +1,112 @@
+use std::f64::consts::PI;
+
+use crate::{
+    TrackSegment, TrackSegmentIndex, core::utils::crossarc_lnglat, ramer_douglas_peucker_by,
+};
+
+/// Highest zoom level of the map at which an anchor can appear.
+pub const MAX_ANCHOR_ZOOM: u8 = 22;
+
+/// Details smaller than this (in meters) do not get an anchor.
+const ANCHOR_EPSILON: f64 = 1.0;
+
+const EARTH_RADIUS_METERS: f64 = 6371008.8;
+
+/// Lowest map zoom level at which an anchor selected at `distance` meters from the line of its
+/// neighbours is worth showing: the smaller the detail, the higher the zoom. The ends of a
+/// segment (no distance) are always shown.
+pub fn anchor_zoom(lat: f64, distance: Option<f64>) -> u8 {
+    let Some(distance) = distance else {
+        return 0;
+    };
+    let width = EARTH_RADIUS_METERS * (lat * PI / 180.0).cos() / distance;
+    width.log2().round().clamp(0.0, MAX_ANCHOR_ZOOM as f64) as u8
+}
+
+/// The anchors of a segment, as `(index, zoom)` sorted by index: the trackpoints kept by the
+/// Ramer-Douglas-Peucker simplification of its path, the ones for smaller details being shown at
+/// higher zoom levels only.
+pub fn compute_anchors(trkseg: &TrackSegment) -> Vec<(usize, u8)> {
+    let measure = |start: TrackSegmentIndex, end: TrackSegmentIndex, idx: TrackSegmentIndex| {
+        crossarc_lnglat(
+            trkseg[start].coordinates,
+            trkseg[end].coordinates,
+            trkseg[idx].coordinates,
+        )
+    };
+    ramer_douglas_peucker_by(trkseg, &measure, ANCHOR_EPSILON)
+        .into_iter()
+        .map(|(idx, distance)| (idx.flat, anchor_zoom(trkseg[idx].coordinates.lat, distance)))
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{LngLat, Trackpoint, TrackpointChunk};
+
+    use super::*;
+
+    fn segment(points: &[(f64, f64)]) -> TrackSegment {
+        let mut trkseg = TrackSegment::default();
+        let mut chunk = TrackpointChunk::default();
+        for (lng, lat) in points {
+            chunk.trkpt.push(Trackpoint {
+                coordinates: LngLat {
+                    lng: *lng,
+                    lat: *lat,
+                },
+                ..Default::default()
+            });
+        }
+        trkseg.push(chunk);
+        trkseg
+    }
+
+    #[test]
+    fn test_zoom_depends_on_the_size_of_the_detail() {
+        assert_eq!(anchor_zoom(45.0, None), 0);
+        // 2^13 meters is close to the radius of the earth divided by 1 km
+        assert_eq!(anchor_zoom(0.0, Some(1_000.0)), 13);
+        assert!(anchor_zoom(0.0, Some(10.0)) > anchor_zoom(0.0, Some(1_000.0)));
+        assert_eq!(anchor_zoom(0.0, Some(1e-9)), MAX_ANCHOR_ZOOM);
+        assert_eq!(anchor_zoom(0.0, Some(1e9)), 0);
+        // the poles do not give NaN or a panic
+        assert_eq!(anchor_zoom(90.0, Some(10.0)), 0);
+    }
+
+    #[test]
+    fn test_anchors_of_a_straight_line_are_its_ends() {
+        let line: Vec<_> = (0..10).map(|i| (i as f64 * 0.001, 0.0)).collect();
+        assert_eq!(compute_anchors(&segment(&line)), vec![(0, 0), (9, 0)]);
+    }
+
+    #[test]
+    fn test_anchors_keep_the_corners() {
+        // a big corner and a small bump
+        let points = [
+            (0.0, 0.0),
+            (0.01, 0.0),
+            (0.02, 0.0),
+            (0.02, 0.01),
+            (0.02, 0.02),
+            (0.02, 0.020005),
+            (0.02, 0.03),
+        ];
+        let anchors = compute_anchors(&segment(&points));
+        let indices: Vec<_> = anchors.iter().map(|(i, _)| *i).collect();
+        assert_eq!(indices, vec![0, 2, 6]);
+        assert_eq!(anchors[0].1, 0);
+        assert_eq!(anchors[2].1, 0);
+        assert!(anchors[1].1 > 0);
+    }
+
+    #[test]
+    fn test_anchors_of_short_segments() {
+        assert!(compute_anchors(&segment(&[])).is_empty());
+        assert_eq!(compute_anchors(&segment(&[(1.0, 2.0)])), vec![(0, 0)]);
+        assert_eq!(
+            compute_anchors(&segment(&[(1.0, 2.0), (1.0, 2.1)])),
+            vec![(0, 0), (1, 0)]
+        );
+    }
+}
@@ -0,0 +1,10 @@
+mod anchors;
+mod reverse;
+mod simplify;
+mod smooth;
+mod timestamps;
+
+pub use anchors::*;
+pub use reverse::*;
+pub use simplify::*;
+pub use timestamps::*;
@@ -0,0 +1,232 @@
+//! Reversing a path: the order of its trackpoints, and of the segments and tracks that hold them.
+//!
+//! The timestamps are mirrored, so that the reversed path goes through the same period of time:
+//! a trackpoint at time `t` of a part that spans `start..end` ends up at `start + end - t`. When
+//! the part is made of several ones (the segments of a track, the tracks of a file), the gaps
+//! between them are kept: every part comes after the previous one in the new order, as late as the
+//! original one came after the part that followed it.
+
+use crate::{Track, TrackSegment, Trackpoint};
+
+/// The time of the first trackpoint of a segment.
+pub fn start_time(segment: &TrackSegment) -> Option<i64> {
+    segment.iter().next().and_then(|trkpt| trkpt.time)
+}
+
+/// The time of the last trackpoint of a segment.
+pub fn end_time(segment: &TrackSegment) -> Option<i64> {
+    segment.last_index().and_then(|idx| segment[idx].time)
+}
+
+/// The time of the first trackpoint of a track.
+pub fn track_start_time(track: &Track) -> Option<i64> {
+    track.trkseg.first().and_then(start_time)
+}
+
+/// The time of the last trackpoint of a track.
+pub fn track_end_time(track: &Track) -> Option<i64> {
+    track.trkseg.last().and_then(end_time)
+}
+
+/// Reverses the trackpoints of a segment.
+///
+/// `original_next` is the time at which what came after the segment started, and `new_previous`
+/// the time at which what comes before it now ends: the segment is mirrored to start there. Both
+/// are those of the segment itself if the segment is reversed on its own, which are the ones
+/// used when they are missing (`new_previous` is the start of the segment, and `original_next`
+/// follows from the duration of the segment). Without timestamps, the trackpoints are only put
+/// in the opposite order.
+pub fn reverse_segment(
+    segment: &mut TrackSegment,
+    original_next: Option<i64>,
+    new_previous: Option<i64>,
+) {
+    let (original_start, original_end) = (start_time(segment), end_time(segment));
+    let new_previous = new_previous.or(original_start);
+    let original_next = original_next.or_else(|| {
+        // the segment lasts as long as before
+        Some(new_previous? + original_end? - original_start?)
+    });
+
+    let len = segment.len();
+    let mut points: Vec<Trackpoint> = segment.iter().cloned().collect();
+    if let (Some(next), Some(previous), Some(end)) = (original_next, new_previous, original_end) {
+        let new_start = previous + next - end;
+        for point in points.iter_mut() {
+            point.time = point.time.map(|time| new_start + (end - time));
+        }
+    }
+    points.reverse();
+    segment.splice(0, len, points);
+    segment.rev_id = Default::default();
+}
+
+/// Makes a segment go back where it started: a reversed copy of it is added after its last
+/// trackpoint, without the first trackpoint of the copy, which is the last one of the segment.
+///
+/// The timestamps of the copy go on from the end of the segment: it would start at the time of the
+/// last trackpoint, and it lasts as long as the segment. Only the end of the segment changes, so
+/// its other chunks stay shared.
+pub fn round_trip(segment: &mut TrackSegment) {
+    let len = segment.len();
+    let end = end_time(segment);
+    let mut back = segment.clone();
+    reverse_segment(&mut back, end, end);
+    segment.splice(len, len, back.iter().skip(1).cloned().collect());
+    segment.rev_id = Default::default();
+}
+
+/// Reverses the segments of a track, and their trackpoints: see [`reverse_segment`] for the
+/// meaning of the times, which are the ones of the track as a whole.
+pub fn reverse_segments(
+    segments: &mut [TrackSegment],
+    original_next: Option<i64>,
+    new_previous: Option<i64>,
+) {
+    segments.reverse();
+    let (mut next, mut previous) = (original_next, new_previous);
+    for segment in segments.iter_mut() {
+        // the next one is the one that was before, which started here
+        let original_start = start_time(segment);
+        reverse_segment(segment, next, previous);
+        next = original_start;
+        previous = end_time(segment);
+    }
+}
+
+/// Reverses the tracks of a file, and their segments and trackpoints.
+pub fn reverse_tracks(tracks: &mut [Track], original_next: Option<i64>, new_previous: Option<i64>) {
+    tracks.reverse();
+    let (mut next, mut previous) = (original_next, new_previous);
+    for track in tracks.iter_mut() {
+        let original_start = track_start_time(track);
+        reverse_segments(&mut track.trkseg, next, previous);
+        next = original_start;
+        previous = track_end_time(track);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::LngLat;
+
+    use super::*;
+
+    fn segment(points: &[(f64, Option<i64>)]) -> TrackSegment {
+        let mut segment = TrackSegment::default();
+        let points = points
+            .iter()
+            .map(|(lng, time)| Trackpoint {
+                coordinates: LngLat {
+                    lng: *lng,
+                    lat: 0.0,
+                },
+                time: *time,
+                ..Default::default()
+            })
+            .collect();
+        segment.splice(0, 0, points);
+        segment
+    }
+
+    fn lngs(segment: &TrackSegment) -> Vec<f64> {
+        segment.iter().map(|p| p.coordinates.lng).collect()
+    }
+
+    fn times(segment: &TrackSegment) -> Vec<Option<i64>> {
+        segment.iter().map(|p| p.time).collect()
+    }
+
+    #[test]
+    fn test_a_segment_is_mirrored_in_its_own_time_span() {
+        let mut s = segment(&[(0.0, Some(0)), (1.0, Some(10)), (2.0, Some(40))]);
+        let (start, end) = (start_time(&s), end_time(&s));
+        reverse_segment(&mut s, end, start);
+        assert_eq!(lngs(&s), [2.0, 1.0, 0.0]);
+        // same span, the durations between points follow the points
+        assert_eq!(times(&s), [Some(0), Some(30), Some(40)]);
+    }
+
+    #[test]
+    fn test_reverse_segment_defaults() {
+        // without the times around, the segment is mirrored where it is
+        let mut s = segment(&[(0.0, Some(100)), (1.0, Some(130))]);
+        reverse_segment(&mut s, None, None);
+        assert_eq!(times(&s), [Some(100), Some(130)]);
+        assert_eq!(lngs(&s), [1.0, 0.0]);
+    }
+
+    #[test]
+    fn test_a_segment_without_times_is_only_reversed() {
+        let mut s = segment(&[(0.0, None), (1.0, None), (2.0, None)]);
+        reverse_segment(&mut s, None, None);
+        assert_eq!(lngs(&s), [2.0, 1.0, 0.0]);
+        assert_eq!(times(&s), [None, None, None]);
+    }
+
+    #[test]
+    fn test_round_trip_goes_back_in_time_from_the_end() {
+        let mut s = segment(&[(0.0, Some(0)), (1.0, Some(10)), (2.0, Some(40))]);
+        let first = s.rev_id;
+        round_trip(&mut s);
+        assert_ne!(s.rev_id, first);
+        // the last trackpoint is the turning point, it is not repeated
+        assert_eq!(lngs(&s), [0.0, 1.0, 2.0, 1.0, 0.0]);
+        // the way back lasts as long as the way there, and starts when it ended
+        assert_eq!(times(&s), [Some(0), Some(10), Some(40), Some(70), Some(80)]);
+        // and it is a segment whose ends are anchors
+        assert_eq!(s[0].anchor, Some(0));
+        assert_eq!(s[4].anchor, Some(0));
+    }
+
+    #[test]
+    fn test_round_trip_without_times() {
+        let mut s = segment(&[(0.0, None), (1.0, None)]);
+        round_trip(&mut s);
+        assert_eq!(lngs(&s), [0.0, 1.0, 0.0]);
+        assert_eq!(times(&s), [None; 3]);
+    }
+
+    #[test]
+    fn test_segments_keep_the_gaps_between_them() {
+        // 0..20, then 100..120: a gap of 80
+        let mut segments = vec![
+            segment(&[(0.0, Some(0)), (1.0, Some(10)), (2.0, Some(20))]),
+            segment(&[(3.0, Some(100)), (4.0, Some(110)), (5.0, Some(120))]),
+        ];
+        let (end, start) = (end_time(&segments[1]), start_time(&segments[0]));
+        reverse_segments(&mut segments, end, start);
+        assert_eq!(lngs(&segments[0]), [5.0, 4.0, 3.0]);
+        assert_eq!(lngs(&segments[1]), [2.0, 1.0, 0.0]);
+        assert_eq!(times(&segments[0]), [Some(0), Some(10), Some(20)]);
+        // the gap is still 80
+        assert_eq!(times(&segments[1]), [Some(100), Some(110), Some(120)]);
+    }
+
+    #[test]
+    fn test_tracks_are_reversed_like_segments() {
+        let track = |segments: Vec<TrackSegment>| Track {
+            trkseg: segments,
+            ..Default::default()
+        };
+        let mut tracks = vec![
+            track(vec![
+                segment(&[(0.0, Some(0)), (1.0, Some(10))]),
+                segment(&[(2.0, Some(50)), (3.0, Some(60))]),
+            ]),
+            track(vec![segment(&[(4.0, Some(200)), (5.0, Some(230))])]),
+        ];
+        let (end, start) = (track_end_time(&tracks[1]), track_start_time(&tracks[0]));
+        reverse_tracks(&mut tracks, end, start);
+        let all: Vec<f64> = tracks
+            .iter()
+            .flat_map(|t| t.trkseg.iter().flat_map(lngs))
+            .collect();
+        assert_eq!(all, [5.0, 4.0, 3.0, 2.0, 1.0, 0.0]);
+        // 3 segments: durations 10, 10, 30 and gaps 40 and 140 are reversed to 30, 10, 10 and
+        // gaps 140 and 40 (the first part of the time is the longest)
+        assert_eq!(times(&tracks[0].trkseg[0]), [Some(0), Some(30)]);
+        assert_eq!(times(&tracks[1].trkseg[0]), [Some(170), Some(180)]);
+        assert_eq!(times(&tracks[1].trkseg[1]), [Some(220), Some(230)]);
+    }
+}
@@ -0,0 +1,232 @@
+use crate::{
+    core::gpx::{TrackSegment, TrackSegmentIndex},
+    core::utils::{crossarc, crossarc_lnglat},
+};
+
+pub fn ramer_douglas_peucker<F>(
+    trkseg: &TrackSegment,
+    mapping: &F,
+    epsilon: f64,
+) -> Vec<TrackSegmentIndex>
+where
+    F: Fn(TrackSegmentIndex) -> (f64, f64),
+{
+    let measure = |start, end, idx| {
+        let (start, end, pt) = (mapping(start), mapping(end), mapping(idx));
+        crossarc(start.0, start.1, end.0, end.1, pt.0, pt.1)
+    };
+    ramer_douglas_peucker_by(trkseg, &measure, epsilon)
+        .into_iter()
+        .map(|(idx, _)| idx)
+        .collect()
+}
+
+/// Ramer-Douglas-Peucker with any distance from a point (the last argument) to the line made of
+/// two others (the first ones). Gives the kept points, with the distance at which each of them
+/// was selected (`None` for the ends of the segment, which are always kept).
+pub fn ramer_douglas_peucker_by<M>(
+    trkseg: &TrackSegment,
+    measure: &M,
+    epsilon: f64,
+) -> Vec<(TrackSegmentIndex, Option<f64>)>
+where
+    M: Fn(TrackSegmentIndex, TrackSegmentIndex, TrackSegmentIndex) -> f64,
+{
+    match trkseg.len() {
+        0 => vec![],
+        1 => vec![(trkseg.first_index().unwrap(), None)],
+        2 => vec![
+            (trkseg.first_index().unwrap(), None),
+            (trkseg.last_index().unwrap(), None),
+        ],
+        _ => {
+            let first = trkseg.first_index().unwrap();
+            let last = trkseg.last_index().unwrap();
+
+            let mut kept = vec![(first, None)];
+            ramer_douglas_peucker_helper(trkseg, first, last, measure, epsilon, &mut kept);
+            kept.push((last, None));
+            kept
+        }
+    }
+}
+
+fn ramer_douglas_peucker_helper<M>(
+    trkseg: &TrackSegment,
+    start: TrackSegmentIndex,
+    end: TrackSegmentIndex,
+    measure: &M,
+    epsilon: f64,
+    kept: &mut Vec<(TrackSegmentIndex, Option<f64>)>,
+) where
+    M: Fn(TrackSegmentIndex, TrackSegmentIndex, TrackSegmentIndex) -> f64,
+{
+    let mut max_idx = None;
+    let mut max_dist = 0.0;
+
+    let mut cur = trkseg.next_index(Some(start));
+    while let Some(idx) = cur {
+        if idx == end {
+            break;
+        }
+
+        let dist = measure(start, end, idx);
+        if dist > max_dist {
+            max_idx = Some(idx);
+            max_dist = dist;
+        }
+
+        cur = trkseg.next_index(cur);
+    }
+
+    if let Some(idx) = max_idx.filter(|_| max_dist > epsilon) {
+        ramer_douglas_peucker_helper(trkseg, start, idx, measure, epsilon, kept);
+        kept.push((idx, Some(max_dist)));
+        ramer_douglas_peucker_helper(trkseg, idx, end, measure, epsilon, kept);
+    }
+}
+
+/// Lowest tolerance (in meters) of the reduction of a segment, see [`reduction_distances`].
+pub const MIN_REDUCE_TOLERANCE: f64 = 0.1;
+
+/// The distance (in meters) from a trackpoint to the line between two others of a segment.
+fn lnglat_measure(
+    trkseg: &TrackSegment,
+) -> impl Fn(TrackSegmentIndex, TrackSegmentIndex, TrackSegmentIndex) -> f64 + '_ {
+    move |start, end, idx| {
+        crossarc_lnglat(
+            trkseg[start].coordinates,
+            trkseg[end].coordinates,
+            trkseg[idx].coordinates,
+        )
+    }
+}
+
+/// The indices of the trackpoints of a segment that are kept when it is reduced with `tolerance`
+/// meters (Ramer-Douglas-Peucker), in order. The ends are always kept.
+pub fn reduce_indices(trkseg: &TrackSegment, tolerance: f64) -> Vec<usize> {
+    ramer_douglas_peucker_by(trkseg, &lnglat_measure(trkseg), tolerance)
+        .into_iter()
+        .map(|(idx, _)| idx.flat)
+        .collect()
+}
+
+/// For each trackpoint of a segment, the tolerance (in meters) up to which it is kept by
+/// [`reduce_indices`]: infinite for the ends, which are always kept, zero for the trackpoints that
+/// are not selected even at [`MIN_REDUCE_TOLERANCE`]. A trackpoint is kept with a tolerance if its
+/// value is greater than it.
+///
+/// A trackpoint is only selected if the ones that split the path before it are, so its value is
+/// the smallest distance at which it or one of them was selected.
+pub fn reduction_distances(trkseg: &TrackSegment) -> Vec<f64> {
+    let mut distances = vec![0.0; trkseg.len()];
+    let (Some(first), Some(last)) = (trkseg.first_index(), trkseg.last_index()) else {
+        return distances;
+    };
+    distances[first.flat] = f64::INFINITY;
+    distances[last.flat] = f64::INFINITY;
+    if trkseg.len() > 2 {
+        let measure = lnglat_measure(trkseg);
+        reduction_distances_helper(trkseg, first, last, &measure, f64::INFINITY, &mut distances);
+    }
+    distances
+}
+
+fn reduction_distances_helper<M>(
+    trkseg: &TrackSegment,
+    start: TrackSegmentIndex,
+    end: TrackSegmentIndex,
+    measure: &M,
+    bound: f64,
+    distances: &mut [f64],
+) where
+    M: Fn(TrackSegmentIndex, TrackSegmentIndex, TrackSegmentIndex) -> f64,
+{
+    let mut max_idx = None;
+    let mut max_dist = 0.0;
+    let mut cur = trkseg.next_index(Some(start));
+    while let Some(idx) = cur {
+        if idx == end {
+            break;
+        }
+        let dist = measure(start, end, idx);
+        if dist > max_dist {
+            max_idx = Some(idx);
+            max_dist = dist;
+        }
+        cur = trkseg.next_index(cur);
+    }
+
+    if let Some(idx) = max_idx.filter(|_| max_dist > MIN_REDUCE_TOLERANCE) {
+        let distance = max_dist.min(bound);
+        distances[idx.flat] = distance;
+        reduction_distances_helper(trkseg, start, idx, measure, distance, distances);
+        reduction_distances_helper(trkseg, idx, end, measure, distance, distances);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{Trackpoint, TrackpointChunk};
+
+    use super::*;
+
+    fn segment(eles: &[f64]) -> TrackSegment {
+        let mut trkseg = TrackSegment::default();
+        // several small chunks, to also exercise the chunk boundaries
+        for part in eles.chunks(3) {
+            let mut chunk = TrackpointChunk::default();
+            for ele in part {
+                chunk.trkpt.push(Trackpoint {
+                    ele: *ele,
+                    ..Default::default()
+                });
+            }
+            trkseg.push(chunk);
+        }
+        trkseg
+    }
+
+    fn simplify(eles: &[f64], epsilon: f64) -> Vec<usize> {
+        let trkseg = segment(eles);
+        ramer_douglas_peucker(&trkseg, &|idx| (idx.flat as f64, trkseg[idx].ele), epsilon)
+            .iter()
+            .map(|idx| idx.flat)
+            .collect()
+    }
+
+    #[test]
+    fn test_empty_and_single_point() {
+        assert!(simplify(&[], 1.0).is_empty());
+        assert_eq!(simplify(&[5.0], 1.0), vec![0]);
+    }
+
+    #[test]
+    fn test_collinear_points_are_removed() {
+        let eles: Vec<f64> = (0..20).map(|i| i as f64 * 2.0).collect();
+        assert_eq!(simplify(&eles, 0.1), vec![0, 19]);
+    }
+
+    #[test]
+    fn test_peak_is_kept_when_above_epsilon() {
+        let eles = [0.0, 0.0, 0.0, 10.0, 0.0, 0.0, 0.0];
+        assert_eq!(simplify(&eles, 5.0), vec![0, 3, 6]);
+    }
+
+    #[test]
+    fn test_peak_is_dropped_when_below_epsilon() {
+        let eles = [0.0, 0.0, 0.0, 0.5, 0.0, 0.0, 0.0];
+        assert_eq!(simplify(&eles, 1.0), vec![0, 6]);
+    }
+
+    #[test]
+    fn test_indices_are_sorted_and_keep_extremities() {
+        let eles = [0.0, 5.0, -3.0, 8.0, 1.0, 9.0, -4.0, 2.0, 7.0, 0.0];
+        let kept = simplify(&eles, 0.5);
+        assert_eq!(kept.first(), Some(&0));
+        assert_eq!(kept.last(), Some(&9));
+        assert!(kept.windows(2).all(|w| w[0] < w[1]));
+        // a larger epsilon never keeps more points
+        assert!(simplify(&eles, 5.0).len() <= kept.len());
+    }
+}
@@ -0,0 +1,141 @@
+#[macro_export]
+macro_rules! for_each_window {
+    (
+        $trkseg:expr,
+        $left:expr,
+        $right:expr,
+        $window:expr,
+        |$a:ident, $b:ident| $distance:expr,
+        |$i:ident, $l:ident, $r:ident| $body:block,
+    ) => {{
+        let mut window_start = $left.unwrap_or_default();
+        let mut window_center = $left;
+        let mut window_end = $left.unwrap_or_default();
+        while let Some(idx) = window_center {
+            // advance left if needed
+            while window_start != idx && {
+                let $a = window_start;
+                let $b = idx;
+                $distance
+            } > $window {
+                if let Some(next) = $trkseg.next_index(Some(window_start)) {
+                    if next == idx {
+                        break;
+                    }
+                    window_start = next;
+                } else {
+                    break;
+                }
+            }
+            // advance right if needed
+            window_end = window_end.max(idx);
+            while let Some(next) = $trkseg.next_index(Some(window_end)) {
+                if window_end != idx && {
+                    let $a = idx;
+                    let $b = next;
+                    $distance
+                } > $window {
+                    break;
+                }
+                window_end = next;
+            }
+            // apply body
+            let $i = idx;
+            let $l = window_start;
+            let $r = window_end;
+            $body
+            // go next
+            if window_center == $right {
+                break;
+            }
+            window_center = $trkseg.next_index(window_center);
+        }
+    }};
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{TrackSegment, Trackpoint, TrackpointChunk};
+
+    fn segment(eles: &[f64]) -> TrackSegment {
+        let mut trkseg = TrackSegment::default();
+        // several small chunks, to also exercise the chunk boundaries
+        for part in eles.chunks(3) {
+            let mut chunk = TrackpointChunk::default();
+            for ele in part {
+                chunk.trkpt.push(Trackpoint {
+                    ele: *ele,
+                    ..Default::default()
+                });
+            }
+            trkseg.push(chunk);
+        }
+        trkseg
+    }
+
+    /// Returns (center, left, right) flat indices for each visited center.
+    fn windows(len: usize, window: f64) -> Vec<(usize, usize, usize)> {
+        let trkseg = segment(&vec![0.0; len]);
+        let mut visited = vec![];
+        for_each_window!(
+            trkseg,
+            trkseg.first_index(),
+            trkseg.last_index(),
+            window,
+            |a, b| (b.flat - a.flat) as f64,
+            |i, l, r| {
+                visited.push((i.flat, l.flat, r.flat));
+            },
+        );
+        visited
+    }
+
+    #[test]
+    fn test_window_bounds() {
+        let visited = windows(10, 2.0);
+        assert_eq!(visited.len(), 10);
+        for (i, l, r) in visited {
+            assert_eq!(l, i.saturating_sub(2), "left of {i}");
+            assert_eq!(r, (i + 2).min(9), "right of {i}");
+        }
+    }
+
+    #[test]
+    fn test_window_always_includes_neighbours() {
+        for (i, l, r) in windows(6, 0.0) {
+            assert_eq!((l, r), (i.saturating_sub(1), (i + 1).min(5)));
+        }
+    }
+
+    #[test]
+    fn test_window_larger_than_segment() {
+        for (_, l, r) in windows(5, 100.0) {
+            assert_eq!((l, r), (0, 4));
+        }
+    }
+
+    #[test]
+    fn test_window_sub_range() {
+        let trkseg = segment(&[0.0; 10]);
+        let mut centers = vec![];
+        let mut first = trkseg.first_index();
+        for _ in 0..3 {
+            first = trkseg.next_index(first);
+        }
+        let mut last = first;
+        for _ in 0..2 {
+            last = trkseg.next_index(last);
+        }
+        for_each_window!(
+            trkseg,
+            first,
+            last,
+            1.0,
+            |a, b| (b.flat - a.flat) as f64,
+            |i, _l, _r| {
+                centers.push(i.flat);
+            },
+        );
+        assert_eq!(centers, vec![3, 4, 5]);
+    }
+}
@@ -0,0 +1,465 @@
+use crate::{Statistics, TrackSegment, Trackpoint, distance};
+
+/// The new timestamps of the trackpoints of `segments`, one after the other: each segment goes on
+/// from the end of the previous one, the first one starts at `start_time` (in milliseconds).
+///
+/// A segment that has timestamps keeps its durations multiplied by `ratio`; one that has none
+/// (judged by its first trackpoint) follows the previous trackpoint at `speed` (km/h). See
+/// [`shifted_and_compressed`] and [`with_timestamps`].
+pub fn changed_segment_times(
+    segments: &[&TrackSegment],
+    start_time: i64,
+    speed: f64,
+    ratio: f64,
+) -> Vec<Vec<Option<i64>>> {
+    let mut last: Option<Trackpoint> = None;
+    segments
+        .iter()
+        .map(|segment| {
+            let points: Vec<Trackpoint> = segment.iter().cloned().collect();
+            let Some(first) = points.first() else {
+                return vec![];
+            };
+            let start = last.clone().unwrap_or_else(|| {
+                let mut start = first.clone();
+                start.time = Some(start_time);
+                start
+            });
+            let points = if first.time.is_none() {
+                with_timestamps(points, Some(speed), Some(&start), Some(start_time))
+            } else {
+                shifted_and_compressed(points, Some(speed), ratio, &start)
+            };
+            last = points.last().cloned();
+            points.iter().map(|point| point.time).collect()
+        })
+        .collect()
+}
+
+/// Makes up timestamps for the trackpoints of `segments`, one after the other: they start at
+/// `start_time` (in milliseconds) and last `total_time` seconds together, the longer and the
+/// steeper an interval the more of it. Each segment goes on from the end of the previous one.
+pub fn artificial_segment_times(
+    segments: &[&TrackSegment],
+    start_time: i64,
+    total_time: f64,
+) -> Vec<Vec<Option<i64>>> {
+    let mut weights: Vec<Vec<f64>> = segments
+        .iter()
+        .map(|segment| {
+            let points: Vec<Trackpoint> = segment.iter().cloned().collect();
+            let slopes: Vec<f64> = Statistics::compute(segment)
+                .local
+                .iter()
+                .map(|l| l.slope)
+                .collect();
+            artificial_weights(&points, &slopes)
+        })
+        .collect();
+    let mut total: f64 = weights.iter().flatten().sum();
+    if total.is_nan() || total <= 0.0 {
+        // no distance to share the time by: every interval takes as long
+        for weights in &mut weights {
+            weights.iter_mut().for_each(|w| *w = 1.0);
+        }
+        total = weights.iter().map(Vec::len).sum::<usize>() as f64;
+    }
+    let ms_per_weight = if total > 0.0 {
+        total_time * 1000.0 / total
+    } else {
+        0.0
+    };
+
+    let mut start = start_time;
+    segments
+        .iter()
+        .zip(&weights)
+        .map(|(segment, weights)| {
+            let points: Vec<Trackpoint> = segment.iter().cloned().collect();
+            if points.is_empty() {
+                return vec![];
+            }
+            let points = with_artificial_timestamps(points, weights, ms_per_weight, start);
+            // the next segment goes on from the end of this one
+            start = points.last().and_then(|point| point.time).unwrap_or(start);
+            points.iter().map(|point| point.time).collect()
+        })
+        .collect()
+}
+
+/// Replaces the trackpoints `start..end` of `trkpt` by `points`, keeping the timestamps of the
+/// whole path consistent. It is the work of the old `replaceTrackPoints` of the TS library.
+///
+/// The timestamps only matter if the path has some, or if `speed` (in km/h) is given: then the
+/// new points that have none get some (a trackpoint after the previous one at `speed`, or one
+/// second after it without a speed), and so do the points before or after the range if they
+/// had none. `start_time` is the time of the first trackpoint when nothing else gives it.
+/// New points that have timestamps are shifted if they are too early to follow the previous
+/// trackpoint, and so are the points after the range. With `remove_gaps`, the new points are
+/// also brought closer to the previous trackpoint if they come long after it.
+///
+/// Panics if `start..end` is not inside `trkpt`.
+pub fn replace_trackpoints(
+    trkpt: &mut Vec<Trackpoint>,
+    start: usize,
+    end: usize,
+    mut points: Vec<Trackpoint>,
+    speed: Option<f64>,
+    start_time: Option<i64>,
+    remove_gaps: bool,
+) {
+    assert!(start <= end && end <= trkpt.len());
+    let has_times = trkpt.first().is_some_and(|first| first.time.is_some());
+
+    if speed.is_some() || has_times {
+        if start > 0 && trkpt[0].time.is_none() {
+            // the points before the range have no timestamps
+            let before: Vec<_> = trkpt.drain(..start).collect();
+            trkpt.splice(0..0, with_timestamps(before, speed, None, start_time));
+        }
+
+        if !points.is_empty() {
+            let last = start.checked_sub(1).map(|i| &trkpt[i]);
+            let missing =
+                points[0].time.is_none() || points.get(1).is_some_and(|p| p.time.is_none());
+            if missing {
+                points = with_timestamps(points, speed, last, start_time);
+            } else if let Some(last) = last {
+                if is_before(points[0].time, last.time) {
+                    // too early
+                    points = shifted_and_compressed(points, speed, 1.0, last);
+                } else if remove_gaps {
+                    if same_place(&points[0], last) {
+                        // the same place: the new points start at the previous trackpoint, which
+                        // is the new first one
+                        if is_before(last.time, points[0].time) {
+                            points = shifted_and_compressed(points, speed, 1.0, last);
+                            points.remove(0);
+                        }
+                    } else if matches!((points[0].time, last.time), (Some(new), Some(old)) if new - old > 1000)
+                    {
+                        // another place: the new points start one second after the previous one
+                        let mut artificial_last = points[0].clone();
+                        artificial_last.time = last.time.map(|time| time + 1000);
+                        points = shifted_and_compressed(points, speed, 1.0, &artificial_last);
+                    }
+                }
+            }
+        }
+
+        if end < trkpt.len() {
+            // the points after the range
+            let last = points
+                .last()
+                .or_else(|| start.checked_sub(1).map(|i| &trkpt[i]))
+                .cloned();
+            if trkpt[end].time.is_none() {
+                let after: Vec<_> = trkpt.drain(end..).collect();
+                let after = with_timestamps(after, speed, last.as_ref(), start_time);
+                trkpt.extend(after);
+            } else if let Some(last) = last
+                && is_before(trkpt[end].time, last.time)
+            {
+                let after: Vec<_> = trkpt.drain(end..).collect();
+                trkpt.extend(shifted_and_compressed(after, speed, 1.0, &last));
+            }
+        }
+    }
+
+    trkpt.splice(start..end, points);
+}
+
+/// How long each interval between two consecutive trackpoints of a segment should last, relative
+/// to the others, for a made-up pace: the longer the interval, and the steeper it goes up, the
+/// longer. `slopes` has the slope (in %) at each trackpoint.
+pub fn artificial_weights(points: &[Trackpoint], slopes: &[f64]) -> Vec<f64> {
+    points
+        .windows(2)
+        .zip(slopes)
+        .map(|(pair, slope)| {
+            let km = distance(pair[0].coordinates, pair[1].coordinates);
+            km * (0.5 + 1.0 / (1.0 + (-0.2 * slope).exp()))
+        })
+        .collect()
+}
+
+/// `points` with made-up timestamps: the first one is at `start`, and each next one follows the
+/// previous one after `weights[i]` times `ms_per_weight` milliseconds (see [`artificial_weights`]).
+pub fn with_artificial_timestamps(
+    mut points: Vec<Trackpoint>,
+    weights: &[f64],
+    ms_per_weight: f64,
+    start: i64,
+) -> Vec<Trackpoint> {
+    let mut elapsed = 0.0;
+    for (i, point) in points.iter_mut().enumerate() {
+        if i > 0 {
+            elapsed += weights[i - 1] * ms_per_weight;
+        }
+        point.time = Some(start + elapsed as i64);
+    }
+    points
+}
+
+fn same_place(a: &Trackpoint, b: &Trackpoint) -> bool {
+    a.coordinates.lng == b.coordinates.lng && a.coordinates.lat == b.coordinates.lat
+}
+
+/// Whether both times are known and `a` is before `b`.
+fn is_before(a: Option<i64>, b: Option<i64>) -> bool {
+    matches!((a, b), (Some(a), Some(b)) if a < b)
+}
+
+/// The time at which `b` is reached after `a`, at `speed` km/h: one second later without a
+/// speed, unknown if `a` has no time.
+///
+/// The old code gave an invalid date for a null or negative speed: it is as if there was none.
+fn timestamp_after(a: &Trackpoint, b: &Trackpoint, speed: Option<f64>) -> Option<i64> {
+    let time = a.time?;
+    match speed.filter(|speed| speed.is_finite() && *speed > 0.0) {
+        None => Some(time + 1000),
+        Some(speed) => {
+            let km = distance(a.coordinates, b.coordinates);
+            Some(time + (3_600_000.0 * km / speed) as i64)
+        }
+    }
+}
+
+/// `points` with the timestamps that follow `last` (the trackpoint before them), one after the
+/// other. Without `last`, the first one is at `start_time`.
+///
+/// Unlike the old code, a `last` without a time does not get `start_time` itself, only the copy
+/// used here.
+pub fn with_timestamps(
+    points: Vec<Trackpoint>,
+    speed: Option<f64>,
+    last: Option<&Trackpoint>,
+    start_time: Option<i64>,
+) -> Vec<Trackpoint> {
+    let Some(first) = points.first() else {
+        return points;
+    };
+    let mut last = match last {
+        Some(last) if last.time.is_some() => last.clone(),
+        other => {
+            let mut last = other.unwrap_or(first).clone();
+            last.time = start_time;
+            last
+        }
+    };
+    points
+        .into_iter()
+        .map(|mut point| {
+            point.time = timestamp_after(&last, &point, speed);
+            last = point.clone();
+            point
+        })
+        .collect()
+}
+
+/// `points` with their timestamps moved so that the first one follows `last`, and their durations
+/// multiplied by `ratio`. The ones that have no timestamp follow the previous one, as in
+/// [`with_timestamps`]. Without a time for `last`, or for the first point, none is known.
+pub fn shifted_and_compressed(
+    points: Vec<Trackpoint>,
+    speed: Option<f64>,
+    ratio: f64,
+    last: &Trackpoint,
+) -> Vec<Trackpoint> {
+    let Some(first) = points.first() else {
+        return points;
+    };
+    let start = timestamp_after(last, first, speed);
+    let first_time = first.time;
+    let mut previous = first.clone();
+    points
+        .into_iter()
+        .map(|point| {
+            let mut shifted = point.clone();
+            shifted.time = match point.time {
+                None => timestamp_after(&previous, &point, speed),
+                Some(time) => start
+                    .zip(first_time)
+                    .map(|(start, first)| start + (ratio * (time - first) as f64) as i64),
+            };
+            previous = shifted.clone();
+            shifted
+        })
+        .collect()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::LngLat;
+
+    use super::*;
+
+    /// A point every 1 km along the equator... about, at 0.009 degrees of longitude.
+    fn point(i: usize, time: Option<i64>) -> Trackpoint {
+        Trackpoint {
+            coordinates: LngLat {
+                lng: i as f64 * 0.009,
+                lat: 0.0,
+            },
+            time,
+            ..Default::default()
+        }
+    }
+
+    fn timed(range: std::ops::Range<usize>, start: i64, step: i64) -> Vec<Trackpoint> {
+        range
+            .map(|i| point(i, Some(start + step * i as i64)))
+            .collect()
+    }
+
+    fn untimed(range: std::ops::Range<usize>) -> Vec<Trackpoint> {
+        range.map(|i| point(i, None)).collect()
+    }
+
+    fn times(trkpt: &[Trackpoint]) -> Vec<Option<i64>> {
+        trkpt.iter().map(|p| p.time).collect()
+    }
+
+    #[test]
+    fn test_without_times_nor_speed_it_is_a_splice() {
+        let mut trkpt = untimed(0..5);
+        replace_trackpoints(&mut trkpt, 1, 3, untimed(10..13), None, None, false);
+        assert_eq!(trkpt.len(), 6);
+        assert!(trkpt.iter().all(|p| p.time.is_none()));
+        assert_eq!(trkpt[1].coordinates.lng, point(10, None).coordinates.lng);
+        assert_eq!(trkpt[4].coordinates.lng, point(3, None).coordinates.lng);
+    }
+
+    #[test]
+    fn test_new_points_follow_the_previous_one_at_the_speed() {
+        // 1 km in 10 s is 360 km/h
+        let mut trkpt = timed(0..4, 0, 10_000);
+        let km = distance(point(0, None).coordinates, point(1, None).coordinates);
+        let speed = 36.0 * km / 0.01; // the time of 1 point to the next is 100 s
+        replace_trackpoints(&mut trkpt, 2, 3, untimed(2..4), Some(speed), None, false);
+        let expected = 10_000 + (3_600_000.0 * km / speed) as i64;
+        assert_eq!(trkpt[2].time, Some(expected));
+        assert!(trkpt[2].time > trkpt[1].time);
+        // the points after follow the new ones, they were not too early
+        assert_eq!(trkpt.len(), 5);
+        assert_eq!(trkpt[4].time, Some(30_000));
+    }
+
+    #[test]
+    fn test_without_a_speed_new_points_are_one_second_apart() {
+        let mut trkpt = timed(0..3, 5_000, 60_000);
+        replace_trackpoints(&mut trkpt, 1, 2, untimed(10..13), None, None, false);
+        assert_eq!(
+            times(&trkpt[..4]),
+            [Some(5_000), Some(6_000), Some(7_000), Some(8_000)]
+        );
+        // what comes after was after, it is kept
+        assert_eq!(trkpt[4].time, Some(125_000));
+    }
+
+    #[test]
+    fn test_the_points_after_are_shifted_if_they_are_too_early() {
+        let mut trkpt = timed(0..4, 0, 10_000);
+        // 30 new points, one second apart: the last one is at 30 s, but the next original
+        // trackpoint is at 20 s
+        replace_trackpoints(&mut trkpt, 1, 2, untimed(10..40), None, None, false);
+        assert_eq!(trkpt.len(), 33);
+        assert_eq!(trkpt[1].time, Some(1_000));
+        assert_eq!(trkpt[30].time, Some(30_000));
+        // the following points keep the duration between them, after the new ones
+        assert_eq!(trkpt[31].time, Some(31_000));
+        assert_eq!(trkpt[32].time, Some(41_000));
+    }
+
+    #[test]
+    fn test_a_path_without_times_gets_them_from_the_speed_and_start_time() {
+        let mut trkpt = untimed(0..4);
+        replace_trackpoints(
+            &mut trkpt,
+            3,
+            4,
+            untimed(3..6),
+            Some(10.0),
+            Some(1_000),
+            false,
+        );
+        let times: Vec<_> = times(&trkpt);
+        assert_eq!(times[0], Some(1_000));
+        assert!(times.iter().all(Option::is_some));
+        assert!(times.windows(2).all(|w| w[0].unwrap() < w[1].unwrap()));
+    }
+
+    #[test]
+    fn test_an_unusable_speed_is_as_if_there_was_none() {
+        for speed in [0.0, -5.0, f64::NAN, f64::INFINITY] {
+            let mut trkpt = timed(0..2, 0, 10_000);
+            replace_trackpoints(&mut trkpt, 2, 2, untimed(2..4), Some(speed), None, false);
+            assert_eq!(
+                times(&trkpt),
+                [Some(0), Some(10_000), Some(11_000), Some(12_000)],
+                "{speed}"
+            );
+        }
+    }
+
+    #[test]
+    fn test_new_points_with_times_that_are_too_early_are_shifted() {
+        let mut trkpt = timed(0..3, 100_000, 10_000);
+        // they are at 0, 5 s: they are moved to follow the trackpoint at 110 s
+        let new = vec![point(5, Some(0)), point(6, Some(5_000))];
+        replace_trackpoints(&mut trkpt, 2, 3, new, None, None, false);
+        // they follow the previous trackpoint after one second, keeping their own durations
+        assert_eq!(trkpt[2].time, Some(111_000));
+        assert_eq!(trkpt[3].time, Some(116_000));
+    }
+
+    #[test]
+    fn test_remove_gaps_at_the_same_place_and_elsewhere() {
+        // same place: the first new point is the previous trackpoint
+        let mut trkpt = timed(0..3, 0, 10_000);
+        let new = vec![point(2, Some(500_000)), point(3, Some(510_000))];
+        replace_trackpoints(&mut trkpt, 3, 3, new.clone(), None, None, true);
+        assert_eq!(trkpt.len(), 4);
+        // without a speed, it is one second after the previous trackpoint, not at its time
+        assert_eq!(trkpt[3].time, Some(31_000));
+        // with a speed, the distance is zero
+        let mut trkpt = timed(0..3, 0, 10_000);
+        replace_trackpoints(&mut trkpt, 3, 3, new, Some(10.0), None, true);
+        assert_eq!(trkpt[3].time, Some(30_000));
+
+        // another place: one second after the previous one
+        let mut trkpt = timed(0..3, 0, 10_000);
+        let new = vec![point(5, Some(500_000)), point(6, Some(510_000))];
+        replace_trackpoints(&mut trkpt, 3, 3, new, None, None, true);
+        assert_eq!(trkpt.len(), 5);
+        // the old code adds the second twice with no speed, see `timestamp_after`
+        assert_eq!(trkpt[3].time, Some(22_000));
+        assert_eq!(trkpt[4].time, Some(32_000));
+
+        // without removing the gaps they stay
+        let mut trkpt = timed(0..3, 0, 10_000);
+        let new = vec![point(5, Some(500_000)), point(6, Some(510_000))];
+        replace_trackpoints(&mut trkpt, 3, 3, new, None, None, false);
+        assert_eq!(trkpt[3].time, Some(500_000));
+    }
+
+    #[test]
+    fn test_removing_points_adapts_nothing_if_the_next_one_is_after() {
+        let mut trkpt = timed(0..5, 0, 10_000);
+        replace_trackpoints(&mut trkpt, 1, 3, vec![], None, None, false);
+        assert_eq!(times(&trkpt), [Some(0), Some(30_000), Some(40_000)]);
+        // from the beginning
+        replace_trackpoints(&mut trkpt, 0, 2, vec![], None, None, false);
+        assert_eq!(times(&trkpt), [Some(40_000)]);
+        replace_trackpoints(&mut trkpt, 0, 1, vec![], None, None, false);
+        assert!(trkpt.is_empty());
+    }
+
+    #[test]
+    fn test_points_without_a_known_previous_time_get_none() {
+        // nothing gives a time to start with
+        let mut trkpt = untimed(0..2);
+        replace_trackpoints(&mut trkpt, 2, 2, untimed(2..4), Some(10.0), None, false);
+        assert!(trkpt.iter().all(|p| p.time.is_none()));
+    }
+}
@@ -0,0 +1,103 @@
+/// Maps the values of a category of trackpoint data (the surface, the highway...) to small codes,
+/// so that the trackpoints only hold a `u8` instead of a string.
+///
+/// The codes are the positions of the names in the order of first appearance. The table only
+/// grows: a code never changes meaning, so it stays valid in every state of the history.
+#[derive(Debug, Default, Clone, PartialEq)]
+pub struct Categories(Vec<String>);
+
+impl Categories {
+    /// A table with these names, in the order of their codes (at most [`Self::CAPACITY`] of them
+    /// are kept).
+    pub fn from_names(mut names: Vec<String>) -> Self {
+        names.truncate(Self::CAPACITY);
+        Self(names)
+    }
+
+    /// Maximum number of distinct values.
+    pub const CAPACITY: usize = u8::MAX as usize;
+
+    /// The code of `name`, which is added to the table if it is new. `None` if the table is full.
+    pub fn code(&mut self, name: &str) -> Option<u8> {
+        let index = match self.0.iter().position(|known| known == name) {
+            Some(index) => index,
+            None if self.0.len() < Self::CAPACITY => {
+                self.0.push(name.to_owned());
+                self.0.len() - 1
+            }
+            None => return None,
+        };
+        u8::try_from(index).ok()
+    }
+
+    /// The name of a code, `None` if it is unknown.
+    pub fn name(&self, code: u8) -> Option<&str> {
+        self.0.get(usize::from(code)).map(String::as_str)
+    }
+
+    /// All the names, in the order of their codes.
+    pub fn names(&self) -> &[String] {
+        &self.0
+    }
+}
+
+/// The categories of the data of the trackpoints. There is one table per engine, shared by all
+/// its files.
+#[derive(Debug, Default, Clone, PartialEq)]
+pub struct TrackpointCategories {
+    pub surface: Categories,
+    pub highway: Categories,
+    pub sac_scale: Categories,
+    pub mtb_scale: Categories,
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_codes_follow_the_order_of_appearance() {
+        let mut categories = Categories::default();
+        assert_eq!(categories.code("asphalt"), Some(0));
+        assert_eq!(categories.code("gravel"), Some(1));
+        // a known name keeps its code
+        assert_eq!(categories.code("asphalt"), Some(0));
+        assert_eq!(categories.names(), ["asphalt", "gravel"]);
+    }
+
+    #[test]
+    fn test_names_of_codes() {
+        let mut categories = Categories::default();
+        let code = categories.code("asphalt").unwrap();
+        assert_eq!(categories.name(code), Some("asphalt"));
+        assert_eq!(categories.name(code + 1), None);
+        assert_eq!(Categories::default().name(0), None);
+    }
+
+    #[test]
+    fn test_a_full_table_gives_no_code_to_new_names() {
+        let mut categories = Categories::default();
+        for i in 0..Categories::CAPACITY {
+            assert_eq!(categories.code(&i.to_string()), Some(i as u8));
+        }
+        assert_eq!(categories.code("one too many"), None);
+        assert_eq!(categories.names().len(), Categories::CAPACITY);
+        // the known ones still have their code, the last one included
+        assert_eq!(categories.code("0"), Some(0));
+        assert_eq!(categories.code("254"), Some(254));
+        assert_eq!(categories.name(254), Some("254"));
+    }
+
+    #[test]
+    fn test_the_categories_are_independent() {
+        let mut categories = TrackpointCategories::default();
+        categories.surface.code("asphalt");
+        assert_eq!(categories.highway.code("path"), Some(0));
+        assert_eq!(categories.sac_scale.code("hiking"), Some(0));
+        assert_eq!(categories.mtb_scale.code("1"), Some(0));
+        assert_eq!(categories.surface.names(), ["asphalt"]);
+        assert_eq!(categories.highway.names(), ["path"]);
+        assert_eq!(categories.sac_scale.names(), ["hiking"]);
+        assert_eq!(categories.mtb_scale.names(), ["1"]);
+    }
+}
@@ -0,0 +1,133 @@
+use crate::{Trackpoint, Waypoint};
+
+use super::common::uuid_id;
+
+/// A run of items, shared between the successive versions of a [`crate::Chunked`] list: a chunk
+/// that is not touched by an edit is not copied.
+///
+/// A chunk has an identity, which changes whenever the content does (a modified chunk is a new
+/// one): what is derived from a chunk, or kept of it, is up to date as long as the identity is.
+pub trait Chunk {
+    type Item: Clone;
+
+    /// Maximum number of items of a chunk.
+    const MAX_SIZE: usize;
+
+    /// A chunk with a new identity, holding `items`.
+    fn new(items: Vec<Self::Item>) -> Self;
+
+    /// Gives the chunk a new identity, after its items were changed in place.
+    fn renew(&mut self);
+
+    fn items(&self) -> &Vec<Self::Item>;
+
+    fn items_mut(&mut self) -> &mut Vec<Self::Item>;
+
+    fn is_full(&self) -> bool {
+        self.items().len() >= Self::MAX_SIZE
+    }
+}
+
+const MAX_TRKPT_CHUNK_SIZE: usize = 4096;
+
+uuid_id!(TrackpointChunkId);
+
+#[derive(Debug, Default)]
+pub struct TrackpointChunk {
+    pub id: TrackpointChunkId,
+    pub trkpt: Vec<Trackpoint>,
+}
+
+impl Chunk for TrackpointChunk {
+    type Item = Trackpoint;
+    const MAX_SIZE: usize = MAX_TRKPT_CHUNK_SIZE;
+
+    fn new(trkpt: Vec<Trackpoint>) -> Self {
+        Self {
+            trkpt,
+            ..Default::default()
+        }
+    }
+
+    fn renew(&mut self) {
+        self.id = Default::default();
+    }
+
+    fn items(&self) -> &Vec<Trackpoint> {
+        &self.trkpt
+    }
+
+    fn items_mut(&mut self) -> &mut Vec<Trackpoint> {
+        &mut self.trkpt
+    }
+}
+
+uuid_id!(WaypointChunkId);
+
+const MAX_WPT_CHUNK_SIZE: usize = 128;
+
+#[derive(Debug, Default)]
+pub struct WaypointChunk {
+    pub id: WaypointChunkId,
+    pub wpt: Vec<Waypoint>,
+}
+
+impl Chunk for WaypointChunk {
+    type Item = Waypoint;
+    const MAX_SIZE: usize = MAX_WPT_CHUNK_SIZE;
+
+    fn new(wpt: Vec<Waypoint>) -> Self {
+        Self {
+            wpt,
+            ..Default::default()
+        }
+    }
+
+    fn renew(&mut self) {
+        self.id = Default::default();
+    }
+
+    fn items(&self) -> &Vec<Waypoint> {
+        &self.wpt
+    }
+
+    fn items_mut(&mut self) -> &mut Vec<Waypoint> {
+        &mut self.wpt
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_trackpoint_chunk_full() {
+        let mut chunk = TrackpointChunk::default();
+        assert!(!chunk.is_full());
+        for _ in 0..MAX_TRKPT_CHUNK_SIZE - 1 {
+            chunk.trkpt.push(Trackpoint::default());
+        }
+        assert!(!chunk.is_full());
+        chunk.trkpt.push(Trackpoint::default());
+        assert!(chunk.is_full());
+    }
+
+    #[test]
+    fn test_waypoint_chunk_full() {
+        let mut chunk = WaypointChunk::default();
+        assert!(!chunk.is_full());
+        for _ in 0..MAX_WPT_CHUNK_SIZE {
+            chunk.wpt.push(Waypoint::default());
+        }
+        assert!(chunk.is_full());
+    }
+
+    #[test]
+    fn test_new_chunks_have_their_own_identity() {
+        let a = TrackpointChunk::new(vec![Trackpoint::default()]);
+        let b = TrackpointChunk::new(vec![Trackpoint::default()]);
+        assert_ne!(a.id, b.id);
+        assert_eq!(a.items().len(), 1);
+        assert_ne!(WaypointChunk::new(vec![]).id, WaypointChunk::new(vec![]).id);
+    }
+}
@@ -0,0 +1,619 @@
+use std::{ops::Index, rc::Rc};
+
+use crate::Chunk;
+
+/// A list of items, stored in [`Chunk`]s that are shared between its versions: editing it only
+/// copies the chunks around the change, so that a version costs little more than the change.
+///
+/// There are no empty chunks.
+#[derive(Debug)]
+pub struct Chunked<C: Chunk> {
+    chunks: Vec<Rc<C>>,
+    cumul_length: Vec<usize>,
+}
+
+impl<C: Chunk> Clone for Chunked<C> {
+    fn clone(&self) -> Self {
+        Self {
+            chunks: self.chunks.clone(),
+            cumul_length: self.cumul_length.clone(),
+        }
+    }
+}
+
+impl<C: Chunk> Default for Chunked<C> {
+    fn default() -> Self {
+        Self {
+            chunks: vec![],
+            cumul_length: vec![],
+        }
+    }
+}
+
+/// The position of an item: in which chunk, where in it, and among all the items.
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default, PartialOrd, Ord)]
+pub struct ChunkIndex {
+    pub chunk: usize,
+    pub pos: usize,
+    pub flat: usize,
+}
+
+impl<C: Chunk> Chunked<C> {
+    /// Adds a chunk at the end, which is dropped if it is empty.
+    pub fn push(&mut self, chunk: C) {
+        self.push_shared(Rc::new(chunk));
+    }
+
+    pub fn push_shared(&mut self, chunk: Rc<C>) {
+        if chunk.items().is_empty() {
+            return;
+        }
+        self.cumul_length
+            .push(self.cumul_length.last().copied().unwrap_or_default() + chunk.items().len());
+        self.chunks.push(chunk);
+    }
+
+    pub fn chunks(&self) -> &[Rc<C>] {
+        &self.chunks
+    }
+
+    /// Replaces the items in `start..end` by `items`. Panics if the range is out of bounds.
+    ///
+    /// Chunks that are not concerned are kept as they are (shared), only the chunks around the
+    /// range are copied and refilled.
+    pub fn splice(&mut self, start: usize, end: usize, items: Vec<C::Item>) {
+        assert!(
+            start <= end && end <= self.len(),
+            "splice range out of bounds"
+        );
+        let old = std::mem::take(&mut self.chunks);
+        self.cumul_length.clear();
+
+        let mut items = Some(items);
+        let mut pending = vec![];
+        let mut offset = 0;
+        for chunk in old {
+            let (lo, hi) = (offset, offset + chunk.items().len());
+            offset = hi;
+            // a chunk ending at `start` is extended unless it is full, to avoid tiny chunks
+            if hi < start || (hi == start && chunk.is_full()) {
+                self.push_shared(chunk);
+                continue;
+            }
+            if let Some(items) = items.take() {
+                self.fill(&mut pending, chunk.items()[..start - lo].iter().cloned());
+                self.fill(&mut pending, items);
+            }
+            if hi <= end {
+                continue;
+            }
+            if lo >= end {
+                self.flush(&mut pending);
+                self.push_shared(chunk);
+            } else {
+                self.fill(&mut pending, chunk.items()[end - lo..].iter().cloned());
+            }
+        }
+        if let Some(items) = items {
+            self.fill(&mut pending, items);
+        }
+        self.flush(&mut pending);
+    }
+
+    fn fill(&mut self, pending: &mut Vec<C::Item>, items: impl IntoIterator<Item = C::Item>) {
+        for item in items {
+            pending.push(item);
+            if pending.len() >= C::MAX_SIZE {
+                self.flush(pending);
+            }
+        }
+    }
+
+    fn flush(&mut self, pending: &mut Vec<C::Item>) {
+        self.push(C::new(std::mem::take(pending)));
+    }
+
+    /// Edits the items of the chunks that contain an item accepted by `filter`.
+    ///
+    /// `f` receives a copy of the items of such a chunk and returns whether it changed them. A
+    /// changed chunk is replaced by a new one (so that what is derived from it is computed
+    /// again) and the chunks left empty are dropped. The other chunks are kept. Returns whether
+    /// anything changed.
+    pub fn edit(
+        &mut self,
+        filter: impl Fn(&C::Item) -> bool,
+        mut f: impl FnMut(&mut Vec<C::Item>) -> bool,
+    ) -> bool {
+        let mut changed = false;
+        let old = std::mem::take(&mut self.chunks);
+        self.cumul_length.clear();
+        for chunk in old {
+            if !chunk.items().iter().any(&filter) {
+                self.push_shared(chunk);
+                continue;
+            }
+            let mut items = chunk.items().clone();
+            if !f(&mut items) {
+                self.push_shared(chunk);
+                continue;
+            }
+            changed = true;
+            self.push(C::new(items));
+        }
+        changed
+    }
+
+    /// Changes what is in the chunk `chunk`, but not how many items there are. A chunk that is
+    /// shared is copied first, so that the other versions do not change.
+    fn replace_chunk(&mut self, chunk: usize, f: impl FnOnce(&mut Vec<C::Item>)) {
+        let len = self.chunks[chunk].items().len();
+        match Rc::get_mut(&mut self.chunks[chunk]) {
+            Some(unique) => {
+                f(unique.items_mut());
+                unique.renew();
+            }
+            None => {
+                let mut items = self.chunks[chunk].items().clone();
+                f(&mut items);
+                self.chunks[chunk] = Rc::new(C::new(items));
+            }
+        }
+        debug_assert_eq!(self.chunks[chunk].items().len(), len);
+    }
+
+    /// Applies `f` to the item at `index`, which is copied in a new chunk. Panics if there is no
+    /// such item.
+    pub fn update(&mut self, index: usize, f: impl FnOnce(&mut C::Item)) {
+        let ChunkIndex { chunk, pos, .. } = self.locate(index).unwrap();
+        self.replace_chunk(chunk, |items| f(&mut items[pos]));
+    }
+
+    /// Applies `f` to every item, with its index, in new chunks.
+    pub fn update_all(&mut self, mut f: impl FnMut(usize, &mut C::Item)) {
+        let mut offset = 0;
+        for chunk in 0..self.chunks.len() {
+            let len = self.chunks[chunk].items().len();
+            self.replace_chunk(chunk, |items| {
+                for (i, item) in items.iter_mut().enumerate() {
+                    f(offset + i, item);
+                }
+            });
+            offset += len;
+        }
+    }
+
+    pub fn len(&self) -> usize {
+        self.cumul_length.last().copied().unwrap_or_default()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.chunks.is_empty()
+    }
+
+    pub fn iter(&self) -> ChunkedIter<'_, C> {
+        ChunkedIter::new(self)
+    }
+
+    pub fn first_index(&self) -> Option<ChunkIndex> {
+        self.next_index(None)
+    }
+
+    pub fn last_index(&self) -> Option<ChunkIndex> {
+        self.prev_index(None)
+    }
+
+    pub fn next_index(&self, cur: Option<ChunkIndex>) -> Option<ChunkIndex> {
+        let mut next = cur.map_or_default(|idx| ChunkIndex {
+            chunk: idx.chunk,
+            pos: idx.pos + 1,
+            flat: idx.flat + 1,
+        });
+        loop {
+            if next.chunk >= self.chunks.len() {
+                return None;
+            }
+            if next.pos == self.chunks[next.chunk].items().len() {
+                next.chunk += 1;
+                next.pos = 0;
+            } else {
+                return Some(next);
+            }
+        }
+    }
+
+    pub fn prev_index(&self, cur: Option<ChunkIndex>) -> Option<ChunkIndex> {
+        let mut prev = cur.unwrap_or(ChunkIndex {
+            chunk: self.chunks.len(),
+            pos: 0,
+            flat: self.cumul_length.last().copied().unwrap_or_default(),
+        });
+        if prev.pos == 0 {
+            while prev.chunk > 0 {
+                prev.chunk -= 1;
+                if !self.chunks[prev.chunk].items().is_empty() {
+                    prev.pos = self.chunks[prev.chunk].items().len() - 1;
+                    prev.flat -= 1;
+                    return Some(prev);
+                }
+            }
+            None
+        } else {
+            prev.pos -= 1;
+            prev.flat -= 1;
+            Some(prev)
+        }
+    }
+
+    /// The position of the item `idx` among all the items.
+    pub fn locate(&self, idx: usize) -> Option<ChunkIndex> {
+        let chunk = self.cumul_length.partition_point(|l| idx >= *l);
+        if chunk >= self.chunks.len() {
+            return None;
+        }
+        let pos = if chunk > 0 {
+            idx - self.cumul_length[chunk - 1]
+        } else {
+            idx
+        };
+        if pos >= self.chunks[chunk].items().len() {
+            None
+        } else {
+            Some(ChunkIndex {
+                chunk,
+                pos,
+                flat: idx,
+            })
+        }
+    }
+}
+
+impl<C: Chunk> Index<ChunkIndex> for Chunked<C> {
+    type Output = C::Item;
+
+    fn index(&self, idx: ChunkIndex) -> &Self::Output {
+        &self.chunks[idx.chunk].items()[idx.pos]
+    }
+}
+
+impl<C: Chunk> Index<usize> for Chunked<C> {
+    type Output = C::Item;
+
+    fn index(&self, idx: usize) -> &Self::Output {
+        &self[self.locate(idx).unwrap()]
+    }
+}
+
+impl<'a, C: Chunk> IntoIterator for &'a Chunked<C> {
+    type Item = &'a C::Item;
+    type IntoIter = ChunkedIter<'a, C>;
+
+    fn into_iter(self) -> Self::IntoIter {
+        self.iter()
+    }
+}
+
+pub struct ChunkedIter<'a, C: Chunk> {
+    chunked: &'a Chunked<C>,
+    /// The item returned last.
+    idx: Option<ChunkIndex>,
+    exhausted: bool,
+}
+
+impl<C: Chunk> Clone for ChunkedIter<'_, C> {
+    fn clone(&self) -> Self {
+        Self {
+            chunked: self.chunked,
+            idx: self.idx,
+            exhausted: self.exhausted,
+        }
+    }
+}
+
+impl<'a, C: Chunk> ChunkedIter<'a, C> {
+    pub fn new(chunked: &'a Chunked<C>) -> Self {
+        Self {
+            chunked,
+            idx: None,
+            exhausted: false,
+        }
+    }
+
+    fn move_to(&mut self, idx: Option<ChunkIndex>) -> Option<&'a C::Item> {
+        self.exhausted = idx.is_none();
+        self.idx = idx.or(self.idx);
+        idx.map(|idx| &self.chunked[idx])
+    }
+}
+
+impl<'a, C: Chunk> Iterator for ChunkedIter<'a, C> {
+    type Item = &'a C::Item;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        if self.exhausted {
+            return None;
+        }
+        let next = self.chunked.next_index(self.idx);
+        self.move_to(next)
+    }
+
+    fn nth(&mut self, n: usize) -> Option<Self::Item> {
+        if self.exhausted {
+            return None;
+        }
+        let target = self.idx.map_or(0, |idx| idx.flat + 1).saturating_add(n);
+        let next = self.chunked.locate(target);
+        self.move_to(next)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Chunks of at most 3 numbers, with an identity like the real ones.
+    #[derive(Debug)]
+    struct Numbers {
+        id: usize,
+        items: Vec<u32>,
+    }
+
+    thread_local! {
+        static NEXT_ID: std::cell::Cell<usize> = const { std::cell::Cell::new(0) };
+    }
+
+    fn next_id() -> usize {
+        NEXT_ID.with(|id| id.replace(id.get() + 1))
+    }
+
+    impl Chunk for Numbers {
+        type Item = u32;
+        const MAX_SIZE: usize = 3;
+
+        fn new(items: Vec<u32>) -> Self {
+            Self {
+                id: next_id(),
+                items,
+            }
+        }
+
+        fn renew(&mut self) {
+            self.id = next_id();
+        }
+
+        fn items(&self) -> &Vec<u32> {
+            &self.items
+        }
+
+        fn items_mut(&mut self) -> &mut Vec<u32> {
+            &mut self.items
+        }
+    }
+
+    /// The numbers `0..n` in chunks of 3.
+    fn numbers(n: u32) -> Chunked<Numbers> {
+        let mut chunked = Chunked::default();
+        for start in (0..n).step_by(3) {
+            chunked.push(Numbers::new((start..(start + 3).min(n)).collect()));
+        }
+        chunked
+    }
+
+    fn values(chunked: &Chunked<Numbers>) -> Vec<u32> {
+        chunked.iter().copied().collect()
+    }
+
+    fn ids(chunked: &Chunked<Numbers>) -> Vec<usize> {
+        chunked.chunks().iter().map(|chunk| chunk.id).collect()
+    }
+
+    fn assert_consistent(chunked: &Chunked<Numbers>) {
+        let sizes: Vec<usize> = chunked.chunks().iter().map(|c| c.items.len()).collect();
+        assert!(
+            sizes
+                .iter()
+                .all(|&size| 0 < size && size <= Numbers::MAX_SIZE)
+        );
+        assert_eq!(chunked.len(), sizes.iter().sum::<usize>());
+        for index in 0..chunked.len() {
+            assert_eq!(chunked.locate(index).unwrap().flat, index);
+        }
+        assert!(chunked.locate(chunked.len()).is_none());
+    }
+
+    #[test]
+    fn test_push_drops_empty_chunks() {
+        let mut chunked = numbers(4);
+        chunked.push(Numbers::new(vec![]));
+        assert_eq!(chunked.chunks().len(), 2);
+        assert_eq!(chunked.len(), 4);
+        assert!(Chunked::<Numbers>::default().is_empty());
+        assert!(!chunked.is_empty());
+    }
+
+    #[test]
+    fn test_locate_index_and_iterate() {
+        let chunked = numbers(7);
+        assert_eq!(
+            chunked.locate(4),
+            Some(ChunkIndex {
+                chunk: 1,
+                pos: 1,
+                flat: 4
+            })
+        );
+        assert_eq!(chunked[4], 4);
+        assert_eq!(chunked[chunked.locate(6).unwrap()], 6);
+        assert!(chunked.locate(7).is_none());
+        assert_eq!(values(&chunked), (0..7).collect::<Vec<_>>());
+        assert_eq!(chunked.iter().count(), 7);
+        assert_eq!((&chunked).into_iter().last(), Some(&6));
+        assert_eq!(values(&Chunked::default()), Vec::<u32>::new());
+    }
+
+    #[test]
+    fn test_first_last_next_and_previous_index() {
+        let chunked = numbers(7);
+        let first = chunked.first_index().unwrap();
+        let last = chunked.last_index().unwrap();
+        assert_eq!((first.flat, last.flat), (0, 6));
+        assert_eq!((last.chunk, last.pos), (2, 0));
+
+        let mut forward = vec![];
+        let mut cur = None;
+        while let Some(next) = chunked.next_index(cur) {
+            forward.push(chunked[next]);
+            cur = Some(next);
+        }
+        assert_eq!(forward, (0..7).collect::<Vec<_>>());
+
+        let mut backward = vec![];
+        let mut cur = None;
+        while let Some(prev) = chunked.prev_index(cur) {
+            backward.push(chunked[prev]);
+            cur = Some(prev);
+        }
+        assert_eq!(backward, (0..7).rev().collect::<Vec<_>>());
+
+        let empty = Chunked::<Numbers>::default();
+        assert!(empty.first_index().is_none() && empty.last_index().is_none());
+    }
+
+    #[test]
+    #[allow(clippy::iter_nth_zero)]
+    fn test_iterator_nth_goes_on_from_the_current_item() {
+        let chunked = numbers(10);
+        let mut iter = chunked.iter();
+        assert_eq!(iter.nth(1), Some(&1));
+        assert_eq!(iter.next(), Some(&2));
+        // skips 3 and 4
+        assert_eq!(iter.nth(2), Some(&5));
+        assert_eq!(iter.nth(0), Some(&6));
+        assert_eq!(iter.nth(2), Some(&9));
+        assert_eq!(iter.nth(0), None);
+        assert_eq!(iter.next(), None, "an exhausted iterator stays exhausted");
+
+        assert_eq!(values(&numbers(10)).iter().skip(4).count(), 6);
+        assert_eq!(
+            chunked.iter().skip(4).copied().collect::<Vec<_>>(),
+            (4..10).collect::<Vec<_>>()
+        );
+        assert_eq!(
+            chunked.iter().step_by(4).copied().collect::<Vec<_>>(),
+            vec![0, 4, 8]
+        );
+    }
+
+    #[test]
+    fn test_splice_replaces_inserts_deletes_and_appends() {
+        let mut chunked = numbers(10);
+        chunked.splice(2, 5, vec![100, 101]);
+        assert_eq!(values(&chunked), [0, 1, 100, 101, 5, 6, 7, 8, 9]);
+        assert_consistent(&chunked);
+
+        chunked.splice(0, 0, vec![50]);
+        assert_eq!(values(&chunked)[..3], [50, 0, 1]);
+        chunked.splice(chunked.len(), chunked.len(), vec![7, 7, 7, 7]);
+        assert_eq!(values(&chunked)[chunked.len() - 5..], [9, 7, 7, 7, 7]);
+        assert_consistent(&chunked);
+
+        let len = chunked.len();
+        chunked.splice(0, len, vec![]);
+        assert!(chunked.is_empty());
+        assert_eq!(chunked.len(), 0);
+    }
+
+    #[test]
+    #[should_panic(expected = "splice range out of bounds")]
+    fn test_splice_out_of_bounds_panics() {
+        numbers(4).splice(2, 5, vec![]);
+    }
+
+    #[test]
+    fn test_splice_keeps_the_chunks_it_does_not_touch() {
+        let mut chunked = numbers(12);
+        let before = ids(&chunked);
+        // inside the second chunk
+        chunked.splice(4, 5, vec![40]);
+        let after = ids(&chunked);
+        assert_eq!(after.len(), before.len());
+        assert_eq!(
+            (after[0], after[2], after[3]),
+            (before[0], before[2], before[3])
+        );
+        assert_ne!(after[1], before[1]);
+    }
+
+    #[test]
+    fn test_edit_replaces_only_the_changed_chunks() {
+        let mut chunked = numbers(9);
+        let before = ids(&chunked);
+
+        // nothing is changed: nothing is replaced
+        assert!(!chunked.edit(|n| *n == 4, |_| false));
+        assert_eq!(ids(&chunked), before);
+
+        // the filter picks the chunk, the hook changes it
+        assert!(chunked.edit(
+            |n| *n == 4,
+            |items| {
+                items[1] = 400;
+                true
+            }
+        ));
+        let after = ids(&chunked);
+        assert_eq!((after[0], after[2]), (before[0], before[2]));
+        assert_ne!(after[1], before[1]);
+        assert_eq!(values(&chunked), [0, 1, 2, 3, 400, 5, 6, 7, 8]);
+
+        // a chunk left empty is dropped
+        assert!(chunked.edit(
+            |n| *n == 0,
+            |items| {
+                items.clear();
+                true
+            }
+        ));
+        assert_eq!(chunked.chunks().len(), 2);
+        assert_consistent(&chunked);
+    }
+
+    #[test]
+    fn test_update_copies_the_chunk_so_that_other_versions_do_not_change() {
+        let mut chunked = numbers(6);
+        let version = chunked.clone();
+        let before = ids(&chunked);
+        chunked.update(4, |n| *n = 40);
+        assert_eq!(values(&chunked), [0, 1, 2, 3, 40, 5]);
+        assert_eq!(values(&version), (0..6).collect::<Vec<_>>());
+        assert_eq!(ids(&version), before);
+        assert_eq!(ids(&chunked)[0], before[0]);
+        assert_ne!(ids(&chunked)[1], before[1]);
+    }
+
+    #[test]
+    fn test_updated_chunks_get_a_new_identity_even_when_nothing_shares_them() {
+        // what is derived from or kept of a chunk is keyed by its identity
+        let mut chunked = numbers(6);
+        let before = ids(&chunked);
+        chunked.update(1, |n| *n += 1);
+        assert_ne!(ids(&chunked)[0], before[0]);
+        assert_eq!(ids(&chunked)[1], before[1]);
+
+        let before = ids(&chunked);
+        chunked.update_all(|_, n| *n += 1);
+        let after = ids(&chunked);
+        assert!(before.iter().zip(&after).all(|(a, b)| a != b));
+    }
+
+    #[test]
+    fn test_update_all_gives_the_index_of_each_item() {
+        let mut chunked = numbers(8);
+        let mut seen = vec![];
+        chunked.update_all(|index, n| {
+            seen.push(index);
+            *n = 10 * index as u32;
+        });
+        assert_eq!(seen, (0..8).collect::<Vec<_>>());
+        assert_eq!(values(&chunked), [0, 10, 20, 30, 40, 50, 60, 70]);
+    }
+}
@@ -0,0 +1,114 @@
+/// Defines an identifier made of a UUID, which is a new one by default.
+macro_rules! uuid_id {
+    ($(#[$meta:meta])* $name:ident) => {
+        $(#[$meta])*
+        #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+        pub struct $name(pub uuid::Uuid);
+
+        impl Default for $name {
+            fn default() -> Self {
+                Self(uuid::Uuid::new_v4())
+            }
+        }
+    };
+}
+
+pub(crate) use uuid_id;
+
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
+pub struct Link {
+    pub href: String,
+    pub text: Option<String>,
+}
+
+#[derive(Debug, Default, Clone, Copy)]
+pub struct LngLat {
+    pub lng: f64,
+    pub lat: f64,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct LngLatBounds {
+    pub sw: LngLat,
+    pub ne: LngLat,
+}
+
+impl Default for LngLatBounds {
+    fn default() -> Self {
+        Self {
+            sw: LngLat {
+                lng: 180.0,
+                lat: 90.0,
+            },
+            ne: LngLat {
+                lng: -180.0,
+                lat: -90.0,
+            },
+        }
+    }
+}
+
+impl LngLatBounds {
+    pub fn extend(&mut self, coordinates: LngLat) {
+        self.sw.lng = self.sw.lng.min(coordinates.lng);
+        self.sw.lat = self.sw.lat.min(coordinates.lat);
+        self.ne.lng = self.ne.lng.max(coordinates.lng);
+        self.ne.lat = self.ne.lat.max(coordinates.lat);
+    }
+
+    pub fn merge(&mut self, other: &LngLatBounds) {
+        self.sw.lng = self.sw.lng.min(other.sw.lng);
+        self.sw.lat = self.sw.lat.min(other.sw.lat);
+        self.ne.lng = self.ne.lng.max(other.ne.lng);
+        self.ne.lat = self.ne.lat.max(other.ne.lat);
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_bounds_extend() {
+        let mut bounds = LngLatBounds::default();
+        bounds.extend(LngLat {
+            lng: 4.0,
+            lat: 50.0,
+        });
+        assert_eq!((bounds.sw.lng, bounds.sw.lat), (4.0, 50.0));
+        assert_eq!((bounds.ne.lng, bounds.ne.lat), (4.0, 50.0));
+
+        bounds.extend(LngLat {
+            lng: 6.0,
+            lat: 45.0,
+        });
+        bounds.extend(LngLat {
+            lng: 5.0,
+            lat: 48.0,
+        });
+        assert_eq!((bounds.sw.lng, bounds.sw.lat), (4.0, 45.0));
+        assert_eq!((bounds.ne.lng, bounds.ne.lat), (6.0, 50.0));
+    }
+
+    #[test]
+    fn test_bounds_merge() {
+        let mut a = LngLatBounds::default();
+        a.extend(LngLat { lng: 0.0, lat: 0.0 });
+        a.extend(LngLat { lng: 1.0, lat: 1.0 });
+        let mut b = LngLatBounds::default();
+        b.extend(LngLat {
+            lng: -2.0,
+            lat: 0.5,
+        });
+        b.extend(LngLat { lng: 0.5, lat: 3.0 });
+
+        a.merge(&b);
+        assert_eq!((a.sw.lng, a.sw.lat), (-2.0, 0.0));
+        assert_eq!((a.ne.lng, a.ne.lat), (1.0, 3.0));
+
+        // merging an empty bounds changes nothing
+        a.merge(&LngLatBounds::default());
+        assert_eq!((a.sw.lng, a.sw.lat), (-2.0, 0.0));
+        assert_eq!((a.ne.lng, a.ne.lat), (1.0, 3.0));
+    }
+}
@@ -0,0 +1,31 @@
+use crate::{Link, Track, Waypoints};
+
+use super::common::uuid_id;
+
+uuid_id!(FileId);
+
+#[derive(Debug, Default, Clone)]
+pub struct File {
+    pub id: FileId,
+    pub info: FileInfo,
+    pub trk: Vec<Track>,
+    pub wpt: Waypoints,
+}
+
+#[derive(Debug, Default, Clone, PartialEq)]
+pub struct FileInfo {
+    pub name: String,
+    pub desc: Option<String>,
+    pub author: Option<Author>,
+    pub links: Vec<Link>,
+    pub time: Option<i64>,
+}
+
+#[derive(Debug, Default, Clone, PartialEq)]
+pub struct Author {
+    pub name: Option<String>,
+    /// `id@domain`, which the file gives as the two attributes of an `email` element.
+    pub email: Option<String>,
+    /// The author has a single link, unlike the other elements.
+    pub link: Option<Link>,
+}
@@ -0,0 +1,21 @@
+mod categories;
+mod chunk;
+mod chunked;
+mod common;
+mod file;
+mod segment;
+mod track;
+mod trackpoint;
+mod waypoint;
+mod waypoints;
+
+pub use categories::*;
+pub use chunk::*;
+pub use chunked::*;
+pub use common::*;
+pub use file::*;
+pub use segment::*;
+pub use track::*;
+pub use trackpoint::*;
+pub use waypoint::*;
+pub use waypoints::*;
@@ -0,0 +1,411 @@
+use std::ops::Deref;
+use std::rc::Rc;
+
+use crate::{ChunkIndex, Chunked, ChunkedIter, Trackpoint, TrackpointChunk, compute_anchors};
+
+use super::common::uuid_id;
+
+uuid_id!(TrackSegmentId);
+
+uuid_id!(TrackSegmentRevisionId);
+
+#[derive(Debug, Default, Clone)]
+pub struct TrackSegment {
+    pub id: TrackSegmentId,
+    pub rev_id: TrackSegmentRevisionId,
+    points: Chunked<TrackpointChunk>,
+}
+
+/// The position of a trackpoint in a segment.
+pub type TrackSegmentIndex = ChunkIndex;
+
+pub type TrackSegmentIterator<'a> = ChunkedIter<'a, TrackpointChunk>;
+
+impl Deref for TrackSegment {
+    type Target = Chunked<TrackpointChunk>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.points
+    }
+}
+
+impl TrackSegment {
+    /// Adds a chunk after the last trackpoint, which is dropped if it is empty.
+    pub fn push(&mut self, chunk: TrackpointChunk) {
+        self.points.push(chunk);
+        self.rev_id = Default::default();
+    }
+
+    /// Adds a chunk that is shared with something else after the last trackpoint.
+    pub fn push_shared(&mut self, chunk: Rc<TrackpointChunk>) {
+        self.points.push_shared(chunk);
+        self.rev_id = Default::default();
+    }
+
+    /// Applies `f` to the trackpoint at `index`, see [`Chunked::update`]. Panics if there is no
+    /// such trackpoint.
+    pub fn update(&mut self, index: usize, f: impl FnOnce(&mut Trackpoint)) {
+        self.points.update(index, f);
+        self.rev_id = Default::default();
+    }
+
+    /// Applies `f` to every trackpoint, with its index, see [`Chunked::update_all`].
+    pub fn update_all(&mut self, f: impl FnMut(usize, &mut Trackpoint)) {
+        self.points.update_all(f);
+        self.rev_id = Default::default();
+    }
+
+    /// Replaces the points in `start..end` by `points`, see [`Chunked::splice`]. The first and
+    /// last trackpoints are anchors afterwards.
+    pub fn splice(&mut self, start: usize, end: usize, points: Vec<Trackpoint>) {
+        self.points.splice(start, end, points);
+        self.rev_id = Default::default();
+        self.ensure_end_anchors();
+    }
+
+    /// The first and the last trackpoints are always anchors, shown at every zoom level.
+    ///
+    /// It is done by [`TrackSegment::splice`]; commands that build segments in another way need to
+    /// call it.
+    pub fn ensure_end_anchors(&mut self) {
+        let Some(last) = self.len().checked_sub(1) else {
+            return;
+        };
+        for index in [0, last] {
+            if self[index].anchor != Some(0) {
+                self.set_anchor(index, 0);
+            }
+        }
+    }
+
+    /// Makes the trackpoint at `index` an anchor shown from the map zoom level `zoom`. Panics if
+    /// there is no such trackpoint.
+    pub fn set_anchor(&mut self, index: usize, zoom: u8) {
+        self.update(index, |trkpt| trkpt.anchor = Some(zoom));
+    }
+
+    /// Sets the anchors of the trackpoints from the details of the path of the segment (see
+    /// [`compute_anchors`]), forgetting the previous ones.
+    pub fn compute_anchors(&mut self) {
+        let anchors = compute_anchors(self);
+        let mut anchors = anchors.into_iter().peekable();
+        self.update_all(|index, trkpt| {
+            trkpt.anchor = match anchors.peek() {
+                Some(&(anchor, zoom)) if anchor == index => {
+                    anchors.next();
+                    Some(zoom)
+                }
+                _ => None,
+            };
+        });
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::Chunk;
+
+    use super::*;
+
+    fn create_track_segment(nb_chunks: usize) -> TrackSegment {
+        let mut trkseg = TrackSegment::default();
+        let mut count = 0;
+        for n in 1..=nb_chunks {
+            let mut chunk = TrackpointChunk::default();
+            for _ in 0..n {
+                chunk.trkpt.push(Trackpoint {
+                    ele: count as f64,
+                    ..Default::default()
+                });
+                count += 1;
+            }
+            trkseg.push(chunk);
+        }
+        trkseg
+    }
+
+    fn eles(trkseg: &TrackSegment) -> Vec<f64> {
+        trkseg.iter().map(|p| p.ele).collect()
+    }
+
+    fn points(eles: &[f64]) -> Vec<Trackpoint> {
+        eles.iter()
+            .map(|&ele| Trackpoint {
+                ele,
+                ..Default::default()
+            })
+            .collect()
+    }
+
+    #[test]
+    fn test_splice_replace_insert_delete_append() {
+        // chunks of 1..=5 points: [0] [1 2] [3 4 5] [6 7 8 9] [10..=14]
+        let mut trkseg = create_track_segment(5);
+        trkseg.splice(4, 8, points(&[-1.0, -2.0]));
+        let mut expected: Vec<f64> = (0..4).map(f64::from).collect();
+        expected.extend([-1.0, -2.0]);
+        expected.extend((8..15).map(f64::from));
+        assert_eq!(eles(&trkseg), expected);
+        assert_eq!(trkseg.len(), expected.len());
+        for i in 0..trkseg.len() {
+            assert_eq!(trkseg[i].ele, expected[i]);
+        }
+
+        trkseg.splice(2, 2, points(&[100.0]));
+        expected.insert(2, 100.0);
+        assert_eq!(eles(&trkseg), expected);
+
+        trkseg.splice(0, 3, vec![]);
+        expected.drain(..3);
+        assert_eq!(eles(&trkseg), expected);
+
+        let len = trkseg.len();
+        trkseg.splice(len, len, points(&[7.0, 8.0]));
+        expected.extend([7.0, 8.0]);
+        assert_eq!(eles(&trkseg), expected);
+
+        let len = trkseg.len();
+        trkseg.splice(0, len, vec![]);
+        assert_eq!(trkseg.len(), 0);
+        assert!(trkseg.first_index().is_none());
+    }
+
+    fn anchors(trkseg: &TrackSegment) -> Vec<Option<u8>> {
+        trkseg.iter().map(|p| p.anchor).collect()
+    }
+
+    #[test]
+    fn test_splice_keeps_the_ends_anchors() {
+        let mut trkseg = TrackSegment::default();
+        assert_eq!(anchors(&trkseg), vec![]);
+        trkseg.splice(0, 0, points(&[0.0, 1.0, 2.0]));
+        assert_eq!(anchors(&trkseg), [Some(0), None, Some(0)]);
+
+        // new ends: the previous ones stay anchors
+        trkseg.splice(3, 3, points(&[3.0]));
+        trkseg.splice(0, 0, points(&[-1.0]));
+        assert_eq!(anchors(&trkseg), [Some(0), Some(0), None, Some(0), Some(0)]);
+
+        // removing the ends: the new ones become anchors
+        trkseg.splice(4, 5, vec![]);
+        trkseg.splice(0, 2, vec![]);
+        assert_eq!(anchors(&trkseg), [Some(0), Some(0)]);
+
+        // a single point is both ends
+        trkseg.splice(1, 2, vec![]);
+        assert_eq!(anchors(&trkseg), [Some(0)]);
+    }
+
+    #[test]
+    fn test_compute_anchors_replaces_the_previous_ones() {
+        let mut trkseg = TrackSegment::default();
+        let line: Vec<_> = (0..10)
+            .map(|i| Trackpoint {
+                coordinates: crate::LngLat {
+                    lng: i as f64 * 0.001,
+                    lat: 0.0,
+                },
+                anchor: Some(5),
+                ..Default::default()
+            })
+            .collect();
+        trkseg.splice(0, 0, line);
+        trkseg.compute_anchors();
+        let mut expected = vec![None; 10];
+        expected[0] = Some(0);
+        expected[9] = Some(0);
+        assert_eq!(anchors(&trkseg), expected);
+    }
+
+    #[test]
+    fn test_splice_keeps_untouched_chunks_shared() {
+        let mut trkseg = create_track_segment(5);
+        // the ends are anchors already, or their chunks would be copied
+        trkseg.ensure_end_anchors();
+        let before = trkseg.chunks().to_vec();
+        // inside the third chunk only
+        trkseg.splice(4, 5, points(&[-1.0]));
+        assert!(Rc::ptr_eq(&trkseg.chunks()[0], &before[0]));
+        assert!(Rc::ptr_eq(&trkseg.chunks()[1], &before[1]));
+        assert!(Rc::ptr_eq(trkseg.chunks().last().unwrap(), &before[4]));
+        assert!(Rc::ptr_eq(
+            &trkseg.chunks()[trkseg.chunks().len() - 2],
+            &before[3]
+        ));
+    }
+
+    #[test]
+    fn test_splice_append_extends_last_chunk_and_respects_max_size() {
+        let mut trkseg = TrackSegment::default();
+        for i in 0..10_000 {
+            let len = trkseg.len();
+            trkseg.splice(len, len, points(&[i as f64]));
+        }
+        assert_eq!(trkseg.len(), 10_000);
+        assert!(trkseg.chunks().len() <= 3);
+        assert!(trkseg.chunks().iter().all(|c| c.trkpt.len() <= 4096));
+        assert_eq!(trkseg[9_999].ele, 9_999.0);
+        assert_eq!(trkseg.len(), 10_000);
+    }
+
+    #[test]
+    fn test_len() {
+        let nb_chunks = 10;
+        let trkseg = create_track_segment(nb_chunks);
+        assert_eq!(trkseg.len(), nb_chunks * (nb_chunks + 1) / 2);
+    }
+
+    #[test]
+    fn test_locate() {
+        let nb_chunks = 10;
+        let trkseg = create_track_segment(nb_chunks);
+        for i in 0..trkseg.len() {
+            let idx = trkseg.locate(i);
+            assert!(idx.is_some());
+            assert_eq!(trkseg[idx.unwrap()].ele, i as f64);
+        }
+
+        assert!(trkseg.locate(trkseg.len()).is_none());
+    }
+
+    #[test]
+    fn test_index() {
+        let nb_chunks = 10;
+        let trkseg = create_track_segment(nb_chunks);
+        for i in 0..trkseg.len() {
+            assert_eq!(trkseg[i].ele, i as f64);
+        }
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_index_out_of_bounds_1() {
+        let nb_chunks = 10;
+        let trkseg = create_track_segment(nb_chunks);
+        let _ = trkseg[trkseg.len()];
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_index_out_of_bounds_2() {
+        let nb_chunks = 10;
+        let trkseg = create_track_segment(nb_chunks);
+        let _ = trkseg[TrackSegmentIndex {
+            chunk: trkseg.chunks().len(),
+            pos: 0,
+            flat: 0,
+        }];
+    }
+
+    #[test]
+    fn test_iter() {
+        let nb_chunks = 10;
+        let trkseg = create_track_segment(nb_chunks);
+        for (i, trkpt) in trkseg.iter().enumerate() {
+            assert!(std::ptr::eq(&trkseg[i], trkpt));
+        }
+    }
+
+    #[test]
+    fn test_iter_nth() {
+        let nb_chunks = 10;
+        let trkseg = create_track_segment(nb_chunks);
+        let tenth = trkseg.iter().nth(10);
+        assert!(tenth.is_some());
+        assert!(std::ptr::eq(&trkseg[10], tenth.unwrap()));
+    }
+
+    #[test]
+    fn test_iter_skip() {
+        let nb_chunks = 10;
+        let trkseg = create_track_segment(nb_chunks);
+        for (i, trkpt) in trkseg.iter().enumerate().skip(5) {
+            assert!(std::ptr::eq(&trkseg[i], trkpt));
+        }
+    }
+
+    #[test]
+    fn test_first_last_index() {
+        assert!(TrackSegment::default().first_index().is_none());
+        assert!(TrackSegment::default().last_index().is_none());
+
+        let trkseg = create_track_segment(5); // 15 points in chunks of 1..=5
+        let first = trkseg.first_index().unwrap();
+        let last = trkseg.last_index().unwrap();
+        assert_eq!((first.chunk, first.pos, first.flat), (0, 0, 0));
+        assert_eq!((last.chunk, last.pos, last.flat), (4, 4, 14));
+        assert_eq!(trkseg[last].ele, 14.0);
+        assert_eq!(trkseg.locate(14), Some(last));
+        assert!(trkseg.next_index(Some(last)).is_none());
+        assert!(trkseg.prev_index(Some(first)).is_none());
+    }
+
+    #[test]
+    fn test_prev_next_are_inverse() {
+        let trkseg = create_track_segment(6);
+        let mut idx = trkseg.last_index();
+        let mut visited = vec![];
+        while let Some(i) = idx {
+            assert_eq!(trkseg.locate(i.flat), Some(i));
+            visited.push(i.flat);
+            idx = trkseg.prev_index(Some(i));
+        }
+        assert_eq!(visited, (0..trkseg.len()).rev().collect::<Vec<_>>());
+
+        let mut idx = trkseg.first_index();
+        while let Some(i) = idx {
+            let next = trkseg.next_index(Some(i));
+            if let Some(n) = next {
+                assert_eq!(trkseg.prev_index(Some(n)), Some(i));
+            }
+            idx = next;
+        }
+    }
+
+    fn points_of(n: usize) -> Vec<Trackpoint> {
+        (0..n).map(|_| Trackpoint::default()).collect()
+    }
+
+    #[test]
+    fn test_every_change_gives_a_new_revision() {
+        type Change = (&'static str, fn(&mut TrackSegment));
+        let changes: [Change; 7] = [
+            ("push", |s| s.push(TrackpointChunk::new(points_of(1)))),
+            ("push_shared", |s| {
+                s.push_shared(Rc::new(TrackpointChunk::new(points_of(1))))
+            }),
+            ("update", |s| s.update(0, |p| p.ele += 1.0)),
+            ("update_all", |s| s.update_all(|_, p| p.ele += 1.0)),
+            ("splice", |s| s.splice(1, 2, points_of(2))),
+            ("set_anchor", |s| s.set_anchor(1, 5)),
+            ("compute_anchors", |s| s.compute_anchors()),
+        ];
+        for (name, change) in changes {
+            let mut trkseg = create_track_segment(3);
+            let before = trkseg.rev_id;
+            change(&mut trkseg);
+            assert_ne!(trkseg.rev_id, before, "{name}");
+        }
+        // reading does not
+        let trkseg = create_track_segment(3);
+        let before = trkseg.rev_id;
+        let _ = trkseg.iter().count();
+        assert_eq!(trkseg.rev_id, before);
+    }
+
+    #[test]
+    fn test_ends_are_anchors_after_a_splice() {
+        let mut trkseg = create_track_segment(3);
+        trkseg.splice(0, 1, points_of(2));
+        let last = trkseg.len() - 1;
+        assert_eq!(trkseg[0].anchor, Some(0));
+        assert_eq!(trkseg[last].anchor, Some(0));
+
+        // nothing to anchor in an empty segment
+        let mut empty = TrackSegment::default();
+        empty.ensure_end_anchors();
+        assert!(empty.is_empty());
+    }
+}
@@ -0,0 +1,25 @@
+use crate::{Link, TrackSegment};
+
+use super::common::uuid_id;
+
+uuid_id!(TrackId);
+
+#[derive(Debug, Default, Clone)]
+pub struct Track {
+    pub id: TrackId,
+    pub info: TrackInfo,
+    pub trkseg: Vec<TrackSegment>,
+}
+
+#[derive(Debug, Default, Clone, PartialEq)]
+pub struct TrackInfo {
+    pub name: Option<String>,
+    pub cmt: Option<String>,
+    pub desc: Option<String>,
+    pub src: Option<String>,
+    pub links: Vec<Link>,
+    pub type_: Option<String>,
+    pub color: Option<String>,
+    pub opacity: Option<f64>,
+    pub width: Option<f64>,
+}
@@ -0,0 +1,24 @@
+use crate::LngLat;
+
+#[derive(Debug, Default, Clone)]
+pub struct Trackpoint {
+    pub coordinates: LngLat,
+    pub ele: f64,
+    pub time: Option<i64>,
+    pub atemp: Option<i16>,
+    pub hr: Option<u16>,
+    pub cad: Option<u16>,
+    pub power: Option<u16>,
+    /// Code of the surface, see [`crate::TrackpointCategories`].
+    pub surface: Option<u8>,
+    /// Code of the highway, see [`crate::TrackpointCategories`].
+    pub highway: Option<u8>,
+    /// Code of the SAC hiking scale, see [`crate::TrackpointCategories`].
+    pub sac_scale: Option<u8>,
+    /// Code of the mountain biking scale, see [`crate::TrackpointCategories`].
+    pub mtb_scale: Option<u8>,
+    /// Whether the trackpoint is an anchor of the routing tool (a point the user can drag to
+    /// reroute the segment): the lowest map zoom level at which it is shown. The first and last
+    /// trackpoints of a segment are always anchors that are always shown (zoom 0).
+    pub anchor: Option<u8>,
+}
@@ -0,0 +1,35 @@
+use crate::{Link, LngLat};
+
+use super::common::uuid_id;
+
+uuid_id!(WaypointId);
+
+#[derive(Debug, Default, Clone)]
+pub struct Waypoint {
+    pub id: WaypointId,
+    pub coordinates: LngLat,
+    pub ele: f64,
+    pub time: Option<i64>,
+    pub name: Option<String>,
+    pub cmt: Option<String>,
+    pub desc: Option<String>,
+    pub links: Vec<Link>,
+    pub sym: Option<String>,
+    pub type_: Option<String>,
+}
+
+impl Waypoint {
+    /// Whether the waypoints are the same, whatever their ids.
+    pub fn same_content(&self, other: &Waypoint) -> bool {
+        self.coordinates.lng == other.coordinates.lng
+            && self.coordinates.lat == other.coordinates.lat
+            && self.ele == other.ele
+            && self.time == other.time
+            && self.name == other.name
+            && self.cmt == other.cmt
+            && self.desc == other.desc
+            && self.links == other.links
+            && self.sym == other.sym
+            && self.type_ == other.type_
+    }
+}
@@ -0,0 +1,315 @@
+use std::ops::Deref;
+
+use crate::{Chunked, Waypoint, WaypointChunk, WaypointId};
+
+use super::common::uuid_id;
+
+uuid_id!(FileWaypointsRevisionId);
+
+/// The waypoints of a file, in chunks that are shared between the versions of the file (see
+/// [`Chunked`]).
+///
+/// Everything that changes the waypoints changes the revision too, which is why there is no
+/// mutable access to the list itself: the revision tells what is derived from the waypoints
+/// (coordinates for the map...) that it is out of date.
+#[derive(Debug, Default, Clone)]
+pub struct Waypoints {
+    chunks: Chunked<WaypointChunk>,
+    /// Changes when the waypoints do.
+    pub rev_id: FileWaypointsRevisionId,
+}
+
+impl Deref for Waypoints {
+    type Target = Chunked<WaypointChunk>;
+
+    fn deref(&self) -> &Self::Target {
+        &self.chunks
+    }
+}
+
+impl Waypoints {
+    /// Waypoints made of the given chunks, which are used as they are.
+    pub fn new(chunks: impl IntoIterator<Item = WaypointChunk>) -> Self {
+        let mut waypoints = Self::default();
+        for chunk in chunks {
+            waypoints.push(chunk);
+        }
+        waypoints
+    }
+
+    /// Adds a chunk after the last waypoint.
+    pub fn push(&mut self, chunk: WaypointChunk) {
+        self.chunks.push(chunk);
+        self.rev_id = Default::default();
+    }
+
+    /// Adds a chunk that is shared with something else after the last waypoint.
+    pub fn push_shared(&mut self, chunk: std::rc::Rc<WaypointChunk>) {
+        self.chunks.push_shared(chunk);
+        self.rev_id = Default::default();
+    }
+
+    /// Replaces the waypoints in `start..end` by `waypoints`, see [`Chunked::splice`].
+    pub fn splice(&mut self, start: usize, end: usize, waypoints: Vec<Waypoint>) {
+        self.chunks.splice(start, end, waypoints);
+        self.rev_id = Default::default();
+    }
+
+    /// Inserts waypoints, so that the first one is at `index` among the waypoints (at the end if
+    /// the index is past it). Only the chunks around the insertion are copied.
+    pub fn insert_at(&mut self, index: usize, waypoints: Vec<Waypoint>) {
+        if waypoints.is_empty() {
+            return;
+        }
+        let index = index.min(self.len());
+        self.splice(index, index, waypoints);
+    }
+
+    /// Inserts waypoints right after the waypoint `after`, or at the end if there is none (or if
+    /// it is not there). See [`Waypoints::insert_at`].
+    pub fn insert_after(&mut self, after: Option<WaypointId>, waypoints: Vec<Waypoint>) {
+        let index = after
+            .and_then(|after| self.position(after))
+            .map_or(usize::MAX, |i| i + 1);
+        self.insert_at(index, waypoints);
+    }
+
+    /// The position of the waypoint among the waypoints.
+    pub fn position(&self, id: WaypointId) -> Option<usize> {
+        self.iter().position(|wpt| wpt.id == id)
+    }
+
+    /// Edits the waypoints of the chunks that contain one accepted by `filter`, see
+    /// [`Chunked::edit`]. Returns whether anything changed.
+    pub fn edit(
+        &mut self,
+        filter: impl Fn(&Waypoint) -> bool,
+        f: impl FnMut(&mut Vec<Waypoint>) -> bool,
+    ) -> bool {
+        let changed = self.chunks.edit(filter, f);
+        if changed {
+            self.rev_id = Default::default();
+        }
+        changed
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use super::*;
+
+    fn waypoint() -> Waypoint {
+        Waypoint::default()
+    }
+
+    fn waypoints_with(chunks: &[usize]) -> (Waypoints, Vec<WaypointId>) {
+        let mut waypoints = Waypoints::default();
+        let mut ids = vec![];
+        for n in chunks {
+            let wpt: Vec<_> = (0..*n).map(|_| waypoint()).collect();
+            ids.extend(wpt.iter().map(|w| w.id));
+            waypoints.push(WaypointChunk {
+                wpt,
+                ..Default::default()
+            });
+        }
+        (waypoints, ids)
+    }
+
+    fn ids(waypoints: &Waypoints) -> Vec<WaypointId> {
+        waypoints.iter().map(|w| w.id).collect()
+    }
+
+    #[test]
+    fn test_new_and_push() {
+        let (waypoints, ids_) = waypoints_with(&[2, 1]);
+        assert_eq!(waypoints.len(), 3);
+        assert_eq!(waypoints.chunks().len(), 2);
+        assert_eq!(ids(&waypoints), ids_);
+        assert_eq!(waypoints.position(ids_[2]), Some(2));
+        assert_eq!(waypoints.position(WaypointId::default()), None);
+        // empty chunks are dropped
+        let waypoints = Waypoints::new([WaypointChunk::default()]);
+        assert!(waypoints.is_empty());
+    }
+
+    #[test]
+    fn test_insert_at_the_end() {
+        let (mut waypoints, before) = waypoints_with(&[2, 1]);
+        let first = waypoints.chunks()[0].clone();
+        let rev = waypoints.rev_id;
+        let new = vec![waypoint(), waypoint()];
+        let new_ids: Vec<_> = new.iter().map(|w| w.id).collect();
+        waypoints.insert_after(None, new);
+        assert_eq!(ids(&waypoints), [before.clone(), new_ids].concat());
+        // the chunk that is not touched is kept, the last one is extended
+        assert_eq!(waypoints.chunks().len(), 2);
+        assert!(Rc::ptr_eq(&waypoints.chunks()[0], &first));
+        assert_ne!(waypoints.rev_id, rev);
+        // an unknown waypoint is an insertion at the end too
+        let (mut waypoints, before) = waypoints_with(&[2]);
+        let one = waypoint();
+        let one_id = one.id;
+        waypoints.insert_after(Some(WaypointId::default()), vec![one]);
+        assert_eq!(ids(&waypoints), [before, vec![one_id]].concat());
+    }
+
+    #[test]
+    fn test_insert_after_the_last_waypoint_of_a_chunk_keeps_the_next_ones() {
+        let (mut waypoints, before) = waypoints_with(&[2, 2]);
+        let last = waypoints.chunks()[1].clone();
+        let one = waypoint();
+        let one_id = one.id;
+        waypoints.insert_after(Some(before[1]), vec![one]);
+        assert_eq!(
+            ids(&waypoints),
+            [&before[..2], &[one_id], &before[2..]].concat()
+        );
+        assert_eq!(waypoints.chunks().len(), 2);
+        assert!(Rc::ptr_eq(&waypoints.chunks()[1], &last));
+    }
+
+    #[test]
+    fn test_insert_in_the_middle_of_a_chunk_cuts_it() {
+        let (mut waypoints, before) = waypoints_with(&[3, 1]);
+        let last = waypoints.chunks()[1].clone();
+        let new = vec![waypoint(), waypoint()];
+        let new_ids: Vec<_> = new.iter().map(|w| w.id).collect();
+        waypoints.insert_after(Some(before[0]), new);
+        assert_eq!(
+            ids(&waypoints),
+            [&before[..1], &new_ids[..], &before[1..]].concat()
+        );
+        // the cut chunk is refilled, the other one is kept
+        assert_eq!(waypoints.chunks().len(), 2);
+        assert!(Rc::ptr_eq(&waypoints.chunks()[1], &last));
+    }
+
+    #[test]
+    fn test_insert_nothing() {
+        let (mut waypoints, before) = waypoints_with(&[2]);
+        let rev = waypoints.rev_id;
+        waypoints.insert_after(Some(before[0]), vec![]);
+        assert_eq!(ids(&waypoints), before);
+        assert_eq!(waypoints.rev_id, rev);
+    }
+
+    #[test]
+    fn test_insert_many_fills_chunks() {
+        let mut waypoints = Waypoints::default();
+        let new: Vec<_> = (0..300).map(|_| waypoint()).collect();
+        let new_ids: Vec<_> = new.iter().map(|w| w.id).collect();
+        waypoints.insert_after(None, new);
+        assert_eq!(ids(&waypoints), new_ids);
+        assert_eq!(waypoints.chunks().len(), 3);
+        assert!(waypoints.chunks()[..2].iter().all(|chunk| {
+            use crate::Chunk;
+            chunk.is_full()
+        }));
+    }
+
+    #[test]
+    fn test_insert_at_an_index() {
+        // at the start
+        let (mut waypoints, before) = waypoints_with(&[2, 1]);
+        let first = waypoints.chunks()[0].clone();
+        let one = waypoint();
+        let one_id = one.id;
+        waypoints.insert_at(0, vec![one]);
+        assert_eq!(ids(&waypoints), [vec![one_id], before.clone()].concat());
+        // the existing chunks are kept
+        assert_eq!(waypoints.chunks().len(), 3);
+        assert!(Rc::ptr_eq(&waypoints.chunks()[1], &first));
+
+        // between two chunks
+        let (mut waypoints, before) = waypoints_with(&[2, 1]);
+        let last = waypoints.chunks()[1].clone();
+        let one = waypoint();
+        let one_id = one.id;
+        waypoints.insert_at(2, vec![one]);
+        assert_eq!(
+            ids(&waypoints),
+            [&before[..2], &[one_id], &before[2..]].concat()
+        );
+        assert!(Rc::ptr_eq(&waypoints.chunks()[1], &last));
+
+        // inside a chunk
+        let (mut waypoints, before) = waypoints_with(&[3]);
+        let one = waypoint();
+        let one_id = one.id;
+        waypoints.insert_at(1, vec![one]);
+        assert_eq!(
+            ids(&waypoints),
+            [&before[..1], &[one_id], &before[1..]].concat()
+        );
+
+        // at the end, or past it
+        for index in [3, 100, usize::MAX] {
+            let (mut waypoints, before) = waypoints_with(&[3]);
+            let one = waypoint();
+            let one_id = one.id;
+            waypoints.insert_at(index, vec![one]);
+            assert_eq!(ids(&waypoints), [before, vec![one_id]].concat());
+        }
+
+        // in a file without waypoints
+        let mut waypoints = Waypoints::default();
+        let one = waypoint();
+        let one_id = one.id;
+        waypoints.insert_at(0, vec![one]);
+        assert_eq!(ids(&waypoints), vec![one_id]);
+    }
+
+    #[test]
+    fn test_splice_replaces_waypoints() {
+        let (mut waypoints, before) = waypoints_with(&[2, 2]);
+        let rev = waypoints.rev_id;
+        waypoints.splice(1, 3, vec![]);
+        assert_eq!(ids(&waypoints), [before[0], before[3]]);
+        assert_ne!(waypoints.rev_id, rev);
+    }
+
+    #[test]
+    fn test_edit_changes_the_chunks_with_a_match_only() {
+        let (mut waypoints, before) = waypoints_with(&[2, 2, 1]);
+        let (first, last) = (waypoints.chunks()[0].clone(), waypoints.chunks()[2].clone());
+        let rev = waypoints.rev_id;
+        let target = before[2];
+        let changed = waypoints.edit(
+            |wpt| wpt.id == target,
+            |wpts| {
+                wpts.retain(|wpt| wpt.id != target);
+                true
+            },
+        );
+        assert!(changed);
+        assert_ne!(waypoints.rev_id, rev);
+        assert_eq!(ids(&waypoints), [&before[..2], &before[3..]].concat());
+        // the chunks without a match are the same ones, the changed one is new
+        assert!(Rc::ptr_eq(&waypoints.chunks()[0], &first));
+        assert!(Rc::ptr_eq(&waypoints.chunks()[2], &last));
+        assert_eq!(waypoints.chunks().len(), 3);
+
+        // a chunk left empty is dropped
+        let (mut waypoints, before) = waypoints_with(&[1, 2]);
+        waypoints.edit(
+            |wpt| wpt.id == before[0],
+            |wpts| {
+                wpts.clear();
+                true
+            },
+        );
+        assert_eq!(waypoints.chunks().len(), 1);
+        assert_eq!(ids(&waypoints), before[1..]);
+
+        // a chunk that is not changed is kept, and so is the revision
+        let (mut waypoints, before) = waypoints_with(&[2]);
+        let (chunk, rev) = (waypoints.chunks()[0].clone(), waypoints.rev_id);
+        assert!(!waypoints.edit(|wpt| wpt.id == before[0], |_| false));
+        assert!(Rc::ptr_eq(&waypoints.chunks()[0], &chunk));
+        assert_eq!(waypoints.rev_id, rev);
+        assert!(!waypoints.edit(|_| false, |_| true));
+    }
+}
@@ -0,0 +1,5 @@
+mod parse;
+mod write;
+
+pub use parse::*;
+pub use write::*;
@@ -0,0 +1,766 @@
+use std::io;
+
+use chrono::DateTime;
+use quick_xml::Writer;
+use quick_xml::events::{BytesDecl, BytesText, Event};
+
+use crate::{File, Link, Track, Trackpoint, TrackpointCategories, Waypoint};
+
+/// What the written file contains: the data of the trackpoints that are `false` are left out.
+/// The same type tells which data a file has, see [`File::exportable_data`].
+///
+/// With `as_route`, the file is written with routes instead of tracks, see [`write`]. It is not
+/// data: it is off in `ALL` and `NONE`, and in what [`File::exportable_data`] gives.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct ExportOptions {
+    pub time: bool,
+    pub hr: bool,
+    pub cad: bool,
+    pub atemp: bool,
+    pub power: bool,
+    /// The OpenStreetMap data: surface, highway, SAC scale and MTB scale.
+    pub osm: bool,
+    /// Writes every segment as a route (`rte`) instead of a track.
+    pub as_route: bool,
+}
+
+impl ExportOptions {
+    pub const ALL: Self = Self::of(true);
+    pub const NONE: Self = Self::of(false);
+
+    const fn of(value: bool) -> Self {
+        Self {
+            time: value,
+            hr: value,
+            cad: value,
+            atemp: value,
+            power: value,
+            osm: value,
+            as_route: false,
+        }
+    }
+
+    /// The options that are on in `self` or in `other`.
+    pub fn union(self, other: Self) -> Self {
+        Self {
+            time: self.time || other.time,
+            hr: self.hr || other.hr,
+            cad: self.cad || other.cad,
+            atemp: self.atemp || other.atemp,
+            power: self.power || other.power,
+            osm: self.osm || other.osm,
+            as_route: self.as_route || other.as_route,
+        }
+    }
+}
+
+impl File {
+    /// The data that the trackpoints of the file have (and waypoints for the time), which the
+    /// options of [`write`] can leave out.
+    pub fn exportable_data(&self) -> ExportOptions {
+        let mut data = ExportOptions::NONE;
+        for point in self
+            .trk
+            .iter()
+            .flat_map(|trk| &trk.trkseg)
+            .flat_map(|seg| seg.iter())
+        {
+            data.time |= point.time.is_some();
+            data.hr |= point.hr.is_some();
+            data.cad |= point.cad.is_some();
+            data.atemp |= point.atemp.is_some();
+            data.power |= point.power.is_some();
+            data.osm |= point.surface.is_some()
+                || point.highway.is_some()
+                || point.sac_scale.is_some()
+                || point.mtb_scale.is_some();
+            if data == ExportOptions::ALL {
+                break;
+            }
+        }
+        data
+    }
+}
+
+const SCHEMA_LOCATION: &str = "http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/1/1/gpx.xsd http://www.garmin.com/xmlschemas/GpxExtensions/v3 http://www.garmin.com/xmlschemas/GpxExtensionsv3.xsd http://www.garmin.com/xmlschemas/TrackPointExtension/v1 http://www.garmin.com/xmlschemas/TrackPointExtensionv1.xsd http://www.garmin.com/xmlschemas/PowerExtension/v1 http://www.garmin.com/xmlschemas/PowerExtensionv1.xsd http://www.topografix.com/GPX/gpx_style/0/2 http://www.topografix.com/GPX/gpx_style/0/2/gpx_style.xsd";
+
+type XmlWriter = Writer<Vec<u8>>;
+
+/// Writes a file as GPX 1.1, in UTF-8. The surface, highway, SAC scale and MTB scale of the trackpoints are
+/// the names of their codes in `categories`.
+///
+/// The segments are written as tracks, or with `options.as_route` as routes: a segment becomes a
+/// `rte` that has the information of its track, its anchors are the `rtept` and the trackpoints
+/// between two anchors are the `gpxx:rpt` of the `rtept` before them (which only have a
+/// position, unlike the `rtept`). The first and last trackpoints always are `rtept`.
+pub fn write(file: &File, categories: &TrackpointCategories, options: ExportOptions) -> Vec<u8> {
+    let mut writer = Writer::new_with_indent(Vec::new(), b' ', 4);
+    // writing to memory does not fail
+    write_file(&mut writer, file, categories, options).expect("writing to memory");
+    writer.into_inner()
+}
+
+fn write_file(
+    w: &mut XmlWriter,
+    file: &File,
+    categories: &TrackpointCategories,
+    options: ExportOptions,
+) -> io::Result<()> {
+    w.write_event(Event::Decl(BytesDecl::new("1.0", Some("UTF-8"), None)))?;
+    w.create_element("gpx")
+        .with_attributes([
+            ("creator", "https://gpx.studio"),
+            ("version", "1.1"),
+            ("xmlns", "http://www.topografix.com/GPX/1/1"),
+            ("xmlns:xsi", "http://www.w3.org/2001/XMLSchema-instance"),
+            ("xsi:schemaLocation", SCHEMA_LOCATION),
+            (
+                "xmlns:gpxtpx",
+                "http://www.garmin.com/xmlschemas/TrackPointExtension/v1",
+            ),
+            (
+                "xmlns:gpxx",
+                "http://www.garmin.com/xmlschemas/GpxExtensions/v3",
+            ),
+            (
+                "xmlns:gpxpx",
+                "http://www.garmin.com/xmlschemas/PowerExtension/v1",
+            ),
+            (
+                "xmlns:gpx_style",
+                "http://www.topografix.com/GPX/gpx_style/0/2",
+            ),
+        ])
+        .write_inner_content(|w| {
+            write_metadata(w, file, options)?;
+            for wpt in file.wpt.iter() {
+                write_waypoint(w, wpt, options)?;
+            }
+            for trk in &file.trk {
+                // a single unnamed track is named like the file
+                let name = match (&trk.info.name, file.trk.len()) {
+                    (Some(name), _) if !name.is_empty() => Some(name.as_str()),
+                    (_, 1) => Some(file.info.name.as_str()),
+                    _ => None,
+                };
+                if options.as_route {
+                    for segment in trk.trkseg.iter().filter(|segment| !segment.is_empty()) {
+                        write_route(w, trk, segment, name, categories, options)?;
+                    }
+                } else {
+                    write_track(w, trk, name, categories, options)?;
+                }
+            }
+            Ok(())
+        })?;
+    Ok(())
+}
+
+fn text(w: &mut XmlWriter, name: &str, value: &str) -> io::Result<()> {
+    if !value.is_empty() {
+        w.create_element(name)
+            .write_text_content(BytesText::new(value))?;
+    }
+    Ok(())
+}
+
+fn optional_text(w: &mut XmlWriter, name: &str, value: &Option<String>) -> io::Result<()> {
+    text(w, name, value.as_deref().unwrap_or_default())
+}
+
+fn number(w: &mut XmlWriter, name: &str, value: impl std::fmt::Display) -> io::Result<()> {
+    text(w, name, &value.to_string())
+}
+
+fn time(w: &mut XmlWriter, millis: Option<i64>) -> io::Result<()> {
+    if let Some(time) = millis.and_then(DateTime::from_timestamp_millis) {
+        text(
+            w,
+            "time",
+            &time.format("%Y-%m-%dT%H:%M:%S%.3fZ").to_string(),
+        )?;
+    }
+    Ok(())
+}
+
+fn link(w: &mut XmlWriter, link: &Link) -> io::Result<()> {
+    if !link.href.is_empty() {
+        w.create_element("link")
+            .with_attribute(("href", link.href.as_str()))
+            .write_inner_content(|w| optional_text(w, "text", &link.text))?;
+    }
+    Ok(())
+}
+
+fn links(w: &mut XmlWriter, links: &[Link]) -> io::Result<()> {
+    links.iter().try_for_each(|l| link(w, l))
+}
+
+fn write_metadata(w: &mut XmlWriter, file: &File, options: ExportOptions) -> io::Result<()> {
+    let info = &file.info;
+    let time = options.time.then_some(info.time).flatten();
+    if info.name.is_empty()
+        && info.desc.is_none()
+        && info.author.is_none()
+        && info.links.is_empty()
+        && time.is_none()
+    {
+        return Ok(());
+    }
+    w.create_element("metadata").write_inner_content(|w| {
+        text(w, "name", &info.name)?;
+        optional_text(w, "desc", &info.desc)?;
+        if let Some(author) = &info.author {
+            w.create_element("author").write_inner_content(|w| {
+                optional_text(w, "name", &author.name)?;
+                if let Some((id, domain)) = author.email.as_deref().and_then(|e| e.split_once('@'))
+                {
+                    w.create_element("email")
+                        .with_attributes([("id", id), ("domain", domain)])
+                        .write_empty()?;
+                }
+                author.link.iter().try_for_each(|l| link(w, l))
+            })?;
+        }
+        links(w, &info.links)?;
+        self::time(w, time)
+    })?;
+    Ok(())
+}
+
+fn write_coordinates<'a>(
+    w: &'a mut XmlWriter,
+    name: &'a str,
+    coordinates: crate::LngLat,
+) -> quick_xml::writer::ElementWriter<'a, Vec<u8>> {
+    w.create_element(name).with_attributes([
+        ("lat", coordinates.lat.to_string().as_str()),
+        ("lon", coordinates.lng.to_string().as_str()),
+    ])
+}
+
+fn write_waypoint(w: &mut XmlWriter, wpt: &Waypoint, options: ExportOptions) -> io::Result<()> {
+    write_coordinates(w, "wpt", wpt.coordinates).write_inner_content(|w| {
+        number(w, "ele", wpt.ele)?;
+        if options.time {
+            time(w, wpt.time)?;
+        }
+        optional_text(w, "name", &wpt.name)?;
+        optional_text(w, "cmt", &wpt.cmt)?;
+        optional_text(w, "desc", &wpt.desc)?;
+        links(w, &wpt.links)?;
+        optional_text(w, "sym", &wpt.sym)?;
+        optional_text(w, "type", &wpt.type_)
+    })?;
+    Ok(())
+}
+
+/// The information of a track that its routes have too: name, comment, description, source,
+/// links, type and style.
+fn write_track_info(
+    w: &mut XmlWriter,
+    name: Option<&str>,
+    info: &crate::TrackInfo,
+) -> io::Result<()> {
+    text(w, "name", name.unwrap_or_default())?;
+    optional_text(w, "cmt", &info.cmt)?;
+    optional_text(w, "desc", &info.desc)?;
+    optional_text(w, "src", &info.src)?;
+    links(w, &info.links)?;
+    optional_text(w, "type", &info.type_)?;
+    if info.color.is_some() || info.opacity.is_some() || info.width.is_some() {
+        w.create_element("extensions").write_inner_content(|w| {
+            w.create_element("gpx_style:line")
+                .write_inner_content(|w| {
+                    optional_text(w, "gpx_style:color", &info.color)?;
+                    if let Some(opacity) = info.opacity {
+                        number(w, "gpx_style:opacity", opacity)?;
+                    }
+                    if let Some(width) = info.width {
+                        number(w, "gpx_style:width", width)?;
+                    }
+                    Ok(())
+                })?;
+            Ok(())
+        })?;
+    }
+    Ok(())
+}
+
+fn write_track(
+    w: &mut XmlWriter,
+    trk: &Track,
+    name: Option<&str>,
+    categories: &TrackpointCategories,
+    options: ExportOptions,
+) -> io::Result<()> {
+    w.create_element("trk").write_inner_content(|w| {
+        write_track_info(w, name, &trk.info)?;
+        for segment in &trk.trkseg {
+            w.create_element("trkseg").write_inner_content(|w| {
+                for point in segment.iter() {
+                    write_point(w, "trkpt", point, &[], categories, options)?;
+                }
+                Ok(())
+            })?;
+        }
+        Ok(())
+    })?;
+    Ok(())
+}
+
+fn write_route(
+    w: &mut XmlWriter,
+    trk: &Track,
+    segment: &crate::TrackSegment,
+    name: Option<&str>,
+    categories: &TrackpointCategories,
+    options: ExportOptions,
+) -> io::Result<()> {
+    w.create_element("rte").write_inner_content(|w| {
+        write_track_info(w, name, &trk.info)?;
+        let points: Vec<&Trackpoint> = segment.iter().collect();
+        let last = points.len() - 1;
+        let is_anchor = |i: usize| i == 0 || i == last || points[i].anchor.is_some();
+        let mut i = 0;
+        while i < points.len() {
+            // the trackpoints up to the next anchor
+            let mut next = i + 1;
+            while next < points.len() && !is_anchor(next) {
+                next += 1;
+            }
+            write_point(
+                w,
+                "rtept",
+                points[i],
+                &points[i + 1..next],
+                categories,
+                options,
+            )?;
+            i = next;
+        }
+        Ok(())
+    })?;
+    Ok(())
+}
+
+/// A trackpoint or a route point (`tag`). A route point has the `path` that leads to the next one,
+/// of which only the positions are written.
+fn write_point(
+    w: &mut XmlWriter,
+    tag: &str,
+    point: &Trackpoint,
+    path: &[&Trackpoint],
+    categories: &TrackpointCategories,
+    options: ExportOptions,
+) -> io::Result<()> {
+    let atemp = point.atemp.filter(|_| options.atemp);
+    let hr = point.hr.filter(|_| options.hr);
+    let cad = point.cad.filter(|_| options.cad);
+    let power = point.power.filter(|_| options.power);
+    let osm = [
+        ("surface", point.surface, &categories.surface),
+        ("highway", point.highway, &categories.highway),
+        ("sac_scale", point.sac_scale, &categories.sac_scale),
+        ("mtb_scale", point.mtb_scale, &categories.mtb_scale),
+    ]
+    .map(|(name, code, categories)| {
+        let value = code
+            .filter(|_| options.osm)
+            .and_then(|code| categories.name(code));
+        (name, value)
+    });
+    let has_osm = osm.iter().any(|(_, value)| value.is_some());
+    let has_track_point_extension = atemp.is_some() || hr.is_some() || cad.is_some() || has_osm;
+
+    write_coordinates(w, tag, point.coordinates).write_inner_content(|w| {
+        number(w, "ele", point.ele)?;
+        if options.time {
+            time(w, point.time)?;
+        }
+        if !has_track_point_extension && power.is_none() && path.is_empty() {
+            return Ok(());
+        }
+        w.create_element("extensions").write_inner_content(|w| {
+            if has_track_point_extension {
+                w.create_element("gpxtpx:TrackPointExtension")
+                    .write_inner_content(|w| {
+                        if let Some(atemp) = atemp {
+                            number(w, "gpxtpx:atemp", atemp)?;
+                        }
+                        if let Some(hr) = hr {
+                            number(w, "gpxtpx:hr", hr)?;
+                        }
+                        if let Some(cad) = cad {
+                            number(w, "gpxtpx:cad", cad)?;
+                        }
+                        if has_osm {
+                            w.create_element("gpxtpx:Extensions")
+                                .write_inner_content(|w| {
+                                    for (name, value) in osm {
+                                        text(w, name, value.unwrap_or_default())?;
+                                    }
+                                    Ok(())
+                                })?;
+                        }
+                        Ok(())
+                    })?;
+            }
+            if let Some(power) = power {
+                w.create_element("gpxpx:PowerExtension")
+                    .write_inner_content(|w| number(w, "gpxpx:PowerInWatts", power))?;
+            }
+            if !path.is_empty() {
+                w.create_element("gpxx:RoutePointExtension")
+                    .write_inner_content(|w| {
+                        for point in path {
+                            write_coordinates(w, "gpxx:rpt", point.coordinates).write_empty()?;
+                        }
+                        Ok(())
+                    })?;
+            }
+            Ok(())
+        })?;
+        Ok(())
+    })?;
+    Ok(())
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::parse;
+
+    use super::*;
+
+    fn read(name: &str) -> (File, TrackpointCategories) {
+        let mut categories = TrackpointCategories::default();
+        let data = std::fs::read(format!("data/{name}.gpx")).unwrap();
+        (parse(&data, &mut categories).unwrap(), categories)
+    }
+
+    fn written_text(
+        file: &File,
+        categories: &TrackpointCategories,
+        options: ExportOptions,
+    ) -> String {
+        String::from_utf8(write(file, categories, options)).unwrap()
+    }
+
+    /// Writes a file and reads it again.
+    fn round_trip(name: &str, options: ExportOptions) -> (File, File, TrackpointCategories) {
+        let (file, mut categories) = read(name);
+        let written = write(&file, &categories, options);
+        let again = parse(&written, &mut categories).unwrap();
+        (file, again, categories)
+    }
+
+    fn points(file: &File) -> Vec<Trackpoint> {
+        file.trk
+            .iter()
+            .flat_map(|trk| &trk.trkseg)
+            .flat_map(|seg| seg.iter().cloned())
+            .collect()
+    }
+
+    fn same_points(a: &[Trackpoint], b: &[Trackpoint]) {
+        assert_eq!(a.len(), b.len());
+        for (a, b) in a.iter().zip(b) {
+            assert_eq!(a.coordinates.lat, b.coordinates.lat);
+            assert_eq!(a.coordinates.lng, b.coordinates.lng);
+            assert_eq!(a.ele, b.ele);
+            assert_eq!(a.time, b.time);
+            assert_eq!(a.atemp, b.atemp);
+            assert_eq!(a.hr, b.hr);
+            assert_eq!(a.cad, b.cad);
+            assert_eq!(a.power, b.power);
+            assert_eq!(a.surface, b.surface);
+            assert_eq!(a.highway, b.highway);
+            assert_eq!(a.sac_scale, b.sac_scale);
+            assert_eq!(a.mtb_scale, b.mtb_scale);
+        }
+    }
+
+    #[test]
+    fn test_links_and_the_email_are_written() {
+        let data = std::fs::read("data/with_links.gpx").unwrap();
+        let file = parse(&data, &mut Default::default()).unwrap();
+        let again = parse(
+            &write(&file, &Default::default(), ExportOptions::ALL),
+            &mut Default::default(),
+        )
+        .unwrap();
+
+        assert_eq!(again.info.links, file.info.links);
+        assert_eq!(again.info.links.len(), 2);
+        assert_eq!(again.info.author, file.info.author);
+        assert_eq!(
+            again.info.author.as_ref().unwrap().email.as_deref(),
+            Some("someone@example.com")
+        );
+        let waypoints = |file: &File| file.wpt.iter().map(|w| w.links.clone()).collect::<Vec<_>>();
+        assert_eq!(waypoints(&again), waypoints(&file));
+        assert_eq!(again.wpt.iter().next().unwrap().links.len(), 3);
+        for (a, b) in again.trk.iter().zip(&file.trk) {
+            assert_eq!(a.info.links, b.info.links);
+            assert_eq!(a.info.links.len(), 2);
+        }
+    }
+
+    #[test]
+    fn test_files_survive_a_round_trip() {
+        for name in [
+            "simple",
+            "with_links",
+            "with_time",
+            "with_hr",
+            "with_cad",
+            "with_temp",
+            "with_power_1",
+            "with_power_2",
+            "with_surface",
+            "with_highway",
+            "with_style",
+            "with_waypoint",
+            "with_tracks_and_segments",
+            "self_closing_points",
+        ] {
+            let (file, again, _) = round_trip(name, ExportOptions::ALL);
+            assert_eq!(file.info.name, again.info.name, "{name}");
+            assert_eq!(file.info.desc, again.info.desc, "{name}");
+            assert_eq!(file.info.author, again.info.author, "{name}");
+            assert_eq!(file.trk.len(), again.trk.len(), "{name}");
+            for (a, b) in file.trk.iter().zip(&again.trk) {
+                assert_eq!(a.info, b.info, "{name}");
+                assert_eq!(a.trkseg.len(), b.trkseg.len(), "{name}");
+            }
+            same_points(&points(&file), &points(&again));
+            let waypoints: Vec<_> = file.wpt.iter().collect();
+            let again_waypoints: Vec<_> = again.wpt.iter().collect();
+            assert_eq!(waypoints.len(), again_waypoints.len(), "{name}");
+            for (a, b) in waypoints.iter().zip(&again_waypoints) {
+                assert!(a.same_content(b), "{name}");
+            }
+        }
+    }
+
+    #[test]
+    fn test_options_leave_data_out() {
+        let (file, categories) = read("with_hr");
+        assert!(points(&file).iter().any(|p| p.hr.is_some()));
+        let options = ExportOptions {
+            hr: false,
+            ..ExportOptions::ALL
+        };
+        let written = written_text(&file, &categories, options);
+        assert!(!written.contains("hr>"));
+
+        let (file, categories) = read("with_time");
+        let options = ExportOptions {
+            time: false,
+            ..ExportOptions::ALL
+        };
+        assert!(!written_text(&file, &categories, options).contains("<time>"));
+        assert!(
+            written_text(&file, &categories, ExportOptions::ALL)
+                .contains("<time>2023-12-31T23:00:00.000Z</time>")
+        );
+    }
+
+    #[test]
+    fn test_text_is_escaped_and_the_single_track_gets_the_name_of_the_file() {
+        let (mut file, categories) = read("simple");
+        file.info.name = "a <b> & c".into();
+        file.trk.truncate(1);
+        file.trk[0].info.name = None;
+        let written = write(&file, &categories, ExportOptions::ALL);
+        let text = String::from_utf8(written.clone()).unwrap();
+        assert!(text.contains("a &lt;b&gt; &amp; c"));
+        // the track has the name of the file
+        assert_eq!(text.matches("a &lt;b&gt; &amp; c").count(), 2);
+        // and it is read back as it was
+        let mut categories = categories;
+        let again = parse(&written, &mut categories).unwrap();
+        assert_eq!(again.info.name, "a <b> & c");
+        assert_eq!(again.trk[0].info.name.as_deref(), Some("a <b> & c"));
+    }
+
+    #[test]
+    fn test_exportable_data() {
+        let (file, _) = read("with_time");
+        let data = file.exportable_data();
+        assert!(data.time && !data.hr && !data.osm);
+        let (file, _) = read("with_surface");
+        assert!(file.exportable_data().osm);
+        let (file, _) = read("with_power_2");
+        assert!(file.exportable_data().power);
+    }
+
+    fn as_route() -> ExportOptions {
+        ExportOptions {
+            as_route: true,
+            ..ExportOptions::ALL
+        }
+    }
+
+    fn count(text: &str, pattern: &str) -> usize {
+        text.matches(pattern).count()
+    }
+
+    #[test]
+    fn test_export_as_route_writes_routes_instead_of_tracks() {
+        let (file, categories) = read("with_route_points");
+        let text = written_text(&file, &categories, as_route());
+
+        assert_eq!(count(&text, "<rte>"), 1);
+        assert_eq!(count(&text, "<trk>"), 0);
+        assert_eq!(count(&text, "<trkseg>"), 0);
+        assert_eq!(count(&text, "<trkpt"), 0);
+        // the anchors are the route points, the trackpoints between them the points of their path
+        assert_eq!(count(&text, "<rtept"), 3);
+        assert_eq!(count(&text, "<gpxx:rpt"), 4);
+        assert_eq!(count(&text, "<gpxx:RoutePointExtension>"), 2);
+        // a route has the information of its track
+        assert!(text.contains("<name>Lausanne</name>"));
+        assert!(text.contains("<cmt>comment</cmt>"));
+        assert!(text.contains("<desc>description</desc>"));
+        assert!(text.contains("<type>Cycling</type>"));
+        // and its points only have a position in the path, and an elevation as route points
+        let first_rtept = &text[text.find("<rtept").unwrap()..];
+        let (lat, lng) = (46.54462809674442_f64, 6.658079791814089_f64);
+        assert!(first_rtept.starts_with(&format!("<rtept lat=\"{lat}\" lon=\"{lng}\">")));
+        assert!(first_rtept.contains("<ele>500</ele>"));
+        let (lat, lng) = (46.54441595077515_f64, 6.658358573913574_f64);
+        assert!(text.contains(&format!("<gpxx:rpt lat=\"{lat}\" lon=\"{lng}\"/>")));
+    }
+
+    #[test]
+    fn test_a_route_survives_being_exported_as_a_route() {
+        let (file, mut categories) = read("with_route_points");
+        let written = write(&file, &categories, as_route());
+        let again = parse(&written, &mut categories).unwrap();
+
+        assert_eq!(again.trk.len(), 1);
+        assert_eq!(again.trk[0].info, file.trk[0].info);
+        let (a, b) = (&file.trk[0].trkseg[0], &again.trk[0].trkseg[0]);
+        assert_eq!(a.len(), b.len());
+        for (a, b) in a.iter().zip(b.iter()) {
+            assert_eq!(a.coordinates.lat, b.coordinates.lat);
+            assert_eq!(a.coordinates.lng, b.coordinates.lng);
+            assert_eq!(a.anchor, b.anchor);
+        }
+        // the elevation of the route points is kept, the other ones are worked out again
+        let anchors = |s: &crate::TrackSegment| {
+            s.iter()
+                .filter(|p| p.anchor.is_some())
+                .map(|p| p.ele)
+                .collect::<Vec<_>>()
+        };
+        assert_eq!(anchors(a), anchors(b));
+    }
+
+    #[test]
+    fn test_tracks_become_one_route_per_segment_with_the_information_of_the_track() {
+        let (file, mut categories) = read("with_tracks_and_segments");
+        let segments: usize = file.trk.iter().map(|t| t.trkseg.len()).sum();
+        assert!(segments > 2);
+        let written = write(&file, &categories, as_route());
+        let text = String::from_utf8(written.clone()).unwrap();
+        assert_eq!(count(&text, "<rte>"), segments);
+        assert_eq!(count(&text, "<trk>"), 0);
+        // every route starts and ends with a route point
+        assert_eq!(count(&text, "</rte>"), segments);
+
+        let again = parse(&written, &mut categories).unwrap();
+        assert_eq!(again.trk.len(), segments);
+        let mut routes = again.trk.iter();
+        for track in &file.trk {
+            for segment in &track.trkseg {
+                let route = routes.next().unwrap();
+                // the information of the track, repeated for each of its segments
+                assert_eq!(route.info.name, track.info.name);
+                assert_eq!(route.info.type_, track.info.type_);
+                let (a, b) = (segment, &route.trkseg[0]);
+                assert_eq!(a.len(), b.len());
+                for (a, b) in a.iter().zip(b.iter()) {
+                    assert_eq!(
+                        (a.coordinates.lat, a.coordinates.lng),
+                        (b.coordinates.lat, b.coordinates.lng)
+                    );
+                }
+                // the anchors of the segment are the ones of its route
+                let anchors = |s: &crate::TrackSegment| {
+                    s.iter()
+                        .enumerate()
+                        .filter(|(_, p)| p.anchor.is_some())
+                        .map(|(i, _)| i)
+                        .collect::<Vec<_>>()
+                };
+                assert_eq!(anchors(a), anchors(b));
+            }
+        }
+    }
+
+    #[test]
+    fn test_the_ends_of_a_route_are_route_points_even_without_anchors() {
+        let (mut file, categories) = read("simple");
+        file.trk[0].trkseg[0].update_all(|_, point| point.anchor = None);
+        let len = file.trk[0].trkseg[0].len();
+        let text = written_text(&file, &categories, as_route());
+        assert_eq!(count(&text, "<rtept"), 2);
+        assert_eq!(count(&text, "<gpxx:rpt"), len - 2);
+        // and a single trackpoint is a route of one point
+        file.trk[0].trkseg[0].splice(1, len, vec![]);
+        let text = written_text(&file, &categories, as_route());
+        assert_eq!(count(&text, "<rtept"), 1);
+        assert_eq!(count(&text, "<gpxx:rpt"), 0);
+    }
+
+    #[test]
+    fn test_empty_segments_are_not_routes() {
+        let (mut file, categories) = read("simple");
+        file.trk[0].trkseg.push(crate::TrackSegment::default());
+        let text = written_text(&file, &categories, as_route());
+        assert_eq!(count(&text, "<rte>"), 1);
+    }
+
+    #[test]
+    fn test_routes_have_the_style_of_their_track() {
+        let (file, categories) = read("with_style");
+        let text = written_text(&file, &categories, as_route());
+        assert!(count(&text, "<gpx_style:line>") >= 1);
+        assert_eq!(count(&text, "<gpx_style:line>"), count(&text, "<rte>"));
+        let again = parse(text.as_bytes(), &mut Default::default()).unwrap();
+        assert_eq!(again.trk[0].info.color, file.trk[0].info.color);
+        assert_eq!(again.trk[0].info.width, file.trk[0].info.width);
+    }
+
+    #[test]
+    fn test_route_points_keep_their_data_and_the_options_apply_to_them() {
+        let (file, categories) = read("with_hr");
+        let with_all = written_text(&file, &categories, as_route());
+        assert!(with_all.contains("<gpxtpx:hr>"));
+        let without = written_text(
+            &file,
+            &categories,
+            ExportOptions {
+                hr: false,
+                time: false,
+                as_route: true,
+                ..ExportOptions::ALL
+            },
+        );
+        assert!(!without.contains("<gpxtpx:hr>"));
+        assert!(!without.contains("<time>"));
+    }
+
+    #[test]
+    fn test_the_route_option_is_not_data() {
+        let (file, _) = read("with_route_points");
+        assert!(!file.exportable_data().as_route);
+        // it is a way to write the data, never part of them
+        let all = std::hint::black_box(ExportOptions::ALL);
+        assert!(!all.as_route && !ExportOptions::NONE.as_route);
+        assert!(as_route().union(ExportOptions::NONE).as_route);
+        assert!(!ExportOptions::ALL.union(ExportOptions::NONE).as_route);
+    }
+}
@@ -0,0 +1,11 @@
+mod algorithm;
+pub(crate) mod gpx;
+mod io;
+pub(crate) mod statistics;
+mod utils;
+
+pub use algorithm::*;
+pub use gpx::*;
+pub use io::*;
+pub use statistics::*;
+pub use utils::*;
@@ -0,0 +1,527 @@
+use crate::{
+    LngLat, LngLatBounds, TrackSegment, TrackSegmentIndex, Trackpoint, distance, for_each_window,
+    max_options, min_options, ramer_douglas_peucker, slope, speed, sum_options, time_diff,
+};
+
+/// Time between two trackpoints, to size the windows of a smoothing. It is unknown when one of
+/// them has no time, which is longer than any known time span: the window does not go there.
+#[derive(Clone, Copy, PartialEq, PartialOrd)]
+enum TimeSpan {
+    Known(i64),
+    Unknown,
+}
+
+impl TimeSpan {
+    fn between(end: Option<i64>, start: Option<i64>) -> Self {
+        time_diff(end, start).map_or(Self::Unknown, Self::Known)
+    }
+}
+
+#[derive(Default, Debug)]
+pub struct Statistics {
+    pub global: GlobalStatistics,
+    pub local: Vec<TrackpointStatistics>,
+}
+
+impl Statistics {
+    pub fn total_speed(&self) -> Option<f64> {
+        self.global.total_speed()
+    }
+
+    pub fn moving_speed(&self) -> Option<f64> {
+        self.global.moving_speed()
+    }
+
+    pub fn compute(trkseg: &TrackSegment) -> Self {
+        let mut stats = Self::default();
+        if trkseg.is_empty() {
+            return stats;
+        }
+
+        let mut prev = &trkseg[0];
+        for cur in trkseg.iter() {
+            stats.accumulate(prev, cur);
+            prev = cur;
+        }
+
+        stats.compute_smoothed_speed(trkseg);
+        stats.compute_smoothed_elevation_segments(trkseg);
+        stats.compute_smoothed_slope(trkseg);
+
+        stats
+    }
+
+    fn accumulate(&mut self, prev: &Trackpoint, cur: &Trackpoint) {
+        self.accumulate_distance_and_time(prev, cur);
+        self.update_time_bounds(cur.time);
+        self.update_bounds(cur.coordinates);
+        self.local
+            .push(TrackpointStatistics::from_partial_stats(self));
+    }
+
+    fn accumulate_distance_and_time(&mut self, prev: &Trackpoint, cur: &Trackpoint) {
+        let dist = distance(prev.coordinates, cur.coordinates);
+        let time = time_diff(cur.time, prev.time);
+
+        self.global.total_distance += dist;
+
+        let moving = time
+            .zip(time.and_then(|time| speed(dist, time)))
+            .filter(|(_, speed)| (0.5..=1500.0).contains(speed));
+        if let Some((time, _)) = moving {
+            self.global.moving_distance = self
+                .global
+                .moving_distance
+                .map_or(Some(dist), |d| Some(d + dist));
+            self.global.moving_time = self
+                .global
+                .moving_time
+                .map_or(Some(time), |t| Some(t + time));
+        }
+    }
+
+    fn update_time_bounds(&mut self, time: Option<i64>) {
+        if let Some(time) = time {
+            if self.global.start_time.is_none() {
+                self.global.start_time = Some(time);
+            }
+            self.global.end_time = Some(time);
+            self.global.total_time = time_diff(self.global.end_time, self.global.start_time);
+        }
+    }
+
+    fn update_bounds(&mut self, coordinates: LngLat) {
+        self.global.bounds.extend(coordinates);
+    }
+
+    /// Speed over a window of 10 seconds on each side of the trackpoints that have a time (the
+    /// others have no speed). The windows do not extend to the trackpoints without time: if the
+    /// previous or next trackpoint has none, the window ends at the trackpoint itself on that side.
+    fn compute_smoothed_speed(&mut self, trkseg: &TrackSegment) {
+        for_each_window!(
+            trkseg,
+            trkseg.first_index(),
+            trkseg.last_index(),
+            TimeSpan::Known(10_000),
+            |i, j| TimeSpan::between(trkseg[j].time, trkseg[i].time),
+            |i, left, right| {
+                if trkseg[i].time.is_some() {
+                    let timed = |index: TrackSegmentIndex| {
+                        if trkseg[index].time.is_some() {
+                            index
+                        } else {
+                            i
+                        }
+                    };
+                    let (left, right) = (timed(left), timed(right));
+                    self.local[i.flat].speed = time_diff(trkseg[right].time, trkseg[left].time)
+                        .and_then(|time| {
+                            speed(
+                                self.local[right.flat].total_distance
+                                    - self.local[left.flat].total_distance,
+                                time,
+                            )
+                        });
+                }
+            },
+        );
+    }
+
+    fn compute_smoothed_elevation_segments(&mut self, trkseg: &TrackSegment) {
+        let simplified = self.get_elevation_extremas(trkseg);
+
+        for i in 0..(simplified.len() - 1) {
+            let start = simplified[i];
+            let end = simplified[i + 1];
+            let last = i + 1 == simplified.len() - 1;
+
+            self.compute_smoothed_elevation_gain(trkseg, start, end, last);
+
+            let segment_dist =
+                self.local[end.flat].total_distance - self.local[start.flat].total_distance;
+            let segment_ele = trkseg[end].ele - trkseg[start].ele;
+            let segment_slope = slope(segment_ele, segment_dist);
+            for k in start.flat..(end.flat + last as usize) {
+                self.local[k].slope_segment = SlopeSegment {
+                    slope: segment_slope,
+                    distance: segment_dist,
+                };
+            }
+        }
+    }
+
+    fn compute_smoothed_elevation_gain(
+        &mut self,
+        trkseg: &TrackSegment,
+        start: TrackSegmentIndex,
+        end: TrackSegmentIndex,
+        last: bool,
+    ) {
+        let mut cumul_ele = 0.0;
+        let mut current_left = start;
+        let mut current_right = Some(start);
+        let mut prev_smoothed_ele = trkseg[start].ele;
+
+        for_each_window!(
+            trkseg,
+            Some(start),
+            Some(end),
+            0.1,
+            |i, j| self.local[j.flat].total_distance - self.local[i.flat].total_distance,
+            |i, left, right| {
+                while current_left != left {
+                    cumul_ele -= trkseg[current_left].ele;
+                    current_left = trkseg.next_index(Some(current_left)).unwrap();
+                }
+                while let Some(current) = current_right {
+                    if current > right {
+                        break;
+                    }
+                    cumul_ele += trkseg[current].ele;
+                    current_right = trkseg.next_index(current_right);
+                }
+
+                let smoothed_ele = if i == start || i == end {
+                    trkseg[i].ele
+                } else {
+                    cumul_ele / (right.flat - left.flat + 1) as f64
+                };
+
+                let delta = smoothed_ele - prev_smoothed_ele;
+                if delta > 0.0 {
+                    self.global.elevation_gain += delta;
+                } else if delta < 0.0 {
+                    self.global.elevation_loss -= delta;
+                }
+
+                if i < end || last {
+                    self.local[i.flat].elevation_gain = self.global.elevation_gain;
+                    self.local[i.flat].elevation_loss = self.global.elevation_loss;
+                }
+
+                prev_smoothed_ele = smoothed_ele;
+            },
+        );
+    }
+
+    fn compute_smoothed_slope(&mut self, trkseg: &TrackSegment) {
+        for_each_window!(
+            trkseg,
+            trkseg.first_index(),
+            trkseg.last_index(),
+            0.05,
+            |i, j| self.local[j.flat].total_distance - self.local[i.flat].total_distance,
+            |i, left, right| {
+                let dist =
+                    self.local[right.flat].total_distance - self.local[left.flat].total_distance;
+                let ele = trkseg[right].ele - trkseg[left].ele;
+                self.local[i.flat].slope = slope(ele, dist);
+            },
+        );
+    }
+
+    fn get_elevation_extremas(&self, trkseg: &TrackSegment) -> Vec<TrackSegmentIndex> {
+        ramer_douglas_peucker(
+            trkseg,
+            &|idx| {
+                (
+                    self.local[idx.flat].total_distance * 1000.0,
+                    trkseg[idx].ele,
+                )
+            },
+            20.0,
+        )
+    }
+}
+
+#[derive(Default, Debug)]
+pub struct GlobalStatistics {
+    pub total_distance: f64,
+    pub moving_distance: Option<f64>,
+    pub total_time: Option<i64>,
+    pub moving_time: Option<i64>,
+    pub elevation_gain: f64,
+    pub elevation_loss: f64,
+    pub start_time: Option<i64>,
+    pub end_time: Option<i64>,
+    pub bounds: LngLatBounds,
+}
+
+impl GlobalStatistics {
+    /// Average speed over the total time, unknown if that is not a positive duration (for
+    /// example a range with a single timestamp, or timestamps going backwards).
+    pub fn total_speed(&self) -> Option<f64> {
+        self.total_time.and_then(|t| speed(self.total_distance, t))
+    }
+
+    /// Average speed over the moving time, unknown if there is no moving time.
+    pub fn moving_speed(&self) -> Option<f64> {
+        self.moving_distance
+            .zip(self.moving_time)
+            .and_then(|(d, t)| speed(d, t))
+    }
+
+    pub fn merge(&mut self, other: &GlobalStatistics) {
+        self.total_distance += other.total_distance;
+        self.moving_distance = sum_options(self.moving_distance, other.moving_distance);
+        self.total_time = sum_options(self.total_time, other.total_time);
+        self.moving_time = sum_options(self.moving_time, other.moving_time);
+        self.elevation_gain += other.elevation_gain;
+        self.elevation_loss += other.elevation_loss;
+        self.start_time = min_options(self.start_time, other.start_time);
+        self.end_time = max_options(self.end_time, other.end_time);
+        self.bounds.merge(&other.bounds);
+    }
+}
+
+#[derive(Default, Debug)]
+pub struct TrackpointStatistics {
+    pub total_distance: f64,
+    pub moving_distance: Option<f64>,
+    pub total_time: Option<i64>,
+    pub moving_time: Option<i64>,
+    pub speed: Option<f64>,
+    pub elevation_gain: f64,
+    pub elevation_loss: f64,
+    pub slope: f64,
+    pub slope_segment: SlopeSegment,
+}
+
+impl TrackpointStatistics {
+    fn from_partial_stats(stats: &Statistics) -> Self {
+        Self {
+            total_distance: stats.global.total_distance,
+            moving_distance: stats.global.moving_distance,
+            total_time: stats.global.total_time,
+            moving_time: stats.global.moving_time,
+            // stats below are computed later
+            speed: None,
+            elevation_gain: Default::default(),
+            elevation_loss: Default::default(),
+            slope: Default::default(),
+            slope_segment: Default::default(),
+        }
+    }
+}
+
+#[derive(Default, Debug)]
+pub struct SlopeSegment {
+    pub slope: f64,
+    pub distance: f64,
+}
+
+#[cfg(test)]
+mod tests {
+    use std::{fs::File, io::Read};
+
+    use crate::parse;
+
+    use super::*;
+
+    #[test]
+    fn test_compute_smoothed_speed() {
+        let mut f = File::open("data/with_time.gpx").unwrap();
+        let mut data = String::new();
+        let _ = f.read_to_string(&mut data);
+        let gpx = parse(data.as_bytes(), &mut Default::default()).unwrap();
+
+        let trkseg = &gpx.trk[0].trkseg[0];
+        let stats = Statistics::compute(trkseg);
+        assert_eq!(stats.local.len(), trkseg.len());
+        for trkpt_stats in stats.local.iter() {
+            assert!(trkpt_stats.speed.is_some());
+            let speed = trkpt_stats.speed.unwrap();
+            assert_ne!(speed, f64::NAN);
+            assert!((speed - 20.0).abs() < 0.1);
+        }
+    }
+
+    /// The speeds of the segment of `data/with_time.gpx` (80 trackpoints at 20 km/h) once the
+    /// trackpoints at `holes` have lost their time.
+    fn speeds_with_holes(holes: &[usize]) -> Vec<Option<f64>> {
+        let gpx = load("data/with_time.gpx");
+        let mut segment = gpx.trk[0].trkseg[0].clone();
+        let points: Vec<_> = segment
+            .iter()
+            .enumerate()
+            .map(|(i, trkpt)| {
+                let mut trkpt = trkpt.clone();
+                if holes.contains(&i) {
+                    trkpt.time = None;
+                }
+                trkpt
+            })
+            .collect();
+        segment.splice(0, points.len(), points);
+        Statistics::compute(&segment)
+            .local
+            .iter()
+            .map(|local| local.speed)
+            .collect()
+    }
+
+    /// Without time, there is no speed. With one, the speed is the one of the trackpoints around.
+    fn assert_speeds_with_holes(holes: &[usize]) {
+        let speeds = speeds_with_holes(holes);
+        assert_eq!(speeds.len(), 80);
+        for (i, speed) in speeds.iter().enumerate() {
+            if holes.contains(&i) {
+                assert_eq!(*speed, None, "trackpoint {i}");
+            } else {
+                let speed = speed.unwrap_or_else(|| panic!("no speed for trackpoint {i}"));
+                assert!((speed - 20.0).abs() < 0.1, "trackpoint {i}: {speed}");
+            }
+        }
+    }
+
+    #[test]
+    fn test_speed_without_holes() {
+        assert_speeds_with_holes(&[]);
+    }
+
+    #[test]
+    fn test_speed_with_holes_at_the_beginning() {
+        assert_speeds_with_holes(&[0, 1, 2, 3, 4]);
+    }
+
+    #[test]
+    fn test_speed_with_holes_at_the_end() {
+        assert_speeds_with_holes(&[75, 76, 77, 78, 79]);
+    }
+
+    #[test]
+    fn test_speed_with_holes_at_both_ends() {
+        assert_speeds_with_holes(&[0, 1, 2, 77, 78, 79]);
+    }
+
+    #[test]
+    fn test_speed_with_holes_in_the_middle() {
+        assert_speeds_with_holes(&[40]);
+        assert_speeds_with_holes(&[30, 31, 32, 33, 34]);
+        assert_speeds_with_holes(&(20..60).collect::<Vec<_>>());
+    }
+
+    #[test]
+    fn test_speed_with_scattered_holes() {
+        let holes: Vec<_> = (0..80).step_by(7).collect();
+        assert_speeds_with_holes(&holes);
+    }
+
+    #[test]
+    fn test_speed_without_any_time() {
+        let holes: Vec<_> = (0..80).collect();
+        assert!(speeds_with_holes(&holes).iter().all(Option::is_none));
+    }
+
+    fn load(path: &str) -> crate::File {
+        let mut f = File::open(path).unwrap();
+        let mut data = String::new();
+        let _ = f.read_to_string(&mut data);
+        parse(data.as_bytes(), &mut Default::default()).unwrap()
+    }
+
+    #[test]
+    fn test_compute_empty_segment() {
+        let stats = Statistics::compute(&TrackSegment::default());
+        assert!(stats.local.is_empty());
+        assert_eq!(stats.global.total_distance, 0.0);
+    }
+
+    #[test]
+    fn test_compute_distance_and_bounds() {
+        let gpx = load("data/simple.gpx");
+        let trkseg = &gpx.trk[0].trkseg[0];
+        let stats = Statistics::compute(trkseg);
+
+        assert_eq!(stats.local.len(), trkseg.len());
+        assert_eq!(stats.local[0].total_distance, 0.0);
+        assert!(stats.global.total_distance > 0.0);
+        // cumulative distance never decreases and ends at the global distance
+        assert!(
+            stats
+                .local
+                .windows(2)
+                .all(|w| w[0].total_distance <= w[1].total_distance)
+        );
+        let last = stats.local.last().unwrap();
+        assert!((last.total_distance - stats.global.total_distance).abs() < 1e-9);
+        assert!(stats.global.elevation_gain >= 0.0);
+        assert!(stats.global.elevation_loss >= 0.0);
+
+        // every point lies inside the bounds
+        let b = &stats.global.bounds;
+        for trkpt in trkseg.iter() {
+            assert!(b.sw.lng <= trkpt.coordinates.lng && trkpt.coordinates.lng <= b.ne.lng);
+            assert!(b.sw.lat <= trkpt.coordinates.lat && trkpt.coordinates.lat <= b.ne.lat);
+        }
+    }
+
+    #[test]
+    fn test_compute_time() {
+        let gpx = load("data/with_time.gpx");
+        let stats = Statistics::compute(&gpx.trk[0].trkseg[0]);
+        let total_time = stats.global.total_time.unwrap();
+        assert!(total_time > 0);
+        let speed = stats.global.total_speed().unwrap();
+        assert!((speed - 20.0).abs() < 0.5, "{speed}");
+    }
+
+    #[test]
+    fn test_no_time_without_timestamps() {
+        let gpx = load("data/simple.gpx");
+        let stats = Statistics::compute(&gpx.trk[0].trkseg[0]);
+        assert!(stats.global.total_time.is_none());
+        assert!(stats.global.total_speed().is_none());
+        assert!(stats.local.iter().all(|s| s.speed.is_none()));
+    }
+
+    #[test]
+    fn test_global_merge() {
+        let mut a = GlobalStatistics {
+            total_distance: 1.0,
+            elevation_gain: 10.0,
+            moving_time: Some(5),
+            ..Default::default()
+        };
+        a.bounds.extend(crate::LngLat { lng: 0.0, lat: 0.0 });
+        let mut b = GlobalStatistics {
+            total_distance: 2.0,
+            elevation_loss: 4.0,
+            moving_distance: Some(1.5),
+            moving_time: Some(7),
+            ..Default::default()
+        };
+        b.bounds.extend(crate::LngLat { lng: 2.0, lat: 3.0 });
+
+        a.merge(&b);
+        assert_eq!(a.total_distance, 3.0);
+        assert_eq!(a.elevation_gain, 10.0);
+        assert_eq!(a.elevation_loss, 4.0);
+        assert_eq!(a.moving_distance, Some(1.5));
+        assert_eq!(a.moving_time, Some(12));
+        assert_eq!(a.total_time, None);
+
+        let mut c = GlobalStatistics {
+            start_time: Some(1_000),
+            end_time: Some(4_000),
+            total_time: Some(3_000),
+            ..Default::default()
+        };
+        let d = GlobalStatistics {
+            start_time: Some(10_000),
+            end_time: Some(12_000),
+            total_time: Some(2_000),
+            ..Default::default()
+        };
+        c.merge(&d);
+        // 3 s + 2 s, the gap between the two is ignored
+        assert_eq!(c.total_time, Some(5_000));
+        let mut cumul = GlobalStatistics::default();
+        cumul.merge(&c);
+        cumul.merge(&d);
+        assert_eq!(cumul.start_time, Some(1_000));
+        assert_eq!(cumul.end_time, Some(12_000));
+        assert_eq!(cumul.total_time, Some(7_000));
+        assert_eq!((a.bounds.ne.lng, a.bounds.ne.lat), (2.0, 3.0));
+    }
+}
@@ -0,0 +1,5 @@
+mod compute;
+mod utils;
+
+pub use compute::*;
+pub use utils::*;
@@ -0,0 +1,44 @@
+use std::ops::Add;
+
+pub fn combine_options<T>(a: Option<T>, b: Option<T>, f: impl FnOnce(T, T) -> T) -> Option<T> {
+    match (a, b) {
+        (Some(a), Some(b)) => Some(f(a, b)),
+        (Some(v), None) | (None, Some(v)) => Some(v),
+        (None, None) => None,
+    }
+}
+
+pub fn sum_options<T>(a: Option<T>, b: Option<T>) -> Option<T>
+where
+    T: Add<Output = T>,
+{
+    combine_options(a, b, |a, b| a + b)
+}
+
+pub fn min_options<T>(a: Option<T>, b: Option<T>) -> Option<T>
+where
+    T: Ord,
+{
+    combine_options(a, b, |a, b| a.min(b))
+}
+
+pub fn max_options<T>(a: Option<T>, b: Option<T>) -> Option<T>
+where
+    T: Ord,
+{
+    combine_options(a, b, |a, b| a.max(b))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_sum_options() {
+        assert_eq!(sum_options(Some(1), Some(2)), Some(3));
+        assert_eq!(sum_options(Some(1), None), Some(1));
+        assert_eq!(sum_options(None, Some(2)), Some(2));
+        assert_eq!(sum_options::<i32>(None, None), None);
+        assert_eq!(sum_options(Some(0.5), Some(0.25)), Some(0.75));
+    }
+}
@@ -0,0 +1,208 @@
+use std::f64::consts::PI;
+
+use crate::LngLat;
+
+const TO_RADIANS: f64 = PI / 180.0;
+const EARTH_RADIUS: f64 = 6371.0088;
+
+/// Computes the distance in kilometers between two coordinates using the Haversine formula
+pub fn distance(p1: LngLat, p2: LngLat) -> f64 {
+    let lat1 = p1.lat * TO_RADIANS;
+    let lat2 = p2.lat * TO_RADIANS;
+    let delta_lat = lat2 - lat1;
+    let delta_lng = (p2.lng - p1.lng) * TO_RADIANS;
+
+    let a =
+        (delta_lat / 2.0).sin().powi(2) + lat1.cos() * lat2.cos() * (delta_lng / 2.0).sin().powi(2);
+    let c = 2.0 * a.min(1.0).sqrt().asin();
+    EARTH_RADIUS * c
+}
+
+pub fn time_diff(a: Option<i64>, b: Option<i64>) -> Option<i64> {
+    Some(a? - b?)
+}
+
+/// Computes the speed in km/h for a given distance in kilometers and a time in milliseconds.
+/// Unknown if the time is not a positive duration.
+pub fn speed(distance: f64, time: i64) -> Option<f64> {
+    (time > 0).then(|| distance / (time as f64 / 3_600_000.0))
+}
+
+pub fn slope(ele: f64, distance: f64) -> f64 {
+    if distance == 0.0 {
+        100.0
+    } else {
+        0.1 * ele / distance
+    }
+}
+
+const METERS_PER_LATITUDE_DEGREE: f64 = 111320.0;
+
+/// Approximate planar projection, in meters, around the latitude of `origin` (ignores the
+/// curvature of the earth).
+struct Planar {
+    meters_per_longitude_degree: f64,
+}
+
+impl Planar {
+    fn around(origin: LngLat) -> Self {
+        Self {
+            meters_per_longitude_degree: (origin.lat * TO_RADIANS).cos()
+                * METERS_PER_LATITUDE_DEGREE,
+        }
+    }
+
+    fn to_meters(&self, p: LngLat) -> (f64, f64) {
+        (
+            p.lng * self.meters_per_longitude_degree,
+            p.lat * METERS_PER_LATITUDE_DEGREE,
+        )
+    }
+
+    fn to_degrees(&self, (x, y): (f64, f64)) -> LngLat {
+        LngLat {
+            lng: x / self.meters_per_longitude_degree,
+            lat: y / METERS_PER_LATITUDE_DEGREE,
+        }
+    }
+}
+
+/// Position, between 0 (at `(x1, y1)`) and 1 (at `(x2, y2)`), of the point of the segment that is
+/// the closest to `(x3, y3)`. A degenerate segment (same ends) is a point.
+fn closest_on_segment(x1: f64, y1: f64, x2: f64, y2: f64, x3: f64, y3: f64) -> f64 {
+    let dx = x2 - x1;
+    let dy = y2 - y1;
+    let segment_length_squared = dx * dx + dy * dy;
+    if segment_length_squared == 0.0 {
+        0.0
+    } else {
+        (((x3 - x1) * dx + (y3 - y1) * dy) / segment_length_squared).clamp(0.0, 1.0)
+    }
+}
+
+/// Calculates the point on the line segment defined by p1 and p2 that is closest to the third
+/// point, p3. Uses simple planar geometry (ignores earth curvature).
+pub fn projected(p1: LngLat, p2: LngLat, p3: LngLat) -> LngLat {
+    let planar = Planar::around(p1);
+    let (x1, y1) = planar.to_meters(p1);
+    let (x2, y2) = planar.to_meters(p2);
+    let (x3, y3) = planar.to_meters(p3);
+    let t = closest_on_segment(x1, y1, x2, y2, x3, y3);
+    planar.to_degrees((x1 + t * (x2 - x1), y1 + t * (y2 - y1)))
+}
+
+/// Calculates the perpendicular distance in meters between a line segment (defined by p1 and p2)
+/// and a third point, p3. Uses simple planar geometry (ignores earth curvature).
+pub fn crossarc_lnglat(p1: LngLat, p2: LngLat, p3: LngLat) -> f64 {
+    let planar = Planar::around(p1);
+    let (x1, y1) = planar.to_meters(p1);
+    let (x2, y2) = planar.to_meters(p2);
+    let (x3, y3) = planar.to_meters(p3);
+    crossarc(x1, y1, x2, y2, x3, y3)
+}
+
+/// Distance from the point `(x3, y3)` to the segment `(x1, y1)`-`(x2, y2)`, in the units of the
+/// coordinates (planar geometry).
+pub fn crossarc(x1: f64, y1: f64, x2: f64, y2: f64, x3: f64, y3: f64) -> f64 {
+    let t = closest_on_segment(x1, y1, x2, y2, x3, y3);
+    (x3 - (x1 + t * (x2 - x1))).hypot(y3 - (y1 + t * (y2 - y1)))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    fn p(lng: f64, lat: f64) -> LngLat {
+        LngLat { lng, lat }
+    }
+
+    #[test]
+    fn test_time_diff_and_speed_with_long_durations() {
+        // 40 days in milliseconds, more than an i32 can hold
+        let forty_days = 40 * 24 * 3_600_000_i64;
+        assert!(forty_days > i64::from(i32::MAX));
+        assert_eq!(time_diff(Some(forty_days), Some(0)), Some(forty_days));
+        assert_eq!(time_diff(Some(0), Some(forty_days)), Some(-forty_days));
+        assert_eq!(time_diff(None, Some(1)), None);
+        assert_eq!(time_diff(Some(1), None), None);
+        // 1 km in one hour
+        assert!((speed(1.0, 3_600_000).unwrap() - 1.0).abs() < 1e-12);
+    }
+
+    #[test]
+    fn test_distance() {
+        assert_eq!(distance(p(4.0, 50.0), p(4.0, 50.0)), 0.0);
+        // one degree of latitude
+        let d = distance(p(0.0, 0.0), p(0.0, 1.0));
+        assert!((d - 111.195).abs() < 0.01, "{d}");
+        // symmetric
+        let a = p(4.40, 50.79);
+        let b = p(6.13, 45.90);
+        assert!((distance(a, b) - distance(b, a)).abs() < 1e-9);
+        // half the Earth's circumference, without NaN from rounding
+        let antipodal = distance(p(0.0, 0.0), p(180.0, 0.0));
+        assert!((antipodal - PI * EARTH_RADIUS).abs() < 1e-6);
+    }
+
+    #[test]
+    fn test_time_diff() {
+        assert_eq!(time_diff(Some(5000), Some(2000)), Some(3000));
+        assert_eq!(time_diff(Some(2000), Some(5000)), Some(-3000));
+        assert_eq!(time_diff(None, Some(1)), None);
+        assert_eq!(time_diff(Some(1), None), None);
+    }
+
+    #[test]
+    fn test_speed() {
+        // 1 km in 1 h
+        assert!((speed(1.0, 3_600_000).unwrap() - 1.0).abs() < 1e-12);
+        // 10 km in 30 min
+        assert!((speed(10.0, 1_800_000).unwrap() - 20.0).abs() < 1e-12);
+        // no duration, no speed
+        assert_eq!(speed(1.0, 0), None);
+        assert_eq!(speed(0.0, 0), None);
+        assert_eq!(speed(1.0, -1000), None);
+    }
+
+    #[test]
+    fn test_slope() {
+        // 10 m of elevation over 100 m (distance is expressed in km, hence the 0.1 factor)
+        assert!((slope(10.0, 0.1) - 10.0).abs() < 1e-12);
+        assert!((slope(-5.0, 0.1) + 5.0).abs() < 1e-12);
+        assert_eq!(slope(0.0, 1.0), 0.0);
+        assert_eq!(slope(10.0, 0.0), 100.0);
+    }
+
+    #[test]
+    fn test_crossarc() {
+        // perpendicular distance to the segment (0,0)-(10,0)
+        assert!((crossarc(0.0, 0.0, 10.0, 0.0, 5.0, 3.0) - 3.0).abs() < 1e-12);
+        // beyond the ends: distance to the closest endpoint
+        assert!((crossarc(0.0, 0.0, 10.0, 0.0, 13.0, 4.0) - 5.0).abs() < 1e-12);
+        assert!((crossarc(0.0, 0.0, 10.0, 0.0, -3.0, 4.0) - 5.0).abs() < 1e-12);
+        // point on the segment
+        assert_eq!(crossarc(0.0, 0.0, 10.0, 0.0, 4.0, 0.0), 0.0);
+        // degenerate segment
+        assert!((crossarc(1.0, 1.0, 1.0, 1.0, 4.0, 5.0) - 5.0).abs() < 1e-12);
+    }
+
+    #[test]
+    fn test_projected() {
+        let proj = projected(p(0.0, 0.0), p(1.0, 0.0), p(0.5, 1.0));
+        assert!((proj.lng - 0.5).abs() < 1e-9);
+        assert!(proj.lat.abs() < 1e-9);
+        // clamped to the segment
+        let proj = projected(p(0.0, 0.0), p(1.0, 0.0), p(2.0, 1.0));
+        assert!((proj.lng - 1.0).abs() < 1e-9);
+        // degenerate segment
+        let proj = projected(p(3.0, 4.0), p(3.0, 4.0), p(5.0, 6.0));
+        assert_eq!((proj.lng, proj.lat), (3.0, 4.0));
+    }
+
+    #[test]
+    fn test_crossarc_lnglat() {
+        // about 1 degree of latitude away from an east-west segment on the equator
+        let d = crossarc_lnglat(p(0.0, 0.0), p(1.0, 0.0), p(0.5, 1.0));
+        assert!((d - METERS_PER_LATITUDE_DEGREE).abs() < 1e-6);
+    }
+}
@@ -0,0 +1,39 @@
+use crate::{Command, FileId, SelectMode, Selection};
+
+/// Everything the frontend can ask the engine to do.
+///
+/// Only [`Action::Edit`] changes the files (and records an undo step); the others act on the
+/// history, on the selection or on the file order.
+#[derive(Debug)]
+pub enum Action<'a> {
+    Edit(Command<'a>),
+    Undo,
+    Redo,
+    /// Selects files, tracks, segments or waypoints (or the waypoints node of one file),
+    /// ignoring what does not exist: a selection left with nothing is empty, which deselects
+    /// everything. See [`SelectMode`] for how it combines with the current selection.
+    Select {
+        selection: Selection,
+        mode: SelectMode,
+    },
+    /// Selects all the elements of the same kind as the selected ones, in the same place (see
+    /// [`Selection::all_at_level`]). Does nothing when there is nothing more to select.
+    SelectAll,
+    /// Moves the selection to the next (`down`) or previous element of the same kind, like the
+    /// arrow keys do in the file list (see [`Selection::neighbour`]). With `add`, the element is
+    /// added to the selection (shift + arrow), otherwise it replaces it.
+    ArrowSelect {
+        down: bool,
+        add: bool,
+    },
+    /// Puts the selected elements in the clipboard, to be pasted by [`crate::Paste`]. Does
+    /// nothing when nothing is selected.
+    Copy,
+    /// Like `Copy`, but the elements are moved instead of copied when they are pasted.
+    Cut,
+    /// Moves the files to `index` among the other files, in the given order. Not undoable.
+    Reorder {
+        file_ids: Vec<FileId>,
+        index: usize,
+    },
+}
@@ -0,0 +1,30 @@
+use std::fmt;
+
+use crate::State;
+
+/// The effect of a command on the engine state.
+///
+/// Each command is a small struct holding its arguments, with its effect implemented in its
+/// own file. Effects are built from the reusable patterns in `pattern/`.
+pub trait Apply {
+    fn apply(self, state: &mut State) -> Result<(), CommandError>;
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum CommandError {
+    /// The command would not change anything.
+    NothingToDo,
+    /// The input data could not be parsed.
+    InvalidData(String),
+}
+
+impl fmt::Display for CommandError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Self::NothingToDo => write!(f, "nothing to do"),
+            Self::InvalidData(err) => write!(f, "invalid data: {err}"),
+        }
+    }
+}
+
+impl std::error::Error for CommandError {}
@@ -0,0 +1,161 @@
+use crate::{Apply, CommandError, Edit, Editor, File, State, Track, update_selected};
+
+#[derive(Debug)]
+pub struct Metadata<'a> {
+    pub name: &'a str,
+    pub desc: &'a str,
+}
+
+impl Apply for Metadata<'_> {
+    fn apply(mut self, state: &mut State) -> Result<(), CommandError> {
+        update_selected(state, &mut self);
+        Ok(())
+    }
+}
+
+impl Editor for Metadata<'_> {
+    fn file(&mut self, file: &mut File) -> Edit {
+        file.info.name = self.name.to_owned();
+        file.info.desc = Some(self.desc.to_owned());
+        // a single track is named like the file
+        if let [track] = file.trk.as_mut_slice() {
+            track.info.name = Some(self.name.to_owned());
+        }
+        Edit::Changed
+    }
+
+    fn track(&mut self, track: &mut Track) -> Edit {
+        track.info.name = Some(self.name.to_owned());
+        track.info.desc = Some(self.desc.to_owned());
+        Edit::Changed
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{New, NewTrack, Selection, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    #[test]
+    fn test_metadata_applies_to_selected_file() {
+        let mut fx = Fixture::default();
+        New {
+            name: "first",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        New {
+            name: "second",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap(); // now selected
+        let selected = *fx.selected_files().iter().next().unwrap();
+
+        Metadata {
+            name: "renamed",
+            desc: "description",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        for (id, file) in fx.files.iter() {
+            if *id == selected {
+                assert_eq!(file.info.name, "renamed");
+                assert_eq!(file.info.desc.as_deref(), Some("description"));
+            } else {
+                assert_eq!(file.info.name, "first");
+                assert_eq!(file.info.desc, None);
+            }
+        }
+    }
+
+    #[test]
+    fn test_metadata_applies_to_selected_track() {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks.gpx").unwrap();
+        crate::Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let file = fx.files.values().next().unwrap().clone();
+        fx.selection = Selection::Track {
+            file_id: file.id,
+            trk_ids: HashSet::from([file.trk[0].id]),
+        };
+
+        Metadata {
+            name: "renamed",
+            desc: "",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        let after = &fx.files[&file.id];
+        assert_eq!(after.info.name, file.info.name);
+        assert_eq!(after.trk[0].info.name.as_deref(), Some("renamed"));
+        assert_eq!(after.trk[1].info, file.trk[1].info);
+    }
+
+    /// A new file with `nb_tracks` tracks (without name), selected.
+    fn file_with_tracks(fx: &mut Fixture, nb_tracks: usize) {
+        New {
+            name: "file",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        for _ in 0..nb_tracks {
+            NewTrack.apply(&mut fx.state()).unwrap();
+        }
+    }
+
+    fn rename(fx: &mut Fixture) {
+        Metadata {
+            name: "renamed",
+            desc: "",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+    }
+
+    #[test]
+    fn test_single_track_is_renamed_like_the_file() {
+        let mut fx = Fixture::default();
+        file_with_tracks(&mut fx, 1);
+        rename(&mut fx);
+        let file = fx.files.values().next().unwrap();
+        assert_eq!(file.info.name, "renamed");
+        assert_eq!(file.trk[0].info.name.as_deref(), Some("renamed"));
+    }
+
+    #[test]
+    fn test_single_track_with_a_name_is_renamed_too() {
+        let mut fx = Fixture::default();
+        file_with_tracks(&mut fx, 1);
+        let id = *fx.files.keys().next().unwrap();
+        std::rc::Rc::make_mut(fx.files.get_mut(&id).unwrap()).trk[0]
+            .info
+            .name = Some("track".to_owned());
+        rename(&mut fx);
+        let file = &fx.files[&id];
+        assert_eq!(file.info.name, "renamed");
+        assert_eq!(file.trk[0].info.name.as_deref(), Some("renamed"));
+    }
+
+    #[test]
+    fn test_several_tracks_are_not_renamed() {
+        let mut fx = Fixture::default();
+        file_with_tracks(&mut fx, 2);
+        rename(&mut fx);
+        let file = fx.files.values().next().unwrap();
+        assert_eq!(file.info.name, "renamed");
+        assert!(file.trk.iter().all(|trk| trk.info.name.is_none()));
+    }
+}
@@ -0,0 +1,9 @@
+mod metadata;
+mod new_track;
+mod new_track_segment;
+mod style;
+
+pub use metadata::*;
+pub use new_track::*;
+pub use new_track_segment::*;
+pub use style::*;
@@ -0,0 +1,75 @@
+use crate::{Apply, CommandError, Edit, Editor, File, State, Track, update_selected};
+
+#[derive(Debug)]
+pub struct NewTrack;
+
+impl Apply for NewTrack {
+    fn apply(mut self, state: &mut State) -> Result<(), CommandError> {
+        update_selected(state, &mut self);
+        Ok(())
+    }
+}
+
+impl Editor for NewTrack {
+    fn file(&mut self, file: &mut File) -> Edit {
+        let mut track = Track::default();
+        track.info.color = common(file, |t| &t.info.color);
+        track.info.opacity = common(file, |t| &t.info.opacity);
+        track.info.width = common(file, |t| &t.info.width);
+        file.trk.push(track);
+        Edit::Changed
+    }
+}
+
+/// Returns the value of a style attribute if all existing tracks agree on it.
+fn common<T: Clone + PartialEq>(file: &File, get: impl Fn(&Track) -> &Option<T>) -> Option<T> {
+    let mut tracks = file.trk.iter();
+    let first = get(tracks.next()?);
+    tracks.all(|t| get(t) == first).then(|| first.clone())?
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{New, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    #[test]
+    fn test_new_track() {
+        let mut fx = Fixture::default();
+        New {
+            name: "file",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        NewTrack.apply(&mut fx.state()).unwrap();
+        NewTrack.apply(&mut fx.state()).unwrap();
+        let file = fx.files.values().next().unwrap();
+        assert_eq!(file.trk.len(), 2);
+        assert_ne!(file.trk[0].id, file.trk[1].id);
+    }
+
+    #[test]
+    fn test_new_track_inherits_agreeing_style_only() {
+        let mut fx = Fixture::default();
+        New {
+            name: "file",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        NewTrack.apply(&mut fx.state()).unwrap();
+        NewTrack.apply(&mut fx.state()).unwrap();
+        let file = std::rc::Rc::make_mut(fx.files.values_mut().next().unwrap());
+        for (i, trk) in file.trk.iter_mut().enumerate() {
+            trk.info.color = Some("ff0000".into());
+            trk.info.opacity = Some(0.5 + i as f64 * 0.1);
+        }
+        NewTrack.apply(&mut fx.state()).unwrap();
+        let info = &fx.files.values().next().unwrap().trk[2].info;
+        assert_eq!(info.color.as_deref(), Some("ff0000"));
+        assert_eq!(info.opacity, None);
+        assert_eq!(info.width, None);
+    }
+}
@@ -0,0 +1,41 @@
+use crate::{Apply, CommandError, Edit, Editor, State, Track, TrackSegment, update_selected};
+
+#[derive(Debug)]
+pub struct NewTrackSegment;
+
+impl Apply for NewTrackSegment {
+    fn apply(mut self, state: &mut State) -> Result<(), CommandError> {
+        update_selected(state, &mut self);
+        Ok(())
+    }
+}
+
+impl Editor for NewTrackSegment {
+    fn track(&mut self, track: &mut Track) -> Edit {
+        track.trkseg.push(TrackSegment::default());
+        Edit::Changed
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{New, NewTrack, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    #[test]
+    fn test_new_track_segment_on_each_track_of_selected_file() {
+        let mut fx = Fixture::default();
+        New {
+            name: "file",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        NewTrack.apply(&mut fx.state()).unwrap();
+        NewTrack.apply(&mut fx.state()).unwrap();
+        NewTrackSegment.apply(&mut fx.state()).unwrap();
+        let file = fx.files.values().next().unwrap();
+        assert!(file.trk.iter().all(|t| t.trkseg.len() == 1));
+    }
+}
@@ -0,0 +1,71 @@
+use crate::{Apply, CommandError, Edit, Editor, State, Track, update_selected};
+
+#[derive(Debug)]
+pub struct Style<'a> {
+    pub color: Option<&'a str>,
+    pub opacity: Option<f64>,
+    pub width: Option<f64>,
+}
+
+impl Apply for Style<'_> {
+    fn apply(mut self, state: &mut State) -> Result<(), CommandError> {
+        update_selected(state, &mut self);
+        Ok(())
+    }
+}
+
+impl Editor for Style<'_> {
+    fn track(&mut self, track: &mut Track) -> Edit {
+        if let Some(color) = self.color {
+            track.info.color = Some(color.to_owned());
+        }
+        if self.opacity.is_some() {
+            track.info.opacity = self.opacity;
+        }
+        if self.width.is_some() {
+            track.info.width = self.width;
+        }
+        Edit::Changed
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{Selection, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    #[test]
+    fn test_style_applies_to_all_tracks_of_selected_file_and_keeps_unset_fields() {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_style.gpx").unwrap();
+        crate::Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = *fx.files.keys().next().unwrap();
+        let before = fx.files[&id].clone();
+        assert!(!before.trk.is_empty());
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+
+        Style {
+            color: Some("ff0000"),
+            opacity: None,
+            width: Some(7.0),
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        for (b, a) in before.trk.iter().zip(fx.files[&id].trk.iter()) {
+            assert_eq!(a.info.color.as_deref(), Some("ff0000"));
+            assert_eq!(a.info.width, Some(7.0));
+            assert_eq!(a.info.opacity, b.info.opacity);
+        }
+    }
+}
@@ -0,0 +1,288 @@
+use std::rc::Rc;
+
+use crate::{Apply, CommandError, FileId, Selection, StackEntry, State, Waypoint};
+
+/// Deletes the selected elements. With `whole_files`, the files holding the selected elements
+/// are deleted instead, even if only a track or a waypoint is selected.
+#[derive(Debug)]
+pub struct Delete {
+    pub whole_files: bool,
+}
+
+impl Apply for Delete {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let files = state.selection.to_files();
+        let selection = if self.whole_files {
+            &files
+        } else {
+            &*state.selection
+        };
+        let next = match selection {
+            Selection::File { file_ids } => {
+                state.files.retain(|id, _| !file_ids.contains(id));
+                state.order.0.retain(|id| !file_ids.contains(id));
+                Selection::Empty
+            }
+            Selection::Track { file_id, trk_ids } => {
+                let file = state
+                    .files
+                    .get_mut(file_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let file = Rc::make_mut(file);
+                let len = file.trk.len();
+                file.trk.retain(|trk| !trk_ids.contains(&trk.id));
+                if file.trk.len() == len {
+                    return Err(CommandError::NothingToDo);
+                }
+                Selection::File {
+                    file_ids: [*file_id].into(),
+                }
+            }
+            Selection::TrackSegment {
+                file_id,
+                trk_id,
+                trkseg_ids,
+            } => {
+                let file = state
+                    .files
+                    .get_mut(file_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let file = Rc::make_mut(file);
+                let trk = file
+                    .trk
+                    .iter_mut()
+                    .find(|trk| trk.id == *trk_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let len = trk.trkseg.len();
+                trk.trkseg.retain(|seg| !trkseg_ids.contains(&seg.id));
+                if trk.trkseg.len() == len {
+                    return Err(CommandError::NothingToDo);
+                }
+                Selection::Track {
+                    file_id: *file_id,
+                    trk_ids: [*trk_id].into(),
+                }
+            }
+            Selection::Waypoints { file_id } => delete_waypoints(state.files, *file_id, |_| true)?,
+            Selection::Waypoint { file_id, wpt_ids } => {
+                delete_waypoints(state.files, *file_id, |wpt| wpt_ids.contains(&wpt.id))?
+            }
+            Selection::Empty => return Err(CommandError::NothingToDo),
+        };
+        *state.selection = next;
+        Ok(())
+    }
+}
+
+pub(crate) fn delete_waypoints(
+    files: &mut StackEntry,
+    file_id: FileId,
+    filter: impl Fn(&Waypoint) -> bool,
+) -> Result<Selection, CommandError> {
+    let file = files.get(&file_id).ok_or(CommandError::NothingToDo)?;
+    let mut file = (**file).clone();
+    let changed = file.wpt.edit(&filter, |wpts| {
+        wpts.retain(|wpt| !filter(wpt));
+        true
+    });
+    if !changed {
+        return Err(CommandError::NothingToDo);
+    }
+    files.insert(file_id, Rc::new(file));
+    Ok(Selection::File {
+        file_ids: [file_id].into(),
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::engine::command::fixture::Fixture;
+    use crate::{FileId, Load};
+
+    use super::*;
+
+    fn loaded() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        (fx, id)
+    }
+
+    #[test]
+    fn test_delete_nothing_selected() {
+        let mut fx = Fixture::default();
+        assert_eq!(
+            Delete { whole_files: false }.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_delete_selected_files() {
+        let (mut fx, id) = loaded();
+        crate::New {
+            name: "keep",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let keep = fx.order.0[1];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        Delete { whole_files: false }
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(fx.order.0, vec![keep]);
+        assert!(fx.files.contains_key(&keep) && !fx.files.contains_key(&id));
+        assert!(matches!(fx.selection, Selection::Empty));
+    }
+
+    #[test]
+    fn test_delete_selected_tracks() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].trk.len();
+        let trk_id = fx.files[&id].trk[0].id;
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: HashSet::from([trk_id]),
+        };
+        Delete { whole_files: false }
+            .apply(&mut fx.state())
+            .unwrap();
+        let file = &fx.files[&id];
+        assert_eq!(file.trk.len(), before - 1);
+        assert!(file.trk.iter().all(|t| t.id != trk_id));
+        assert_eq!(fx.selected_files(), HashSet::from([id]));
+    }
+
+    #[test]
+    fn test_delete_selected_segments() {
+        let (mut fx, id) = loaded();
+        let trk = &fx.files[&id].trk[0];
+        let (trk_id, seg_id, before) = (trk.id, trk.trkseg[0].id, trk.trkseg.len());
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id,
+            trkseg_ids: HashSet::from([seg_id]),
+        };
+        Delete { whole_files: false }
+            .apply(&mut fx.state())
+            .unwrap();
+        let trk = &fx.files[&id].trk[0];
+        assert_eq!(trk.trkseg.len(), before - 1);
+        assert!(trk.trkseg.iter().all(|s| s.id != seg_id));
+        assert!(
+            matches!(&fx.selection, Selection::Track { trk_ids, .. } if trk_ids.contains(&trk_id))
+        );
+    }
+
+    fn with_waypoints(fx: &mut Fixture, id: FileId, n: usize) -> Vec<crate::WaypointId> {
+        let wpts: Vec<_> = (0..n).map(|_| Waypoint::default()).collect();
+        let ids = wpts.iter().map(|w| w.id).collect();
+        let mut file = (*fx.files[&id]).clone();
+        file.wpt = crate::Waypoints::new([crate::WaypointChunk {
+            wpt: wpts,
+            ..Default::default()
+        }]);
+        fx.files.insert(id, Rc::new(file));
+        ids
+    }
+
+    #[test]
+    fn test_delete_selected_waypoints() {
+        let (mut fx, id) = loaded();
+        let ids = with_waypoints(&mut fx, id, 3);
+        fx.selection = Selection::Waypoint {
+            file_id: id,
+            wpt_ids: HashSet::from([ids[1]]),
+        };
+        let rev = fx.files[&id].wpt.rev_id;
+        Delete { whole_files: false }
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_ne!(fx.files[&id].wpt.rev_id, rev);
+        let left: Vec<_> = fx.files[&id].wpt.iter().map(|w| w.id).collect();
+        assert_eq!(left, vec![ids[0], ids[2]]);
+        assert_eq!(fx.selected_files(), HashSet::from([id]));
+    }
+
+    #[test]
+    fn test_delete_all_waypoints_of_file() {
+        let (mut fx, id) = loaded();
+        with_waypoints(&mut fx, id, 3);
+        fx.selection = Selection::Waypoints { file_id: id };
+        Delete { whole_files: false }
+            .apply(&mut fx.state())
+            .unwrap();
+        assert!(fx.files[&id].wpt.is_empty());
+        fx.selection = Selection::Waypoints { file_id: id };
+        assert_eq!(
+            Delete { whole_files: false }.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_delete_unknown_ids_is_nothing_to_do() {
+        let (mut fx, id) = loaded();
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: HashSet::from([Default::default()]),
+        };
+        assert_eq!(
+            Delete { whole_files: false }.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_delete_whole_files_of_the_selected_elements() {
+        for selection in [
+            |id: FileId, fx: &Fixture| Selection::Track {
+                file_id: id,
+                trk_ids: HashSet::from([fx.files[&id].trk[0].id]),
+            },
+            |id: FileId, fx: &Fixture| Selection::TrackSegment {
+                file_id: id,
+                trk_id: fx.files[&id].trk[0].id,
+                trkseg_ids: HashSet::from([fx.files[&id].trk[0].trkseg[0].id]),
+            },
+            |id: FileId, _: &Fixture| Selection::Waypoints { file_id: id },
+            |id: FileId, _: &Fixture| Selection::File {
+                file_ids: HashSet::from([id]),
+            },
+        ] {
+            let (mut fx, id) = loaded();
+            crate::New {
+                name: "keep",
+                trackpoint: None,
+            }
+            .apply(&mut fx.state())
+            .unwrap();
+            let keep = fx.order.0[1];
+            fx.selection = selection(id, &fx);
+            Delete { whole_files: true }.apply(&mut fx.state()).unwrap();
+            assert_eq!(fx.order.0, vec![keep]);
+            assert!(!fx.files.contains_key(&id));
+            assert!(matches!(fx.selection, Selection::Empty));
+        }
+    }
+
+    #[test]
+    fn test_delete_whole_files_nothing_selected() {
+        let mut fx = Fixture::default();
+        assert_eq!(
+            Delete { whole_files: true }.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+}
@@ -0,0 +1,48 @@
+use crate::{Apply, CommandError, Selection, State};
+
+#[derive(Debug)]
+pub struct DeleteAll;
+
+impl Apply for DeleteAll {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        if state.files.is_empty() {
+            return Err(CommandError::NothingToDo);
+        }
+        state.files.clear();
+        state.order.0.clear();
+        *state.selection = Selection::Empty;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::engine::command::fixture::Fixture;
+
+    use super::*;
+
+    #[test]
+    fn test_delete_all() {
+        let mut fx = Fixture::default();
+        assert_eq!(
+            DeleteAll.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        crate::New {
+            name: "a",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        crate::New {
+            name: "b",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        assert!(DeleteAll.apply(&mut fx.state()).is_ok());
+        assert!(fx.files.is_empty());
+        assert!(fx.order.0.is_empty());
+        assert!(matches!(fx.selection, Selection::Empty));
+    }
+}
@@ -0,0 +1,120 @@
+use crate::{Apply, CommandError, FileId, Selection, State, WaypointId, delete_waypoints};
+
+/// Deletes a waypoint of a file, whatever is selected (what the delete button of its popup does).
+/// If it was the only selected element, its file gets selected.
+#[derive(Debug)]
+pub struct DeleteWaypoint {
+    pub file_id: FileId,
+    pub waypoint_id: WaypointId,
+}
+
+impl Apply for DeleteWaypoint {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        delete_waypoints(state.files, self.file_id, |wpt| wpt.id == self.waypoint_id)?;
+        if let Selection::Waypoint { file_id, wpt_ids } = &*state.selection
+            && *file_id == self.file_id
+            && wpt_ids.iter().all(|id| *id == self.waypoint_id)
+        {
+            *state.selection = Selection::File {
+                file_ids: [self.file_id].into(),
+            };
+        }
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::{
+        File, Selection, Waypoint, WaypointChunk, engine::command::fixture::Fixture, waypoint_ids,
+    };
+
+    use super::*;
+
+    #[test]
+    fn test_deletes_one_waypoint_without_touching_the_selection() {
+        let mut fx = Fixture::default();
+        let mut file = File::default();
+        file.wpt.push(WaypointChunk {
+            wpt: (0..3)
+                .map(|i| Waypoint {
+                    name: Some(format!("w{i}")),
+                    ..Default::default()
+                })
+                .collect(),
+            ..Default::default()
+        });
+        let id = file.id;
+        let ids: Vec<_> = waypoint_ids(&file).collect();
+        fx.files.insert(id, Rc::new(file));
+        fx.order.0.push(id);
+        fx.selection = Selection::File {
+            file_ids: [id].into(),
+        };
+
+        DeleteWaypoint {
+            file_id: id,
+            waypoint_id: ids[1],
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        let names: Vec<_> = fx.files[&id]
+            .wpt
+            .iter()
+            .map(|wpt| wpt.name.clone().unwrap())
+            .collect();
+        assert_eq!(names, ["w0", "w2"]);
+        assert_eq!(
+            fx.selection,
+            Selection::File {
+                file_ids: [id].into()
+            }
+        );
+    }
+
+    #[test]
+    fn test_deleting_the_selected_waypoint_selects_its_file() {
+        let mut fx = Fixture::default();
+        let mut file = File::default();
+        file.wpt.push(WaypointChunk {
+            wpt: vec![Waypoint::default(), Waypoint::default()],
+            ..Default::default()
+        });
+        let id = file.id;
+        let ids: Vec<_> = waypoint_ids(&file).collect();
+        fx.files.insert(id, Rc::new(file));
+        fx.selection = Selection::Waypoint {
+            file_id: id,
+            wpt_ids: [ids[0]].into(),
+        };
+        DeleteWaypoint {
+            file_id: id,
+            waypoint_id: ids[0],
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        assert_eq!(
+            fx.selection,
+            Selection::File {
+                file_ids: [id].into()
+            }
+        );
+    }
+
+    #[test]
+    fn test_unknown_waypoint_is_nothing_to_do() {
+        let mut fx = Fixture::default();
+        let file = File::default();
+        let id = file.id;
+        fx.files.insert(id, Rc::new(file));
+        let result = DeleteWaypoint {
+            file_id: id,
+            waypoint_id: WaypointId::default(),
+        }
+        .apply(&mut fx.state());
+        assert!(matches!(result, Err(CommandError::NothingToDo)));
+    }
+}
@@ -0,0 +1,298 @@
+use std::{collections::HashSet, rc::Rc};
+
+use crate::{
+    Apply, CommandError, FileId, Selection, StackEntry, State, Waypoint, copy_file, copy_segment,
+    copy_track, copy_waypoint,
+};
+
+#[derive(Debug)]
+pub struct Duplicate;
+
+impl Apply for Duplicate {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let next = match &*state.selection {
+            Selection::File { file_ids } => {
+                let mut copies = HashSet::new();
+                let mut order = Vec::new();
+                for id in state.order.0.iter().filter(|id| file_ids.contains(id)) {
+                    let Some(file) = state.files.get(id) else {
+                        continue;
+                    };
+                    let copy = copy_file(file);
+                    order.push(copy.id);
+                    copies.insert(copy.id);
+                    state.files.insert(copy.id, Rc::new(copy));
+                }
+                if copies.is_empty() {
+                    return Err(CommandError::NothingToDo);
+                }
+                let at = state
+                    .order
+                    .0
+                    .iter()
+                    .rposition(|id| file_ids.contains(id))
+                    .map_or(state.order.0.len(), |i| i + 1);
+                state.order.0.splice(at..at, order);
+                Selection::File { file_ids: copies }
+            }
+            Selection::Track { file_id, trk_ids } => {
+                let file = state
+                    .files
+                    .get_mut(file_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let file = Rc::make_mut(file);
+                let mut copies = HashSet::new();
+                append_copies(
+                    &mut file.trk,
+                    |trk| trk_ids.contains(&trk.id),
+                    |trk| {
+                        let copy = copy_track(trk);
+                        copies.insert(copy.id);
+                        copy
+                    },
+                );
+                if copies.is_empty() {
+                    return Err(CommandError::NothingToDo);
+                }
+                Selection::Track {
+                    file_id: *file_id,
+                    trk_ids: copies,
+                }
+            }
+            Selection::TrackSegment {
+                file_id,
+                trk_id,
+                trkseg_ids,
+            } => {
+                let file = state
+                    .files
+                    .get_mut(file_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let file = Rc::make_mut(file);
+                let trk = file
+                    .trk
+                    .iter_mut()
+                    .find(|trk| trk.id == *trk_id)
+                    .ok_or(CommandError::NothingToDo)?;
+                let mut copies = HashSet::new();
+                append_copies(
+                    &mut trk.trkseg,
+                    |seg| trkseg_ids.contains(&seg.id),
+                    |seg| {
+                        let copy = copy_segment(seg);
+                        copies.insert(copy.id);
+                        copy
+                    },
+                );
+                if copies.is_empty() {
+                    return Err(CommandError::NothingToDo);
+                }
+                Selection::TrackSegment {
+                    file_id: *file_id,
+                    trk_id: *trk_id,
+                    trkseg_ids: copies,
+                }
+            }
+            Selection::Waypoints { file_id } => {
+                duplicate_waypoints(state.files, *file_id, |_| true)?
+            }
+            Selection::Waypoint { file_id, wpt_ids } => {
+                duplicate_waypoints(state.files, *file_id, |wpt| wpt_ids.contains(&wpt.id))?
+            }
+            Selection::Empty => return Err(CommandError::NothingToDo),
+        };
+        *state.selection = next;
+        Ok(())
+    }
+}
+
+fn duplicate_waypoints(
+    files: &mut StackEntry,
+    file_id: FileId,
+    filter: impl Fn(&Waypoint) -> bool,
+) -> Result<Selection, CommandError> {
+    let file = files.get(&file_id).ok_or(CommandError::NothingToDo)?;
+    let selected: Vec<&Waypoint> = file.wpt.iter().filter(|wpt| filter(wpt)).collect();
+    let last = selected.last().ok_or(CommandError::NothingToDo)?.id;
+    let copies: Vec<Waypoint> = selected.into_iter().map(copy_waypoint).collect();
+    let copy_ids = copies.iter().map(|wpt| wpt.id).collect();
+
+    // The copies go right after the last selected waypoint.
+    let mut file = (**file).clone();
+    file.wpt.insert_after(Some(last), copies);
+    files.insert(file_id, Rc::new(file));
+    Ok(Selection::Waypoint {
+        file_id,
+        wpt_ids: copy_ids,
+    })
+}
+
+/// Inserts a copy of each item matching `filter`, as a block after the last matching item.
+fn append_copies<T>(items: &mut Vec<T>, filter: impl Fn(&T) -> bool, copy: impl FnMut(&T) -> T) {
+    let Some(last) = items.iter().rposition(&filter) else {
+        return;
+    };
+    let copies: Vec<T> = items.iter().filter(|item| filter(item)).map(copy).collect();
+    items.splice(last + 1..last + 1, copies);
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::engine::command::fixture::Fixture;
+    use crate::{FileId, Load};
+
+    use super::*;
+
+    fn loaded() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        (fx, id)
+    }
+
+    #[test]
+    fn test_duplicate_nothing_selected() {
+        let mut fx = Fixture::default();
+        assert_eq!(
+            Duplicate.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_duplicate_file() {
+        let (mut fx, id) = loaded();
+        Duplicate.apply(&mut fx.state()).unwrap();
+        assert_eq!(fx.files.len(), 2);
+        let copy_id = fx.order.0[1];
+        assert_eq!(fx.selected_files(), [copy_id].into());
+        let (orig, copy) = (&fx.files[&id], &fx.files[&copy_id]);
+        assert_ne!(copy_id, id);
+        assert_eq!(copy.info.name, orig.info.name);
+        assert_eq!(copy.trk.len(), orig.trk.len());
+        for (a, b) in orig.trk.iter().zip(&copy.trk) {
+            assert_ne!(a.id, b.id);
+            assert_eq!(a.info, b.info);
+            for (a, b) in a.trkseg.iter().zip(&b.trkseg) {
+                assert_ne!(a.id, b.id);
+                assert_eq!(a.len(), b.len());
+            }
+        }
+    }
+
+    #[test]
+    fn test_duplicate_files_go_after_last_selected() {
+        let mut fx = Fixture::default();
+        for name in ["a", "b", "c"] {
+            crate::New {
+                name,
+                trackpoint: None,
+            }
+            .apply(&mut fx.state())
+            .unwrap();
+        }
+        let [a, b, c] = [fx.order.0[0], fx.order.0[1], fx.order.0[2]];
+        fx.selection = Selection::File {
+            file_ids: [a, b].into(),
+        };
+        Duplicate.apply(&mut fx.state()).unwrap();
+        assert_eq!(fx.order.0.len(), 5);
+        assert_eq!(fx.order.0[..2], [a, b]);
+        assert_eq!(fx.order.0[4], c);
+        assert_eq!(
+            fx.selected_files(),
+            fx.order.0[2..4].iter().copied().collect()
+        );
+    }
+
+    #[test]
+    fn test_duplicate_track_appends_copy() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].trk.len();
+        let (trk_id, second_id) = (fx.files[&id].trk[0].id, fx.files[&id].trk[1].id);
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: [trk_id].into(),
+        };
+        Duplicate.apply(&mut fx.state()).unwrap();
+        let file = &fx.files[&id];
+        assert_eq!(file.trk.len(), before + 1);
+        assert_eq!(file.trk[0].id, trk_id);
+        assert_ne!(file.trk[1].id, trk_id);
+        // copies go right after the selected track, not at the end
+        assert_eq!(file.trk[2].id, second_id);
+        assert!(
+            matches!(&fx.selection, Selection::Track { trk_ids, .. } if trk_ids.contains(&file.trk[1].id))
+        );
+    }
+
+    #[test]
+    fn test_duplicate_selected_waypoints() {
+        let (mut fx, id) = loaded();
+        let wpts: Vec<_> = (0..3).map(|_| Waypoint::default()).collect();
+        let ids: Vec<_> = wpts.iter().map(|w| w.id).collect();
+        let mut file = (*fx.files[&id]).clone();
+        file.wpt = crate::Waypoints::new([crate::WaypointChunk {
+            wpt: wpts,
+            ..Default::default()
+        }]);
+        fx.files.insert(id, Rc::new(file));
+        let original_chunk = fx.files[&id].wpt.chunks()[0].clone();
+
+        fx.selection = Selection::Waypoint {
+            file_id: id,
+            wpt_ids: HashSet::from([ids[0]]),
+        };
+        let rev = fx.files[&id].wpt.rev_id;
+        Duplicate.apply(&mut fx.state()).unwrap();
+        assert_ne!(fx.files[&id].wpt.rev_id, rev);
+        let all: Vec<_> = fx.files[&id].wpt.iter().map(|w| w.id).collect();
+        assert_eq!(all.len(), 4);
+        assert!(
+            matches!(&fx.selection, Selection::Waypoint { wpt_ids, .. } if wpt_ids == &HashSet::from([all[1]]))
+        );
+        // the copy comes right after the selected waypoint, in a new chunk
+        assert_eq!(all[..], [ids[0], all[1], ids[1], ids[2]]);
+        assert_eq!(fx.files[&id].wpt.chunks().len(), 1);
+        assert_ne!(fx.files[&id].wpt.chunks()[0].id, original_chunk.id);
+
+        // selecting the last waypoint: the copy goes at the end
+        let last = fx.files[&id].wpt.iter().last().unwrap().id;
+        fx.selection = Selection::Waypoint {
+            file_id: id,
+            wpt_ids: HashSet::from([last]),
+        };
+        Duplicate.apply(&mut fx.state()).unwrap();
+        let all: Vec<_> = fx.files[&id].wpt.iter().map(|w| w.id).collect();
+        assert_eq!(all.len(), 5);
+        assert_eq!(all[..4], [ids[0], all[1], ids[1], ids[2]]);
+
+        fx.selection = Selection::Waypoints { file_id: id };
+        Duplicate.apply(&mut fx.state()).unwrap();
+        assert_eq!(fx.files[&id].wpt.len(), 10);
+    }
+
+    #[test]
+    fn test_duplicate_segment_appends_copy() {
+        let (mut fx, id) = loaded();
+        let trk = &fx.files[&id].trk[0];
+        let (trk_id, seg_id, before) = (trk.id, trk.trkseg[0].id, trk.trkseg.len());
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id,
+            trkseg_ids: [seg_id].into(),
+        };
+        Duplicate.apply(&mut fx.state()).unwrap();
+        let trk = &fx.files[&id].trk[0];
+        assert_eq!(trk.trkseg.len(), before + 1);
+        assert_eq!(trk.trkseg[0].id, seg_id);
+        assert_ne!(trk.trkseg[1].id, seg_id);
+        assert_eq!(trk.trkseg[0].len(), trk.trkseg[1].len());
+    }
+}
@@ -0,0 +1,233 @@
+use crate::{Apply, CommandError, File, State, TrackpointCategories, parse, produce};
+
+#[derive(Debug)]
+pub struct Load<'a> {
+    pub data: &'a [u8],
+    /// Name of the file when the data has none (typically the name of the file on disk, without
+    /// its extension).
+    pub name: &'a str,
+}
+
+impl Load<'_> {
+    fn parse(self, categories: &mut TrackpointCategories) -> Result<File, CommandError> {
+        let mut file = parse(self.data, categories)
+            .map_err(|err| CommandError::InvalidData(err.to_string()))?;
+        if file.info.name.trim().is_empty() {
+            file.info.name = self.name.to_owned();
+        }
+        Ok(file)
+    }
+}
+
+impl Apply for Load<'_> {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        LoadFiles { files: vec![self] }.apply(state)
+    }
+}
+
+/// Loads several files at once, as a single command (one undo step): the files are added at the
+/// end of the list, in the given order, and the first one is selected.
+///
+/// The files that cannot be read are skipped, unless none of them can: then nothing is loaded
+/// and the error is the one of the first file.
+#[derive(Debug)]
+pub struct LoadFiles<'a> {
+    pub files: Vec<Load<'a>>,
+}
+
+impl Apply for LoadFiles<'_> {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let mut files = Vec::with_capacity(self.files.len());
+        let mut first_error = None;
+        for load in self.files {
+            match load.parse(state.categories) {
+                Ok(file) => files.push(file),
+                Err(error) => {
+                    first_error.get_or_insert(error);
+                }
+            }
+        }
+        if files.is_empty() {
+            return Err(first_error.unwrap_or(CommandError::NothingToDo));
+        }
+        produce(state, |_| files);
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::engine::command::fixture::Fixture;
+
+    use super::*;
+
+    #[test]
+    fn test_load() {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks.gpx").unwrap();
+        assert!(
+            Load {
+                data: &data,
+                name: "file",
+            }
+            .apply(&mut fx.state())
+            .is_ok()
+        );
+        assert_eq!(fx.files.len(), 1);
+        let file = fx.files.values().next().unwrap();
+        assert!(!file.trk.is_empty());
+        assert_eq!(fx.selected_files(), [file.id].into());
+    }
+
+    #[test]
+    fn test_load_invalid_file_changes_nothing() {
+        let mut fx = Fixture::default();
+        crate::New {
+            name: "keep",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let selected = fx.selected_files();
+
+        let result = Load {
+            data: b"<gpx><trk></gpx>",
+            name: "file",
+        }
+        .apply(&mut fx.state());
+        assert!(matches!(result, Err(CommandError::InvalidData(_))));
+        assert_eq!(fx.files.len(), 1);
+        assert_eq!(fx.order.0.len(), 1);
+        assert_eq!(fx.selected_files(), selected);
+    }
+
+    fn load_with_name(data: &[u8]) -> String {
+        let mut fx = Fixture::default();
+        Load {
+            data,
+            name: "from disk",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        fx.files.values().next().unwrap().info.name.clone()
+    }
+
+    #[test]
+    fn test_load_keeps_the_name_of_the_file() {
+        let data = br#"<gpx version="1.1"><metadata><name>in the file</name></metadata></gpx>"#;
+        assert_eq!(load_with_name(data), "in the file");
+    }
+
+    #[test]
+    fn test_load_without_name_uses_the_given_name() {
+        let without = br#"<gpx version="1.1"><trk><trkseg></trkseg></trk></gpx>"#;
+        assert_eq!(load_with_name(without), "from disk");
+        let empty = br#"<gpx version="1.1"><metadata><name>  </name></metadata></gpx>"#;
+        assert_eq!(load_with_name(empty), "from disk");
+    }
+
+    fn gpx(name: &str) -> Vec<u8> {
+        format!(r#"<gpx version="1.1"><metadata><name>{name}</name></metadata></gpx>"#).into_bytes()
+    }
+
+    fn load<'a>(data: &'a [u8], name: &'a str) -> Load<'a> {
+        Load { data, name }
+    }
+
+    #[test]
+    fn test_load_several_files() {
+        let mut fx = Fixture::default();
+        crate::New {
+            name: "before",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let before = fx.order.0[0];
+        let (a, b, c) = (gpx("a"), gpx("b"), gpx("c"));
+
+        LoadFiles {
+            files: vec![load(&a, "x"), load(&b, "x"), load(&c, "x")],
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        // added after the others, in the order they were given
+        let names: Vec<_> = fx
+            .order
+            .0
+            .iter()
+            .map(|id| fx.files[id].info.name.clone())
+            .collect();
+        assert_eq!(names, ["before", "a", "b", "c"]);
+        assert_eq!(fx.order.0[0], before);
+        // the first one is selected
+        assert_eq!(fx.selected_files(), [fx.order.0[1]].into());
+    }
+
+    #[test]
+    fn test_load_several_files_skips_the_invalid_ones() {
+        let mut fx = Fixture::default();
+        let (a, c) = (gpx("a"), gpx("c"));
+        LoadFiles {
+            files: vec![load(&a, "x"), load(b"<gpx><trk></gpx>", "x"), load(&c, "x")],
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let names: Vec<_> = fx
+            .order
+            .0
+            .iter()
+            .map(|id| fx.files[id].info.name.clone())
+            .collect();
+        assert_eq!(names, ["a", "c"]);
+    }
+
+    #[test]
+    fn test_load_several_invalid_files_changes_nothing() {
+        let mut fx = Fixture::default();
+        crate::New {
+            name: "keep",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let selected = fx.selected_files();
+
+        let result = LoadFiles {
+            files: vec![
+                load(b"<gpx><trk></gpx>", "x"),
+                load(b"<gpx><wpt></gpx>", "y"),
+            ],
+        }
+        .apply(&mut fx.state());
+        assert!(matches!(result, Err(CommandError::InvalidData(_))));
+        assert_eq!(fx.files.len(), 1);
+        assert_eq!(fx.order.0.len(), 1);
+        assert_eq!(fx.selected_files(), selected);
+
+        // nothing to load
+        assert_eq!(
+            LoadFiles { files: vec![] }.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_each_file_without_name_gets_its_own_name() {
+        let mut fx = Fixture::default();
+        let unnamed = br#"<gpx version="1.1"><trk><trkseg></trkseg></trk></gpx>"#;
+        LoadFiles {
+            files: vec![load(unnamed, "first"), load(unnamed, "second")],
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let names: Vec<_> = fx
+            .order
+            .0
+            .iter()
+            .map(|id| fx.files[id].info.name.clone())
+            .collect();
+        assert_eq!(names, ["first", "second"]);
+    }
+}
@@ -0,0 +1,19 @@
+mod delete;
+mod delete_all;
+mod delete_waypoint;
+mod duplicate;
+mod load;
+mod move_elements;
+mod new;
+mod paste;
+mod transfer;
+
+pub use delete::*;
+pub use delete_all::*;
+pub use delete_waypoint::*;
+pub use duplicate::*;
+pub use load::*;
+pub use move_elements::*;
+pub use new::*;
+pub use paste::*;
+pub use transfer::*;
@@ -0,0 +1,447 @@
+use crate::{
+    Apply, Clipboard, CommandError, Destination, FileId, Place, Selection, State, TrackId, transfer,
+};
+
+/// Where moved elements go: a list of the file tree, and the position in it. The position is
+/// counted among the elements of the list that are not moved, like the position of a dragged
+/// element in the list it is dropped in.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum MoveTarget {
+    /// The list of files.
+    Files { index: usize },
+    /// The tracks of a file.
+    Tracks { file_id: FileId, index: usize },
+    /// The segments of a track.
+    Segments {
+        file_id: FileId,
+        trk_id: TrackId,
+        index: usize,
+    },
+    /// The waypoints of a file.
+    Waypoints { file_id: FileId, index: usize },
+}
+
+/// Moves elements to a place of the file tree (what drag and drop does), with their ids. The
+/// moved elements are selected.
+///
+/// What can go where:
+/// - files: among the files;
+/// - tracks: among the files (each track becomes a file), or among the tracks of a file;
+/// - segments: among the files (each segment becomes a file), among the tracks of a file (each
+///   segment becomes a track), or among the segments of a track;
+/// - waypoints, or all the waypoints of a file (the waypoints node): among the waypoints of a
+///   file.
+#[derive(Debug)]
+pub struct Move {
+    pub what: Selection,
+    pub to: MoveTarget,
+}
+
+impl From<MoveTarget> for Destination {
+    fn from(target: MoveTarget) -> Self {
+        match target {
+            MoveTarget::Files { index } => Destination::Files(Place::Index(index)),
+            MoveTarget::Tracks { file_id, index } => {
+                Destination::Tracks(file_id, Place::Index(index))
+            }
+            MoveTarget::Segments {
+                file_id,
+                trk_id,
+                index,
+            } => Destination::Segments(file_id, trk_id, Place::Index(index)),
+            MoveTarget::Waypoints { file_id, index } => {
+                Destination::Waypoints(file_id, Place::Index(index))
+            }
+        }
+    }
+}
+
+impl Apply for Move {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let clipboard = Clipboard::new(&self.what, state.files, &state.order.0, true)
+            .ok_or(CommandError::NothingToDo)?;
+        *state.selection = transfer(state, &clipboard.content, true, self.to.into())?;
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::{
+        File, Track, TrackInfo, TrackSegment, TrackSegmentId, Waypoint, WaypointChunk, WaypointId,
+        Waypoints, engine::command::fixture::Fixture, new_file, waypoint_ids,
+    };
+
+    use super::*;
+
+    /// A file with the given tracks (name, number of segments) and number of waypoints.
+    fn file(name: &str, tracks: &[(&str, usize)], waypoints: usize) -> File {
+        let mut file = new_file(
+            name,
+            tracks
+                .iter()
+                .map(|(name, segments)| Track {
+                    info: TrackInfo {
+                        name: Some((*name).to_owned()),
+                        ..Default::default()
+                    },
+                    trkseg: (0..*segments).map(|_| TrackSegment::default()).collect(),
+                    ..Default::default()
+                })
+                .collect(),
+        );
+        if waypoints > 0 {
+            file.wpt = Waypoints::new([WaypointChunk {
+                wpt: (0..waypoints).map(|_| Waypoint::default()).collect(),
+                ..Default::default()
+            }]);
+        }
+        file
+    }
+
+    fn add(fx: &mut Fixture, file: File) -> FileId {
+        let id = file.id;
+        fx.files.insert(id, Rc::new(file));
+        fx.order.0.push(id);
+        id
+    }
+
+    fn track_ids(fx: &Fixture, id: FileId) -> Vec<TrackId> {
+        fx.files[&id].trk.iter().map(|trk| trk.id).collect()
+    }
+
+    fn segment_ids(fx: &Fixture, id: FileId, trk: usize) -> Vec<TrackSegmentId> {
+        fx.files[&id].trk[trk].trkseg.iter().map(|s| s.id).collect()
+    }
+
+    fn wpt_ids(fx: &Fixture, id: FileId) -> Vec<WaypointId> {
+        waypoint_ids(&fx.files[&id]).collect()
+    }
+
+    fn do_move(fx: &mut Fixture, what: Selection, to: MoveTarget) -> Result<(), CommandError> {
+        Move { what, to }.apply(&mut fx.state())
+    }
+
+    fn tracks(file_id: FileId, ids: &[TrackId]) -> Selection {
+        Selection::Track {
+            file_id,
+            trk_ids: ids.iter().copied().collect(),
+        }
+    }
+
+    fn segments(file_id: FileId, trk_id: TrackId, ids: &[TrackSegmentId]) -> Selection {
+        Selection::TrackSegment {
+            file_id,
+            trk_id,
+            trkseg_ids: ids.iter().copied().collect(),
+        }
+    }
+
+    fn waypoints(file_id: FileId, ids: &[WaypointId]) -> Selection {
+        Selection::Waypoint {
+            file_id,
+            wpt_ids: ids.iter().copied().collect(),
+        }
+    }
+
+    fn files(ids: &[FileId]) -> Selection {
+        Selection::File {
+            file_ids: ids.iter().copied().collect(),
+        }
+    }
+
+    #[test]
+    fn test_reorder_tracks_in_a_file() {
+        let build = || {
+            let mut fx = Fixture::default();
+            let a = add(
+                &mut fx,
+                file("a", &[("0", 1), ("1", 1), ("2", 1), ("3", 1)], 0),
+            );
+            let t = track_ids(&fx, a);
+            (fx, a, t)
+        };
+        let at = |a, index| MoveTarget::Tracks { file_id: a, index };
+
+        // the position counts the tracks that stay
+        let (mut fx, a, t) = build();
+        do_move(&mut fx, tracks(a, &[t[0]]), at(a, 1)).unwrap();
+        assert_eq!(track_ids(&fx, a), vec![t[1], t[0], t[2], t[3]]);
+        assert_eq!(fx.selection, tracks(a, &[t[0]]));
+
+        let (mut fx, a, t) = build();
+        do_move(&mut fx, tracks(a, &[t[3]]), at(a, 0)).unwrap();
+        assert_eq!(track_ids(&fx, a), vec![t[3], t[0], t[1], t[2]]);
+
+        // several at once, as a block, in their order; past the end is the end
+        let (mut fx, a, t) = build();
+        do_move(&mut fx, tracks(a, &[t[1], t[0]]), at(a, 99)).unwrap();
+        assert_eq!(track_ids(&fx, a), vec![t[2], t[3], t[0], t[1]]);
+        assert_eq!(fx.selection, tracks(a, &[t[0], t[1]]));
+    }
+
+    #[test]
+    fn test_move_tracks_to_another_file_or_to_new_files() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[("t0", 1), ("t1", 1)], 0));
+        let b = add(&mut fx, file("b", &[("b0", 1), ("b1", 1)], 0));
+        let c = add(&mut fx, file("c", &[], 0));
+        let t = track_ids(&fx, a);
+        let b_tracks = track_ids(&fx, b);
+
+        do_move(
+            &mut fx,
+            tracks(a, &[t[0]]),
+            MoveTarget::Tracks {
+                file_id: b,
+                index: 1,
+            },
+        )
+        .unwrap();
+        assert_eq!(track_ids(&fx, a), vec![t[1]]);
+        assert_eq!(track_ids(&fx, b), vec![b_tracks[0], t[0], b_tracks[1]]);
+        assert_eq!(fx.selection, tracks(b, &[t[0]]));
+
+        // as a new file, at a position of the list of files
+        do_move(&mut fx, tracks(a, &[t[1]]), MoveTarget::Files { index: 1 }).unwrap();
+        assert!(track_ids(&fx, a).is_empty());
+        assert_eq!(fx.order.0.len(), 4);
+        let new = fx.order.0[1];
+        assert_eq!(fx.order.0[0], a);
+        assert_eq!(fx.order.0[2..], [b, c]);
+        assert_eq!(track_ids(&fx, new), vec![t[1]]);
+        assert_eq!(fx.files[&new].info.name, "t1");
+        assert_eq!(fx.selection, files(&[new]));
+    }
+
+    #[test]
+    fn test_move_segments() {
+        let build = || {
+            let mut fx = Fixture::default();
+            let a = add(&mut fx, file("a", &[("t0", 3), ("t1", 1)], 0));
+            let t = track_ids(&fx, a);
+            (fx, a, t)
+        };
+
+        // within a track
+        let (mut fx, a, t) = build();
+        let s = segment_ids(&fx, a, 0);
+        do_move(
+            &mut fx,
+            segments(a, t[0], &[s[2]]),
+            MoveTarget::Segments {
+                file_id: a,
+                trk_id: t[0],
+                index: 0,
+            },
+        )
+        .unwrap();
+        assert_eq!(segment_ids(&fx, a, 0), vec![s[2], s[0], s[1]]);
+        assert_eq!(fx.selection, segments(a, t[0], &[s[2]]));
+
+        // to another track
+        let (mut fx, a, t) = build();
+        let s = segment_ids(&fx, a, 0);
+        let other = segment_ids(&fx, a, 1);
+        do_move(
+            &mut fx,
+            segments(a, t[0], &[s[0], s[1]]),
+            MoveTarget::Segments {
+                file_id: a,
+                trk_id: t[1],
+                index: 0,
+            },
+        )
+        .unwrap();
+        assert_eq!(segment_ids(&fx, a, 0), vec![s[2]]);
+        assert_eq!(segment_ids(&fx, a, 1), vec![s[0], s[1], other[0]]);
+
+        // as new tracks of a file
+        let (mut fx, a, t) = build();
+        let s = segment_ids(&fx, a, 0);
+        do_move(
+            &mut fx,
+            segments(a, t[0], &[s[1]]),
+            MoveTarget::Tracks {
+                file_id: a,
+                index: 1,
+            },
+        )
+        .unwrap();
+        assert_eq!(fx.files[&a].trk.len(), 3);
+        assert_eq!(segment_ids(&fx, a, 1), vec![s[1]]);
+        assert_eq!(segment_ids(&fx, a, 0), vec![s[0], s[2]]);
+        assert_eq!(fx.files[&a].trk[0].id, t[0]);
+        assert_eq!(fx.files[&a].trk[2].id, t[1]);
+
+        // as new files
+        let (mut fx, a, t) = build();
+        let s = segment_ids(&fx, a, 0);
+        do_move(
+            &mut fx,
+            segments(a, t[0], &[s[0], s[1]]),
+            MoveTarget::Files { index: 0 },
+        )
+        .unwrap();
+        assert_eq!(fx.order.0.len(), 3);
+        assert_eq!(fx.order.0[2], a);
+        assert_eq!(fx.files[&fx.order.0[0]].info.name, "t0");
+        assert_eq!(segment_ids(&fx, a, 0), vec![s[2]]);
+    }
+
+    #[test]
+    fn test_move_waypoints() {
+        let build = || {
+            let mut fx = Fixture::default();
+            let a = add(&mut fx, file("a", &[], 4));
+            let b = add(&mut fx, file("b", &[], 2));
+            (fx, a, b)
+        };
+        let at = |file_id, index| MoveTarget::Waypoints { file_id, index };
+
+        // within a file
+        let (mut fx, a, _) = build();
+        let w = wpt_ids(&fx, a);
+        do_move(&mut fx, waypoints(a, &[w[3]]), at(a, 1)).unwrap();
+        assert_eq!(wpt_ids(&fx, a), vec![w[0], w[3], w[1], w[2]]);
+        assert_eq!(fx.selection, waypoints(a, &[w[3]]));
+
+        // to the start of another file
+        let (mut fx, a, b) = build();
+        let w = wpt_ids(&fx, a);
+        let before = wpt_ids(&fx, b);
+        do_move(&mut fx, waypoints(a, &[w[0], w[1]]), at(b, 0)).unwrap();
+        assert_eq!(wpt_ids(&fx, a), w[2..].to_vec());
+        assert_eq!(wpt_ids(&fx, b), [&w[..2], &before[..]].concat());
+
+        // all the waypoints of a file
+        let (mut fx, a, b) = build();
+        let w = wpt_ids(&fx, a);
+        let before = wpt_ids(&fx, b);
+        do_move(&mut fx, Selection::Waypoints { file_id: a }, at(b, 1)).unwrap();
+        assert!(wpt_ids(&fx, a).is_empty());
+        assert_eq!(
+            wpt_ids(&fx, b),
+            [&before[..1], &w[..], &before[1..]].concat()
+        );
+    }
+
+    #[test]
+    fn test_move_files() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[], 0));
+        let b = add(&mut fx, file("b", &[], 0));
+        let c = add(&mut fx, file("c", &[], 0));
+        do_move(&mut fx, files(&[c]), MoveTarget::Files { index: 0 }).unwrap();
+        assert_eq!(fx.order.0, vec![c, a, b]);
+        do_move(&mut fx, files(&[c, a]), MoveTarget::Files { index: 1 }).unwrap();
+        assert_eq!(fx.order.0, vec![b, c, a]);
+        assert_eq!(fx.selection, files(&[c, a]));
+    }
+
+    #[test]
+    fn test_what_cannot_be_moved() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[("t", 1)], 1));
+        let t = track_ids(&fx, a);
+        let s = segment_ids(&fx, a, 0);
+        let w = wpt_ids(&fx, a);
+        let before = fx.files[&a].clone();
+        let selection = fx.selection.clone();
+
+        let invalid = [
+            // the wrong kind of list
+            (
+                files(&[a]),
+                MoveTarget::Tracks {
+                    file_id: a,
+                    index: 0,
+                },
+            ),
+            (
+                tracks(a, &t),
+                MoveTarget::Waypoints {
+                    file_id: a,
+                    index: 0,
+                },
+            ),
+            (
+                tracks(a, &t),
+                MoveTarget::Segments {
+                    file_id: a,
+                    trk_id: t[0],
+                    index: 0,
+                },
+            ),
+            (
+                segments(a, t[0], &s),
+                MoveTarget::Waypoints {
+                    file_id: a,
+                    index: 0,
+                },
+            ),
+            (
+                waypoints(a, &w),
+                MoveTarget::Tracks {
+                    file_id: a,
+                    index: 0,
+                },
+            ),
+            (waypoints(a, &w), MoveTarget::Files { index: 0 }),
+            (
+                Selection::Waypoints { file_id: a },
+                MoveTarget::Files { index: 0 },
+            ),
+            (Selection::Empty, MoveTarget::Files { index: 0 }),
+            // elements that do not exist
+            (
+                tracks(a, &[TrackId::default()]),
+                MoveTarget::Files { index: 0 },
+            ),
+            (
+                waypoints(a, &[WaypointId::default()]),
+                MoveTarget::Waypoints {
+                    file_id: a,
+                    index: 0,
+                },
+            ),
+            (files(&[FileId::default()]), MoveTarget::Files { index: 0 }),
+            // a place that does not exist
+            (
+                tracks(a, &t),
+                MoveTarget::Tracks {
+                    file_id: FileId::default(),
+                    index: 0,
+                },
+            ),
+            (
+                segments(a, t[0], &s),
+                MoveTarget::Segments {
+                    file_id: a,
+                    trk_id: TrackId::default(),
+                    index: 0,
+                },
+            ),
+            (
+                waypoints(a, &w),
+                MoveTarget::Waypoints {
+                    file_id: FileId::default(),
+                    index: 0,
+                },
+            ),
+        ];
+        for (what, to) in invalid {
+            assert_eq!(
+                do_move(&mut fx, what.clone(), to),
+                Err(CommandError::NothingToDo),
+                "{what:?} to {to:?}"
+            );
+            // nothing changed
+            assert!(Rc::ptr_eq(&fx.files[&a], &before));
+            assert_eq!(fx.order.0, vec![a]);
+            assert_eq!(fx.selection, selection);
+        }
+    }
+}
@@ -0,0 +1,101 @@
+use crate::{Apply, CommandError, File, LngLat, State, Track, TrackSegment, Trackpoint, produce};
+
+/// Creates an empty file and selects it. With a `trackpoint`, the file starts with a track and a
+/// segment that hold it: it is how the routing tool starts a route on an empty map, in a single
+/// undo step.
+#[derive(Debug)]
+pub struct New<'a> {
+    pub name: &'a str,
+    pub trackpoint: Option<NewTrackpoint>,
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct NewTrackpoint {
+    pub lng: f64,
+    pub lat: f64,
+    pub ele: f64,
+}
+
+impl Apply for New<'_> {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        produce(state, |_| {
+            let mut file = File::default();
+            file.info.name = self.name.to_owned();
+            if let Some(point) = self.trackpoint {
+                let mut segment = TrackSegment::default();
+                // the ends of a segment are anchors of the routing tool
+                segment.splice(
+                    0,
+                    0,
+                    vec![Trackpoint {
+                        coordinates: LngLat {
+                            lng: point.lng,
+                            lat: point.lat,
+                        },
+                        ele: point.ele,
+                        ..Default::default()
+                    }],
+                );
+                file.trk.push(Track {
+                    trkseg: vec![segment],
+                    ..Default::default()
+                });
+            }
+            vec![file]
+        });
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::engine::command::fixture::Fixture;
+
+    use super::*;
+
+    #[test]
+    fn test_new() {
+        let mut fx = Fixture::default();
+        assert!(
+            New {
+                name: "new",
+                trackpoint: None
+            }
+            .apply(&mut fx.state())
+            .is_ok()
+        );
+        assert_eq!(fx.files.len(), 1);
+        let file = fx.files.values().next().unwrap();
+        assert_eq!(file.info.name, "new");
+        assert!(file.trk.is_empty());
+        assert_eq!(fx.selected_files(), [file.id].into());
+        assert_eq!(fx.order.0, vec![file.id]);
+    }
+
+    #[test]
+    fn test_new_with_a_trackpoint() {
+        let mut fx = Fixture::default();
+        let point = NewTrackpoint {
+            lng: 1.0,
+            lat: 2.0,
+            ele: 3.0,
+        };
+        New {
+            name: "new",
+            trackpoint: Some(point),
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let file = fx.files.values().next().unwrap();
+        assert_eq!(file.trk.len(), 1);
+        assert_eq!(file.trk[0].trkseg.len(), 1);
+        let segment = &file.trk[0].trkseg[0];
+        assert_eq!(segment.len(), 1);
+        assert_eq!(segment[0].coordinates.lng, 1.0);
+        assert_eq!(segment[0].coordinates.lat, 2.0);
+        assert_eq!(segment[0].ele, 3.0);
+        // the only trackpoint is an anchor of the routing tool
+        assert_eq!(segment[0].anchor, Some(0));
+        assert_eq!(fx.selected_files(), [file.id].into());
+    }
+}
@@ -0,0 +1,789 @@
+use std::{collections::HashSet, hash::Hash};
+
+use crate::{
+    Apply, ClipboardContent, CommandError, Destination, FileId, Place, Selection, State, TrackId,
+    TrackSegmentId, WaypointId, transfer, waypoint_ids,
+};
+
+/// Pastes what was copied or cut (see [`crate::Clipboard`]).
+///
+/// Where it goes depends on the selection, see [`crate::Clipboard::can_paste`]:
+/// - nothing selected: the files are copied, and tracks and segments become new files (named
+///   like their track, or like the file they come from);
+/// - a file: the tracks are added to it, segments become new tracks in it, and the waypoints are
+///   added to its own;
+/// - a track: the segments are added to it, tracks go after it in its file;
+/// - a segment: the segments go after it in its track;
+/// - the waypoints or a waypoint: the waypoints are added to their file, after the waypoint.
+///
+/// Copies are made, with new ids, and the pasted elements are selected. What was cut is moved
+/// instead, with its ids, the first time: what is still where it was is removed.
+///
+/// What is pasted is always the elements as they were when they were copied or cut, even if they
+/// were changed or deleted since. The clipboard is kept so that it can be pasted again: after
+/// what was cut was moved it is not cut anymore, and the next pastes make copies.
+#[derive(Debug)]
+pub struct Paste;
+
+impl Apply for Paste {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let clipboard = state
+            .clipboard
+            .clone()
+            .filter(|clipboard| clipboard.can_paste(state.selection))
+            .ok_or(CommandError::NothingToDo)?;
+        let cut = clipboard.cut;
+        // always the elements as they were when they were copied or cut
+        let to = destination(state, &clipboard.content)?;
+        let next = transfer(state, &clipboard.content, cut, to)?;
+
+        if cut && let Some(clipboard) = state.clipboard.as_mut() {
+            // moved: the next pastes make copies
+            clipboard.cut = false;
+        }
+        *state.selection = next;
+        Ok(())
+    }
+}
+
+fn track_ids_of(state: &State, file_id: FileId) -> Vec<TrackId> {
+    state
+        .files
+        .get(&file_id)
+        .map(|file| file.trk.iter().map(|trk| trk.id).collect())
+        .unwrap_or_default()
+}
+
+fn segment_ids_of(state: &State, file_id: FileId, trk_id: TrackId) -> Vec<TrackSegmentId> {
+    state
+        .files
+        .get(&file_id)
+        .and_then(|file| file.trk.iter().find(|trk| trk.id == trk_id))
+        .map(|trk| trk.trkseg.iter().map(|seg| seg.id).collect())
+        .unwrap_or_default()
+}
+
+fn waypoint_ids_of(state: &State, file_id: FileId) -> Vec<WaypointId> {
+    state
+        .files
+        .get(&file_id)
+        .map(|file| waypoint_ids(file).collect())
+        .unwrap_or_default()
+}
+
+/// Where the content goes, depending on what is selected.
+fn destination(state: &State, content: &ClipboardContent) -> Result<Destination, CommandError> {
+    let nothing = CommandError::NothingToDo;
+    let last_file = |file_ids: &HashSet<FileId>| {
+        last_selected(state.order.0.iter().copied(), file_ids).ok_or(CommandError::NothingToDo)
+    };
+    Ok(match (content, &*state.selection) {
+        (ClipboardContent::Files(_), _) => Destination::Files(Place::End),
+        (ClipboardContent::Tracks(_) | ClipboardContent::Segments(_), Selection::Empty) => {
+            Destination::Files(Place::End)
+        }
+        (
+            ClipboardContent::Tracks(_) | ClipboardContent::Segments(_),
+            Selection::File { file_ids },
+        ) => Destination::Tracks(last_file(file_ids)?, Place::End),
+        (ClipboardContent::Tracks(_), Selection::Track { file_id, trk_ids }) => {
+            let last =
+                last_selected(track_ids_of(state, *file_id).into_iter(), trk_ids).ok_or(nothing)?;
+            Destination::Tracks(*file_id, Place::After(last))
+        }
+        (ClipboardContent::Segments(_), Selection::Track { file_id, trk_ids }) => {
+            let last =
+                last_selected(track_ids_of(state, *file_id).into_iter(), trk_ids).ok_or(nothing)?;
+            Destination::Segments(*file_id, last, Place::End)
+        }
+        (
+            ClipboardContent::Segments(_),
+            Selection::TrackSegment {
+                file_id,
+                trk_id,
+                trkseg_ids,
+            },
+        ) => {
+            let last = last_selected(
+                segment_ids_of(state, *file_id, *trk_id).into_iter(),
+                trkseg_ids,
+            )
+            .ok_or(nothing)?;
+            Destination::Segments(*file_id, *trk_id, Place::After(last))
+        }
+        (ClipboardContent::Waypoints(_), Selection::File { file_ids }) => {
+            Destination::Waypoints(last_file(file_ids)?, Place::End)
+        }
+        (ClipboardContent::Waypoints(_), Selection::Waypoints { file_id }) => {
+            Destination::Waypoints(*file_id, Place::End)
+        }
+        (ClipboardContent::Waypoints(_), Selection::Waypoint { file_id, wpt_ids }) => {
+            let last = last_selected(waypoint_ids_of(state, *file_id).into_iter(), wpt_ids)
+                .ok_or(nothing)?;
+            Destination::Waypoints(*file_id, Place::After(last))
+        }
+        _ => return Err(nothing),
+    })
+}
+
+/// The last of the `selected` ids in the order of `all`: the element a paste goes after.
+fn last_selected<T: Copy + Eq + Hash>(
+    all: impl Iterator<Item = T>,
+    selected: &HashSet<T>,
+) -> Option<T> {
+    all.filter(|id| selected.contains(id)).last()
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::{
+        Clipboard, ClipboardIds, File, FileId, Track, TrackId, TrackInfo, TrackSegment,
+        TrackSegmentId, Waypoint, WaypointId, Waypoints, engine::command::fixture::Fixture,
+        new_file,
+    };
+
+    use super::*;
+
+    /// A file with the given tracks (name, number of segments) and number of waypoints.
+    fn file(name: &str, tracks: &[(Option<&str>, usize)], waypoints: usize) -> File {
+        let mut file = new_file(
+            name,
+            tracks
+                .iter()
+                .map(|(name, segments)| Track {
+                    info: TrackInfo {
+                        name: name.map(str::to_owned),
+                        ..Default::default()
+                    },
+                    trkseg: (0..*segments).map(|_| TrackSegment::default()).collect(),
+                    ..Default::default()
+                })
+                .collect(),
+        );
+        if waypoints > 0 {
+            file.wpt = Waypoints::new([crate::WaypointChunk {
+                wpt: (0..waypoints).map(|_| Waypoint::default()).collect(),
+                ..Default::default()
+            }]);
+        }
+        file
+    }
+
+    fn add(fx: &mut Fixture, file: File) -> FileId {
+        let id = file.id;
+        fx.files.insert(id, Rc::new(file));
+        fx.order.0.push(id);
+        id
+    }
+
+    fn track_ids(fx: &Fixture, id: FileId) -> Vec<TrackId> {
+        fx.files[&id].trk.iter().map(|trk| trk.id).collect()
+    }
+
+    fn segment_ids(fx: &Fixture, id: FileId, trk: usize) -> Vec<TrackSegmentId> {
+        fx.files[&id].trk[trk].trkseg.iter().map(|s| s.id).collect()
+    }
+
+    fn wpt_ids(fx: &Fixture, id: FileId) -> Vec<WaypointId> {
+        waypoint_ids(&fx.files[&id]).collect()
+    }
+
+    fn names(fx: &Fixture) -> Vec<String> {
+        fx.order
+            .0
+            .iter()
+            .map(|id| fx.files[id].info.name.clone())
+            .collect()
+    }
+
+    fn copy(fx: &mut Fixture, selection: Selection, cut: bool) {
+        fx.clipboard = Clipboard::new(&selection, &fx.files, &fx.order.0, cut);
+    }
+
+    /// The ids of what is in the clipboard, and whether it is cut.
+    fn clipboard_state(fx: &Fixture) -> Option<(ClipboardIds, bool)> {
+        fx.clipboard.as_ref().map(|c| (c.content.ids(), c.cut))
+    }
+
+    fn paste(fx: &mut Fixture) -> Result<(), CommandError> {
+        Paste.apply(&mut fx.state())
+    }
+
+    fn tracks(file_id: FileId, ids: &[TrackId]) -> Selection {
+        Selection::Track {
+            file_id,
+            trk_ids: ids.iter().copied().collect(),
+        }
+    }
+
+    fn segments(file_id: FileId, trk_id: TrackId, ids: &[TrackSegmentId]) -> Selection {
+        Selection::TrackSegment {
+            file_id,
+            trk_id,
+            trkseg_ids: ids.iter().copied().collect(),
+        }
+    }
+
+    fn waypoints(file_id: FileId, ids: &[WaypointId]) -> Selection {
+        Selection::Waypoint {
+            file_id,
+            wpt_ids: ids.iter().copied().collect(),
+        }
+    }
+
+    fn files(ids: &[FileId]) -> Selection {
+        Selection::File {
+            file_ids: ids.iter().copied().collect(),
+        }
+    }
+
+    #[test]
+    fn test_paste_copied_tracks_into_a_file() {
+        let mut fx = Fixture::default();
+        let a = add(
+            &mut fx,
+            file("a", &[(Some("t0"), 1), (Some("t1"), 2), (None, 1)], 0),
+        );
+        let b = add(&mut fx, file("b", &[(Some("b0"), 1)], 0));
+        let source = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[source[0], source[1]]), false);
+        fx.selection = files(&[b]);
+
+        paste(&mut fx).unwrap();
+
+        // the source is untouched, copies with new ids are added at the end
+        assert_eq!(track_ids(&fx, a), source);
+        let in_b = track_ids(&fx, b);
+        assert_eq!(in_b.len(), 3);
+        assert!(!source.contains(&in_b[1]) && !source.contains(&in_b[2]));
+        let names: Vec<_> = fx.files[&b]
+            .trk
+            .iter()
+            .map(|t| t.info.name.clone())
+            .collect();
+        assert_eq!(
+            names,
+            [Some("b0".into()), Some("t0".into()), Some("t1".into())]
+        );
+        // the segments are copies too
+        assert_eq!(fx.files[&b].trk[2].trkseg.len(), 2);
+        assert_ne!(segment_ids(&fx, b, 2), segment_ids(&fx, a, 1));
+        // the pasted tracks are selected, and the clipboard is still there
+        assert_eq!(fx.selection, tracks(b, &in_b[1..]));
+        assert_eq!(
+            clipboard_state(&fx),
+            Some((ClipboardIds::Tracks(vec![source[0], source[1]]), false))
+        );
+    }
+
+    #[test]
+    fn test_paste_cut_tracks_moves_them() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("t0"), 1), (Some("t1"), 1)], 0));
+        let b = add(&mut fx, file("b", &[], 0));
+        let source = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[source[0]]), true);
+        fx.selection = files(&[b]);
+
+        paste(&mut fx).unwrap();
+
+        assert_eq!(track_ids(&fx, a), vec![source[1]]);
+        assert_eq!(track_ids(&fx, b), vec![source[0]]);
+        assert_eq!(fx.selection, tracks(b, &[source[0]]));
+    }
+
+    #[test]
+    fn test_paste_tracks_after_the_selected_track() {
+        let mut fx = Fixture::default();
+        let a = add(
+            &mut fx,
+            file(
+                "a",
+                &[
+                    (Some("0"), 1),
+                    (Some("1"), 1),
+                    (Some("2"), 1),
+                    (Some("3"), 1),
+                ],
+                0,
+            ),
+        );
+        let t = track_ids(&fx, a);
+        // copy: the block goes after the selected track
+        copy(&mut fx, tracks(a, &[t[0], t[1]]), false);
+        fx.selection = tracks(a, &[t[2]]);
+        paste(&mut fx).unwrap();
+        let names: Vec<_> = fx.files[&a]
+            .trk
+            .iter()
+            .map(|t| t.info.name.clone().unwrap())
+            .collect();
+        assert_eq!(names, ["0", "1", "2", "0", "1", "3"]);
+
+        // cut: moved after the selected track
+        let mut fx = Fixture::default();
+        let a = add(
+            &mut fx,
+            file("a", &[(Some("0"), 1), (Some("1"), 1), (Some("2"), 1)], 0),
+        );
+        let t = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[t[0]]), true);
+        fx.selection = tracks(a, &[t[2]]);
+        paste(&mut fx).unwrap();
+        assert_eq!(track_ids(&fx, a), vec![t[1], t[2], t[0]]);
+
+        // the selected track is cut itself: the tracks go at the end
+        let mut fx = Fixture::default();
+        let a = add(
+            &mut fx,
+            file("a", &[(Some("0"), 1), (Some("1"), 1), (Some("2"), 1)], 0),
+        );
+        let t = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[t[0]]), true);
+        fx.selection = tracks(a, &[t[0]]);
+        paste(&mut fx).unwrap();
+        assert_eq!(track_ids(&fx, a), vec![t[1], t[2], t[0]]);
+    }
+
+    #[test]
+    fn test_paste_tracks_as_new_files() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("source", &[(Some("named"), 1), (None, 1)], 0));
+        let t = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[t[0], t[1]]), false);
+        fx.selection = Selection::Empty;
+
+        paste(&mut fx).unwrap();
+
+        // named like the track, or like the file it comes from
+        assert_eq!(names(&fx), ["source", "named", "source"]);
+        assert_eq!(fx.files.len(), 3);
+        let new = &fx.order.0[1..];
+        assert!(
+            matches!(&fx.selection, Selection::File { file_ids } if file_ids.len() == 2 && new.iter().all(|id| file_ids.contains(id)))
+        );
+        assert_eq!(fx.files[&new[0]].trk.len(), 1);
+        // the source keeps its tracks
+        assert_eq!(track_ids(&fx, a), t);
+    }
+
+    #[test]
+    fn test_paste_cut_tracks_as_new_files() {
+        let mut fx = Fixture::default();
+        let a = add(
+            &mut fx,
+            file("source", &[(Some("one"), 1), (Some("two"), 1)], 0),
+        );
+        let t = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[t[0]]), true);
+        fx.selection = Selection::Empty;
+        paste(&mut fx).unwrap();
+        assert_eq!(track_ids(&fx, a), vec![t[1]]);
+        let new = fx.order.0[1];
+        assert_eq!(track_ids(&fx, new), vec![t[0]]);
+    }
+
+    #[test]
+    fn test_paste_segments() {
+        let build = || {
+            let mut fx = Fixture::default();
+            let a = add(&mut fx, file("a", &[(Some("t0"), 3), (Some("t1"), 1)], 0));
+            (fx, a)
+        };
+
+        // at the end of the selected track
+        let (mut fx, a) = build();
+        let s = segment_ids(&fx, a, 0);
+        let t = track_ids(&fx, a);
+        copy(&mut fx, segments(a, t[0], &[s[0]]), false);
+        fx.selection = tracks(a, &[t[1]]);
+        paste(&mut fx).unwrap();
+        assert_eq!(segment_ids(&fx, a, 0), s);
+        let in_t1 = segment_ids(&fx, a, 1);
+        assert_eq!(in_t1.len(), 2);
+        assert_ne!(in_t1[1], s[0]);
+        assert_eq!(fx.selection, segments(a, t[1], &in_t1[1..]));
+
+        // after the selected segment, moved
+        let (mut fx, a) = build();
+        let s = segment_ids(&fx, a, 0);
+        let t = track_ids(&fx, a);
+        copy(&mut fx, segments(a, t[0], &[s[0]]), true);
+        fx.selection = segments(a, t[0], &[s[1]]);
+        paste(&mut fx).unwrap();
+        assert_eq!(segment_ids(&fx, a, 0), vec![s[1], s[0], s[2]]);
+
+        // each segment becomes a track of the selected file
+        let (mut fx, a) = build();
+        let s = segment_ids(&fx, a, 0);
+        let t = track_ids(&fx, a);
+        copy(&mut fx, segments(a, t[0], &[s[0], s[1]]), false);
+        fx.selection = files(&[a]);
+        paste(&mut fx).unwrap();
+        let tracks_now = track_ids(&fx, a);
+        assert_eq!(tracks_now.len(), 4);
+        assert!(
+            fx.files[&a].trk[2..]
+                .iter()
+                .all(|trk| trk.trkseg.len() == 1)
+        );
+        assert_eq!(fx.selection, tracks(a, &tracks_now[2..]));
+
+        // each segment becomes a file, named like its track
+        let (mut fx, a) = build();
+        let s = segment_ids(&fx, a, 0);
+        let t = track_ids(&fx, a);
+        copy(&mut fx, segments(a, t[0], &[s[0], s[1]]), false);
+        fx.selection = Selection::Empty;
+        paste(&mut fx).unwrap();
+        assert_eq!(names(&fx), ["a", "t0", "t0"]);
+        assert!(
+            fx.order.0[1..]
+                .iter()
+                .all(|id| fx.files[id].trk[0].trkseg.len() == 1)
+        );
+    }
+
+    #[test]
+    fn test_paste_waypoints() {
+        let build = || {
+            let mut fx = Fixture::default();
+            let a = add(&mut fx, file("a", &[], 4));
+            let b = add(&mut fx, file("b", &[], 2));
+            (fx, a, b)
+        };
+
+        // to the end of another file
+        let (mut fx, a, b) = build();
+        let w = wpt_ids(&fx, a);
+        let before = wpt_ids(&fx, b);
+        copy(&mut fx, waypoints(a, &[w[1], w[2]]), false);
+        fx.selection = files(&[b]);
+        paste(&mut fx).unwrap();
+        assert_eq!(wpt_ids(&fx, a), w);
+        let now = wpt_ids(&fx, b);
+        assert_eq!(now.len(), 4);
+        assert_eq!(&now[..2], &before[..]);
+        assert!(!w.contains(&now[2]));
+        assert_eq!(fx.selection, waypoints(b, &now[2..]));
+
+        // after the selected waypoint
+        let (mut fx, a, b) = build();
+        let w = wpt_ids(&fx, a);
+        let before = wpt_ids(&fx, b);
+        copy(&mut fx, waypoints(a, &[w[0]]), true);
+        fx.selection = waypoints(b, &[before[0]]);
+        paste(&mut fx).unwrap();
+        assert_eq!(wpt_ids(&fx, a), w[1..].to_vec());
+        assert_eq!(wpt_ids(&fx, b), vec![before[0], w[0], before[1]]);
+
+        // within the file, after a waypoint
+        let (mut fx, a, _) = build();
+        let w = wpt_ids(&fx, a);
+        copy(&mut fx, waypoints(a, &[w[0], w[1]]), true);
+        fx.selection = waypoints(a, &[w[2]]);
+        paste(&mut fx).unwrap();
+        assert_eq!(wpt_ids(&fx, a), vec![w[2], w[0], w[1], w[3]]);
+    }
+
+    #[test]
+    fn test_paste_all_the_waypoints_of_a_file() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[], 3));
+        let b = add(&mut fx, file("b", &[], 1));
+        let w = wpt_ids(&fx, a);
+        copy(&mut fx, Selection::Waypoints { file_id: a }, false);
+        fx.selection = Selection::Waypoints { file_id: b };
+        paste(&mut fx).unwrap();
+        assert_eq!(wpt_ids(&fx, a), w);
+        assert_eq!(wpt_ids(&fx, b).len(), 4);
+
+        // moved: the source has none left
+        copy(&mut fx, Selection::Waypoints { file_id: a }, true);
+        fx.selection = files(&[b]);
+        paste(&mut fx).unwrap();
+        assert!(wpt_ids(&fx, a).is_empty());
+        assert_eq!(&wpt_ids(&fx, b)[4..], &w[..]);
+    }
+
+    #[test]
+    fn test_paste_files() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("t"), 1)], 1));
+        let b = add(&mut fx, file("b", &[], 0));
+        let c = add(&mut fx, file("c", &[], 0));
+        copy(&mut fx, files(&[b, a]), false);
+        fx.selection = files(&[c]);
+        paste(&mut fx).unwrap();
+        // copies, in the order of the files, at the end
+        assert_eq!(names(&fx), ["a", "b", "c", "a", "b"]);
+        assert_eq!(fx.files.len(), 5);
+        assert_eq!(fx.files[&fx.order.0[3]].trk.len(), 1);
+        assert_ne!(track_ids(&fx, fx.order.0[3]), track_ids(&fx, a));
+        assert!(matches!(&fx.selection, Selection::File { file_ids } if file_ids.len() == 2));
+
+        // cut: moved to the end, they keep their ids
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[], 0));
+        let b = add(&mut fx, file("b", &[], 0));
+        let c = add(&mut fx, file("c", &[], 0));
+        copy(&mut fx, files(&[a]), true);
+        fx.selection = Selection::Empty;
+        paste(&mut fx).unwrap();
+        assert_eq!(fx.order.0, vec![b, c, a]);
+        assert_eq!(fx.selection, files(&[a]));
+    }
+
+    #[test]
+    fn test_nothing_to_paste() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("t"), 1)], 1));
+        let t = track_ids(&fx, a);
+        let w = wpt_ids(&fx, a);
+        fx.selection = files(&[a]);
+
+        // an empty clipboard
+        assert_eq!(paste(&mut fx), Err(CommandError::NothingToDo));
+
+        // a target that does not accept it (tracks cannot go to waypoints), the clipboard stays
+        copy(&mut fx, tracks(a, &t), false);
+        fx.selection = waypoints(a, &w);
+        assert_eq!(paste(&mut fx), Err(CommandError::NothingToDo));
+        assert!(fx.clipboard.is_some());
+        assert_eq!(fx.selection, waypoints(a, &w));
+
+        // nothing to copy: what does not exist is not put in the clipboard
+        copy(&mut fx, tracks(a, &[TrackId::default()]), false);
+        fx.selection = files(&[a]);
+        assert_eq!(paste(&mut fx), Err(CommandError::NothingToDo));
+        copy(&mut fx, waypoints(a, &[WaypointId::default()]), false);
+        assert_eq!(paste(&mut fx), Err(CommandError::NothingToDo));
+        copy(&mut fx, files(&[FileId::default()]), false);
+        fx.selection = Selection::Empty;
+        assert_eq!(paste(&mut fx), Err(CommandError::NothingToDo));
+        assert_eq!(fx.files.len(), 1);
+        assert_eq!(fx.order.0, vec![a]);
+    }
+
+    #[test]
+    fn test_paste_a_copy_several_times() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("t0"), 1), (Some("t1"), 1)], 1));
+        let b = add(&mut fx, file("b", &[], 0));
+        let t = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[t[0]]), false);
+        fx.selection = files(&[b]);
+
+        paste(&mut fx).unwrap();
+        paste(&mut fx).unwrap();
+        paste(&mut fx).unwrap();
+
+        // each paste made a copy with new ids, and the source is untouched
+        let in_b = track_ids(&fx, b);
+        assert_eq!(in_b.len(), 3);
+        assert_eq!(in_b.iter().collect::<HashSet<_>>().len(), 3);
+        assert!(in_b.iter().all(|id| !t.contains(id)));
+        assert_eq!(track_ids(&fx, a), t);
+        assert!(fx.clipboard.is_some());
+
+        // the selection is the last copy: the next paste goes after it
+        assert_eq!(fx.selection, tracks(b, &[in_b[2]]));
+        paste(&mut fx).unwrap();
+        assert_eq!(track_ids(&fx, b).len(), 4);
+
+        // the same with other elements
+        let w = wpt_ids(&fx, a);
+        copy(&mut fx, waypoints(a, &w), false);
+        fx.selection = files(&[b]);
+        paste(&mut fx).unwrap();
+        paste(&mut fx).unwrap();
+        assert_eq!(wpt_ids(&fx, b).len(), 2);
+        assert_eq!(wpt_ids(&fx, a), w);
+
+        copy(&mut fx, files(&[b]), false);
+        fx.selection = Selection::Empty;
+        paste(&mut fx).unwrap();
+        paste(&mut fx).unwrap();
+        assert_eq!(fx.files.len(), 4);
+    }
+
+    #[test]
+    fn test_paste_a_cut_moves_the_first_time_then_copies() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("t0"), 1), (Some("t1"), 1)], 0));
+        let b = add(&mut fx, file("b", &[], 0));
+        let c = add(&mut fx, file("c", &[], 0));
+        let t = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[t[0]]), true);
+        fx.selection = files(&[b]);
+
+        paste(&mut fx).unwrap();
+        // moved with its id, and what is in the clipboard now is a copy of it
+        assert_eq!(track_ids(&fx, a), vec![t[1]]);
+        assert_eq!(track_ids(&fx, b), vec![t[0]]);
+        assert_eq!(
+            clipboard_state(&fx),
+            Some((ClipboardIds::Tracks(vec![t[0]]), false))
+        );
+
+        fx.selection = files(&[c]);
+        paste(&mut fx).unwrap();
+        paste(&mut fx).unwrap();
+        // copies: the moved track stays where it was moved to
+        assert_eq!(track_ids(&fx, b), vec![t[0]]);
+        let in_c = track_ids(&fx, c);
+        assert_eq!(in_c.len(), 2);
+        assert!(!in_c.contains(&t[0]));
+        assert_eq!(track_ids(&fx, a), vec![t[1]]);
+    }
+
+    #[test]
+    fn test_paste_cut_files_several_times() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[], 0));
+        let b = add(&mut fx, file("b", &[], 0));
+        copy(&mut fx, files(&[a]), true);
+        fx.selection = Selection::Empty;
+        paste(&mut fx).unwrap();
+        assert_eq!(fx.order.0, vec![b, a]);
+        // the next pastes copy it
+        paste(&mut fx).unwrap();
+        assert_eq!(fx.files.len(), 3);
+        assert_eq!(fx.order.0[..2], [b, a]);
+    }
+
+    /// Renames the first track of the file, as an edit would.
+    fn rename_track(fx: &mut Fixture, id: FileId, name: &str) {
+        let file = std::rc::Rc::make_mut(fx.files.get_mut(&id).unwrap());
+        file.trk[0].info.name = Some(name.to_owned());
+    }
+
+    #[test]
+    fn test_paste_the_elements_as_they_were_when_copied() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("original"), 1)], 0));
+        let b = add(&mut fx, file("b", &[], 0));
+        let t = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[t[0]]), false);
+        rename_track(&mut fx, a, "edited");
+        fx.selection = files(&[b]);
+
+        paste(&mut fx).unwrap();
+        let pasted = &fx.files[&b].trk[0];
+        assert_eq!(pasted.info.name.as_deref(), Some("original"));
+        // the source keeps what was done to it
+        assert_eq!(fx.files[&a].trk[0].info.name.as_deref(), Some("edited"));
+
+        // and each time
+        paste(&mut fx).unwrap();
+        assert!(
+            fx.files[&b]
+                .trk
+                .iter()
+                .all(|trk| trk.info.name.as_deref() == Some("original"))
+        );
+        assert_eq!(fx.files[&b].trk.len(), 2);
+    }
+
+    #[test]
+    fn test_paste_a_cut_as_it_was_when_cut() {
+        let mut fx = Fixture::default();
+        let a = add(
+            &mut fx,
+            file("a", &[(Some("original"), 1), (Some("other"), 1)], 0),
+        );
+        let b = add(&mut fx, file("b", &[], 0));
+        let t = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[t[0]]), true);
+        rename_track(&mut fx, a, "edited");
+        fx.selection = files(&[b]);
+
+        paste(&mut fx).unwrap();
+        // what is in the clipboard is moved, the edited version is not what is pasted
+        assert_eq!(track_ids(&fx, a), vec![t[1]]);
+        assert_eq!(track_ids(&fx, b), vec![t[0]]);
+        assert_eq!(fx.files[&b].trk[0].info.name.as_deref(), Some("original"));
+    }
+
+    #[test]
+    fn test_paste_after_the_elements_were_deleted() {
+        let delete_file = |fx: &mut Fixture, id: FileId| {
+            fx.files.remove(&id);
+            fx.order.0.retain(|other| *other != id);
+        };
+
+        // copied tracks, waypoints, segments and files are still there to be pasted
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("t"), 2)], 2));
+        let b = add(&mut fx, file("b", &[], 0));
+        let t = track_ids(&fx, a);
+
+        copy(&mut fx, tracks(a, &t), false);
+        fx.selection = files(&[b]);
+        delete_file(&mut fx, a);
+        paste(&mut fx).unwrap();
+        assert_eq!(fx.files[&b].trk.len(), 1);
+        assert_eq!(fx.files[&b].trk[0].trkseg.len(), 2);
+        // the copy of a track comes from a file that is gone: named like the track
+        fx.selection = Selection::Empty;
+        paste(&mut fx).unwrap();
+        assert_eq!(names(&fx), ["b", "t"]);
+
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("t"), 2)], 2));
+        let b = add(&mut fx, file("b", &[], 0));
+        let (t, s) = (track_ids(&fx, a), segment_ids(&fx, a, 0));
+        copy(&mut fx, segments(a, t[0], &s), false);
+        fx.selection = files(&[b]);
+        delete_file(&mut fx, a);
+        paste(&mut fx).unwrap();
+        assert_eq!(fx.files[&b].trk.len(), 2);
+
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("t"), 2)], 2));
+        let b = add(&mut fx, file("b", &[], 0));
+        let w = wpt_ids(&fx, a);
+        copy(&mut fx, waypoints(a, &w), false);
+        fx.selection = files(&[b]);
+        delete_file(&mut fx, a);
+        paste(&mut fx).unwrap();
+        assert_eq!(wpt_ids(&fx, b).len(), 2);
+
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("t"), 1)], 0));
+        copy(&mut fx, files(&[a]), false);
+        fx.selection = Selection::Empty;
+        delete_file(&mut fx, a);
+        assert!(fx.files.is_empty());
+        paste(&mut fx).unwrap();
+        paste(&mut fx).unwrap();
+        assert_eq!(fx.files.len(), 2);
+        assert_eq!(names(&fx), ["a", "a"]);
+        let _ = (s, w);
+    }
+
+    #[test]
+    fn test_paste_a_cut_after_the_elements_were_deleted() {
+        let mut fx = Fixture::default();
+        let a = add(&mut fx, file("a", &[(Some("t0"), 1), (Some("t1"), 1)], 0));
+        let b = add(&mut fx, file("b", &[], 0));
+        let t = track_ids(&fx, a);
+        copy(&mut fx, tracks(a, &[t[0]]), true);
+        // deleted before it is pasted
+        std::rc::Rc::make_mut(fx.files.get_mut(&a).unwrap())
+            .trk
+            .retain(|trk| trk.id != t[0]);
+        fx.selection = files(&[b]);
+
+        paste(&mut fx).unwrap();
+        // nothing to remove, the track is where it was pasted, with its id
+        assert_eq!(track_ids(&fx, a), vec![t[1]]);
+        assert_eq!(track_ids(&fx, b), vec![t[0]]);
+        assert_eq!(
+            clipboard_state(&fx),
+            Some((ClipboardIds::Tracks(vec![t[0]]), false))
+        );
+    }
+}
@@ -0,0 +1,361 @@
+//! Copying or moving elements to a place of the file tree: what paste and move are made of.
+//! The elements come as the content of a clipboard, and a destination says where they go among
+//! the elements already there.
+
+use std::{collections::HashSet, rc::Rc};
+
+use crate::{
+    ClipboardContent, ClipboardSegment, ClipboardTrack, CommandError, File, FileId, Selection,
+    State, Track, TrackId, TrackSegment, TrackSegmentId, Waypoint, WaypointId, copy_file,
+    copy_segment, copy_track, copy_waypoint,
+};
+
+/// Where elements are put, among the others of the same list.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Place<T> {
+    /// After all of them.
+    End,
+    /// Right after the one with this id, or at the end if it is not there (anymore).
+    After(T),
+    /// At this position (at the end if it is past it).
+    Index(usize),
+}
+
+impl<T: Copy + PartialEq> Place<T> {
+    /// The position in the list of `ids`.
+    pub fn position(&self, ids: &[T]) -> usize {
+        match self {
+            Place::End => ids.len(),
+            Place::After(id) => ids
+                .iter()
+                .position(|other| other == id)
+                .map_or(ids.len(), |i| i + 1),
+            Place::Index(index) => (*index).min(ids.len()),
+        }
+    }
+}
+
+/// Where elements go. What can go where:
+/// - files: among the files;
+/// - tracks: among the files (each track becomes a file, named like the track, or like the file
+///   it comes from), or among the tracks of a file;
+/// - segments: among the files (each segment becomes a file with a track, named like its track,
+///   or like its file), among the tracks of a file (each segment becomes a track), or among the
+///   segments of a track;
+/// - waypoints: among the waypoints of a file.
+#[derive(Debug, Clone, Copy)]
+pub enum Destination {
+    Files(Place<FileId>),
+    Tracks(FileId, Place<TrackId>),
+    Segments(FileId, TrackId, Place<TrackSegmentId>),
+    Waypoints(FileId, Place<WaypointId>),
+}
+
+pub fn waypoint_ids(file: &File) -> impl Iterator<Item = WaypointId> + '_ {
+    file.wpt.iter().map(|wpt| wpt.id)
+}
+
+fn file_mut<'a>(state: &'a mut State, id: FileId) -> Result<&'a mut File, CommandError> {
+    state
+        .files
+        .get_mut(&id)
+        .map(Rc::make_mut)
+        .ok_or(CommandError::NothingToDo)
+}
+
+pub fn new_file(name: &str, trk: Vec<Track>) -> File {
+    let mut file = File {
+        trk,
+        ..Default::default()
+    };
+    file.info.name = name.to_owned();
+    file
+}
+
+/// Adds the files to the state, at `place` in the order of the files.
+fn add_files(state: &mut State, files: Vec<Rc<File>>, place: Place<FileId>) -> Selection {
+    let at = place.position(&state.order.0);
+    let ids: Vec<FileId> = files.iter().map(|file| file.id).collect();
+    for file in files {
+        state.files.insert(file.id, file);
+    }
+    state.order.0.splice(at..at, ids.iter().copied());
+    Selection::File {
+        file_ids: ids.into_iter().collect(),
+    }
+}
+
+/// Removes the elements of the content from the files, wherever they are.
+pub fn remove_elements(state: &mut State, content: &ClipboardContent) {
+    match content {
+        ClipboardContent::Files(files) => {
+            let ids: HashSet<FileId> = files.iter().map(|file| file.id).collect();
+            state.files.retain(|id, _| !ids.contains(id));
+            state.order.0.retain(|id| !ids.contains(id));
+        }
+        ClipboardContent::Tracks(tracks) => {
+            let ids: HashSet<TrackId> = tracks.iter().map(|trk| trk.track.id).collect();
+            for file in state.files.values_mut() {
+                if file.trk.iter().any(|trk| ids.contains(&trk.id)) {
+                    Rc::make_mut(file).trk.retain(|trk| !ids.contains(&trk.id));
+                }
+            }
+        }
+        ClipboardContent::Segments(segments) => {
+            let ids: HashSet<TrackSegmentId> = segments.iter().map(|seg| seg.segment.id).collect();
+            for file in state.files.values_mut() {
+                let contains = |trk: &Track| trk.trkseg.iter().any(|seg| ids.contains(&seg.id));
+                if file.trk.iter().any(contains) {
+                    for trk in Rc::make_mut(file).trk.iter_mut() {
+                        trk.trkseg.retain(|seg| !ids.contains(&seg.id));
+                    }
+                }
+            }
+        }
+        ClipboardContent::Waypoints(waypoints) => {
+            let ids: HashSet<WaypointId> = waypoints.iter().map(|wpt| wpt.id).collect();
+            for file in state.files.values_mut() {
+                if waypoint_ids(file).any(|id| ids.contains(&id)) {
+                    Rc::make_mut(file).wpt.edit(
+                        |wpt| ids.contains(&wpt.id),
+                        |wpts| {
+                            wpts.retain(|wpt| !ids.contains(&wpt.id));
+                            true
+                        },
+                    );
+                }
+            }
+        }
+    }
+}
+
+/// Puts the elements of the content at the destination: copies of them, or the elements
+/// themselves, with their ids, when `cut` (they are removed from where they are first). Returns
+/// the selection of what was put.
+pub fn transfer(
+    state: &mut State,
+    content: &ClipboardContent,
+    cut: bool,
+    to: Destination,
+) -> Result<Selection, CommandError> {
+    // the destination has to be there, before anything is changed
+    let exists = match to {
+        Destination::Files(_) => true,
+        Destination::Tracks(file_id, _) => state.files.contains_key(&file_id),
+        Destination::Segments(file_id, trk_id, _) => state
+            .files
+            .get(&file_id)
+            .is_some_and(|file| file.trk.iter().any(|trk| trk.id == trk_id)),
+        Destination::Waypoints(file_id, _) => state.files.contains_key(&file_id),
+    };
+    let valid = matches!(
+        (content, to),
+        (ClipboardContent::Files(_), Destination::Files(_))
+            | (
+                ClipboardContent::Tracks(_),
+                Destination::Files(_) | Destination::Tracks(..)
+            )
+            | (
+                ClipboardContent::Segments(_),
+                Destination::Files(_) | Destination::Tracks(..) | Destination::Segments(..),
+            )
+            | (ClipboardContent::Waypoints(_), Destination::Waypoints(..))
+    );
+    let empty = match content {
+        ClipboardContent::Files(files) => files.is_empty(),
+        ClipboardContent::Tracks(tracks) => tracks.is_empty(),
+        ClipboardContent::Segments(segments) => segments.is_empty(),
+        ClipboardContent::Waypoints(waypoints) => waypoints.is_empty(),
+    };
+    if !exists || !valid || empty {
+        return Err(CommandError::NothingToDo);
+    }
+
+    if cut {
+        remove_elements(state, content);
+    }
+    let copy = !cut;
+    match (content, to) {
+        (ClipboardContent::Files(files), Destination::Files(place)) => {
+            let files = files
+                .iter()
+                .map(|file| {
+                    if copy {
+                        Rc::new(copy_file(file))
+                    } else {
+                        file.clone()
+                    }
+                })
+                .collect();
+            Ok(add_files(state, files, place))
+        }
+        (ClipboardContent::Tracks(tracks), to) => transfer_tracks(state, tracks, copy, to),
+        (ClipboardContent::Segments(segments), to) => transfer_segments(state, segments, copy, to),
+        (ClipboardContent::Waypoints(waypoints), Destination::Waypoints(file_id, place)) => {
+            transfer_waypoints(state, waypoints, copy, file_id, place)
+        }
+        _ => Err(CommandError::NothingToDo),
+    }
+}
+
+fn transfer_tracks(
+    state: &mut State,
+    tracks: &[ClipboardTrack],
+    copy: bool,
+    to: Destination,
+) -> Result<Selection, CommandError> {
+    let tracks: Vec<(Track, &str)> = tracks
+        .iter()
+        .map(|clip| {
+            let track = if copy {
+                copy_track(&clip.track)
+            } else {
+                clip.track.clone()
+            };
+            (track, clip.file_name.as_str())
+        })
+        .collect();
+    match to {
+        Destination::Files(place) => {
+            let files = tracks
+                .into_iter()
+                .map(|(track, file_name)| {
+                    let name = track
+                        .info
+                        .name
+                        .clone()
+                        .unwrap_or_else(|| file_name.to_owned());
+                    Rc::new(new_file(&name, vec![track]))
+                })
+                .collect();
+            Ok(add_files(state, files, place))
+        }
+        Destination::Tracks(file_id, place) => {
+            let tracks: Vec<Track> = tracks.into_iter().map(|(track, _)| track).collect();
+            let ids: HashSet<TrackId> = tracks.iter().map(|trk| trk.id).collect();
+            let file = file_mut(state, file_id)?;
+            let existing: Vec<TrackId> = file.trk.iter().map(|trk| trk.id).collect();
+            let at = place.position(&existing);
+            file.trk.splice(at..at, tracks);
+            Ok(Selection::Track {
+                file_id,
+                trk_ids: ids,
+            })
+        }
+        _ => Err(CommandError::NothingToDo),
+    }
+}
+
+fn transfer_segments(
+    state: &mut State,
+    segments: &[ClipboardSegment],
+    copy: bool,
+    to: Destination,
+) -> Result<Selection, CommandError> {
+    let segments: Vec<(TrackSegment, &str)> = segments
+        .iter()
+        .map(|clip| {
+            let segment = if copy {
+                copy_segment(&clip.segment)
+            } else {
+                clip.segment.clone()
+            };
+            (segment, clip.name.as_str())
+        })
+        .collect();
+    // a segment on its own needs a track
+    let own_track = |segment: TrackSegment| Track {
+        trkseg: vec![segment],
+        ..Default::default()
+    };
+    match to {
+        Destination::Files(place) => {
+            let files = segments
+                .into_iter()
+                .map(|(segment, name)| Rc::new(new_file(name, vec![own_track(segment)])))
+                .collect();
+            Ok(add_files(state, files, place))
+        }
+        Destination::Tracks(file_id, place) => {
+            let tracks: Vec<Track> = segments
+                .into_iter()
+                .map(|(segment, _)| own_track(segment))
+                .collect();
+            let ids = tracks.iter().map(|trk| trk.id).collect();
+            let file = file_mut(state, file_id)?;
+            let existing: Vec<TrackId> = file.trk.iter().map(|trk| trk.id).collect();
+            let at = place.position(&existing);
+            file.trk.splice(at..at, tracks);
+            Ok(Selection::Track {
+                file_id,
+                trk_ids: ids,
+            })
+        }
+        Destination::Segments(file_id, trk_id, place) => {
+            let segments: Vec<TrackSegment> =
+                segments.into_iter().map(|(segment, _)| segment).collect();
+            let ids: HashSet<TrackSegmentId> = segments.iter().map(|seg| seg.id).collect();
+            let trk = file_mut(state, file_id)?
+                .trk
+                .iter_mut()
+                .find(|trk| trk.id == trk_id)
+                .ok_or(CommandError::NothingToDo)?;
+            let existing: Vec<TrackSegmentId> = trk.trkseg.iter().map(|seg| seg.id).collect();
+            let at = place.position(&existing);
+            trk.trkseg.splice(at..at, segments);
+            Ok(Selection::TrackSegment {
+                file_id,
+                trk_id,
+                trkseg_ids: ids,
+            })
+        }
+        Destination::Waypoints(..) => Err(CommandError::NothingToDo),
+    }
+}
+
+fn transfer_waypoints(
+    state: &mut State,
+    waypoints: &[Waypoint],
+    copy: bool,
+    file_id: FileId,
+    place: Place<WaypointId>,
+) -> Result<Selection, CommandError> {
+    let waypoints: Vec<Waypoint> = waypoints
+        .iter()
+        .map(|wpt| {
+            if copy {
+                copy_waypoint(wpt)
+            } else {
+                wpt.clone()
+            }
+        })
+        .collect();
+    let ids = waypoints.iter().map(|wpt| wpt.id).collect();
+    let file = file_mut(state, file_id)?;
+    let existing: Vec<WaypointId> = waypoint_ids(file).collect();
+    file.wpt.insert_at(place.position(&existing), waypoints);
+    Ok(Selection::Waypoint {
+        file_id,
+        wpt_ids: ids,
+    })
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_place_position() {
+        let ids = [1, 2, 3];
+        assert_eq!(Place::End.position(&ids), 3);
+        assert_eq!(Place::After(1).position(&ids), 1);
+        assert_eq!(Place::After(3).position(&ids), 3);
+        // not there: at the end
+        assert_eq!(Place::After(9).position(&ids), 3);
+        assert_eq!(Place::Index(0).position(&ids), 0);
+        assert_eq!(Place::Index(2).position(&ids), 2);
+        assert_eq!(Place::Index(10).position(&ids), 3);
+        assert_eq!(Place::<i32>::End.position(&[]), 0);
+        assert_eq!(Place::<i32>::Index(4).position(&[]), 0);
+    }
+}
@@ -0,0 +1,34 @@
+//! Shared helpers for the tests of the commands.
+
+use std::collections::HashSet;
+
+use crate::{Clipboard, FileId, FileOrder, Selection, StackEntry, State, TrackpointCategories};
+
+#[derive(Default)]
+pub struct Fixture {
+    pub files: StackEntry,
+    pub selection: Selection,
+    pub order: FileOrder,
+    pub clipboard: Option<Clipboard>,
+    pub categories: TrackpointCategories,
+}
+
+impl Fixture {
+    pub fn state(&mut self) -> State<'_> {
+        State {
+            categories: &mut self.categories,
+            files: &mut self.files,
+            selection: &mut self.selection,
+            order: &mut self.order,
+            clipboard: &mut self.clipboard,
+        }
+    }
+
+    /// Ids of the selected files, empty unless the selection is a file selection.
+    pub fn selected_files(&self) -> HashSet<FileId> {
+        match &self.selection {
+            Selection::File { file_ids } => file_ids.clone(),
+            _ => HashSet::new(),
+        }
+    }
+}
@@ -0,0 +1,89 @@
+mod apply;
+mod edit;
+mod file;
+#[cfg(test)]
+pub(crate) mod fixture;
+mod pattern;
+mod tools;
+
+pub use apply::*;
+pub use edit::*;
+pub use file::*;
+pub use pattern::*;
+pub use tools::*;
+
+use crate::State;
+
+/// A user action that edits the files. Each variant wraps the command's own struct, whose
+/// effect is implemented in its own file (see `Apply`).
+///
+/// Bulk data (coordinates, file bytes) is borrowed straight from the wasm-bindgen argument
+/// buffers, so a command is built without copying; the engine only copies what it keeps.
+#[derive(Debug)]
+pub enum Command<'a> {
+    New(New<'a>),
+    Load(Load<'a>),
+    LoadFiles(LoadFiles<'a>),
+    Duplicate(Duplicate),
+    Delete(Delete),
+    Paste(Paste),
+    Move(Move),
+    DeleteAll(DeleteAll),
+    DeleteWaypoint(DeleteWaypoint),
+    Metadata(Metadata<'a>),
+    Style(Style<'a>),
+    NewTrack(NewTrack),
+    NewTrackSegment(NewTrackSegment),
+    Reverse(Reverse),
+    RoundTrip(RoundTrip),
+    Route(Route<'a>),
+    NewWaypoint(NewWaypoint<'a>),
+    EditWaypoint(EditWaypoint<'a>),
+    MoveWaypoint(MoveWaypoint),
+    Crop(Crop),
+    Reduce(Reduce),
+    Split(Split),
+    Time(Time),
+    Merge(Merge),
+    Extract(Extract),
+    InsertAnchor(InsertAnchor),
+    Elevation(Elevation<'a>),
+    Clean(Clean),
+    ChangeLoopStart(ChangeLoopStart),
+}
+
+impl Apply for Command<'_> {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        match self {
+            Command::New(c) => c.apply(state),
+            Command::Load(c) => c.apply(state),
+            Command::LoadFiles(c) => c.apply(state),
+            Command::Duplicate(c) => c.apply(state),
+            Command::Delete(c) => c.apply(state),
+            Command::Paste(c) => c.apply(state),
+            Command::Move(c) => c.apply(state),
+            Command::DeleteAll(c) => c.apply(state),
+            Command::DeleteWaypoint(c) => c.apply(state),
+            Command::Metadata(c) => c.apply(state),
+            Command::Style(c) => c.apply(state),
+            Command::NewTrack(c) => c.apply(state),
+            Command::NewTrackSegment(c) => c.apply(state),
+            Command::Reverse(c) => c.apply(state),
+            Command::RoundTrip(c) => c.apply(state),
+            Command::Route(c) => c.apply(state),
+            Command::NewWaypoint(c) => c.apply(state),
+            Command::EditWaypoint(c) => c.apply(state),
+            Command::MoveWaypoint(c) => c.apply(state),
+            Command::Crop(c) => c.apply(state),
+            Command::Reduce(c) => c.apply(state),
+            Command::Split(c) => c.apply(state),
+            Command::Time(c) => c.apply(state),
+            Command::Merge(c) => c.apply(state),
+            Command::Extract(c) => c.apply(state),
+            Command::InsertAnchor(c) => c.apply(state),
+            Command::Elevation(c) => c.apply(state),
+            Command::Clean(c) => c.apply(state),
+            Command::ChangeLoopStart(c) => c.apply(state),
+        }
+    }
+}
@@ -0,0 +1,35 @@
+use crate::{File, Track, TrackSegment, Waypoint};
+
+// The trackpoints of a segment are shared chunks, so copying elements is cheap.
+
+/// A copy of the segment, with a new id.
+pub fn copy_segment(segment: &TrackSegment) -> TrackSegment {
+    let mut copy = segment.clone();
+    copy.id = Default::default();
+    copy
+}
+
+/// A copy of the track and of its segments, with new ids.
+pub fn copy_track(track: &Track) -> Track {
+    Track {
+        id: Default::default(),
+        trkseg: track.trkseg.iter().map(copy_segment).collect(),
+        ..track.clone()
+    }
+}
+
+/// A copy of the file and of its tracks and segments, with new ids.
+pub fn copy_file(file: &File) -> File {
+    File {
+        id: Default::default(),
+        trk: file.trk.iter().map(copy_track).collect(),
+        ..file.clone()
+    }
+}
+
+/// A copy of the waypoint, with a new id.
+pub fn copy_waypoint(waypoint: &Waypoint) -> Waypoint {
+    let mut copy = waypoint.clone();
+    copy.id = Default::default();
+    copy
+}
@@ -0,0 +1,11 @@
+mod copy;
+mod produce;
+mod update_segments;
+mod update_selected;
+mod update_waypoint;
+
+pub use copy::*;
+pub use produce::*;
+pub use update_segments::*;
+pub use update_selected::*;
+pub use update_waypoint::*;
@@ -0,0 +1,81 @@
+use std::rc::Rc;
+
+use crate::{File, Selection, State};
+
+/// Pure producer: adds the files returned by `f` to the state and selects the first one.
+pub fn produce<F>(state: &mut State, f: F)
+where
+    F: FnOnce(&State) -> Vec<File>,
+{
+    *state.selection = Selection::Empty;
+    for file in f(state) {
+        let file_id = file.id;
+        state.files.insert(file_id, Rc::new(file));
+        state.order.0.push(file_id);
+        if matches!(*state.selection, Selection::Empty) {
+            *state.selection = Selection::File {
+                file_ids: [file_id].into(),
+            };
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::engine::command::fixture::Fixture;
+
+    use super::*;
+
+    fn named(name: &str) -> File {
+        let mut file = File::default();
+        file.info.name = name.to_string();
+        file
+    }
+
+    #[test]
+    fn test_produce_adds_orders_and_selects_first() {
+        let mut fx = Fixture::default();
+        let (a, b) = (named("a"), named("b"));
+        let (id_a, id_b) = (a.id, b.id);
+        produce(&mut fx.state(), |_| vec![a, b]);
+
+        assert_eq!(fx.files.len(), 2);
+        assert_eq!(fx.order.0, vec![id_a, id_b]);
+        assert_eq!(fx.selected_files(), HashSet::from([id_a]));
+    }
+
+    #[test]
+    fn test_produce_replaces_selection_and_keeps_order() {
+        let mut fx = Fixture::default();
+        let a = named("a");
+        let id_a = a.id;
+        produce(&mut fx.state(), |_| vec![a]);
+        let b = named("b");
+        let id_b = b.id;
+        produce(&mut fx.state(), |_| vec![b]);
+
+        assert_eq!(fx.order.0, vec![id_a, id_b]);
+        assert_eq!(fx.selected_files(), HashSet::from([id_b]));
+    }
+
+    #[test]
+    fn test_produce_nothing_clears_selection() {
+        let mut fx = Fixture::default();
+        produce(&mut fx.state(), |_| vec![named("a")]);
+        produce(&mut fx.state(), |_| vec![]);
+        assert!(matches!(fx.selection, Selection::Empty));
+        assert_eq!(fx.files.len(), 1);
+    }
+
+    #[test]
+    fn test_produce_sees_current_state() {
+        let mut fx = Fixture::default();
+        produce(&mut fx.state(), |_| vec![named("a")]);
+        produce(&mut fx.state(), |state| {
+            assert_eq!(state.files.len(), 1);
+            vec![]
+        });
+    }
+}
@@ -0,0 +1,91 @@
+use std::collections::HashMap;
+use std::rc::Rc;
+
+use crate::{File, FileId, SegmentLocation, State, TrackSegment};
+
+/// Edits the segments at `locations`, calling `f` with the position of each location in the slice
+/// and its segment, in that order.
+///
+/// Each file concerned is copied once (cheap, trackpoints are shared chunks) and stored back as a
+/// new snapshot. The segments take care of their own revision (see [`TrackSegment`]).
+pub fn update_segments(
+    state: &mut State,
+    locations: &[SegmentLocation],
+    mut f: impl FnMut(usize, &mut TrackSegment),
+) {
+    let mut files: HashMap<FileId, File> = HashMap::new();
+    for (i, location) in locations.iter().enumerate() {
+        let file = files
+            .entry(location.file_id)
+            .or_insert_with(|| (*state.files[&location.file_id]).clone());
+        f(i, &mut file.trk[location.trk].trkseg[location.seg]);
+    }
+    for (file_id, file) in files {
+        state.files.insert(file_id, Rc::new(file));
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::engine::command::fixture::Fixture;
+
+    use super::*;
+
+    fn fixture() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        let file = Rc::new(crate::parse(&data, &mut Default::default()).unwrap());
+        let id = file.id;
+        fx.files.insert(id, file);
+        (fx, id)
+    }
+
+    #[test]
+    fn test_only_the_given_segments_are_edited_in_order() {
+        let (mut fx, id) = fixture();
+        let before = fx.files[&id].clone();
+        let locations = [
+            SegmentLocation {
+                file_id: id,
+                trk: 1,
+                seg: 0,
+            },
+            SegmentLocation {
+                file_id: id,
+                trk: 0,
+                seg: 0,
+            },
+        ];
+        let mut calls = vec![];
+        update_segments(&mut fx.state(), &locations, |i, segment| {
+            calls.push(i);
+            segment.update(0, |trkpt| trkpt.ele = 1234.0);
+        });
+
+        assert_eq!(calls, vec![0, 1]);
+        let after = &fx.files[&id];
+        assert!(!Rc::ptr_eq(after, &before));
+        for (trk, seg) in [(1, 0), (0, 0)] {
+            assert_eq!(after.trk[trk].trkseg[seg][0].ele, 1234.0);
+            assert_ne!(
+                after.trk[trk].trkseg[seg].rev_id,
+                before.trk[trk].trkseg[seg].rev_id
+            );
+        }
+        // the other segments are the same ones
+        assert_eq!(
+            after.trk[0].trkseg[1].rev_id,
+            before.trk[0].trkseg[1].rev_id
+        );
+    }
+
+    #[test]
+    fn test_no_location_leaves_the_files_alone() {
+        let (mut fx, id) = fixture();
+        let before = fx.files[&id].clone();
+        update_segments(&mut fx.state(), &[], |_, _| panic!("nothing to edit"));
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+    }
+}
@@ -0,0 +1,337 @@
+use std::rc::Rc;
+
+use crate::{File, FileId, Selection, StackEntry, State, Track, TrackSegment, Waypoint};
+
+/// What an [`Editor`] hook did to the element it was given.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum Edit {
+    Unchanged,
+    Changed,
+}
+
+impl Edit {
+    fn merge(self, other: Edit) -> Edit {
+        if self == Edit::Changed || other == Edit::Changed {
+            Edit::Changed
+        } else {
+            Edit::Unchanged
+        }
+    }
+}
+
+/// Independent edit of each selected element, without needing the rest of the state.
+///
+/// A selected file, track or segment is passed to the hook of its own level. By default a
+/// file is forwarded to its tracks and a track to its segments, so an editor only overrides
+/// the level(s) it cares about (metadata: file and track, style: track, reverse: segment).
+/// Waypoints are only edited when selected, never through their file.
+pub trait Editor {
+    fn file(&mut self, file: &mut File) -> Edit {
+        edit_each(&mut file.trk, |trk| self.track(trk))
+    }
+
+    fn track(&mut self, track: &mut Track) -> Edit {
+        edit_each(&mut track.trkseg, |seg| edit_segment(self, seg))
+    }
+
+    fn segment(&mut self, _segment: &mut TrackSegment) -> Edit {
+        Edit::Unchanged
+    }
+
+    fn waypoint(&mut self, _waypoint: &mut Waypoint) -> Edit {
+        Edit::Unchanged
+    }
+}
+
+/// Calls the segment hook and gives the segment a new revision id if it changed, so that
+/// derived data (statistics) is recomputed.
+fn edit_segment<E: Editor + ?Sized>(editor: &mut E, segment: &mut TrackSegment) -> Edit {
+    let edit = editor.segment(segment);
+    if edit == Edit::Changed {
+        segment.rev_id = Default::default();
+    }
+    edit
+}
+
+fn edit_each<T>(items: &mut [T], f: impl FnMut(&mut T) -> Edit) -> Edit {
+    edit_where(items, |_| true, f)
+}
+
+fn edit_where<T>(
+    items: &mut [T],
+    filter: impl Fn(&T) -> bool,
+    mut f: impl FnMut(&mut T) -> Edit,
+) -> Edit {
+    items
+        .iter_mut()
+        .filter(|item| filter(item))
+        .fold(Edit::Unchanged, |acc, item| acc.merge(f(item)))
+}
+
+/// Edits a copy of the file (cheap, track points are shared chunks) and stores it back as a
+/// new snapshot only if something changed.
+fn update_file(files: &mut StackEntry, id: FileId, f: impl FnOnce(&mut File) -> Edit) {
+    let Some(current) = files.get(&id) else {
+        return;
+    };
+    let mut file = (**current).clone();
+    if f(&mut file) == Edit::Changed {
+        files.insert(id, Rc::new(file));
+    }
+}
+
+fn edit_waypoints<E: Editor + ?Sized>(
+    file: &mut File,
+    filter: impl Fn(&Waypoint) -> bool,
+    editor: &mut E,
+) -> Edit {
+    let changed = file.wpt.edit(&filter, |wpts| {
+        edit_where(wpts, &filter, |wpt| editor.waypoint(wpt)) == Edit::Changed
+    });
+    if changed {
+        Edit::Changed
+    } else {
+        Edit::Unchanged
+    }
+}
+
+/// Applies the editor to every selected file, track or segment.
+pub fn update_selected<E: Editor>(state: &mut State, editor: &mut E) {
+    match &*state.selection {
+        Selection::File { file_ids } => {
+            for id in file_ids {
+                update_file(state.files, *id, |file| editor.file(file));
+            }
+        }
+        Selection::Track { file_id, trk_ids } => {
+            update_file(state.files, *file_id, |file| {
+                edit_where(
+                    &mut file.trk,
+                    |trk| trk_ids.contains(&trk.id),
+                    |trk| editor.track(trk),
+                )
+            });
+        }
+        Selection::TrackSegment {
+            file_id,
+            trk_id,
+            trkseg_ids,
+        } => {
+            update_file(state.files, *file_id, |file| {
+                edit_where(
+                    &mut file.trk,
+                    |trk| trk.id == *trk_id,
+                    |trk| {
+                        edit_where(
+                            &mut trk.trkseg,
+                            |seg| trkseg_ids.contains(&seg.id),
+                            |seg| edit_segment(editor, seg),
+                        )
+                    },
+                )
+            });
+        }
+        Selection::Waypoints { file_id } => {
+            update_file(state.files, *file_id, |file| {
+                edit_waypoints(file, |_| true, editor)
+            });
+        }
+        Selection::Waypoint { file_id, wpt_ids } => {
+            update_file(state.files, *file_id, |file| {
+                edit_waypoints(file, |wpt| wpt_ids.contains(&wpt.id), editor)
+            });
+        }
+        Selection::Empty => {}
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::engine::command::fixture::Fixture;
+
+    use super::*;
+
+    struct Rename;
+
+    impl Editor for Rename {
+        fn file(&mut self, file: &mut File) -> Edit {
+            file.info.name.push('!');
+            Edit::Changed
+        }
+
+        fn track(&mut self, track: &mut Track) -> Edit {
+            track.info.name = Some("track".to_string());
+            Edit::Changed
+        }
+
+        fn segment(&mut self, _: &mut TrackSegment) -> Edit {
+            Edit::Changed
+        }
+    }
+
+    struct Nothing;
+    impl Editor for Nothing {}
+
+    fn fixture_with_tracks() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        let file = Rc::new(crate::parse(&data, &mut Default::default()).unwrap());
+        let id = file.id;
+        fx.files.insert(id, file);
+        (fx, id)
+    }
+
+    #[test]
+    fn test_only_selected_files_are_updated() {
+        let mut fx = Fixture::default();
+        let (a, b, c) = (File::default(), File::default(), File::default());
+        let ids = [a.id, b.id, c.id];
+        for file in [a, b, c] {
+            fx.files.insert(file.id, Rc::new(file));
+        }
+        let untouched = fx.files[&ids[2]].clone();
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([ids[0], ids[1]]),
+        };
+
+        update_selected(&mut fx.state(), &mut Rename);
+
+        assert_eq!(fx.files[&ids[0]].info.name, "!");
+        assert_eq!(fx.files[&ids[1]].info.name, "!");
+        assert!(Rc::ptr_eq(&fx.files[&ids[2]], &untouched));
+    }
+
+    #[test]
+    fn test_unchanged_file_keeps_its_snapshot() {
+        let (mut fx, id) = fixture_with_tracks();
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        let before = fx.files[&id].clone();
+        update_selected(&mut fx.state(), &mut Nothing);
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+    }
+
+    #[test]
+    fn test_track_selection_uses_track_hook() {
+        let (mut fx, id) = fixture_with_tracks();
+        let trk_id = fx.files[&id].trk[0].id;
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: HashSet::from([trk_id]),
+        };
+        update_selected(&mut fx.state(), &mut Rename);
+
+        let file = &fx.files[&id];
+        assert_eq!(file.info.name, "with_tracks_and_segments");
+        assert_eq!(file.trk[0].info.name.as_deref(), Some("track"));
+        assert_ne!(file.trk[1].info.name.as_deref(), Some("track"));
+    }
+
+    #[test]
+    fn test_segment_selection_bumps_revision_id() {
+        let (mut fx, id) = fixture_with_tracks();
+        let before = fx.files[&id].clone();
+        let trk = &before.trk[0];
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: trk.id,
+            trkseg_ids: HashSet::from([trk.trkseg[0].id]),
+        };
+        update_selected(&mut fx.state(), &mut Rename);
+
+        let after = &fx.files[&id];
+        assert_ne!(after.trk[0].trkseg[0].rev_id, trk.trkseg[0].rev_id);
+        assert_eq!(after.trk[0].trkseg[1].rev_id, trk.trkseg[1].rev_id);
+        assert_eq!(
+            after.trk[1].trkseg[0].rev_id,
+            before.trk[1].trkseg[0].rev_id
+        );
+    }
+
+    #[test]
+    fn test_file_selection_cascades_to_segments() {
+        struct SegmentsOnly;
+        impl Editor for SegmentsOnly {
+            fn segment(&mut self, _: &mut TrackSegment) -> Edit {
+                Edit::Changed
+            }
+        }
+        let (mut fx, id) = fixture_with_tracks();
+        let before = fx.files[&id].clone();
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        update_selected(&mut fx.state(), &mut SegmentsOnly);
+        for (b, a) in before.trk.iter().zip(fx.files[&id].trk.iter()) {
+            for (b, a) in b.trkseg.iter().zip(a.trkseg.iter()) {
+                assert_ne!(b.rev_id, a.rev_id);
+            }
+        }
+    }
+
+    #[test]
+    fn test_waypoint_selection_edits_only_selected_waypoints() {
+        struct Name;
+        impl Editor for Name {
+            fn waypoint(&mut self, wpt: &mut Waypoint) -> Edit {
+                wpt.name = Some("x".into());
+                Edit::Changed
+            }
+        }
+        let (mut fx, id) = fixture_with_tracks();
+        let wpts: Vec<_> = (0..3).map(|_| Waypoint::default()).collect();
+        let ids: Vec<_> = wpts.iter().map(|w| w.id).collect();
+        let mut file = (*fx.files[&id]).clone();
+        file.wpt = crate::Waypoints::new([crate::WaypointChunk {
+            wpt: wpts,
+            ..Default::default()
+        }]);
+        fx.files.insert(id, Rc::new(file));
+        let chunk_id = fx.files[&id].wpt.chunks()[0].id;
+
+        // A file selection never touches waypoints.
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        update_selected(&mut fx.state(), &mut Name);
+        assert!(fx.files[&id].wpt.iter().all(|w| w.name.is_none()));
+
+        fx.selection = Selection::Waypoint {
+            file_id: id,
+            wpt_ids: HashSet::from([ids[1]]),
+        };
+        let rev = fx.files[&id].wpt.rev_id;
+        update_selected(&mut fx.state(), &mut Name);
+        assert_ne!(fx.files[&id].wpt.rev_id, rev);
+        assert_ne!(fx.files[&id].wpt.chunks()[0].id, chunk_id);
+        let named: Vec<_> = fx.files[&id].wpt.iter().map(|w| w.name.is_some()).collect();
+        assert_eq!(named, [false, true, false]);
+
+        fx.selection = Selection::Waypoints { file_id: id };
+        update_selected(&mut fx.state(), &mut Name);
+        assert!(fx.files[&id].wpt.iter().all(|w| w.name.is_some()));
+    }
+
+    #[test]
+    fn test_missing_files_and_other_selections_are_ignored() {
+        let mut fx = Fixture::default();
+        let file = File::default();
+        let id = file.id;
+        fx.files.insert(id, Rc::new(file));
+        let before = fx.files[&id].clone();
+
+        for selection in [
+            Selection::File {
+                file_ids: HashSet::from([FileId::default()]),
+            },
+            Selection::Empty,
+        ] {
+            fx.selection = selection;
+            update_selected(&mut fx.state(), &mut Rename);
+            assert!(Rc::ptr_eq(&fx.files[&id], &before));
+        }
+    }
+}
@@ -0,0 +1,29 @@
+use std::rc::Rc;
+
+use crate::{CommandError, FileId, State, Waypoint, WaypointId};
+
+/// Changes one waypoint of a file with `f`, whatever is selected. Nothing to do if the file or
+/// the waypoint does not exist.
+pub fn update_waypoint(
+    state: &mut State,
+    file_id: FileId,
+    waypoint_id: WaypointId,
+    f: impl Fn(&mut Waypoint),
+) -> Result<(), CommandError> {
+    let file = state.files.get(&file_id).ok_or(CommandError::NothingToDo)?;
+    let mut file = (**file).clone();
+    let changed = file.wpt.edit(
+        |wpt| wpt.id == waypoint_id,
+        |wpts| {
+            wpts.iter_mut()
+                .filter(|wpt| wpt.id == waypoint_id)
+                .for_each(&f);
+            true
+        },
+    );
+    if !changed {
+        return Err(CommandError::NothingToDo);
+    }
+    state.files.insert(file_id, Rc::new(file));
+    Ok(())
+}
@@ -0,0 +1,144 @@
+use std::rc::Rc;
+
+use crate::{Apply, CommandError, State, Trackpoint, replace_trackpoints};
+
+use super::route::find_target;
+
+/// Makes the trackpoint `index` of the selection (see `RoutingBuffer`) the start of its segment,
+/// which is a loop: the trackpoints before it, and itself, are copied after the last trackpoint
+/// of the segment, and the original ones are removed. The trackpoint is both the first and the
+/// last one, which closes the loop on it.
+///
+/// The copies keep their durations, and start one second after the previous last trackpoint if
+/// the segment has timestamps (see [`replace_trackpoints`]).
+///
+/// It is how the routing tool starts a loop somewhere else. The first and last trackpoints are
+/// anchors shown at every zoom level, as any end of a segment.
+#[derive(Debug)]
+pub struct ChangeLoopStart {
+    pub index: u32,
+}
+
+impl Apply for ChangeLoopStart {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let index = self.index as usize;
+        let target = find_target(state, index, index)?.ok_or(CommandError::NothingToDo)?;
+        let mut file = (*state.files[&target.location.file_id]).clone();
+        let segment = &mut file.trk[target.location.trk].trkseg[target.location.seg];
+        let (start, len) = (target.start, segment.len());
+        if start == 0 || start >= len {
+            // it already is the start, or it is not a trackpoint
+            return Err(CommandError::NothingToDo);
+        }
+
+        // the trackpoint itself ends the loop as well
+        let moved: Vec<Trackpoint> = segment.iter().take(start + 1).cloned().collect();
+        // the copies are shifted after the last trackpoint, which is all that matters of the rest
+        let mut tail = vec![segment[len - 1].clone()];
+        replace_trackpoints(&mut tail, 1, 1, moved, None, None, false);
+        tail.remove(0);
+
+        // only the chunks at the ends of the segment change: the others stay shared
+        segment.splice(len, len, tail);
+        segment.splice(0, start, vec![]);
+        segment.rev_id = Default::default();
+        state.files.insert(target.location.file_id, Rc::new(file));
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{FileId, Load, Selection, TrackSegment, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded(path: &str) -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read(path).unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        (fx, id)
+    }
+
+    fn first_segment(fx: &Fixture, id: FileId) -> TrackSegment {
+        fx.files[&id].trk[0].trkseg[0].clone()
+    }
+
+    #[test]
+    fn test_the_points_before_move_to_the_end_and_the_loop_closes_on_the_start() {
+        let (mut fx, id) = loaded("data/simple.gpx");
+        let before = first_segment(&fx, id);
+        let n = before.len();
+        assert!(n > 10);
+
+        ChangeLoopStart { index: 4 }.apply(&mut fx.state()).unwrap();
+        let after = first_segment(&fx, id);
+        // the trackpoint is repeated at the end
+        assert_eq!(after.len(), n + 1);
+        assert_ne!(after.rev_id, before.rev_id);
+        let lng = |s: &TrackSegment, i: usize| s[i].coordinates.lng;
+        for i in 0..=n {
+            assert_eq!(lng(&after, i), lng(&before, (i + 4) % n), "{i}");
+        }
+        assert_eq!(lng(&after, n), lng(&after, 0));
+        // the start and the end of the new segment are anchors, whatever they were
+        assert_eq!(after[0].anchor, Some(0));
+        assert_eq!(after[n].anchor, Some(0));
+    }
+
+    #[test]
+    fn test_the_moved_part_is_shifted_after_the_last_point() {
+        let (mut fx, id) = loaded("data/with_time.gpx");
+        let before = first_segment(&fx, id);
+        let n = before.len();
+        ChangeLoopStart { index: 30 }
+            .apply(&mut fx.state())
+            .unwrap();
+        let after = first_segment(&fx, id);
+        assert_eq!(after.len(), n + 1);
+        let times: Vec<_> = after.iter().map(|p| p.time.unwrap()).collect();
+        assert!(times.windows(2).all(|w| w[0] < w[1]), "{times:?}");
+        // the part that was after the index is untouched
+        for i in 0..n - 30 {
+            assert_eq!(after[i].time, before[30 + i].time);
+        }
+        // the copies follow the last point by a second, and keep their durations
+        let last = before[n - 1].time.unwrap();
+        assert_eq!(after[n - 30].time, Some(last + 1000));
+        for i in n - 30..n {
+            let original = i - (n - 30);
+            assert_eq!(
+                after[i + 1].time.unwrap() - after[i].time.unwrap(),
+                before[original + 1].time.unwrap() - before[original].time.unwrap(),
+                "{i}"
+            );
+        }
+    }
+
+    #[test]
+    fn test_nothing_to_do_on_the_start_or_out_of_the_trackpoints() {
+        let (mut fx, id) = loaded("data/simple.gpx");
+        let before = fx.files[&id].clone();
+        assert_eq!(
+            ChangeLoopStart { index: 0 }.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        let total = first_segment(&fx, id).len() as u32;
+        assert!(matches!(
+            ChangeLoopStart { index: total + 5 }.apply(&mut fx.state()),
+            Err(CommandError::InvalidData(_))
+        ));
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+    }
+}
@@ -0,0 +1,402 @@
+use std::{collections::HashSet, rc::Rc};
+
+use crate::{
+    Apply, CommandError, Edit, Editor, File, FileId, LngLat, LngLatBounds, Selection, State,
+    TrackSegment, TrackSegmentId, Trackpoint, Waypoint, delete_waypoints, update_selected,
+};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum CleanType {
+    Inside,
+    Outside,
+}
+
+/// Removes the trackpoints and/or waypoints of the selection lying inside (or outside) a
+/// rectangle. A selected file cleans its tracks and its waypoints, a selected track or segment
+/// only trackpoints, selected waypoints only waypoints.
+#[derive(Debug)]
+pub struct Clean {
+    pub bounds: LngLatBounds,
+    pub type_: CleanType,
+    pub trkpt: bool,
+    pub wpt: bool,
+}
+
+impl Clean {
+    fn contains(&self, c: LngLat) -> bool {
+        (self.bounds.sw.lng..=self.bounds.ne.lng).contains(&c.lng)
+            && (self.bounds.sw.lat..=self.bounds.ne.lat).contains(&c.lat)
+    }
+
+    fn removes(&self, c: LngLat) -> bool {
+        self.contains(c) == (self.type_ == CleanType::Inside)
+    }
+}
+
+impl Apply for Clean {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        match &*state.selection {
+            Selection::Waypoint { file_id, .. } | Selection::Waypoints { file_id } => {
+                let file_id = *file_id;
+                if !self.wpt {
+                    return Err(CommandError::NothingToDo);
+                }
+                let wpt_ids = match &*state.selection {
+                    Selection::Waypoint { wpt_ids, .. } => Some(wpt_ids.clone()),
+                    _ => None,
+                };
+                let selected =
+                    |wpt: &Waypoint| wpt_ids.as_ref().is_none_or(|ids| ids.contains(&wpt.id));
+                *state.selection = delete_waypoints(state.files, file_id, |wpt| {
+                    selected(wpt) && self.removes(wpt.coordinates)
+                })?;
+                Ok(())
+            }
+            Selection::Empty => Err(CommandError::NothingToDo),
+            _ => {
+                let mut cleaner = Cleaner {
+                    clean: &self,
+                    changed: false,
+                    emptied: HashSet::new(),
+                    wpt_files: HashSet::new(),
+                };
+                update_selected(state, &mut cleaner);
+                if cleaner.changed {
+                    prune(state, &cleaner.emptied, &cleaner.wpt_files);
+                    Ok(())
+                } else {
+                    Err(CommandError::NothingToDo)
+                }
+            }
+        }
+    }
+}
+
+struct Cleaner<'a> {
+    clean: &'a Clean,
+    changed: bool,
+    /// Segments left without trackpoints by the clean.
+    emptied: HashSet<TrackSegmentId>,
+    /// Files that lost waypoints.
+    wpt_files: HashSet<FileId>,
+}
+
+impl Editor for Cleaner<'_> {
+    fn file(&mut self, file: &mut File) -> Edit {
+        let mut edit = Edit::Unchanged;
+        for trk in &mut file.trk {
+            if self.track(trk) == Edit::Changed {
+                edit = Edit::Changed;
+            }
+        }
+        if self.clean.wpt
+            && file.wpt.edit(
+                |wpt| self.clean.removes(wpt.coordinates),
+                |wpts| {
+                    wpts.retain(|wpt| !self.clean.removes(wpt.coordinates));
+                    true
+                },
+            )
+        {
+            edit = Edit::Changed;
+            self.wpt_files.insert(file.id);
+        }
+        self.changed |= edit == Edit::Changed;
+        edit
+    }
+
+    fn segment(&mut self, segment: &mut TrackSegment) -> Edit {
+        if !self.clean.trkpt || !segment.iter().any(|pt| self.clean.removes(pt.coordinates)) {
+            return Edit::Unchanged;
+        }
+        let kept: Vec<Trackpoint> = segment
+            .iter()
+            .filter(|pt| !self.clean.removes(pt.coordinates))
+            .cloned()
+            .collect();
+        if kept.is_empty() {
+            self.emptied.insert(segment.id);
+        }
+        segment.splice(0, segment.len(), kept);
+        self.changed = true;
+        Edit::Changed
+    }
+}
+
+/// Removes what the clean left empty: the emptied segments, the tracks that lost all their
+/// segments and the files that lost something and have nothing left. The selection falls back
+/// to the closest element still existing.
+fn prune(state: &mut State, emptied: &HashSet<TrackSegmentId>, wpt_files: &HashSet<FileId>) {
+    let ids: Vec<FileId> = state
+        .files
+        .iter()
+        .filter(|(id, file)| {
+            wpt_files.contains(id)
+                || file
+                    .trk
+                    .iter()
+                    .any(|trk| trk.trkseg.iter().any(|seg| emptied.contains(&seg.id)))
+        })
+        .map(|(id, _)| *id)
+        .collect();
+    for id in ids {
+        let mut file = (*state.files[&id]).clone();
+        let lost_something = !emptied.is_empty() || wpt_files.contains(&id);
+        file.trk.retain_mut(|trk| {
+            let len = trk.trkseg.len();
+            trk.trkseg.retain(|seg| !emptied.contains(&seg.id));
+            trk.trkseg.len() == len || !trk.trkseg.is_empty()
+        });
+        if lost_something && file.trk.is_empty() && file.wpt.is_empty() {
+            state.files.remove(&id);
+            state.order.0.retain(|f| *f != id);
+        } else {
+            state.files.insert(id, Rc::new(file));
+        }
+    }
+    *state.selection = fixed_selection(state);
+}
+
+fn fixed_selection(state: &State) -> Selection {
+    let files = &*state.files;
+    match &*state.selection {
+        Selection::File { file_ids } => {
+            let file_ids: HashSet<_> = file_ids
+                .iter()
+                .filter(|id| files.contains_key(id))
+                .copied()
+                .collect();
+            if file_ids.is_empty() {
+                Selection::Empty
+            } else {
+                Selection::File { file_ids }
+            }
+        }
+        Selection::Track { file_id, trk_ids } => {
+            let Some(file) = files.get(file_id) else {
+                return Selection::Empty;
+            };
+            let trk_ids: HashSet<_> = file
+                .trk
+                .iter()
+                .map(|trk| trk.id)
+                .filter(|id| trk_ids.contains(id))
+                .collect();
+            if trk_ids.is_empty() {
+                Selection::File {
+                    file_ids: [*file_id].into(),
+                }
+            } else {
+                Selection::Track {
+                    file_id: *file_id,
+                    trk_ids,
+                }
+            }
+        }
+        Selection::TrackSegment {
+            file_id,
+            trk_id,
+            trkseg_ids,
+        } => {
+            let Some(file) = files.get(file_id) else {
+                return Selection::Empty;
+            };
+            let Some(trk) = file.trk.iter().find(|trk| trk.id == *trk_id) else {
+                return Selection::File {
+                    file_ids: [*file_id].into(),
+                };
+            };
+            let trkseg_ids: HashSet<_> = trk
+                .trkseg
+                .iter()
+                .map(|seg| seg.id)
+                .filter(|id| trkseg_ids.contains(id))
+                .collect();
+            if trkseg_ids.is_empty() {
+                Selection::Track {
+                    file_id: *file_id,
+                    trk_ids: [*trk_id].into(),
+                }
+            } else {
+                Selection::TrackSegment {
+                    file_id: *file_id,
+                    trk_id: *trk_id,
+                    trkseg_ids,
+                }
+            }
+        }
+        Selection::Waypoints { file_id } | Selection::Waypoint { file_id, .. } => {
+            if files.contains_key(file_id) {
+                Selection::File {
+                    file_ids: [*file_id].into(),
+                }
+            } else {
+                Selection::Empty
+            }
+        }
+        Selection::Empty => Selection::Empty,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{FileId, Load, WaypointChunk, Waypoints, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        (fx, id)
+    }
+
+    fn bounds(w: f64, s: f64, e: f64, n: f64) -> LngLatBounds {
+        LngLatBounds {
+            sw: LngLat { lng: w, lat: s },
+            ne: LngLat { lng: e, lat: n },
+        }
+    }
+
+    fn clean(bounds: LngLatBounds, type_: CleanType) -> Clean {
+        Clean {
+            bounds,
+            type_,
+            trkpt: true,
+            wpt: true,
+        }
+    }
+
+    fn count(fx: &Fixture, id: FileId) -> usize {
+        fx.files
+            .get(&id)
+            .into_iter()
+            .flat_map(|file| &file.trk)
+            .flat_map(|trk| &trk.trkseg)
+            .map(|seg| seg.len())
+            .sum()
+    }
+
+    #[test]
+    fn test_inside_everything_removes_all_trackpoints() {
+        let (mut fx, id) = loaded();
+        assert!(count(&fx, id) > 0);
+        clean(bounds(-180.0, -90.0, 180.0, 90.0), CleanType::Inside)
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(count(&fx, id), 0);
+        // nothing is left of the file
+        assert!(!fx.files.contains_key(&id));
+        assert!(fx.order.0.is_empty());
+        assert_eq!(fx.selection, Selection::Empty);
+    }
+
+    #[test]
+    fn test_emptied_segments_and_tracks_are_removed() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].clone();
+        let seg = &before.trk[0].trkseg[0];
+        let pts: Vec<_> = seg.iter().map(|p| p.coordinates).collect();
+        let mut b = LngLatBounds::default();
+        pts.iter().for_each(|c| b.extend(*c));
+        clean(b, CleanType::Inside).apply(&mut fx.state()).unwrap();
+        let after = &fx.files[&id];
+        assert!(after.trk.iter().all(|t| !t.trkseg.is_empty()));
+        assert!(
+            after
+                .trk
+                .iter()
+                .flat_map(|t| &t.trkseg)
+                .all(|s| !s.is_empty())
+        );
+    }
+
+    #[test]
+    fn test_outside_everything_changes_nothing() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].clone();
+        let result =
+            clean(bounds(-180.0, -90.0, 180.0, 90.0), CleanType::Outside).apply(&mut fx.state());
+        assert!(matches!(result, Err(CommandError::NothingToDo)));
+        // the file was not even copied
+        assert!(std::rc::Rc::ptr_eq(&fx.files[&id], &before));
+    }
+
+    #[test]
+    fn test_partial_clean_only_removes_points_inside_and_bumps_revision() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].clone();
+        let first = before.trk[0].trkseg[0].iter().next().unwrap().coordinates;
+        let total = count(&fx, id);
+        // tiny rectangle around the first point
+        let b = bounds(
+            first.lng - 1e-9,
+            first.lat - 1e-9,
+            first.lng + 1e-9,
+            first.lat + 1e-9,
+        );
+        clean(b, CleanType::Inside).apply(&mut fx.state()).unwrap();
+        let removed = total - count(&fx, id);
+        assert!(removed >= 1);
+        let seg = &fx.files[&id].trk[0].trkseg[0];
+        assert_ne!(seg.rev_id, before.trk[0].trkseg[0].rev_id);
+        assert!(seg.iter().all(|pt| !b_contains(&b, pt.coordinates)));
+    }
+
+    fn b_contains(b: &LngLatBounds, c: LngLat) -> bool {
+        c.lng >= b.sw.lng && c.lng <= b.ne.lng && c.lat >= b.sw.lat && c.lat <= b.ne.lat
+    }
+
+    #[test]
+    fn test_waypoints_flag_and_selection() {
+        let (mut fx, id) = loaded();
+        let mut file = (*fx.files[&id]).clone();
+        file.wpt = Waypoints::new([WaypointChunk {
+            wpt: vec![Waypoint::default(), Waypoint::default()],
+            ..Default::default()
+        }]);
+        let ids: Vec<_> = file.wpt.iter().map(|w| w.id).collect();
+        fx.files.insert(id, std::rc::Rc::new(file));
+        let everywhere = bounds(-180.0, -90.0, 180.0, 90.0);
+        let wpt_count = |fx: &Fixture| fx.files.get(&id).map_or(0, |f| f.wpt.len());
+
+        // trackpoints only: waypoints are kept
+        Clean {
+            wpt: false,
+            ..clean(everywhere, CleanType::Inside)
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        assert_eq!(wpt_count(&fx), 2);
+
+        // one selected waypoint
+        fx.selection = Selection::Waypoint {
+            file_id: id,
+            wpt_ids: HashSet::from([ids[0]]),
+        };
+        clean(everywhere, CleanType::Inside)
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(wpt_count(&fx), 1);
+
+        // whole file
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        clean(everywhere, CleanType::Inside)
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(wpt_count(&fx), 0);
+    }
+}
@@ -0,0 +1,335 @@
+use std::{
+    collections::{HashMap, HashSet},
+    rc::Rc,
+};
+
+use crate::{
+    Apply, CommandError, File, FileId, SegmentLocation, Selection, State, TrackSegment,
+    TrackSegmentId,
+};
+
+/// Keeps the trackpoints `start` to `end` (both included) of the selection, which are counted
+/// over its segments one after the other (as in the `RoutingBuffer`), and removes the others.
+///
+/// The segments that have no trackpoint left are removed. So are the tracks that have no segment
+/// left, if tracks or files are selected (not if only segments are), and the files that have no
+/// trackpoint left, if files are selected. A range that goes past the last trackpoint stops at it.
+#[derive(Debug)]
+pub struct Crop {
+    pub start: u32,
+    pub end: u32,
+}
+
+/// What happens to a selected segment.
+struct Plan {
+    location: SegmentLocation,
+    /// The trackpoints that are kept, `None` if the segment goes away.
+    keep: Option<(usize, usize)>,
+    len: usize,
+}
+
+impl Apply for Crop {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let (start, end) = (self.start as usize, self.end as usize);
+        if start > end {
+            return Err(CommandError::InvalidData(
+                "invalid trackpoints range".into(),
+            ));
+        }
+
+        let mut offset = 0;
+        let plans: Vec<Plan> = state
+            .selection
+            .segment_locations(state.files, &state.order.0)
+            .into_iter()
+            .map(|location| {
+                let len =
+                    state.files[&location.file_id].trk[location.trk].trkseg[location.seg].len();
+                let keep = (len > 0 && start < offset + len && end >= offset)
+                    .then(|| (start.saturating_sub(offset), (end - offset).min(len - 1)));
+                offset += len;
+                Plan {
+                    location,
+                    keep,
+                    len,
+                }
+            })
+            .collect();
+        if plans
+            .iter()
+            .all(|plan| plan.keep == Some((0, plan.len.saturating_sub(1))))
+        {
+            // everything is kept as it is, or there is nothing
+            return Err(CommandError::NothingToDo);
+        }
+
+        // the files and tracks to prune, the segments to remove
+        let (prune_tracks, prune_files) = match &*state.selection {
+            Selection::File { .. } => (true, true),
+            Selection::Track { .. } => (true, false),
+            _ => (false, false),
+        };
+        let mut files: HashMap<FileId, File> = HashMap::new();
+        let mut removed: HashSet<TrackSegmentId> = HashSet::new();
+        let mut had_points: HashSet<FileId> = HashSet::new();
+        for plan in &plans {
+            let SegmentLocation { file_id, trk, seg } = plan.location;
+            let file = files
+                .entry(file_id)
+                .or_insert_with(|| (*state.files[&file_id]).clone());
+            if plan.len > 0 {
+                had_points.insert(file_id);
+            }
+            let segment = &mut file.trk[trk].trkseg[seg];
+            match plan.keep {
+                None => {
+                    removed.insert(segment.id);
+                }
+                Some((from, to)) => crop_segment(segment, from, to),
+            }
+        }
+
+        let mut gone: Vec<FileId> = vec![];
+        for (file_id, file) in files.iter_mut() {
+            // the tracks that lost segments
+            let touched: Vec<bool> = file
+                .trk
+                .iter_mut()
+                .map(|track| {
+                    let before = track.trkseg.len();
+                    track
+                        .trkseg
+                        .retain(|segment| !removed.contains(&segment.id));
+                    before != track.trkseg.len()
+                })
+                .collect();
+            if prune_tracks {
+                let mut touched = touched.into_iter();
+                file.trk
+                    .retain(|track| !(touched.next().unwrap() && track.trkseg.is_empty()));
+            }
+            if prune_files && file.trk.is_empty() && had_points.contains(file_id) {
+                gone.push(*file_id);
+            }
+        }
+
+        for (file_id, file) in files {
+            if gone.contains(&file_id) {
+                state.files.remove(&file_id);
+                state.order.0.retain(|id| *id != file_id);
+            } else {
+                state.files.insert(file_id, Rc::new(file));
+            }
+        }
+        Ok(())
+    }
+}
+
+/// Keeps the trackpoints `from` to `to` of a segment, which are in it. Only the chunks at the ends
+/// are changed.
+fn crop_segment(segment: &mut TrackSegment, from: usize, to: usize) {
+    let len = segment.len();
+    if from == 0 && to + 1 >= len {
+        return;
+    }
+    segment.splice(to + 1, len, vec![]);
+    segment.splice(0, from, vec![]);
+    segment.rev_id = Default::default();
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{Load, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded(path: &str) -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read(path).unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        (fx, id)
+    }
+
+    fn crop(start: u32, end: u32) -> Crop {
+        Crop { start, end }
+    }
+
+    /// The longitudes of the trackpoints of a file, one list per segment.
+    fn paths(file: &File) -> Vec<Vec<f64>> {
+        file.trk
+            .iter()
+            .flat_map(|track| &track.trkseg)
+            .map(|segment| segment.iter().map(|p| p.coordinates.lng).collect())
+            .collect()
+    }
+
+    #[test]
+    fn test_crop_a_file_keeps_the_range_over_its_segments() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let before = paths(&fx.files[&id]);
+        let flat: Vec<f64> = before.iter().flatten().copied().collect();
+        let (start, end) = (2, flat.len() - 3);
+
+        crop(start as u32, end as u32)
+            .apply(&mut fx.state())
+            .unwrap();
+
+        let after: Vec<f64> = paths(&fx.files[&id]).iter().flatten().copied().collect();
+        assert_eq!(after, flat[start..=end]);
+        // the ends of the segments that are left are anchors
+        for track in &fx.files[&id].trk {
+            for segment in &track.trkseg {
+                assert!(!segment.is_empty());
+                assert_eq!(segment[0].anchor, Some(0));
+                assert_eq!(segment[segment.len() - 1].anchor, Some(0));
+            }
+        }
+    }
+
+    #[test]
+    fn test_what_is_outside_goes_away() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let file = fx.files[&id].clone();
+        let lens: Vec<Vec<usize>> = file
+            .trk
+            .iter()
+            .map(|t| t.trkseg.iter().map(|segment| segment.len()).collect())
+            .collect();
+        assert!(lens.len() >= 2);
+        // from the start of the last track to the end
+        let before_last: usize = lens[..lens.len() - 1].iter().flatten().sum();
+        crop(before_last as u32, u32::MAX)
+            .apply(&mut fx.state())
+            .unwrap();
+
+        let after = &fx.files[&id];
+        // the other tracks are gone, the last one is whole
+        assert_eq!(after.trk.len(), 1);
+        assert_eq!(after.trk[0].id, file.trk.last().unwrap().id);
+        assert_eq!(
+            after.trk[0]
+                .trkseg
+                .iter()
+                .map(|segment| segment.len())
+                .collect::<Vec<_>>(),
+            *lens.last().unwrap()
+        );
+        // the selection followed
+        assert!(matches!(&fx.selection, Selection::File { .. }));
+    }
+
+    #[test]
+    fn test_crop_inside_a_segment_changes_it_only() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let file = fx.files[&id].clone();
+        let trk = &file.trk[0];
+        assert!(trk.trkseg.len() >= 2);
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: trk.id,
+            trkseg_ids: HashSet::from([trk.trkseg[1].id]),
+        };
+        let len = trk.trkseg[1].len();
+        assert!(len > 4);
+        crop(1, len as u32 - 2).apply(&mut fx.state()).unwrap();
+
+        let after = &fx.files[&id].trk[0];
+        assert_eq!(after.trkseg[1].len(), len - 2);
+        assert_ne!(after.trkseg[1].rev_id, trk.trkseg[1].rev_id);
+        // the other segments are not in the selection, whatever the range
+        assert_eq!(after.trkseg[0].rev_id, trk.trkseg[0].rev_id);
+        assert_eq!(fx.files[&id].trk.len(), file.trk.len());
+    }
+
+    #[test]
+    fn test_segments_out_of_the_range_are_removed_but_not_their_track() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let trk = fx.files[&id].trk[0].clone();
+        assert!(trk.trkseg.len() >= 2);
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: trk.id,
+            trkseg_ids: trk.trkseg.iter().map(|s| s.id).collect(),
+        };
+        // only the first segment, entirely
+        let first = trk.trkseg[0].len();
+        crop(0, first as u32 - 1).apply(&mut fx.state()).unwrap();
+        let after = &fx.files[&id].trk[0];
+        assert_eq!(after.trkseg.len(), 1);
+        assert_eq!(after.trkseg[0].id, trk.trkseg[0].id);
+
+        // nothing at all: the segments go, the track stays
+        crop(100_000, 100_001).apply(&mut fx.state()).unwrap();
+        assert!(fx.files[&id].trk[0].trkseg.is_empty());
+    }
+
+    #[test]
+    fn test_files_out_of_the_range_are_deleted() {
+        let (mut fx, first) = loaded("data/simple.gpx");
+        let data = std::fs::read("data/with_time.gpx").unwrap();
+        Load {
+            data: &data,
+            name: "second",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let second = fx.order.0[1];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([first, second]),
+        };
+        let first_len: usize = fx.files[&first]
+            .trk
+            .iter()
+            .flat_map(|t| &t.trkseg)
+            .map(|segment| segment.len())
+            .sum();
+
+        crop(first_len as u32 + 1, u32::MAX)
+            .apply(&mut fx.state())
+            .unwrap();
+        assert!(!fx.files.contains_key(&first));
+        assert_eq!(fx.order.0, [second]);
+        let kept: usize = fx.files[&second]
+            .trk
+            .iter()
+            .flat_map(|t| &t.trkseg)
+            .map(|segment| segment.len())
+            .sum();
+        assert!(kept > 0);
+    }
+
+    #[test]
+    fn test_nothing_to_do_or_invalid() {
+        let (mut fx, id) = loaded("data/simple.gpx");
+        let before = fx.files[&id].clone();
+        // the whole selection
+        assert_eq!(
+            crop(0, u32::MAX).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        assert!(matches!(
+            crop(5, 2).apply(&mut fx.state()),
+            Err(CommandError::InvalidData(_))
+        ));
+        fx.selection = Selection::Empty;
+        assert_eq!(
+            crop(0, 3).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        fx.selection = Selection::Waypoints { file_id: id };
+        assert_eq!(
+            crop(0, 3).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+    }
+}
@@ -0,0 +1,162 @@
+use crate::{Apply, CommandError, FileId, State, WaypointId, set_waypoint_fields, update_waypoint};
+
+/// Changes a waypoint of a file, whatever is selected (what the form of the waypoint tool does):
+/// its name, description, icon, link, position and elevation. The strings that are empty remove
+/// the field.
+#[derive(Debug)]
+pub struct EditWaypoint<'a> {
+    pub file_id: FileId,
+    pub waypoint_id: WaypointId,
+    pub lng: f64,
+    pub lat: f64,
+    pub ele: f64,
+    pub name: &'a str,
+    pub desc: &'a str,
+    pub icon: &'a str,
+    pub link: &'a str,
+}
+
+impl Apply for EditWaypoint<'_> {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        update_waypoint(state, self.file_id, self.waypoint_id, |wpt| {
+            set_waypoint_fields(
+                wpt,
+                (self.lng, self.lat, self.ele),
+                self.name,
+                self.desc,
+                self.icon,
+                self.link,
+            )
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::{
+        File, Link, Waypoint, WaypointChunk, engine::command::fixture::Fixture, waypoint_ids,
+    };
+
+    use super::*;
+
+    #[test]
+    fn test_edit_the_given_waypoint() {
+        let mut fx = Fixture::default();
+        let mut file = File::default();
+        file.wpt.push(WaypointChunk {
+            wpt: vec![
+                Waypoint {
+                    name: Some("old".into()),
+                    desc: Some("old description".into()),
+                    cmt: Some("old comment".into()),
+                    sym: Some("Flag".into()),
+                    links: vec![
+                        Link {
+                            href: "https://old".into(),
+                            text: None,
+                        },
+                        Link {
+                            href: "https://second".into(),
+                            text: Some("second".into()),
+                        },
+                    ],
+                    ..Default::default()
+                },
+                Waypoint {
+                    name: Some("other".into()),
+                    ..Default::default()
+                },
+            ],
+            ..Default::default()
+        });
+        let id = file.id;
+        let ids: Vec<_> = waypoint_ids(&file).collect();
+        fx.files.insert(id, Rc::new(file));
+
+        EditWaypoint {
+            file_id: id,
+            waypoint_id: ids[0],
+            lng: 4.5,
+            lat: 50.5,
+            ele: 12.0,
+            name: "new",
+            desc: "new description",
+            icon: "Summit",
+            link: "",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        let wpts: Vec<_> = fx.files[&id].wpt.iter().collect();
+        let edited = wpts[0];
+        assert_eq!(edited.id, ids[0]);
+        assert_eq!(edited.name.as_deref(), Some("new"));
+        assert_eq!(edited.desc.as_deref(), Some("new description"));
+        assert_eq!(edited.cmt.as_deref(), Some("new description"));
+        assert_eq!(edited.sym.as_deref(), Some("Summit"));
+        // an empty link removes the first one, the others are not the form's business
+        assert_eq!(edited.links.len(), 1);
+        assert_eq!(edited.links[0].href, "https://second");
+        assert_eq!(
+            (edited.coordinates.lng, edited.coordinates.lat, edited.ele),
+            (4.5, 50.5, 12.0)
+        );
+        // the other waypoint is as it was
+        assert_eq!(wpts[1].name.as_deref(), Some("other"));
+    }
+
+    #[test]
+    fn test_the_link_of_the_form_is_the_first_one() {
+        let mut fx = Fixture::default();
+        let mut file = File::default();
+        file.wpt.push(WaypointChunk {
+            wpt: vec![Waypoint {
+                links: vec![
+                    Link {
+                        href: "https://first".into(),
+                        text: Some("first".into()),
+                    },
+                    Link {
+                        href: "https://second".into(),
+                        text: None,
+                    },
+                ],
+                ..Default::default()
+            }],
+            ..Default::default()
+        });
+        let (id, wpt_id) = (file.id, waypoint_ids(&file).next().unwrap());
+        fx.files.insert(id, Rc::new(file));
+        let edit = |fx: &mut Fixture, link: &str| {
+            EditWaypoint {
+                file_id: id,
+                waypoint_id: wpt_id,
+                lng: 0.0,
+                lat: 0.0,
+                ele: 0.0,
+                name: "",
+                desc: "",
+                icon: "",
+                link,
+            }
+            .apply(&mut fx.state())
+            .unwrap();
+            fx.files[&id].wpt.iter().next().unwrap().links.clone()
+        };
+
+        // the same link keeps its text
+        let links = edit(&mut fx, "https://first");
+        assert_eq!(links.len(), 2);
+        assert_eq!(links[0].text.as_deref(), Some("first"));
+        // another one replaces the first, and the text that described the old one
+        let links = edit(&mut fx, "https://other");
+        assert_eq!(links.len(), 2);
+        assert_eq!(
+            (links[0].href.as_str(), links[0].text.clone()),
+            ("https://other", None)
+        );
+        assert_eq!(links[1].href, "https://second");
+    }
+}
@@ -0,0 +1,133 @@
+use crate::{Apply, CommandError, State, update_segments};
+
+/// Sets the elevation of the trackpoints of the selected segments (the ones of the statistics of
+/// the selection, in the same order): `ele` has one elevation per trackpoint.
+#[derive(Debug)]
+pub struct Elevation<'a> {
+    pub ele: &'a [f64],
+}
+
+impl Apply for Elevation<'_> {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let locations = state
+            .selection
+            .segment_locations(state.files, &state.order.0);
+        let count: usize = locations
+            .iter()
+            .map(|location| {
+                state.files[&location.file_id].trk[location.trk].trkseg[location.seg].len()
+            })
+            .sum();
+        if count == 0 {
+            return Err(CommandError::NothingToDo);
+        }
+        if count != self.ele.len() {
+            return Err(CommandError::InvalidData(format!(
+                "{} elevations for {count} trackpoints",
+                self.ele.len()
+            )));
+        }
+
+        let mut ele = self.ele.iter().copied();
+        update_segments(state, &locations, |_, segment| {
+            segment.update_all(|_, pt| pt.ele = ele.next().unwrap_or(pt.ele));
+        });
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{FileId, Load, Selection, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded(path: &str) -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read(path).unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        (fx, id)
+    }
+
+    fn trackpoint_elevations(fx: &Fixture, id: FileId) -> Vec<f64> {
+        fx.files[&id]
+            .trk
+            .iter()
+            .flat_map(|trk| {
+                trk.trkseg
+                    .iter()
+                    .flat_map(|seg| seg.iter().map(|pt| pt.ele))
+            })
+            .collect()
+    }
+
+    #[test]
+    fn test_a_file_gets_elevation_on_all_its_trackpoints() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let count = trackpoint_elevations(&fx, id).len();
+        let ele: Vec<f64> = (0..count).map(|i| 100.0 + i as f64).collect();
+
+        Elevation { ele: &ele }.apply(&mut fx.state()).unwrap();
+
+        assert_eq!(trackpoint_elevations(&fx, id), ele);
+    }
+
+    #[test]
+    fn test_segments_only_touch_their_trackpoints() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let before = trackpoint_elevations(&fx, id);
+        let track = &fx.files[&id].trk[0];
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: track.id,
+            trkseg_ids: HashSet::from([track.trkseg[0].id]),
+        };
+        let rev_ids: Vec<_> = track.trkseg.iter().map(|seg| seg.rev_id).collect();
+        let len = track.trkseg[0].len();
+
+        Elevation {
+            ele: &vec![5.0; len],
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        let after = trackpoint_elevations(&fx, id);
+        assert_eq!(after[..len], vec![5.0; len]);
+        assert_eq!(after[len..], before[len..]);
+        let segments = &fx.files[&id].trk[0].trkseg;
+        assert_ne!(segments[0].rev_id, rev_ids[0]);
+        assert_eq!(segments[1].rev_id, rev_ids[1]);
+    }
+
+    #[test]
+    fn test_wrong_number_of_elevations() {
+        let (mut fx, id) = loaded("data/simple.gpx");
+        let before = trackpoint_elevations(&fx, id);
+        assert!(matches!(
+            Elevation { ele: &[1.0] }.apply(&mut fx.state()),
+            Err(CommandError::InvalidData(_))
+        ));
+        assert_eq!(trackpoint_elevations(&fx, id), before);
+    }
+
+    #[test]
+    fn test_nothing_selected() {
+        let (mut fx, _) = loaded("data/simple.gpx");
+        fx.selection = Selection::Empty;
+        assert!(matches!(
+            Elevation { ele: &[] }.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        ));
+    }
+}
@@ -0,0 +1,570 @@
+use std::{collections::HashSet, rc::Rc};
+
+use crate::{
+    Apply, CommandError, File, FileId, LngLat, LngLatBounds, Selection, State, Track, TrackId,
+    TrackSegment, Waypoint, Waypoints, copy_waypoint, crossarc_lnglat, distance,
+};
+
+/// Splits the selected elements that are made of several segments into elements that have one
+/// each:
+///
+/// - files: a file with several tracks becomes one file per track, in which the track is split
+///   into one track per segment. A file with a single track becomes one file per segment. The new
+///   files are in the place of the file, which goes, and are selected. They are named after the
+///   track, or the file, and numbered. The waypoints go to the files that have the segments
+///   closest to them (to the first file if the file has no trackpoint).
+/// - tracks: each selected track is replaced by one track per segment, which are selected. They
+///   are named after the track and numbered.
+///
+/// What has a single segment is left as it is. There is nothing to do if nothing was changed.
+#[derive(Debug)]
+pub struct Extract;
+
+impl Apply for Extract {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let selection = state.selection.clone();
+        match &selection {
+            Selection::File { file_ids } => extract_files(state, file_ids),
+            Selection::Track { file_id, trk_ids } => extract_tracks(state, *file_id, trk_ids),
+            _ => Err(CommandError::NothingToDo),
+        }
+    }
+}
+
+fn extract_files(state: &mut State, file_ids: &HashSet<FileId>) -> Result<(), CommandError> {
+    // the files that have something to extract, with the files that come out of them
+    let mut extracted: Vec<(FileId, Vec<File>)> = vec![];
+    for id in state.order.0.iter().filter(|id| file_ids.contains(id)) {
+        let file = &state.files[id];
+        let segments: usize = file.trk.iter().map(|track| track.trkseg.len()).sum();
+        if segments > 1 {
+            extracted.push((*id, extract_file(file)));
+        }
+    }
+    if extracted.is_empty() {
+        return Err(CommandError::NothingToDo);
+    }
+
+    let mut order = vec![];
+    for id in state.order.0.iter() {
+        match extracted.iter().find(|(original, _)| original == id) {
+            Some((_, files)) => order.extend(files.iter().map(|file| file.id)),
+            None => order.push(*id),
+        }
+    }
+    let mut selected: HashSet<FileId> = file_ids.clone();
+    for (original, files) in extracted {
+        state.files.remove(&original);
+        selected.remove(&original);
+        for file in files {
+            selected.insert(file.id);
+            state.files.insert(file.id, Rc::new(file));
+        }
+    }
+    state.order.0 = order;
+    *state.selection = Selection::File { file_ids: selected };
+    Ok(())
+}
+
+/// The files that a file with several segments becomes.
+fn extract_file(file: &File) -> Vec<File> {
+    // for each new file: its tracks and its name, and the segments that go with it
+    struct Part {
+        tracks: Vec<Track>,
+        name: String,
+    }
+    let (parts, owner): (Vec<Part>, Vec<usize>) = if file.trk.len() > 1 {
+        // one file per track, the segments of a track follow it
+        let parts = file
+            .trk
+            .iter()
+            .enumerate()
+            .map(|(i, track)| Part {
+                tracks: split_track(track),
+                name: track
+                    .info
+                    .name
+                    .clone()
+                    .unwrap_or_else(|| format!("{} ({})", file.info.name, i + 1)),
+            })
+            .collect();
+        let owner = file
+            .trk
+            .iter()
+            .enumerate()
+            .flat_map(|(i, track)| track.trkseg.iter().map(move |_| i))
+            .collect();
+        (parts, owner)
+    } else {
+        // one file per segment
+        let track = &file.trk[0];
+        let base = track
+            .info
+            .name
+            .clone()
+            .unwrap_or_else(|| file.info.name.clone());
+        let parts = track
+            .trkseg
+            .iter()
+            .enumerate()
+            .map(|(i, segment)| Part {
+                tracks: vec![Track {
+                    id: if i == 0 { track.id } else { Default::default() },
+                    trkseg: vec![segment.clone()],
+                    ..track.clone()
+                }],
+                name: format!("{base} ({})", i + 1),
+            })
+            .collect();
+        let owner = (0..track.trkseg.len()).collect();
+        (parts, owner)
+    };
+
+    // the waypoints go with the segments that are the closest to them
+    let segments: Vec<&TrackSegment> = file.trk.iter().flat_map(|track| &track.trkseg).collect();
+    let mut waypoints: Vec<Vec<Waypoint>> = vec![vec![]; parts.len()];
+    for waypoint in file.wpt.iter() {
+        let mut owners: Vec<usize> = closest_segments(&segments, waypoint.coordinates)
+            .into_iter()
+            .map(|segment| owner[segment])
+            .collect();
+        owners.sort_unstable();
+        owners.dedup();
+        if owners.is_empty() {
+            owners.push(0);
+        }
+        for (n, part) in owners.into_iter().enumerate() {
+            // a waypoint that goes to several files has a new id in all but the first
+            waypoints[part].push(if n == 0 {
+                waypoint.clone()
+            } else {
+                copy_waypoint(waypoint)
+            });
+        }
+    }
+
+    parts
+        .into_iter()
+        .zip(waypoints)
+        .map(|(part, waypoints)| {
+            let mut extracted = File {
+                id: Default::default(),
+                trk: part.tracks,
+                wpt: Waypoints::default(),
+                ..file.clone()
+            };
+            extracted.info.name = part.name;
+            extracted.wpt.insert_at(0, waypoints);
+            extracted
+        })
+        .collect()
+}
+
+fn extract_tracks(
+    state: &mut State,
+    file_id: FileId,
+    trk_ids: &HashSet<TrackId>,
+) -> Result<(), CommandError> {
+    let file = state.files.get(&file_id).ok_or(CommandError::NothingToDo)?;
+    let mut changed = false;
+    let mut tracks = vec![];
+    let mut selected: HashSet<TrackId> = trk_ids.clone();
+    for track in &file.trk {
+        if trk_ids.contains(&track.id) && track.trkseg.len() > 1 {
+            changed = true;
+            selected.remove(&track.id);
+            let pieces = split_track(track);
+            selected.extend(pieces.iter().map(|piece| piece.id));
+            tracks.extend(pieces);
+        } else {
+            tracks.push(track.clone());
+        }
+    }
+    if !changed {
+        return Err(CommandError::NothingToDo);
+    }
+    let mut file = (**file).clone();
+    file.trk = tracks;
+    state.files.insert(file_id, Rc::new(file));
+    *state.selection = Selection::Track {
+        file_id,
+        trk_ids: selected,
+    };
+    Ok(())
+}
+
+/// The tracks that a track becomes: one per segment, the first one with the id of the track. The
+/// others have the same info, with the name of the track and the number of the segment, if it has
+/// a name. A track with at most one segment stays as it is.
+fn split_track(track: &Track) -> Vec<Track> {
+    if track.trkseg.len() <= 1 {
+        return vec![track.clone()];
+    }
+    track
+        .trkseg
+        .iter()
+        .enumerate()
+        .map(|(i, segment)| {
+            let mut piece = Track {
+                id: if i == 0 { track.id } else { Default::default() },
+                trkseg: vec![segment.clone()],
+                ..track.clone()
+            };
+            piece.info.name = track
+                .info
+                .name
+                .as_ref()
+                .map(|name| format!("{name} ({})", i + 1));
+            piece
+        })
+        .collect()
+}
+
+/// The indices of the segments that have the trackpoint that is the closest to `point`, which are
+/// several when the closest trackpoints are as close.
+///
+/// The segments are looked at from the closest to the farthest bounds, which is how they are
+/// left out: the ones whose bounds are farther than the closest trackpoint found.
+fn closest_segments(segments: &[&TrackSegment], point: LngLat) -> Vec<usize> {
+    let mut by_bounds: Vec<(f64, usize)> = segments
+        .iter()
+        .enumerate()
+        .filter(|(_, segment)| !segment.is_empty())
+        .map(|(i, segment)| {
+            let mut bounds = LngLatBounds::default();
+            segment
+                .iter()
+                .for_each(|trkpt| bounds.extend(trkpt.coordinates));
+            (distance_to_bounds(&bounds, point), i)
+        })
+        .collect();
+    by_bounds.sort_by(|a, b| a.0.total_cmp(&b.0));
+
+    let mut closest = f64::MAX;
+    let mut indices: Vec<usize> = vec![];
+    for (bounds_distance, i) in by_bounds {
+        if bounds_distance > closest {
+            break;
+        }
+        for trkpt in segments[i].iter() {
+            // in meters, like the distances to the bounds
+            let d = distance(trkpt.coordinates, point) * 1000.0;
+            if d < closest {
+                closest = d;
+                indices = vec![i];
+            } else if d == closest {
+                indices.push(i);
+            }
+        }
+    }
+    indices.sort_unstable();
+    indices.dedup();
+    indices
+}
+
+/// 0 inside the bounds, else the distance in meters to the closest side.
+fn distance_to_bounds(bounds: &LngLatBounds, point: LngLat) -> f64 {
+    let (sw, ne) = (bounds.sw, bounds.ne);
+    if (sw.lng..=ne.lng).contains(&point.lng) && (sw.lat..=ne.lat).contains(&point.lat) {
+        return 0.0;
+    }
+    let nw = LngLat {
+        lng: sw.lng,
+        lat: ne.lat,
+    };
+    let se = LngLat {
+        lng: ne.lng,
+        lat: sw.lat,
+    };
+    [(nw, ne), (ne, se), (se, sw), (sw, nw)]
+        .into_iter()
+        .map(|(a, b)| crossarc_lnglat(a, b, point))
+        .fold(f64::MAX, f64::min)
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{TrackInfo, Trackpoint, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    /// A segment of 5 trackpoints along the equator, from the longitude `from`.
+    fn segment(from: f64) -> TrackSegment {
+        let mut segment = TrackSegment::default();
+        let points = (0..5)
+            .map(|i| Trackpoint {
+                coordinates: LngLat {
+                    lng: from + i as f64 * 0.001,
+                    lat: 0.0,
+                },
+                ..Default::default()
+            })
+            .collect();
+        segment.splice(0, 0, points);
+        segment
+    }
+
+    fn track(name: Option<&str>, from: &[f64]) -> Track {
+        Track {
+            info: TrackInfo {
+                name: name.map(str::to_string),
+                ..Default::default()
+            },
+            trkseg: from.iter().map(|from| segment(*from)).collect(),
+            ..Default::default()
+        }
+    }
+
+    fn waypoint(name: &str, lng: f64) -> Waypoint {
+        Waypoint {
+            name: Some(name.into()),
+            coordinates: LngLat { lng, lat: 0.001 },
+            ..Default::default()
+        }
+    }
+
+    fn fixture(file: File) -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let id = file.id;
+        fx.files.insert(id, Rc::new(file));
+        fx.order.0.push(id);
+        fx.selection = Selection::File {
+            file_ids: [id].into(),
+        };
+        (fx, id)
+    }
+
+    fn file(name: &str, tracks: Vec<Track>, waypoints: Vec<Waypoint>) -> File {
+        let mut file = File {
+            trk: tracks,
+            ..Default::default()
+        };
+        file.info.name = name.into();
+        file.wpt.insert_at(0, waypoints);
+        file
+    }
+
+    fn names(fx: &Fixture) -> Vec<String> {
+        fx.order
+            .0
+            .iter()
+            .map(|id| fx.files[id].info.name.clone())
+            .collect()
+    }
+
+    #[test]
+    fn test_a_file_with_one_track_becomes_one_file_per_segment() {
+        let original = file(
+            "route",
+            vec![track(Some("climb"), &[0.0, 10.0, 20.0])],
+            // near the first segment, near the last one, and in between, closer to the middle one
+            vec![
+                waypoint("a", 0.002),
+                waypoint("c", 20.002),
+                waypoint("b", 10.0),
+            ],
+        );
+        let track_id = original.trk[0].id;
+        let segment_ids: Vec<_> = original.trk[0].trkseg.iter().map(|s| s.id).collect();
+        let (mut fx, id) = fixture(original);
+        let other = file("other", vec![track(None, &[50.0])], vec![]);
+        let other_id = other.id;
+        fx.files.insert(other_id, Rc::new(other));
+        fx.order.0.push(other_id);
+
+        Extract.apply(&mut fx.state()).unwrap();
+
+        // in the place of the file, in order, named after the track
+        assert!(!fx.files.contains_key(&id));
+        assert_eq!(names(&fx), ["climb (1)", "climb (2)", "climb (3)", "other"]);
+        assert_eq!(fx.order.0[3], other_id);
+        for (i, file_id) in fx.order.0[..3].iter().enumerate() {
+            let file = &fx.files[file_id];
+            assert_eq!(file.trk.len(), 1);
+            assert_eq!(file.trk[0].trkseg.len(), 1);
+            assert_eq!(file.trk[0].trkseg[0].id, segment_ids[i]);
+            assert_eq!(file.trk[0].info.name.as_deref(), Some("climb"));
+        }
+        assert_eq!(fx.files[&fx.order.0[0]].trk[0].id, track_id);
+        // the waypoints are with the closest segment
+        let waypoints = |i: usize| -> Vec<String> {
+            fx.files[&fx.order.0[i]]
+                .wpt
+                .iter()
+                .map(|w| w.name.clone().unwrap())
+                .collect()
+        };
+        assert_eq!(waypoints(0), ["a"]);
+        assert_eq!(waypoints(1), ["b"]);
+        assert_eq!(waypoints(2), ["c"]);
+        // the new files are selected, the other one is not
+        assert!(matches!(&fx.selection, Selection::File { file_ids }
+            if file_ids.len() == 3 && !file_ids.contains(&other_id)));
+    }
+
+    #[test]
+    fn test_a_file_with_several_tracks_becomes_one_file_per_track() {
+        let original = file(
+            "route",
+            vec![
+                track(Some("first"), &[0.0, 10.0]),
+                track(None, &[20.0]),
+                track(Some("third"), &[30.0, 40.0]),
+            ],
+            vec![],
+        );
+        let ids: Vec<_> = original.trk.iter().map(|t| t.id).collect();
+        let (mut fx, _) = fixture(original);
+        Extract.apply(&mut fx.state()).unwrap();
+
+        // named after the track, or the file
+        assert_eq!(names(&fx), ["first", "route (2)", "third"]);
+        let tracks = |i: usize| &fx.files[&fx.order.0[i]].trk;
+        // a track with several segments is split in as many tracks
+        assert_eq!(tracks(0).len(), 2);
+        assert_eq!(tracks(0)[0].info.name.as_deref(), Some("first (1)"));
+        assert_eq!(tracks(0)[1].info.name.as_deref(), Some("first (2)"));
+        assert_eq!(tracks(0)[0].id, ids[0]);
+        // and one that has a single segment is not renamed
+        assert_eq!(tracks(1).len(), 1);
+        assert_eq!(tracks(1)[0].id, ids[1]);
+        assert_eq!(tracks(1)[0].info.name, None);
+        assert_eq!(tracks(2).len(), 2);
+    }
+
+    #[test]
+    fn test_waypoints_with_closest_segments_that_tie_are_copied() {
+        // the segments share a trackpoint, where the waypoint is: it is as close to both
+        let a = segment(0.0);
+        let b = segment(a[4].coordinates.lng);
+        let shared = Waypoint {
+            name: Some("mid".into()),
+            coordinates: a[4].coordinates,
+            ..Default::default()
+        };
+        let original = file(
+            "f",
+            vec![Track {
+                trkseg: vec![a, b],
+                ..Default::default()
+            }],
+            vec![shared, waypoint("lost", 100.0)],
+        );
+        let (mut fx, _) = fixture(original);
+        Extract.apply(&mut fx.state()).unwrap();
+        let first = &fx.files[&fx.order.0[0]];
+        let second = &fx.files[&fx.order.0[1]];
+        // the tie goes to both, with different ids
+        let mid_in = |f: &File| {
+            f.wpt
+                .iter()
+                .find(|w| w.name.as_deref() == Some("mid"))
+                .map(|w| w.id)
+        };
+        assert!(mid_in(first).is_some() && mid_in(second).is_some());
+        assert_ne!(mid_in(first), mid_in(second));
+        // a far waypoint goes to its closest segment, which is the last one
+        assert!(second.wpt.iter().any(|w| w.name.as_deref() == Some("lost")));
+    }
+
+    #[test]
+    fn test_a_waypoint_of_a_file_without_trackpoints_is_kept() {
+        let mut empty = TrackSegment::default();
+        empty.rev_id = Default::default();
+        let original = file(
+            "f",
+            vec![Track {
+                trkseg: vec![empty.clone(), TrackSegment::default()],
+                ..Default::default()
+            }],
+            vec![waypoint("w", 1.0)],
+        );
+        let (mut fx, _) = fixture(original);
+        Extract.apply(&mut fx.state()).unwrap();
+        assert_eq!(fx.files[&fx.order.0[0]].wpt.len(), 1);
+        assert_eq!(fx.files[&fx.order.0[1]].wpt.len(), 0);
+    }
+
+    #[test]
+    fn test_extract_tracks_in_place() {
+        let original = file(
+            "route",
+            vec![
+                track(Some("a"), &[0.0]),
+                track(Some("b"), &[10.0, 20.0, 30.0]),
+                track(None, &[40.0, 50.0]),
+            ],
+            vec![],
+        );
+        let ids: Vec<_> = original.trk.iter().map(|t| t.id).collect();
+        let (mut fx, id) = fixture(original);
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: [ids[1], ids[2]].into(),
+        };
+
+        Extract.apply(&mut fx.state()).unwrap();
+
+        let file = &fx.files[&id];
+        let names: Vec<_> = file.trk.iter().map(|t| t.info.name.clone()).collect();
+        assert_eq!(
+            names,
+            [
+                Some("a".into()),
+                Some("b (1)".into()),
+                Some("b (2)".into()),
+                Some("b (3)".into()),
+                None,
+                None
+            ]
+        );
+        assert_eq!(file.trk.len(), 6);
+        assert!(file.trk.iter().all(|t| t.trkseg.len() == 1));
+        assert_eq!(file.trk[0].id, ids[0]);
+        assert_eq!(file.trk[1].id, ids[1]);
+        // the new tracks are selected
+        let Selection::Track { trk_ids, .. } = &fx.selection else {
+            panic!("tracks are selected");
+        };
+        assert_eq!(trk_ids.len(), 5);
+        assert!(trk_ids.contains(&ids[1]) && !trk_ids.contains(&ids[0]));
+    }
+
+    #[test]
+    fn test_nothing_to_extract() {
+        // a single segment
+        let original = file("f", vec![track(Some("t"), &[0.0])], vec![]);
+        let track_id = original.trk[0].id;
+        let segment_id = original.trk[0].trkseg[0].id;
+        let (mut fx, id) = fixture(original);
+        let before = fx.files[&id].clone();
+        assert_eq!(
+            Extract.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: [track_id].into(),
+        };
+        assert_eq!(
+            Extract.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        for selection in [
+            Selection::Empty,
+            Selection::Waypoints { file_id: id },
+            Selection::TrackSegment {
+                file_id: id,
+                trk_id: track_id,
+                trkseg_ids: [segment_id].into(),
+            },
+        ] {
+            fx.selection = selection;
+            assert_eq!(
+                Extract.apply(&mut fx.state()),
+                Err(CommandError::NothingToDo)
+            );
+        }
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+    }
+}
@@ -0,0 +1,230 @@
+use std::rc::Rc;
+
+use crate::{Apply, CommandError, LngLat, SegmentLocation, State, Trackpoint, distance, projected};
+
+/// Under this distance (in meters) to a trackpoint, that trackpoint becomes the anchor instead of
+/// a new one being inserted next to it.
+const SNAP_DISTANCE: f64 = 1.0;
+
+/// Makes an anchor of the routing tool, shown at every zoom level, of the point of the selected
+/// segments that is the closest to the given coordinates. That is the trackpoint itself if the
+/// coordinates are on one, otherwise a new trackpoint is inserted on the path, at the position
+/// of the coordinates projected on it, with an elevation and a time in between the ones of its
+/// neighbours.
+#[derive(Debug)]
+pub struct InsertAnchor {
+    pub lng: f64,
+    pub lat: f64,
+}
+
+/// Where the anchor goes: between the trackpoints `before` and `before + 1` of a segment, at
+/// `ratio` of the distance from the first one, which is `projection`. `distance` is the one from
+/// there to the coordinates, in meters.
+struct Position {
+    location: SegmentLocation,
+    before: usize,
+    ratio: f64,
+    projection: LngLat,
+    distance: f64,
+}
+
+impl Apply for InsertAnchor {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let target = LngLat {
+            lng: self.lng,
+            lat: self.lat,
+        };
+        let mut closest: Option<Position> = None;
+        for location in state
+            .selection
+            .segment_locations(state.files, &state.order.0)
+        {
+            let segment = &state.files[&location.file_id].trk[location.trk].trkseg[location.seg];
+            let mut points = segment.iter();
+            let Some(mut previous) = points.next() else {
+                continue;
+            };
+            if segment.len() == 1 {
+                // a single point is its own path
+                let d = distance(previous.coordinates, target) * 1000.0;
+                if closest.as_ref().is_none_or(|c| d < c.distance) {
+                    closest = Some(Position {
+                        location,
+                        before: 0,
+                        ratio: 0.0,
+                        projection: previous.coordinates,
+                        distance: d,
+                    });
+                }
+            }
+            for (i, point) in points.enumerate() {
+                let projection = projected(previous.coordinates, point.coordinates, target);
+                let d = distance(projection, target) * 1000.0;
+                if closest.as_ref().is_none_or(|c| d < c.distance) {
+                    let length = distance(previous.coordinates, point.coordinates);
+                    let ratio = if length > 0.0 {
+                        distance(previous.coordinates, projection) / length
+                    } else {
+                        0.0
+                    };
+                    closest = Some(Position {
+                        location,
+                        before: i,
+                        ratio,
+                        projection,
+                        distance: d,
+                    });
+                }
+                previous = point;
+            }
+        }
+        let closest = closest.ok_or(CommandError::NothingToDo)?;
+
+        let mut file = (*state.files[&closest.location.file_id]).clone();
+        let segment = &mut file.trk[closest.location.trk].trkseg[closest.location.seg];
+        let before = closest.before;
+        // on a trackpoint already, if it is closer than `SNAP_DISTANCE`
+        let snapped = if segment.len() == 1 {
+            Some(0)
+        } else {
+            let (a, b) = (&segment[before], &segment[before + 1]);
+            let meters = 1000.0 * distance(a.coordinates, b.coordinates);
+            if closest.ratio * meters < SNAP_DISTANCE {
+                Some(before)
+            } else if (1.0 - closest.ratio) * meters < SNAP_DISTANCE {
+                Some(before + 1)
+            } else {
+                None
+            }
+        };
+        if let Some(index) = snapped {
+            if segment[index].anchor == Some(0) {
+                return Err(CommandError::NothingToDo);
+            }
+            segment.set_anchor(index, 0);
+        } else {
+            let (a, b) = (&segment[before], &segment[before + 1]);
+            let ratio = closest.ratio;
+            let mut point: Trackpoint = a.clone();
+            point.coordinates = closest.projection;
+            point.ele = (1.0 - ratio) * a.ele + ratio * b.ele;
+            point.time = a
+                .time
+                .zip(b.time)
+                .map(|(a, b)| ((1.0 - ratio) * a as f64 + ratio * b as f64) as i64);
+            point.anchor = Some(0);
+            segment.splice(before + 1, before + 1, vec![point]);
+        }
+        segment.rev_id = Default::default();
+        state.files.insert(closest.location.file_id, Rc::new(file));
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{FileId, Load, Selection, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded(path: &str) -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read(path).unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        (fx, id)
+    }
+
+    fn first_segment(fx: &Fixture, id: FileId) -> crate::TrackSegment {
+        fx.files[&id].trk[0].trkseg[0].clone()
+    }
+
+    #[test]
+    fn test_a_point_is_inserted_between_its_neighbours() {
+        let (mut fx, id) = loaded("data/with_time.gpx");
+        let before = first_segment(&fx, id);
+        let (a, b) = (&before[10], &before[11]);
+        // a bit off the line, closer to the middle of the two points
+        let target = LngLat {
+            lng: (a.coordinates.lng + b.coordinates.lng) / 2.0 + 1e-6,
+            lat: (a.coordinates.lat + b.coordinates.lat) / 2.0 + 1e-6,
+        };
+        InsertAnchor {
+            lng: target.lng,
+            lat: target.lat,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        let after = first_segment(&fx, id);
+        assert_eq!(after.len(), before.len() + 1);
+        assert_ne!(after.rev_id, before.rev_id);
+        let point = &after[11];
+        assert_eq!(point.anchor, Some(0));
+        assert_eq!(after[10].coordinates.lng, a.coordinates.lng);
+        assert_eq!(after[12].coordinates.lng, b.coordinates.lng);
+        // between its neighbours, with the interpolated elevation and time
+        let ratio = (point.time.unwrap() - a.time.unwrap()) as f64
+            / (b.time.unwrap() - a.time.unwrap()) as f64;
+        assert!((0.3..0.7).contains(&ratio), "{ratio}");
+        let expected = a.ele + ratio * (b.ele - a.ele);
+        assert!(
+            (point.ele - expected).abs() < 0.5,
+            "{} {expected}",
+            point.ele
+        );
+    }
+
+    #[test]
+    fn test_a_trackpoint_that_is_hit_becomes_the_anchor() {
+        let (mut fx, id) = loaded("data/with_time.gpx");
+        let before = first_segment(&fx, id);
+        assert_eq!(before[10].anchor.is_some(), before[10].anchor == Some(0));
+        let point = &before[10];
+        InsertAnchor {
+            lng: point.coordinates.lng,
+            lat: point.coordinates.lat,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let after = first_segment(&fx, id);
+        assert_eq!(after.len(), before.len());
+        let anchors = (0..after.len())
+            .filter(|i| after[*i].anchor == Some(0))
+            .count();
+        assert!(anchors >= 3, "{anchors}");
+        assert!(
+            after
+                .iter()
+                .zip(before.iter())
+                .all(|(a, b)| a.coordinates.lng == b.coordinates.lng)
+        );
+        // doing it again changes nothing
+        let again = InsertAnchor {
+            lng: point.coordinates.lng,
+            lat: point.coordinates.lat,
+        }
+        .apply(&mut fx.state());
+        assert!(again.is_ok() || again == Err(CommandError::NothingToDo));
+    }
+
+    #[test]
+    fn test_nothing_to_do_without_a_segment() {
+        let (mut fx, _) = loaded("data/with_time.gpx");
+        fx.selection = Selection::Empty;
+        assert_eq!(
+            InsertAnchor { lng: 1.0, lat: 1.0 }.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+}
@@ -0,0 +1,586 @@
+use std::{collections::HashSet, rc::Rc};
+
+use crate::{
+    Apply, CommandError, FileId, GlobalStatistics, Selection, State, Statistics, Track, TrackId,
+    TrackSegment, TrackSegmentId, Waypoint, Waypoints, replace_trackpoints,
+};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum MergeType {
+    /// The trackpoints of the elements are connected in a single segment.
+    Connect,
+    /// The elements are put together, in the first one, which keeps them as they are.
+    Group,
+}
+
+/// Merges the selected elements into the first of them:
+///
+/// - files: the other files are deleted. The tracks of all of them are in the first file, as
+///   they are with `Group`, or all connected in the first track with `Connect`. The waypoints of
+///   all of them are in the first file too, except the ones that are the same.
+/// - tracks of a file: the first track gets their segments, as they are with `Group`, or all
+///   connected in one segment with `Connect`. The other tracks are removed.
+/// - segments of a track: they are all connected in a segment at the position of the first one
+///   with `Connect`. With `Group` they are put one after the other, at that position.
+///
+/// The segment made by `Connect` goes on in time, if there are timestamps, at the moving speed
+/// of the selection, see [`replace_trackpoints`], which `remove_gaps` is given.
+///
+/// There is nothing to do when there is nothing to merge: a single file to group, a single track
+/// that has no more than one segment, a single segment...
+#[derive(Debug)]
+pub struct Merge {
+    pub type_: MergeType,
+    pub remove_gaps: bool,
+}
+
+impl Apply for Merge {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let selection = state.selection.clone();
+        match &selection {
+            Selection::File { file_ids } => self.merge_files(state, file_ids),
+            Selection::Track { file_id, trk_ids } => self.merge_tracks(state, *file_id, trk_ids),
+            Selection::TrackSegment {
+                file_id,
+                trk_id,
+                trkseg_ids,
+            } => self.merge_segments(state, *file_id, *trk_id, trkseg_ids),
+            Selection::Empty | Selection::Waypoints { .. } | Selection::Waypoint { .. } => {
+                Err(CommandError::NothingToDo)
+            }
+        }
+    }
+}
+
+impl Merge {
+    fn merge_files(
+        &self,
+        state: &mut State,
+        file_ids: &HashSet<FileId>,
+    ) -> Result<(), CommandError> {
+        // in the order of the files
+        let ordered: Vec<FileId> = state
+            .order
+            .0
+            .iter()
+            .filter(|id| file_ids.contains(id))
+            .chain(file_ids.iter().filter(|id| !state.order.0.contains(id)))
+            .filter(|id| state.files.contains_key(id))
+            .copied()
+            .collect();
+        let Some(&target_id) = ordered.first() else {
+            return Err(CommandError::NothingToDo);
+        };
+
+        let mut tracks: Vec<Track> = vec![];
+        let mut waypoints: Vec<Waypoint> = vec![];
+        for id in &ordered {
+            let file = &state.files[id];
+            tracks.extend(file.trk.iter().cloned());
+            for waypoint in file.wpt.iter() {
+                if !waypoints.iter().any(|kept| kept.same_content(waypoint)) {
+                    waypoints.push(waypoint.clone());
+                }
+            }
+        }
+        let segments: Vec<TrackSegment> = tracks
+            .iter()
+            .flat_map(|track| track.trkseg.iter().cloned())
+            .collect();
+
+        match self.type_ {
+            MergeType::Group if ordered.len() == 1 => return Err(CommandError::NothingToDo),
+            MergeType::Connect if ordered.len() == 1 && segments.len() <= 1 => {
+                return Err(CommandError::NothingToDo);
+            }
+            MergeType::Connect if !segments.is_empty() => {
+                // a single track, which is the first one, with the connected segment
+                let merged = connect(&segments, segments[0].id, self.remove_gaps);
+                let first = Track {
+                    trkseg: vec![merged],
+                    ..tracks[0].clone()
+                };
+                tracks = vec![first];
+            }
+            _ => {}
+        }
+
+        let mut target = (*state.files[&target_id]).clone();
+        target.trk = tracks;
+        target.wpt = Waypoints::default();
+        target.wpt.insert_at(0, waypoints);
+        for id in &ordered[1..] {
+            state.files.remove(id);
+        }
+        state.order.0.retain(|id| !ordered[1..].contains(id));
+        state.files.insert(target_id, Rc::new(target));
+        Ok(())
+    }
+
+    fn merge_tracks(
+        &self,
+        state: &mut State,
+        file_id: FileId,
+        trk_ids: &HashSet<TrackId>,
+    ) -> Result<(), CommandError> {
+        let file = state.files.get(&file_id).ok_or(CommandError::NothingToDo)?;
+        let selected: Vec<usize> = (0..file.trk.len())
+            .filter(|i| trk_ids.contains(&file.trk[*i].id))
+            .collect();
+        let Some(&first) = selected.first() else {
+            return Err(CommandError::NothingToDo);
+        };
+        let segments: Vec<TrackSegment> = selected
+            .iter()
+            .flat_map(|i| file.trk[*i].trkseg.iter().cloned())
+            .collect();
+        if selected.len() == 1 && (self.type_ == MergeType::Group || segments.len() <= 1) {
+            return Err(CommandError::NothingToDo);
+        }
+
+        let merged = match self.type_ {
+            MergeType::Group => segments,
+            MergeType::Connect if segments.is_empty() => vec![],
+            MergeType::Connect => {
+                vec![connect(&segments, segments[0].id, self.remove_gaps)]
+            }
+        };
+        let mut file = (**file).clone();
+        file.trk[first].trkseg = merged;
+        let mut index = 0;
+        file.trk.retain(|_| {
+            index += 1;
+            !selected[1..].contains(&(index - 1))
+        });
+        state.files.insert(file_id, Rc::new(file));
+        Ok(())
+    }
+
+    fn merge_segments(
+        &self,
+        state: &mut State,
+        file_id: FileId,
+        trk_id: TrackId,
+        ids: &HashSet<TrackSegmentId>,
+    ) -> Result<(), CommandError> {
+        let file = state.files.get(&file_id).ok_or(CommandError::NothingToDo)?;
+        let trk = file
+            .trk
+            .iter()
+            .position(|trk| trk.id == trk_id)
+            .ok_or(CommandError::NothingToDo)?;
+        let segments = &file.trk[trk].trkseg;
+        let selected: Vec<usize> = (0..segments.len())
+            .filter(|i| ids.contains(&segments[*i].id))
+            .collect();
+        if selected.len() < 2 {
+            return Err(CommandError::NothingToDo);
+        }
+        let first = selected[0];
+        let chosen: Vec<TrackSegment> = selected.iter().map(|i| segments[*i].clone()).collect();
+        let merged = match self.type_ {
+            MergeType::Connect => vec![connect(&chosen, chosen[0].id, self.remove_gaps)],
+            MergeType::Group => {
+                if selected.iter().enumerate().all(|(i, s)| *s == first + i) {
+                    // already one after the other
+                    return Err(CommandError::NothingToDo);
+                }
+                chosen
+            }
+        };
+
+        let mut file = (**file).clone();
+        let mut remaining: Vec<TrackSegment> = file.trk[trk]
+            .trkseg
+            .iter()
+            .filter(|segment| !ids.contains(&segment.id))
+            .cloned()
+            .collect();
+        // the ones before the first selected one are all kept
+        remaining.splice(first..first, merged);
+        file.trk[trk].trkseg = remaining;
+        state.files.insert(file_id, Rc::new(file));
+        Ok(())
+    }
+}
+
+/// The segments connected in a single one, which has the id `id`: the trackpoints of the second
+/// go after the ones of the first and so on.
+///
+/// If there are timestamps, the new segment goes on in time, see [`replace_trackpoints`]: the
+/// trackpoints that have none get some, at the moving speed of the segments, and the ones that
+/// are too early follow the previous ones. The time of the first trackpoint is the one it has, or
+/// the one it would have if it was as far in time from the first timed one as its distance
+/// says.
+fn connect(segments: &[TrackSegment], id: TrackSegmentId, remove_gaps: bool) -> TrackSegment {
+    let mut global = GlobalStatistics::default();
+    let mut distance = 0.0;
+    // the first time, and the distance from the start at which it is
+    let mut first_timed: Option<(i64, f64)> = None;
+    for segment in segments {
+        let stats = Statistics::compute(segment);
+        if first_timed.is_none() {
+            first_timed = segment.iter().zip(&stats.local).find_map(|(point, local)| {
+                point
+                    .time
+                    .map(|time| (time, distance + local.total_distance))
+            });
+        }
+        distance += stats.global.total_distance;
+        global.merge(&stats.global);
+    }
+    let speed = global.moving_speed().filter(|speed| *speed > 0.0);
+    let start_time = speed
+        .and_then(|speed| first_timed.map(|(time, km)| time - (3_600_000.0 * km / speed) as i64));
+
+    let mut points = vec![];
+    for segment in segments {
+        let end = points.len();
+        replace_trackpoints(
+            &mut points,
+            end,
+            end,
+            segment.iter().cloned().collect(),
+            speed,
+            start_time,
+            remove_gaps,
+        );
+    }
+    let mut merged = TrackSegment::default();
+    merged.splice(0, 0, points);
+    merged.id = id;
+    merged
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::{File, Load, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn load(fx: &mut Fixture, path: &str) -> FileId {
+        let data = std::fs::read(path).unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        *fx.order.0.last().unwrap()
+    }
+
+    fn merge(type_: MergeType) -> Merge {
+        Merge {
+            type_,
+            remove_gaps: false,
+        }
+    }
+
+    fn select_files(fx: &mut Fixture, ids: &[FileId]) {
+        fx.selection = Selection::File {
+            file_ids: ids.iter().copied().collect(),
+        };
+    }
+
+    fn points(file: &File) -> usize {
+        file.trk
+            .iter()
+            .flat_map(|t| &t.trkseg)
+            .map(|s| s.len())
+            .sum()
+    }
+
+    fn waypoint(name: &str) -> Waypoint {
+        Waypoint {
+            name: Some(name.into()),
+            ..Default::default()
+        }
+    }
+
+    #[test]
+    fn test_group_files() {
+        let mut fx = Fixture::default();
+        let a = load(&mut fx, "data/with_tracks_and_segments.gpx");
+        let b = load(&mut fx, "data/simple.gpx");
+        let mut file_a = (*fx.files[&a]).clone();
+        file_a
+            .wpt
+            .insert_at(0, vec![waypoint("x"), waypoint("same")]);
+        fx.files.insert(a, Rc::new(file_a));
+        let mut file_b = (*fx.files[&b]).clone();
+        file_b
+            .wpt
+            .insert_at(0, vec![waypoint("same"), waypoint("y")]);
+        fx.files.insert(b, Rc::new(file_b));
+        let (before_a, before_b) = (fx.files[&a].clone(), fx.files[&b].clone());
+        select_files(&mut fx, &[b, a]);
+
+        merge(MergeType::Group).apply(&mut fx.state()).unwrap();
+
+        // the first file (in the order of the files) gets everything, the other one goes
+        assert_eq!(fx.order.0, [a]);
+        assert!(!fx.files.contains_key(&b));
+        let merged = &fx.files[&a];
+        assert_eq!(merged.trk.len(), before_a.trk.len() + before_b.trk.len());
+        assert_eq!(merged.trk[0].id, before_a.trk[0].id);
+        assert_eq!(
+            merged.trk.last().unwrap().id,
+            before_b.trk.last().unwrap().id
+        );
+        assert_eq!(points(merged), points(&before_a) + points(&before_b));
+        // the waypoints that are the same are only once
+        let names: Vec<_> = merged.wpt.iter().map(|w| w.name.clone().unwrap()).collect();
+        assert_eq!(names, ["x", "same", "y"]);
+        assert_eq!(merged.info, before_a.info);
+        // a single file has nothing to group
+        select_files(&mut fx, &[a]);
+        assert_eq!(
+            merge(MergeType::Group).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_connect_files() {
+        let mut fx = Fixture::default();
+        let a = load(&mut fx, "data/with_tracks_and_segments.gpx");
+        let b = load(&mut fx, "data/simple.gpx");
+        let (before_a, before_b) = (fx.files[&a].clone(), fx.files[&b].clone());
+        select_files(&mut fx, &[a, b]);
+
+        merge(MergeType::Connect).apply(&mut fx.state()).unwrap();
+
+        let merged = &fx.files[&a];
+        assert_eq!(fx.order.0, [a]);
+        // a single track, with a single segment that has all the trackpoints in order
+        assert_eq!(merged.trk.len(), 1);
+        assert_eq!(merged.trk[0].id, before_a.trk[0].id);
+        assert_eq!(merged.trk[0].trkseg.len(), 1);
+        let segment = &merged.trk[0].trkseg[0];
+        assert_eq!(segment.len(), points(&before_a) + points(&before_b));
+        let expected: Vec<f64> = before_a
+            .trk
+            .iter()
+            .chain(&before_b.trk)
+            .flat_map(|t| &t.trkseg)
+            .flat_map(|s| s.iter().map(|p| p.coordinates.lng))
+            .collect();
+        let lngs: Vec<f64> = segment.iter().map(|p| p.coordinates.lng).collect();
+        assert_eq!(lngs, expected);
+        assert_eq!(segment.id, before_a.trk[0].trkseg[0].id);
+        assert_eq!(segment[0].anchor, Some(0));
+    }
+
+    #[test]
+    fn test_connect_goes_on_in_time() {
+        let mut fx = Fixture::default();
+        // the same times twice: the second part would be too early
+        let a = load(&mut fx, "data/with_time.gpx");
+        let b = load(&mut fx, "data/with_time.gpx");
+        select_files(&mut fx, &[a, b]);
+        merge(MergeType::Connect).apply(&mut fx.state()).unwrap();
+        let segment = &fx.files[&a].trk[0].trkseg[0];
+        let times: Vec<i64> = segment.iter().map(|p| p.time.unwrap()).collect();
+        assert_eq!(times.len(), 160);
+        assert!(times.windows(2).all(|w| w[0] <= w[1]), "{times:?}");
+        assert!(times[80] > times[79]);
+    }
+
+    #[test]
+    fn test_connect_without_gaps_brings_the_parts_closer() {
+        let mut fx = Fixture::default();
+        let a = load(&mut fx, "data/with_time.gpx");
+        // the second file comes a day later
+        let b = {
+            let data = std::fs::read("data/with_time.gpx").unwrap();
+            Load {
+                data: &data,
+                name: "late",
+            }
+            .apply(&mut fx.state())
+            .unwrap();
+            *fx.order.0.last().unwrap()
+        };
+        let mut file = (*fx.files[&b]).clone();
+        for track in file.trk.iter_mut() {
+            for segment in track.trkseg.iter_mut() {
+                let points: Vec<_> = segment
+                    .iter()
+                    .map(|p| {
+                        let mut p = p.clone();
+                        p.time = p.time.map(|t| t + 86_400_000);
+                        p
+                    })
+                    .collect();
+                let len = segment.len();
+                segment.splice(0, len, points);
+            }
+        }
+        fx.files.insert(b, Rc::new(file));
+        let gap = |fx: &Fixture, remove_gaps: bool| {
+            let mut fx2 = Fixture {
+                files: fx.files.clone(),
+                order: crate::FileOrder(fx.order.0.clone()),
+                selection: Selection::File {
+                    file_ids: [a, b].into(),
+                },
+                ..Default::default()
+            };
+            Merge {
+                type_: MergeType::Connect,
+                remove_gaps,
+            }
+            .apply(&mut fx2.state())
+            .unwrap();
+            let segment = &fx2.files[&a].trk[0].trkseg[0];
+            segment[80].time.unwrap() - segment[79].time.unwrap()
+        };
+        let with_gap = gap(&fx, false);
+        let without = gap(&fx, true);
+        assert!(with_gap > 80_000_000, "{with_gap}");
+        assert!(without < 60_000, "{without}");
+    }
+
+    #[test]
+    fn test_merge_tracks() {
+        let mut fx = Fixture::default();
+        let id = load(&mut fx, "data/with_tracks_and_segments.gpx");
+        let file = fx.files[&id].clone();
+        assert!(file.trk.len() >= 2);
+        let ids: HashSet<TrackId> = file.trk.iter().map(|t| t.id).collect();
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: ids,
+        };
+        let segments: usize = file.trk.iter().map(|t| t.trkseg.len()).sum();
+
+        merge(MergeType::Group).apply(&mut fx.state()).unwrap();
+        let merged = &fx.files[&id];
+        assert_eq!(merged.trk.len(), 1);
+        assert_eq!(merged.trk[0].id, file.trk[0].id);
+        assert_eq!(merged.trk[0].trkseg.len(), segments);
+        assert_eq!(points(merged), points(&file));
+
+        // connected: a single segment
+        fx.files.insert(id, file.clone());
+        merge(MergeType::Connect).apply(&mut fx.state()).unwrap();
+        let merged = &fx.files[&id];
+        assert_eq!(merged.trk.len(), 1);
+        assert_eq!(merged.trk[0].trkseg.len(), 1);
+        assert_eq!(merged.trk[0].trkseg[0].len(), points(&file));
+
+        // one track with a single segment: nothing to do
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: [file.trk[0].id].into(),
+        };
+        for type_ in [MergeType::Group, MergeType::Connect] {
+            assert_eq!(
+                merge(type_).apply(&mut fx.state()),
+                Err(CommandError::NothingToDo)
+            );
+        }
+    }
+
+    #[test]
+    fn test_connect_the_segments_of_a_track() {
+        let mut fx = Fixture::default();
+        let id = load(&mut fx, "data/with_tracks_and_segments.gpx");
+        let file = fx.files[&id].clone();
+        let (index, track) = file
+            .trk
+            .iter()
+            .enumerate()
+            .find(|(_, t)| t.trkseg.len() >= 2)
+            .unwrap();
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: [track.id].into(),
+        };
+        merge(MergeType::Connect).apply(&mut fx.state()).unwrap();
+        let merged = &fx.files[&id].trk[index];
+        assert_eq!(merged.id, track.id);
+        assert_eq!(merged.trkseg.len(), 1);
+        assert_eq!(
+            merged.trkseg[0].len(),
+            track.trkseg.iter().map(|s| s.len()).sum::<usize>()
+        );
+        // the other tracks are untouched
+        assert_eq!(fx.files[&id].trk.len(), file.trk.len());
+    }
+
+    #[test]
+    fn test_merge_segments() {
+        let mut fx = Fixture::default();
+        let id = load(&mut fx, "data/with_tracks_and_segments.gpx");
+        // a track with three segments
+        let mut three = (*fx.files[&id]).clone();
+        let base = three.trk[0].trkseg[0].clone();
+        three.trk[0].trkseg = (0..3).map(|_| crate::copy_segment(&base)).collect();
+        fx.files.insert(id, Rc::new(three));
+        let file = fx.files[&id].clone();
+        let (index, track) = (0, &file.trk[0]);
+        let segments = &track.trkseg;
+        // the first and the last ones
+        let (first, last) = (&segments[0], &segments[2]);
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: track.id,
+            trkseg_ids: [first.id, last.id].into(),
+        };
+
+        // grouped: next to each other, at the place of the first one
+        merge(MergeType::Group).apply(&mut fx.state()).unwrap();
+        let ids: Vec<_> = fx.files[&id].trk[index]
+            .trkseg
+            .iter()
+            .map(|s| s.id)
+            .collect();
+        assert_eq!(ids[..3], [first.id, last.id, segments[1].id]);
+
+        // connected: one segment, with the id of the first one, at its place
+        fx.files.insert(id, file.clone());
+        merge(MergeType::Connect).apply(&mut fx.state()).unwrap();
+        let merged = &fx.files[&id].trk[index].trkseg;
+        assert_eq!(merged.len(), segments.len() - 1);
+        assert_eq!(merged[0].id, first.id);
+        assert_eq!(merged[0].len(), first.len() + last.len());
+        assert_eq!(merged[1].id, segments[1].id);
+
+        // a single segment, or segments that are already together: nothing to do
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: track.id,
+            trkseg_ids: [first.id].into(),
+        };
+        assert_eq!(
+            merge(MergeType::Connect).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        fx.files.insert(id, file.clone());
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: track.id,
+            trkseg_ids: [first.id, segments[1].id].into(),
+        };
+        assert_eq!(
+            merge(MergeType::Group).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_nothing_to_merge() {
+        let mut fx = Fixture::default();
+        let id = load(&mut fx, "data/simple.gpx");
+        let before = fx.files[&id].clone();
+        for selection in [Selection::Empty, Selection::Waypoints { file_id: id }] {
+            fx.selection = selection;
+            assert_eq!(
+                merge(MergeType::Connect).apply(&mut fx.state()),
+                Err(CommandError::NothingToDo)
+            );
+        }
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+    }
+}
@@ -0,0 +1,33 @@
+mod change_loop_start;
+mod clean;
+mod crop;
+mod edit_waypoint;
+mod elevation;
+mod extract;
+mod insert_anchor;
+mod merge;
+mod move_waypoint;
+mod new_waypoint;
+mod reduce;
+mod reverse;
+mod round_trip;
+mod route;
+mod split;
+mod time;
+
+pub use change_loop_start::*;
+pub use clean::*;
+pub use crop::*;
+pub use edit_waypoint::*;
+pub use elevation::*;
+pub use extract::*;
+pub use insert_anchor::*;
+pub use merge::*;
+pub use move_waypoint::*;
+pub use new_waypoint::*;
+pub use reduce::*;
+pub use reverse::*;
+pub use round_trip::*;
+pub use route::*;
+pub use split::*;
+pub use time::*;
@@ -0,0 +1,107 @@
+use crate::{Apply, CommandError, FileId, LngLat, State, WaypointId, update_waypoint};
+
+/// Moves a waypoint of a file, whatever is selected (what a drag does): only its position and
+/// elevation change.
+#[derive(Debug)]
+pub struct MoveWaypoint {
+    pub file_id: FileId,
+    pub waypoint_id: WaypointId,
+    pub lng: f64,
+    pub lat: f64,
+    pub ele: f64,
+}
+
+impl Apply for MoveWaypoint {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        update_waypoint(state, self.file_id, self.waypoint_id, |wpt| {
+            wpt.coordinates = LngLat {
+                lng: self.lng,
+                lat: self.lat,
+            };
+            wpt.ele = self.ele;
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::{
+        File, Selection, Waypoint, WaypointChunk, engine::command::fixture::Fixture, waypoint_ids,
+    };
+
+    use super::*;
+
+    fn fixture() -> (Fixture, crate::FileId, Vec<crate::WaypointId>) {
+        let mut fx = Fixture::default();
+        let mut file = File::default();
+        file.wpt.push(WaypointChunk {
+            wpt: (0..3)
+                .map(|i| Waypoint {
+                    name: Some(format!("w{i}")),
+                    ..Default::default()
+                })
+                .collect(),
+            ..Default::default()
+        });
+        let id = file.id;
+        let ids = waypoint_ids(&file).collect();
+        fx.files.insert(id, Rc::new(file));
+        fx.order.0.push(id);
+        (fx, id, ids)
+    }
+
+    #[test]
+    fn test_only_the_given_waypoint_moves_whatever_is_selected() {
+        let (mut fx, id, ids) = fixture();
+        let rev = fx.files[&id].wpt.rev_id;
+
+        MoveWaypoint {
+            file_id: id,
+            waypoint_id: ids[1],
+            lng: 4.0,
+            lat: 50.0,
+            ele: 42.0,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        let wpts: Vec<_> = fx.files[&id].wpt.iter().collect();
+        assert_eq!(wpts.len(), 3);
+        assert_eq!(
+            (
+                wpts[1].coordinates.lng,
+                wpts[1].coordinates.lat,
+                wpts[1].ele
+            ),
+            (4.0, 50.0, 42.0)
+        );
+        // the other fields and the other waypoints are as they were
+        assert_eq!(wpts[1].name.as_deref(), Some("w1"));
+        assert_eq!(wpts[1].id, ids[1]);
+        assert_eq!((wpts[0].coordinates.lng, wpts[0].ele), (0.0, 0.0));
+        assert_eq!((wpts[2].coordinates.lat, wpts[2].ele), (0.0, 0.0));
+        // the coordinates changed, which is noticed by what is derived from them
+        assert_ne!(fx.files[&id].wpt.rev_id, rev);
+        assert_eq!(fx.selection, Selection::Empty);
+    }
+
+    #[test]
+    fn test_unknown_waypoint_or_file_is_nothing_to_do() {
+        let (mut fx, id, ids) = fixture();
+        let before = fx.files[&id].clone();
+        for (file_id, waypoint_id) in [(id, WaypointId::default()), (FileId::default(), ids[0])] {
+            let result = MoveWaypoint {
+                file_id,
+                waypoint_id,
+                lng: 1.0,
+                lat: 1.0,
+                ele: 1.0,
+            }
+            .apply(&mut fx.state());
+            assert!(matches!(result, Err(CommandError::NothingToDo)));
+        }
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+    }
+}
@@ -0,0 +1,270 @@
+use std::rc::Rc;
+
+use crate::{Apply, CommandError, File, FileId, Link, LngLat, Selection, State, Waypoint};
+
+/// Adds a waypoint at the end of the waypoints of each selected file (or of the file of the
+/// selected elements). The strings are empty when the waypoint does not have the field.
+#[derive(Debug)]
+pub struct NewWaypoint<'a> {
+    pub lng: f64,
+    pub lat: f64,
+    pub ele: f64,
+    pub name: &'a str,
+    pub desc: &'a str,
+    pub icon: &'a str,
+    pub link: &'a str,
+}
+
+fn non_empty(text: &str) -> Option<String> {
+    (!text.is_empty()).then(|| text.to_owned())
+}
+
+/// Sets the fields of a waypoint: the strings that are empty remove the field.
+pub fn set_waypoint_fields(
+    waypoint: &mut Waypoint,
+    position: (f64, f64, f64),
+    name: &str,
+    desc: &str,
+    icon: &str,
+    link: &str,
+) {
+    let (lng, lat, ele) = position;
+    waypoint.coordinates = LngLat { lng, lat };
+    waypoint.ele = ele;
+    waypoint.name = non_empty(name);
+    waypoint.desc = non_empty(desc);
+    // the description is also the comment, as it is what the other applications show
+    waypoint.cmt = non_empty(desc);
+    waypoint.sym = non_empty(icon);
+    // the form has a single link: it is the first one, the others are left as they are
+    match (non_empty(link), waypoint.links.first_mut()) {
+        (Some(href), Some(first)) if first.href != href => *first = Link { href, text: None },
+        (Some(href), None) => waypoint.links.push(Link { href, text: None }),
+        (None, Some(_)) => {
+            waypoint.links.remove(0);
+        }
+        _ => (),
+    }
+}
+
+impl Apply for NewWaypoint<'_> {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let file_ids: Vec<FileId> = match &*state.selection {
+            Selection::Empty => vec![],
+            Selection::File { file_ids } => state
+                .order
+                .0
+                .iter()
+                .filter(|id| file_ids.contains(id))
+                .copied()
+                .collect(),
+            Selection::Track { file_id, .. }
+            | Selection::TrackSegment { file_id, .. }
+            | Selection::Waypoints { file_id }
+            | Selection::Waypoint { file_id, .. } => vec![*file_id],
+        };
+        let file_ids: Vec<FileId> = file_ids
+            .into_iter()
+            .filter(|id| state.files.contains_key(id))
+            .collect();
+        if file_ids.is_empty() {
+            return Err(CommandError::NothingToDo);
+        }
+
+        for id in file_ids {
+            let mut waypoint = Waypoint::default();
+            set_waypoint_fields(
+                &mut waypoint,
+                (self.lng, self.lat, self.ele),
+                self.name,
+                self.desc,
+                self.icon,
+                self.link,
+            );
+            let file: &mut File = Rc::make_mut(state.files.get_mut(&id).unwrap());
+            file.wpt.insert_at(usize::MAX, vec![waypoint]);
+        }
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{New, TrackId, TrackSegmentId, engine::command::fixture::Fixture, waypoint_ids};
+
+    use super::*;
+
+    fn new_waypoint(name: &str) -> NewWaypoint<'_> {
+        NewWaypoint {
+            lng: 4.5,
+            lat: 50.25,
+            ele: 123.0,
+            name,
+            desc: "a description",
+            icon: "Summit",
+            link: "https://example.com",
+        }
+    }
+
+    fn waypoints(fx: &Fixture, id: FileId) -> Vec<Waypoint> {
+        fx.files[&id].wpt.iter().cloned().collect()
+    }
+
+    #[test]
+    fn test_new_waypoint_in_the_selected_file() {
+        let mut fx = Fixture::default();
+        New {
+            name: "a",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        New {
+            name: "b",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let (a, b) = (fx.order.0[0], fx.order.0[1]);
+        let rev = fx.files[&b].wpt.rev_id;
+
+        // b is selected
+        new_waypoint("peak").apply(&mut fx.state()).unwrap();
+        assert!(waypoints(&fx, a).is_empty());
+        let created = waypoints(&fx, b);
+        assert_eq!(created.len(), 1);
+        let wpt = &created[0];
+        assert_eq!(
+            (wpt.coordinates.lng, wpt.coordinates.lat, wpt.ele),
+            (4.5, 50.25, 123.0)
+        );
+        assert_eq!(wpt.name.as_deref(), Some("peak"));
+        assert_eq!(wpt.desc.as_deref(), Some("a description"));
+        assert_eq!(wpt.cmt.as_deref(), Some("a description"));
+        assert_eq!(wpt.sym.as_deref(), Some("Summit"));
+        assert_eq!(
+            wpt.links.first().map(|l| l.href.as_str()),
+            Some("https://example.com")
+        );
+        assert_ne!(fx.files[&b].wpt.rev_id, rev);
+
+        // added after the others
+        let mut second = new_waypoint("second");
+        second.lng = 5.0;
+        second.apply(&mut fx.state()).unwrap();
+        let names: Vec<_> = waypoints(&fx, b)
+            .iter()
+            .map(|w| w.name.clone().unwrap())
+            .collect();
+        assert_eq!(names, ["peak", "second"]);
+        // and not selected
+        assert_eq!(fx.selected_files(), [b].into());
+    }
+
+    #[test]
+    fn test_empty_fields_are_not_set() {
+        let mut fx = Fixture::default();
+        New {
+            name: "a",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let a = fx.order.0[0];
+        NewWaypoint {
+            lng: 1.0,
+            lat: 2.0,
+            ele: 0.0,
+            name: "",
+            desc: "",
+            icon: "",
+            link: "",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let wpt = &waypoints(&fx, a)[0];
+        assert!(wpt.name.is_none() && wpt.desc.is_none() && wpt.cmt.is_none());
+        assert!(wpt.sym.is_none() && wpt.links.is_empty());
+    }
+
+    #[test]
+    fn test_each_selected_file_gets_its_own_waypoint() {
+        let mut fx = Fixture::default();
+        for name in ["a", "b", "c"] {
+            New {
+                name,
+                trackpoint: None,
+            }
+            .apply(&mut fx.state())
+            .unwrap();
+        }
+        let ids = fx.order.0.clone();
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([ids[0], ids[2]]),
+        };
+        new_waypoint("w").apply(&mut fx.state()).unwrap();
+        assert_eq!(waypoints(&fx, ids[0]).len(), 1);
+        assert!(waypoints(&fx, ids[1]).is_empty());
+        assert_eq!(waypoints(&fx, ids[2]).len(), 1);
+        // not the same waypoint
+        assert_ne!(waypoints(&fx, ids[0])[0].id, waypoints(&fx, ids[2])[0].id);
+    }
+
+    #[test]
+    fn test_the_file_of_the_selected_elements_is_used() {
+        for selection in [
+            |id| Selection::Track {
+                file_id: id,
+                trk_ids: [TrackId::default()].into(),
+            },
+            |id| Selection::TrackSegment {
+                file_id: id,
+                trk_id: TrackId::default(),
+                trkseg_ids: [TrackSegmentId::default()].into(),
+            },
+            |id| Selection::Waypoints { file_id: id },
+            |id| Selection::Waypoint {
+                file_id: id,
+                wpt_ids: HashSet::new(),
+            },
+        ] {
+            let mut fx = Fixture::default();
+            New {
+                name: "a",
+                trackpoint: None,
+            }
+            .apply(&mut fx.state())
+            .unwrap();
+            let a = fx.order.0[0];
+            fx.selection = selection(a);
+            new_waypoint("w").apply(&mut fx.state()).unwrap();
+            assert_eq!(waypoint_ids(&fx.files[&a]).count(), 1);
+        }
+    }
+
+    #[test]
+    fn test_nothing_selected_or_unknown_file() {
+        let mut fx = Fixture::default();
+        New {
+            name: "a",
+            trackpoint: None,
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        fx.selection = Selection::Empty;
+        assert_eq!(
+            new_waypoint("w").apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        fx.selection = Selection::Waypoints {
+            file_id: FileId::default(),
+        };
+        assert_eq!(
+            new_waypoint("w").apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        assert_eq!(fx.files.len(), 1);
+    }
+}
@@ -0,0 +1,149 @@
+use crate::{Apply, CommandError, State, reduce_indices, update_segments};
+
+/// Removes the trackpoints of the selected segments that are less than `tolerance` meters away
+/// from the line of their neighbours (Ramer-Douglas-Peucker, see [`reduce_indices`]). The ends of the segments are
+/// kept.
+#[derive(Debug)]
+pub struct Reduce {
+    pub tolerance: f64,
+}
+
+impl Apply for Reduce {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        if !(self.tolerance.is_finite() && self.tolerance > 0.0) {
+            return Err(CommandError::InvalidData(format!(
+                "tolerance {} should be positive",
+                self.tolerance
+            )));
+        }
+
+        let locations = state
+            .selection
+            .segment_locations(state.files, &state.order.0);
+        let mut changed = vec![];
+        let mut kept_points = vec![];
+        for location in &locations {
+            let segment = &state.files[&location.file_id].trk[location.trk].trkseg[location.seg];
+            let kept = reduce_indices(segment, self.tolerance);
+            if kept.len() == segment.len() {
+                continue;
+            }
+            changed.push(*location);
+            kept_points.push(kept.iter().map(|&i| segment[i].clone()).collect::<Vec<_>>());
+        }
+        if changed.is_empty() {
+            return Err(CommandError::NothingToDo);
+        }
+
+        update_segments(state, &changed, |i, segment| {
+            let len = segment.len();
+            segment.splice(0, len, std::mem::take(&mut kept_points[i]));
+        });
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{FileId, Load, Selection, engine::command::fixture::Fixture, reduction_distances};
+
+    use super::*;
+
+    fn loaded(path: &str) -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read(path).unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        (fx, id)
+    }
+
+    fn count(fx: &Fixture, id: FileId) -> usize {
+        fx.files[&id]
+            .trk
+            .iter()
+            .flat_map(|trk| &trk.trkseg)
+            .map(|seg| seg.len())
+            .sum()
+    }
+
+    #[test]
+    fn test_a_larger_tolerance_keeps_fewer_points_and_the_ends() {
+        let (mut fx, id) = loaded("data/with_time.gpx");
+        let before = count(&fx, id);
+        let first = fx.files[&id].trk[0].trkseg[0][0].coordinates;
+
+        Reduce { tolerance: 5.0 }.apply(&mut fx.state()).unwrap();
+        let medium = count(&fx, id);
+        assert!(medium < before);
+        assert_eq!(fx.files[&id].trk[0].trkseg[0][0].coordinates.lng, first.lng);
+
+        Reduce { tolerance: 500.0 }.apply(&mut fx.state()).unwrap();
+        assert!(count(&fx, id) < medium);
+    }
+
+    #[test]
+    fn test_the_distances_tell_which_points_are_kept() {
+        for path in ["data/with_time.gpx", "data/with_tracks_and_segments.gpx"] {
+            let (fx, id) = loaded(path);
+            for seg in fx.files[&id].trk.iter().flat_map(|trk| &trk.trkseg) {
+                let distances = reduction_distances(seg);
+                for tolerance in [0.1, 0.5, 1.0, 3.0, 10.0, 30.0, 100.0, 1000.0] {
+                    let from_distances: Vec<usize> = (0..seg.len())
+                        .filter(|&i| distances[i] > tolerance)
+                        .collect();
+                    assert_eq!(
+                        from_distances,
+                        reduce_indices(seg, tolerance),
+                        "{path} {tolerance}"
+                    );
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn test_only_the_selected_segments_are_reduced() {
+        let (mut fx, id) = loaded("data/with_time.gpx");
+        let others: usize = fx.files[&id]
+            .trk
+            .iter()
+            .flat_map(|t| &t.trkseg)
+            .skip(1)
+            .map(|s| s.len())
+            .sum();
+        let expected = reduce_indices(&fx.files[&id].trk[0].trkseg[0], 5.0).len();
+        fx.selection = {
+            let track = &fx.files[&id].trk[0];
+            Selection::TrackSegment {
+                file_id: id,
+                trk_id: track.id,
+                trkseg_ids: HashSet::from([track.trkseg[0].id]),
+            }
+        };
+        Reduce { tolerance: 5.0 }.apply(&mut fx.state()).unwrap();
+        assert_eq!(count(&fx, id), expected + others);
+    }
+
+    #[test]
+    fn test_invalid_tolerance_and_nothing_to_remove() {
+        let (mut fx, _) = loaded("data/simple.gpx");
+        assert!(matches!(
+            Reduce { tolerance: 0.0 }.apply(&mut fx.state()),
+            Err(CommandError::InvalidData(_))
+        ));
+        assert!(matches!(
+            Reduce { tolerance: 1e-9 }.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        ));
+    }
+}
@@ -0,0 +1,294 @@
+use std::rc::Rc;
+
+use crate::{
+    Apply, CommandError, File, FileId, Selection, State, TrackId, TrackSegmentId, end_time,
+    reverse_segment, reverse_segments, reverse_tracks, start_time, track_end_time,
+    track_start_time,
+};
+
+/// Reverses the direction of the selected elements: the whole of each selected file (its tracks,
+/// the segments of its tracks and their trackpoints are in the opposite order), of each selected
+/// track (its segments and their trackpoints), or each selected segment on its own (its
+/// trackpoints). The timestamps are mirrored, see [`reverse_segment`].
+#[derive(Debug)]
+pub struct Reverse;
+
+impl Apply for Reverse {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let locations = state
+            .selection
+            .segment_locations(state.files, &state.order.0);
+        let points: usize = locations
+            .iter()
+            .map(|location| {
+                state.files[&location.file_id].trk[location.trk].trkseg[location.seg].len()
+            })
+            .sum();
+        if points <= 1 {
+            return Err(CommandError::NothingToDo);
+        }
+
+        let mut files: Vec<(FileId, File)> = vec![];
+        let mut edit = |file_id: &FileId, f: &dyn Fn(&mut File)| {
+            if let Some(file) = state.files.get(file_id) {
+                let mut file = (**file).clone();
+                f(&mut file);
+                files.push((*file_id, file));
+            }
+        };
+        match &*state.selection {
+            Selection::File { file_ids } => {
+                for file_id in file_ids {
+                    edit(file_id, &|file| {
+                        let end = file.trk.last().and_then(track_end_time);
+                        let start = file.trk.first().and_then(track_start_time);
+                        reverse_tracks(&mut file.trk, end, start);
+                    });
+                }
+            }
+            Selection::Track { file_id, trk_ids } => edit(file_id, &|file| {
+                reverse_selected_tracks(file, trk_ids);
+            }),
+            Selection::TrackSegment {
+                file_id,
+                trk_id,
+                trkseg_ids,
+            } => edit(file_id, &|file| {
+                reverse_selected_segments(file, *trk_id, trkseg_ids);
+            }),
+            Selection::Empty | Selection::Waypoints { .. } | Selection::Waypoint { .. } => {}
+        }
+
+        for (file_id, file) in files {
+            state.files.insert(file_id, Rc::new(file));
+        }
+        Ok(())
+    }
+}
+
+fn reverse_selected_tracks(file: &mut File, ids: &std::collections::HashSet<TrackId>) {
+    for track in file.trk.iter_mut().filter(|track| ids.contains(&track.id)) {
+        let end = track.trkseg.last().and_then(end_time);
+        let start = track.trkseg.first().and_then(start_time);
+        reverse_segments(&mut track.trkseg, end, start);
+    }
+}
+
+fn reverse_selected_segments(
+    file: &mut File,
+    track_id: TrackId,
+    ids: &std::collections::HashSet<TrackSegmentId>,
+) {
+    for track in file.trk.iter_mut().filter(|track| track.id == track_id) {
+        for segment in track
+            .trkseg
+            .iter_mut()
+            .filter(|segment| ids.contains(&segment.id))
+        {
+            let (end, start) = (end_time(segment), start_time(segment));
+            reverse_segment(segment, end, start);
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{Load, TrackSegment, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded(path: &str) -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read(path).unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        (fx, id)
+    }
+
+    fn all_segments(fx: &Fixture, id: FileId) -> Vec<TrackSegment> {
+        fx.files[&id]
+            .trk
+            .iter()
+            .flat_map(|track| track.trkseg.iter().cloned())
+            .collect()
+    }
+
+    fn lngs(segment: &TrackSegment) -> Vec<f64> {
+        segment.iter().map(|p| p.coordinates.lng).collect()
+    }
+
+    #[test]
+    fn test_reversing_a_file_reverses_tracks_segments_and_points() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let before = all_segments(&fx, id);
+        assert!(before.len() >= 3);
+        let (tracks_before, ids_before): (Vec<usize>, Vec<_>) = (
+            fx.files[&id].trk.iter().map(|t| t.trkseg.len()).collect(),
+            fx.files[&id].trk.iter().map(|t| t.id).collect(),
+        );
+
+        Reverse.apply(&mut fx.state()).unwrap();
+
+        let after = all_segments(&fx, id);
+        assert_eq!(after.len(), before.len());
+        // the whole path is the opposite one
+        let path =
+            |segments: &[TrackSegment]| -> Vec<f64> { segments.iter().flat_map(lngs).collect() };
+        let mut expected = path(&before);
+        expected.reverse();
+        assert_eq!(path(&after), expected);
+        // the tracks are in the opposite order, each with the same number of segments
+        let tracks_after: Vec<usize> = fx.files[&id].trk.iter().map(|t| t.trkseg.len()).collect();
+        let mut reversed = tracks_before.clone();
+        reversed.reverse();
+        assert_eq!(tracks_after, reversed);
+        let ids_after: Vec<_> = fx.files[&id].trk.iter().map(|t| t.id).collect();
+        let mut reversed_ids = ids_before;
+        reversed_ids.reverse();
+        assert_eq!(ids_after, reversed_ids);
+        // the segments changed, and they still end where they should
+        assert!(after.iter().all(|s| s.rev_id != before[0].rev_id));
+        for segment in &after {
+            assert_eq!(segment[0].anchor, Some(0));
+            assert_eq!(segment[segment.len() - 1].anchor, Some(0));
+        }
+    }
+
+    #[test]
+    fn test_reversing_a_file_twice_gives_the_same_path_and_times() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let before = all_segments(&fx, id);
+        let times = |segments: &[TrackSegment]| -> Vec<Option<i64>> {
+            segments
+                .iter()
+                .flat_map(|s| s.iter().map(|p| p.time))
+                .collect()
+        };
+        Reverse.apply(&mut fx.state()).unwrap();
+        Reverse.apply(&mut fx.state()).unwrap();
+        let after = all_segments(&fx, id);
+        for (a, b) in before.iter().zip(&after) {
+            assert_eq!(lngs(a), lngs(b));
+            assert_eq!(a.id, b.id);
+        }
+        assert_eq!(times(&before), times(&after));
+    }
+
+    #[test]
+    fn test_reversing_segments_keeps_the_others() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let file = fx.files[&id].clone();
+        let trk = &file.trk[0];
+        assert!(trk.trkseg.len() >= 2);
+        let target = &trk.trkseg[1];
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: trk.id,
+            trkseg_ids: HashSet::from([target.id]),
+        };
+        Reverse.apply(&mut fx.state()).unwrap();
+
+        let after = &fx.files[&id].trk[0];
+        // the segment is reversed in place
+        let mut expected = lngs(target);
+        expected.reverse();
+        assert_eq!(lngs(&after.trkseg[1]), expected);
+        assert_eq!(after.trkseg[1].id, target.id);
+        assert_ne!(after.trkseg[1].rev_id, target.rev_id);
+        // the other ones are the same
+        for (i, segment) in trk.trkseg.iter().enumerate().filter(|(i, _)| *i != 1) {
+            assert_eq!(after.trkseg[i].rev_id, segment.rev_id, "{i}");
+        }
+        assert_eq!(fx.files[&id].trk.len(), file.trk.len());
+    }
+
+    #[test]
+    fn test_reversing_tracks_reverses_their_segments_in_place() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let file = fx.files[&id].clone();
+        let (index, trk) = file
+            .trk
+            .iter()
+            .enumerate()
+            .find(|(_, t)| t.trkseg.len() >= 2)
+            .unwrap();
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: HashSet::from([trk.id]),
+        };
+        Reverse.apply(&mut fx.state()).unwrap();
+
+        let after = &fx.files[&id];
+        // the track stays where it is, its segments are the opposite way
+        assert_eq!(after.trk[index].id, trk.id);
+        let path = |t: &crate::Track| -> Vec<f64> { t.trkseg.iter().flat_map(lngs).collect() };
+        let mut expected = path(trk);
+        expected.reverse();
+        assert_eq!(path(&after.trk[index]), expected);
+        // and the other tracks do not change
+        for (i, other) in file.trk.iter().enumerate().filter(|(i, _)| *i != index) {
+            assert_eq!(path(&after.trk[i]), path(other));
+        }
+    }
+
+    #[test]
+    fn test_times_are_mirrored() {
+        let (mut fx, id) = loaded("data/with_time.gpx");
+        let before = all_segments(&fx, id).remove(0);
+        Reverse.apply(&mut fx.state()).unwrap();
+        let after = all_segments(&fx, id).remove(0);
+        let (start, end) = (start_time(&before).unwrap(), end_time(&before).unwrap());
+        // the same period of time, the first point of the new path is the last one
+        assert_eq!(start_time(&after), Some(start));
+        assert_eq!(end_time(&after), Some(end));
+        let n = before.len();
+        for i in 0..n {
+            assert_eq!(
+                after[i].time.unwrap(),
+                start + end - before[n - 1 - i].time.unwrap()
+            );
+            assert_eq!(after[i].coordinates.lng, before[n - 1 - i].coordinates.lng);
+        }
+    }
+
+    #[test]
+    fn test_nothing_to_reverse() {
+        let (mut fx, id) = loaded("data/simple.gpx");
+        let before = fx.files[&id].clone();
+        fx.selection = Selection::Empty;
+        assert_eq!(
+            Reverse.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        fx.selection = Selection::Waypoints { file_id: id };
+        assert_eq!(
+            Reverse.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+
+        // a single trackpoint has no direction
+        let mut file = (*fx.files[&id]).clone();
+        let segment = &mut file.trk[0].trkseg[0];
+        let len = segment.len();
+        segment.splice(1, len, vec![]);
+        fx.files.insert(id, Rc::new(file));
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        assert_eq!(
+            Reverse.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+}
@@ -0,0 +1,144 @@
+use crate::{Apply, CommandError, State, round_trip, update_segments};
+
+/// Makes each selected segment come back to where it started: the segments of the selected files
+/// and tracks, and the selected segments, get a reversed copy of themselves after their last
+/// trackpoint (see [`round_trip`]).
+///
+/// There is nothing to do for segments with fewer than two trackpoints, which have no way back.
+#[derive(Debug)]
+pub struct RoundTrip;
+
+impl Apply for RoundTrip {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let locations: Vec<_> = state
+            .selection
+            .segment_locations(state.files, &state.order.0)
+            .into_iter()
+            .filter(|l| state.files[&l.file_id].trk[l.trk].trkseg[l.seg].len() >= 2)
+            .collect();
+        if locations.is_empty() {
+            return Err(CommandError::NothingToDo);
+        }
+        update_segments(state, &locations, |_, segment| round_trip(segment));
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+    use std::rc::Rc;
+
+    use crate::{
+        FileId, Load, Selection, TrackSegment, end_time, engine::command::fixture::Fixture,
+    };
+
+    use super::*;
+
+    fn loaded(path: &str) -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read(path).unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        (fx, id)
+    }
+
+    fn segments(fx: &Fixture, id: FileId) -> Vec<TrackSegment> {
+        fx.files[&id]
+            .trk
+            .iter()
+            .flat_map(|track| track.trkseg.iter().cloned())
+            .collect()
+    }
+
+    fn lngs(segment: &TrackSegment) -> Vec<f64> {
+        segment.iter().map(|p| p.coordinates.lng).collect()
+    }
+
+    #[test]
+    fn test_every_segment_of_a_file_comes_back() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let before = segments(&fx, id);
+        RoundTrip.apply(&mut fx.state()).unwrap();
+        let after = segments(&fx, id);
+        assert_eq!(after.len(), before.len());
+        for (a, b) in after.iter().zip(&before) {
+            if b.len() < 2 {
+                assert_eq!(a.len(), b.len());
+                assert_eq!(a.rev_id, b.rev_id);
+                continue;
+            }
+            assert_eq!(a.id, b.id);
+            // the last trackpoint is not repeated
+            assert_eq!(a.len(), 2 * b.len() - 1);
+            let mut expected = lngs(b);
+            expected.extend(lngs(b).into_iter().rev().skip(1));
+            assert_eq!(lngs(a), expected);
+        }
+    }
+
+    #[test]
+    fn test_only_the_selected_segment_comes_back() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+        let file = fx.files[&id].clone();
+        let trk = &file.trk[0];
+        assert!(trk.trkseg.len() >= 2);
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: trk.id,
+            trkseg_ids: HashSet::from([trk.trkseg[1].id]),
+        };
+        RoundTrip.apply(&mut fx.state()).unwrap();
+        let after = &fx.files[&id].trk[0];
+        assert_eq!(after.trkseg[1].len(), 2 * trk.trkseg[1].len() - 1);
+        assert_eq!(after.trkseg[0].rev_id, trk.trkseg[0].rev_id);
+    }
+
+    #[test]
+    fn test_times_go_on_from_the_end() {
+        let (mut fx, id) = loaded("data/with_time.gpx");
+        let before = segments(&fx, id).remove(0);
+        RoundTrip.apply(&mut fx.state()).unwrap();
+        let after = segments(&fx, id).remove(0);
+        let n = before.len();
+        let end = end_time(&before).unwrap();
+        assert_eq!(after.len(), 2 * n - 1);
+        // the original part is untouched
+        for i in 0..n {
+            assert_eq!(after[i].time, before[i].time);
+        }
+        // the way back goes on from the end, and lasts as long as the way there
+        for i in 1..n {
+            assert_eq!(
+                after[n - 1 + i].time.unwrap(),
+                2 * end - before[n - 1 - i].time.unwrap()
+            );
+        }
+        assert_eq!(end_time(&after), Some(2 * end - before[0].time.unwrap()));
+    }
+
+    #[test]
+    fn test_nothing_to_do_without_a_way_back() {
+        let (mut fx, id) = loaded("data/simple.gpx");
+        let before = fx.files[&id].clone();
+        fx.selection = Selection::Empty;
+        assert_eq!(
+            RoundTrip.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        fx.selection = Selection::Waypoints { file_id: id };
+        assert_eq!(
+            RoundTrip.apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+    }
+}
@@ -0,0 +1,810 @@
+use std::rc::Rc;
+
+use crate::{
+    Apply, Categories, CommandError, FileId, SegmentLocation, Selection, State, Statistics, Track,
+    TrackSegment, Trackpoint, distance, replace_trackpoints,
+};
+
+/// The values of an OSM attribute (surface, highway...) of the new trackpoints of a [`Route`], as
+/// the intervals of consecutive trackpoints that share one: `starts[i]` is the index of the first
+/// trackpoint of the interval `i`, and `values[i]` its value, 0 when unknown, else 1 + the index
+/// of its name in `names`. No intervals means that the attribute is unknown everywhere.
+#[derive(Debug, Default, Clone, Copy)]
+pub struct RouteCategory<'a> {
+    pub starts: &'a [u32],
+    pub values: &'a [u8],
+    pub names: &'a [String],
+}
+
+impl RouteCategory<'_> {
+    /// The code in `categories` of the value of each of the `len` new trackpoints. A name is
+    /// added to the table of the categories if it is new.
+    fn codes(
+        &self,
+        categories: &mut Categories,
+        len: usize,
+    ) -> Result<Vec<Option<u8>>, CommandError> {
+        if self.starts.len() != self.values.len() {
+            return Err(invalid("intervals of different lengths"));
+        }
+        let mut codes = vec![None; len];
+        for (i, (start, value)) in self.starts.iter().zip(self.values).enumerate() {
+            let end = self.starts.get(i + 1).map_or(len, |end| *end as usize);
+            let start = *start as usize;
+            if start > end || end > len {
+                return Err(invalid("intervals out of the trackpoints"));
+            }
+            if *value == 0 {
+                continue;
+            }
+            let name = self
+                .names
+                .get(usize::from(*value) - 1)
+                .ok_or_else(|| invalid("unknown name of category"))?;
+            codes[start..end].fill(categories.code(name));
+        }
+        Ok(codes)
+    }
+}
+
+/// Replaces the trackpoints `start..end` of a segment of the selection by the given ones (a pure
+/// insertion when `start == end`, a pure removal when there are no new points). It is how the
+/// routing tool reroutes a part of a segment, extends it, or removes the end of it.
+///
+/// `start` and `end` are indices in the trackpoints of the selection (see `RoutingBuffer`): the
+/// range has to be in a single segment, and `start == end == the number of trackpoints` appends
+/// to the last one. If the selection has no trackpoints at all, they go to its last segment, which
+/// is created if needed (in the last track, or in a new one, of the last selected file).
+///
+/// The timestamps follow: the new points get some if the segment has, at the speed it had on the
+/// replaced part (see [`replace_trackpoints`]).
+///
+/// The new points listed in `anchors` become anchors of the routing tool, shown at every zoom
+/// level. The anchors of the segment out of the range are kept, and the ends of the segment are
+/// anchors anyway. The ones right before and after the range, between which the route goes, become
+/// shown at every zoom level as well.
+#[derive(Debug)]
+pub struct Route<'a> {
+    pub start: u32,
+    pub end: u32,
+    pub lng: &'a [f64],
+    pub lat: &'a [f64],
+    pub ele: &'a [f64],
+    pub surface: RouteCategory<'a>,
+    pub highway: RouteCategory<'a>,
+    pub sac_scale: RouteCategory<'a>,
+    pub mtb_scale: RouteCategory<'a>,
+    /// Indices among the new trackpoints.
+    pub anchors: &'a [u32],
+}
+
+fn invalid(message: &str) -> CommandError {
+    CommandError::InvalidData(message.into())
+}
+
+/// A segment of the selection, and the range of its trackpoints that is concerned.
+pub(super) struct Target {
+    pub location: SegmentLocation,
+    pub start: usize,
+    pub end: usize,
+}
+
+impl Apply for Route<'_> {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let (start, end) = (self.start as usize, self.end as usize);
+        let len = self.lng.len();
+        if start > end || self.lat.len() != len || self.ele.len() != len {
+            return Err(invalid("invalid trackpoints range"));
+        }
+        if self.anchors.iter().any(|anchor| *anchor as usize >= len) {
+            return Err(invalid("anchor out of the new trackpoints"));
+        }
+        if start == end && len == 0 {
+            return Err(CommandError::NothingToDo);
+        }
+
+        let categories = &mut *state.categories;
+        let surface = self.surface.codes(&mut categories.surface, len)?;
+        let highway = self.highway.codes(&mut categories.highway, len)?;
+        let sac_scale = self.sac_scale.codes(&mut categories.sac_scale, len)?;
+        let mtb_scale = self.mtb_scale.codes(&mut categories.mtb_scale, len)?;
+        let points: Vec<Trackpoint> = (0..len)
+            .map(|i| Trackpoint {
+                coordinates: crate::LngLat {
+                    lng: self.lng[i],
+                    lat: self.lat[i],
+                },
+                ele: self.ele[i],
+                surface: surface[i],
+                highway: highway[i],
+                sac_scale: sac_scale[i],
+                mtb_scale: mtb_scale[i],
+                ..Default::default()
+            })
+            .collect();
+        let mut points = points;
+        for anchor in self.anchors {
+            points[*anchor as usize].anchor = Some(0);
+        }
+
+        let mut file;
+        let target = match find_target(state, start, end)? {
+            Some(target) => {
+                file = (*state.files[&target.location.file_id]).clone();
+                target
+            }
+            None => {
+                let (file_id, trk) = container(state).ok_or(CommandError::NothingToDo)?;
+                if start != 0 || end != 0 {
+                    return Err(invalid("trackpoints range out of bounds"));
+                }
+                file = (*state.files[&file_id]).clone();
+                // the segment of the last track, which may be new
+                let trk = match trk.or_else(|| file.trk.len().checked_sub(1)) {
+                    Some(trk) => trk,
+                    None => {
+                        file.trk.push(Track::default());
+                        file.trk.len() - 1
+                    }
+                };
+                if file.trk[trk].trkseg.is_empty() {
+                    file.trk[trk].trkseg.push(TrackSegment::default());
+                }
+                let seg = file.trk[trk].trkseg.len() - 1;
+                Target {
+                    location: SegmentLocation { file_id, trk, seg },
+                    start: 0,
+                    end: 0,
+                }
+            }
+        };
+
+        let segment = &mut file.trk[target.location.trk].trkseg[target.location.seg];
+        let new_len = points.len();
+        let (speed, start_time) = speed_and_start_time(segment, &target, &points);
+        let has_times = !segment.is_empty() && segment[0].time.is_some();
+        if speed.is_some() || has_times {
+            // the timestamps of the whole segment can change
+            let mut all: Vec<Trackpoint> = segment.iter().cloned().collect();
+            let old_len = all.len();
+            replace_trackpoints(
+                &mut all,
+                target.start,
+                target.end,
+                points,
+                speed,
+                start_time,
+                false,
+            );
+            segment.splice(0, old_len, all);
+        } else {
+            segment.splice(target.start, target.end, points);
+        }
+        // the anchors next to the new points are the ones that were moved or removed around:
+        // they become permanent
+        for index in [target.start.checked_sub(1), Some(target.start + new_len)]
+            .into_iter()
+            .flatten()
+        {
+            if index < segment.len() && segment[index].anchor.is_some_and(|zoom| zoom != 0) {
+                segment.set_anchor(index, 0);
+            }
+        }
+        segment.rev_id = Default::default();
+        state.files.insert(target.location.file_id, Rc::new(file));
+        Ok(())
+    }
+}
+
+/// The segment of the trackpoints `start..end` of the selection.
+pub(super) fn find_target(
+    state: &State,
+    start: usize,
+    end: usize,
+) -> Result<Option<Target>, CommandError> {
+    let locations = state
+        .selection
+        .segment_locations(state.files, &state.order.0);
+    let segments: Vec<(SegmentLocation, usize)> = locations
+        .into_iter()
+        .map(|location| {
+            let segment = &state.files[&location.file_id].trk[location.trk].trkseg[location.seg];
+            (location, segment.len())
+        })
+        .collect();
+    let total: usize = segments.iter().map(|(_, len)| len).sum();
+
+    if total == 0 {
+        // an empty segment of the selection, if there is one
+        return match segments.last() {
+            Some((location, _)) if start == 0 && end == 0 => Ok(Some(Target {
+                location: *location,
+                start: 0,
+                end: 0,
+            })),
+            Some(_) => Err(invalid("trackpoints range out of bounds")),
+            None => Ok(None),
+        };
+    }
+
+    let mut offset = 0;
+    for (location, len) in segments.iter().filter(|(_, len)| *len > 0) {
+        // appending to the selection is appending to its last segment
+        let appends = offset + len == total && start == total;
+        if start >= offset && (start < offset + len || appends) {
+            if end > offset + len {
+                return Err(invalid("trackpoints range over several segments"));
+            }
+            return Ok(Some(Target {
+                location: *location,
+                start: start - offset,
+                end: end - offset,
+            }));
+        }
+        offset += len;
+    }
+    Err(invalid("trackpoints range out of bounds"))
+}
+
+/// The file, and the track (if the selection is one), where to create a segment in a selection
+/// that has none.
+fn container(state: &State) -> Option<(FileId, Option<usize>)> {
+    match &*state.selection {
+        Selection::File { file_ids } => {
+            let id = state
+                .order
+                .0
+                .iter()
+                .rev()
+                .find(|id| file_ids.contains(id))
+                .or_else(|| file_ids.iter().next())?;
+            state.files.contains_key(id).then_some((*id, None))
+        }
+        Selection::Track { file_id, trk_ids } => {
+            let trk = state
+                .files
+                .get(file_id)?
+                .trk
+                .iter()
+                .rposition(|trk| trk_ids.contains(&trk.id))?;
+            Some((*file_id, Some(trk)))
+        }
+        _ => None,
+    }
+}
+
+/// The speed at which the new points are reached and the time of the first one, when the segment
+/// has times to keep consistent: the speed is the one that the segment had on the part that is
+/// replaced, adjusted so that the moving speed of the whole segment stays what it was.
+///
+/// The replaced part goes from the trackpoint before the range (the anchor that stays) to the one
+/// after it, or to the ends of the segment: the new points are the route between them.
+///
+/// This is what the routing tool computed from the statistics of the segment before.
+fn speed_and_start_time(
+    segment: &TrackSegment,
+    target: &Target,
+    points: &[Trackpoint],
+) -> (Option<f64>, Option<i64>) {
+    let time_at = |index: usize| {
+        (index < segment.len())
+            .then(|| segment[index].time)
+            .flatten()
+    };
+    let start_time = time_at(target.start);
+    if points.is_empty() || segment.is_empty() {
+        return (None, start_time);
+    }
+    let stats = Statistics::compute(segment);
+    let Some(moving_speed) = stats.global.moving_speed().filter(|speed| *speed > 0.0) else {
+        return (None, start_time);
+    };
+
+    // the statistics where the replaced part starts and ends
+    let first_index = target.start.saturating_sub(1);
+    let last_index = target.end.min(segment.len() - 1);
+    let (first, last) = (&stats.local[first_index], &stats.local[last_index]);
+    let moving_distance =
+        |stats: &crate::TrackpointStatistics| stats.moving_distance.unwrap_or(0.0);
+    let moving_time = |stats: &crate::TrackpointStatistics| stats.moving_time.unwrap_or(0);
+    let total_time = |stats: &crate::TrackpointStatistics| stats.total_time.unwrap_or(0);
+
+    let replacing_distance: f64 = points
+        .windows(2)
+        .map(|pair| distance(pair[0].coordinates, pair[1].coordinates))
+        .sum();
+    let replaced_distance = moving_distance(last) - moving_distance(first);
+    let global_moving_distance = stats.global.moving_distance.unwrap_or(0.0);
+    let new_distance = global_moving_distance + replacing_distance - replaced_distance;
+    // in milliseconds
+    let new_time = new_distance / moving_speed * 3_600_000.0;
+    let remaining_time = stats.global.moving_time.unwrap_or(0) as f64
+        - (moving_time(last) - moving_time(first)) as f64;
+    let mut replacing_time = new_time - remaining_time;
+    if replacing_time <= 0.0 {
+        // fall back to the time that the replaced part took
+        replacing_time = (total_time(last) - total_time(first)) as f64;
+    }
+    let speed = replacing_distance / (replacing_time / 3_600_000.0);
+
+    let start_time = start_time.or_else(|| {
+        // The first trackpoint has no time: the new points end when the last replaced one did,
+        // after the time they take and the time that the segment was not moving until then.
+        // (Suspicious: without a time for the last one either, it is "0", the year 1970.)
+        let end_time = time_at(last_index);
+        let stopped = (total_time(last) - moving_time(last)) as f64;
+        Some(end_time.unwrap_or(0) - (replacing_time + stopped) as i64)
+    });
+    (Some(speed), start_time)
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{File, Load, TrackSegmentId, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn load(fx: &mut Fixture, path: &str) -> FileId {
+        let data = std::fs::read(path).unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        *fx.order.0.last().unwrap()
+    }
+
+    fn select_file(fx: &mut Fixture, id: FileId) {
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+    }
+
+    /// The first segment of the file with segments, selected.
+    fn loaded() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let id = load(&mut fx, "data/with_tracks_and_segments.gpx");
+        let trk = &fx.files[&id].trk[0];
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id: trk.id,
+            trkseg_ids: HashSet::from([trk.trkseg[0].id]),
+        };
+        (fx, id)
+    }
+
+    fn route<'a>(
+        start: u32,
+        end: u32,
+        lng: &'a [f64],
+        lat: &'a [f64],
+        ele: &'a [f64],
+    ) -> Route<'a> {
+        Route {
+            start,
+            end,
+            lng,
+            lat,
+            ele,
+            surface: Default::default(),
+            highway: Default::default(),
+            sac_scale: Default::default(),
+            mtb_scale: Default::default(),
+            anchors: &[],
+        }
+    }
+
+    fn segment(fx: &Fixture, id: FileId, trk: usize, seg: usize) -> &TrackSegment {
+        &fx.files[&id].trk[trk].trkseg[seg]
+    }
+
+    #[test]
+    fn test_route_replaces_points_of_the_selected_segment_only() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].clone();
+        let len = before.trk[0].trkseg[0].len();
+        assert!(len >= 3);
+
+        route(1, 3, &[1.0, 2.0, 3.0], &[4.0, 5.0, 6.0], &[7.0, 8.0, 9.0])
+            .apply(&mut fx.state())
+            .unwrap();
+
+        let after = &fx.files[&id];
+        let (old, new) = (&before.trk[0].trkseg[0], &after.trk[0].trkseg[0]);
+        assert_eq!(new.len(), len + 1);
+        assert_eq!(new[0].coordinates.lng, old[0].coordinates.lng);
+        assert_eq!(new[1].coordinates.lng, 1.0);
+        assert_eq!(new[3].coordinates.lat, 6.0);
+        assert_eq!(new[3].ele, 9.0);
+        assert_eq!(new[4].coordinates.lng, old[3].coordinates.lng);
+        assert_ne!(new.rev_id, old.rev_id);
+        assert_eq!(new.id, old.id);
+        // other segments and tracks keep their revision
+        for (b, a) in before.trk.iter().zip(&after.trk) {
+            for (b, a) in b.trkseg.iter().zip(&a.trkseg) {
+                if a.id != new.id {
+                    assert_eq!(a.rev_id, b.rev_id);
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn test_route_append_and_remove() {
+        let (mut fx, id) = loaded();
+        let len = fx.files[&id].trk[0].trkseg[0].len() as u32;
+        route(len, len, &[1.0], &[2.0], &[3.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        let seg = segment(&fx, id, 0, 0);
+        assert_eq!(seg.len(), len as usize + 1);
+        assert_eq!(seg[len as usize].ele, 3.0);
+
+        route(0, len + 1, &[], &[], &[])
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(segment(&fx, id, 0, 0).len(), 0);
+    }
+
+    #[test]
+    fn test_route_invalid_arguments_change_nothing() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].clone();
+        let len = before.trk[0].trkseg[0].len() as u32;
+        let results = [
+            route(2, 1, &[], &[], &[]).apply(&mut fx.state()),
+            route(0, 0, &[1.0], &[], &[]).apply(&mut fx.state()),
+            route(0, len + 1, &[], &[], &[]).apply(&mut fx.state()),
+            route(len + 1, len + 1, &[1.0], &[1.0], &[1.0]).apply(&mut fx.state()),
+            Route {
+                anchors: &[1],
+                ..route(0, 0, &[1.0], &[1.0], &[1.0])
+            }
+            .apply(&mut fx.state()),
+        ];
+        assert!(
+            results
+                .iter()
+                .all(|r| matches!(r, Err(CommandError::InvalidData(_)))),
+            "{results:?}"
+        );
+        assert_eq!(
+            route(0, 0, &[], &[], &[]).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+    }
+
+    #[test]
+    fn test_route_needs_a_selection_with_a_file() {
+        let (mut fx, _) = loaded();
+        fx.selection = Selection::Empty;
+        assert_eq!(
+            route(0, 0, &[1.0], &[1.0], &[1.0]).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+    }
+
+    #[test]
+    fn test_route_indices_are_in_the_selection() {
+        let (mut fx, id) = loaded();
+        let file = fx.files[&id].clone();
+        select_file(&mut fx, id);
+        let lens: Vec<_> = file
+            .trk
+            .iter()
+            .flat_map(|trk| trk.trkseg.iter().map(|segment| segment.len()))
+            .collect();
+        assert!(lens.len() >= 2);
+
+        // inside the second segment
+        let second = lens[0] as u32;
+        route(second + 1, second + 2, &[1.0], &[2.0], &[3.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        let (trk, seg) = (0, 1);
+        let segments_before: Vec<_> = file.trk.iter().flat_map(|t| &t.trkseg).collect();
+        let files = fx.files[&id].clone();
+        let segments_after: Vec<_> = files.trk.iter().flat_map(|t| &t.trkseg).collect();
+        for (i, (b, a)) in segments_before.iter().zip(&segments_after).enumerate() {
+            assert_eq!(a.rev_id != b.rev_id, i == 1, "segment {i}");
+        }
+        assert_eq!(segment(&fx, id, trk, seg)[1].coordinates.lng, 1.0);
+
+        // a range over two segments
+        let total: usize = lens.iter().sum();
+        assert!(matches!(
+            route(second - 1, second + 1, &[], &[], &[]).apply(&mut fx.state()),
+            Err(CommandError::InvalidData(_))
+        ));
+        // after the last point: the last segment
+        let before = segments_after.last().unwrap().len();
+        let total = total as u32;
+        route(total, total, &[1.0], &[2.0], &[3.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        let last = fx.files[&id].trk.last().unwrap().trkseg.last().unwrap();
+        assert_eq!(last.len(), before + 1);
+    }
+
+    #[test]
+    fn test_route_creates_the_segment_of_a_selection_that_has_none() {
+        let mut fx = Fixture::default();
+        let file = File::default();
+        let id = file.id;
+        fx.files.insert(id, Rc::new(file));
+        fx.order.0.push(id);
+        select_file(&mut fx, id);
+
+        route(0, 0, &[1.0, 2.0], &[1.0, 2.0], &[3.0, 4.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(fx.files[&id].trk.len(), 1);
+        assert_eq!(segment(&fx, id, 0, 0).len(), 2);
+        // the ends are anchors
+        assert_eq!(segment(&fx, id, 0, 0)[0].anchor, Some(0));
+        assert_eq!(segment(&fx, id, 0, 0)[1].anchor, Some(0));
+
+        // a track with no segments
+        let mut file = (*fx.files[&id]).clone();
+        file.trk[0].trkseg.clear();
+        let trk_id = file.trk[0].id;
+        fx.files.insert(id, Rc::new(file));
+        fx.selection = Selection::Track {
+            file_id: id,
+            trk_ids: HashSet::from([trk_id]),
+        };
+        route(0, 0, &[5.0], &[5.0], &[5.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(fx.files[&id].trk.len(), 1);
+        assert_eq!(segment(&fx, id, 0, 0).len(), 1);
+
+        // an empty segment is the target as well
+        let mut file = (*fx.files[&id]).clone();
+        file.trk[0].trkseg[0] = TrackSegment::default();
+        let seg_id: TrackSegmentId = file.trk[0].trkseg[0].id;
+        fx.files.insert(id, Rc::new(file));
+        fx.selection = Selection::TrackSegment {
+            file_id: id,
+            trk_id,
+            trkseg_ids: HashSet::from([seg_id]),
+        };
+        route(0, 0, &[6.0], &[6.0], &[6.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        assert_eq!(segment(&fx, id, 0, 0).len(), 1);
+        assert_eq!(fx.files[&id].trk[0].trkseg.len(), 1);
+    }
+
+    #[test]
+    fn test_route_anchors() {
+        let (mut fx, id) = loaded();
+        let len = segment(&fx, id, 0, 0).len();
+        assert!(len > 4);
+        let anchors_before: Vec<_> = segment(&fx, id, 0, 0).iter().map(|p| p.anchor).collect();
+
+        // 5 new points replacing the 2 in the middle, two of them are anchors
+        let (lng, lat, ele) = ([1.0; 5], [2.0; 5], [3.0; 5]);
+        Route {
+            anchors: &[1, 3],
+            ..route(1, 3, &lng, &lat, &ele)
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let anchors: Vec<_> = segment(&fx, id, 0, 0).iter().map(|p| p.anchor).collect();
+        assert_eq!(anchors.len(), len + 3);
+        assert_eq!(anchors[2], Some(0));
+        assert_eq!(anchors[4], Some(0));
+        assert_eq!(anchors[1], None);
+        assert_eq!(anchors[3], None);
+        assert_eq!(anchors[5], None);
+        // the others stay as they were, the ends are always anchors
+        assert_eq!(anchors[0], Some(0));
+        assert_eq!(anchors[len + 2], Some(0));
+        assert_eq!(anchors[len + 2 - 1], anchors_before[len - 2]);
+    }
+
+    #[test]
+    fn test_route_makes_the_anchors_around_the_range_permanent() {
+        let (mut fx, id) = loaded();
+        let mut file = (*fx.files[&id]).clone();
+        let len = file.trk[0].trkseg[0].len();
+        assert!(len > 8);
+        // anchors shown from different zoom levels, around and away from the range 4..6
+        for (index, zoom) in [(1, 7), (3, 9), (6, 12), (8, 14)] {
+            file.trk[0].trkseg[0].set_anchor(index, zoom);
+        }
+        fx.files.insert(id, Rc::new(file));
+
+        route(4, 6, &[1.0, 2.0], &[3.0, 4.0], &[5.0, 6.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        let anchors: Vec<_> = segment(&fx, id, 0, 0).iter().map(|p| p.anchor).collect();
+        assert_eq!(anchors.len(), len);
+        // right before and after the new points: permanent
+        assert_eq!(anchors[3], Some(0));
+        assert_eq!(anchors[6], Some(0));
+        // the others are as they were
+        assert_eq!(anchors[1], Some(7));
+        assert_eq!(anchors[8], Some(14));
+    }
+
+    #[test]
+    fn test_route_categories() {
+        let (mut fx, id) = loaded();
+        let names = ["asphalt".to_string(), "gravel".to_string()];
+        let (lng, lat, ele) = ([1.0; 4], [2.0; 4], [3.0; 4]);
+        // asphalt, asphalt, unknown, gravel
+        Route {
+            surface: RouteCategory {
+                starts: &[0, 2, 3],
+                values: &[1, 0, 2],
+                names: &names,
+            },
+            highway: RouteCategory {
+                starts: &[0],
+                values: &[1],
+                names: &["track".to_string()],
+            },
+            ..route(0, 0, &lng, &lat, &ele)
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let file = fx.files[&id].clone();
+        let seg = &file.trk[0].trkseg[0];
+        let asphalt = fx.categories.surface.code("asphalt");
+        let gravel = fx.categories.surface.code("gravel");
+        let surfaces: Vec<_> = (0..4).map(|i| seg[i].surface).collect();
+        assert_eq!(surfaces, [asphalt, asphalt, None, gravel]);
+        let track = fx.categories.highway.code("track");
+        assert!((0..4).all(|i| seg[i].highway == track));
+        assert!((0..4).all(|i| seg[i].sac_scale.is_none() && seg[i].mtb_scale.is_none()));
+
+        // broken intervals or names
+        let broken = [
+            RouteCategory {
+                starts: &[0, 1],
+                values: &[1],
+                names: &names,
+            },
+            RouteCategory {
+                starts: &[5],
+                values: &[1],
+                names: &names,
+            },
+            RouteCategory {
+                starts: &[0],
+                values: &[3],
+                names: &names,
+            },
+        ];
+        for surface in broken {
+            let result = Route {
+                surface,
+                ..route(0, 0, &lng, &lat, &ele)
+            }
+            .apply(&mut fx.state());
+            assert!(matches!(result, Err(CommandError::InvalidData(_))));
+        }
+    }
+
+    /// A segment of `data/with_time.gpx`, selected: 80 trackpoints at 20 km/h.
+    fn timed() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let id = load(&mut fx, "data/with_time.gpx");
+        select_file(&mut fx, id);
+        (fx, id)
+    }
+
+    fn times(seg: &TrackSegment) -> Vec<i64> {
+        seg.iter().map(|p| p.time.unwrap()).collect()
+    }
+
+    #[test]
+    fn test_route_gives_times_to_the_new_points() {
+        let (mut fx, id) = timed();
+        let seg = segment(&fx, id, 0, 0);
+        let (n, before) = (seg.len(), times(seg));
+        let duration = before[n - 1] - before[0];
+
+        // replace the points 20..40 by the straight line between them, with 5 points
+        let (a, b) = (seg[20].coordinates, seg[39].coordinates);
+        let at = |t: f64| (a.lng + t * (b.lng - a.lng), a.lat + t * (b.lat - a.lat));
+        let positions: Vec<_> = (0..5).map(|i| at(i as f64 / 4.0)).collect();
+        let lng: Vec<_> = positions.iter().map(|p| p.0).collect();
+        let lat: Vec<_> = positions.iter().map(|p| p.1).collect();
+        route(20, 40, &lng, &lat, &[0.0; 5])
+            .apply(&mut fx.state())
+            .unwrap();
+
+        let seg = segment(&fx, id, 0, 0);
+        assert_eq!(seg.len(), n - 15);
+        let after = times(seg);
+        assert!(after.windows(2).all(|w| w[0] < w[1]), "{after:?}");
+        // the points before are untouched
+        assert_eq!(after[..20], before[..20]);
+        // the speed of the replaced part is the one of the segment: the duration of the segment
+        // is about the same as on the same distance
+        let stats = Statistics::compute(seg);
+        let speed = stats.global.moving_speed().unwrap();
+        assert!((speed - 20.0).abs() < 1.0, "{speed}");
+        assert!(after[after.len() - 1] - after[0] <= duration);
+    }
+
+    #[test]
+    fn test_route_between_anchors_that_stay_keeps_them_untouched() {
+        let (mut fx, id) = timed();
+        let seg = segment(&fx, id, 0, 0);
+        let (n, before) = (seg.len(), times(seg));
+        let (a, b) = (seg[20].clone(), seg[39].clone());
+        // 5 points on the line between the anchors 20 and 39, which are not replaced
+        let at = |t: f64| {
+            (
+                a.coordinates.lng + t * (b.coordinates.lng - a.coordinates.lng),
+                a.coordinates.lat + t * (b.coordinates.lat - a.coordinates.lat),
+            )
+        };
+        let positions: Vec<_> = (1..=5).map(|i| at(i as f64 / 6.0)).collect();
+        let lng: Vec<_> = positions.iter().map(|p| p.0).collect();
+        let lat: Vec<_> = positions.iter().map(|p| p.1).collect();
+        route(21, 39, &lng, &lat, &[0.0; 5])
+            .apply(&mut fx.state())
+            .unwrap();
+
+        let seg = segment(&fx, id, 0, 0);
+        assert_eq!(seg.len(), n - 18 + 5);
+        let after = times(seg);
+        assert!(after.windows(2).all(|w| w[0] < w[1]), "{after:?}");
+        // the anchors keep their coordinates and times, and what is before them
+        assert_eq!(after[..=20], before[..=20]);
+        assert_eq!(seg[26].coordinates.lng, b.coordinates.lng);
+        assert_eq!(after[26], before[39]);
+        // and what comes after is unchanged as well
+        assert_eq!(after[27..], before[40..]);
+        let speed = Statistics::compute(seg).global.moving_speed().unwrap();
+        assert!((speed - 20.0).abs() < 1.0, "{speed}");
+    }
+
+    #[test]
+    fn test_route_appending_to_a_segment_with_times() {
+        let (mut fx, id) = timed();
+        let seg = segment(&fx, id, 0, 0);
+        let n = seg.len();
+        let last = seg[n - 1].clone();
+        // replace the last point and go 1 km further east
+        let lng = [last.coordinates.lng, last.coordinates.lng + 0.009];
+        let lat = [last.coordinates.lat; 2];
+        route(n as u32 - 1, n as u32, &lng, &lat, &[0.0; 2])
+            .apply(&mut fx.state())
+            .unwrap();
+        let seg = segment(&fx, id, 0, 0);
+        assert_eq!(seg.len(), n + 1);
+        // the replaced point is reached at the speed of the segment: about at its time
+        assert!((seg[n - 1].time.unwrap() - last.time.unwrap()).abs() < 1000);
+        let (a, b) = (seg[n - 1].time.unwrap(), seg[n].time.unwrap());
+        // the new point is reached at about 20 km/h
+        let km = distance(seg[n - 1].coordinates, seg[n].coordinates);
+        let seconds = (b - a) as f64 / 1000.0;
+        let expected = 3600.0 * km / 20.0;
+        assert!(
+            (seconds - expected).abs() < 0.1 * expected,
+            "{seconds} {expected}"
+        );
+    }
+
+    #[test]
+    fn test_route_does_not_invent_times() {
+        let mut fx = Fixture::default();
+        let id = load(&mut fx, "data/simple.gpx");
+        select_file(&mut fx, id);
+        assert!(segment(&fx, id, 0, 0).iter().all(|p| p.time.is_none()));
+        route(0, 2, &[1.0, 2.0], &[3.0, 4.0], &[5.0, 6.0])
+            .apply(&mut fx.state())
+            .unwrap();
+        assert!(segment(&fx, id, 0, 0).iter().all(|p| p.time.is_none()));
+    }
+}
@@ -0,0 +1,339 @@
+use std::rc::Rc;
+
+use crate::{
+    Apply, CommandError, File, State, Track, TrackSegment, Waypoints, copy_segment, copy_track,
+    copy_waypoint,
+};
+
+use super::route::find_target;
+
+/// What is cut in two where the trackpoint is.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum SplitType {
+    /// The file becomes two files, which both have the waypoints (copies, in the second one).
+    Files,
+    /// The track becomes two tracks.
+    Tracks,
+    /// The segment becomes two segments.
+    Segments,
+}
+
+/// Cuts the file, the track or the segment of the trackpoint `at` of the selection (see
+/// `RoutingBuffer`) in two, there: the trackpoint is the last one of the first part and the first
+/// one of the second part.
+///
+/// The first part keeps the ids of what is cut, the second one has new ids, as the elements that
+/// come after the trackpoint (the following segments of the track, the following tracks of the
+/// file), which are moved to it. When the file is cut, the new file comes right after it. The
+/// selection does not change.
+#[derive(Debug)]
+pub struct Split {
+    pub at: u32,
+    pub split_type: SplitType,
+}
+
+impl Apply for Split {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        let at = self.at as usize;
+        let target = find_target(state, at, at)?.ok_or(CommandError::NothingToDo)?;
+        let location = target.location;
+        let (file_id, trk, seg, index) =
+            (location.file_id, location.trk, location.seg, target.start);
+        let mut file = (*state.files[&file_id]).clone();
+        if index >= file.trk[trk].trkseg[seg].len() {
+            return Err(CommandError::InvalidData(
+                "trackpoint out of the segment".into(),
+            ));
+        }
+
+        let track = file.trk[trk].clone();
+        let segment = &track.trkseg[seg];
+        let (first, second) = (keep_up_to(segment, index), keep_from(segment, index));
+        // the track is cut: what is before the segment, and its first part, then the second part
+        // and what is after it
+        let split_track = || {
+            let mut first_track = track.clone();
+            first_track.trkseg.truncate(seg);
+            first_track.trkseg.push(first.clone());
+            let mut second_track = Track {
+                id: Default::default(),
+                trkseg: vec![second.clone()],
+                ..track.clone()
+            };
+            second_track
+                .trkseg
+                .extend(track.trkseg[seg + 1..].iter().map(copy_segment));
+            (first_track, second_track)
+        };
+
+        match self.split_type {
+            SplitType::Segments => {
+                file.trk[trk].trkseg.splice(seg..=seg, [first, second]);
+            }
+            SplitType::Tracks => {
+                let (first_track, second_track) = split_track();
+                file.trk.splice(trk..=trk, [first_track, second_track]);
+            }
+            SplitType::Files => {
+                let (first_track, second_track) = split_track();
+                let mut second_file = File {
+                    id: Default::default(),
+                    trk: vec![second_track],
+                    wpt: Waypoints::default(),
+                    ..file.clone()
+                };
+                second_file
+                    .trk
+                    .extend(file.trk[trk + 1..].iter().map(copy_track));
+                second_file
+                    .wpt
+                    .insert_at(0, file.wpt.iter().map(copy_waypoint).collect());
+
+                file.trk.truncate(trk);
+                file.trk.push(first_track);
+                let position = state.order.0.iter().position(|id| *id == file_id);
+                state.order.0.insert(
+                    position.map_or(state.order.0.len(), |p| p + 1),
+                    second_file.id,
+                );
+                state.files.insert(second_file.id, Rc::new(second_file));
+            }
+        }
+        state.files.insert(file_id, Rc::new(file));
+        Ok(())
+    }
+}
+
+/// The trackpoints of the segment up to `index` (included), in the same segment.
+fn keep_up_to(segment: &TrackSegment, index: usize) -> TrackSegment {
+    let mut part = segment.clone();
+    let len = part.len();
+    part.splice(index + 1, len, vec![]);
+    part.rev_id = Default::default();
+    part
+}
+
+/// The trackpoints of the segment from `index` (included), in a new segment.
+fn keep_from(segment: &TrackSegment, index: usize) -> TrackSegment {
+    let mut part = copy_segment(segment);
+    part.splice(0, index, vec![]);
+    part.rev_id = Default::default();
+    part
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{FileId, Load, Selection, TrackSegmentId, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        (fx, id)
+    }
+
+    fn split(at: u32, split_type: SplitType) -> Split {
+        Split { at, split_type }
+    }
+
+    fn lngs(segment: &TrackSegment) -> Vec<f64> {
+        segment.iter().map(|p| p.coordinates.lng).collect()
+    }
+
+    fn path(file: &File) -> Vec<f64> {
+        file.trk
+            .iter()
+            .flat_map(|t| &t.trkseg)
+            .flat_map(lngs)
+            .collect()
+    }
+
+    /// The index in the selection of the trackpoint `local` of the segment `seg` of the track `trk`.
+    fn index(file: &File, trk: usize, seg: usize, local: usize) -> u32 {
+        let before: usize = file
+            .trk
+            .iter()
+            .enumerate()
+            .flat_map(|(t, track)| {
+                track
+                    .trkseg
+                    .iter()
+                    .enumerate()
+                    .map(move |(s, segment)| ((t, s), segment.len()))
+            })
+            .take_while(|((t, s), _)| (*t, *s) != (trk, seg))
+            .map(|(_, len)| len)
+            .sum();
+        (before + local) as u32
+    }
+
+    /// A segment with enough trackpoints, and its position.
+    fn long_segment(file: &File) -> (usize, usize) {
+        file.trk
+            .iter()
+            .enumerate()
+            .flat_map(|(t, track)| (0..track.trkseg.len()).map(move |s| (t, s)))
+            .find(|(t, s)| file.trk[*t].trkseg[*s].len() > 4)
+            .unwrap()
+    }
+
+    #[test]
+    fn test_split_segments() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].clone();
+        let (trk, seg) = long_segment(&before);
+        let original = &before.trk[trk].trkseg[seg];
+        let len = original.len();
+
+        split(index(&before, trk, seg, 2), SplitType::Segments)
+            .apply(&mut fx.state())
+            .unwrap();
+
+        let after = &fx.files[&id];
+        assert_eq!(after.trk.len(), before.trk.len());
+        let segments = &after.trk[trk].trkseg;
+        assert_eq!(segments.len(), before.trk[trk].trkseg.len() + 1);
+        let (a, b) = (&segments[seg], &segments[seg + 1]);
+        // the point is the end of the first part and the start of the second
+        assert_eq!(lngs(a), lngs(original)[..=2]);
+        assert_eq!(lngs(b), lngs(original)[2..]);
+        assert_eq!(a.len() + b.len(), len + 1);
+        // the first part keeps the id, the second one is new
+        assert_eq!(a.id, original.id);
+        assert_ne!(b.id, original.id);
+        assert_ne!(a.rev_id, original.rev_id);
+        // the ends are anchors
+        assert_eq!(a[a.len() - 1].anchor, Some(0));
+        assert_eq!(b[0].anchor, Some(0));
+        // the rest of the file is untouched
+        for (i, segment) in before.trk[trk].trkseg.iter().enumerate() {
+            if i != seg {
+                let moved = if i > seg { i + 1 } else { i };
+                assert_eq!(segments[moved].rev_id, segment.rev_id);
+            }
+        }
+    }
+
+    #[test]
+    fn test_split_tracks() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].clone();
+        let (trk, seg) = long_segment(&before);
+
+        split(index(&before, trk, seg, 3), SplitType::Tracks)
+            .apply(&mut fx.state())
+            .unwrap();
+
+        let after = &fx.files[&id];
+        assert_eq!(after.trk.len(), before.trk.len() + 1);
+        let (a, b) = (&after.trk[trk], &after.trk[trk + 1]);
+        assert_eq!(a.id, before.trk[trk].id);
+        assert_ne!(b.id, a.id);
+        // the segments before are in the first track, the ones after in the second one
+        assert_eq!(a.trkseg.len(), seg + 1);
+        assert_eq!(b.trkseg.len(), before.trk[trk].trkseg.len() - seg);
+        // the segments before are the same ones, with the same trackpoints
+        for (kept, original) in a.trkseg[..seg].iter().zip(&before.trk[trk].trkseg[..seg]) {
+            assert_eq!((kept.id, kept.rev_id), (original.id, original.rev_id));
+            let chunks = |segment: &TrackSegment| -> Vec<_> {
+                segment.chunks().iter().map(|chunk| chunk.id).collect()
+            };
+            assert_eq!(chunks(kept), chunks(original));
+        }
+        // new ids for everything that moved, so that they are unique
+        let ids: HashSet<TrackSegmentId> = after
+            .trk
+            .iter()
+            .flat_map(|t| t.trkseg.iter().map(|s| s.id))
+            .collect();
+        assert_eq!(
+            ids.len(),
+            after.trk.iter().map(|t| t.trkseg.len()).sum::<usize>()
+        );
+        // the path goes on, with the point twice
+        let mut expected = path(&before);
+        let at = index(&before, trk, seg, 3) as usize;
+        expected.insert(at, expected[at]);
+        assert_eq!(path(after), expected);
+        // the info of the track is the same
+        assert_eq!(a.info, b.info);
+    }
+
+    #[test]
+    fn test_split_files() {
+        let (mut fx, id) = loaded();
+        let mut file = (*fx.files[&id]).clone();
+        let wpt = crate::Waypoint {
+            name: Some("w".into()),
+            ..Default::default()
+        };
+        file.wpt.insert_at(0, vec![wpt.clone()]);
+        fx.files.insert(id, Rc::new(file));
+        let before = fx.files[&id].clone();
+        let (trk, seg) = long_segment(&before);
+        let at = index(&before, trk, seg, 1);
+
+        split(at, SplitType::Files).apply(&mut fx.state()).unwrap();
+
+        assert_eq!(fx.files.len(), 2);
+        let second_id = fx.order.0[1];
+        assert_eq!(fx.order.0[0], id);
+        assert_ne!(second_id, id);
+        let (a, b) = (&fx.files[&id], &fx.files[&second_id]);
+        // the first file stops at the point, the second one starts there
+        let all = path(&before);
+        assert_eq!(path(a), all[..=at as usize]);
+        assert_eq!(path(b), all[at as usize..]);
+        assert_eq!(a.info, b.info);
+        // each has the waypoints, the copy has its own ids
+        assert_eq!(a.wpt.len(), 1);
+        assert_eq!(b.wpt.len(), 1);
+        assert_ne!(a.wpt[0].id, b.wpt[0].id);
+        assert_eq!(b.wpt[0].name, wpt.name);
+        // nothing is shared by id between the two
+        let ids = |f: &File| -> HashSet<_> {
+            f.trk
+                .iter()
+                .flat_map(|t| std::iter::once(t.id.0).chain(t.trkseg.iter().map(|s| s.id.0)))
+                .collect()
+        };
+        assert!(ids(a).is_disjoint(&ids(b)));
+        // the selection is the same
+        assert!(matches!(&fx.selection, Selection::File { file_ids } if file_ids.contains(&id)));
+    }
+
+    #[test]
+    fn test_invalid_or_nothing() {
+        let (mut fx, id) = loaded();
+        let before = fx.files[&id].clone();
+        let total = path(&before).len() as u32;
+        assert!(matches!(
+            split(total + 5, SplitType::Segments).apply(&mut fx.state()),
+            Err(CommandError::InvalidData(_))
+        ));
+        // after the last trackpoint: appending, not a trackpoint
+        assert!(matches!(
+            split(total, SplitType::Segments).apply(&mut fx.state()),
+            Err(CommandError::InvalidData(_))
+        ));
+        fx.selection = Selection::Empty;
+        assert_eq!(
+            split(0, SplitType::Files).apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        );
+        assert!(Rc::ptr_eq(&fx.files[&id], &before));
+    }
+}
@@ -0,0 +1,193 @@
+use crate::{
+    Apply, CommandError, State, TrackSegment, artificial_segment_times, changed_segment_times,
+    update_segments,
+};
+
+/// How the timestamps of the selection are set.
+#[derive(Debug, Clone, Copy)]
+pub enum TimeKind {
+    /// Starts at `Time::start_time`. The trackpoints that have timestamps keep their durations
+    /// multiplied by `ratio`, and the ones that have none follow the previous one at `speed`
+    /// (km/h).
+    Change { speed: f64, ratio: f64 },
+    /// Makes timestamps up for the whole selection, which lasts `total_time` seconds: the longer
+    /// and the steeper an interval, the more time it takes.
+    Artificial { total_time: f64 },
+}
+
+/// Sets the timestamps of the selected segments, one after the other: each one goes on from the
+/// end of the previous one, the first one starts at `start_time` (in milliseconds).
+#[derive(Debug)]
+pub struct Time {
+    pub start_time: i64,
+    pub kind: TimeKind,
+}
+
+impl Apply for Time {
+    fn apply(self, state: &mut State) -> Result<(), CommandError> {
+        match self.kind {
+            TimeKind::Change { speed, ratio } => {
+                if !(speed.is_finite() && speed > 0.0 && ratio.is_finite() && ratio > 0.0) {
+                    return Err(CommandError::InvalidData(format!(
+                        "speed {speed} and ratio {ratio} should be positive"
+                    )));
+                }
+            }
+            TimeKind::Artificial { total_time } => {
+                if !(total_time.is_finite() && total_time >= 0.0) {
+                    return Err(CommandError::InvalidData(format!(
+                        "total time {total_time} should not be negative"
+                    )));
+                }
+            }
+        }
+
+        let locations = state
+            .selection
+            .segment_locations(state.files, &state.order.0);
+        let segments: Vec<&TrackSegment> = locations
+            .iter()
+            .map(|l| &state.files[&l.file_id].trk[l.trk].trkseg[l.seg])
+            .collect();
+        if segments.iter().all(|segment| segment.is_empty()) {
+            return Err(CommandError::NothingToDo);
+        }
+
+        let times = match self.kind {
+            TimeKind::Change { speed, ratio } => {
+                changed_segment_times(&segments, self.start_time, speed, ratio)
+            }
+            TimeKind::Artificial { total_time } => {
+                artificial_segment_times(&segments, self.start_time, total_time)
+            }
+        };
+
+        update_segments(state, &locations, |i, segment| {
+            let times = &times[i];
+            segment.update_all(|j, pt| pt.time = times.get(j).copied().flatten());
+        });
+        Ok(())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::collections::HashSet;
+
+    use crate::{FileId, Load, Selection, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded(path: &str) -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read(path).unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        fx.selection = Selection::File {
+            file_ids: HashSet::from([id]),
+        };
+        (fx, id)
+    }
+
+    fn all_times(fx: &Fixture, id: FileId) -> Vec<Option<i64>> {
+        fx.files[&id]
+            .trk
+            .iter()
+            .flat_map(|trk| {
+                trk.trkseg
+                    .iter()
+                    .flat_map(|seg| seg.iter().map(|pt| pt.time))
+            })
+            .collect()
+    }
+
+    #[test]
+    fn test_artificial_timestamps_last_the_total_time() {
+        let (mut fx, id) = loaded("data/with_tracks_and_segments.gpx");
+
+        Time {
+            start_time: 1_000_000,
+            kind: TimeKind::Artificial { total_time: 3600.0 },
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        let times: Vec<i64> = all_times(&fx, id).into_iter().map(Option::unwrap).collect();
+        assert_eq!(times[0], 1_000_000);
+        assert!(times.windows(2).all(|w| w[0] <= w[1]));
+        assert!((times.last().unwrap() - 1_000_000 - 3_600_000).abs() <= times.len() as i64);
+    }
+
+    #[test]
+    fn test_change_starts_at_the_start_time_and_follows_the_speed() {
+        let (mut fx, id) = loaded("data/simple.gpx");
+        Time {
+            start_time: 5_000,
+            kind: TimeKind::Change {
+                speed: 10.0,
+                ratio: 1.0,
+            },
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        let times: Vec<i64> = all_times(&fx, id).into_iter().map(Option::unwrap).collect();
+        assert_eq!(times[0], 5_000);
+        assert!(times.windows(2).all(|w| w[0] <= w[1]));
+        assert!(times.last() > times.first());
+    }
+
+    #[test]
+    fn test_change_shifts_existing_timestamps_and_scales_them() {
+        let (mut fx, id) = loaded("data/with_time.gpx");
+        let before: Vec<i64> = all_times(&fx, id).into_iter().map(Option::unwrap).collect();
+
+        Time {
+            start_time: 0,
+            kind: TimeKind::Change {
+                speed: 10.0,
+                ratio: 2.0,
+            },
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+
+        let after: Vec<i64> = all_times(&fx, id).into_iter().map(Option::unwrap).collect();
+        assert_eq!(after[0], 0);
+        let (d_before, d_after) = (before[1] - before[0], after[1] - after[0]);
+        assert!((d_after - 2 * d_before).abs() <= 1);
+    }
+
+    #[test]
+    fn test_invalid_input_and_empty_selection() {
+        let (mut fx, id) = loaded("data/simple.gpx");
+        let before = all_times(&fx, id);
+        assert!(matches!(
+            Time {
+                start_time: 0,
+                kind: TimeKind::Change {
+                    speed: 0.0,
+                    ratio: 1.0
+                }
+            }
+            .apply(&mut fx.state()),
+            Err(CommandError::InvalidData(_))
+        ));
+        assert_eq!(all_times(&fx, id), before);
+
+        fx.selection = Selection::Empty;
+        assert!(matches!(
+            Time {
+                start_time: 0,
+                kind: TimeKind::Artificial { total_time: 10.0 }
+            }
+            .apply(&mut fx.state()),
+            Err(CommandError::NothingToDo)
+        ));
+    }
+}
@@ -0,0 +1,156 @@
+use std::collections::{HashMap, HashSet};
+
+use crate::{
+    FileId, FileWaypointsRevisionId, StackEntry as Files, TrackSegmentId, TrackSegmentRevisionId,
+};
+
+/// Coordinates buffers, as flat `[lng, lat, lng, lat, ...]` arrays so that they can be handed
+/// to the UI without per-point calls: one per track segment (its trackpoints) and one per file
+/// (its waypoints). A buffer is only rebuilt when the revision of its segment (or the waypoints
+/// of its file) changes, so editing a segment does not touch the buffers of the others.
+#[derive(Debug, Default)]
+pub struct CoordinatesCache {
+    segments: HashMap<TrackSegmentId, (TrackSegmentRevisionId, Vec<f64>)>,
+    waypoints: HashMap<FileId, (FileWaypointsRevisionId, Vec<f64>)>,
+}
+
+impl CoordinatesCache {
+    pub fn update(&mut self, files: Option<&Files>) {
+        let mut segments = HashSet::new();
+        let mut waypoints = HashSet::new();
+        for file in files.into_iter().flat_map(|files| files.values()) {
+            waypoints.insert(file.id);
+            if self
+                .waypoints
+                .get(&file.id)
+                .is_none_or(|(r, _)| *r != file.wpt.rev_id)
+            {
+                let mut coordinates = Vec::new();
+                for wpt in file.wpt.iter() {
+                    coordinates.extend([wpt.coordinates.lng, wpt.coordinates.lat]);
+                }
+                self.waypoints
+                    .insert(file.id, (file.wpt.rev_id, coordinates));
+            }
+            for seg in file.trk.iter().flat_map(|trk| &trk.trkseg) {
+                segments.insert(seg.id);
+                if self
+                    .segments
+                    .get(&seg.id)
+                    .is_none_or(|(r, _)| *r != seg.rev_id)
+                {
+                    let mut coordinates = Vec::with_capacity(seg.len() * 2);
+                    for trkpt in seg.iter() {
+                        coordinates.extend([trkpt.coordinates.lng, trkpt.coordinates.lat]);
+                    }
+                    self.segments.insert(seg.id, (seg.rev_id, coordinates));
+                }
+            }
+        }
+        self.segments.retain(|id, _| segments.contains(id));
+        self.waypoints.retain(|id, _| waypoints.contains(id));
+    }
+
+    /// Coordinates of the trackpoints of a segment, empty if it does not exist.
+    pub fn segment(&self, id: &TrackSegmentId) -> &[f64] {
+        self.segments.get(id).map_or(&[], |(_, c)| c)
+    }
+
+    /// Coordinates of the waypoints of a file, empty if it does not exist.
+    pub fn waypoints(&self, id: &FileId) -> &[f64] {
+        self.waypoints.get(id).map_or(&[], |(_, c)| c)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::{Apply, LngLat, Load, Waypoint, WaypointChunk, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let id = fx.order.0[0];
+        (fx, id)
+    }
+
+    #[test]
+    fn test_segment_buffers_match_trackpoints() {
+        let (fx, id) = loaded();
+        let mut cache = CoordinatesCache::default();
+        cache.update(Some(&fx.files));
+        for seg in fx.files[&id].trk.iter().flat_map(|t| &t.trkseg) {
+            let buffer = cache.segment(&seg.id);
+            assert_eq!(buffer.len(), seg.len() * 2);
+            for (i, p) in seg.iter().enumerate() {
+                assert_eq!(buffer[2 * i], p.coordinates.lng);
+                assert_eq!(buffer[2 * i + 1], p.coordinates.lat);
+            }
+        }
+        assert!(cache.segment(&TrackSegmentId::default()).is_empty());
+    }
+
+    #[test]
+    fn test_only_changed_buffers_are_rebuilt_and_stale_ones_dropped() {
+        let (mut fx, id) = loaded();
+        let mut cache = CoordinatesCache::default();
+        cache.update(Some(&fx.files));
+        let ids: Vec<_> = fx.files[&id]
+            .trk
+            .iter()
+            .flat_map(|t| &t.trkseg)
+            .map(|s| s.id)
+            .collect();
+        assert!(ids.len() >= 2);
+        let ptr = |c: &CoordinatesCache, i: usize| c.segment(&ids[i]).as_ptr();
+        let (p0, p1) = (ptr(&cache, 0), ptr(&cache, 1));
+
+        let mut file = (*fx.files[&id]).clone();
+        let seg = &mut file.trk[0].trkseg[0];
+        seg.splice(0, 0, vec![Default::default()]);
+        seg.rev_id = Default::default();
+        let len = seg.len();
+        fx.files.insert(id, Rc::new(file));
+        cache.update(Some(&fx.files));
+        assert_eq!(cache.segment(&ids[0]).len(), len * 2);
+        assert_ne!(ptr(&cache, 0), p0);
+        assert_eq!(ptr(&cache, 1), p1);
+
+        cache.update(None);
+        assert!(cache.segment(&ids[0]).is_empty());
+        assert!(cache.waypoints(&id).is_empty());
+    }
+
+    #[test]
+    fn test_waypoint_buffer() {
+        let (mut fx, id) = loaded();
+        let wpt = |lng, lat| Waypoint {
+            coordinates: LngLat { lng, lat },
+            ..Default::default()
+        };
+        let mut file = (*fx.files[&id]).clone();
+        file.wpt = crate::Waypoints::new([
+            WaypointChunk {
+                wpt: vec![wpt(1.0, 2.0)],
+                ..Default::default()
+            },
+            WaypointChunk {
+                wpt: vec![wpt(3.0, 4.0)],
+                ..Default::default()
+            },
+        ]);
+        fx.files.insert(id, Rc::new(file));
+        let mut cache = CoordinatesCache::default();
+        cache.update(Some(&fx.files));
+        assert_eq!(cache.waypoints(&id), [1.0, 2.0, 3.0, 4.0]);
+    }
+}
@@ -0,0 +1,155 @@
+use crate::{
+    File, FileId, FileWaypointsRevisionId, TrackId, TrackSegmentId, TrackSegmentRevisionId,
+    WaypointId,
+};
+
+/// What the UI needs to display a file: its name and the structure of its tracks and waypoints,
+/// with the ids that reference every element. Coordinates are not part of it, they are read
+/// from the buffers of the [`CoordinatesCache`](crate::CoordinatesCache) (the `i`-th waypoint
+/// of a file is the `i`-th coordinates pair of its waypoint buffer, same for the trackpoints of
+/// a segment).
+#[derive(Debug, Clone, PartialEq)]
+pub struct FileStructure {
+    pub id: FileId,
+    pub name: String,
+    pub desc: Option<String>,
+    pub tracks: Vec<TrackNode>,
+    pub waypoints: Vec<WaypointNode>,
+    /// Changes whenever the waypoints of the file (hence their buffer) change.
+    pub wpt_rev_id: FileWaypointsRevisionId,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct TrackNode {
+    pub id: TrackId,
+    pub name: Option<String>,
+    pub desc: Option<String>,
+    /// Style of the track, only when the file defines it.
+    pub color: Option<String>,
+    pub opacity: Option<f64>,
+    pub width: Option<f64>,
+    pub segments: Vec<SegmentNode>,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct SegmentNode {
+    pub id: TrackSegmentId,
+    /// Changes whenever the trackpoints of the segment (hence their buffer) change.
+    pub rev_id: TrackSegmentRevisionId,
+    pub len: usize,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct WaypointNode {
+    pub id: WaypointId,
+    pub name: Option<String>,
+    pub sym: Option<String>,
+}
+
+impl FileStructure {
+    pub fn new(file: &File) -> Self {
+        Self {
+            id: file.id,
+            name: file.info.name.clone(),
+            desc: file.info.desc.clone(),
+            tracks: file
+                .trk
+                .iter()
+                .map(|trk| TrackNode {
+                    id: trk.id,
+                    name: trk.info.name.clone(),
+                    desc: trk.info.desc.clone(),
+                    color: trk.info.color.clone(),
+                    opacity: trk.info.opacity,
+                    width: trk.info.width,
+                    segments: trk
+                        .trkseg
+                        .iter()
+                        .map(|seg| SegmentNode {
+                            id: seg.id,
+                            rev_id: seg.rev_id,
+                            len: seg.len(),
+                        })
+                        .collect(),
+                })
+                .collect(),
+            waypoints: file
+                .wpt
+                .iter()
+                .map(|wpt| WaypointNode {
+                    id: wpt.id,
+                    name: wpt.name.clone(),
+                    sym: wpt.sym.clone(),
+                })
+                .collect(),
+            wpt_rev_id: file.wpt.rev_id,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use crate::{Apply, Load, Waypoint, WaypointChunk, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    #[test]
+    fn test_structure_of_a_file() {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let file = &fx.files[&fx.order.0[0]];
+        let node = FileStructure::new(file);
+        assert_eq!(
+            (node.id, &node.name, &node.desc),
+            (file.id, &file.info.name, &file.info.desc)
+        );
+        assert_eq!(node.tracks.len(), file.trk.len());
+        for (n, t) in node.tracks.iter().zip(&file.trk) {
+            assert_eq!((n.id, &n.name, &n.desc), (t.id, &t.info.name, &t.info.desc));
+            assert_eq!(
+                (&n.color, n.opacity, n.width),
+                (&t.info.color, t.info.opacity, t.info.width)
+            );
+            assert_eq!(n.segments.len(), t.trkseg.len());
+            for (n, s) in n.segments.iter().zip(&t.trkseg) {
+                assert_eq!((n.id, n.rev_id, n.len), (s.id, s.rev_id, s.len()));
+            }
+        }
+    }
+
+    #[test]
+    fn test_waypoints_in_buffer_order_and_revision() {
+        let mut file = crate::File::default();
+        let wpt = |n: &str| Waypoint {
+            name: Some(n.to_string()),
+            ..Default::default()
+        };
+        let before = file.wpt.rev_id;
+        file.wpt = crate::Waypoints::new([
+            WaypointChunk {
+                wpt: vec![wpt("a"), wpt("b")],
+                ..Default::default()
+            },
+            WaypointChunk {
+                wpt: vec![wpt("c")],
+                ..Default::default()
+            },
+        ]);
+        let node = FileStructure::new(&file);
+        let names: Vec<_> = node
+            .waypoints
+            .iter()
+            .map(|w| w.name.clone().unwrap())
+            .collect();
+        assert_eq!(names, ["a", "b", "c"]);
+        assert_ne!(node.wpt_rev_id, before);
+        assert_eq!(node.wpt_rev_id, file.wpt.rev_id);
+    }
+}
@@ -0,0 +1,92 @@
+use std::collections::HashMap;
+
+use crate::{Diff, FileId, FileStructure, StackEntry as Files};
+
+/// The structure of each file, only recomputed for the files that changed according to the
+/// [`Diff`] of the stack.
+#[derive(Debug, Default)]
+pub struct FileStructureCache {
+    map: HashMap<FileId, FileStructure>,
+}
+
+impl FileStructureCache {
+    /// Brings the cache in line with `files`, given what changed since the last update.
+    pub fn update(&mut self, files: Option<&Files>, diff: Option<&Diff>) {
+        if let Some(diff) = diff {
+            for id in diff.removed.iter() {
+                self.map.remove(id);
+            }
+            for id in diff.added.iter().chain(&diff.modified) {
+                if let Some(file) = files.and_then(|files| files.get(id)) {
+                    self.map.insert(*id, FileStructure::new(file));
+                }
+            }
+        }
+    }
+
+    pub fn get(&self, id: &FileId) -> Option<&FileStructure> {
+        self.map.get(id)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::{Apply, Load, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    #[test]
+    fn test_only_files_of_the_diff_are_recomputed() {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        Load {
+            data: &data,
+            name: "file",
+        }
+        .apply(&mut fx.state())
+        .unwrap();
+        let (a, b) = (fx.order.0[0], fx.order.0[1]);
+
+        let mut cache = FileStructureCache::default();
+        cache.update(
+            Some(&fx.files),
+            Some(&Diff {
+                added: vec![a, b],
+                ..Default::default()
+            }),
+        );
+        let before = cache.get(&b).unwrap() as *const FileStructure;
+
+        let mut file = (*fx.files[&a]).clone();
+        file.info.name = "renamed".into();
+        fx.files.insert(a, Rc::new(file));
+        cache.update(
+            Some(&fx.files),
+            Some(&Diff {
+                modified: vec![a],
+                ..Default::default()
+            }),
+        );
+        assert_eq!(cache.get(&a).unwrap().name, "renamed");
+        assert!(std::ptr::eq(cache.get(&b).unwrap(), before));
+
+        fx.files.remove(&b);
+        cache.update(
+            Some(&fx.files),
+            Some(&Diff {
+                removed: vec![b],
+                ..Default::default()
+            }),
+        );
+        assert!(cache.get(&b).is_none());
+        assert!(cache.get(&a).is_some());
+    }
+}
@@ -0,0 +1,13 @@
+mod coordinates_cache;
+mod file_structure;
+mod file_structure_cache;
+mod routing_buffer;
+mod statistics_buffer;
+mod statistics_cache;
+
+pub use coordinates_cache::*;
+pub use file_structure::*;
+pub use file_structure_cache::*;
+pub use routing_buffer::*;
+pub use statistics_buffer::*;
+pub use statistics_cache::*;
@@ -0,0 +1,162 @@
+use crate::{FileId, Selection, StackEntry, TrackSegmentId, TrackSegmentRevisionId};
+
+/// What the routing tool needs about the selected segments (see
+/// [`Selection::segment_locations`]): where their anchors are among their trackpoints.
+///
+/// Trackpoints are numbered like in the [`crate::StatisticsBuffer`], over all the selected
+/// segments one after the other, except that the segments that are not covered by the routing
+/// tool (waypoints) are left out.
+#[derive(Debug, Default)]
+pub struct RoutingBuffer {
+    /// The index of each anchor in the selection, in order. The first and last trackpoints of a
+    /// segment always are anchors.
+    pub anchor_indices: Vec<u32>,
+    /// The lowest map zoom level at which each anchor is shown.
+    pub anchor_zooms: Vec<u8>,
+    /// Index in the selection of the first trackpoint of each selected segment that has some,
+    /// which tells which segment an anchor or a trackpoint belongs to.
+    pub segment_starts: Vec<u32>,
+    /// Id of each selected segment that has trackpoints, as `segment_starts`.
+    pub segment_ids: Vec<TrackSegmentId>,
+    /// Changes when the selected segments, or their trackpoints, change. Commands that refer to
+    /// trackpoints by their index in the selection carry it, to be refused if the selection is
+    /// not the one the indices were taken from anymore.
+    pub revision: u32,
+    /// What the revision stands for.
+    signature: Vec<(TrackSegmentId, TrackSegmentRevisionId)>,
+}
+
+impl RoutingBuffer {
+    pub fn update(&mut self, files: Option<&StackEntry>, selection: &Selection, order: &[FileId]) {
+        self.anchor_indices.clear();
+        self.anchor_zooms.clear();
+        self.segment_starts.clear();
+        self.segment_ids.clear();
+
+        let mut signature = vec![];
+        let mut index = 0;
+        for location in files
+            .map(|files| selection.segment_locations(files, order))
+            .unwrap_or_default()
+        {
+            let segment = &files.unwrap()[&location.file_id].trk[location.trk].trkseg[location.seg];
+            signature.push((segment.id, segment.rev_id));
+            if segment.is_empty() {
+                continue;
+            }
+            self.segment_starts.push(index as u32);
+            self.segment_ids.push(segment.id);
+            for trkpt in segment.iter() {
+                if let Some(zoom) = trkpt.anchor {
+                    self.anchor_indices.push(index as u32);
+                    self.anchor_zooms.push(zoom);
+                }
+                index += 1;
+            }
+        }
+
+        if signature != self.signature {
+            self.revision = self.revision.wrapping_add(1);
+            self.signature = signature;
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::{collections::HashSet, rc::Rc};
+
+    use crate::parse;
+
+    use super::*;
+
+    fn loaded() -> (StackEntry, FileId) {
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        let file = parse(&data, &mut Default::default()).unwrap();
+        let id = file.id;
+        let mut files = StackEntry::default();
+        files.insert(id, Rc::new(file));
+        (files, id)
+    }
+
+    fn file_selection(id: FileId) -> Selection {
+        Selection::File {
+            file_ids: HashSet::from([id]),
+        }
+    }
+
+    #[test]
+    fn test_anchors_and_starts_follow_the_selected_segments() {
+        let (files, id) = loaded();
+        let lengths: Vec<usize> = files[&id]
+            .trk
+            .iter()
+            .flat_map(|trk| trk.trkseg.iter().map(|segment| segment.len()))
+            .collect();
+        let mut buffer = RoutingBuffer::default();
+        buffer.update(Some(&files), &file_selection(id), &[id]);
+
+        // an empty segment has no start
+        assert_eq!(buffer.segment_ids.len(), buffer.segment_starts.len());
+        let mut start = 0;
+        let expected: Vec<u32> = lengths
+            .iter()
+            .filter(|len| **len > 0)
+            .map(|len| {
+                start += len;
+                (start - len) as u32
+            })
+            .collect();
+        assert_eq!(buffer.segment_starts, expected);
+        // the ends of the segments are always anchors, shown at every zoom level
+        assert_eq!(buffer.anchor_indices.len(), buffer.anchor_zooms.len());
+        assert!(buffer.anchor_indices.windows(2).all(|w| w[0] < w[1]));
+        let total: usize = lengths.iter().sum();
+        let ends = expected
+            .iter()
+            .copied()
+            .chain(expected.iter().skip(1).map(|start| start - 1))
+            .chain([total as u32 - 1]);
+        for end in ends {
+            let position = buffer.anchor_indices.iter().position(|i| *i == end);
+            assert_eq!(position.map(|p| buffer.anchor_zooms[p]), Some(0), "{end}");
+        }
+    }
+
+    #[test]
+    fn test_nothing_without_segments() {
+        let (files, id) = loaded();
+        let mut buffer = RoutingBuffer::default();
+        buffer.update(Some(&files), &Selection::Empty, &[id]);
+        assert!(buffer.anchor_indices.is_empty() && buffer.segment_starts.is_empty());
+        // waypoints are not covered by the routing tool
+        buffer.update(Some(&files), &Selection::Waypoints { file_id: id }, &[id]);
+        assert!(buffer.anchor_indices.is_empty() && buffer.segment_starts.is_empty());
+        buffer.update(None, &file_selection(id), &[id]);
+        assert!(buffer.anchor_indices.is_empty() && buffer.segment_starts.is_empty());
+    }
+
+    #[test]
+    fn test_revision_changes_with_the_selected_segments() {
+        let (mut files, id) = loaded();
+        let mut buffer = RoutingBuffer::default();
+        buffer.update(Some(&files), &file_selection(id), &[id]);
+        let first = buffer.revision;
+
+        // the same segments: the indices still mean the same trackpoints
+        buffer.update(Some(&files), &file_selection(id), &[id]);
+        assert_eq!(buffer.revision, first);
+
+        // other trackpoints in the same segment
+        let mut file = (*files[&id]).clone();
+        file.trk[0].trkseg[0].rev_id = Default::default();
+        files.insert(id, Rc::new(file));
+        buffer.update(Some(&files), &file_selection(id), &[id]);
+        assert_ne!(buffer.revision, first);
+        let second = buffer.revision;
+
+        // another selection
+        buffer.update(Some(&files), &Selection::Empty, &[id]);
+        assert_ne!(buffer.revision, second);
+    }
+}
@@ -0,0 +1,693 @@
+use crate::{GlobalStatistics, Statistics, TrackSegment, sum_options};
+
+/// Value of the timestamps of the trackpoints that have none.
+pub const NO_TIME: i64 = i64::MIN;
+
+/// Flattened statistics of the selected segments, one entry per trackpoint, in selection order.
+///
+/// The distance, time, moving and elevation values are cumulative over the whole selection (the
+/// second segment continues where the first one ended), so the statistics of any range of
+/// trackpoints are the difference between its two ends: see [`StatisticsBuffer::slice`].
+/// Times are in milliseconds, distances in kilometers, speeds in km/h. Missing times are
+/// [`NO_TIME`], missing measures are NaN.
+///
+/// The optional values (`moving_distance`, `total_time`, `moving_time`, `speed`, `time`, `hr`,
+/// `cad`, `atemp`, `power`) are `None` when no trackpoint of the selection has one, and the OSM
+/// attributes are stored as [`Intervals`]. The cumulative ones can only be missing before the
+/// first trackpoint that has them, where they are 0.
+#[derive(Debug, Default)]
+pub struct StatisticsBuffer {
+    /// Statistics of the whole selection.
+    pub global: GlobalStatistics,
+    pub total_distance: Vec<f64>,
+    pub moving_distance: Option<Vec<f64>>,
+    pub total_time: Option<Vec<i64>>,
+    pub moving_time: Option<Vec<i64>>,
+    pub speed: Option<Vec<f64>>,
+    pub elevation_gain: Vec<f64>,
+    pub elevation_loss: Vec<f64>,
+    pub slope: Vec<f64>,
+    pub slope_segment_slope: Vec<f64>,
+    pub slope_segment_distance: Vec<f64>,
+    pub lng: Vec<f64>,
+    pub lat: Vec<f64>,
+    pub ele: Vec<f64>,
+    /// Timestamps, in milliseconds since the epoch.
+    pub time: Option<Vec<i64>>,
+    pub hr: Option<Vec<f64>>,
+    pub cad: Option<Vec<f64>>,
+    pub atemp: Option<Vec<f64>>,
+    pub power: Option<Vec<f64>>,
+    /// Surface of the trackpoints, see [`Intervals`].
+    pub surface: Intervals,
+    /// Highway of the trackpoints, as the surface.
+    pub highway: Intervals,
+    /// SAC hiking scale of the trackpoints, as the surface.
+    pub sac_scale: Intervals,
+    /// Mountain biking scale of the trackpoints, as the surface.
+    pub mtb_scale: Intervals,
+}
+
+/// A value per trackpoint that rarely changes from one trackpoint to the next, stored as the
+/// intervals of trackpoints that share it.
+///
+/// The values are 0 when unknown, else 1 + the code in the categories of the engine (so that it
+/// is never 0 for a known value). `starts[i]` is the index of the first trackpoint of the
+/// interval `i`, which ends where the next one starts, or at the last trackpoint for the last one.
+/// Both are empty when there are no trackpoints.
+#[derive(Debug, Default, PartialEq, Eq)]
+pub struct Intervals {
+    pub starts: Vec<u32>,
+    pub values: Vec<u8>,
+}
+
+impl Intervals {
+    fn clear(&mut self) {
+        self.starts.clear();
+        self.values.clear();
+    }
+
+    /// Adds the value of the trackpoint at `index`, the indices being pushed in order.
+    fn push(&mut self, index: usize, value: u8) {
+        if self.values.last() != Some(&value) {
+            self.starts.push(index as u32);
+            self.values.push(value);
+        }
+    }
+}
+
+/// 0 for an unknown value, else the code plus one. The categories hold at most 255 values, so it
+/// fits.
+fn unknown_or_next(code: Option<u8>) -> u8 {
+    code.and_then(|code| code.checked_add(1)).unwrap_or(0)
+}
+
+/// Adds the value of the trackpoint at `index` to an optional column, the indices being pushed in
+/// order. The column is created at the first present value, the previous trackpoints getting
+/// `missing`.
+fn push_optional<T: Copy>(column: &mut Option<Vec<T>>, index: usize, value: Option<T>, missing: T) {
+    match (column.as_mut(), value) {
+        (Some(column), value) => column.push(value.unwrap_or(missing)),
+        (None, Some(value)) => {
+            let mut new_column = vec![missing; index];
+            new_column.push(value);
+            *column = Some(new_column);
+        }
+        (None, None) => {}
+    }
+}
+
+impl StatisticsBuffer {
+    pub fn len(&self) -> usize {
+        self.total_distance.len()
+    }
+
+    pub fn is_empty(&self) -> bool {
+        self.total_distance.is_empty()
+    }
+
+    /// `selected`: the segments and their statistics, in order.
+    pub fn update(&mut self, selected: &[(&TrackSegment, &Statistics)]) {
+        self.global = GlobalStatistics::default();
+        self.total_distance.clear();
+        self.moving_distance = None;
+        self.total_time = None;
+        self.moving_time = None;
+        self.speed = None;
+        self.elevation_gain.clear();
+        self.elevation_loss.clear();
+        self.slope.clear();
+        self.slope_segment_slope.clear();
+        self.slope_segment_distance.clear();
+        self.lng.clear();
+        self.lat.clear();
+        self.ele.clear();
+        self.time = None;
+        self.hr = None;
+        self.cad = None;
+        self.atemp = None;
+        self.power = None;
+        self.surface.clear();
+        self.highway.clear();
+        self.sac_scale.clear();
+        self.mtb_scale.clear();
+
+        for (segment, stats) in selected {
+            for (trkpt, trkpt_stats) in segment.iter().zip(stats.local.iter()) {
+                let index = self.total_distance.len();
+                let cumul_stats = &self.global;
+                self.total_distance
+                    .push(cumul_stats.total_distance + trkpt_stats.total_distance);
+                push_optional(
+                    &mut self.moving_distance,
+                    index,
+                    sum_options(cumul_stats.moving_distance, trkpt_stats.moving_distance),
+                    0.0,
+                );
+                push_optional(
+                    &mut self.total_time,
+                    index,
+                    sum_options(cumul_stats.total_time, trkpt_stats.total_time),
+                    0,
+                );
+                push_optional(
+                    &mut self.moving_time,
+                    index,
+                    sum_options(cumul_stats.moving_time, trkpt_stats.moving_time),
+                    0,
+                );
+                push_optional(&mut self.speed, index, trkpt_stats.speed, f64::NAN);
+                self.elevation_gain
+                    .push(cumul_stats.elevation_gain + trkpt_stats.elevation_gain);
+                self.elevation_loss
+                    .push(cumul_stats.elevation_loss + trkpt_stats.elevation_loss);
+                self.slope.push(trkpt_stats.slope);
+                self.slope_segment_slope
+                    .push(trkpt_stats.slope_segment.slope);
+                self.slope_segment_distance
+                    .push(trkpt_stats.slope_segment.distance);
+                self.lng.push(trkpt.coordinates.lng);
+                self.lat.push(trkpt.coordinates.lat);
+                self.ele.push(trkpt.ele);
+                push_optional(&mut self.time, index, trkpt.time, NO_TIME);
+                push_optional(&mut self.hr, index, trkpt.hr.map(f64::from), f64::NAN);
+                push_optional(&mut self.cad, index, trkpt.cad.map(f64::from), f64::NAN);
+                push_optional(&mut self.atemp, index, trkpt.atemp.map(f64::from), f64::NAN);
+                push_optional(&mut self.power, index, trkpt.power.map(f64::from), f64::NAN);
+                self.surface.push(index, unknown_or_next(trkpt.surface));
+                self.highway.push(index, unknown_or_next(trkpt.highway));
+                self.sac_scale.push(index, unknown_or_next(trkpt.sac_scale));
+                self.mtb_scale.push(index, unknown_or_next(trkpt.mtb_scale));
+            }
+            self.global.merge(&stats.global);
+        }
+    }
+
+    /// Statistics of the trackpoints from `start` to `end` (both included) of the selection, for
+    /// example the part of an elevation profile the user dragged over. `None` if the range is
+    /// not inside the selection.
+    ///
+    /// It is done in constant time, from the cumulative values at both ends: the bounds and
+    /// the averages are the ones of the whole selection, they are not computed for the range.
+    pub fn slice(&self, start: usize, end: usize) -> Option<GlobalStatistics> {
+        if start > end || end >= self.len() {
+            return None;
+        }
+
+        let delta = |values: &[f64]| values[end] - values[start];
+        // the total time is the span of the timestamps, which is negative where they go backwards
+        let delta_time = |values: &[i64]| (values[end] - values[start]).max(0);
+        let time = |i: usize| {
+            let time = self.time.as_ref()?[i];
+            (time != NO_TIME).then_some(time)
+        };
+        Some(GlobalStatistics {
+            total_distance: delta(&self.total_distance),
+            moving_distance: self.moving_distance.as_deref().map(delta),
+            total_time: self.total_time.as_deref().map(delta_time),
+            moving_time: self.moving_time.as_deref().map(delta_time),
+            elevation_gain: delta(&self.elevation_gain),
+            elevation_loss: delta(&self.elevation_loss),
+            start_time: time(start),
+            end_time: time(end),
+            bounds: self.global.bounds,
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::parse;
+
+    use super::*;
+
+    fn computed(path: &str) -> (TrackSegment, Statistics) {
+        let data = std::fs::read(path).unwrap();
+        let file = parse(&data, &mut Default::default()).unwrap();
+        let segment = file.trk[0].trkseg[0].clone();
+        let stats = Statistics::compute(&segment);
+        (segment, stats)
+    }
+
+    /// The value of the trackpoint at `index`, 0 before the first interval.
+    fn value_at(intervals: &Intervals, index: usize) -> u8 {
+        match intervals
+            .starts
+            .partition_point(|start| *start as usize <= index)
+        {
+            0 => 0,
+            next => intervals.values[next - 1],
+        }
+    }
+
+    fn all_lengths(buffer: &StatisticsBuffer) -> Vec<usize> {
+        vec![
+            buffer.total_distance.len(),
+            buffer.elevation_gain.len(),
+            buffer.elevation_loss.len(),
+            buffer.slope.len(),
+            buffer.slope_segment_slope.len(),
+            buffer.slope_segment_distance.len(),
+            buffer.lng.len(),
+            buffer.lat.len(),
+            buffer.ele.len(),
+        ]
+    }
+
+    #[test]
+    fn test_empty() {
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[]);
+        assert!(buffer.is_empty());
+        assert!(buffer.speed.is_none());
+        assert_eq!(buffer.global.total_distance, 0.0);
+        assert!(buffer.slice(0, 0).is_none());
+    }
+
+    #[test]
+    fn test_single_segment_matches_local_stats() {
+        let (segment, s) = computed("data/simple.gpx");
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+
+        let n = s.local.len();
+        assert!(all_lengths(&buffer).iter().all(|len| *len == n));
+        assert_eq!(buffer.len(), n);
+        for (i, local) in s.local.iter().enumerate() {
+            assert_eq!(buffer.total_distance[i], local.total_distance);
+            assert_eq!(buffer.slope[i], local.slope);
+        }
+        // the trackpoints
+        for (i, trkpt) in segment.iter().enumerate() {
+            assert_eq!(buffer.lng[i], trkpt.coordinates.lng);
+            assert_eq!(buffer.lat[i], trkpt.coordinates.lat);
+            assert_eq!(buffer.ele[i], trkpt.ele);
+        }
+    }
+
+    #[test]
+    fn test_global_is_the_merge_of_the_segments() {
+        let (segment, s) = computed("data/simple.gpx");
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s), (&segment, &s)]);
+
+        let global = &buffer.global;
+        assert!((global.total_distance - 2.0 * s.global.total_distance).abs() < 1e-9);
+        assert!((global.elevation_gain - 2.0 * s.global.elevation_gain).abs() < 1e-9);
+        assert!((global.elevation_loss - 2.0 * s.global.elevation_loss).abs() < 1e-9);
+        // and it is the last cumulative value of the points
+        assert_eq!(
+            global.total_distance,
+            *buffer.total_distance.last().unwrap()
+        );
+
+        buffer.update(&[(&segment, &s)]);
+        assert_eq!(buffer.global.total_distance, s.global.total_distance);
+        buffer.update(&[]);
+        assert_eq!(buffer.global.total_distance, 0.0);
+    }
+
+    #[test]
+    fn test_distances_accumulate_over_segments() {
+        let (segment, s) = computed("data/simple.gpx");
+        let n = s.local.len();
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s), (&segment, &s)]);
+
+        assert_eq!(buffer.total_distance.len(), 2 * n);
+        // the second segment starts where the first one ended
+        assert_eq!(buffer.total_distance[n], s.global.total_distance);
+        assert!((buffer.total_distance[2 * n - 1] - 2.0 * s.global.total_distance).abs() < 1e-9);
+        assert!(buffer.total_distance.windows(2).all(|w| w[0] <= w[1]));
+        assert!((buffer.elevation_gain[2 * n - 1] - 2.0 * s.global.elevation_gain).abs() < 1e-9);
+    }
+
+    #[test]
+    fn test_total_time_accumulates_over_segments() {
+        let (segment, s) = computed("data/with_time.gpx");
+        let n = s.local.len();
+        let duration = s.global.total_time.unwrap();
+        assert!(duration > 0);
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s), (&segment, &s)]);
+
+        let total_time = buffer.total_time.as_ref().unwrap();
+        assert_eq!(total_time[n - 1], duration);
+        assert_eq!(total_time[n], duration);
+        assert_eq!(total_time[2 * n - 1], 2 * duration);
+        assert!(total_time.windows(2).all(|w| w[0] <= w[1]));
+        assert!(buffer.time.unwrap().iter().all(|t| *t != NO_TIME));
+    }
+
+    #[test]
+    fn test_absent_optional_values_have_no_buffer() {
+        let (segment, s) = computed("data/simple.gpx");
+        assert!(segment.iter().all(|trkpt| trkpt.time.is_none()));
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+        assert!(buffer.time.is_none());
+        assert!(buffer.hr.is_none());
+        assert!(buffer.cad.is_none());
+        assert!(buffer.atemp.is_none());
+        assert!(buffer.power.is_none());
+        assert_eq!(buffer.global.total_time, None);
+        assert_eq!(buffer.len(), s.local.len());
+        // they need times
+        assert!(buffer.speed.is_none());
+        assert!(buffer.moving_distance.is_none());
+        assert!(buffer.total_time.is_none());
+        assert!(buffer.moving_time.is_none());
+        // the slices do not need them
+        let slice = buffer.slice(0, 2).unwrap();
+        assert_eq!((slice.start_time, slice.end_time), (None, None));
+    }
+
+    #[test]
+    fn test_present_optional_values_have_one_entry_per_trackpoint() {
+        let (segment, s) = computed("data/with_time.gpx");
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+        assert_eq!(buffer.time.as_ref().unwrap().len(), buffer.len());
+        assert!(buffer.hr.is_none());
+
+        let data = std::fs::read("data/with_hr.gpx").unwrap();
+        let file = parse(&data, &mut Default::default()).unwrap();
+        let segment = file.trk[0].trkseg[0].clone();
+        let s = Statistics::compute(&segment);
+        buffer.update(&[(&segment, &s)]);
+        let hr = buffer.hr.as_ref().unwrap();
+        assert_eq!(hr.len(), buffer.len());
+        assert!(hr.iter().any(|v| !v.is_nan()));
+    }
+
+    #[test]
+    fn test_a_value_missing_for_some_trackpoints_is_a_sentinel() {
+        let (mut segment, _) = computed("data/with_time.gpx");
+        let n = segment.len();
+        let mut point = segment[1].clone();
+        point.time = None;
+        point.hr = Some(120);
+        segment.splice(1, 2, vec![point]);
+        let s = Statistics::compute(&segment);
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+        let time = buffer.time.as_ref().unwrap();
+        assert_eq!(time.len(), n);
+        assert_eq!(time[1], NO_TIME);
+        assert_ne!(time[0], NO_TIME);
+        // the first trackpoint has no heart rate: it is filled once the first one is found
+        let hr = buffer.hr.as_ref().unwrap();
+        assert_eq!(hr.len(), n);
+        assert_eq!(hr[1], 120.0);
+        assert!(hr[0].is_nan() && hr[2].is_nan());
+        assert!(buffer.cad.is_none());
+    }
+
+    #[test]
+    fn test_cumulative_values_are_zero_before_the_first_one() {
+        let (mut segment, _) = computed("data/with_time.gpx");
+        let n = segment.len();
+        let mut first = segment[0].clone();
+        first.time = None;
+        segment.splice(0, 1, vec![first]);
+        let s = Statistics::compute(&segment);
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+
+        let total_time = buffer.total_time.as_ref().unwrap();
+        assert_eq!(total_time.len(), n);
+        assert_eq!(total_time[0], 0);
+        assert_eq!(total_time[n - 1], s.global.total_time.unwrap());
+        assert!(total_time.windows(2).all(|w| w[0] <= w[1]));
+        // so a slice that starts on the first trackpoint is right
+        assert_eq!(
+            buffer.slice(0, n - 1).unwrap().total_time,
+            s.global.total_time
+        );
+    }
+
+    #[test]
+    fn test_surface_and_highway_intervals() {
+        let (segment, s) = computed("data/with_highway.gpx");
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+
+        // 0 for the trackpoints that have none, else the code of the engine plus one
+        let surface = &buffer.surface;
+        assert_eq!(surface.starts, [0, 2, 3]);
+        assert_eq!(surface.values, [1, 0, 2]);
+        let highway = &buffer.highway;
+        assert_eq!(
+            (&highway.starts[..], &highway.values[..]),
+            (&[0, 2, 3, 4][..], &[1, 0, 2, 0][..])
+        );
+        let sac_scale = &buffer.sac_scale;
+        assert_eq!(
+            (&sac_scale.starts[..], &sac_scale.values[..]),
+            (&[0, 3, 4][..], &[0, 1, 2][..])
+        );
+        let mtb_scale = &buffer.mtb_scale;
+        assert_eq!(
+            (&mtb_scale.starts[..], &mtb_scale.values[..]),
+            (&[0, 3][..], &[0, 1][..])
+        );
+        assert!(all_lengths(&buffer).iter().all(|len| *len == 5));
+
+        // and they can be looked up
+        let values: Vec<u8> = (0..6).map(|i| value_at(&buffer.surface, i)).collect();
+        assert_eq!(values, [1, 1, 0, 2, 2, 2]);
+    }
+
+    #[test]
+    fn test_intervals_merge_equal_neighbours_across_segments() {
+        let (mut segment, _) = computed("data/simple.gpx");
+        let points: Vec<_> = segment
+            .iter()
+            .map(|trkpt| {
+                let mut trkpt = trkpt.clone();
+                trkpt.surface = Some(4);
+                trkpt
+            })
+            .collect();
+        segment.splice(0, points.len(), points);
+        let s = Statistics::compute(&segment);
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s), (&segment, &s)]);
+        // one interval for the two segments
+        assert_eq!(buffer.surface.starts, [0]);
+        assert_eq!(buffer.surface.values, [5]);
+        // and a single one of unknown values when nothing is known
+        assert_eq!(buffer.highway.values, [0]);
+    }
+
+    #[test]
+    fn test_codes_of_the_trackpoints_are_used_as_they_are() {
+        let (mut segment, _) = computed("data/simple.gpx");
+        let mut point = segment[0].clone();
+        point.surface = Some(7);
+        point.highway = Some(254);
+        point.sac_scale = Some(0);
+        point.mtb_scale = Some(3);
+        segment.splice(0, 1, vec![point]);
+        let s = Statistics::compute(&segment);
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+        let at = |i: usize| {
+            (
+                value_at(&buffer.surface, i),
+                value_at(&buffer.highway, i),
+                value_at(&buffer.sac_scale, i),
+                value_at(&buffer.mtb_scale, i),
+            )
+        };
+        assert_eq!(at(0), (8, 255, 1, 4));
+        assert_eq!(at(1), (0, 0, 0, 0));
+    }
+
+    #[test]
+    fn test_unknown_intervals_without_surface_and_highway() {
+        let (segment, s) = computed("data/simple.gpx");
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+        // a single interval of unknown values
+        assert_eq!(buffer.surface.starts, [0]);
+        assert_eq!(buffer.surface.values, [0]);
+        assert_eq!(buffer.highway.starts, [0]);
+        assert_eq!(buffer.highway.values, [0]);
+        assert_eq!(buffer.sac_scale.values, [0]);
+        assert_eq!(buffer.mtb_scale.values, [0]);
+        // and they are reset by the next update
+        buffer.update(&[]);
+        assert_eq!(buffer.surface, Intervals::default());
+        assert_eq!(buffer.highway, Intervals::default());
+        assert_eq!(buffer.sac_scale, Intervals::default());
+        assert_eq!(buffer.mtb_scale, Intervals::default());
+        assert_eq!(value_at(&buffer.surface, 0), 0);
+    }
+
+    #[test]
+    fn test_update_replaces_previous_content() {
+        let (segment, s) = computed("data/simple.gpx");
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+        buffer.update(&[(&segment, &s)]);
+        assert_eq!(buffer.total_distance.len(), s.local.len());
+        assert!(all_lengths(&buffer).iter().all(|len| *len == s.local.len()));
+        buffer.update(&[]);
+        assert!(buffer.total_distance.is_empty());
+        assert!(all_lengths(&buffer).iter().all(|len| *len == 0));
+    }
+
+    #[test]
+    fn test_slice_of_the_whole_selection_is_the_global_statistics() {
+        let (segment, s) = computed("data/with_time.gpx");
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s), (&segment, &s)]);
+
+        let slice = buffer.slice(0, buffer.len() - 1).unwrap();
+        let global = &buffer.global;
+        assert!((slice.total_distance - global.total_distance).abs() < 1e-9);
+        assert!((slice.elevation_gain - global.elevation_gain).abs() < 1e-9);
+        assert!((slice.elevation_loss - global.elevation_loss).abs() < 1e-9);
+        assert_eq!(slice.total_time, global.total_time);
+        assert_eq!(slice.moving_time, global.moving_time);
+        assert_eq!(slice.start_time, global.start_time);
+        assert_eq!(slice.end_time, global.end_time);
+    }
+
+    #[test]
+    fn test_slices_of_corrupt_timestamps_are_never_negative_nor_infinite() {
+        let (mut segment, _) = computed("data/with_time.gpx");
+        let n = segment.len();
+        assert!(n > 40);
+        // timestamps that go back, then forward, and some that are missing
+        let times: Vec<_> = segment.iter().map(|p| p.time.unwrap()).collect();
+        segment.update_all(|i, pt| {
+            pt.time = match i {
+                10..=19 => Some(times[29 - i]),
+                20..=24 => None,
+                25..=29 => Some(times[0] - 1_000 * i as i64),
+                _ => pt.time,
+            };
+        });
+        let stats = Statistics::compute(&segment);
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &stats)]);
+
+        for start in 0..n {
+            for end in start..n {
+                let slice = buffer.slice(start, end).unwrap();
+                for time in [slice.total_time, slice.moving_time].into_iter().flatten() {
+                    assert!(time >= 0, "time of {start}..={end}");
+                }
+                for speed in [slice.total_speed(), slice.moving_speed()]
+                    .into_iter()
+                    .flatten()
+                {
+                    assert!(
+                        speed.is_finite() && speed >= 0.0,
+                        "speed of {start}..={end}"
+                    );
+                }
+            }
+        }
+    }
+
+    #[test]
+    fn test_slice_of_a_range() {
+        let (segment, s) = computed("data/with_time.gpx");
+        let n = s.local.len();
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+
+        let (start, end) = (n / 4, n / 2);
+        let slice = buffer.slice(start, end).unwrap();
+        assert!(
+            (slice.total_distance - (buffer.total_distance[end] - buffer.total_distance[start]))
+                .abs()
+                < 1e-12
+        );
+        assert_eq!(
+            slice.total_time,
+            Some(
+                buffer.total_time.as_ref().unwrap()[end]
+                    - buffer.total_time.as_ref().unwrap()[start]
+            )
+        );
+        assert_eq!(
+            slice.moving_time,
+            Some(
+                buffer.moving_time.as_ref().unwrap()[end]
+                    - buffer.moving_time.as_ref().unwrap()[start]
+            )
+        );
+        assert_eq!(slice.start_time, Some(buffer.time.as_ref().unwrap()[start]));
+        assert_eq!(slice.end_time, Some(buffer.time.as_ref().unwrap()[end]));
+        assert!(slice.total_distance < buffer.global.total_distance);
+        assert!(slice.total_speed().is_some());
+
+        // a single point has nothing between its ends
+        let point = buffer.slice(start, start).unwrap();
+        assert_eq!(point.total_distance, 0.0);
+        assert_eq!(point.total_time, Some(0));
+    }
+
+    #[test]
+    fn test_slice_keeps_the_bounds_of_the_selection() {
+        let data = std::fs::read("data/with_hr.gpx").unwrap();
+        let file = parse(&data, &mut Default::default()).unwrap();
+        let segment = file.trk[0].trkseg[0].clone();
+        let s = Statistics::compute(&segment);
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+
+        let slice = buffer.slice(1, 3).unwrap();
+        let (global, bounds) = (&buffer.global, &slice.bounds);
+        assert_eq!(
+            (bounds.sw.lng, bounds.sw.lat),
+            (global.bounds.sw.lng, global.bounds.sw.lat)
+        );
+        assert_eq!(
+            (bounds.ne.lng, bounds.ne.lat),
+            (global.bounds.ne.lng, global.bounds.ne.lat)
+        );
+    }
+
+    #[test]
+    fn test_durations_are_not_limited_to_24_days() {
+        // 30 days of recording, in milliseconds
+        let (segment, mut s) = computed("data/with_time.gpx");
+        let month = 30 * 24 * 3_600_000_i64;
+        s.global.total_time = Some(month);
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s), (&segment, &s)]);
+        assert_eq!(buffer.global.total_time, Some(2 * month));
+        assert!(2 * month > i64::from(i32::MAX));
+    }
+
+    #[test]
+    fn test_slice_across_segments() {
+        let (segment, s) = computed("data/simple.gpx");
+        let n = s.local.len();
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s), (&segment, &s)]);
+
+        // from the middle of the first segment to the middle of the second one
+        let slice = buffer.slice(n / 2, n + n / 2).unwrap();
+        let expected = buffer.total_distance[n + n / 2] - buffer.total_distance[n / 2];
+        assert!((slice.total_distance - expected).abs() < 1e-9);
+        assert_eq!(slice.total_time, None);
+    }
+
+    #[test]
+    fn test_slice_out_of_range() {
+        let (segment, s) = computed("data/simple.gpx");
+        let mut buffer = StatisticsBuffer::default();
+        buffer.update(&[(&segment, &s)]);
+        let n = buffer.len();
+        assert!(buffer.slice(0, n).is_none());
+        assert!(buffer.slice(n, n).is_none());
+        assert!(buffer.slice(5, 4).is_none());
+        assert!(buffer.slice(0, n - 1).is_some());
+    }
+}
@@ -0,0 +1,299 @@
+use std::collections::{HashMap, HashSet, hash_map::Entry};
+
+use crate::{
+    File, FileId, GlobalStatistics, Selection, StackEntry, Statistics, Track, TrackSegment,
+    TrackSegmentRevisionId,
+};
+
+/// A segment and its statistics.
+pub type SelectedSegment<'a> = (&'a TrackSegment, &'a Statistics);
+
+#[derive(Debug, Default)]
+pub struct StatisticsCache {
+    map: HashMap<TrackSegmentRevisionId, Statistics>,
+}
+
+impl StatisticsCache {
+    pub fn update(&mut self, state: Option<&StackEntry>) {
+        let mut stale: HashSet<TrackSegmentRevisionId> = self.map.keys().copied().collect();
+        if let Some(state) = state {
+            for file in state.values() {
+                for trk in file.trk.iter() {
+                    for trkseg in trk.trkseg.iter() {
+                        match self.map.entry(trkseg.rev_id) {
+                            Entry::Occupied(_) => {
+                                stale.remove(&trkseg.rev_id);
+                            }
+                            Entry::Vacant(e) => {
+                                e.insert(Statistics::compute(trkseg));
+                            }
+                        }
+                    }
+                }
+            }
+        }
+        for id in stale.iter() {
+            self.map.remove(id);
+        }
+    }
+
+    /// Statistics of the segments of the selection.
+    pub fn get<'a>(
+        &'a self,
+        state: Option<&'a StackEntry>,
+        selection: &Selection,
+    ) -> Vec<&'a Statistics> {
+        self.selected(state, selection, &[])
+            .into_iter()
+            .map(|(_, stats)| stats)
+            .collect()
+    }
+
+    /// The segments of the selection with their statistics. The segments of several selected
+    /// files follow `order` (the files missing from it come last).
+    pub fn selected<'a>(
+        &'a self,
+        state: Option<&'a StackEntry>,
+        selection: &Selection,
+        order: &[FileId],
+    ) -> Vec<SelectedSegment<'a>> {
+        let mut selected = vec![];
+        if let Some(state) = state {
+            match selection {
+                Selection::Empty => (),
+                Selection::File { file_ids } => {
+                    let ordered = order
+                        .iter()
+                        .filter(|id| file_ids.contains(id))
+                        .chain(file_ids.iter().filter(|id| !order.contains(id)));
+                    for id in ordered {
+                        if let Some(file) = state.get(id) {
+                            self.add_file_stats(file, &mut selected);
+                        }
+                    }
+                }
+                Selection::Track { file_id, trk_ids } => {
+                    if let Some(file) = state.get(file_id) {
+                        for trk in file.trk.iter() {
+                            if trk_ids.contains(&trk.id) {
+                                self.add_track_stats(trk, &mut selected);
+                            }
+                        }
+                    }
+                }
+                Selection::TrackSegment {
+                    file_id,
+                    trk_id,
+                    trkseg_ids,
+                } => {
+                    if let Some(file) = state.get(file_id) {
+                        for trk in file.trk.iter() {
+                            if *trk_id == trk.id {
+                                for trkseg in trk.trkseg.iter() {
+                                    if trkseg_ids.contains(&trkseg.id) {
+                                        self.add_segment_stats(trkseg, &mut selected);
+                                    }
+                                }
+                                break;
+                            }
+                        }
+                    }
+                }
+                Selection::Waypoints { file_id } => {
+                    if let Some(file) = state.get(file_id) {
+                        self.add_file_stats(file, &mut selected);
+                    }
+                }
+                Selection::Waypoint {
+                    file_id,
+                    wpt_ids: _,
+                } => {
+                    if let Some(file) = state.get(file_id) {
+                        self.add_file_stats(file, &mut selected);
+                    }
+                }
+            }
+        }
+        selected
+    }
+
+    /// Global statistics of a file: its segments merged, in order.
+    pub fn file_global(&self, file: &File) -> GlobalStatistics {
+        let mut selected = vec![];
+        self.add_file_stats(file, &mut selected);
+        let mut global = GlobalStatistics::default();
+        for (_, stats) in selected {
+            global.merge(&stats.global);
+        }
+        global
+    }
+
+    fn add_file_stats<'a>(&'a self, file: &'a File, selected: &mut Vec<SelectedSegment<'a>>) {
+        for trk in file.trk.iter() {
+            self.add_track_stats(trk, selected);
+        }
+    }
+
+    fn add_track_stats<'a>(&'a self, trk: &'a Track, selected: &mut Vec<SelectedSegment<'a>>) {
+        for trkseg in trk.trkseg.iter() {
+            self.add_segment_stats(trkseg, selected);
+        }
+    }
+
+    fn add_segment_stats<'a>(
+        &'a self,
+        trkseg: &'a TrackSegment,
+        selected: &mut Vec<SelectedSegment<'a>>,
+    ) {
+        if let Some(stats) = self.map.get(&trkseg.rev_id) {
+            selected.push((trkseg, stats));
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::{collections::HashSet, rc::Rc};
+
+    use crate::{FileId, parse};
+
+    use super::*;
+
+    fn state(path: &str) -> (StackEntry, Rc<File>) {
+        let data = std::fs::read(path).unwrap();
+        let file = Rc::new(parse(&data, &mut Default::default()).unwrap());
+        let mut state = StackEntry::default();
+        state.insert(file.id, file.clone());
+        (state, file)
+    }
+
+    fn file_selection(id: FileId) -> Selection {
+        Selection::File {
+            file_ids: HashSet::from([id]),
+        }
+    }
+
+    #[test]
+    fn test_update_and_select_file() {
+        let (state, file) = state("data/with_tracks_and_segments.gpx");
+        let nb_segments: usize = file.trk.iter().map(|t| t.trkseg.len()).sum();
+        let mut cache = StatisticsCache::default();
+        cache.update(Some(&state));
+        assert_eq!(cache.map.len(), nb_segments);
+
+        assert_eq!(
+            cache.get(Some(&state), &file_selection(file.id)).len(),
+            nb_segments
+        );
+        assert!(cache.get(Some(&state), &Selection::Empty).is_empty());
+        assert!(cache.get(None, &file_selection(file.id)).is_empty());
+        // unknown file
+        assert!(
+            cache
+                .get(Some(&state), &file_selection(FileId::default()))
+                .is_empty()
+        );
+    }
+
+    #[test]
+    fn test_select_track_and_segment() {
+        let (state, file) = state("data/with_tracks_and_segments.gpx");
+        let mut cache = StatisticsCache::default();
+        cache.update(Some(&state));
+
+        let trk = &file.trk[0];
+        let selection = Selection::Track {
+            file_id: file.id,
+            trk_ids: HashSet::from([trk.id]),
+        };
+        assert_eq!(cache.get(Some(&state), &selection).len(), trk.trkseg.len());
+
+        let trkseg = &trk.trkseg[1];
+        let selection = Selection::TrackSegment {
+            file_id: file.id,
+            trk_id: trk.id,
+            trkseg_ids: HashSet::from([trkseg.id]),
+        };
+        let stats = cache.get(Some(&state), &selection);
+        assert_eq!(stats.len(), 1);
+        assert_eq!(stats[0].local.len(), trkseg.len());
+
+        // a segment id under the wrong track selects nothing
+        let selection = Selection::TrackSegment {
+            file_id: file.id,
+            trk_id: file.trk[1].id,
+            trkseg_ids: HashSet::from([trkseg.id]),
+        };
+        assert!(cache.get(Some(&state), &selection).is_empty());
+    }
+
+    #[test]
+    fn test_unchanged_segments_are_not_recomputed() {
+        let (state, file) = state("data/simple.gpx");
+        let mut cache = StatisticsCache::default();
+        cache.update(Some(&state));
+        let before: *const Statistics = cache.get(Some(&state), &file_selection(file.id))[0];
+
+        // a new snapshot of the file that shares its segments (same revision ids)
+        let mut next = StackEntry::default();
+        let renamed = {
+            let mut f = (*file).clone();
+            f.info.name = "other".to_string();
+            Rc::new(f)
+        };
+        next.insert(renamed.id, renamed);
+        cache.update(Some(&next));
+        let after: *const Statistics = cache.get(Some(&next), &file_selection(file.id))[0];
+        assert!(std::ptr::eq(before, after));
+    }
+
+    #[test]
+    fn test_modified_segment_is_recomputed_and_stale_entries_dropped() {
+        let (state, file) = state("data/simple.gpx");
+        let mut cache = StatisticsCache::default();
+        cache.update(Some(&state));
+        let old_rev = file.trk[0].trkseg[0].rev_id;
+        assert!(cache.map.contains_key(&old_rev));
+
+        let mut f = (*file).clone();
+        f.trk[0].trkseg[0].rev_id = Default::default();
+        let new_rev = f.trk[0].trkseg[0].rev_id;
+        let mut next = StackEntry::default();
+        next.insert(f.id, Rc::new(f));
+        cache.update(Some(&next));
+        assert!(cache.map.contains_key(&new_rev));
+        assert!(!cache.map.contains_key(&old_rev));
+
+        cache.update(None);
+        assert!(cache.map.is_empty());
+    }
+
+    #[test]
+    fn test_segments_of_several_files_follow_the_given_order() {
+        let (mut state, first) = state("data/simple.gpx");
+        let (other, second) = {
+            let data = std::fs::read("data/with_time.gpx").unwrap();
+            let file = Rc::new(parse(&data, &mut Default::default()).unwrap());
+            (file.clone(), file)
+        };
+        state.insert(other.id, other);
+        let mut cache = StatisticsCache::default();
+        cache.update(Some(&state));
+        let selection = Selection::File {
+            file_ids: HashSet::from([first.id, second.id]),
+        };
+
+        let ids = |order: &[FileId]| -> Vec<_> {
+            cache
+                .selected(Some(&state), &selection, order)
+                .iter()
+                .map(|(segment, _)| segment.id)
+                .collect()
+        };
+        let (a, b) = (first.trk[0].trkseg[0].id, second.trk[0].trkseg[0].id);
+        assert_eq!(ids(&[first.id, second.id]), vec![a, b]);
+        assert_eq!(ids(&[second.id, first.id]), vec![b, a]);
+        // the files that are not in the order come last
+        assert_eq!(ids(&[second.id]), vec![b, a]);
+    }
+}
@@ -0,0 +1,372 @@
+mod action;
+mod command;
+mod derived;
+mod outcome;
+mod state;
+
+pub use action::*;
+pub use command::*;
+pub use derived::*;
+pub use outcome::*;
+pub use state::*;
+
+use crate::{
+    ExportOptions, FileId, GlobalStatistics, Restored, Snapshot, TrackSegmentId, Trackpoint,
+    TrackpointCategories, Waypoint, WaypointId, reduction_distances, write,
+};
+
+#[derive(Debug, Default)]
+pub struct Engine {
+    stack: Stack,
+    selection: Selection,
+    order: FileOrder,
+    statistics_cache: StatisticsCache,
+    coordinates_cache: CoordinatesCache,
+    structure_cache: FileStructureCache,
+    statistics_buffer: StatisticsBuffer,
+    routing_buffer: RoutingBuffer,
+    categories: TrackpointCategories,
+    clipboard: Option<Clipboard>,
+    /// What the tests of the last action read, see `Engine::run`.
+    #[cfg(test)]
+    last: Outcome,
+}
+
+impl Engine {
+    pub fn statistics(&self) -> &StatisticsBuffer {
+        &self.statistics_buffer
+    }
+
+    /// The anchors of the routing tool among the trackpoints of the selection.
+    pub fn routing(&self) -> &RoutingBuffer {
+        &self.routing_buffer
+    }
+
+    /// The names of the surfaces and highways that the trackpoints refer to by code.
+    pub fn categories(&self) -> &TrackpointCategories {
+        &self.categories
+    }
+
+    /// Files in display order.
+    pub fn order(&self) -> &[FileId] {
+        &self.order.0
+    }
+
+    /// Name, tracks, segments and waypoints (with their ids) of a file.
+    pub fn file_structure(&self, id: &FileId) -> Option<&FileStructure> {
+        self.structure_cache.get(id)
+    }
+
+    /// Global statistics (distance, time, elevation, bounds...) of a file.
+    pub fn file_statistics(&self, id: &FileId) -> Option<GlobalStatistics> {
+        let file = self.stack.current()?.get(id)?;
+        Some(self.statistics_cache.file_global(file))
+    }
+
+    /// What was copied or cut and is waiting to be pasted.
+    pub fn clipboard(&self) -> Option<&Clipboard> {
+        self.clipboard.as_ref()
+    }
+
+    /// Whether the clipboard can be pasted with the current selection.
+    pub fn can_paste(&self) -> bool {
+        self.clipboard
+            .as_ref()
+            .is_some_and(|clipboard| clipboard.can_paste(&self.selection))
+    }
+
+    /// A waypoint of a file, with all its data. `None` if it does not exist.
+    pub fn waypoint(&self, file_id: &FileId, id: &WaypointId) -> Option<&Waypoint> {
+        self.stack
+            .current()?
+            .get(file_id)?
+            .wpt
+            .iter()
+            .find(|wpt| wpt.id == *id)
+    }
+
+    /// A trackpoint of a segment of a file. `None` if it does not exist.
+    pub fn trackpoint(
+        &self,
+        file_id: &FileId,
+        segment_id: &TrackSegmentId,
+        index: usize,
+    ) -> Option<&Trackpoint> {
+        let segment = self
+            .stack
+            .current()?
+            .get(file_id)?
+            .trk
+            .iter()
+            .flat_map(|trk| &trk.trkseg)
+            .find(|seg| seg.id == *segment_id)?;
+        (index < segment.len()).then(|| &segment[index])
+    }
+
+    /// For each trackpoint of the selection (numbered as in the statistics), the tolerance up to
+    /// which `Reduce` keeps it, see [`reduction_distances`].
+    pub fn reduction_distances(&self) -> Vec<f64> {
+        let Some(files) = self.stack.current() else {
+            return vec![];
+        };
+        self.selection
+            .segment_locations(files, &self.order.0)
+            .iter()
+            .flat_map(|location| {
+                reduction_distances(
+                    &files[&location.file_id].trk[location.trk].trkseg[location.seg],
+                )
+            })
+            .collect()
+    }
+
+    /// What there is to keep of the engine, see [`crate::Persister`].
+    pub fn snapshot(&self) -> Snapshot {
+        Snapshot {
+            files: self.stack.current().cloned().unwrap_or_default(),
+            order: self.order.0.clone(),
+            categories: self.categories.clone(),
+        }
+    }
+
+    /// Puts files in an engine that has none, typically the ones read from the storage. They are
+    /// the state to start from: they cannot be undone. The files are reported as added, and the
+    /// order, the selection and the clipboard as changed.
+    pub fn restore(&mut self, restored: Restored) -> Outcome {
+        let files: StackEntry = restored
+            .files
+            .into_iter()
+            .map(|file| (file.id, file))
+            .collect();
+        self.categories = restored.categories;
+        self.order = FileOrder(restored.order);
+        self.selection = Selection::Empty;
+        self.clipboard = None;
+        let mut diff = Some(Diff {
+            added: files.keys().copied().collect(),
+            ..Default::default()
+        });
+        self.stack = Stack::restored(files);
+        self.refresh(diff.as_ref());
+        sort_diff(&mut diff, &self.order.0);
+        let outcome = Outcome {
+            changed: true,
+            diff,
+            order_changed: true,
+            selection_changed: true,
+            clipboard_changed: true,
+            error: None,
+        };
+        #[cfg(test)]
+        {
+            self.last = outcome.clone();
+        }
+        outcome
+    }
+
+    /// A file as GPX (UTF-8), `None` if it does not exist.
+    pub fn export(&self, id: &FileId, options: ExportOptions) -> Option<Vec<u8>> {
+        let file = self.stack.current()?.get(id)?;
+        Some(write(file, &self.categories, options))
+    }
+
+    /// The data that the given files have, which the options of `export` can leave out.
+    pub fn exportable_data(&self, ids: &[FileId]) -> ExportOptions {
+        let Some(files) = self.stack.current() else {
+            return ExportOptions::NONE;
+        };
+        ids.iter()
+            .filter_map(|id| files.get(id))
+            .fold(ExportOptions::NONE, |data, file| {
+                data.union(file.exportable_data())
+            })
+    }
+
+    /// Whether there is something to undo.
+    pub fn can_undo(&self) -> bool {
+        self.stack.can_undo()
+    }
+
+    /// Whether there is something to redo.
+    pub fn can_redo(&self) -> bool {
+        self.stack.can_redo()
+    }
+
+    /// Currently selected elements.
+    pub fn selection(&self) -> &Selection {
+        &self.selection
+    }
+
+    /// Coordinates (`[lng, lat, ...]`) of the trackpoints of a segment.
+    pub fn segment_coordinates(&self, id: &TrackSegmentId) -> &[f64] {
+        self.coordinates_cache.segment(id)
+    }
+
+    /// Coordinates (`[lng, lat, ...]`) of the waypoints of a file.
+    pub fn waypoint_coordinates(&self, id: &FileId) -> &[f64] {
+        self.coordinates_cache.waypoints(id)
+    }
+
+    /// Single entry point for every action coming from the frontend. Says what it changed.
+    pub fn execute(&mut self, action: Action) -> Outcome {
+        let selection_before = self.selection.clone();
+        let order_before = self.order.0.clone();
+        let clipboard_before = self.clipboard.clone();
+        let is_edit = matches!(action, Action::Edit(_));
+        let mut error = None;
+        // the files change iff there is a diff, but selection and order actions have none
+        let mut diff = match action {
+            Action::Edit(command) => self.edit(command).unwrap_or_else(|err| {
+                error = Some(err);
+                None
+            }),
+            Action::Undo => self.stack.undo(),
+            Action::Redo => self.stack.redo(),
+            Action::Select { selection, mode } => {
+                self.selection.select(self.stack.current(), selection, mode);
+                None
+            }
+            Action::SelectAll => {
+                if let Some(files) = self.stack.current() {
+                    self.selection.select_all(files, &self.order.0);
+                }
+                None
+            }
+            Action::ArrowSelect { down, add } => {
+                if let Some(files) = self.stack.current() {
+                    self.selection
+                        .select_neighbour(files, &self.order.0, down, add);
+                }
+                None
+            }
+            Action::Copy => {
+                self.copy(false);
+                None
+            }
+            Action::Cut => {
+                self.copy(true);
+                None
+            }
+            Action::Reorder { file_ids, index } => {
+                self.order.move_files(&file_ids, index);
+                None
+            }
+        };
+        let changed = diff.is_some()
+            || self.selection != selection_before
+            || self.order.0 != order_before
+            || self.clipboard != clipboard_before;
+        if is_edit && !changed && error.is_none() {
+            error = Some(CommandError::NothingToDo);
+        }
+        if changed {
+            self.refresh(diff.as_ref());
+            sort_diff(&mut diff, &self.order.0);
+        }
+        // after the refresh, which also syncs the order and selection with the files (undo, redo)
+        let outcome = Outcome {
+            changed,
+            diff,
+            order_changed: self.order.0 != order_before,
+            selection_changed: self.selection != selection_before,
+            clipboard_changed: self.clipboard != clipboard_before,
+            error,
+        };
+        #[cfg(test)]
+        {
+            self.last = outcome.clone();
+        }
+        outcome
+    }
+
+    /// Puts the selection in the clipboard, if there is one.
+    fn copy(&mut self, cut: bool) {
+        if let Some(files) = self.stack.current()
+            && let Some(clipboard) = Clipboard::new(&self.selection, files, &self.order.0, cut)
+        {
+            self.clipboard = Some(clipboard);
+        }
+    }
+
+    fn edit(&mut self, command: Command) -> Result<Option<Diff>, CommandError> {
+        self.stack.create_and_push_next(|files| {
+            let mut state = State {
+                categories: &mut self.categories,
+                files,
+                selection: &mut self.selection,
+                order: &mut self.order,
+                clipboard: &mut self.clipboard,
+            };
+            command.apply(&mut state)
+        })
+    }
+
+    /// Brings everything derived from the files back in line with the current stack entry.
+    fn refresh(&mut self, diff: Option<&Diff>) {
+        let current = self.stack.current();
+        match current {
+            Some(files) => {
+                // files coming back after an undo/redo are added at the end of the order
+                self.order.sync(files);
+                self.selection.retain_existing(files);
+            }
+            None => {
+                self.order.0.clear();
+                self.selection = Selection::Empty;
+            }
+        }
+        self.statistics_cache.update(current);
+        self.coordinates_cache.update(current);
+        self.structure_cache.update(current, diff);
+        self.routing_buffer
+            .update(current, &self.selection, &self.order.0);
+        self.statistics_buffer
+            .update(
+                &self
+                    .statistics_cache
+                    .selected(current, &self.selection, &self.order.0),
+            );
+    }
+}
+
+/// Puts the files of a diff in the order of the files (the stack does not know it), so that
+/// whatever is done with them one after the other, like giving them colors, follows it.
+fn sort_diff(diff: &mut Option<Diff>, order: &[FileId]) {
+    let position = |id: &FileId| order.iter().position(|other| other == id);
+    if let Some(diff) = diff {
+        diff.added.sort_by_key(position);
+        diff.modified.sort_by_key(position);
+    }
+}
+
+#[cfg(test)]
+impl Engine {
+    /// Executes an action and tells whether it changed anything. What it did is kept for the
+    /// accessors below, which the tests read right after.
+    pub(crate) fn run(&mut self, action: Action) -> bool {
+        self.execute(action).changed
+    }
+
+    pub(crate) fn last_diff(&self) -> Option<&Diff> {
+        self.last.diff.as_ref()
+    }
+
+    pub(crate) fn last_error(&self) -> Option<&CommandError> {
+        self.last.error.as_ref()
+    }
+
+    pub(crate) fn order_changed(&self) -> bool {
+        self.last.order_changed
+    }
+
+    pub(crate) fn selection_changed(&self) -> bool {
+        self.last.selection_changed
+    }
+
+    pub(crate) fn clipboard_changed(&self) -> bool {
+        self.last.clipboard_changed
+    }
+}
+
+#[cfg(test)]
+mod tests;
Author	SHA1	Message	Date
vcoppe	dc36de2a48	import and export of routes, ref #192	2026-10-09 09:26:38 +02:00
vcoppe	da9abbae5e	refactoring and tests	2026-10-09 08:58:00 +02:00
vcoppe	3bb553d6b5	remove unused fields	2026-10-08 21:19:53 +02:00
vcoppe	83b76bb838	fix link fields	2026-10-08 21:13:44 +02:00
vcoppe	42a55e6759	progress	2026-10-08 21:04:29 +02:00
vcoppe	b085a1d476	cleaning	2026-10-08 19:04:46 +02:00
vcoppe	840e943626	update readme	2026-10-08 18:41:27 +02:00
vcoppe	16e2e0f679	remove todo	2026-10-08 18:37:46 +02:00
vcoppe	0f9557ea82	remove gpx js package	2026-10-08 18:37:40 +02:00
vcoppe	67a4c090bd	progress	2026-10-08 18:34:19 +02:00
vcoppe	606a0e974a	export	2026-10-08 09:24:15 +02:00
vcoppe	e8c4eb92f9	handle corrupt time data	2026-10-08 08:59:53 +02:00
vcoppe	f0851086c0	fix reactivity	2026-10-08 08:47:14 +02:00
vcoppe	bec1ce4c9b	reduce	2026-10-08 08:36:29 +02:00
vcoppe	b29c4cdb08	fix bounds for waypoints	2026-10-08 08:15:22 +02:00
vcoppe	63ba8596a7	time tool	2026-10-08 08:12:44 +02:00
vcoppe	82d2f79da0	progress	2026-10-07 22:20:40 +02:00
vcoppe	f642d60f42	merge	2026-10-07 19:57:27 +02:00
vcoppe	24b877c4ee	split	2026-10-07 19:38:21 +02:00
vcoppe	e07ec97e12	crop	2026-10-07 18:54:00 +02:00
vcoppe	290f4d8c44	reverse	2026-10-07 18:45:56 +02:00
vcoppe	a48608840f	reverse	2026-10-07 18:36:00 +02:00
vcoppe	df07892e76	refactoring	2026-10-07 18:22:30 +02:00
vcoppe	594dd8979a	routing	2026-10-07 17:58:17 +02:00
vcoppe	29850c1c8f	speed fix	2026-10-07 09:35:27 +02:00
vcoppe	adbe4a2693	copy on wasm side to avoid any data corruption	2026-10-07 08:57:37 +02:00
vcoppe	b843a18441	reduce data exchanges across boundary	2026-10-07 08:45:50 +02:00
vcoppe	da8a9e3d84	handle self closing elements	2026-10-04 22:01:23 +02:00
vcoppe	c6bd5b06e8	clean tool	2026-10-04 20:38:46 +02:00
vcoppe	c04367dd86	progress	2026-10-04 19:19:53 +02:00
vcoppe	5e2f506120	progress	2026-10-04 19:14:41 +02:00
vcoppe	c536e6247b	progress	2026-10-04 17:29:57 +02:00
vcoppe	594d714b7f	small fix	2026-10-04 17:19:35 +02:00
vcoppe	543fecadb8	fix popups	2026-10-04 17:09:41 +02:00
vcoppe	017d8521d6	use engine info	2026-10-04 16:27:03 +02:00
vcoppe	78e9d45072	small fix	2026-10-04 16:21:48 +02:00
vcoppe	7651d859c4	progress	2026-10-04 16:11:44 +02:00
vcoppe	ec448b72e2	progress	2026-10-04 15:47:09 +02:00
vcoppe	bf946f179a	progress	2026-10-04 15:26:58 +02:00
vcoppe	9ff9b5475a	progress	2026-10-04 15:03:37 +02:00
vcoppe	55f1d275b7	progress	2026-10-04 14:49:53 +02:00
vcoppe	1d534881f8	progress	2026-10-04 13:18:18 +02:00
vcoppe	03cbacfbb4	fix	2026-10-04 12:33:15 +02:00
vcoppe	9d0905959b	fix markers	2026-10-04 12:23:42 +02:00
vcoppe	b7ca462f58	progress	2026-10-04 11:52:46 +02:00
vcoppe	9015da4876	fixes	2026-10-04 11:07:12 +02:00
vcoppe	f458a1104f	progress	2026-10-04 11:00:46 +02:00
vcoppe	caba9388af	progress	2026-10-04 10:29:39 +02:00
vcoppe	763a7406ce	progress	2026-10-04 10:15:51 +02:00
vcoppe	68c8933c35	progress	2026-10-04 09:55:08 +02:00
vcoppe	84b1558b2e	progress	2026-10-04 09:50:34 +02:00
vcoppe	cd870f0186	visibility	2026-10-04 09:40:17 +02:00
vcoppe	9ac2a2b69c	progress	2026-10-04 08:53:00 +02:00
vcoppe	86aba8f4b1	progress	2026-10-04 08:26:15 +02:00
vcoppe	74b674e8e8	progress	2026-10-04 08:21:39 +02:00
vcoppe	f1904bc12f	cleaning	2026-10-03 20:54:05 +02:00
vcoppe	9afba53e5d	progress	2026-10-03 19:50:38 +02:00
vcoppe	fd76e0fa46	progress	2026-10-03 19:17:58 +02:00
vcoppe	438a87f06f	progress	2026-10-03 19:08:56 +02:00
vcoppe	a994e16f51	splice	2026-10-03 18:03:13 +02:00
vcoppe	639e7491eb	merge methods into 1	2026-10-03 17:47:04 +02:00
vcoppe	891a08a3cc	progress	2026-10-03 17:42:26 +02:00
vcoppe	0c07164dec	remove (copy) in name	2026-10-03 17:26:53 +02:00
vcoppe	f133d55889	progress	2026-10-03 17:21:16 +02:00
vcoppe	fbb636cb06	progress	2026-10-03 16:52:21 +02:00
vcoppe	bddceb28aa	keep style info	2026-10-03 16:43:53 +02:00
vcoppe	bff84fa24c	progress	2026-10-03 16:40:17 +02:00
vcoppe	64914f9aa0	progress	2026-10-03 16:16:47 +02:00
vcoppe	2abf46c747	progress	2026-10-03 15:33:44 +02:00
vcoppe	888f41e979	refactoring	2026-10-03 13:56:16 +02:00
vcoppe	17533586ef	progress	2026-10-03 13:41:58 +02:00
vcoppe	c6ad088947	fix	2026-10-03 13:40:49 +02:00
vcoppe	87d6d5f30e	change type	2026-10-03 11:49:10 +02:00
vcoppe	dbe894b3a3	reorganize	2026-10-03 10:03:22 +02:00
vcoppe	a921d4b9cd	fixes	2026-10-02 18:50:10 +02:00
vcoppe	b7db73cf77	progress	2026-10-02 18:06:45 +02:00
vcoppe	5868595a6c	progress	2026-10-01 18:42:31 +02:00
vcoppe	eb8e09b835	progress	2026-09-30 19:19:23 +02:00
vcoppe	41dc853f65	progress	2026-09-25 12:09:58 +02:00
vcoppe	27c0a57cc1	progress	2026-09-24 20:55:30 +02:00
vcoppe	497ac120ec	progress	2026-09-23 19:53:39 +02:00
vcoppe	a486016d96	progress	2026-09-21 23:49:57 +02:00
vcoppe	cc5f5653ef	progress	2026-09-20 13:58:27 +02:00
vcoppe	20222c450d	parsing continued	2026-09-18 09:50:04 +02:00
vcoppe	69049e1345	parsing start	2026-09-18 09:03:51 +02:00
vcoppe	ed6264444f	wasm first steps	2026-07-14 18:36:30 +02:00