progress

gpx-rs/engine/Cargo.toml

@@ -5,5 +5,7 @@ edition = "2024"
 
 [dependencies]
 chrono = "0.4.45"
+postcard = { version = "1.1.3", features = ["use-std"] }
 quick-xml = "0.42.0"
-uuid = { version = "1.26.1", features = ["v4"] }
+serde = { version = "1.0.229", features = ["derive"] }
+uuid = { version = "1.26.1", features = ["serde", "v4"] }

gpx-rs/engine/data/with_route_extensions.gpx

@@ -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>

gpx-rs/engine/src/core/gpx/categories.rs

@@ -3,7 +3,7 @@
 ///
 /// 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)]
+#[derive(Debug, Default, Clone, PartialEq, serde::Serialize, serde::Deserialize)]
 pub struct Categories(Vec<String>);
 
 impl Categories {
@@ -36,7 +36,7 @@ impl Categories {
 
 /// The categories of the data of the trackpoints. There is one table per engine, shared by all
 /// its files.
-#[derive(Debug, Default, Clone, PartialEq)]
+#[derive(Debug, Default, Clone, PartialEq, serde::Serialize, serde::Deserialize)]
 pub struct TrackpointCategories {
     pub surface: Categories,
     pub highway: Categories,

gpx-rs/engine/src/core/gpx/chunk.rs

@@ -5,8 +5,8 @@ use crate::{Trackpoint, Waypoint};
 /// 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.
 ///
-/// Chunks are equal when they have the same identity, which is cheap to compare and changes
-/// whenever the content does (a modified chunk is a new one).
+/// 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;
 
@@ -27,8 +27,8 @@ pub trait Chunk {
 
 const MAX_TRKPT_CHUNK_SIZE: usize = 4096;
 
-#[derive(Debug, PartialEq, Eq)]
-pub struct TrackpointChunkId(Uuid);
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
+pub struct TrackpointChunkId(pub Uuid);
 
 impl Default for TrackpointChunkId {
     fn default() -> Self {
@@ -42,12 +42,6 @@ pub struct TrackpointChunk {
     pub trkpt: Vec<Trackpoint>,
 }
 
-impl PartialEq for TrackpointChunk {
-    fn eq(&self, other: &Self) -> bool {
-        self.id == other.id
-    }
-}
-
 impl Chunk for TrackpointChunk {
     type Item = Trackpoint;
     const MAX_SIZE: usize = MAX_TRKPT_CHUNK_SIZE;
@@ -68,8 +62,8 @@ impl Chunk for TrackpointChunk {
     }
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub struct WaypointChunkId(Uuid);
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
+pub struct WaypointChunkId(pub Uuid);
 
 impl Default for WaypointChunkId {
     fn default() -> Self {
@@ -85,12 +79,6 @@ pub struct WaypointChunk {
     pub wpt: Vec<Waypoint>,
 }
 
-impl PartialEq for WaypointChunk {
-    fn eq(&self, other: &Self) -> bool {
-        self.id == other.id
-    }
-}
-
 impl Chunk for WaypointChunk {
     type Item = Waypoint;
     const MAX_SIZE: usize = MAX_WPT_CHUNK_SIZE;
@@ -141,20 +129,8 @@ mod tests {
     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, b);
+        assert_ne!(a.id, b.id);
         assert_eq!(a.items().len(), 1);
-        assert_ne!(WaypointChunk::new(vec![]), WaypointChunk::new(vec![]));
-    }
-
-    #[test]
-    fn test_chunk_equality_is_by_id() {
-        let a = TrackpointChunk::default();
-        let b = TrackpointChunk::default();
-        assert_ne!(a, b);
-        let c = TrackpointChunk {
-            id: TrackpointChunkId(a.id.0),
-            trkpt: vec![Trackpoint::default()],
-        };
-        assert_eq!(a, c);
+        assert_ne!(WaypointChunk::new(vec![]).id, WaypointChunk::new(vec![]).id);
     }
 }

gpx-rs/engine/src/core/gpx/chunked.rs

@@ -6,7 +6,7 @@ use crate::Chunk;
 /// copies the chunks around the change, so that a version costs little more than the change.
 ///
 /// There are no empty chunks.
-#[derive(Debug, PartialEq)]
+#[derive(Debug)]
 pub struct Chunked<C: Chunk> {
     chunks: Vec<Rc<C>>,
     cumul_length: Vec<usize>,

gpx-rs/engine/src/core/gpx/common.rs

@@ -1,10 +1,10 @@
-#[derive(Debug, Default, Clone, PartialEq, Eq)]
+#[derive(Debug, Default, Clone, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
 pub struct Link {
     pub href: String,
     pub text: Option<String>,
 }
 
-#[derive(Debug, Default, Clone, Copy)]
+#[derive(Debug, Default, Clone, Copy, serde::Serialize, serde::Deserialize)]
 pub struct LngLat {
     pub lng: f64,
     pub lat: f64,

gpx-rs/engine/src/core/gpx/file.rs

@@ -2,7 +2,7 @@ use uuid::Uuid;
 
 use crate::{Link, Track, Waypoints};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
 pub struct FileId(pub Uuid);
 
 impl Default for FileId {
@@ -11,16 +11,15 @@ impl Default for FileId {
     }
 }
 
-#[derive(Debug, Default, Clone, PartialEq)]
+#[derive(Debug, Default, Clone)]
 pub struct File {
     pub id: FileId,
     pub info: FileInfo,
     pub trk: Vec<Track>,
     pub wpt: Waypoints,
-    // TODO routes
 }
 
-#[derive(Debug, Default, Clone, PartialEq)]
+#[derive(Debug, Default, Clone, PartialEq, serde::Serialize, serde::Deserialize)]
 pub struct FileInfo {
     pub name: String,
     pub desc: Option<String>,
@@ -29,7 +28,7 @@ pub struct FileInfo {
     pub time: Option<i64>,
 }
 
-#[derive(Debug, Default, Clone, PartialEq)]
+#[derive(Debug, Default, Clone, PartialEq, serde::Serialize, serde::Deserialize)]
 pub struct Author {
     pub name: Option<String>,
     pub email: Option<String>,

gpx-rs/engine/src/core/gpx/segment.rs

@@ -4,7 +4,7 @@ use uuid::Uuid;
 
 use crate::{ChunkIndex, Chunked, ChunkedIter, Trackpoint, TrackpointChunk, compute_anchors};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
 pub struct TrackSegmentId(pub Uuid);
 
 impl Default for TrackSegmentId {
@@ -22,7 +22,7 @@ impl Default for TrackSegmentRevisionId {
     }
 }
 
-#[derive(Debug, Default, Clone, PartialEq)]
+#[derive(Debug, Default, Clone)]
 pub struct TrackSegment {
     pub id: TrackSegmentId,
     pub rev_id: TrackSegmentRevisionId,

gpx-rs/engine/src/core/gpx/track.rs

@@ -2,7 +2,7 @@ use uuid::Uuid;
 
 use crate::{Link, TrackSegment};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
 pub struct TrackId(pub Uuid);
 
 impl Default for TrackId {
@@ -11,14 +11,14 @@ impl Default for TrackId {
     }
 }
 
-#[derive(Debug, Default, Clone, PartialEq)]
+#[derive(Debug, Default, Clone)]
 pub struct Track {
     pub id: TrackId,
     pub info: TrackInfo,
     pub trkseg: Vec<TrackSegment>,
 }
 
-#[derive(Debug, Default, Clone, PartialEq)]
+#[derive(Debug, Default, Clone, PartialEq, serde::Serialize, serde::Deserialize)]
 pub struct TrackInfo {
     pub name: Option<String>,
     pub cmt: Option<String>,

gpx-rs/engine/src/core/gpx/trackpoint.rs

@@ -1,6 +1,6 @@
 use crate::LngLat;
 
-#[derive(Debug, Default, Clone)]
+#[derive(Debug, Default, Clone, serde::Serialize, serde::Deserialize)]
 pub struct Trackpoint {
     pub coordinates: LngLat,
     pub ele: f64,

gpx-rs/engine/src/core/gpx/waypoint.rs

@@ -2,7 +2,7 @@ use uuid::Uuid;
 
 use crate::{Link, LngLat};
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, serde::Serialize, serde::Deserialize)]
 pub struct WaypointId(pub Uuid);
 
 impl Default for WaypointId {
@@ -11,7 +11,7 @@ impl Default for WaypointId {
     }
 }
 
-#[derive(Debug, Default, Clone)]
+#[derive(Debug, Default, Clone, serde::Serialize, serde::Deserialize)]
 pub struct Waypoint {
     pub id: WaypointId,
     pub coordinates: LngLat,

gpx-rs/engine/src/core/gpx/waypoints.rs

@@ -19,7 +19,7 @@ impl Default for FileWaypointsRevisionId {
 /// 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, PartialEq)]
+#[derive(Debug, Default, Clone)]
 pub struct Waypoints {
     chunks: Chunked<WaypointChunk>,
     /// Changes when the waypoints do.
@@ -50,6 +50,12 @@ impl Waypoints {
         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);

gpx-rs/engine/src/core/io/parse.rs

@@ -21,6 +21,7 @@ enum GPXElement {
     Track(Track),
     Segment(TrackSegment),
     Trackpoint(Trackpoint),
+    RoutePoint(LngLat),
     Waypoint(Waypoint),
     Elevation,
     Time,
@@ -51,6 +52,11 @@ fn parse_coordinates(attributes: Attributes<'_>) -> LngLat {
     coordinates
 }
 
+/// Whether the element is a point of the detailed path of a route point (`gpxx:rpt`).
+fn is_route_point_extension(name: &str) -> bool {
+    name == "rpt" || name.ends_with(":rpt")
+}
+
 /// Whether the element holds a value, which is its text.
 fn holds_text(element: Option<&GPXElement>) -> bool {
     matches!(
@@ -262,6 +268,10 @@ pub fn parse(data: &[u8], categories: &mut TrackpointCategories) -> Result<File,
     let mut stack: Vec<GPXElement> = vec![];
     let mut trkpt_chunk = TrackpointChunk::default();
     let mut wpt_chunk = WaypointChunk::default();
+    // Routes are read as tracks of a single segment, which is what `rte_segment` collects the points of. A route
+    // point that comes with the detailed path of the route to the next one (`gpxx:rpt`) is replaced by it.
+    let mut rte_segment = TrackSegment::default();
+    let mut rpt_points: Vec<Trackpoint> = vec![];
     // the text of the element at the top of the stack, up to now
     let mut text = String::new();
     loop {
@@ -283,11 +293,11 @@ pub fn parse(data: &[u8], categories: &mut TrackpointCategories) -> Result<File,
                     stack.push(GPXElement::Link(link));
                 }
                 "text" => stack.push(GPXElement::Text),
-                "trk" => stack.push(GPXElement::Track(Track::default())),
+                "trk" | "rte" => stack.push(GPXElement::Track(Track::default())),
                 "trkseg" => {
                     stack.push(GPXElement::Segment(TrackSegment::default()));
                 }
-                "trkpt" => {
+                "trkpt" | "rtept" => {
                     stack.push(GPXElement::Trackpoint(Trackpoint {
                         coordinates: parse_coordinates(e.attributes()),
                         ..Default::default()
@@ -299,6 +309,9 @@ pub fn parse(data: &[u8], categories: &mut TrackpointCategories) -> Result<File,
                         ..Default::default()
                     }));
                 }
+                name if is_route_point_extension(name) => {
+                    stack.push(GPXElement::RoutePoint(parse_coordinates(e.attributes())));
+                }
                 "ele" => stack.push(GPXElement::Elevation),
                 "time" => stack.push(GPXElement::Time),
                 e if e.ends_with("atemp") => stack.push(GPXElement::Temperature),
@@ -330,6 +343,25 @@ pub fn parse(data: &[u8], categories: &mut TrackpointCategories) -> Result<File,
                         }
                     }
                 }
+                "rtept" => {
+                    if let Some(GPXElement::Track(_)) = stack.last() {
+                        trkpt_chunk.trkpt.push(Trackpoint {
+                            coordinates: parse_coordinates(e.attributes()),
+                            ..Default::default()
+                        });
+                        if trkpt_chunk.is_full() {
+                            rte_segment.push(std::mem::take(&mut trkpt_chunk));
+                        }
+                    }
+                }
+                name if is_route_point_extension(name) => {
+                    if let Some(GPXElement::Trackpoint(_)) = stack.last() {
+                        rpt_points.push(Trackpoint {
+                            coordinates: parse_coordinates(e.attributes()),
+                            ..Default::default()
+                        });
+                    }
+                }
                 "wpt" => {
                     wpt_chunk.wpt.push(Waypoint {
                         coordinates: parse_coordinates(e.attributes()),
@@ -385,6 +417,42 @@ pub fn parse(data: &[u8], categories: &mut TrackpointCategories) -> Result<File,
                             gpx.trk.push(trk);
                         }
                     }
+                    "rte" => {
+                        if let Some(GPXElement::Track(mut trk)) = stack.pop() {
+                            rte_segment.push(std::mem::take(&mut trkpt_chunk));
+                            if !rte_segment.is_empty() {
+                                let mut trkseg = std::mem::take(&mut rte_segment);
+                                trkseg.compute_anchors();
+                                trk.trkseg.push(trkseg);
+                            }
+                            gpx.trk.push(trk);
+                        }
+                    }
+                    "rtept" => {
+                        if let Some(GPXElement::Trackpoint(rtept)) = stack.pop()
+                            && let Some(GPXElement::Track(_)) = stack.last()
+                        {
+                            let points = if rpt_points.is_empty() {
+                                vec![rtept]
+                            } else {
+                                std::mem::take(&mut rpt_points)
+                            };
+                            for point in points {
+                                trkpt_chunk.trkpt.push(point);
+                                if trkpt_chunk.is_full() {
+                                    rte_segment.push(std::mem::take(&mut trkpt_chunk));
+                                }
+                            }
+                        }
+                    }
+                    name if is_route_point_extension(name) => {
+                        if let Some(GPXElement::RoutePoint(coordinates)) = stack.pop() {
+                            rpt_points.push(Trackpoint {
+                                coordinates,
+                                ..Default::default()
+                            });
+                        }
+                    }
                     "trkseg" => {
                         if let Some(GPXElement::Segment(mut trkseg)) = stack.pop()
                             && let Some(GPXElement::Track(trk)) = stack.last_mut()
@@ -571,6 +639,52 @@ mod tests {
         assert_eq!(trkpt.ele, 115.5);
     }
 
+    #[test]
+    fn test_parse_routes_as_tracks() {
+        let gpx = parse_data("with_routes");
+
+        assert_eq!(gpx.trk.len(), 2);
+        let trk = &gpx.trk[0];
+        assert_eq!(trk.info.name.as_deref(), Some("route 1"));
+        assert_eq!(trk.info.type_.as_deref(), Some("Cycling"));
+        assert_eq!(trk.trkseg.len(), 1);
+        let trkseg = &trk.trkseg[0];
+        assert_eq!(trkseg.len(), 49);
+        let trkpt = &trkseg[0];
+        assert_eq!(trkpt.coordinates.lat, 50.790867);
+        assert_eq!(trkpt.coordinates.lng, 4.404968);
+        assert_eq!(trkpt.ele, 109.0);
+
+        let trk = &gpx.trk[1];
+        assert_eq!(trk.info.name.as_deref(), Some("route 2"));
+        assert_eq!(trk.trkseg[0].len(), 28);
+    }
+
+    #[test]
+    fn test_parse_route_point_extensions() {
+        let gpx = parse_data("with_route_extensions");
+
+        // a route without points has no segment
+        assert_eq!(gpx.trk.len(), 2);
+        assert!(gpx.trk[1].trkseg.is_empty());
+
+        let trk = &gpx.trk[0];
+        assert_eq!(trk.info.name.as_deref(), Some("with extensions"));
+        assert_eq!(trk.trkseg.len(), 1);
+        let points: Vec<_> = trk.trkseg[0].iter().collect();
+        // the detailed path replaces the route point it comes with
+        let coordinates: Vec<_> = points
+            .iter()
+            .map(|p| (p.coordinates.lat, p.coordinates.lng))
+            .collect();
+        assert_eq!(
+            coordinates,
+            [(1.1, 1.1), (1.2, 1.2), (2.0, 2.0), (3.0, 3.0)]
+        );
+        assert_eq!(points[2].ele, 20.0);
+        assert!(points[2].time.is_some());
+    }
+
     #[test]
     fn test_parse_segments() {
         let gpx = parse_data("with_segments");

gpx-rs/engine/src/engine/command/tools/clean.rs

@@ -329,7 +329,8 @@ mod tests {
         let result =
             clean(bounds(-180.0, -90.0, 180.0, 90.0), CleanType::Outside).apply(&mut fx.state());
         assert!(matches!(result, Err(CommandError::NothingToDo)));
-        assert_eq!(fx.files[&id], before);
+        // the file was not even copied
+        assert!(std::rc::Rc::ptr_eq(&fx.files[&id], &before));
     }
 
     #[test]

gpx-rs/engine/src/engine/command/tools/reduce.rs

@@ -1,6 +1,6 @@
 use std::rc::Rc;
 
-use crate::{Apply, CommandError, File, State, Trackpoint, reduce_indices, reduction_distances};
+use crate::{Apply, CommandError, File, State, Trackpoint, reduce_indices};
 
 /// 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
@@ -56,7 +56,7 @@ impl Apply for Reduce {
 mod tests {
     use std::collections::HashSet;
 
-    use crate::{FileId, Load, Selection, engine::command::fixture::Fixture};
+    use crate::{FileId, Load, Selection, engine::command::fixture::Fixture, reduction_distances};
 
     use super::*;
 

gpx-rs/engine/src/engine/command/tools/split.rs

@@ -245,7 +245,14 @@ mod tests {
         // 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);
-        assert_eq!(a.trkseg[..seg], before.trk[trk].trkseg[..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

gpx-rs/engine/src/engine/engine.rs

@@ -2,9 +2,10 @@
 
 use crate::{
     Action, Apply, Clipboard, Command, CoordinatesCache, Diff, ExportOptions, FileId, FileOrder,
-    FileStructure, FileStructureCache, GlobalStatistics, RoutingBuffer, SelectMode, Selection,
-    Stack, State, StatisticsBuffer, StatisticsCache, TrackSegmentId, Trackpoint,
-    TrackpointCategories, Waypoint, WaypointId, reduction_distances, write,
+    FileStructure, FileStructureCache, GlobalStatistics, Restored, RoutingBuffer, SelectMode,
+    Selection, Snapshot, Stack, StackEntry, State, StatisticsBuffer, StatisticsCache,
+    TrackSegmentId, Trackpoint, TrackpointCategories, Waypoint, WaypointId, reduction_distances,
+    write,
 };
 
 #[derive(Debug, Default)]
@@ -118,6 +119,40 @@ impl Engine {
             .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 that were added are reported as
+    /// the last diff, and the order as changed.
+    pub fn restore(&mut self, restored: Restored) {
+        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;
+        self.diff = Some(Diff {
+            added: files.keys().copied().collect(),
+            ..Default::default()
+        });
+        self.stack = Stack::restored(files);
+        self.refresh();
+        self.sort_diff();
+        self.order_changed = true;
+        self.selection_changed = true;
+        self.clipboard_changed = true;
+    }
+
     /// 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)?;
@@ -243,6 +278,7 @@ impl Engine {
             || self.clipboard != clipboard_before;
         if changed {
             self.refresh();
+            self.sort_diff();
         }
         // after the refresh, which also syncs the order and selection with the files (undo, redo)
         self.order_changed = self.order.0 != order_before;
@@ -273,6 +309,16 @@ impl Engine {
         })
     }
 
+    /// Puts the files of the last 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(&mut self) {
+        let position = |id: &FileId| self.order.0.iter().position(|other| other == id);
+        if let Some(diff) = &mut self.diff {
+            diff.added.sort_by_key(position);
+            diff.modified.sort_by_key(position);
+        }
+    }
+
     /// Brings everything derived from the files back in line with the current stack entry.
     fn refresh(&mut self) {
         let current = self.stack.current();
@@ -1166,6 +1212,33 @@ mod tests {
         assert_eq!(track_ids(&engine, a), tracks);
     }
 
+    #[test]
+    fn test_added_files_are_reported_in_the_order_of_the_files() {
+        use crate::LoadFiles;
+
+        let mut engine = Engine::default();
+        let datas: Vec<Vec<u8>> = (0..12)
+            .map(|i| {
+                format!(r#"<gpx version="1.1"><metadata><name>{i}</name></metadata></gpx>"#)
+                    .into_bytes()
+            })
+            .collect();
+        let loads = datas
+            .iter()
+            .map(|data| Load { data, name: "x" })
+            .collect::<Vec<_>>();
+        assert!(edit(
+            &mut engine,
+            Command::LoadFiles(LoadFiles { files: loads })
+        ));
+        assert_eq!(engine.last_diff().unwrap().added, engine.order());
+
+        // files that come back with an undo too
+        assert!(engine.execute(Action::Undo));
+        assert!(engine.execute(Action::Redo));
+        assert_eq!(engine.last_diff().unwrap().added, engine.order());
+    }
+
     #[test]
     fn test_load_several_files_is_one_edit() {
         use crate::LoadFiles;

gpx-rs/engine/src/engine/state/stack.rs

@@ -9,9 +9,21 @@ use crate::{File, FileId};
 pub struct Stack {
     entries: Vec<StackEntry>,
     index: Option<usize>,
+    /// Whether the first entry is the state the stack started from (files restored from the
+    /// storage), which is not undone.
+    restored: bool,
 }
 
 impl Stack {
+    /// A stack whose first entry is `entry`, from which nothing can be undone.
+    pub fn restored(entry: StackEntry) -> Self {
+        Self {
+            entries: vec![entry],
+            index: Some(0),
+            restored: true,
+        }
+    }
+
     pub fn current(&self) -> Option<&StackEntry> {
         self.index.map_or_default(|i| self.get(i))
     }
@@ -32,7 +44,9 @@ impl Stack {
         self.record_diff(|stack| {
             if let Some(i) = stack.index {
                 if i == 0 {
-                    stack.index = None;
+                    if !stack.restored {
+                        stack.index = None;
+                    }
                 } else {
                     stack.index = Some(i - 1);
                 }
@@ -56,7 +70,7 @@ impl Stack {
     }
 
     pub fn can_undo(&self) -> bool {
-        self.index.is_some()
+        self.index.is_some_and(|i| i > 0 || !self.restored)
     }
 
     pub fn can_redo(&self) -> bool {
@@ -97,7 +111,7 @@ impl Stack {
         for id in prev_ids.intersection(&cur_ids) {
             let before = prev.map_or_default(|e| e.get(id));
             let after = cur.map_or_default(|e| e.get(id));
-            if !before.zip(after).is_some_and(|(b, a)| Rc::ptr_eq(b, a)) && before != after {
+            if !before.zip(after).is_some_and(|(b, a)| Rc::ptr_eq(b, a)) {
                 modified.push(*id);
             }
         }
@@ -231,6 +245,34 @@ mod tests {
         assert_eq!(stack.current().unwrap()[&id].info.name, "renamed");
     }
 
+    #[test]
+    fn test_a_file_is_modified_when_it_is_not_the_same_one_anymore() {
+        let mut stack = Stack::default();
+        let id = add_file(&mut stack);
+
+        // a copy, even if it has the same content, is another file for the stack: files are
+        // told apart by their identity, comparing them would read all of them
+        let diff = stack
+            .create_and_push_next(|e| {
+                let copy = (**e.get(&id).unwrap()).clone();
+                e.insert(id, Rc::new(copy));
+                Ok(())
+            })
+            .unwrap();
+        assert_eq!(diff.modified, vec![id]);
+
+        // and the files that were not replaced are not
+        let other = add_file(&mut stack);
+        let diff = stack
+            .create_and_push_next(|e| {
+                let copy = (**e.get(&other).unwrap()).clone();
+                e.insert(other, Rc::new(copy));
+                Ok(())
+            })
+            .unwrap();
+        assert_eq!(diff.modified, vec![other]);
+    }
+
     #[test]
     fn test_push_after_undo_drops_redo_branch() {
         let mut stack = Stack::default();
@@ -249,4 +291,104 @@ mod tests {
         assert!(current.contains_key(&third));
         assert!(!current.contains_key(&second));
     }
+
+    fn restored_entry() -> (StackEntry, FileId) {
+        let file = Rc::new(File::default());
+        let id = file.id;
+        (StackEntry::from([(id, file)]), id)
+    }
+
+    #[test]
+    fn test_restored_stack_starts_from_its_entry() {
+        let (entry, id) = restored_entry();
+        let mut stack = Stack::restored(entry);
+
+        assert!(stack.current().unwrap().contains_key(&id));
+        // there is nothing to go back to, nor forward to
+        assert!(!stack.can_undo());
+        assert!(!stack.can_redo());
+        assert!(stack.undo().is_none());
+        assert!(stack.redo().is_none());
+        assert!(stack.current().unwrap().contains_key(&id));
+    }
+
+    #[test]
+    fn test_restored_stack_cannot_undo_an_empty_entry_either() {
+        let mut stack = Stack::restored(StackEntry::new());
+
+        assert!(stack.current().is_some_and(|files| files.is_empty()));
+        assert!(!stack.can_undo());
+        assert!(stack.undo().is_none());
+        // the stack is not the one of an engine that has done nothing
+        assert!(stack.current().is_some());
+    }
+
+    #[test]
+    fn test_restored_stack_undoes_what_comes_after_it_and_no_further() {
+        let (entry, restored) = restored_entry();
+        let mut stack = Stack::restored(entry);
+
+        let added = add_file(&mut stack);
+        assert!(stack.can_undo());
+        assert!(!stack.can_redo());
+        assert_eq!(stack.current().unwrap().len(), 2);
+
+        // back to the restored files
+        let diff = stack.undo().unwrap();
+        assert_eq!(diff.removed, vec![added]);
+        assert!(diff.added.is_empty() && diff.modified.is_empty());
+        assert_eq!(stack.current().unwrap().len(), 1);
+        assert!(stack.current().unwrap().contains_key(&restored));
+        assert!(!stack.can_undo());
+        assert!(stack.can_redo());
+        assert!(stack.undo().is_none());
+        assert!(stack.current().unwrap().contains_key(&restored));
+
+        let diff = stack.redo().unwrap();
+        assert_eq!(diff.added, vec![added]);
+        assert!(stack.can_undo());
+        assert!(!stack.can_redo());
+
+        // and again
+        assert!(stack.undo().is_some());
+        assert!(stack.undo().is_none());
+        assert!(stack.current().unwrap().contains_key(&restored));
+    }
+
+    #[test]
+    fn test_restored_stack_removing_its_files_can_be_undone() {
+        let (entry, restored) = restored_entry();
+        let mut stack = Stack::restored(entry);
+
+        let diff = stack
+            .create_and_push_next(|e| {
+                e.remove(&restored);
+                Ok(())
+            })
+            .unwrap();
+        assert_eq!(diff.removed, vec![restored]);
+        assert!(stack.current().unwrap().is_empty());
+
+        let diff = stack.undo().unwrap();
+        assert_eq!(diff.added, vec![restored]);
+        assert!(stack.current().unwrap().contains_key(&restored));
+        assert!(!stack.can_undo());
+    }
+
+    #[test]
+    fn test_restored_stack_push_after_undo_drops_redo_branch() {
+        let (entry, restored) = restored_entry();
+        let mut stack = Stack::restored(entry);
+        add_file(&mut stack);
+        stack.undo().unwrap();
+        assert!(stack.can_redo());
+
+        let other = add_file(&mut stack);
+        assert!(!stack.can_redo());
+        assert!(stack.can_undo());
+        let diff = stack.undo().unwrap();
+        assert_eq!(diff.removed, vec![other]);
+        assert!(stack.current().unwrap().contains_key(&restored));
+        assert!(!stack.can_undo());
+    }
 }

gpx-rs/engine/src/lib.rs

@@ -1,5 +1,7 @@
 mod core;
 mod engine;
+mod storage;
 
 pub use core::*;
 pub use engine::*;
+pub use storage::*;

gpx-rs/engine/src/storage/codec.rs

@@ -0,0 +1,130 @@
+//! The binary form of what is stored: a version byte, then the data (postcard).
+
+use std::rc::Rc;
+
+use serde::{Deserialize, Serialize};
+use uuid::Uuid;
+
+use crate::{
+    File, FileInfo, Track, TrackId, TrackInfo, TrackSegment, TrackSegmentId, Trackpoint,
+    TrackpointChunk, TrackpointChunkId, Waypoint, WaypointChunk, WaypointChunkId, Waypoints,
+};
+
+/// Changes when the form of the records does.
+const VERSION: u8 = 1;
+
+pub fn encode<T: Serialize + ?Sized>(value: &T) -> Vec<u8> {
+    postcard::to_extend(value, vec![VERSION]).expect("serializing to memory")
+}
+
+pub fn decode<'a, T: Deserialize<'a>>(bytes: &'a [u8]) -> Option<T> {
+    match bytes.split_first() {
+        Some((&VERSION, data)) => postcard::from_bytes(data).ok(),
+        _ => None,
+    }
+}
+
+/// A file without its trackpoints and waypoints, which are in chunks.
+#[derive(Serialize, Deserialize)]
+pub struct FileRecord {
+    info: FileInfo,
+    tracks: Vec<TrackRecord>,
+    waypoints: Vec<WaypointChunkId>,
+}
+
+#[derive(Serialize, Deserialize)]
+struct TrackRecord {
+    id: TrackId,
+    info: TrackInfo,
+    segments: Vec<SegmentRecord>,
+}
+
+#[derive(Serialize, Deserialize)]
+struct SegmentRecord {
+    id: TrackSegmentId,
+    chunks: Vec<TrackpointChunkId>,
+}
+
+impl FileRecord {
+    pub fn new(file: &File) -> Self {
+        Self {
+            info: file.info.clone(),
+            tracks: file
+                .trk
+                .iter()
+                .map(|track| TrackRecord {
+                    id: track.id,
+                    info: track.info.clone(),
+                    segments: track
+                        .trkseg
+                        .iter()
+                        .map(|segment| SegmentRecord {
+                            id: segment.id,
+                            chunks: segment.chunks().iter().map(|chunk| chunk.id).collect(),
+                        })
+                        .collect(),
+                })
+                .collect(),
+            waypoints: file.wpt.chunks().iter().map(|chunk| chunk.id).collect(),
+        }
+    }
+
+    /// The file made of the record and its chunks, `None` if one is missing. Chunks that several
+    /// files use stay shared.
+    pub fn build(
+        self,
+        id: crate::FileId,
+        trackpoint_chunks: &impl Fn(&TrackpointChunkId) -> Option<Rc<TrackpointChunk>>,
+        waypoint_chunks: &impl Fn(&WaypointChunkId) -> Option<Rc<WaypointChunk>>,
+    ) -> Option<File> {
+        let mut file = File {
+            id,
+            info: self.info,
+            ..Default::default()
+        };
+        for track in self.tracks {
+            let mut trkseg = Vec::with_capacity(track.segments.len());
+            for segment in track.segments {
+                let mut built = TrackSegment::default();
+                built.id = segment.id;
+                for chunk in &segment.chunks {
+                    built.push_shared(trackpoint_chunks(chunk)?);
+                }
+                trkseg.push(built);
+            }
+            file.trk.push(Track {
+                id: track.id,
+                info: track.info,
+                trkseg,
+            });
+        }
+        let mut wpt = Waypoints::default();
+        for chunk in &self.waypoints {
+            wpt.push_shared(waypoint_chunks(chunk)?);
+        }
+        file.wpt = wpt;
+        Some(file)
+    }
+}
+
+pub fn encode_trackpoints(chunk: &TrackpointChunk) -> Vec<u8> {
+    encode(&chunk.trkpt)
+}
+
+pub fn decode_trackpoints(id: Uuid, bytes: &[u8]) -> Option<TrackpointChunk> {
+    Some(TrackpointChunk {
+        id: TrackpointChunkId(id),
+        trkpt: decode::<Vec<Trackpoint>>(bytes)?,
+    })
+}
+
+pub fn encode_waypoints(chunk: &WaypointChunk) -> Vec<u8> {
+    encode(&chunk.wpt)
+}
+
+pub fn decode_waypoints(id: Uuid, bytes: &[u8]) -> Option<WaypointChunk> {
+    Some(WaypointChunk {
+        id: WaypointChunkId(id),
+        wpt: decode::<Vec<Waypoint>>(bytes)?,
+    })
+}

gpx-rs/engine/src/storage/memory.rs

@@ -0,0 +1,105 @@
+use std::cell::RefCell;
+use std::collections::HashMap;
+
+use uuid::Uuid;
+
+use crate::{Batch, FileId, Storage, StorageError, StoredData};
+
+/// A storage that lives as long as the session. It is what an engine without a host storage uses,
+/// and what the tests use.
+#[derive(Debug, Default)]
+pub struct MemoryStorage {
+    state: RefCell<State>,
+}
+
+#[derive(Debug, Default)]
+struct State {
+    files: HashMap<FileId, Vec<u8>>,
+    trackpoint_chunks: HashMap<Uuid, Vec<u8>>,
+    waypoint_chunks: HashMap<Uuid, Vec<u8>>,
+    order: Option<Vec<u8>>,
+    categories: Option<Vec<u8>>,
+    settings: HashMap<String, String>,
+}
+
+impl MemoryStorage {
+    /// How many files and chunks (trackpoints, waypoints) are stored.
+    pub fn counts(&self) -> (usize, usize, usize) {
+        let state = self.state.borrow();
+        (
+            state.files.len(),
+            state.trackpoint_chunks.len(),
+            state.waypoint_chunks.len(),
+        )
+    }
+}
+
+impl Storage for MemoryStorage {
+    async fn load(&self) -> Result<StoredData, StorageError> {
+        let state = self.state.borrow();
+        Ok(StoredData {
+            files: state.files.iter().map(|(k, v)| (*k, v.clone())).collect(),
+            trackpoint_chunks: state
+                .trackpoint_chunks
+                .iter()
+                .map(|(k, v)| (*k, v.clone()))
+                .collect(),
+            waypoint_chunks: state
+                .waypoint_chunks
+                .iter()
+                .map(|(k, v)| (*k, v.clone()))
+                .collect(),
+            order: state.order.clone(),
+            categories: state.categories.clone(),
+        })
+    }
+
+    async fn commit(&self, batch: &Batch) -> Result<(), StorageError> {
+        let mut state = self.state.borrow_mut();
+        state.files.extend(batch.put_files.iter().cloned());
+        for id in &batch.delete_files {
+            state.files.remove(id);
+        }
+        state
+            .trackpoint_chunks
+            .extend(batch.put_trackpoint_chunks.iter().cloned());
+        for id in &batch.delete_trackpoint_chunks {
+            state.trackpoint_chunks.remove(id);
+        }
+        state
+            .waypoint_chunks
+            .extend(batch.put_waypoint_chunks.iter().cloned());
+        for id in &batch.delete_waypoint_chunks {
+            state.waypoint_chunks.remove(id);
+        }
+        if let Some(order) = &batch.order {
+            state.order = Some(order.clone());
+        }
+        if let Some(categories) = &batch.categories {
+            state.categories = Some(categories.clone());
+        }
+        Ok(())
+    }
+
+    async fn load_settings(&self) -> Result<Vec<(String, String)>, StorageError> {
+        let state = self.state.borrow();
+        Ok(state
+            .settings
+            .iter()
+            .map(|(k, v)| (k.clone(), v.clone()))
+            .collect())
+    }
+
+    async fn put_setting(&self, key: &str, value: &str) -> Result<(), StorageError> {
+        self.state
+            .borrow_mut()
+            .settings
+            .insert(key.to_owned(), value.to_owned());
+        Ok(())
+    }
+
+    async fn delete_setting(&self, key: &str) -> Result<(), StorageError> {
+        self.state.borrow_mut().settings.remove(key);
+        Ok(())
+    }
+}

gpx-rs/engine/src/storage/mod.rs

@@ -0,0 +1,85 @@
+//! Keeping the files and the settings between sessions.
+//!
+//! The engine does not know where the data goes: the host (the browser, a desktop app...)
+//! implements [`Storage`], and a [`Persister`] works out what to write after each change.
+//!
+//! The files are not stored as a whole. Their trackpoints and waypoints are stored in chunks (see
+//! [`crate::Chunked`]) that are written once, under their identity, and a file is a small record
+//! that lists the chunks it is made of. An edit only writes the new chunks and the records of the
+//! files that changed; the chunks that nothing refers to anymore are deleted at the same time.
+
+mod codec;
+mod memory;
+mod persister;
+
+pub use memory::*;
+pub use persister::*;
+
+use uuid::Uuid;
+
+use crate::FileId;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct StorageError(pub String);
+
+impl std::fmt::Display for StorageError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "storage error: {}", self.0)
+    }
+}
+
+impl std::error::Error for StorageError {}
+
+/// Everything that is stored about the files, as opaque bytes (see the module documentation).
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
+pub struct StoredData {
+    /// The record of each file.
+    pub files: Vec<(FileId, Vec<u8>)>,
+    pub trackpoint_chunks: Vec<(Uuid, Vec<u8>)>,
+    pub waypoint_chunks: Vec<(Uuid, Vec<u8>)>,
+    /// The order of the files.
+    pub order: Option<Vec<u8>>,
+    /// The categories of the trackpoints, which their chunks refer to.
+    pub categories: Option<Vec<u8>>,
+}
+
+/// A change of the stored data, to be applied all at once: a stored state is always one that the
+/// engine had.
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
+pub struct Batch {
+    pub put_files: Vec<(FileId, Vec<u8>)>,
+    pub delete_files: Vec<FileId>,
+    pub put_trackpoint_chunks: Vec<(Uuid, Vec<u8>)>,
+    pub delete_trackpoint_chunks: Vec<Uuid>,
+    pub put_waypoint_chunks: Vec<(Uuid, Vec<u8>)>,
+    pub delete_waypoint_chunks: Vec<Uuid>,
+    pub order: Option<Vec<u8>>,
+    pub categories: Option<Vec<u8>>,
+}
+
+impl Batch {
+    pub fn is_empty(&self) -> bool {
+        self == &Self::default()
+    }
+}
+
+/// Where the data is kept. The implementation belongs to the host; [`MemoryStorage`] is one that
+/// keeps nothing after the session.
+///
+/// The methods are async because storage often is (IndexedDB), the engine itself is not: it
+/// changes its files at once and the changes are written afterwards, see [`Persister`].
+#[allow(async_fn_in_trait)]
+pub trait Storage {
+    /// Reads the files.
+    async fn load(&self) -> Result<StoredData, StorageError>;
+
+    /// Applies a batch: either all of it is stored, or none.
+    async fn commit(&self, batch: &Batch) -> Result<(), StorageError>;
+
+    /// Reads the settings, as `(key, value)`. The engine does not look into them.
+    async fn load_settings(&self) -> Result<Vec<(String, String)>, StorageError>;
+
+    async fn put_setting(&self, key: &str, value: &str) -> Result<(), StorageError>;
+
+    async fn delete_setting(&self, key: &str) -> Result<(), StorageError>;
+}

gpx-rs/engine/src/storage/persister.rs

@@ -0,0 +1,485 @@
+use std::cell::RefCell;
+use std::collections::{HashMap, HashSet};
+use std::rc::Rc;
+
+use uuid::Uuid;
+
+use super::codec::{
+    FileRecord, decode, decode_trackpoints, decode_waypoints, encode, encode_trackpoints,
+    encode_waypoints,
+};
+use crate::{
+    Batch, File, FileId, StackEntry, Storage, StorageError, TrackpointCategories, TrackpointChunk,
+    WaypointChunk,
+};
+
+/// What there is to keep of the engine: the files of the current state, their order, and the
+/// categories their trackpoints refer to. See [`crate::Engine::snapshot`].
+#[derive(Debug, Default, Clone)]
+pub struct Snapshot {
+    pub files: StackEntry,
+    pub order: Vec<FileId>,
+    pub categories: TrackpointCategories,
+}
+
+/// What was read from the storage, to start an engine with (see [`crate::Engine::restore`]).
+#[derive(Debug, Default)]
+pub struct Restored {
+    pub files: Vec<Rc<File>>,
+    pub order: Vec<FileId>,
+    pub categories: TrackpointCategories,
+    /// The files that could not be read: they are dropped at the next save.
+    pub unreadable: usize,
+}
+
+/// Works out what to write to a [`Storage`] so that it holds a [`Snapshot`], knowing what it
+/// already holds.
+///
+/// A file whose `Rc` is the saved one has not changed, which is what makes a save cheap: only the
+/// files that changed are looked at to find the chunks to write, and the others are only counted
+/// to find the chunks that nothing uses anymore.
+#[derive(Debug, Default)]
+pub struct Persister {
+    /// The files as they are saved.
+    files: HashMap<FileId, Rc<File>>,
+    /// The files that have a record, including the ones that could not be read.
+    stored_files: HashSet<FileId>,
+    trackpoint_chunks: HashSet<Uuid>,
+    waypoint_chunks: HashSet<Uuid>,
+    order: Option<Vec<FileId>>,
+    categories: Option<TrackpointCategories>,
+}
+
+/// What a save writes, and what is stored once it is written.
+struct Plan {
+    batch: Batch,
+    snapshot: Snapshot,
+    trackpoint_chunks: HashSet<Uuid>,
+    waypoint_chunks: HashSet<Uuid>,
+}
+
+impl Persister {
+    /// Reads the files of the storage. The persister then knows that they are saved.
+    pub async fn restore<S: Storage>(&mut self, storage: &S) -> Result<Restored, StorageError> {
+        let data = storage.load().await?;
+        *self = Self::default();
+
+        let categories: Option<TrackpointCategories> = data.categories.as_deref().and_then(decode);
+        let stored_order: Option<Vec<FileId>> = data.order.as_deref().and_then(decode);
+
+        let trackpoint_bytes: HashMap<Uuid, Vec<u8>> = data.trackpoint_chunks.into_iter().collect();
+        let waypoint_bytes: HashMap<Uuid, Vec<u8>> = data.waypoint_chunks.into_iter().collect();
+        // chunks are decoded once, whatever the number of files that use them
+        let trackpoint_cache: RefCell<HashMap<Uuid, Option<Rc<TrackpointChunk>>>> =
+            Default::default();
+        let waypoint_cache: RefCell<HashMap<Uuid, Option<Rc<WaypointChunk>>>> = Default::default();
+        let trackpoint_chunk = |id: &crate::TrackpointChunkId| {
+            trackpoint_cache
+                .borrow_mut()
+                .entry(id.0)
+                .or_insert_with(|| {
+                    let bytes = trackpoint_bytes.get(&id.0)?;
+                    decode_trackpoints(id.0, bytes).map(Rc::new)
+                })
+                .clone()
+        };
+        let waypoint_chunk = |id: &crate::WaypointChunkId| {
+            waypoint_cache
+                .borrow_mut()
+                .entry(id.0)
+                .or_insert_with(|| {
+                    let bytes = waypoint_bytes.get(&id.0)?;
+                    decode_waypoints(id.0, bytes).map(Rc::new)
+                })
+                .clone()
+        };
+
+        let mut restored = Restored {
+            categories: categories.clone().unwrap_or_default(),
+            ..Default::default()
+        };
+        let mut files: HashMap<FileId, Rc<File>> = HashMap::new();
+        for (id, bytes) in &data.files {
+            self.stored_files.insert(*id);
+            let file = decode::<FileRecord>(bytes)
+                .and_then(|record| record.build(*id, &trackpoint_chunk, &waypoint_chunk));
+            match file {
+                Some(file) => {
+                    files.insert(*id, Rc::new(file));
+                }
+                None => restored.unreadable += 1,
+            }
+        }
+
+        restored.order = stored_order
+            .iter()
+            .flatten()
+            .filter(|id| files.contains_key(id))
+            .copied()
+            .collect();
+        let ordered: HashSet<FileId> = restored.order.iter().copied().collect();
+        restored
+            .order
+            .extend(files.keys().filter(|id| !ordered.contains(id)).copied());
+        restored.files = restored.order.iter().map(|id| files[id].clone()).collect();
+
+        self.files = files;
+        self.trackpoint_chunks = trackpoint_bytes.into_keys().collect();
+        self.waypoint_chunks = waypoint_bytes.into_keys().collect();
+        self.order = stored_order;
+        self.categories = categories;
+        Ok(restored)
+    }
+
+    /// Writes what changed since the last save. Nothing is written if nothing changed.
+    pub async fn save<S: Storage>(
+        &mut self,
+        storage: &S,
+        snapshot: Snapshot,
+    ) -> Result<(), StorageError> {
+        let plan = self.plan(snapshot);
+        if plan.batch.is_empty() {
+            self.files = plan.snapshot.files;
+            return Ok(());
+        }
+        storage.commit(&plan.batch).await?;
+
+        self.stored_files = plan.snapshot.files.keys().copied().collect();
+        self.files = plan.snapshot.files;
+        self.trackpoint_chunks = plan.trackpoint_chunks;
+        self.waypoint_chunks = plan.waypoint_chunks;
+        self.order = Some(plan.snapshot.order);
+        self.categories = Some(plan.snapshot.categories);
+        Ok(())
+    }
+
+    fn plan(&self, snapshot: Snapshot) -> Plan {
+        let mut batch = Batch::default();
+        // the chunks that the files use, which the storage has afterwards
+        let mut trackpoint_chunks = HashSet::new();
+        let mut waypoint_chunks = HashSet::new();
+
+        for (id, file) in &snapshot.files {
+            let changed = self
+                .files
+                .get(id)
+                .is_none_or(|saved| !Rc::ptr_eq(saved, file));
+            let segments = file.trk.iter().flat_map(|track| &track.trkseg);
+            for chunk in segments.flat_map(|segment| segment.chunks()) {
+                let new = trackpoint_chunks.insert(chunk.id.0);
+                if changed && new && !self.trackpoint_chunks.contains(&chunk.id.0) {
+                    batch
+                        .put_trackpoint_chunks
+                        .push((chunk.id.0, encode_trackpoints(chunk)));
+                }
+            }
+            for chunk in file.wpt.chunks() {
+                let new = waypoint_chunks.insert(chunk.id.0);
+                if changed && new && !self.waypoint_chunks.contains(&chunk.id.0) {
+                    batch
+                        .put_waypoint_chunks
+                        .push((chunk.id.0, encode_waypoints(chunk)));
+                }
+            }
+            if changed || !self.stored_files.contains(id) {
+                batch.put_files.push((*id, encode(&FileRecord::new(file))));
+            }
+        }
+
+        batch.delete_files = self
+            .stored_files
+            .iter()
+            .filter(|id| !snapshot.files.contains_key(id))
+            .copied()
+            .collect();
+        batch.delete_trackpoint_chunks = self
+            .trackpoint_chunks
+            .difference(&trackpoint_chunks)
+            .copied()
+            .collect();
+        batch.delete_waypoint_chunks = self
+            .waypoint_chunks
+            .difference(&waypoint_chunks)
+            .copied()
+            .collect();
+        if self.order.as_ref() != Some(&snapshot.order) {
+            batch.order = Some(encode(&snapshot.order));
+        }
+        if self.categories.as_ref() != Some(&snapshot.categories) {
+            batch.categories = Some(encode(&snapshot.categories));
+        }
+
+        Plan {
+            batch,
+            snapshot,
+            trackpoint_chunks,
+            waypoint_chunks,
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::cell::RefCell;
+    use std::future::Future;
+    use std::task::{Context, Poll, Waker};
+
+    use crate::{
+        Action, Command, Engine, ExportOptions, Load, MemoryStorage, StoredData, parse, write,
+    };
+
+    use super::*;
+
+    fn block_on<F: Future>(future: F) -> F::Output {
+        let mut future = std::pin::pin!(future);
+        let mut context = Context::from_waker(Waker::noop());
+        loop {
+            if let Poll::Ready(value) = future.as_mut().poll(&mut context) {
+                return value;
+            }
+        }
+    }
+
+    /// A memory storage that remembers the batches it was given.
+    #[derive(Default)]
+    struct Recording {
+        inner: MemoryStorage,
+        batches: RefCell<Vec<Batch>>,
+    }
+
+    impl Storage for Recording {
+        async fn load(&self) -> Result<StoredData, StorageError> {
+            self.inner.load().await
+        }
+
+        async fn commit(&self, batch: &Batch) -> Result<(), StorageError> {
+            self.batches.borrow_mut().push(batch.clone());
+            self.inner.commit(batch).await
+        }
+
+        async fn load_settings(&self) -> Result<Vec<(String, String)>, StorageError> {
+            self.inner.load_settings().await
+        }
+
+        async fn put_setting(&self, key: &str, value: &str) -> Result<(), StorageError> {
+            self.inner.put_setting(key, value).await
+        }
+
+        async fn delete_setting(&self, key: &str) -> Result<(), StorageError> {
+            self.inner.delete_setting(key).await
+        }
+    }
+
+    fn snapshot_of(paths: &[&str]) -> Snapshot {
+        let mut snapshot = Snapshot::default();
+        for path in paths {
+            let data = std::fs::read(path).unwrap();
+            let file = parse(&data, &mut snapshot.categories).unwrap();
+            snapshot.order.push(file.id);
+            snapshot.files.insert(file.id, Rc::new(file));
+        }
+        snapshot
+    }
+
+    fn gpx(file: &File, categories: &TrackpointCategories) -> Vec<u8> {
+        write(file, categories, ExportOptions::ALL)
+    }
+
+    const FILES: [&str; 3] = [
+        "data/with_tracks_and_segments.gpx",
+        "data/with_waypoint.gpx",
+        "data/with_surface.gpx",
+    ];
+
+    #[test]
+    fn test_saved_files_are_restored() {
+        let storage = Recording::default();
+        let snapshot = snapshot_of(&FILES);
+        block_on(Persister::default().save(&storage, snapshot.clone())).unwrap();
+
+        let mut persister = Persister::default();
+        let restored = block_on(persister.restore(&storage)).unwrap();
+        assert_eq!(restored.unreadable, 0);
+        assert_eq!(restored.order, snapshot.order);
+        assert_eq!(restored.categories, snapshot.categories);
+        for file in &restored.files {
+            let original = &snapshot.files[&file.id];
+            assert_eq!(
+                gpx(file, &restored.categories),
+                gpx(original, &snapshot.categories)
+            );
+            // identities that the rest of the engine refers to are kept
+            assert_eq!(file.trk[0].id, original.trk[0].id);
+            assert_eq!(file.trk[0].trkseg[0].id, original.trk[0].trkseg[0].id);
+            assert_eq!(
+                file.trk[0].trkseg[0].chunks()[0].id,
+                original.trk[0].trkseg[0].chunks()[0].id
+            );
+        }
+        // what was just read is saved
+        let again = Snapshot {
+            files: restored.files.iter().map(|f| (f.id, f.clone())).collect(),
+            order: restored.order,
+            categories: restored.categories,
+        };
+        block_on(persister.save(&storage, again)).unwrap();
+        assert_eq!(storage.batches.borrow().len(), 1);
+    }
+
+    #[test]
+    fn test_nothing_is_written_when_nothing_changed() {
+        let storage = Recording::default();
+        let snapshot = snapshot_of(&FILES);
+        let mut persister = Persister::default();
+        block_on(persister.save(&storage, snapshot.clone())).unwrap();
+        block_on(persister.save(&storage, snapshot)).unwrap();
+        assert_eq!(storage.batches.borrow().len(), 1);
+    }
+
+    #[test]
+    fn test_an_edit_writes_what_it_changed_only() {
+        let storage = Recording::default();
+        let mut snapshot = snapshot_of(&FILES);
+        let mut persister = Persister::default();
+        block_on(persister.save(&storage, snapshot.clone())).unwrap();
+        let counts = storage.inner.counts();
+
+        // renaming a file writes its record, not its chunks
+        let id = snapshot.order[0];
+        let mut file = (*snapshot.files[&id]).clone();
+        file.info.name = "renamed".into();
+        snapshot.files.insert(id, Rc::new(file));
+        block_on(persister.save(&storage, snapshot.clone())).unwrap();
+        {
+            let batches = storage.batches.borrow();
+            let batch = batches.last().unwrap();
+            assert_eq!(batch.put_files.len(), 1);
+            assert!(batch.put_trackpoint_chunks.is_empty());
+            assert!(batch.put_waypoint_chunks.is_empty());
+            assert!(batch.delete_trackpoint_chunks.is_empty());
+            assert!(batch.order.is_none() && batch.categories.is_none());
+        }
+        assert_eq!(storage.inner.counts(), counts);
+
+        // changing a trackpoint replaces the chunk that holds it only
+        let mut file = (*snapshot.files[&id]).clone();
+        let chunks_before = file
+            .trk
+            .iter()
+            .flat_map(|t| &t.trkseg)
+            .map(|s| s.chunks().len())
+            .sum::<usize>();
+        file.trk[0].trkseg[0].update(0, |point| point.ele += 1.0);
+        snapshot.files.insert(id, Rc::new(file));
+        block_on(persister.save(&storage, snapshot.clone())).unwrap();
+        {
+            let batches = storage.batches.borrow();
+            let batch = batches.last().unwrap();
+            assert_eq!(batch.put_files.len(), 1);
+            assert_eq!(batch.put_trackpoint_chunks.len(), 1);
+            assert_eq!(batch.delete_trackpoint_chunks.len(), 1);
+        }
+        assert_eq!(storage.inner.counts(), counts);
+        assert!(chunks_before >= 1);
+
+        // a deleted file takes its chunks and its record away
+        snapshot.files.remove(&id);
+        snapshot.order.retain(|other| *other != id);
+        block_on(persister.save(&storage, snapshot)).unwrap();
+        let (files, trackpoint_chunks, _) = storage.inner.counts();
+        assert_eq!(files, counts.0 - 1);
+        assert!(trackpoint_chunks < counts.1);
+    }
+
+    #[test]
+    fn test_chunks_shared_by_files_are_stored_once_and_stay_shared() {
+        let storage = Recording::default();
+        let mut snapshot = snapshot_of(&["data/with_time.gpx"]);
+        let original = snapshot.files[&snapshot.order[0]].clone();
+        let mut copy = (*original).clone();
+        copy.id = FileId::default();
+        snapshot.order.push(copy.id);
+        snapshot.files.insert(copy.id, Rc::new(copy));
+
+        let mut persister = Persister::default();
+        block_on(persister.save(&storage, snapshot)).unwrap();
+        let chunks = original.trk[0].trkseg[0].chunks().len();
+        assert_eq!(storage.inner.counts().1, chunks);
+
+        let restored = block_on(Persister::default().restore(&storage)).unwrap();
+        assert_eq!(restored.files.len(), 2);
+        assert!(Rc::ptr_eq(
+            &restored.files[0].trk[0].trkseg[0].chunks()[0],
+            &restored.files[1].trk[0].trkseg[0].chunks()[0]
+        ));
+    }
+
+    #[test]
+    fn test_unreadable_files_are_skipped_and_dropped_at_the_next_save() {
+        let storage = Recording::default();
+        let snapshot = snapshot_of(&FILES);
+        let mut persister = Persister::default();
+        block_on(persister.save(&storage, snapshot.clone())).unwrap();
+
+        // damage a record, and lose a chunk of another file
+        let broken = snapshot.order[0];
+        block_on(storage.inner.commit(&Batch {
+            put_files: vec![(broken, vec![99, 1, 2])],
+            ..Default::default()
+        }))
+        .unwrap();
+        let mut persister = Persister::default();
+        let restored = block_on(persister.restore(&storage)).unwrap();
+        assert_eq!(restored.unreadable, 1);
+        assert_eq!(restored.files.len(), FILES.len() - 1);
+        assert!(restored.files.iter().all(|file| file.id != broken));
+
+        let kept = Snapshot {
+            files: restored.files.iter().map(|f| (f.id, f.clone())).collect(),
+            order: restored.order,
+            categories: restored.categories,
+        };
+        block_on(persister.save(&storage, kept)).unwrap();
+        assert_eq!(storage.inner.counts().0, FILES.len() - 1);
+    }
+
+    #[test]
+    fn test_an_engine_starts_from_what_is_restored() {
+        let storage = Recording::default();
+        let mut engine = Engine::default();
+        for path in FILES {
+            let data = std::fs::read(path).unwrap();
+            assert!(engine.execute(Action::Edit(Command::Load(Load {
+                data: &data,
+                name: "file",
+            }))));
+        }
+        let snapshot = engine.snapshot();
+        assert_eq!(snapshot.files.len(), FILES.len());
+        block_on(Persister::default().save(&storage, snapshot.clone())).unwrap();
+
+        let restored = block_on(Persister::default().restore(&storage)).unwrap();
+        let mut engine = Engine::default();
+        engine.restore(restored);
+        assert_eq!(engine.snapshot().order, snapshot.order);
+        let diff = engine.last_diff().unwrap();
+        assert_eq!(diff.added.len(), FILES.len());
+        assert!(engine.order_changed());
+        for id in &snapshot.order {
+            assert!(engine.file_structure(id).is_some());
+        }
+
+        // the files that were restored are not undone
+        assert!(!engine.can_undo());
+        assert!(!engine.execute(Action::Undo));
+        let data = std::fs::read(FILES[0]).unwrap();
+        assert!(engine.execute(Action::Edit(Command::Load(Load {
+            data: &data,
+            name: "file",
+        }))));
+        assert!(engine.can_undo());
+        assert!(engine.execute(Action::Undo));
+        assert_eq!(engine.snapshot().files.len(), FILES.len());
+        assert!(!engine.can_undo());
+    }
+}