From 24b877c4ee20784a7c398a954ee600805ed085be Mon Sep 17 00:00:00 2001
From: vcoppe <vianney.coppe@gmail.com>
Date: Wed, 7 Oct 2026 19:38:21 +0200
Subject: [PATCH] split

---
 .../engine/src/engine/command/tools/split.rs  | 327 +++++++++++++++++-
 gpx-rs/wasm/src/lib.rs                        |  30 +-
 .../lib/components/map/gpx-layer/gpx-layer.ts |  10 +-
 .../toolbar/tools/scissors/Scissors.svelte    |  94 ++---
 .../toolbar/tools/scissors/scissors.ts        |  35 +-
 .../toolbar/tools/scissors/split-controls.ts  | 126 ++++---
 website/src/lib/engine.ts                     |  23 ++
 website/src/lib/logic/file-actions.ts         |  67 +---
 8 files changed, 532 insertions(+), 180 deletions(-)

diff --git a/gpx-rs/engine/src/engine/command/tools/split.rs b/gpx-rs/engine/src/engine/command/tools/split.rs
index 34a648b73..f245ec7f1 100644
--- a/gpx-rs/engine/src/engine/command/tools/split.rs
+++ b/gpx-rs/engine/src/engine/command/tools/split.rs
@@ -1,13 +1,332 @@
-use crate::{Apply, CommandError, State};
+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> {
-        // TODO
-        Err(CommandError::NotImplemented("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);
+        assert_eq!(a.trkseg[..seg], before.trk[trk].trkseg[..seg]);
+        // 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));
     }
 }
diff --git a/gpx-rs/wasm/src/lib.rs b/gpx-rs/wasm/src/lib.rs
index 6c4449a8f..5f93beb82 100644
--- a/gpx-rs/wasm/src/lib.rs
+++ b/gpx-rs/wasm/src/lib.rs
@@ -23,6 +23,25 @@ pub enum MergeType {
     Group,
 }
 
+/// What a split cuts in two.
+#[wasm_bindgen]
+#[derive(Clone, Copy)]
+pub enum SplitType {
+    Files,
+    Tracks,
+    Segments,
+}
+
+impl From<SplitType> for engine::SplitType {
+    fn from(t: SplitType) -> Self {
+        match t {
+            SplitType::Files => Self::Files,
+            SplitType::Tracks => Self::Tracks,
+            SplitType::Segments => Self::Segments,
+        }
+    }
+}
+
 #[wasm_bindgen]
 #[derive(Clone, Copy)]
 pub enum CleanType {
@@ -582,9 +601,16 @@ pub fn crop(start: u32, end: u32) -> bool {
     start <= end && edit(Command::Crop(engine::Crop { start, end }))
 }
 
+/// Cuts the file, the track or the segment (see `SplitType`) of the trackpoint `at` of the
+/// selection in two, there: the trackpoint ends the first part and starts the second one. Does
+/// nothing, and returns false, if the revision of the routing buffers is not the given one.
 #[wasm_bindgen]
-pub fn split(at: u32) -> bool {
-    edit(Command::Split(engine::Split { at }))
+pub fn split(revision: u32, at: u32, split_type: SplitType) -> bool {
+    routing_revision_is(revision)
+        && edit(Command::Split(engine::Split {
+            at,
+            split_type: split_type.into(),
+        }))
 }
 
 #[wasm_bindgen]
diff --git a/website/src/lib/components/map/gpx-layer/gpx-layer.ts b/website/src/lib/components/map/gpx-layer/gpx-layer.ts
index 966153101..a3c2006c3 100644
--- a/website/src/lib/components/map/gpx-layer/gpx-layer.ts
+++ b/website/src/lib/components/map/gpx-layer/gpx-layer.ts
@@ -20,7 +20,7 @@ import { isSegmentHidden, isWaypointHidden } from '$lib/file-visibility';
 import { settings } from '$lib/logic/settings';
 import { currentTool, Tool } from '$lib/components/toolbar/tools';
 import { fileActions } from '$lib/logic/file-actions';
-import { splitAs } from '$lib/components/toolbar/tools/scissors/scissors';
+import { splitAtPoint } from '$lib/components/toolbar/tools/scissors/scissors';
 import { mapCursor, MapCursorState } from '$lib/logic/map-cursor';
 import { ANCHOR_LAYER_KEY } from '$lib/components/map/style';
 
@@ -415,7 +415,7 @@ export class GPXLayer {
 
     layerOnClick(e: MapLayerMouseEvent) {
         const properties = e.features![0].properties!;
-        const { trackId, segmentId, trackIndex, segmentIndex } = properties;
+        const { trackId, segmentId } = properties;
         const selectionType = this.selectionState.type;
 
         if (
@@ -436,11 +436,7 @@ export class GPXLayer {
                 return;
             }
 
-            // TODO the engine can split (Command::Split) but needs the index of the trackpoint
-            // fileActions.split(get(splitAs), this.fileId, trackIndex, segmentIndex, {
-            //     lat: e.lngLat.lat,
-            //     lon: e.lngLat.lng,
-            // });
+            splitAtPoint(segmentId, { lng: e.lngLat.lng, lat: e.lngLat.lat });
             return;
         }
 
diff --git a/website/src/lib/components/toolbar/tools/scissors/Scissors.svelte b/website/src/lib/components/toolbar/tools/scissors/Scissors.svelte
index 24f124b6e..b51f031de 100644
--- a/website/src/lib/components/toolbar/tools/scissors/Scissors.svelte
+++ b/website/src/lib/components/toolbar/tools/scissors/Scissors.svelte
@@ -1,21 +1,18 @@
 <script lang="ts">
     import { splitAs, SplitType } from '$lib/components/toolbar/tools/scissors/scissors';
     import Help from '$lib/components/Help.svelte';
-    import { ListRootItem } from '$lib/components/file-list/file-list';
     import { Label } from '$lib/components/ui/label/index.js';
     import { Button } from '$lib/components/ui/button';
     import { Slider } from '$lib/components/ui/slider';
     import * as Select from '$lib/components/ui/select';
     import { Separator } from '$lib/components/ui/separator';
     import { map } from '$lib/components/map/map';
-    import { get } from 'svelte/store';
     import { i18n } from '$lib/i18n.svelte';
     import { onDestroy, onMount, untrack } from 'svelte';
     import { Crop } from '@lucide/svelte';
     import { SplitControls } from './split-controls';
     import { getURLForLanguage } from '$lib/utils';
-    import { selection } from '$lib/logic/selection';
-    import { gpxStatistics, slicedGPXStatistics } from '$lib/logic/statistics';
+    import { slicedStatistics } from '$lib/logic/selection-statistics';
     import { engine } from '$lib/engine';
 
     let props: {
@@ -24,15 +21,35 @@
 
     let splitControls: SplitControls | undefined = undefined;
 
+    const selection = engine.selection;
+    const statistics = engine.statistics;
+
+    // the tool works on files, tracks and segments, not on waypoints
     let validSelection = $derived(
-        $selection.hasAnyChildren(new ListRootItem(), true, ['waypoints']) &&
-            $gpxStatistics.global.length > 0
+        ($selection.type === 'file' ||
+            $selection.type === 'track' ||
+            $selection.type === 'segment') &&
+            $statistics.length > 0
     );
-    let maxSliderValue = $derived(
-        validSelection && $gpxStatistics.global.length > 0 ? $gpxStatistics.global.length - 1 : 1
-    );
-    let sliderValues = $derived([0, maxSliderValue]);
-    let canCrop = $derived(sliderValues[0] != 0 || sliderValues[1] != maxSliderValue);
+    // The slider does work for each of its steps every time it changes, which is too slow with
+    // the thousands of trackpoints of a long track: it has a limited number of steps, which are
+    // spread over the trackpoints.
+    const MAX_STEPS = 500;
+    let length = $derived($statistics.length);
+    let steps = $derived(validSelection ? Math.min(length - 1, MAX_STEPS) : 1);
+    let sliderValues = $state([0, 1]);
+
+    /** The index of the trackpoint of a step of the slider. */
+    function toIndex(step: number) {
+        return steps <= 0 || steps >= length - 1 ? step : Math.round((step * (length - 1)) / steps);
+    }
+
+    /** The step of the slider that is the closest to a trackpoint. */
+    function toStep(index: number) {
+        return steps <= 0 || steps >= length - 1
+            ? index
+            : Math.round((index * steps) / (length - 1));
+    }
 
     onMount(() => {
         if ($map) {
@@ -40,42 +57,33 @@
         }
     });
 
-    function updateSlicedGPXStatistics() {
-        if (validSelection && canCrop) {
-            $slicedGPXStatistics = [
-                get(gpxStatistics).sliced(sliderValues[0], sliderValues[1]),
-                sliderValues[0],
-                sliderValues[1],
-            ];
+    /** The user moved the slider: the part of the selection between its bounds is highlighted. */
+    function updateSlicedStatistics([startStep, endStep]: number[]) {
+        if (validSelection && (startStep !== 0 || endStep !== steps)) {
+            const [start, end] = [toIndex(startStep), toIndex(endStep)];
+            const global = $statistics.slice(start, end);
+            slicedStatistics.set(global && { global, start, end });
         } else {
-            $slicedGPXStatistics = undefined;
-        }
-    }
-
-    function updateSliderValues() {
-        if ($slicedGPXStatistics !== undefined) {
-            sliderValues = [$slicedGPXStatistics[1], $slicedGPXStatistics[2]];
+            slicedStatistics.set(undefined);
         }
     }
 
+    // The slider follows the highlighted part, which can also be chosen on the elevation profile or
+    // reset (when the selection changes): it covers the whole selection when there is none.
+    // It only goes this way, the slider tells about its own changes (`onValueChange`).
     $effect(() => {
-        if (sliderValues) {
-            untrack(() => updateSlicedGPXStatistics());
-        }
-    });
-
-    $effect(() => {
-        if (
-            $slicedGPXStatistics !== undefined &&
-            ($slicedGPXStatistics[1] !== sliderValues[0] ||
-                $slicedGPXStatistics[2] !== sliderValues[1])
-        ) {
-            untrack(() => updateSliderValues());
-        }
+        const sliced = $slicedStatistics;
+        const max = steps;
+        untrack(() => {
+            const bounds = sliced ? [toStep(sliced.start), toStep(sliced.end)] : [0, max];
+            if (sliderValues[0] !== bounds[0] || sliderValues[1] !== bounds[1]) {
+                sliderValues = bounds;
+            }
+        });
     });
 
     onDestroy(() => {
-        $slicedGPXStatistics = undefined;
+        slicedStatistics.set(undefined);
         if (splitControls) {
             splitControls.destroy();
         }
@@ -86,7 +94,8 @@
     <div class="p-2">
         <Slider
             bind:value={sliderValues}
-            max={maxSliderValue}
+            onValueChange={updateSlicedStatistics}
+            max={steps}
             step={1}
             type="multiple"
             disabled={!validSelection}
@@ -94,8 +103,9 @@
     </div>
     <Button
         variant="outline"
-        disabled={!validSelection || !canCrop}
-        onclick={() => engine.crop(sliderValues[0], sliderValues[1])}
+        disabled={!validSelection || !$slicedStatistics}
+        onclick={() =>
+            $slicedStatistics && engine.crop($slicedStatistics.start, $slicedStatistics.end)}
     >
         <Crop size="16" />{i18n._('toolbar.scissors.crop')}
     </Button>
diff --git a/website/src/lib/components/toolbar/tools/scissors/scissors.ts b/website/src/lib/components/toolbar/tools/scissors/scissors.ts
index c44c748ad..290d3991d 100644
--- a/website/src/lib/components/toolbar/tools/scissors/scissors.ts
+++ b/website/src/lib/components/toolbar/tools/scissors/scissors.ts
@@ -1,9 +1,32 @@
-import { writable, type Writable } from 'svelte/store';
+import { get, writable, type Writable } from 'svelte/store';
+import { engine, type SplitType as EngineSplitType } from '$lib/engine';
+import { closestPointIndexIn } from '$lib/closest-point';
 
-export enum SplitType {
-    FILES = 'files',
-    TRACKS = 'tracks',
-    SEGMENTS = 'segments',
-}
+/** What a split cuts in two, the values being the ones of the engine. */
+export const SplitType = {
+    FILES: 'files',
+    TRACKS: 'tracks',
+    SEGMENTS: 'segments',
+} as const satisfies Record<string, EngineSplitType>;
+export type SplitType = (typeof SplitType)[keyof typeof SplitType];
 
 export let splitAs: Writable<SplitType> = writable(SplitType.FILES);
+
+/**
+ * Splits at the trackpoint of a selected segment that is the closest to `point`, as `splitAs` says.
+ * The statistics of the engine need to have the anchors (the scissors tool asks for them).
+ */
+export function splitAtPoint(segmentId: string, point: { lng: number; lat: number }) {
+    const statistics = get(engine.statistics);
+    const anchors = statistics.anchors;
+    const segment = anchors?.segmentIds.indexOf(segmentId) ?? -1;
+    if (!anchors || segment < 0) {
+        return;
+    }
+    const starts = anchors.segmentStarts;
+    const end = segment + 1 < starts.length ? starts[segment + 1] : statistics.length;
+    const index = closestPointIndexIn(statistics.lng, statistics.lat, starts[segment], end, point);
+    if (index !== undefined) {
+        engine.split(anchors.revision, index, get(splitAs));
+    }
+}
diff --git a/website/src/lib/components/toolbar/tools/scissors/split-controls.ts b/website/src/lib/components/toolbar/tools/scissors/split-controls.ts
index bc5bf6d95..3242349d0 100644
--- a/website/src/lib/components/toolbar/tools/scissors/split-controls.ts
+++ b/website/src/lib/components/toolbar/tools/scissors/split-controls.ts
@@ -1,22 +1,32 @@
-import { ListTrackSegmentItem } from '$lib/components/file-list/file-list';
 import { currentTool, Tool } from '$lib/components/toolbar/tools';
 import { splitAs } from '$lib/components/toolbar/tools/scissors/scissors';
 import { Scissors } from 'lucide-static';
-import { selection } from '$lib/logic/selection';
-import { gpxStatistics } from '$lib/logic/statistics';
 import { get } from 'svelte/store';
-import { fileStateCollection } from '$lib/logic/file-state';
-import { fileActions } from '$lib/logic/file-actions';
 import { mapCursor, MapCursorState } from '$lib/logic/map-cursor';
 import type { GeoJSONSource } from 'maplibre-gl';
 import { ANCHOR_LAYER_KEY } from '$lib/components/map/style';
 import type { MapLayerEventManager } from '$lib/components/map/map-layer-event-manager';
 import { loadSVGIcon } from '$lib/utils';
+import {
+    engine,
+    type Selection,
+    type SelectionStatistics,
+    type StatisticsRequest,
+} from '$lib/engine';
 
+/**
+ * The anchors inside the segments of the selection, where a click splits the file, the track or
+ * the segment: a command of the engine, which finds them by the index of their trackpoint in the
+ * selection.
+ */
 export class SplitControls {
     map: maplibregl.Map;
     layerEventManager: MapLayerEventManager;
     unsubscribes: Function[] = [];
+    /** What the tool needs from the engine, while it shows the anchors. */
+    request: StatisticsRequest = engine.requestStatistics();
+    selection: Selection = { type: 'empty' };
+    statistics: SelectionStatistics | undefined = undefined;
 
     layerOnMouseEnterBinded: (e: any) => void = this.layerOnMouseEnter.bind(this);
     layerOnMouseLeaveBinded: () => void = this.layerOnMouseLeave.bind(this);
@@ -36,13 +46,29 @@ export class SplitControls {
             </svg>`
         );
 
-        this.unsubscribes.push(gpxStatistics.subscribe(this.addIfNeeded.bind(this)));
+        this.unsubscribes.push(
+            engine.statistics.subscribe((statistics) => {
+                this.statistics = statistics;
+                this.addIfNeeded();
+            })
+        );
         this.unsubscribes.push(currentTool.subscribe(this.addIfNeeded.bind(this)));
-        this.unsubscribes.push(selection.subscribe(this.addIfNeeded.bind(this)));
+        this.unsubscribes.push(
+            engine.selection.subscribe((selection) => {
+                this.selection = selection;
+                this.addIfNeeded();
+            })
+        );
     }
 
     addIfNeeded() {
-        let scissors = get(currentTool) === Tool.SCISSORS;
+        // the tool works on files, tracks and segments, not on waypoints
+        const scissors =
+            get(currentTool) === Tool.SCISSORS &&
+            (this.selection.type === 'file' ||
+                this.selection.type === 'track' ||
+                this.selection.type === 'segment');
+        this.request.set(scissors ? ['anchors'] : []);
         if (!scissors) {
             this.remove();
             return;
@@ -51,44 +77,42 @@ export class SplitControls {
         this.updateControls();
     }
 
-    updateControls() {
-        let data: GeoJSON.FeatureCollection = {
-            type: 'FeatureCollection',
-            features: [],
-        };
-        selection.applyToOrderedSelectedItemsFromFile((fileId, level, items) => {
-            let file = fileStateCollection.getFile(fileId);
-
-            if (file) {
-                file.forEachSegment((segment, trackIndex, segmentIndex) => {
-                    if (
-                        get(selection).hasAnyParent(
-                            new ListTrackSegmentItem(fileId, trackIndex, segmentIndex)
-                        )
-                    ) {
-                        for (let i = 1; i < segment.trkpt.length - 1; i++) {
-                            let point = segment.trkpt[i];
-                            if (point._data.anchor) {
-                                data.features.push({
-                                    type: 'Feature',
-                                    geometry: {
-                                        type: 'Point',
-                                        coordinates: [point.getLongitude(), point.getLatitude()],
-                                    },
-                                    properties: {
-                                        fileId: fileId,
-                                        trackIndex: trackIndex,
-                                        segmentIndex: segmentIndex,
-                                        pointIndex: i,
-                                        minZoom: point._data.zoom,
-                                    },
-                                });
-                            }
-                        }
-                    }
+    /** The anchors that are inside a segment, which is not where it starts or ends. */
+    inner(): GeoJSON.Feature[] {
+        const statistics = this.statistics;
+        const anchors = statistics?.anchors;
+        if (!statistics || !anchors) {
+            return [];
+        }
+        const starts = anchors.segmentStarts;
+        const features: GeoJSON.Feature[] = [];
+        let segment = 0;
+        for (let i = 0; i < anchors.indices.length; i++) {
+            const index = anchors.indices[i];
+            // the anchors are sorted: the segment can only be the same or a following one
+            while (segment + 1 < starts.length && starts[segment + 1] <= index) {
+                segment++;
+            }
+            const end = segment + 1 < starts.length ? starts[segment + 1] : statistics.length;
+            if (index > starts[segment] && index < end - 1) {
+                features.push({
+                    type: 'Feature',
+                    geometry: {
+                        type: 'Point',
+                        coordinates: [statistics.lng[index], statistics.lat[index]],
+                    },
+                    properties: { index, minZoom: anchors.zooms[i] },
                 });
             }
-        }, false);
+        }
+        return features;
+    }
+
+    updateControls() {
+        const data: GeoJSON.FeatureCollection = {
+            type: 'FeatureCollection',
+            features: this.inner(),
+        };
 
         try {
             let source = this.map.getSource('split-controls') as GeoJSONSource | undefined;
@@ -161,19 +185,15 @@ export class SplitControls {
     }
 
     layerOnClick(e: maplibregl.MapLayerMouseEvent) {
-        let coordinates = (e.features![0].geometry as GeoJSON.Point).coordinates;
-        fileActions.split(
-            get(splitAs),
-            e.features![0].properties!.fileId,
-            e.features![0].properties!.trackIndex,
-            e.features![0].properties!.segmentIndex,
-            { lon: coordinates[0], lat: coordinates[1] },
-            e.features![0].properties!.pointIndex
-        );
+        const revision = this.statistics?.anchors?.revision;
+        if (revision !== undefined) {
+            engine.split(revision, e.features![0].properties!.index, get(splitAs));
+        }
     }
 
     destroy() {
         this.remove();
+        this.request.release();
         this.unsubscribes.forEach((unsubscribe) => unsubscribe());
     }
 }
diff --git a/website/src/lib/engine.ts b/website/src/lib/engine.ts
index a3fc9f7b8..5020ba732 100644
--- a/website/src/lib/engine.ts
+++ b/website/src/lib/engine.ts
@@ -32,6 +32,9 @@ export type {
 
 type Wasm = typeof import('gpx-rs');
 
+/** What a split cuts in two: the file, the track or the segment of the trackpoint. */
+export type SplitType = 'files' | 'tracks' | 'segments';
+
 /**
  * How elements combine with the current selection: they `replace` it, are `add`ed to it, or are
  * `toggle`d (the ones already selected are removed). Adding and toggling only merge with elements
@@ -645,6 +648,26 @@ class Engine {
         return this.run((w) => w.reverse());
     }
 
+    /**
+     * Cuts the file, the track or the segment (see `SplitType`) of the trackpoint `at` of the
+     * selection in two, there: the trackpoint ends the first part and starts the second one. The
+     * first part keeps the ids, the second one (and what follows) gets new ones. `revision` is the
+     * one of `SelectionAnchors`, which `at` is an index of.
+     */
+    split(revision: number, at: number, splitType: SplitType) {
+        return this.run((w) =>
+            w.split(
+                revision,
+                at,
+                {
+                    files: w.SplitType.Files,
+                    tracks: w.SplitType.Tracks,
+                    segments: w.SplitType.Segments,
+                }[splitType]
+            )
+        );
+    }
+
     /**
      * Keeps the trackpoints `start` to `end` (both included) of the selection, counted over its
      * segments one after the other, and removes the others, with the segments, tracks and files
diff --git a/website/src/lib/logic/file-actions.ts b/website/src/lib/logic/file-actions.ts
index e776c4656..a995c9c0c 100644
--- a/website/src/lib/logic/file-actions.ts
+++ b/website/src/lib/logic/file-actions.ts
@@ -2,7 +2,6 @@ import { fileStateCollection } from '$lib/logic/file-state';
 import { fileActionManager } from '$lib/logic/file-action-manager';
 import { applyToOrderedItemsFromFile, copied, cut, selection } from '$lib/logic/selection';
 import { currentTool, Tool } from '$lib/components/toolbar/tools';
-import { SplitType } from '$lib/components/toolbar/tools/scissors/scissors';
 import {
     ListFileItem,
     ListLevel,
@@ -20,13 +19,12 @@ import {
     TrackPoint,
     TrackSegment,
     Waypoint,
-    type Coordinates,
     type LineStyleExtension,
     type WaypointType,
 } from 'gpx';
 import { get } from 'svelte/store';
 import { settings } from '$lib/logic/settings';
-import { getClosestLinePoint, getClosestTrackSegments, getElevation } from '$lib/utils';
+import { getClosestTrackSegments, getElevation } from '$lib/utils';
 import { gpxStatistics } from '$lib/logic/statistics';
 import { boundsManager } from './bounds';
 import { engine } from '$lib/engine';
@@ -333,69 +331,6 @@ export const fileActions = {
             });
         });
     },
-    split(
-        splitType: SplitType,
-        fileId: string,
-        trackIndex: number,
-        segmentIndex: number,
-        coordinates: Coordinates,
-        trkptIndex?: number
-    ) {
-        return fileActionManager.applyGlobal((draft) => {
-            let file = fileStateCollection.getFile(fileId);
-            if (file) {
-                let segment = file.trk[trackIndex].trkseg[segmentIndex];
-                let minIndex = 0;
-                if (trkptIndex === undefined) {
-                    // Find the point closest to split
-                    let closest = getClosestLinePoint(segment.trkpt, coordinates);
-                    minIndex = closest._data.index;
-                } else {
-                    minIndex = trkptIndex;
-                }
-                let absoluteIndex = minIndex;
-                file.forEachSegment((seg, trkIndex, segIndex) => {
-                    if (
-                        (trkIndex < trackIndex && splitType === SplitType.FILES) ||
-                        (trkIndex === trackIndex && segIndex < segmentIndex)
-                    ) {
-                        absoluteIndex += seg.trkpt.length;
-                    }
-                });
-                if (splitType === SplitType.FILES) {
-                    let newFile = draft.get(fileId);
-                    if (newFile) {
-                        newFile.crop(0, absoluteIndex);
-                        let newFile2 = file.clone();
-                        newFile2._data.id = getFileIds(1)[0];
-                        newFile2.crop(absoluteIndex, file.getNumberOfTrackPoints() - 1);
-                        draft.set(newFile2._data.id, freeze(newFile2));
-                    }
-                } else if (splitType === SplitType.TRACKS) {
-                    let newFile = draft.get(fileId);
-                    if (newFile) {
-                        let start = file.trk[trackIndex].clone();
-                        start.crop(0, absoluteIndex);
-                        let end = file.trk[trackIndex].clone();
-                        end.crop(absoluteIndex, file.trk[trackIndex].getNumberOfTrackPoints() - 1);
-                        newFile.replaceTracks(trackIndex, trackIndex, [start, end]);
-                    }
-                } else if (splitType === SplitType.SEGMENTS) {
-                    let newFile = draft.get(fileId);
-                    if (newFile) {
-                        let start = segment.clone();
-                        start.crop(0, minIndex);
-                        let end = segment.clone();
-                        end.crop(minIndex, segment.trkpt.length - 1);
-                        newFile.replaceTrackSegments(trackIndex, segmentIndex, segmentIndex, [
-                            start,
-                            end,
-                        ]);
-                    }
-                }
-            }
-        });
-    },
     reduce: (itemsAndPoints: Map<ListItem, TrackPoint[]>) => {
         if (itemsAndPoints.size === 0) {
             return;