progress

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

@@ -31,7 +31,7 @@ impl TrackpointChunk {
     }
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
 pub struct WaypointChunkId(Uuid);
 
 impl Default for WaypointChunkId {

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

@@ -5,7 +5,7 @@ use uuid::Uuid;
 use crate::{Trackpoint, TrackpointChunk};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct TrackSegmentId(Uuid);
+pub struct TrackSegmentId(pub Uuid);
 
 impl Default for TrackSegmentId {
     fn default() -> Self {
@@ -14,7 +14,7 @@ impl Default for TrackSegmentId {
 }
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct TrackSegmentRevisionId(Uuid);
+pub struct TrackSegmentRevisionId(pub Uuid);
 
 impl Default for TrackSegmentRevisionId {
     fn default() -> Self {

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

@@ -3,7 +3,7 @@ use uuid::Uuid;
 use crate::{Link, TrackSegment};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct TrackId(Uuid);
+pub struct TrackId(pub Uuid);
 
 impl Default for TrackId {
     fn default() -> Self {

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

@@ -3,7 +3,7 @@ use uuid::Uuid;
 use crate::{Link, LngLat};
 
 #[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
-pub struct WaypointId(Uuid);
+pub struct WaypointId(pub Uuid);
 
 impl Default for WaypointId {
     fn default() -> Self {

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

@@ -3,7 +3,7 @@ mod command;
 mod edit;
 mod file;
 #[cfg(test)]
-mod fixture;
+pub(crate) mod fixture;
 mod pattern;
 mod tools;
 

gpx-rs/engine/src/engine/derived/coordinates_cache.rs

@@ -0,0 +1,149 @@
+use std::collections::{HashMap, HashSet};
+
+use crate::{
+    FileId, StackEntry as Files, TrackSegmentId, TrackSegmentRevisionId, waypoints_revision,
+};
+
+/// Coordinates buffers, as flat `[lng, lat, lng, lat, ...]` arrays so that they can be handed
+/// to the UI without per-point calls: one per track segment (its trackpoints) and one per file
+/// (its waypoints). A buffer is only rebuilt when the revision of its segment (or the waypoints
+/// of its file) changes, so editing a segment does not touch the buffers of the others.
+#[derive(Debug, Default)]
+pub struct CoordinatesCache {
+    segments: HashMap<TrackSegmentId, (TrackSegmentRevisionId, Vec<f64>)>,
+    waypoints: HashMap<FileId, (u64, Vec<f64>)>,
+}
+
+impl CoordinatesCache {
+    pub fn update(&mut self, files: Option<&Files>) {
+        let mut segments = HashSet::new();
+        let mut waypoints = HashSet::new();
+        for file in files.into_iter().flat_map(|files| files.values()) {
+            waypoints.insert(file.id);
+            let rev = waypoints_revision(file);
+            if self.waypoints.get(&file.id).is_none_or(|(r, _)| *r != rev) {
+                let coordinates = file
+                    .wpt
+                    .iter()
+                    .flat_map(|chunk| &chunk.wpt)
+                    .flat_map(|wpt| [wpt.coordinates.lng, wpt.coordinates.lat])
+                    .collect();
+                self.waypoints.insert(file.id, (rev, coordinates));
+            }
+            for seg in file.trk.iter().flat_map(|trk| &trk.trkseg) {
+                segments.insert(seg.id);
+                if self
+                    .segments
+                    .get(&seg.id)
+                    .is_none_or(|(r, _)| *r != seg.rev_id)
+                {
+                    let coordinates = seg
+                        .iter()
+                        .flat_map(|trkpt| [trkpt.coordinates.lng, trkpt.coordinates.lat])
+                        .collect();
+                    self.segments.insert(seg.id, (seg.rev_id, coordinates));
+                }
+            }
+        }
+        self.segments.retain(|id, _| segments.contains(id));
+        self.waypoints.retain(|id, _| waypoints.contains(id));
+    }
+
+    /// Coordinates of the trackpoints of a segment, empty if it does not exist.
+    pub fn segment(&self, id: &TrackSegmentId) -> &[f64] {
+        self.segments.get(id).map_or(&[], |(_, c)| c)
+    }
+
+    /// Coordinates of the waypoints of a file, empty if it does not exist.
+    pub fn waypoints(&self, id: &FileId) -> &[f64] {
+        self.waypoints.get(id).map_or(&[], |(_, c)| c)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::{Apply, LngLat, Load, Waypoint, WaypointChunk, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    fn loaded() -> (Fixture, FileId) {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load { data: &data }.apply(&mut fx.state()).unwrap();
+        let id = fx.order.0[0];
+        (fx, id)
+    }
+
+    #[test]
+    fn test_segment_buffers_match_trackpoints() {
+        let (fx, id) = loaded();
+        let mut cache = CoordinatesCache::default();
+        cache.update(Some(&fx.files));
+        for seg in fx.files[&id].trk.iter().flat_map(|t| &t.trkseg) {
+            let buffer = cache.segment(&seg.id);
+            assert_eq!(buffer.len(), seg.len() * 2);
+            for (i, p) in seg.iter().enumerate() {
+                assert_eq!(buffer[2 * i], p.coordinates.lng);
+                assert_eq!(buffer[2 * i + 1], p.coordinates.lat);
+            }
+        }
+        assert!(cache.segment(&TrackSegmentId::default()).is_empty());
+    }
+
+    #[test]
+    fn test_only_changed_buffers_are_rebuilt_and_stale_ones_dropped() {
+        let (mut fx, id) = loaded();
+        let mut cache = CoordinatesCache::default();
+        cache.update(Some(&fx.files));
+        let ids: Vec<_> = fx.files[&id]
+            .trk
+            .iter()
+            .flat_map(|t| &t.trkseg)
+            .map(|s| s.id)
+            .collect();
+        assert!(ids.len() >= 2);
+        let ptr = |c: &CoordinatesCache, i: usize| c.segment(&ids[i]).as_ptr();
+        let (p0, p1) = (ptr(&cache, 0), ptr(&cache, 1));
+
+        let mut file = (*fx.files[&id]).clone();
+        let seg = &mut file.trk[0].trkseg[0];
+        seg.splice(0, 0, vec![Default::default()]);
+        seg.rev_id = Default::default();
+        let len = seg.len();
+        fx.files.insert(id, Rc::new(file));
+        cache.update(Some(&fx.files));
+        assert_eq!(cache.segment(&ids[0]).len(), len * 2);
+        assert_ne!(ptr(&cache, 0), p0);
+        assert_eq!(ptr(&cache, 1), p1);
+
+        cache.update(None);
+        assert!(cache.segment(&ids[0]).is_empty());
+        assert!(cache.waypoints(&id).is_empty());
+    }
+
+    #[test]
+    fn test_waypoint_buffer() {
+        let (mut fx, id) = loaded();
+        let wpt = |lng, lat| Waypoint {
+            coordinates: LngLat { lng, lat },
+            ..Default::default()
+        };
+        let mut file = (*fx.files[&id]).clone();
+        file.wpt = vec![
+            Rc::new(WaypointChunk {
+                wpt: vec![wpt(1.0, 2.0)],
+                ..Default::default()
+            }),
+            Rc::new(WaypointChunk {
+                wpt: vec![wpt(3.0, 4.0)],
+                ..Default::default()
+            }),
+        ];
+        fx.files.insert(id, Rc::new(file));
+        let mut cache = CoordinatesCache::default();
+        cache.update(Some(&fx.files));
+        assert_eq!(cache.waypoints(&id), [1.0, 2.0, 3.0, 4.0]);
+    }
+}

gpx-rs/engine/src/engine/derived/file_structure.rs

@@ -0,0 +1,140 @@
+use std::hash::{Hash, Hasher};
+
+use crate::{File, FileId, TrackId, TrackSegmentId, TrackSegmentRevisionId, WaypointId};
+
+/// What the UI needs to display a file: its name and the structure of its tracks and waypoints,
+/// with the ids that reference every element. Coordinates are not part of it, they are read
+/// from the buffers of the [`CoordinatesCache`](crate::CoordinatesCache) (the `i`-th waypoint
+/// of a file is the `i`-th coordinates pair of its waypoint buffer, same for the trackpoints of
+/// a segment).
+#[derive(Debug, Clone, PartialEq)]
+pub struct FileStructure {
+    pub id: FileId,
+    pub name: String,
+    pub tracks: Vec<TrackNode>,
+    pub waypoints: Vec<WaypointNode>,
+    /// Changes whenever the waypoints of the file (hence their buffer) change.
+    pub waypoints_rev: u64,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct TrackNode {
+    pub id: TrackId,
+    pub name: Option<String>,
+    pub segments: Vec<SegmentNode>,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct SegmentNode {
+    pub id: TrackSegmentId,
+    /// Changes whenever the trackpoints of the segment (hence their buffer) change.
+    pub rev_id: TrackSegmentRevisionId,
+    pub len: usize,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct WaypointNode {
+    pub id: WaypointId,
+    pub name: Option<String>,
+}
+
+impl FileStructure {
+    pub fn new(file: &File) -> Self {
+        Self {
+            id: file.id,
+            name: file.info.name.clone(),
+            tracks: file
+                .trk
+                .iter()
+                .map(|trk| TrackNode {
+                    id: trk.id,
+                    name: trk.info.name.clone(),
+                    segments: trk
+                        .trkseg
+                        .iter()
+                        .map(|seg| SegmentNode {
+                            id: seg.id,
+                            rev_id: seg.rev_id,
+                            len: seg.len(),
+                        })
+                        .collect(),
+                })
+                .collect(),
+            waypoints: file
+                .wpt
+                .iter()
+                .flat_map(|chunk| &chunk.wpt)
+                .map(|wpt| WaypointNode {
+                    id: wpt.id,
+                    name: wpt.name.clone(),
+                })
+                .collect(),
+            waypoints_rev: waypoints_revision(file),
+        }
+    }
+}
+
+/// Identifies the current waypoints of a file: chunks are immutable, so their ids are enough.
+pub fn waypoints_revision(file: &File) -> u64 {
+    let mut hasher = std::collections::hash_map::DefaultHasher::new();
+    for chunk in &file.wpt {
+        chunk.id.hash(&mut hasher);
+    }
+    hasher.finish()
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::{Apply, Load, Waypoint, WaypointChunk, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    #[test]
+    fn test_structure_of_a_file() {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load { data: &data }.apply(&mut fx.state()).unwrap();
+        let file = &fx.files[&fx.order.0[0]];
+        let node = FileStructure::new(file);
+        assert_eq!((node.id, &node.name), (file.id, &file.info.name));
+        assert_eq!(node.tracks.len(), file.trk.len());
+        for (n, t) in node.tracks.iter().zip(&file.trk) {
+            assert_eq!((n.id, &n.name), (t.id, &t.info.name));
+            assert_eq!(n.segments.len(), t.trkseg.len());
+            for (n, s) in n.segments.iter().zip(&t.trkseg) {
+                assert_eq!((n.id, n.rev_id, n.len), (s.id, s.rev_id, s.len()));
+            }
+        }
+    }
+
+    #[test]
+    fn test_waypoints_in_buffer_order_and_revision() {
+        let mut file = crate::File::default();
+        let wpt = |n: &str| Waypoint {
+            name: Some(n.to_string()),
+            ..Default::default()
+        };
+        let before = waypoints_revision(&file);
+        file.wpt = vec![
+            Rc::new(WaypointChunk {
+                wpt: vec![wpt("a"), wpt("b")],
+                ..Default::default()
+            }),
+            Rc::new(WaypointChunk {
+                wpt: vec![wpt("c")],
+                ..Default::default()
+            }),
+        ];
+        let node = FileStructure::new(&file);
+        let names: Vec<_> = node
+            .waypoints
+            .iter()
+            .map(|w| w.name.clone().unwrap())
+            .collect();
+        assert_eq!(names, ["a", "b", "c"]);
+        assert_ne!(node.waypoints_rev, before);
+        assert_eq!(node.waypoints_rev, waypoints_revision(&file));
+    }
+}

gpx-rs/engine/src/engine/derived/file_structure_cache.rs

@@ -0,0 +1,82 @@
+use std::collections::HashMap;
+
+use crate::{Diff, FileId, FileStructure, StackEntry as Files};
+
+/// The structure of each file, only recomputed for the files that changed according to the
+/// [`Diff`] of the stack.
+#[derive(Debug, Default)]
+pub struct FileStructureCache {
+    map: HashMap<FileId, FileStructure>,
+}
+
+impl FileStructureCache {
+    /// Brings the cache in line with `files`, given what changed since the last update.
+    pub fn update(&mut self, files: Option<&Files>, diff: &Option<Diff>) {
+        if let Some(diff) = diff {
+            for id in diff.removed.iter() {
+                self.map.remove(id);
+            }
+            for id in diff.added.iter().chain(&diff.modified) {
+                if let Some(file) = files.and_then(|files| files.get(id)) {
+                    self.map.insert(*id, FileStructure::new(file));
+                }
+            }
+        }
+    }
+
+    pub fn get(&self, id: &FileId) -> Option<&FileStructure> {
+        self.map.get(id)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::rc::Rc;
+
+    use crate::{Apply, Load, engine::command::fixture::Fixture};
+
+    use super::*;
+
+    #[test]
+    fn test_only_files_of_the_diff_are_recomputed() {
+        let mut fx = Fixture::default();
+        let data = std::fs::read("data/with_tracks_and_segments.gpx").unwrap();
+        Load { data: &data }.apply(&mut fx.state()).unwrap();
+        Load { data: &data }.apply(&mut fx.state()).unwrap();
+        let (a, b) = (fx.order.0[0], fx.order.0[1]);
+
+        let mut cache = FileStructureCache::default();
+        cache.update(
+            Some(&fx.files),
+            &Some(Diff {
+                added: vec![a, b],
+                ..Default::default()
+            }),
+        );
+        let before = cache.get(&b).unwrap() as *const FileStructure;
+
+        let mut file = (*fx.files[&a]).clone();
+        file.info.name = "renamed".into();
+        fx.files.insert(a, Rc::new(file));
+        cache.update(
+            Some(&fx.files),
+            &Some(Diff {
+                modified: vec![a],
+                ..Default::default()
+            }),
+        );
+        assert_eq!(cache.get(&a).unwrap().name, "renamed");
+        assert!(std::ptr::eq(cache.get(&b).unwrap(), before));
+
+        fx.files.remove(&b);
+        cache.update(
+            Some(&fx.files),
+            &Some(Diff {
+                removed: vec![b],
+                ..Default::default()
+            }),
+        );
+        assert!(cache.get(&b).is_none());
+        assert!(cache.get(&a).is_some());
+    }
+}

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

@@ -1,5 +1,11 @@
+mod coordinates_cache;
+mod file_structure;
+mod file_structure_cache;
 mod statistics_buffer;
 mod statistics_cache;
 
+pub use coordinates_cache::*;
+pub use file_structure::*;
+pub use file_structure_cache::*;
 pub use statistics_buffer::*;
 pub use statistics_cache::*;

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

@@ -3,8 +3,8 @@
 use std::collections::HashSet;
 
 use crate::{
-    Action, Apply, Command, FileId, FileOrder, Selection, Stack, State, StatisticsBuffer,
-    StatisticsCache,
+    Action, Apply, Command, CoordinatesCache, Diff, FileId, FileOrder, FileStructure,
+    FileStructureCache, Selection, Stack, State, StatisticsBuffer, StatisticsCache, TrackSegmentId,
 };
 
 #[derive(Debug, Default)]
@@ -13,6 +13,10 @@ pub struct Engine {
     selection: Selection,
     order: FileOrder,
     statistics_cache: StatisticsCache,
+    coordinates_cache: CoordinatesCache,
+    structure_cache: FileStructureCache,
+    diff: Option<Diff>,
+    order_changed: bool,
     statistics_buffer: StatisticsBuffer,
 }
 
@@ -21,18 +25,51 @@ impl Engine {
         &self.statistics_buffer
     }
 
+    /// Files in display order.
+    pub fn order(&self) -> &[FileId] {
+        &self.order.0
+    }
+
+    /// Name, tracks, segments and waypoints (with their ids) of a file.
+    pub fn file_structure(&self, id: &FileId) -> Option<&FileStructure> {
+        self.structure_cache.get(id)
+    }
+
+    /// Which files the last action added, removed or modified.
+    pub fn last_diff(&self) -> &Option<Diff> {
+        &self.diff
+    }
+
+    /// Whether the last action changed the order of the files.
+    pub fn order_changed(&self) -> bool {
+        self.order_changed
+    }
+
+    /// Coordinates (`[lng, lat, ...]`) of the trackpoints of a segment.
+    pub fn segment_coordinates(&self, id: &TrackSegmentId) -> &[f64] {
+        self.coordinates_cache.segment(id)
+    }
+
+    /// Coordinates (`[lng, lat, ...]`) of the waypoints of a file.
+    pub fn waypoint_coordinates(&self, id: &FileId) -> &[f64] {
+        self.coordinates_cache.waypoints(id)
+    }
+
     /// Single entry point for every action coming from the frontend. Returns whether anything
     /// changed.
     pub fn execute(&mut self, action: Action) -> bool {
-        let changed = match action {
+        let selection_before = self.selection.clone();
+        let order_before = self.order.0.clone();
+        // the files change iff there is a diff, but selection and order actions have none
+        self.diff = match action {
             Action::Edit(command) => self.edit(command),
-            Action::Undo => self.stack.undo().is_some(),
-            Action::Redo => self.stack.redo().is_some(),
+            Action::Undo => self.stack.undo(),
+            Action::Redo => self.stack.redo(),
             Action::Select { file_ids } => {
                 self.selection = Selection::File {
                     file_ids: file_ids.into_iter().collect(),
                 };
-                true
+                None
             }
             Action::AddSelect { file_ids } => {
                 match &mut self.selection {
@@ -43,33 +80,37 @@ impl Engine {
                         }
                     }
                 }
-                true
+                None
+            }
+            Action::Reorder { file_ids, index } => {
+                self.order.move_files(&file_ids, index);
+                None
             }
-            Action::Reorder { file_ids, index } => self.order.move_files(&file_ids, index),
             Action::SelectAll => {
                 self.selection = Selection::File {
                     file_ids: self.order.0.iter().copied().collect(),
                 };
-                true
+                None
             }
         };
+        let selection_changed = self.selection != selection_before;
+        self.order_changed = self.order.0 != order_before;
+        let changed = self.diff.is_some() || selection_changed || self.order_changed;
         if changed {
             self.refresh();
         }
         changed
     }
 
-    fn edit(&mut self, command: Command) -> bool {
-        self.stack
-            .create_and_push_next(|files| {
-                let mut state = State {
-                    files,
-                    selection: &mut self.selection,
-                    order: &mut self.order,
-                };
-                command.apply(&mut state).map_err(|err| err.to_string())
-            })
-            .is_some()
+    fn edit(&mut self, command: Command) -> Option<Diff> {
+        self.stack.create_and_push_next(|files| {
+            let mut state = State {
+                files,
+                selection: &mut self.selection,
+                order: &mut self.order,
+            };
+            command.apply(&mut state).map_err(|err| err.to_string())
+        })
     }
 
     /// Brings everything derived from the files back in line with the current stack entry.
@@ -87,6 +128,8 @@ impl Engine {
             }
         }
         self.statistics_cache.update(current);
+        self.coordinates_cache.update(current);
+        self.structure_cache.update(current, &self.diff);
         self.statistics_buffer
             .update(&self.statistics_cache.get(current, &self.selection));
     }
@@ -280,6 +323,64 @@ mod tests {
         assert_eq!(engine.order.0, vec![a, b, c]);
     }
 
+    #[test]
+    fn test_structures_and_coordinates_follow_actions() {
+        let mut engine = Engine::default();
+        assert!(engine.order().is_empty());
+        load(&mut engine, "data/simple.gpx");
+        let loaded_id = engine.order()[0];
+        let diff = engine.last_diff();
+        assert!(diff.is_some());
+        let diff = diff.as_ref().unwrap();
+        assert_eq!(diff.added, vec![loaded_id]);
+        assert!(engine.order_changed());
+
+        new(&mut engine, "empty");
+        let empty_id = engine.order()[1];
+        // only the new file is reported, the other one is not recomputed
+        let diff = engine.last_diff();
+        assert!(diff.is_some());
+        let diff = diff.as_ref().unwrap();
+        assert_eq!(diff.added, vec![empty_id]);
+        assert!(diff.modified.is_empty() && diff.removed.is_empty());
+        assert_eq!(engine.file_structure(&empty_id).unwrap().name, "empty");
+
+        let structure = engine.file_structure(&loaded_id).unwrap();
+        let seg = &structure.tracks[0].segments[0];
+        let (seg_id, len) = (seg.id, seg.len);
+        assert_eq!(engine.segment_coordinates(&seg_id).len(), len * 2);
+        assert!(engine.waypoint_coordinates(&loaded_id).is_empty());
+
+        // reordering only changes the order
+        assert!(engine.execute(Action::Reorder {
+            file_ids: vec![loaded_id],
+            index: 1
+        }));
+        assert_eq!(engine.order(), [empty_id, loaded_id]);
+        assert!(engine.last_diff().is_none());
+        assert!(engine.order_changed());
+
+        // an action that changes nothing reports nothing
+        assert!(!engine.execute(Action::Reorder {
+            file_ids: vec![loaded_id],
+            index: 1
+        }));
+        assert!(engine.last_diff().is_none());
+        assert!(!engine.order_changed());
+
+        // undo removes the empty file, redoing the load removes the other one too
+        assert!(engine.execute(Action::Undo));
+        let diff = engine.last_diff();
+        assert!(diff.is_some());
+        let diff = diff.as_ref().unwrap();
+        assert_eq!(diff.removed, vec![empty_id]);
+        assert!(engine.file_structure(&empty_id).is_none());
+        assert!(engine.execute(Action::Undo));
+        assert!(engine.order().is_empty());
+        assert!(engine.file_structure(&loaded_id).is_none());
+        assert!(engine.segment_coordinates(&seg_id).is_empty());
+    }
+
     #[test]
     fn test_undo_updates_statistics() {
         let mut engine = Engine::default();

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

@@ -2,7 +2,7 @@ use std::collections::HashSet;
 
 use crate::{FileId, StackEntry, TrackId, TrackSegmentId, WaypointId};
 
-#[derive(Debug, Default)]
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
 pub enum Selection {
     #[default]
     Empty,

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

@@ -117,7 +117,8 @@ impl Stack {
 
 pub type StackEntry = HashMap<FileId, Rc<File>>;
 
-#[derive(Debug, Default)]
+/// Which files were added, removed or modified by a change of the current stack entry.
+#[derive(Debug, Default, Clone, PartialEq, Eq)]
 pub struct Diff {
     pub added: Vec<FileId>,
     pub removed: Vec<FileId>,

gpx-rs/wasm/src/lib.rs

@@ -6,13 +6,15 @@
 //! - File bytes cross as `Uint8Array` (`&[u8]`), strings as `&str`.
 //! - File ids cross as one flat `Uint8Array` of concatenated 16-byte UUIDs (no `Array<string>`).
 //! - Rectangles cross as four numbers instead of an object.
+//! - Ids read from the file tree are hyphenated UUID strings; the functions reading buffers take
+//!   them as such.
 //! - Every function returns `false` when its arguments are invalid or the command did nothing.
 use std::cell::RefCell;
 
 use wasm_bindgen::prelude::*;
 
 use gpx_engine::{self as engine, Action, Command, Engine, FileId, LngLat, LngLatBounds};
-use js_sys::{Float64Array, Int32Array};
+use js_sys::{Array, Float64Array, Int32Array, Object, Reflect};
 
 #[wasm_bindgen]
 #[derive(Clone, Copy)]
@@ -319,3 +321,179 @@ pub fn add_select(file_ids_bytes: &[u8]) -> bool {
 pub fn select_all() -> bool {
     execute(Action::SelectAll)
 }
+
+// File order and structures
+//
+// The files are described by one ordered list of ids and one structure object per file, so that
+// the UI can react to what changed only: after each action, `last_update` tells which
+// structures to (re)read or drop and whether the order changed. Ids are UUID strings. The
+// trackpoints of a segment and the waypoints of a file are in the same order as the coordinates
+// of their buffers (see below).
+
+#[wasm_bindgen(typescript_custom_section)]
+const FILE_STRUCTURE_TS: &str = r#"
+export interface FilesUpdate {
+    orderChanged: boolean;
+    /** Files to read the structure of. */
+    added: string[];
+    /** Files whose structure changed: reread it. */
+    modified: string[];
+    /** Files that do not exist anymore: drop their structure. */
+    removed: string[];
+}
+export interface FileStructure {
+    id: string;
+    name: string;
+    tracks: TrackNode[];
+    waypoints: WaypointNode[];
+    /** Changes when the waypoints of the file change: refetch their coordinates. */
+    waypointsRev: string;
+}
+export interface TrackNode {
+    id: string;
+    name?: string;
+    segments: SegmentNode[];
+}
+export interface SegmentNode {
+    id: string;
+    /** Changes when the trackpoints of the segment change: refetch their coordinates. */
+    rev: string;
+    /** Number of trackpoints. */
+    length: number;
+}
+export interface WaypointNode {
+    id: string;
+    name?: string;
+}
+"#;
+
+#[wasm_bindgen]
+extern "C" {
+    #[wasm_bindgen(typescript_type = "FilesUpdate")]
+    pub type FilesUpdate;
+    #[wasm_bindgen(typescript_type = "FileStructure | undefined")]
+    pub type FileStructure;
+    #[wasm_bindgen(typescript_type = "string[]")]
+    pub type FileOrder;
+}
+
+fn set(object: &Object, key: &str, value: impl Into<JsValue>) {
+    Reflect::set(object, &key.into(), &value.into()).unwrap();
+}
+
+fn array<T>(items: &[T], f: impl Fn(&T) -> JsValue) -> Array {
+    items.iter().map(f).collect()
+}
+
+fn ids(items: &[FileId]) -> Array {
+    array(items, |id| id.0.to_string().into())
+}
+
+fn named_node(id: uuid::Uuid, name: Option<&str>) -> Object {
+    let node = Object::new();
+    set(&node, "id", id.to_string());
+    if let Some(name) = name {
+        set(&node, "name", name);
+    }
+    node
+}
+
+fn structure_object(file: &engine::FileStructure) -> Object {
+    let node = named_node(file.id.0, Some(&file.name));
+    set(
+        &node,
+        "tracks",
+        array(&file.tracks, |trk| {
+            let node = named_node(trk.id.0, trk.name.as_deref());
+            set(
+                &node,
+                "segments",
+                array(&trk.segments, |seg| {
+                    let node = named_node(seg.id.0, None);
+                    set(&node, "rev", seg.rev_id.0.to_string());
+                    set(&node, "length", seg.len as f64);
+                    node.into()
+                }),
+            );
+            node.into()
+        }),
+    );
+    set(
+        &node,
+        "waypoints",
+        array(&file.waypoints, |wpt| {
+            named_node(wpt.id.0, wpt.name.as_deref()).into()
+        }),
+    );
+    set(&node, "waypointsRev", format!("{:x}", file.waypoints_rev));
+    node
+}
+
+fn with_engine<T>(f: impl FnOnce(&Engine) -> T) -> Option<T> {
+    ENGINE.with(|engine| engine.borrow().as_ref().map(f))
+}
+
+/// Ids of the files in display order.
+#[wasm_bindgen]
+pub fn file_order() -> FileOrder {
+    let order = with_engine(|e| ids(e.order())).unwrap_or_default();
+    order.unchecked_into()
+}
+
+/// Structure of a file, `undefined` if the id is unknown.
+#[wasm_bindgen]
+pub fn file_structure(file_id: &str) -> FileStructure {
+    let structure = uuid::Uuid::parse_str(file_id)
+        .ok()
+        .and_then(|id| {
+            with_engine(|e| e.file_structure(&FileId(id)).map(structure_object)).flatten()
+        })
+        .map_or(JsValue::UNDEFINED, JsValue::from);
+    structure.unchecked_into()
+}
+
+/// What the last action changed. Read it right after each action.
+#[wasm_bindgen]
+pub fn last_update() -> FilesUpdate {
+    let update = Object::new();
+    with_engine(|e| {
+        let diff = e.last_diff().clone().unwrap_or_default();
+        set(&update, "orderChanged", e.order_changed());
+        set(&update, "added", ids(&diff.added));
+        set(&update, "modified", ids(&diff.modified));
+        set(&update, "removed", ids(&diff.removed));
+    });
+    update.unchecked_into()
+}
+
+// Coordinates buffers
+//
+// Like the statistics buffers, these are views into wasm memory, invalidated by the next
+// command (and any allocation): read or copy them right away. They are flat `[lng, lat, ...]`
+// arrays. Compare `rev` / `waypointsRev` of the file structures with the previous ones to know which
+// buffers actually changed.
+
+fn coordinates_view(f: impl FnOnce(&Engine) -> Option<&[f64]>) -> Float64Array {
+    ENGINE.with(|engine| match engine.borrow().as_ref().and_then(f) {
+        Some(coordinates) => unsafe { Float64Array::view(coordinates) },
+        None => Float64Array::new_with_length(0),
+    })
+}
+
+/// Coordinates of the trackpoints of a segment (empty if the id is unknown).
+#[wasm_bindgen]
+pub fn segment_coordinates(segment_id: &str) -> Float64Array {
+    match uuid::Uuid::parse_str(segment_id) {
+        Ok(id) => coordinates_view(|e| Some(e.segment_coordinates(&engine::TrackSegmentId(id)))),
+        Err(_) => Float64Array::new_with_length(0),
+    }
+}
+
+/// Coordinates of the waypoints of a file (empty if the id is unknown).
+#[wasm_bindgen]
+pub fn waypoint_coordinates(file_id: &str) -> Float64Array {
+    match uuid::Uuid::parse_str(file_id) {
+        Ok(id) => coordinates_view(|e| Some(e.waypoint_coordinates(&FileId(id)))),
+        Err(_) => Float64Array::new_with_length(0),
+    }
+}