use std::collections::HashSet;
use std::rc::Rc;

use crate::{
    ClipboardIds, Delete, DeleteAll, File, Load, Metadata, New, NewTrack, Paste, Style, TrackId,
    TrackSegmentId,
};

use super::*;

/// An engine that remembers what the last action it was given did, for the tests to read right
/// after (see `run`).
#[derive(Default)]
struct TestEngine {
    engine: Engine,
    last: Outcome,
    last_error: Option<CommandError>,
}

impl std::ops::Deref for TestEngine {
    type Target = Engine;

    fn deref(&self) -> &Engine {
        &self.engine
    }
}

impl std::ops::DerefMut for TestEngine {
    fn deref_mut(&mut self) -> &mut Engine {
        &mut self.engine
    }
}

impl TestEngine {
    /// Executes an action and tells whether it changed anything.
    fn run(&mut self, action: Action) -> bool {
        let result = self.engine.execute(action);
        self.last = result.clone().unwrap_or_default();
        self.last_error = result.as_ref().err().cloned();
        result.is_ok_and(|outcome| outcome.changed)
    }

    fn restore(&mut self, restored: Restored) -> Outcome {
        let outcome = self.engine.restore(restored);
        self.last = outcome.clone();
        self.last_error = None;
        outcome
    }

    fn last_diff(&self) -> Option<&Diff> {
        self.last.diff.as_ref()
    }

    fn last_error(&self) -> Option<&CommandError> {
        self.last_error.as_ref()
    }

    fn order_changed(&self) -> bool {
        self.last.order_changed
    }

    fn selection_changed(&self) -> bool {
        self.last.selection_changed
    }

    fn clipboard_changed(&self) -> bool {
        self.last.clipboard_changed
    }
}

fn expand(intervals: &crate::Intervals, len: usize) -> Vec<u8> {
    let mut values = Vec::new();
    for (i, value) in intervals.values.iter().enumerate() {
        let end = intervals.starts.get(i + 1).map_or(len, |end| *end as usize);
        values.resize(end, *value);
    }
    values
}

fn edit(engine: &mut TestEngine, command: Command) -> bool {
    engine.run(Action::Edit(command))
}

fn new(engine: &mut TestEngine, name: &str) -> bool {
    edit(
        engine,
        Command::New(New {
            name,
            trackpoint: None,
        }),
    )
}

fn load(engine: &mut TestEngine, path: &str) -> bool {
    let data = std::fs::read(path).unwrap();
    edit(
        engine,
        Command::Load(Load {
            data: &data,
            name: "file",
        }),
    )
}

fn selected(engine: &Engine) -> Vec<FileId> {
    match &engine.selection {
        Selection::File { file_ids } => file_ids.iter().copied().collect(),
        _ => vec![],
    }
}

#[test]
fn test_load_file() {
    let mut engine = TestEngine::default();
    assert!(load(&mut engine, "data/simple.gpx"));
    assert_eq!(engine.statistics_buffer.total_distance.len(), 80);
}

#[test]
fn test_new_file_has_no_statistics() {
    let mut engine = TestEngine::default();
    assert!(new(&mut engine, "empty"));
    assert_eq!(engine.history.current().unwrap().len(), 1);
    assert_eq!(engine.order.0.len(), 1);
    assert!(engine.statistics().total_distance.is_empty());
}

#[test]
fn test_statistics_follow_selection() {
    let mut engine = TestEngine::default();
    assert!(load(&mut engine, "data/simple.gpx"));
    let n = engine.statistics().total_distance.len();
    assert!(n > 0);

    // a newly created (empty) file becomes the selection
    assert!(new(&mut engine, "empty"));
    assert!(engine.statistics().total_distance.is_empty());
    assert_eq!(engine.history.current().unwrap().len(), 2);

    // loading a file selects it again
    assert!(load(&mut engine, "data/simple.gpx"));
    assert_eq!(engine.statistics().total_distance.len(), n);
}

#[test]
fn test_invalid_load_is_rejected() {
    let mut engine = TestEngine::default();
    assert!(!edit(
        &mut engine,
        Command::Load(Load {
            data: b"<gpx><trk></gpx>",
            name: "file",
        })
    ));
    assert!(engine.history.current().is_none());
    assert!(!engine.history.can_undo(&[]));
    assert!(engine.order.0.is_empty());
}

#[test]
fn test_command_with_nothing_to_do_is_rejected() {
    let mut engine = TestEngine::default();
    new(&mut engine, "file");
    assert!(!edit(&mut engine, Command::Reverse(crate::Reverse)));
    assert!(!engine.history.can_redo(&[]));
    assert_eq!(engine.history.current().unwrap().len(), 1);
}

#[test]
fn test_metadata_renames_selected_file() {
    let mut engine = TestEngine::default();
    new(&mut engine, "before");
    assert!(edit(
        &mut engine,
        Command::Metadata(Metadata {
            name: "after",
            desc: "about",
        })
    ));
    let file = engine.history.current().unwrap().values().next().unwrap();
    assert_eq!(file.info.name, "after");
    assert_eq!(file.info.desc.as_deref(), Some("about"));
}

#[test]
fn test_metadata_without_selection_does_not_modify_files() {
    let mut engine = TestEngine::default();
    new(&mut engine, "file");
    engine.selection = Selection::Empty;
    edit(
        &mut engine,
        Command::Metadata(Metadata {
            name: "renamed",
            desc: "",
        }),
    );
    let file = engine.history.current().unwrap().values().next().unwrap();
    assert_eq!(file.info.name, "file");
}

#[test]
fn test_edit_changes_statistics_when_segments_change() {
    let mut engine = TestEngine::default();
    load(&mut engine, "data/simple.gpx");
    let before = engine
        .statistics_cache
        .get(engine.history.current(), &engine.selection)[0] as *const _;
    edit(&mut engine, Command::NewTrack(NewTrack));
    edit(
        &mut engine,
        Command::Style(Style {
            color: Some("ff0000"),
            opacity: None,
            width: None,
        }),
    );
    // styling does not touch the segments: their statistics are reused
    let after = engine
        .statistics_cache
        .get(engine.history.current(), &engine.selection)[0] as *const _;
    assert!(std::ptr::eq(before, after));
}

#[test]
fn test_undo_redo_keep_selection_and_order_consistent() {
    let mut engine = TestEngine::default();
    new(&mut engine, "a");
    let a = selected(&engine)[0];
    new(&mut engine, "b");
    let b = selected(&engine)[0];
    assert_eq!(engine.order.0, vec![a, b]);

    assert!(engine.run(Action::Undo));
    assert_eq!(engine.order.0, vec![a]);
    assert!(selected(&engine).is_empty());

    assert!(engine.run(Action::Redo));
    assert_eq!(engine.order.0, vec![a, b]);

    assert!(engine.run(Action::Undo));
    assert!(engine.run(Action::Undo));
    assert!(engine.order.0.is_empty());
    assert!(!engine.run(Action::Undo));
    assert!(engine.history.current().is_none());
}

#[test]
fn test_reorder_is_not_undoable_and_returning_files_go_last() {
    let mut engine = TestEngine::default();
    new(&mut engine, "a");
    let a = engine.order.0[0];
    new(&mut engine, "b");
    let b = engine.order.0[1];
    new(&mut engine, "c");
    let c = engine.order.0[2];

    assert!(engine.run(Action::Reorder {
        file_ids: vec![c],
        index: 0
    }));
    assert_eq!(engine.order.0, vec![c, a, b]);
    assert!(!engine.run(Action::Reorder {
        file_ids: vec![c],
        index: 0
    }));

    // undoing the creation of c does not undo the reorder
    assert!(engine.run(Action::Undo));
    assert_eq!(engine.order.0, vec![a, b]);
    // c comes back at the end
    assert!(engine.run(Action::Redo));
    assert_eq!(engine.order.0, vec![a, b, c]);
}

#[test]
fn test_structures_and_coordinates_follow_actions() {
    let mut engine = TestEngine::default();
    assert!(engine.order().is_empty());
    load(&mut engine, "data/simple.gpx");
    let loaded_id = engine.order()[0];
    let diff = engine.last_diff().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().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.run(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.run(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.run(Action::Undo));
    let diff = engine.last_diff().unwrap();
    assert_eq!(diff.removed, vec![empty_id]);
    assert!(engine.order_changed());
    assert!(engine.file_structure(&empty_id).is_none());
    assert!(engine.run(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_selection_changed_flag() {
    let mut engine = TestEngine::default();
    new(&mut engine, "a");
    let a = engine.order()[0];
    // a new file is selected by the edit
    assert!(engine.selection_changed());
    assert!(!select_files(&mut engine, &[a]));
    assert!(!engine.selection_changed());
    assert!(select_files(&mut engine, &[]));
    assert!(engine.selection_changed());
    // undoing drops the selected file from the selection
    select_files(&mut engine, &[a]);
    assert!(engine.run(Action::Undo));
    assert!(engine.selection_changed());
    assert_eq!(engine.selection(), &Selection::Empty);
}

#[test]
fn test_undo_updates_statistics() {
    let mut engine = TestEngine::default();
    load(&mut engine, "data/simple.gpx");
    assert!(!engine.statistics().total_distance.is_empty());
    engine.run(Action::Undo);
    assert!(engine.statistics().total_distance.is_empty());
    engine.run(Action::Redo);
    select_all(&mut engine);
    assert_eq!(engine.statistics().total_distance.len(), 80);
}

#[test]
fn test_selection_actions() {
    let mut engine = TestEngine::default();
    new(&mut engine, "a");
    let a = selected(&engine)[0];
    new(&mut engine, "b");
    let b = selected(&engine)[0];
    assert_eq!(selected(&engine), vec![b]);

    assert!(select_files(&mut engine, &[a]));
    assert_eq!(selected(&engine), vec![a]);

    assert!(select_elements(&mut engine, files(&[b]), SelectMode::Add));
    assert_eq!(selected(&engine).len(), 2);

    select_files(&mut engine, &[]);
    assert!(select_all(&mut engine));
    assert_eq!(selected(&engine).len(), 2);
}

#[test]
fn test_selection_does_not_create_undo_steps() {
    let mut engine = TestEngine::default();
    new(&mut engine, "a");
    select_all(&mut engine);
    engine.run(Action::Undo);
    assert!(engine.history.current().is_none());
}

fn select_elements(engine: &mut TestEngine, selection: Selection, mode: SelectMode) -> bool {
    engine.run(Action::Select { selection, mode })
}

fn files(ids: &[FileId]) -> Selection {
    Selection::File {
        file_ids: ids.iter().copied().collect(),
    }
}

fn select_files(engine: &mut TestEngine, ids: &[FileId]) -> bool {
    select_elements(engine, files(ids), SelectMode::Replace)
}

fn select_all(engine: &mut TestEngine) -> bool {
    let ids = engine.order().to_vec();
    select_files(engine, &ids)
}

#[test]
fn test_select_elements() {
    let mut engine = TestEngine::default();
    load(&mut engine, "data/with_tracks_and_segments.gpx");
    let file = engine
        .history
        .current()
        .unwrap()
        .values()
        .next()
        .unwrap()
        .clone();
    assert!(file.trk.len() >= 2 && file.trk[0].trkseg.len() >= 2);
    let (t0, t1) = (file.trk[0].id, file.trk[1].id);
    let (s0, s1) = (file.trk[0].trkseg[0].id, file.trk[0].trkseg[1].id);

    // tracks, then more tracks
    let tracks = |ids: &[TrackId]| Selection::Track {
        file_id: file.id,
        trk_ids: ids.iter().copied().collect(),
    };
    assert!(select_elements(
        &mut engine,
        tracks(&[t0]),
        SelectMode::Replace
    ));
    assert_eq!(engine.selection(), &tracks(&[t0]));
    assert!(select_elements(&mut engine, tracks(&[t1]), SelectMode::Add));
    assert_eq!(engine.selection(), &tracks(&[t0, t1]));

    // segments of a track, added only within the same track
    let segments = |trk_id, ids: &[TrackSegmentId]| Selection::TrackSegment {
        file_id: file.id,
        trk_id,
        trkseg_ids: ids.iter().copied().collect(),
    };
    assert!(select_elements(
        &mut engine,
        segments(t0, &[s0]),
        SelectMode::Add
    ));
    assert_eq!(engine.selection(), &segments(t0, &[s0]));
    assert!(select_elements(
        &mut engine,
        segments(t0, &[s1]),
        SelectMode::Add
    ));
    assert_eq!(engine.selection(), &segments(t0, &[s0, s1]));
    // the statistics follow the selected segments
    assert_eq!(
        engine.statistics().total_distance.len(),
        file.trk[0].trkseg[0].len() + file.trk[0].trkseg[1].len()
    );

    // the waypoints node
    let node = Selection::Waypoints { file_id: file.id };
    assert!(select_elements(
        &mut engine,
        node.clone(),
        SelectMode::Replace
    ));
    assert!(!select_elements(&mut engine, node.clone(), SelectMode::Add));
    assert_eq!(engine.selection(), &node);
    assert!(!engine.selection_changed());

    // unknown elements and files are ignored when adding
    let unknown = tracks(&[TrackId::default()]);
    assert!(!select_elements(
        &mut engine,
        unknown.clone(),
        SelectMode::Add
    ));
    let unknown_file = Selection::Waypoints {
        file_id: FileId::default(),
    };
    assert!(!select_elements(
        &mut engine,
        unknown_file.clone(),
        SelectMode::Add
    ));
    assert!(!select_elements(
        &mut engine,
        Selection::Empty,
        SelectMode::Add
    ));
    assert_eq!(engine.selection(), &node);

    // and select nothing otherwise
    assert!(select_elements(&mut engine, unknown, SelectMode::Replace));
    assert_eq!(engine.selection(), &Selection::Empty);
    select_elements(&mut engine, node, SelectMode::Replace);
    assert!(select_elements(
        &mut engine,
        unknown_file,
        SelectMode::Replace
    ));
    assert_eq!(engine.selection(), &Selection::Empty);
}

#[test]
fn test_toggle_elements() {
    let mut engine = TestEngine::default();
    load(&mut engine, "data/with_tracks_and_segments.gpx");
    let file = engine
        .history
        .current()
        .unwrap()
        .values()
        .next()
        .unwrap()
        .clone();
    let (t0, t1) = (file.trk[0].id, file.trk[1].id);
    let tracks = |ids: &[TrackId]| Selection::Track {
        file_id: file.id,
        trk_ids: ids.iter().copied().collect(),
    };
    let toggle = |engine: &mut TestEngine, ids: &[TrackId]| {
        select_elements(engine, tracks(ids), SelectMode::Toggle)
    };

    select_elements(&mut engine, tracks(&[t0]), SelectMode::Replace);
    assert!(toggle(&mut engine, &[t1]));
    assert_eq!(engine.selection(), &tracks(&[t0, t1]));
    assert!(toggle(&mut engine, &[t0]));
    assert_eq!(engine.selection(), &tracks(&[t1]));
    // toggling the last element deselects everything
    assert!(toggle(&mut engine, &[t1]));
    assert_eq!(engine.selection(), &Selection::Empty);
    // unknown elements change nothing
    assert!(!toggle(&mut engine, &[TrackId::default()]));
    assert_eq!(engine.selection(), &Selection::Empty);
}

#[test]
fn test_selected_elements_are_dropped_when_they_disappear() {
    let mut engine = TestEngine::default();
    load(&mut engine, "data/with_tracks_and_segments.gpx");
    let file = engine
        .history
        .current()
        .unwrap()
        .values()
        .next()
        .unwrap()
        .clone();
    let trk_id = file.trk[0].id;
    select_elements(
        &mut engine,
        Selection::Track {
            file_id: file.id,
            trk_ids: [trk_id].into(),
        },
        SelectMode::Replace,
    );
    engine.run(Action::Undo);
    assert_eq!(engine.selection(), &Selection::Empty);
}

#[test]
fn test_can_undo_and_redo() {
    let mut engine = TestEngine::default();
    assert!(!engine.can_undo() && !engine.can_redo());
    new(&mut engine, "a");
    assert!(engine.can_undo() && !engine.can_redo());
    assert!(engine.run(Action::Undo));
    assert!(!engine.can_undo() && engine.can_redo());
    // selecting does not change the history
    new(&mut engine, "b");
    let a = engine.order()[0];
    select_files(&mut engine, &[a]);
    assert!(engine.can_undo() && !engine.can_redo());
    assert!(engine.run(Action::Undo));
    assert!(engine.run(Action::Redo));
    assert!(engine.can_undo() && !engine.can_redo());
}

#[test]
fn test_select_all_follows_the_selected_level() {
    let mut engine = TestEngine::default();
    new(&mut engine, "a");
    new(&mut engine, "b");
    let order = engine.order().to_vec();
    select_files(&mut engine, &[order[0]]);

    // files
    assert!(engine.run(Action::SelectAll));
    assert_eq!(engine.selection(), &files(&order));
    // everything is selected already
    assert!(!engine.run(Action::SelectAll));

    // the tracks of a file
    let load = |engine: &mut TestEngine| load(engine, "data/with_tracks_and_segments.gpx");
    load(&mut engine);
    let file = engine
        .history
        .current()
        .unwrap()
        .values()
        .find(|f| !f.trk.is_empty())
        .unwrap()
        .clone();
    let tracks: HashSet<_> = file.trk.iter().map(|t| t.id).collect();
    assert!(tracks.len() >= 2);
    select_elements(
        &mut engine,
        Selection::Track {
            file_id: file.id,
            trk_ids: [file.trk[0].id].into(),
        },
        SelectMode::Replace,
    );
    assert!(engine.run(Action::SelectAll));
    assert_eq!(
        engine.selection(),
        &Selection::Track {
            file_id: file.id,
            trk_ids: tracks
        }
    );

    // nothing selected: all the files
    select_elements(&mut engine, Selection::Empty, SelectMode::Replace);
    assert!(engine.run(Action::SelectAll));
    assert!(matches!(engine.selection(), Selection::File { file_ids } if file_ids.len() == 3));
    // the waypoints node: nothing more to select
    select_elements(
        &mut engine,
        Selection::Waypoints { file_id: file.id },
        SelectMode::Replace,
    );
    assert!(!engine.run(Action::SelectAll));
    assert_eq!(
        engine.selection(),
        &Selection::Waypoints { file_id: file.id }
    );
}

#[test]
fn test_arrow_select() {
    let mut engine = TestEngine::default();
    new(&mut engine, "file");
    for _ in 0..3 {
        edit(&mut engine, Command::NewTrack(NewTrack));
    }
    let file = engine
        .history
        .current()
        .unwrap()
        .values()
        .next()
        .unwrap()
        .clone();
    let ids: Vec<TrackId> = file.trk.iter().map(|t| t.id).collect();
    assert_eq!(ids.len(), 3);
    let tracks = |ids: &[TrackId]| Selection::Track {
        file_id: file.id,
        trk_ids: ids.iter().copied().collect(),
    };
    let arrow = |engine: &mut TestEngine, down, add| engine.run(Action::ArrowSelect { down, add });

    select_elements(&mut engine, tracks(&[ids[0]]), SelectMode::Replace);
    // without shift the next one replaces the selection
    assert!(arrow(&mut engine, true, false));
    assert_eq!(engine.selection(), &tracks(&[ids[1]]));
    assert!(engine.selection_changed());
    // with shift it is added
    assert!(arrow(&mut engine, true, true));
    assert_eq!(engine.selection(), &tracks(&[ids[1], ids[2]]));
    // the selection grows from its end, and the other way round from its start
    assert!(arrow(&mut engine, false, true));
    assert_eq!(engine.selection(), &tracks(&[ids[0], ids[1], ids[2]]));
    // at the ends nothing happens
    assert!(!arrow(&mut engine, false, false));
    assert!(!arrow(&mut engine, true, true));
    assert_eq!(engine.selection(), &tracks(&[ids[0], ids[1], ids[2]]));
    // and there is nothing to move without selection
    select_elements(&mut engine, Selection::Empty, SelectMode::Replace);
    assert!(!arrow(&mut engine, true, false));
    assert_eq!(engine.selection(), &Selection::Empty);
}

#[test]
fn test_arrow_select_does_not_create_undo_steps() {
    let mut engine = TestEngine::default();
    new(&mut engine, "a");
    new(&mut engine, "b");
    let a = engine.order()[0];
    select_files(&mut engine, &[a]);
    let before = engine.can_redo();
    assert!(engine.run(Action::ArrowSelect {
        down: true,
        add: false
    }));
    assert_eq!(engine.can_redo(), before);
    assert_eq!(engine.selection(), &files(&[engine.order()[1]]));
    assert!(engine.run(Action::Undo));
    assert_eq!(engine.order().len(), 1);
}

/// A file named `name` with `n` tracks, selected.
fn file_with_tracks(engine: &mut TestEngine, name: &str, n: usize) -> FileId {
    new(engine, name);
    for _ in 0..n {
        edit(engine, Command::NewTrack(NewTrack));
    }
    *engine.order().last().unwrap()
}

fn track_ids(engine: &Engine, id: FileId) -> Vec<TrackId> {
    engine
        .file_structure(&id)
        .unwrap()
        .tracks
        .iter()
        .map(|t| t.id)
        .collect()
}

fn paste(engine: &mut TestEngine) -> bool {
    edit(engine, Command::Paste(Paste))
}

#[test]
fn test_copy_and_paste() {
    let mut engine = TestEngine::default();
    let a = file_with_tracks(&mut engine, "a", 2);
    let b = file_with_tracks(&mut engine, "b", 0);
    assert!(engine.clipboard().is_none() && !engine.can_paste());

    // nothing selected, nothing copied
    select_elements(&mut engine, Selection::Empty, SelectMode::Replace);
    assert!(!engine.run(Action::Copy));
    assert!(engine.clipboard().is_none());

    let tracks = track_ids(&engine, a);
    let selected_tracks = Selection::Track {
        file_id: a,
        trk_ids: tracks.iter().copied().collect(),
    };
    select_elements(&mut engine, selected_tracks.clone(), SelectMode::Replace);
    assert!(engine.run(Action::Copy));
    assert!(engine.clipboard_changed() && !engine.selection_changed());
    assert_eq!(
        engine.clipboard().map(|c| (c.content.ids(), c.cut)),
        Some((ClipboardIds::Tracks(tracks.clone()), false))
    );
    // tracks cannot be pasted onto themselves... but into a track, a file or the list of files
    assert!(engine.can_paste());
    select_elements(&mut engine, files(&[b]), SelectMode::Replace);
    assert!(engine.can_paste());
    select_elements(
        &mut engine,
        Selection::Waypoints { file_id: b },
        SelectMode::Replace,
    );
    assert!(!engine.can_paste());
    select_elements(&mut engine, files(&[b]), SelectMode::Replace);

    // pasting is an edit
    assert!(paste(&mut engine));
    assert_eq!(track_ids(&engine, a), tracks);
    assert_eq!(track_ids(&engine, b).len(), 2);
    // a copy stays in the clipboard, to be pasted again
    assert!(engine.clipboard().is_some() && !engine.clipboard_changed());
    assert!(
        matches!(engine.selection(), Selection::Track { file_id, trk_ids } if *file_id == b && trk_ids.len() == 2)
    );
    assert!(engine.can_paste());
    assert!(paste(&mut engine));
    assert_eq!(track_ids(&engine, b).len(), 4);
    assert_eq!(track_ids(&engine, a), tracks);

    // and it can be undone
    assert!(engine.run(Action::Undo));
    assert_eq!(track_ids(&engine, b).len(), 2);
    assert!(engine.run(Action::Undo));
    assert!(track_ids(&engine, b).is_empty());
}

#[test]
fn test_cut_and_paste_moves_after_the_paste() {
    let mut engine = TestEngine::default();
    let a = file_with_tracks(&mut engine, "a", 2);
    let b = file_with_tracks(&mut engine, "b", 0);
    let tracks = track_ids(&engine, a);
    select_elements(
        &mut engine,
        Selection::Track {
            file_id: a,
            trk_ids: [tracks[0]].into(),
        },
        SelectMode::Replace,
    );
    assert!(engine.run(Action::Cut));
    assert!(engine.clipboard().is_some_and(|c| c.cut));
    // nothing moves before the paste
    assert_eq!(track_ids(&engine, a), tracks);

    select_elements(&mut engine, files(&[b]), SelectMode::Replace);
    assert!(paste(&mut engine));
    assert_eq!(track_ids(&engine, a), vec![tracks[1]]);
    assert_eq!(track_ids(&engine, b), vec![tracks[0]]);
    assert!(engine.run(Action::Undo));
    assert_eq!(track_ids(&engine, a), tracks);
    assert!(track_ids(&engine, b).is_empty());
}

#[test]
fn test_clipboard_survives_what_happens_to_the_elements() {
    let mut engine = TestEngine::default();
    let a = file_with_tracks(&mut engine, "a", 2);
    let tracks = track_ids(&engine, a);
    select_elements(
        &mut engine,
        Selection::Track {
            file_id: a,
            trk_ids: tracks.iter().copied().collect(),
        },
        SelectMode::Replace,
    );
    engine.run(Action::Copy);
    let clipboard = engine.clipboard().cloned();
    assert!(clipboard.is_some());

    // one of the tracks is deleted, then the whole file: the clipboard is not affected
    select_elements(
        &mut engine,
        Selection::Track {
            file_id: a,
            trk_ids: [tracks[0]].into(),
        },
        SelectMode::Replace,
    );
    assert!(edit(
        &mut engine,
        Command::Delete(Delete { whole_files: false })
    ));
    select_elements(&mut engine, files(&[a]), SelectMode::Replace);
    assert!(edit(&mut engine, Command::DeleteAll(DeleteAll)));
    assert_eq!(engine.clipboard(), clipboard.as_ref());
    assert!(!engine.clipboard_changed());

    // both tracks are pasted in a new file, as they were when they were copied
    let b = file_with_tracks(&mut engine, "b", 0);
    select_files(&mut engine, &[b]);
    assert!(engine.can_paste());
    assert!(paste(&mut engine));
    let pasted = track_ids(&engine, b);
    assert_eq!(pasted.len(), 2);
    // copies, with new ids
    assert!(pasted.iter().all(|id| !tracks.contains(id)));
    // and again
    assert!(paste(&mut engine));
    assert_eq!(track_ids(&engine, b).len(), 4);
}

#[test]
fn test_copy_replaces_the_clipboard_and_does_not_change_the_history() {
    let mut engine = TestEngine::default();
    let a = file_with_tracks(&mut engine, "a", 0);
    let b = file_with_tracks(&mut engine, "b", 0);
    select_files(&mut engine, &[a]);
    engine.run(Action::Copy);
    select_files(&mut engine, &[b]);
    assert!(engine.run(Action::Cut));
    assert_eq!(
        engine.clipboard().map(|c| (c.content.ids(), c.cut)),
        Some((ClipboardIds::Files(vec![b]), true))
    );
    // the same elements again are a new copy
    assert!(engine.run(Action::Cut));
    assert!(engine.clipboard_changed());
    // only the creations of the files are in the history
    assert!(engine.run(Action::Undo));
    assert!(engine.run(Action::Undo));
    assert!(!engine.can_undo());
}

#[test]
fn test_move_elements_is_an_edit_and_selects_what_moved() {
    use crate::{Move, MoveTarget};

    let mut engine = TestEngine::default();
    let a = file_with_tracks(&mut engine, "a", 3);
    let tracks = track_ids(&engine, a);
    let moved = Selection::Track {
        file_id: a,
        trk_ids: [tracks[2]].into(),
    };
    assert!(edit(
        &mut engine,
        Command::Move(Move {
            what: moved.clone(),
            to: MoveTarget::Tracks {
                file_id: a,
                index: 0
            },
        })
    ));
    assert_eq!(track_ids(&engine, a), vec![tracks[2], tracks[0], tracks[1]]);
    assert_eq!(engine.selection(), &moved);

    // invalid moves change nothing
    assert!(!edit(
        &mut engine,
        Command::Move(Move {
            what: moved,
            to: MoveTarget::Waypoints {
                file_id: a,
                index: 0
            },
        })
    ));

    assert!(engine.run(Action::Undo));
    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 = TestEngine::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.run(Action::Undo));
    assert!(engine.run(Action::Redo));
    assert_eq!(engine.last_diff().unwrap().added, engine.order());
}

#[test]
fn test_load_several_files_is_one_edit() {
    use crate::LoadFiles;

    let mut engine = TestEngine::default();
    new(&mut engine, "before");
    let gpx = |name: &str| {
        format!(r#"<gpx version="1.1"><metadata><name>{name}</name></metadata></gpx>"#).into_bytes()
    };
    let (a, b) = (gpx("a"), gpx("b"));
    assert!(edit(
        &mut engine,
        Command::LoadFiles(LoadFiles {
            files: vec![
                Load {
                    data: &a,
                    name: "x"
                },
                Load {
                    data: &b,
                    name: "x"
                },
            ],
        })
    ));
    assert_eq!(engine.order().len(), 3);
    let diff = engine.last_diff().unwrap();
    assert_eq!(diff.added.len(), 2);
    // the first one that was loaded is selected
    assert_eq!(engine.selection(), &files(&[engine.order()[1]]));

    // a single undo removes both
    assert!(engine.run(Action::Undo));
    assert_eq!(engine.order().len(), 1);
    assert!(engine.run(Action::Redo));
    assert_eq!(engine.order().len(), 3);
}

#[test]
fn test_create_edit_and_move_a_waypoint() {
    use crate::{EditWaypoint, MoveWaypoint, NewWaypoint};

    let mut engine = TestEngine::default();
    new(&mut engine, "file");
    let file = engine.order()[0];
    assert!(edit(
        &mut engine,
        Command::NewWaypoint(NewWaypoint {
            lng: 4.0,
            lat: 50.0,
            ele: 10.0,
            name: "created",
            desc: "",
            icon: "Flag",
            link: "",
        })
    ));
    let id = engine.file_structure(&file).unwrap().waypoints[0].id;
    let waypoint = engine.waypoint(&file, &id).unwrap();
    assert_eq!(waypoint.name.as_deref(), Some("created"));
    assert_eq!(waypoint.sym.as_deref(), Some("Flag"));
    assert_eq!(waypoint.ele, 10.0);
    // unknown waypoint or file
    assert!(engine.waypoint(&file, &Default::default()).is_none());
    assert!(engine.waypoint(&Default::default(), &id).is_none());

    // no selection needed
    assert!(edit(
        &mut engine,
        Command::MoveWaypoint(MoveWaypoint {
            file_id: file,
            waypoint_id: id,
            lng: 5.0,
            lat: 51.0,
            ele: 20.0,
        })
    ));
    let moved = engine.waypoint(&file, &id).unwrap();
    assert_eq!(
        (moved.coordinates.lng, moved.coordinates.lat, moved.ele),
        (5.0, 51.0, 20.0)
    );
    assert_eq!(moved.name.as_deref(), Some("created"));
    // the coordinates buffer follows
    assert_eq!(engine.waypoint_coordinates(&file), &[5.0, 51.0]);

    assert!(edit(
        &mut engine,
        Command::EditWaypoint(EditWaypoint {
            file_id: file,
            waypoint_id: id,
            lng: 6.0,
            lat: 52.0,
            ele: 30.0,
            name: "edited",
            desc: "text",
            icon: "",
            link: "https://example.com",
        })
    ));
    let edited = engine.waypoint(&file, &id).unwrap();
    assert_eq!(edited.name.as_deref(), Some("edited"));
    assert_eq!(edited.cmt.as_deref(), Some("text"));
    assert!(edited.sym.is_none());
    assert_eq!(engine.waypoint_coordinates(&file), &[6.0, 52.0]);

    // each of them can be undone
    assert!(engine.run(Action::Undo));
    assert_eq!(
        engine.waypoint(&file, &id).unwrap().name.as_deref(),
        Some("created")
    );
    assert!(engine.run(Action::Undo));
    assert_eq!(engine.waypoint_coordinates(&file), &[4.0, 50.0]);

    // deleting does not need a selection either
    assert!(edit(
        &mut engine,
        Command::DeleteWaypoint(crate::DeleteWaypoint {
            file_id: file,
            waypoint_id: id,
        })
    ));
    assert!(engine.waypoint(&file, &id).is_none());
    assert!(engine.waypoint_coordinates(&file).is_empty());
    assert!(engine.run(Action::Undo));
    assert!(engine.waypoint(&file, &id).is_some());
}

#[test]
fn test_categories_are_shared_and_kept_by_the_history() {
    let mut engine = TestEngine::default();
    assert!(engine.categories().surface.names().is_empty());

    load(&mut engine, "data/with_highway.gpx");
    assert_eq!(engine.categories().surface.names(), ["asphalt", "gravel"]);
    assert_eq!(
        engine.categories().highway.names(),
        ["residential", "track"]
    );
    // the trackpoints of the selection refer to them
    assert_eq!(expand(&engine.statistics().surface, 5), [1, 1, 0, 2, 2]);
    assert_eq!(expand(&engine.statistics().highway, 5), [1, 1, 0, 2, 0]);
    assert_eq!(
        engine.categories().sac_scale.names(),
        ["mountain_hiking", "hiking"]
    );
    assert_eq!(expand(&engine.statistics().sac_scale, 5), [0, 0, 0, 1, 2]);
    assert_eq!(expand(&engine.statistics().mtb_scale, 5), [0, 0, 0, 1, 1]);

    // a second file goes on with the same table
    load(&mut engine, "data/with_surface.gpx");
    assert_eq!(
        engine.categories().surface.names(),
        ["asphalt", "gravel", "cobblestone"]
    );
    assert_eq!(engine.statistics().len(), 80);
    let surface = expand(&engine.statistics().surface, 80);
    assert_eq!(surface[0], 1);
    assert_eq!(surface.iter().filter(|c| **c == 3).count(), 1);

    // undoing does not forget what was learned: the codes stay valid in every state
    assert!(engine.run(Action::Undo));
    assert!(engine.run(Action::Undo));
    assert_eq!(
        engine.categories().surface.names(),
        ["asphalt", "gravel", "cobblestone"]
    );
    assert!(engine.run(Action::Redo));
    let first = engine.order()[0];
    select_files(&mut engine, &[first]);
    assert_eq!(expand(&engine.statistics().surface, 5), [1, 1, 0, 2, 2]);
}

#[test]
fn test_trackpoint() {
    let mut engine = TestEngine::default();
    load(&mut engine, "data/simple.gpx");
    let file = engine.order()[0];
    let structure = engine.file_structure(&file).unwrap();
    let seg = &structure.tracks[0].segments[0];
    let (seg_id, len) = (seg.id, seg.len);
    let coordinates = engine.segment_coordinates(&seg_id).to_vec();
    let last = engine.trackpoint(&file, &seg_id, len - 1).unwrap();
    assert_eq!(
        [last.coordinates.lng, last.coordinates.lat],
        coordinates[(len - 1) * 2..]
    );
    assert!(engine.trackpoint(&file, &seg_id, len).is_none());
    assert!(engine.trackpoint(&Default::default(), &seg_id, 0).is_none());
}

#[test]
fn test_export_writes_the_file_as_it_is() {
    let mut engine = TestEngine::default();
    assert!(
        engine
            .export(&FileId::default(), ExportOptions::ALL)
            .is_none()
    );

    load(&mut engine, "data/with_time.gpx");
    let id = engine.order()[0];
    let bytes = engine.export(&id, ExportOptions::ALL).unwrap();
    let again = crate::parse(&bytes, &mut engine.categories().clone()).unwrap();
    let file = engine.history.current().unwrap()[&id].clone();
    assert_eq!(again.trk.len(), file.trk.len());
    assert_eq!(again.trk[0].trkseg[0].len(), file.trk[0].trkseg[0].len());
    assert!(again.trk[0].trkseg[0][0].time.is_some());

    // the options leave data out
    let bytes = engine.export(&id, ExportOptions::NONE).unwrap();
    let again = crate::parse(&bytes, &mut engine.categories().clone()).unwrap();
    assert!(again.trk[0].trkseg[0].iter().all(|p| p.time.is_none()));

    // a file that is gone cannot be exported
    engine.run(Action::Edit(Command::DeleteAll(DeleteAll)));
    assert!(engine.export(&id, ExportOptions::ALL).is_none());
}

#[test]
fn test_exportable_data_is_the_union_over_the_files() {
    let mut engine = TestEngine::default();
    assert_eq!(engine.exportable_data(&[]), ExportOptions::NONE);

    load(&mut engine, "data/simple.gpx");
    load(&mut engine, "data/with_time.gpx");
    let (plain, timed) = (engine.order()[0], engine.order()[1]);
    assert!(!engine.exportable_data(&[plain]).time);
    assert!(engine.exportable_data(&[timed]).time);
    assert!(engine.exportable_data(&[plain, timed]).time);
    // unknown files have nothing
    assert_eq!(
        engine.exportable_data(&[FileId::default()]),
        ExportOptions::NONE
    );
    assert!(!engine.exportable_data(&[plain, FileId::default()]).time);
}

#[test]
fn test_file_statistics_are_the_ones_of_the_whole_file() {
    let mut engine = TestEngine::default();
    assert!(engine.file_statistics(&FileId::default()).is_none());

    load(&mut engine, "data/simple.gpx");
    let id = engine.order()[0];
    let stats = engine.file_statistics(&id).unwrap();
    assert!(stats.total_distance > 0.0);
    let last = engine.statistics().total_distance.last().copied().unwrap();
    assert!((stats.total_distance - last).abs() < 1e-9);
    assert!(engine.file_statistics(&FileId::default()).is_none());

    // statistics of a file do not depend on the selection
    engine.run(Action::Select {
        selection: Selection::Empty,
        mode: SelectMode::Replace,
    });
    assert_eq!(
        engine.file_statistics(&id).unwrap().total_distance,
        stats.total_distance
    );

    engine.run(Action::Undo);
    assert!(engine.file_statistics(&id).is_none());
}

#[test]
fn test_reduction_distances_follow_the_selection() {
    let mut engine = TestEngine::default();
    assert!(engine.reduction_distances().is_empty());

    load(&mut engine, "data/simple.gpx");
    let n = engine.statistics().total_distance.len();
    let distances = engine.reduction_distances();
    assert_eq!(distances.len(), n);
    assert!(distances.iter().all(|d| !d.is_nan()));

    engine.run(Action::Select {
        selection: Selection::Empty,
        mode: SelectMode::Replace,
    });
    assert!(engine.reduction_distances().is_empty());
}

#[test]
fn test_routing_describes_the_anchors_of_the_selection() {
    let mut engine = TestEngine::default();
    assert!(engine.routing().anchor_indices.is_empty());

    load(&mut engine, "data/simple.gpx");
    let n = engine.statistics().total_distance.len() as u32;
    let routing = engine.routing();
    assert_eq!(routing.segment_starts, vec![0]);
    assert_eq!(routing.segment_ids.len(), 1);
    // the ends of a segment are always anchors
    assert_eq!(routing.anchor_indices.first(), Some(&0));
    assert_eq!(routing.anchor_indices.last(), Some(&(n - 1)));
    assert_eq!(routing.anchor_indices.len(), routing.anchor_zooms.len());
    assert_eq!(routing.anchor_zooms[0], 0);

    // the revision follows what the indices refer to
    let revision = routing.revision;
    engine.run(Action::Select {
        selection: Selection::Empty,
        mode: SelectMode::Replace,
    });
    assert!(engine.routing().anchor_indices.is_empty());
    assert_ne!(engine.routing().revision, revision);
    // nothing changed for the routing: same revision
    let revision = engine.routing().revision;
    engine.run(Action::Select {
        selection: Selection::Empty,
        mode: SelectMode::Replace,
    });
    assert_eq!(engine.routing().revision, revision);
}

#[test]
fn test_last_error_tells_why_an_edit_did_nothing() {
    let mut engine = TestEngine::default();
    assert!(engine.last_error().is_none());

    // invalid data
    assert!(!edit(
        &mut engine,
        Command::Load(Load {
            data: b"<gpx><trk></gpx>",
            name: "file",
        })
    ));
    assert!(matches!(
        engine.last_error(),
        Some(CommandError::InvalidData(_))
    ));

    // nothing to change
    new(&mut engine, "file");
    assert!(engine.last_error().is_none());
    assert!(!edit(&mut engine, Command::Reverse(crate::Reverse)));
    assert_eq!(engine.last_error(), Some(&CommandError::NothingToDo));

    // the next action starts afresh, whatever it is
    engine.run(Action::Undo);
    assert!(engine.last_error().is_none());
    assert!(!edit(&mut engine, Command::Reverse(crate::Reverse)));
    assert!(engine.last_error().is_some());
    new(&mut engine, "other");
    assert!(engine.last_error().is_none());
}

#[test]
fn test_an_edit_that_changes_nothing_is_not_an_undo_step() {
    let mut engine = TestEngine::default();
    new(&mut engine, "file");
    // "file" is selected: naming it the same still builds a new file, but selecting nothing
    // leaves nothing to rename
    engine.run(Action::Select {
        selection: Selection::Empty,
        mode: SelectMode::Replace,
    });
    assert!(!edit(
        &mut engine,
        Command::Metadata(Metadata {
            name: "renamed",
            desc: "",
        })
    ));
    assert_eq!(engine.last_error(), Some(&CommandError::NothingToDo));
    assert!(engine.last_diff().is_none());

    // one step to undo: the creation
    assert!(engine.run(Action::Undo));
    assert!(!engine.can_undo());
    assert!(engine.order().is_empty());
}

#[test]
fn test_execute_returns_what_the_action_did() {
    let mut engine = TestEngine::default();
    let data = std::fs::read("data/simple.gpx").unwrap();
    let outcome = engine
        .execute(Action::Edit(Command::Load(Load {
            data: &data,
            name: "file",
        })))
        .unwrap();
    assert!(outcome.changed);
    assert_eq!(outcome.diff.as_ref().unwrap().added, engine.order());
    assert!(outcome.order_changed && outcome.selection_changed);
    assert!(!outcome.clipboard_changed);

    // the outcome of an action does not depend on what is done after it
    let kept = outcome.clone();
    engine.execute(Action::Undo).unwrap();
    assert_eq!(outcome, kept);

    // a selection only changes the selection
    engine.execute(Action::Redo).unwrap();
    let selection = files(engine.order());
    let outcome = engine
        .execute(Action::Select {
            selection,
            mode: SelectMode::Replace,
        })
        .unwrap();
    assert!(outcome.changed && outcome.selection_changed);
    assert!(outcome.diff.is_none() && !outcome.order_changed);

    // an edit with nothing to do says why
    engine
        .execute(Action::Select {
            selection: Selection::Empty,
            mode: SelectMode::Replace,
        })
        .unwrap();
    let result = engine.execute(Action::Edit(Command::Reverse(crate::Reverse)));
    assert_eq!(result, Err(CommandError::NothingToDo));

    // a failing one too
    let result = engine.execute(Action::Edit(Command::Load(Load {
        data: b"<gpx><trk></gpx>",
        name: "file",
    })));
    assert!(matches!(result, Err(CommandError::InvalidData(_))));
}

// What the engine does when it is overwritten with what is stored

fn restored_from(engine: &Engine, keep: &[FileId], extra: Vec<Rc<File>>) -> crate::Restored {
    let mut files: Vec<Rc<File>> = keep
        .iter()
        .map(|id| engine.snapshot().files[id].clone())
        .collect();
    files.extend(extra);
    crate::Restored {
        order: files.iter().map(|file| file.id).collect(),
        files,
        categories: engine.categories().clone(),
    }
}

#[test]
fn test_overwriting_reports_what_was_added_removed_and_modified() {
    let mut engine = TestEngine::default();
    new(&mut engine, "kept");
    new(&mut engine, "modified");
    new(&mut engine, "removed");
    let [kept, modified, removed] = engine.order()[..] else {
        panic!()
    };
    let mut changed = (*engine.snapshot().files[&modified]).clone();
    changed.info.name = "other name".into();
    let added = File::default();
    let added_id = added.id;

    let restored = restored_from(&engine, &[kept], vec![Rc::new(changed), Rc::new(added)]);
    let outcome = engine.restore(restored);
    assert!(outcome.changed);
    let diff = outcome.diff.unwrap();
    assert_eq!(diff.added, vec![added_id]);
    assert_eq!(diff.removed, vec![removed]);
    assert_eq!(diff.modified, vec![modified]);
    assert!(outcome.order_changed);
    assert_eq!(engine.order(), &[kept, modified, added_id]);
}

#[test]
fn test_overwriting_with_the_same_files_changes_nothing() {
    let mut engine = TestEngine::default();
    new(&mut engine, "a");
    let ids = engine.order().to_vec();
    let outcome = engine.restore(restored_from(&engine, &ids, vec![]));
    assert!(!outcome.changed);
    assert!(outcome.diff.is_none());
}

#[test]
fn test_overwriting_forgets_the_history() {
    let mut engine = TestEngine::default();
    new(&mut engine, "a");
    new(&mut engine, "b");
    assert!(engine.can_undo());
    let ids = engine.order().to_vec();
    engine.restore(restored_from(&engine, &ids, vec![]));
    assert!(!engine.can_undo());
}

mod per_file_history {
    use super::*;

    fn new_file(engine: &mut Engine<PerFileHistory>, name: &str) -> FileId {
        engine
            .execute(Action::Edit(Command::New(New {
                name,
                trackpoint: None,
            })))
            .unwrap();
        *engine.order().last().unwrap()
    }

    fn select(engine: &mut Engine<PerFileHistory>, ids: &[FileId]) {
        engine
            .execute(Action::Select {
                selection: Selection::File {
                    file_ids: ids.iter().copied().collect(),
                },
                mode: SelectMode::Replace,
            })
            .unwrap();
    }

    fn rename(engine: &mut Engine<PerFileHistory>, name: &str) {
        engine
            .execute(Action::Edit(Command::Metadata(Metadata { name, desc: "" })))
            .unwrap();
    }

    fn name_of(engine: &Engine<PerFileHistory>, id: FileId) -> String {
        engine.file_structure(&id).unwrap().name.clone()
    }

    #[test]
    fn test_creating_a_file_is_not_undoable() {
        let mut engine = Engine::<PerFileHistory>::default();
        let id = new_file(&mut engine, "file");
        assert!(!engine.can_undo());
        assert!(!engine.execute(Action::Undo).unwrap().changed);
        assert_eq!(engine.order(), [id]);
    }

    #[test]
    fn test_undo_follows_the_selected_files() {
        let mut engine = Engine::<PerFileHistory>::default();
        let a = new_file(&mut engine, "a");
        let b = new_file(&mut engine, "b");

        select(&mut engine, &[a]);
        rename(&mut engine, "a2");
        select(&mut engine, &[b]);
        rename(&mut engine, "b2");

        // b is selected: only its change is undone
        assert!(engine.can_undo());
        let outcome = engine.execute(Action::Undo).unwrap();
        assert_eq!(outcome.diff.unwrap().modified, vec![b]);
        assert_eq!(name_of(&engine, b), "b");
        assert_eq!(name_of(&engine, a), "a2");
        assert!(!engine.can_undo());
        assert!(engine.can_redo());

        select(&mut engine, &[a]);
        assert!(engine.can_undo());
        assert!(!engine.can_redo());
        engine.execute(Action::Undo).unwrap();
        assert_eq!(name_of(&engine, a), "a");

        select(&mut engine, &[b]);
        engine.execute(Action::Redo).unwrap();
        assert_eq!(name_of(&engine, b), "b2");
    }

    #[test]
    fn test_undo_without_selection_does_nothing() {
        let mut engine = Engine::<PerFileHistory>::default();
        new_file(&mut engine, "a");
        rename(&mut engine, "a2");
        engine
            .execute(Action::Select {
                selection: Selection::Empty,
                mode: SelectMode::Replace,
            })
            .unwrap();
        assert!(!engine.can_undo());
        assert!(!engine.execute(Action::Undo).unwrap().changed);
    }

    #[test]
    fn test_deleting_a_file_drops_its_history() {
        let mut engine = Engine::<PerFileHistory>::default();
        let id = new_file(&mut engine, "a");
        rename(&mut engine, "a2");
        engine
            .execute(Action::Edit(Command::Delete(Delete { whole_files: false })))
            .unwrap();
        assert!(engine.order().is_empty());
        assert!(!engine.execute(Action::Undo).unwrap().changed);
        assert!(engine.file_structure(&id).is_none());
    }
}