src/tui/app/machine/browse.rs

@@ -77,7 +77,7 @@ impl<MH: IMusicHoard> IAppInteractBrowse for AppMachine<MH, AppBrowse> {
         let orig = ListSelection::get(&self.inner.selection);
         self.inner
             .selection
-            .reset_artist(self.inner.music_hoard.get_collection());
+            .reset(self.inner.music_hoard.get_collection());
         AppMachine::search(self.inner, orig).into()
     }
 

src/tui/app/machine/search.rs

@@ -1,13 +1,13 @@
 use aho_corasick::AhoCorasick;
 use once_cell::sync::Lazy;
 
-use musichoard::collection::artist::Artist;
+use musichoard::collection::{album::Album, artist::Artist, track::Track};
 
 use crate::tui::{
     app::{
         machine::{App, AppInner, AppMachine},
-        selection::ListSelection,
-        AppPublic, AppState, IAppInteractSearch,
+        selection::{ListSelection, SelectionState},
+        AppPublic, AppState, Category, IAppInteractSearch,
     },
     lib::IMusicHoard,
 };
@@ -67,7 +67,7 @@ impl<MH: IMusicHoard> IAppInteractSearch for AppMachine<MH, AppSearch> {
 
     fn append_character(mut self, ch: char) -> Self::APP {
         self.state.string.push(ch);
-        let index = self.inner.selection.artist.state.list.selected();
+        let index = self.inner.selection.selected();
         self.state.memo.push(AppSearchMemo { index, char: true });
         self.incremental_search(false);
         self.into()
@@ -75,7 +75,7 @@ impl<MH: IMusicHoard> IAppInteractSearch for AppMachine<MH, AppSearch> {
 
     fn search_next(mut self) -> Self::APP {
         if !self.state.string.is_empty() {
-            let index = self.inner.selection.artist.state.list.selected();
+            let index = self.inner.selection.selected();
             self.state.memo.push(AppSearchMemo { index, char: false });
             self.incremental_search(true);
         }
@@ -88,7 +88,7 @@ impl<MH: IMusicHoard> IAppInteractSearch for AppMachine<MH, AppSearch> {
             if memo.char {
                 self.state.string.pop();
             }
-            self.inner.selection.select_artist(collection, memo.index);
+            self.inner.selection.select(collection, memo.index);
         }
         self.into()
     }
@@ -109,12 +109,18 @@ impl<MH: IMusicHoard> IAppInteractSearch for AppMachine<MH, AppSearch> {
 
 trait IAppInteractSearchPrivate {
     fn incremental_search(&mut self, next: bool);
-    fn incremental_search_predicate(
-        case_sensitive: bool,
-        char_sensitive: bool,
-        search_name: &str,
-        probe: &Artist,
-    ) -> bool;
+    fn next<P, T>(pred: P, name: &str, next: bool, st: SelectionState<'_, T>) -> Option<usize>
+    where
+        P: FnMut(bool, bool, &str, &T) -> bool;
+
+    fn search_artists(name: &str, next: bool, st: SelectionState<'_, Artist>) -> Option<usize>;
+    fn search_albums(name: &str, next: bool, st: SelectionState<'_, Album>) -> Option<usize>;
+    fn search_tracks(name: &str, next: bool, st: SelectionState<'_, Track>) -> Option<usize>;
+
+    fn predicate_artists(case_sens: bool, char_sens: bool, search: &str, probe: &Artist) -> bool;
+    fn predicate_albums(case_sens: bool, char_sens: bool, search: &str, probe: &Album) -> bool;
+    fn predicate_tracks(case_sens: bool, char_sens: bool, search: &str, probe: &Track) -> bool;
+    fn predicate_title(case_sens: bool, char_sens: bool, search: &str, title: &str) -> bool;
 
     fn is_case_sensitive(artist_name: &str) -> bool;
     fn is_char_sensitive(artist_name: &str) -> bool;
@@ -123,50 +129,86 @@ trait IAppInteractSearchPrivate {
 
 impl<MH: IMusicHoard> IAppInteractSearchPrivate for AppMachine<MH, AppSearch> {
     fn incremental_search(&mut self, next: bool) {
-        let artists = self.inner.music_hoard.get_collection();
-        let artist_name = &self.state.string;
+        let collection = self.inner.music_hoard.get_collection();
+        let search = &self.state.string;
 
-        let sel = &mut self.inner.selection;
-        if let Some(mut index) = sel.selected_artist() {
-            let case_sensitive = Self::is_case_sensitive(artist_name);
-            let char_sensitive = Self::is_char_sensitive(artist_name);
-            let search = Self::normalize_search(artist_name, !case_sensitive, !char_sensitive);
+        let sel = &self.inner.selection;
+        let result = match sel.active {
+            Category::Artist => sel
+                .state_artist(collection)
+                .and_then(|state| Self::search_artists(search, next, state)),
+            Category::Album => sel
+                .state_album(collection)
+                .and_then(|state| Self::search_albums(search, next, state)),
+            Category::Track => sel
+                .state_track(collection)
+                .and_then(|state| Self::search_tracks(search, next, state)),
+        };
 
-            if next && ((index + 1) < artists.len()) {
-                index += 1;
-            }
-            let slice = &artists[index..];
-
-            let result = slice.iter().position(|probe| {
-                Self::incremental_search_predicate(case_sensitive, char_sensitive, &search, probe)
-            });
-
-            if let Some(slice_index) = result {
-                sel.select_artist(artists, Some(index + slice_index));
-            }
+        if result.is_some() {
+            let collection = self.inner.music_hoard.get_collection();
+            self.inner.selection.select(collection, result);
         }
     }
 
-    fn incremental_search_predicate(
-        case_sensitive: bool,
-        char_sensitive: bool,
-        search_name: &str,
-        probe: &Artist,
-    ) -> bool {
-        let name = Self::normalize_search(&probe.id.name, !case_sensitive, !char_sensitive);
-        let mut result = name.starts_with(search_name);
+    fn search_artists(name: &str, next: bool, st: SelectionState<'_, Artist>) -> Option<usize> {
+        Self::next(Self::predicate_artists, name, next, st)
+    }
+
+    fn search_albums(name: &str, next: bool, st: SelectionState<'_, Album>) -> Option<usize> {
+        Self::next(Self::predicate_albums, name, next, st)
+    }
+
+    fn search_tracks(name: &str, next: bool, st: SelectionState<'_, Track>) -> Option<usize> {
+        Self::next(Self::predicate_tracks, name, next, st)
+    }
+
+    fn next<P, T>(mut pred: P, name: &str, next: bool, st: SelectionState<'_, T>) -> Option<usize>
+    where
+        P: FnMut(bool, bool, &str, &T) -> bool,
+    {
+        let case_sens = Self::is_case_sensitive(name);
+        let char_sens = Self::is_char_sensitive(name);
+        let search = Self::normalize_search(name, !case_sens, !char_sens);
+
+        let mut index = st.index;
+        if next && ((index + 1) < st.list.len()) {
+            index += 1;
+        }
+
+        let slice = &st.list[index..];
+        slice
+            .iter()
+            .position(|probe| pred(case_sens, char_sens, &search, probe))
+            .map(|slice_index| index + slice_index)
+    }
+
+    fn predicate_artists(case_sens: bool, char_sens: bool, search: &str, probe: &Artist) -> bool {
+        let name = Self::normalize_search(&probe.id.name, !case_sens, !char_sens);
+        let mut result = name.starts_with(search);
 
         if let Some(ref probe_sort) = probe.sort {
             if !result {
-                let name =
-                    Self::normalize_search(&probe_sort.name, !case_sensitive, !char_sensitive);
-                result = name.starts_with(search_name);
+                let name = Self::normalize_search(&probe_sort.name, !case_sens, !char_sens);
+                result = name.starts_with(search);
             }
         }
 
         result
     }
 
+    fn predicate_albums(case_sens: bool, char_sens: bool, search: &str, probe: &Album) -> bool {
+        Self::predicate_title(case_sens, char_sens, search, &probe.id.title)
+    }
+
+    fn predicate_tracks(case_sens: bool, char_sens: bool, search: &str, probe: &Track) -> bool {
+        Self::predicate_title(case_sens, char_sens, search, &probe.id.title)
+    }
+
+    fn predicate_title(case_sens: bool, char_sens: bool, search: &str, title: &str) -> bool {
+        Self::normalize_search(title, !case_sens, !char_sens).starts_with(search)
+    }
+
     fn is_case_sensitive(artist_name: &str) -> bool {
         artist_name
             .chars()
@@ -330,6 +372,54 @@ mod tests {
         assert_eq!(search.inner.selection.artist.state.list.selected(), Some(3));
     }
 
+    #[test]
+    fn album_incremental_search() {
+        let mut search =
+            AppMachine::search(inner(music_hoard(COLLECTION.to_owned())), orig(Some(1)));
+        search.inner.selection.active = Category::Album;
+
+        let sel = &search.inner.selection;
+        assert_eq!(sel.artist.album.state.list.selected(), Some(0));
+
+        search.state.string = String::from("album_title ");
+        search.incremental_search(false);
+
+        let sel = &search.inner.selection;
+        assert_eq!(sel.artist.album.state.list.selected(), Some(0));
+
+        let search = search.append_character('a').unwrap_search();
+        let search = search.append_character('.').unwrap_search();
+        let search = search.append_character('b').unwrap_search();
+
+        let sel = &search.inner.selection;
+        assert_eq!(sel.artist.album.state.list.selected(), Some(1));
+    }
+
+    #[test]
+    fn track_incremental_search() {
+        let mut search =
+            AppMachine::search(inner(music_hoard(COLLECTION.to_owned())), orig(Some(1)));
+        search.inner.selection.active = Category::Track;
+
+        let sel = &search.inner.selection;
+        assert_eq!(sel.artist.album.track.state.list.selected(), Some(0));
+
+        search.state.string = String::from("track ");
+        search.incremental_search(false);
+
+        let sel = &search.inner.selection;
+        assert_eq!(sel.artist.album.track.state.list.selected(), Some(0));
+
+        let search = search.append_character('a').unwrap_search();
+        let search = search.append_character('.').unwrap_search();
+        let search = search.append_character('a').unwrap_search();
+        let search = search.append_character('.').unwrap_search();
+        let search = search.append_character('2').unwrap_search();
+
+        let sel = &search.inner.selection;
+        assert_eq!(sel.artist.album.track.state.list.selected(), Some(1));
+    }
+
     #[test]
     fn search() {
         let search = AppMachine::search(inner(music_hoard(COLLECTION.to_owned())), orig(Some(2)));

src/tui/app/selection.rs

@@ -1,931 +0,0 @@
-use musichoard::collection::{
-    album::{Album, AlbumId},
-    artist::{Artist, ArtistId},
-    track::{Track, TrackId},
-    Collection,
-};
-use ratatui::widgets::ListState;
-use std::cmp;
-
-#[derive(Copy, Clone, Debug, PartialEq, Eq)]
-pub enum Category {
-    Artist,
-    Album,
-    Track,
-}
-
-#[derive(Clone, Debug, Default)]
-pub struct WidgetState {
-    pub list: ListState,
-    pub height: usize,
-}
-
-impl PartialEq for WidgetState {
-    fn eq(&self, other: &Self) -> bool {
-        self.list.selected().eq(&other.list.selected()) && self.height.eq(&other.height)
-    }
-}
-
-pub struct Selection {
-    pub active: Category,
-    pub artist: ArtistSelection,
-}
-
-#[derive(Clone, Debug, PartialEq)]
-pub struct ArtistSelection {
-    pub state: WidgetState,
-    pub album: AlbumSelection,
-}
-
-#[derive(Clone, Debug, PartialEq)]
-pub struct AlbumSelection {
-    pub state: WidgetState,
-    pub track: TrackSelection,
-}
-
-#[derive(Clone, Debug, PartialEq)]
-pub struct TrackSelection {
-    pub state: WidgetState,
-}
-
-pub enum Delta {
-    Line,
-    Page,
-}
-
-impl Delta {
-    fn as_usize(&self, state: &WidgetState) -> usize {
-        match self {
-            Delta::Line => 1,
-            Delta::Page => state.height.saturating_sub(1),
-        }
-    }
-}
-
-impl Selection {
-    pub fn new(artists: &[Artist]) -> Self {
-        Selection {
-            active: Category::Artist,
-            artist: ArtistSelection::initialise(artists),
-        }
-    }
-
-    pub fn select_by_list(&mut self, selected: ListSelection) {
-        self.artist.state.list = selected.artist;
-        self.artist.album.state.list = selected.album;
-        self.artist.album.track.state.list = selected.track;
-    }
-
-    pub fn select_by_id(&mut self, artists: &[Artist], selected: IdSelection) {
-        self.artist.reinitialise(artists, selected.artist);
-    }
-
-    pub fn select_artist(&mut self, artists: &[Artist], index: Option<usize>) {
-        self.artist.select(artists, index);
-    }
-
-    pub fn selected_artist(&self) -> Option<usize> {
-        self.artist.selected()
-    }
-
-    pub fn reset_artist(&mut self, artists: &[Artist]) {
-        if self.artist.state.list.selected() != Some(0) {
-            self.select_by_id(artists, IdSelection { artist: None });
-        }
-    }
-
-    pub fn increment_category(&mut self) {
-        self.active = match self.active {
-            Category::Artist => Category::Album,
-            Category::Album => Category::Track,
-            Category::Track => Category::Track,
-        };
-    }
-
-    pub fn decrement_category(&mut self) {
-        self.active = match self.active {
-            Category::Artist => Category::Artist,
-            Category::Album => Category::Artist,
-            Category::Track => Category::Album,
-        };
-    }
-
-    pub fn increment_selection(&mut self, collection: &Collection, delta: Delta) {
-        match self.active {
-            Category::Artist => self.increment_artist(collection, delta),
-            Category::Album => self.increment_album(collection, delta),
-            Category::Track => self.increment_track(collection, delta),
-        }
-    }
-
-    pub fn decrement_selection(&mut self, collection: &Collection, delta: Delta) {
-        match self.active {
-            Category::Artist => self.decrement_artist(collection, delta),
-            Category::Album => self.decrement_album(collection, delta),
-            Category::Track => self.decrement_track(collection, delta),
-        }
-    }
-
-    fn increment_artist(&mut self, artists: &[Artist], delta: Delta) {
-        self.artist.increment(artists, delta);
-    }
-
-    fn decrement_artist(&mut self, artists: &[Artist], delta: Delta) {
-        self.artist.decrement(artists, delta);
-    }
-
-    fn increment_album(&mut self, artists: &[Artist], delta: Delta) {
-        self.artist.increment_album(artists, delta);
-    }
-
-    fn decrement_album(&mut self, artists: &[Artist], delta: Delta) {
-        self.artist.decrement_album(artists, delta);
-    }
-
-    fn increment_track(&mut self, artists: &[Artist], delta: Delta) {
-        self.artist.increment_track(artists, delta);
-    }
-
-    fn decrement_track(&mut self, artists: &[Artist], delta: Delta) {
-        self.artist.decrement_track(artists, delta);
-    }
-}
-
-impl ArtistSelection {
-    fn initialise(artists: &[Artist]) -> Self {
-        let mut selection = ArtistSelection {
-            state: WidgetState::default(),
-            album: AlbumSelection::initialise(&[]),
-        };
-        selection.reinitialise(artists, None);
-        selection
-    }
-
-    fn reinitialise(&mut self, artists: &[Artist], active: Option<IdSelectArtist>) {
-        if let Some(active) = active {
-            let result = artists.binary_search_by(|a| a.get_sort_key().cmp(&active.artist_id));
-            match result {
-                Ok(index) => self.reinitialise_with_index(artists, index, active.album),
-                Err(index) => self.reinitialise_with_index(artists, index, None),
-            }
-        } else {
-            self.reinitialise_with_index(artists, 0, None)
-        }
-    }
-
-    fn reinitialise_with_index(
-        &mut self,
-        artists: &[Artist],
-        index: usize,
-        active_album: Option<IdSelectAlbum>,
-    ) {
-        if artists.is_empty() {
-            self.state.list.select(None);
-            self.album = AlbumSelection::initialise(&[]);
-        } else if index >= artists.len() {
-            let end = artists.len() - 1;
-            self.state.list.select(Some(end));
-            self.album = AlbumSelection::initialise(&artists[end].albums);
-        } else {
-            self.state.list.select(Some(index));
-            self.album
-                .reinitialise(&artists[index].albums, active_album);
-        }
-    }
-
-    fn selected(&self) -> Option<usize> {
-        self.state.list.selected()
-    }
-
-    fn select(&mut self, artists: &[Artist], to: Option<usize>) {
-        match to {
-            Some(to) => self.select_to(artists, to),
-            None => self.state.list.select(None),
-        }
-    }
-
-    fn select_to(&mut self, artists: &[Artist], mut to: usize) {
-        to = cmp::min(to, artists.len() - 1);
-        if self.state.list.selected() != Some(to) {
-            self.state.list.select(Some(to));
-            self.album = AlbumSelection::initialise(&artists[to].albums);
-        }
-    }
-
-    fn increment_by(&mut self, artists: &[Artist], by: usize) {
-        if let Some(index) = self.state.list.selected() {
-            let result = index.saturating_add(by);
-            self.select_to(artists, result);
-        }
-    }
-
-    fn increment(&mut self, artists: &[Artist], delta: Delta) {
-        self.increment_by(artists, delta.as_usize(&self.state));
-    }
-
-    fn increment_album(&mut self, artists: &[Artist], delta: Delta) {
-        if let Some(index) = self.state.list.selected() {
-            self.album.increment(&artists[index].albums, delta);
-        }
-    }
-
-    fn increment_track(&mut self, artists: &[Artist], delta: Delta) {
-        if let Some(index) = self.state.list.selected() {
-            self.album.increment_track(&artists[index].albums, delta);
-        }
-    }
-
-    fn decrement_by(&mut self, artists: &[Artist], by: usize) {
-        if let Some(index) = self.state.list.selected() {
-            let result = index.saturating_sub(by);
-            if self.state.list.selected() != Some(result) {
-                self.state.list.select(Some(result));
-                self.album = AlbumSelection::initialise(&artists[result].albums);
-            }
-        }
-    }
-
-    fn decrement(&mut self, artists: &[Artist], delta: Delta) {
-        self.decrement_by(artists, delta.as_usize(&self.state));
-    }
-
-    fn decrement_album(&mut self, artists: &[Artist], delta: Delta) {
-        if let Some(index) = self.state.list.selected() {
-            self.album.decrement(&artists[index].albums, delta);
-        }
-    }
-
-    fn decrement_track(&mut self, artists: &[Artist], delta: Delta) {
-        if let Some(index) = self.state.list.selected() {
-            self.album.decrement_track(&artists[index].albums, delta);
-        }
-    }
-}
-
-impl AlbumSelection {
-    fn initialise(albums: &[Album]) -> Self {
-        let mut selection = AlbumSelection {
-            state: WidgetState::default(),
-            track: TrackSelection::initialise(&[]),
-        };
-        selection.reinitialise(albums, None);
-        selection
-    }
-
-    fn reinitialise(&mut self, albums: &[Album], album: Option<IdSelectAlbum>) {
-        if let Some(album) = album {
-            let result = albums.binary_search_by(|a| a.get_sort_key().cmp(&album.album_id));
-            match result {
-                Ok(index) => self.reinitialise_with_index(albums, index, album.track),
-                Err(index) => self.reinitialise_with_index(albums, index, None),
-            }
-        } else {
-            self.reinitialise_with_index(albums, 0, None)
-        }
-    }
-
-    fn reinitialise_with_index(
-        &mut self,
-        albums: &[Album],
-        index: usize,
-        active_track: Option<IdSelectTrack>,
-    ) {
-        if albums.is_empty() {
-            self.state.list.select(None);
-            self.track = TrackSelection::initialise(&[]);
-        } else if index >= albums.len() {
-            let end = albums.len() - 1;
-            self.state.list.select(Some(end));
-            self.track = TrackSelection::initialise(&albums[end].tracks);
-        } else {
-            self.state.list.select(Some(index));
-            self.track.reinitialise(&albums[index].tracks, active_track);
-        }
-    }
-
-    fn increment_by(&mut self, albums: &[Album], by: usize) {
-        if let Some(index) = self.state.list.selected() {
-            let mut result = index.saturating_add(by);
-            if result >= albums.len() {
-                result = albums.len() - 1;
-            }
-            if self.state.list.selected() != Some(result) {
-                self.state.list.select(Some(result));
-                self.track = TrackSelection::initialise(&albums[result].tracks);
-            }
-        }
-    }
-
-    fn increment(&mut self, albums: &[Album], delta: Delta) {
-        self.increment_by(albums, delta.as_usize(&self.state));
-    }
-
-    fn increment_track(&mut self, albums: &[Album], delta: Delta) {
-        if let Some(index) = self.state.list.selected() {
-            self.track.increment(&albums[index].tracks, delta);
-        }
-    }
-
-    fn decrement_by(&mut self, albums: &[Album], by: usize) {
-        if let Some(index) = self.state.list.selected() {
-            let result = index.saturating_sub(by);
-            if self.state.list.selected() != Some(result) {
-                self.state.list.select(Some(result));
-                self.track = TrackSelection::initialise(&albums[result].tracks);
-            }
-        }
-    }
-
-    fn decrement(&mut self, albums: &[Album], delta: Delta) {
-        self.decrement_by(albums, delta.as_usize(&self.state));
-    }
-
-    fn decrement_track(&mut self, albums: &[Album], delta: Delta) {
-        if let Some(index) = self.state.list.selected() {
-            self.track.decrement(&albums[index].tracks, delta);
-        }
-    }
-}
-
-impl TrackSelection {
-    fn initialise(tracks: &[Track]) -> Self {
-        let mut selection = TrackSelection {
-            state: WidgetState::default(),
-        };
-        selection.reinitialise(tracks, None);
-        selection
-    }
-
-    fn reinitialise(&mut self, tracks: &[Track], track: Option<IdSelectTrack>) {
-        if let Some(track) = track {
-            let result = tracks.binary_search_by(|t| t.get_sort_key().cmp(&track.track_id));
-            match result {
-                Ok(index) | Err(index) => self.reinitialise_with_index(tracks, index),
-            }
-        } else {
-            self.reinitialise_with_index(tracks, 0)
-        }
-    }
-
-    fn reinitialise_with_index(&mut self, tracks: &[Track], index: usize) {
-        if tracks.is_empty() {
-            self.state.list.select(None);
-        } else if index >= tracks.len() {
-            self.state.list.select(Some(tracks.len() - 1));
-        } else {
-            self.state.list.select(Some(index));
-        }
-    }
-
-    fn increment_by(&mut self, tracks: &[Track], by: usize) {
-        if let Some(index) = self.state.list.selected() {
-            let mut result = index.saturating_add(by);
-            if result >= tracks.len() {
-                result = tracks.len() - 1;
-            }
-            if self.state.list.selected() != Some(result) {
-                self.state.list.select(Some(result));
-            }
-        }
-    }
-
-    fn increment(&mut self, tracks: &[Track], delta: Delta) {
-        self.increment_by(tracks, delta.as_usize(&self.state));
-    }
-
-    fn decrement_by(&mut self, _tracks: &[Track], by: usize) {
-        if let Some(index) = self.state.list.selected() {
-            let result = index.saturating_sub(by);
-            if self.state.list.selected() != Some(result) {
-                self.state.list.select(Some(result));
-            }
-        }
-    }
-
-    fn decrement(&mut self, tracks: &[Track], delta: Delta) {
-        self.decrement_by(tracks, delta.as_usize(&self.state));
-    }
-}
-
-pub struct ListSelection {
-    pub artist: ListState,
-    pub album: ListState,
-    pub track: ListState,
-}
-
-impl ListSelection {
-    pub fn get(selection: &Selection) -> Self {
-        ListSelection {
-            artist: selection.artist.state.list.clone(),
-            album: selection.artist.album.state.list.clone(),
-            track: selection.artist.album.track.state.list.clone(),
-        }
-    }
-}
-
-pub struct IdSelection {
-    artist: Option<IdSelectArtist>,
-}
-
-struct IdSelectArtist {
-    artist_id: ArtistId,
-    album: Option<IdSelectAlbum>,
-}
-
-struct IdSelectAlbum {
-    album_id: AlbumId,
-    track: Option<IdSelectTrack>,
-}
-
-struct IdSelectTrack {
-    track_id: TrackId,
-}
-
-impl IdSelection {
-    pub fn get(collection: &Collection, selection: &Selection) -> Self {
-        IdSelection {
-            artist: IdSelectArtist::get(collection, &selection.artist),
-        }
-    }
-}
-
-impl IdSelectArtist {
-    fn get(artists: &[Artist], selection: &ArtistSelection) -> Option<Self> {
-        selection.state.list.selected().map(|index| {
-            let artist = &artists[index];
-            IdSelectArtist {
-                artist_id: artist.get_sort_key().clone(),
-                album: IdSelectAlbum::get(&artist.albums, &selection.album),
-            }
-        })
-    }
-}
-
-impl IdSelectAlbum {
-    fn get(albums: &[Album], selection: &AlbumSelection) -> Option<Self> {
-        selection.state.list.selected().map(|index| {
-            let album = &albums[index];
-            IdSelectAlbum {
-                album_id: album.get_sort_key().clone(),
-                track: IdSelectTrack::get(&album.tracks, &selection.track),
-            }
-        })
-    }
-}
-
-impl IdSelectTrack {
-    fn get(tracks: &[Track], selection: &TrackSelection) -> Option<Self> {
-        selection.state.list.selected().map(|index| {
-            let track = &tracks[index];
-            IdSelectTrack {
-                track_id: track.get_sort_key().clone(),
-            }
-        })
-    }
-}
-
-#[cfg(test)]
-mod tests {
-    use crate::tui::testmod::COLLECTION;
-
-    use super::*;
-
-    #[test]
-    fn track_selection() {
-        let tracks = &COLLECTION[0].albums[0].tracks;
-        assert!(tracks.len() > 1);
-
-        let mut empty = TrackSelection::initialise(&[]);
-        assert_eq!(empty.state.list.selected(), None);
-
-        empty.increment(tracks, Delta::Line);
-        assert_eq!(empty.state.list.selected(), None);
-
-        empty.decrement(tracks, Delta::Line);
-        assert_eq!(empty.state.list.selected(), None);
-
-        let mut sel = TrackSelection::initialise(tracks);
-        assert_eq!(sel.state.list.selected(), Some(0));
-
-        sel.decrement(tracks, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(0));
-
-        sel.increment(tracks, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(1));
-
-        sel.decrement(tracks, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(0));
-
-        for _ in 0..(tracks.len() + 5) {
-            sel.increment(tracks, Delta::Line);
-        }
-        assert_eq!(sel.state.list.selected(), Some(tracks.len() - 1));
-    }
-
-    #[test]
-    fn track_delta_page() {
-        let tracks = &COLLECTION[0].albums[0].tracks;
-        assert!(tracks.len() > 1);
-
-        let empty = TrackSelection::initialise(&[]);
-        assert_eq!(empty.state.list.selected(), None);
-
-        let mut sel = TrackSelection::initialise(tracks);
-        assert_eq!(sel.state.list.selected(), Some(0));
-
-        assert!(tracks.len() >= 4);
-        sel.state.height = 3;
-
-        sel.decrement(tracks, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(0));
-
-        sel.increment(tracks, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(2));
-
-        sel.decrement(tracks, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(0));
-
-        for _ in 0..(tracks.len() + 5) {
-            sel.increment(tracks, Delta::Page);
-        }
-        assert_eq!(sel.state.list.selected(), Some(tracks.len() - 1));
-    }
-
-    #[test]
-    fn track_reinitialise() {
-        let tracks = &COLLECTION[0].albums[0].tracks;
-        assert!(tracks.len() > 1);
-
-        let mut sel = TrackSelection::initialise(tracks);
-        sel.state.list.select(Some(tracks.len() - 1));
-
-        // Re-initialise.
-        let expected = sel.clone();
-        let active_track = IdSelectTrack::get(tracks, &sel);
-        sel.reinitialise(tracks, active_track);
-        assert_eq!(sel, expected);
-
-        // Re-initialise out-of-bounds.
-        let mut expected = sel.clone();
-        expected.decrement(tracks, Delta::Line);
-        let active_track = IdSelectTrack::get(tracks, &sel);
-        sel.reinitialise(&tracks[..(tracks.len() - 1)], active_track);
-        assert_eq!(sel, expected);
-
-        // Re-initialise empty.
-        let expected = TrackSelection::initialise(&[]);
-        let active_track = IdSelectTrack::get(tracks, &sel);
-        sel.reinitialise(&[], active_track);
-        assert_eq!(sel, expected);
-    }
-
-    #[test]
-    fn album_selection() {
-        let albums = &COLLECTION[0].albums;
-        assert!(albums.len() > 1);
-
-        let mut empty = AlbumSelection::initialise(&[]);
-        assert_eq!(empty.state.list.selected(), None);
-        assert_eq!(empty.track.state.list.selected(), None);
-
-        empty.increment(albums, Delta::Line);
-        assert_eq!(empty.state.list.selected(), None);
-        assert_eq!(empty.track.state.list.selected(), None);
-
-        empty.decrement(albums, Delta::Line);
-        assert_eq!(empty.state.list.selected(), None);
-        assert_eq!(empty.track.state.list.selected(), None);
-
-        let mut sel = AlbumSelection::initialise(albums);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.track.state.list.selected(), Some(0));
-
-        sel.increment_track(albums, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.track.state.list.selected(), Some(1));
-
-        // Verify that decrement that doesn't change index does not reset track.
-        sel.decrement(albums, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.track.state.list.selected(), Some(1));
-
-        sel.increment(albums, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(1));
-        assert_eq!(sel.track.state.list.selected(), Some(0));
-
-        sel.decrement(albums, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.track.state.list.selected(), Some(0));
-
-        for _ in 0..(albums.len() + 5) {
-            sel.increment(albums, Delta::Line);
-        }
-        assert_eq!(sel.state.list.selected(), Some(albums.len() - 1));
-        assert_eq!(sel.track.state.list.selected(), Some(0));
-
-        sel.increment_track(albums, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(albums.len() - 1));
-        assert_eq!(sel.track.state.list.selected(), Some(1));
-
-        // Verify that increment that doesn't change index does not reset track.
-        sel.increment(albums, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(albums.len() - 1));
-        assert_eq!(sel.track.state.list.selected(), Some(1));
-    }
-
-    #[test]
-    fn album_delta_page() {
-        let albums = &COLLECTION[1].albums;
-        assert!(albums.len() > 1);
-
-        let empty = AlbumSelection::initialise(&[]);
-        assert_eq!(empty.state.list.selected(), None);
-
-        let mut sel = AlbumSelection::initialise(albums);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.track.state.list.selected(), Some(0));
-
-        assert!(albums.len() >= 4);
-        sel.state.height = 3;
-
-        sel.increment_track(albums, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.track.state.list.selected(), Some(1));
-
-        // Verify that decrement that doesn't change index does not reset track.
-        sel.decrement(albums, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.track.state.list.selected(), Some(1));
-
-        sel.increment(albums, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(2));
-        assert_eq!(sel.track.state.list.selected(), Some(0));
-
-        sel.decrement(albums, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.track.state.list.selected(), Some(0));
-
-        for _ in 0..(albums.len() + 5) {
-            sel.increment(albums, Delta::Page);
-        }
-        assert_eq!(sel.state.list.selected(), Some(albums.len() - 1));
-        assert_eq!(sel.track.state.list.selected(), Some(0));
-
-        sel.increment_track(albums, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(albums.len() - 1));
-        assert_eq!(sel.track.state.list.selected(), Some(1));
-
-        // Verify that increment that doesn't change index does not reset track.
-        sel.increment(albums, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(albums.len() - 1));
-        assert_eq!(sel.track.state.list.selected(), Some(1));
-    }
-
-    #[test]
-    fn album_reinitialise() {
-        let albums = &COLLECTION[0].albums;
-        assert!(albums.len() > 1);
-
-        let mut sel = AlbumSelection::initialise(albums);
-        sel.state.list.select(Some(albums.len() - 1));
-        sel.track.state.list.select(Some(1));
-
-        // Re-initialise.
-        let expected = sel.clone();
-        let active_album = IdSelectAlbum::get(albums, &sel);
-        sel.reinitialise(albums, active_album);
-        assert_eq!(sel, expected);
-
-        // Re-initialise out-of-bounds.
-        let mut expected = sel.clone();
-        expected.decrement(albums, Delta::Line);
-        let active_album = IdSelectAlbum::get(albums, &sel);
-        sel.reinitialise(&albums[..(albums.len() - 1)], active_album);
-        assert_eq!(sel, expected);
-
-        // Re-initialise empty.
-        let expected = AlbumSelection::initialise(&[]);
-        let active_album = IdSelectAlbum::get(albums, &sel);
-        sel.reinitialise(&[], active_album);
-        assert_eq!(sel, expected);
-    }
-
-    #[test]
-    fn artist_selection() {
-        let artists = &COLLECTION;
-        assert!(artists.len() > 1);
-
-        let mut empty = ArtistSelection::initialise(&[]);
-        assert_eq!(empty.state.list.selected(), None);
-        assert_eq!(empty.album.state.list.selected(), None);
-
-        empty.increment(artists, Delta::Line);
-        assert_eq!(empty.state.list.selected(), None);
-        assert_eq!(empty.album.state.list.selected(), None);
-
-        empty.decrement(artists, Delta::Line);
-        assert_eq!(empty.state.list.selected(), None);
-        assert_eq!(empty.album.state.list.selected(), None);
-
-        let mut sel = ArtistSelection::initialise(artists);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.album.state.list.selected(), Some(0));
-
-        sel.increment_album(artists, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.album.state.list.selected(), Some(1));
-
-        // Verify that decrement that doesn't change index does not reset album.
-        sel.decrement(artists, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.album.state.list.selected(), Some(1));
-
-        sel.increment(artists, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(1));
-        assert_eq!(sel.album.state.list.selected(), Some(0));
-
-        sel.decrement(artists, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.album.state.list.selected(), Some(0));
-
-        for _ in 0..(artists.len() + 5) {
-            sel.increment(artists, Delta::Line);
-        }
-        assert_eq!(sel.state.list.selected(), Some(artists.len() - 1));
-        assert_eq!(sel.album.state.list.selected(), Some(0));
-
-        sel.increment_album(artists, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(artists.len() - 1));
-        assert_eq!(sel.album.state.list.selected(), Some(1));
-
-        // Verify that increment that doesn't change index does not reset album.
-        sel.increment(artists, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(artists.len() - 1));
-        assert_eq!(sel.album.state.list.selected(), Some(1));
-    }
-
-    #[test]
-    fn artist_delta_page() {
-        let artists = &COLLECTION;
-        assert!(artists.len() > 1);
-
-        let empty = ArtistSelection::initialise(&[]);
-        assert_eq!(empty.state.list.selected(), None);
-
-        let mut sel = ArtistSelection::initialise(artists);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.album.state.list.selected(), Some(0));
-
-        assert!(artists.len() >= 4);
-        sel.state.height = 3;
-
-        sel.increment_album(artists, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.album.state.list.selected(), Some(1));
-
-        // Verify that decrement that doesn't change index does not reset album.
-        sel.decrement(artists, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.album.state.list.selected(), Some(1));
-
-        sel.increment(artists, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(2));
-        assert_eq!(sel.album.state.list.selected(), Some(0));
-
-        sel.decrement(artists, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(0));
-        assert_eq!(sel.album.state.list.selected(), Some(0));
-
-        for _ in 0..(artists.len() + 5) {
-            sel.increment(artists, Delta::Page);
-        }
-        assert_eq!(sel.state.list.selected(), Some(artists.len() - 1));
-        assert_eq!(sel.album.state.list.selected(), Some(0));
-
-        sel.increment_album(artists, Delta::Line);
-        assert_eq!(sel.state.list.selected(), Some(artists.len() - 1));
-        assert_eq!(sel.album.state.list.selected(), Some(1));
-
-        // Verify that increment that doesn't change index does not reset album.
-        sel.increment(artists, Delta::Page);
-        assert_eq!(sel.state.list.selected(), Some(artists.len() - 1));
-        assert_eq!(sel.album.state.list.selected(), Some(1));
-    }
-
-    #[test]
-    fn artist_reinitialise() {
-        let artists = &COLLECTION;
-        assert!(artists.len() > 1);
-
-        let mut sel = ArtistSelection::initialise(artists);
-        sel.state.list.select(Some(artists.len() - 1));
-        sel.album.state.list.select(Some(1));
-
-        // Re-initialise.
-        let expected = sel.clone();
-        let active_artist = IdSelectArtist::get(artists, &sel);
-        sel.reinitialise(artists, active_artist);
-        assert_eq!(sel, expected);
-
-        // Re-initialise out-of-bounds.
-        let mut expected = sel.clone();
-        expected.decrement(artists, Delta::Line);
-        let active_artist = IdSelectArtist::get(artists, &sel);
-        sel.reinitialise(&artists[..(artists.len() - 1)], active_artist);
-        assert_eq!(sel, expected);
-
-        // Re-initialise empty.
-        let expected = ArtistSelection::initialise(&[]);
-        let active_artist = IdSelectArtist::get(artists, &sel);
-        sel.reinitialise(&[], active_artist);
-        assert_eq!(sel, expected);
-    }
-
-    #[test]
-    fn selection() {
-        let mut selection = Selection::new(&COLLECTION);
-
-        assert_eq!(selection.active, Category::Artist);
-        assert_eq!(selection.artist.state.list.selected(), Some(0));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(0));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(0));
-
-        selection.increment_selection(&COLLECTION, Delta::Line);
-        assert_eq!(selection.active, Category::Artist);
-        assert_eq!(selection.artist.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(0));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(0));
-
-        selection.increment_category();
-        assert_eq!(selection.active, Category::Album);
-        assert_eq!(selection.artist.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(0));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(0));
-
-        selection.increment_selection(&COLLECTION, Delta::Line);
-        assert_eq!(selection.active, Category::Album);
-        assert_eq!(selection.artist.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(0));
-
-        selection.increment_category();
-        assert_eq!(selection.active, Category::Track);
-        assert_eq!(selection.artist.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(0));
-
-        selection.increment_selection(&COLLECTION, Delta::Line);
-        assert_eq!(selection.active, Category::Track);
-        assert_eq!(selection.artist.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(1));
-
-        selection.increment_category();
-        assert_eq!(selection.active, Category::Track);
-        assert_eq!(selection.artist.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(1));
-
-        selection.decrement_selection(&COLLECTION, Delta::Line);
-        assert_eq!(selection.active, Category::Track);
-        assert_eq!(selection.artist.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(0));
-
-        selection.increment_selection(&COLLECTION, Delta::Line);
-        selection.decrement_category();
-        assert_eq!(selection.active, Category::Album);
-        assert_eq!(selection.artist.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(1));
-
-        selection.decrement_selection(&COLLECTION, Delta::Line);
-        assert_eq!(selection.active, Category::Album);
-        assert_eq!(selection.artist.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(0));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(0));
-
-        selection.increment_selection(&COLLECTION, Delta::Line);
-        selection.decrement_category();
-        assert_eq!(selection.active, Category::Artist);
-        assert_eq!(selection.artist.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(0));
-
-        selection.decrement_selection(&COLLECTION, Delta::Line);
-        assert_eq!(selection.active, Category::Artist);
-        assert_eq!(selection.artist.state.list.selected(), Some(0));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(0));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(0));
-
-        selection.increment_category();
-        selection.increment_selection(&COLLECTION, Delta::Line);
-        selection.decrement_category();
-        selection.decrement_selection(&COLLECTION, Delta::Line);
-        selection.decrement_category();
-        assert_eq!(selection.active, Category::Artist);
-        assert_eq!(selection.artist.state.list.selected(), Some(0));
-        assert_eq!(selection.artist.album.state.list.selected(), Some(1));
-        assert_eq!(selection.artist.album.track.state.list.selected(), Some(0));
-    }
-}

src/tui/app/selection/album.rs

@@ -0,0 +1,342 @@
+use std::cmp;
+
+use musichoard::collection::{
+    album::{Album, AlbumId},
+    track::Track,
+};
+
+use crate::tui::app::selection::{
+    track::{IdSelectTrack, TrackSelection},
+    Delta, SelectionState, WidgetState,
+};
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct AlbumSelection {
+    pub state: WidgetState,
+    pub track: TrackSelection,
+}
+
+impl AlbumSelection {
+    pub fn initialise(albums: &[Album]) -> Self {
+        let mut selection = AlbumSelection {
+            state: WidgetState::default(),
+            track: TrackSelection::initialise(&[]),
+        };
+        selection.reinitialise(albums, None);
+        selection
+    }
+
+    pub fn reinitialise(&mut self, albums: &[Album], album: Option<IdSelectAlbum>) {
+        if let Some(album) = album {
+            let result = albums.binary_search_by(|a| a.get_sort_key().cmp(&album.album_id));
+            match result {
+                Ok(index) => self.reinitialise_with_index(albums, index, album.track),
+                Err(index) => self.reinitialise_with_index(albums, index, None),
+            }
+        } else {
+            self.reinitialise_with_index(albums, 0, None)
+        }
+    }
+
+    fn reinitialise_with_index(
+        &mut self,
+        albums: &[Album],
+        index: usize,
+        active_track: Option<IdSelectTrack>,
+    ) {
+        if albums.is_empty() {
+            self.state.list.select(None);
+            self.track = TrackSelection::initialise(&[]);
+        } else if index >= albums.len() {
+            let end = albums.len() - 1;
+            self.state.list.select(Some(end));
+            self.track = TrackSelection::initialise(&albums[end].tracks);
+        } else {
+            self.state.list.select(Some(index));
+            self.track.reinitialise(&albums[index].tracks, active_track);
+        }
+    }
+
+    pub fn selected(&self) -> Option<usize> {
+        self.state.list.selected()
+    }
+
+    pub fn selected_track(&self) -> Option<usize> {
+        self.track.selected()
+    }
+
+    pub fn select(&mut self, albums: &[Album], to: Option<usize>) {
+        match to {
+            Some(to) => self.select_to(albums, to),
+            None => self.state.list.select(None),
+        }
+    }
+
+    pub fn select_track(&mut self, albums: &[Album], to: Option<usize>) {
+        if let Some(index) = self.state.list.selected() {
+            self.track.select(&albums[index].tracks, to);
+        }
+    }
+
+    fn select_to(&mut self, albums: &[Album], mut to: usize) {
+        to = cmp::min(to, albums.len() - 1);
+        if self.state.list.selected() != Some(to) {
+            self.state.list.select(Some(to));
+            self.track = TrackSelection::initialise(&albums[to].tracks);
+        }
+    }
+
+    pub fn selection_state<'a>(&self, list: &'a [Album]) -> Option<SelectionState<'a, Album>> {
+        let selected = self.state.list.selected();
+        selected.map(|index| SelectionState { list, index })
+    }
+
+    pub fn state_tracks<'a>(&self, albums: &'a [Album]) -> Option<SelectionState<'a, Track>> {
+        let selected = self.state.list.selected();
+        selected.and_then(|index| self.track.selection_state(&albums[index].tracks))
+    }
+
+    pub fn reset(&mut self, albums: &[Album]) {
+        if self.state.list.selected() != Some(0) {
+            self.reinitialise(albums, None);
+        }
+    }
+
+    pub fn reset_track(&mut self, albums: &[Album]) {
+        if let Some(index) = self.state.list.selected() {
+            self.track.reset(&albums[index].tracks);
+        }
+    }
+
+    pub fn increment(&mut self, albums: &[Album], delta: Delta) {
+        self.increment_by(albums, delta.as_usize(&self.state));
+    }
+
+    pub fn increment_track(&mut self, albums: &[Album], delta: Delta) {
+        if let Some(index) = self.state.list.selected() {
+            self.track.increment(&albums[index].tracks, delta);
+        }
+    }
+
+    fn increment_by(&mut self, albums: &[Album], by: usize) {
+        if let Some(index) = self.state.list.selected() {
+            let mut result = index.saturating_add(by);
+            if result >= albums.len() {
+                result = albums.len() - 1;
+            }
+            if self.state.list.selected() != Some(result) {
+                self.state.list.select(Some(result));
+                self.track = TrackSelection::initialise(&albums[result].tracks);
+            }
+        }
+    }
+
+    pub fn decrement(&mut self, albums: &[Album], delta: Delta) {
+        self.decrement_by(albums, delta.as_usize(&self.state));
+    }
+
+    pub fn decrement_track(&mut self, albums: &[Album], delta: Delta) {
+        if let Some(index) = self.state.list.selected() {
+            self.track.decrement(&albums[index].tracks, delta);
+        }
+    }
+
+    fn decrement_by(&mut self, albums: &[Album], by: usize) {
+        if let Some(index) = self.state.list.selected() {
+            let result = index.saturating_sub(by);
+            if self.state.list.selected() != Some(result) {
+                self.state.list.select(Some(result));
+                self.track = TrackSelection::initialise(&albums[result].tracks);
+            }
+        }
+    }
+}
+
+pub struct IdSelectAlbum {
+    album_id: AlbumId,
+    track: Option<IdSelectTrack>,
+}
+
+impl IdSelectAlbum {
+    pub fn get(albums: &[Album], selection: &AlbumSelection) -> Option<Self> {
+        selection.state.list.selected().map(|index| {
+            let album = &albums[index];
+            IdSelectAlbum {
+                album_id: album.get_sort_key().clone(),
+                track: IdSelectTrack::get(&album.tracks, &selection.track),
+            }
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tui::testmod::COLLECTION;
+
+    use super::*;
+
+    #[test]
+    fn album_select() {
+        let albums = &COLLECTION[0].albums;
+        assert!(albums.len() > 1);
+
+        let mut sel = AlbumSelection::initialise(albums);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.select(albums, None);
+        assert_eq!(sel.selected(), None);
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.select(albums, Some(albums.len()));
+        assert_eq!(sel.selected(), Some(albums.len() - 1));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.select_track(albums, None);
+        assert_eq!(sel.selected(), Some(albums.len() - 1));
+        assert_eq!(sel.selected_track(), None);
+
+        sel.reset_track(albums);
+        assert_eq!(sel.selected(), Some(albums.len() - 1));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.select_track(albums, Some(1));
+        assert_eq!(sel.selected(), Some(albums.len() - 1));
+        assert_eq!(sel.selected_track(), Some(1));
+
+        sel.reset(albums);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+    }
+
+    #[test]
+    fn album_delta_line() {
+        let albums = &COLLECTION[0].albums;
+        assert!(albums.len() > 1);
+
+        let mut empty = AlbumSelection::initialise(&[]);
+        assert_eq!(empty.selected(), None);
+        assert_eq!(empty.selected_track(), None);
+
+        empty.increment(albums, Delta::Line);
+        assert_eq!(empty.selected(), None);
+        assert_eq!(empty.selected_track(), None);
+
+        empty.decrement(albums, Delta::Line);
+        assert_eq!(empty.selected(), None);
+        assert_eq!(empty.selected_track(), None);
+
+        let mut sel = AlbumSelection::initialise(albums);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.increment_track(albums, Delta::Line);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_track(), Some(1));
+
+        // Verify that decrement that doesn't change index does not reset track.
+        sel.decrement(albums, Delta::Line);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_track(), Some(1));
+
+        sel.increment(albums, Delta::Line);
+        assert_eq!(sel.selected(), Some(1));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.decrement(albums, Delta::Line);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        for _ in 0..(albums.len() + 5) {
+            sel.increment(albums, Delta::Line);
+        }
+        assert_eq!(sel.selected(), Some(albums.len() - 1));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.increment_track(albums, Delta::Line);
+        assert_eq!(sel.selected(), Some(albums.len() - 1));
+        assert_eq!(sel.selected_track(), Some(1));
+
+        // Verify that increment that doesn't change index does not reset track.
+        sel.increment(albums, Delta::Line);
+        assert_eq!(sel.selected(), Some(albums.len() - 1));
+        assert_eq!(sel.selected_track(), Some(1));
+    }
+
+    #[test]
+    fn album_delta_page() {
+        let albums = &COLLECTION[1].albums;
+        assert!(albums.len() > 1);
+
+        let empty = AlbumSelection::initialise(&[]);
+        assert_eq!(empty.selected(), None);
+
+        let mut sel = AlbumSelection::initialise(albums);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        assert!(albums.len() >= 4);
+        sel.state.height = 3;
+
+        sel.increment_track(albums, Delta::Line);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_track(), Some(1));
+
+        // Verify that decrement that doesn't change index does not reset track.
+        sel.decrement(albums, Delta::Page);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_track(), Some(1));
+
+        sel.increment(albums, Delta::Page);
+        assert_eq!(sel.selected(), Some(2));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.decrement(albums, Delta::Page);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        for _ in 0..(albums.len() + 5) {
+            sel.increment(albums, Delta::Page);
+        }
+        assert_eq!(sel.selected(), Some(albums.len() - 1));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.increment_track(albums, Delta::Line);
+        assert_eq!(sel.selected(), Some(albums.len() - 1));
+        assert_eq!(sel.selected_track(), Some(1));
+
+        // Verify that increment that doesn't change index does not reset track.
+        sel.increment(albums, Delta::Page);
+        assert_eq!(sel.selected(), Some(albums.len() - 1));
+        assert_eq!(sel.selected_track(), Some(1));
+    }
+
+    #[test]
+    fn album_reinitialise() {
+        let albums = &COLLECTION[0].albums;
+        assert!(albums.len() > 1);
+
+        let mut sel = AlbumSelection::initialise(albums);
+        sel.state.list.select(Some(albums.len() - 1));
+        sel.track.state.list.select(Some(1));
+
+        // Re-initialise.
+        let expected = sel.clone();
+        let active_album = IdSelectAlbum::get(albums, &sel);
+        sel.reinitialise(albums, active_album);
+        assert_eq!(sel, expected);
+
+        // Re-initialise out-of-bounds.
+        let mut expected = sel.clone();
+        expected.decrement(albums, Delta::Line);
+        let active_album = IdSelectAlbum::get(albums, &sel);
+        sel.reinitialise(&albums[..(albums.len() - 1)], active_album);
+        assert_eq!(sel, expected);
+
+        // Re-initialise empty.
+        let expected = AlbumSelection::initialise(&[]);
+        let active_album = IdSelectAlbum::get(albums, &sel);
+        sel.reinitialise(&[], active_album);
+        assert_eq!(sel, expected);
+    }
+}

src/tui/app/selection/artist.rs

@@ -0,0 +1,393 @@
+use std::cmp;
+
+use musichoard::collection::{
+    album::Album,
+    artist::{Artist, ArtistId},
+    track::Track,
+};
+
+use crate::tui::app::selection::{
+    album::{AlbumSelection, IdSelectAlbum},
+    Delta, SelectionState, WidgetState,
+};
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct ArtistSelection {
+    pub state: WidgetState,
+    pub album: AlbumSelection,
+}
+
+impl ArtistSelection {
+    pub fn initialise(artists: &[Artist]) -> Self {
+        let mut selection = ArtistSelection {
+            state: WidgetState::default(),
+            album: AlbumSelection::initialise(&[]),
+        };
+        selection.reinitialise(artists, None);
+        selection
+    }
+
+    pub fn reinitialise(&mut self, artists: &[Artist], active: Option<IdSelectArtist>) {
+        if let Some(active) = active {
+            let result = artists.binary_search_by(|a| a.get_sort_key().cmp(&active.artist_id));
+            match result {
+                Ok(index) => self.reinitialise_with_index(artists, index, active.album),
+                Err(index) => self.reinitialise_with_index(artists, index, None),
+            }
+        } else {
+            self.reinitialise_with_index(artists, 0, None)
+        }
+    }
+
+    fn reinitialise_with_index(
+        &mut self,
+        artists: &[Artist],
+        index: usize,
+        active_album: Option<IdSelectAlbum>,
+    ) {
+        if artists.is_empty() {
+            self.state.list.select(None);
+            self.album = AlbumSelection::initialise(&[]);
+        } else if index >= artists.len() {
+            let end = artists.len() - 1;
+            self.state.list.select(Some(end));
+            self.album = AlbumSelection::initialise(&artists[end].albums);
+        } else {
+            self.state.list.select(Some(index));
+            self.album
+                .reinitialise(&artists[index].albums, active_album);
+        }
+    }
+
+    pub fn selected(&self) -> Option<usize> {
+        self.state.list.selected()
+    }
+
+    pub fn selected_album(&self) -> Option<usize> {
+        self.album.selected()
+    }
+
+    pub fn selected_track(&self) -> Option<usize> {
+        self.album.selected_track()
+    }
+
+    pub fn select(&mut self, artists: &[Artist], to: Option<usize>) {
+        match to {
+            Some(to) => self.select_to(artists, to),
+            None => self.state.list.select(None),
+        }
+    }
+
+    pub fn select_album(&mut self, artists: &[Artist], to: Option<usize>) {
+        if let Some(index) = self.state.list.selected() {
+            self.album.select(&artists[index].albums, to);
+        }
+    }
+
+    pub fn select_track(&mut self, artists: &[Artist], to: Option<usize>) {
+        if let Some(index) = self.state.list.selected() {
+            self.album.select_track(&artists[index].albums, to);
+        }
+    }
+
+    fn select_to(&mut self, artists: &[Artist], mut to: usize) {
+        to = cmp::min(to, artists.len() - 1);
+        if self.state.list.selected() != Some(to) {
+            self.state.list.select(Some(to));
+            self.album = AlbumSelection::initialise(&artists[to].albums);
+        }
+    }
+
+    pub fn selection_state<'a>(&self, list: &'a [Artist]) -> Option<SelectionState<'a, Artist>> {
+        let selected = self.state.list.selected();
+        selected.map(|index| SelectionState { list, index })
+    }
+
+    pub fn state_album<'a>(&self, artists: &'a [Artist]) -> Option<SelectionState<'a, Album>> {
+        let selected = self.state.list.selected();
+        selected.and_then(|index| self.album.selection_state(&artists[index].albums))
+    }
+
+    pub fn state_track<'a>(&self, artists: &'a [Artist]) -> Option<SelectionState<'a, Track>> {
+        let selected = self.state.list.selected();
+        selected.and_then(|index| self.album.state_tracks(&artists[index].albums))
+    }
+
+    pub fn reset(&mut self, artists: &[Artist]) {
+        if self.state.list.selected() != Some(0) {
+            self.reinitialise(artists, None);
+        }
+    }
+
+    pub fn reset_album(&mut self, artists: &[Artist]) {
+        if let Some(index) = self.state.list.selected() {
+            self.album.reset(&artists[index].albums);
+        }
+    }
+
+    pub fn reset_track(&mut self, artists: &[Artist]) {
+        if let Some(index) = self.state.list.selected() {
+            self.album.reset_track(&artists[index].albums);
+        }
+    }
+
+    pub fn increment(&mut self, artists: &[Artist], delta: Delta) {
+        self.increment_by(artists, delta.as_usize(&self.state));
+    }
+
+    pub fn increment_album(&mut self, artists: &[Artist], delta: Delta) {
+        if let Some(index) = self.state.list.selected() {
+            self.album.increment(&artists[index].albums, delta);
+        }
+    }
+
+    pub fn increment_track(&mut self, artists: &[Artist], delta: Delta) {
+        if let Some(index) = self.state.list.selected() {
+            self.album.increment_track(&artists[index].albums, delta);
+        }
+    }
+
+    fn increment_by(&mut self, artists: &[Artist], by: usize) {
+        if let Some(index) = self.state.list.selected() {
+            let result = index.saturating_add(by);
+            self.select_to(artists, result);
+        }
+    }
+
+    pub fn decrement(&mut self, artists: &[Artist], delta: Delta) {
+        self.decrement_by(artists, delta.as_usize(&self.state));
+    }
+
+    pub fn decrement_album(&mut self, artists: &[Artist], delta: Delta) {
+        if let Some(index) = self.state.list.selected() {
+            self.album.decrement(&artists[index].albums, delta);
+        }
+    }
+
+    pub fn decrement_track(&mut self, artists: &[Artist], delta: Delta) {
+        if let Some(index) = self.state.list.selected() {
+            self.album.decrement_track(&artists[index].albums, delta);
+        }
+    }
+
+    fn decrement_by(&mut self, artists: &[Artist], by: usize) {
+        if let Some(index) = self.state.list.selected() {
+            let result = index.saturating_sub(by);
+            if self.state.list.selected() != Some(result) {
+                self.state.list.select(Some(result));
+                self.album = AlbumSelection::initialise(&artists[result].albums);
+            }
+        }
+    }
+}
+
+pub struct IdSelectArtist {
+    artist_id: ArtistId,
+    album: Option<IdSelectAlbum>,
+}
+
+impl IdSelectArtist {
+    pub fn get(artists: &[Artist], selection: &ArtistSelection) -> Option<Self> {
+        selection.state.list.selected().map(|index| {
+            let artist = &artists[index];
+            IdSelectArtist {
+                artist_id: artist.get_sort_key().clone(),
+                album: IdSelectAlbum::get(&artist.albums, &selection.album),
+            }
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tui::testmod::COLLECTION;
+
+    use super::*;
+
+    #[test]
+    fn artist_select() {
+        let artists = &COLLECTION;
+        assert!(artists.len() > 1);
+
+        let mut sel = ArtistSelection::initialise(artists);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_album(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.select(artists, None);
+        assert_eq!(sel.selected(), None);
+        assert_eq!(sel.selected_album(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.select(artists, Some(artists.len()));
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.selected_album(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.select_track(artists, None);
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.selected_album(), Some(0));
+        assert_eq!(sel.selected_track(), None);
+
+        sel.select_album(artists, None);
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.selected_album(), None);
+        assert_eq!(sel.selected_track(), None);
+
+        sel.reset_album(artists);
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.selected_album(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.select_track(artists, None);
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.selected_album(), Some(0));
+        assert_eq!(sel.selected_track(), None);
+
+        sel.reset_track(artists);
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.selected_album(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.select_album(artists, Some(1));
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.selected_album(), Some(1));
+        assert_eq!(sel.selected_track(), Some(0));
+
+        sel.reset(artists);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.selected_album(), Some(0));
+        assert_eq!(sel.selected_track(), Some(0));
+    }
+
+    #[test]
+    fn artist_delta_line() {
+        let artists = &COLLECTION;
+        assert!(artists.len() > 1);
+
+        let mut empty = ArtistSelection::initialise(&[]);
+        assert_eq!(empty.selected(), None);
+        assert_eq!(empty.album.selected(), None);
+
+        empty.increment(artists, Delta::Line);
+        assert_eq!(empty.selected(), None);
+        assert_eq!(empty.album.selected(), None);
+
+        empty.decrement(artists, Delta::Line);
+        assert_eq!(empty.selected(), None);
+        assert_eq!(empty.album.selected(), None);
+
+        let mut sel = ArtistSelection::initialise(artists);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.album.selected(), Some(0));
+
+        sel.increment_album(artists, Delta::Line);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.album.selected(), Some(1));
+
+        // Verify that decrement that doesn't change index does not reset album.
+        sel.decrement(artists, Delta::Line);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.album.selected(), Some(1));
+
+        sel.increment(artists, Delta::Line);
+        assert_eq!(sel.selected(), Some(1));
+        assert_eq!(sel.album.selected(), Some(0));
+
+        sel.decrement(artists, Delta::Line);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.album.selected(), Some(0));
+
+        for _ in 0..(artists.len() + 5) {
+            sel.increment(artists, Delta::Line);
+        }
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.album.selected(), Some(0));
+
+        sel.increment_album(artists, Delta::Line);
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.album.selected(), Some(1));
+
+        // Verify that increment that doesn't change index does not reset album.
+        sel.increment(artists, Delta::Line);
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.album.selected(), Some(1));
+    }
+
+    #[test]
+    fn artist_delta_page() {
+        let artists = &COLLECTION;
+        assert!(artists.len() > 1);
+
+        let empty = ArtistSelection::initialise(&[]);
+        assert_eq!(empty.selected(), None);
+
+        let mut sel = ArtistSelection::initialise(artists);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.album.selected(), Some(0));
+
+        assert!(artists.len() >= 4);
+        sel.state.height = 3;
+
+        sel.increment_album(artists, Delta::Line);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.album.selected(), Some(1));
+
+        // Verify that decrement that doesn't change index does not reset album.
+        sel.decrement(artists, Delta::Page);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.album.selected(), Some(1));
+
+        sel.increment(artists, Delta::Page);
+        assert_eq!(sel.selected(), Some(2));
+        assert_eq!(sel.album.selected(), Some(0));
+
+        sel.decrement(artists, Delta::Page);
+        assert_eq!(sel.selected(), Some(0));
+        assert_eq!(sel.album.selected(), Some(0));
+
+        for _ in 0..(artists.len() + 5) {
+            sel.increment(artists, Delta::Page);
+        }
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.album.selected(), Some(0));
+
+        sel.increment_album(artists, Delta::Line);
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.album.selected(), Some(1));
+
+        // Verify that increment that doesn't change index does not reset album.
+        sel.increment(artists, Delta::Page);
+        assert_eq!(sel.selected(), Some(artists.len() - 1));
+        assert_eq!(sel.album.selected(), Some(1));
+    }
+
+    #[test]
+    fn artist_reinitialise() {
+        let artists = &COLLECTION;
+        assert!(artists.len() > 1);
+
+        let mut sel = ArtistSelection::initialise(artists);
+        sel.state.list.select(Some(artists.len() - 1));
+        sel.album.state.list.select(Some(1));
+
+        // Re-initialise.
+        let expected = sel.clone();
+        let active_artist = IdSelectArtist::get(artists, &sel);
+        sel.reinitialise(artists, active_artist);
+        assert_eq!(sel, expected);
+
+        // Re-initialise out-of-bounds.
+        let mut expected = sel.clone();
+        expected.decrement(artists, Delta::Line);
+        let active_artist = IdSelectArtist::get(artists, &sel);
+        sel.reinitialise(&artists[..(artists.len() - 1)], active_artist);
+        assert_eq!(sel, expected);
+
+        // Re-initialise empty.
+        let expected = ArtistSelection::initialise(&[]);
+        let active_artist = IdSelectArtist::get(artists, &sel);
+        sel.reinitialise(&[], active_artist);
+        assert_eq!(sel, expected);
+    }
+}

src/tui/app/selection/mod.rs

@@ -0,0 +1,389 @@
+mod album;
+mod artist;
+mod track;
+
+use musichoard::collection::{album::Album, artist::Artist, track::Track, Collection};
+use ratatui::widgets::ListState;
+
+use artist::{ArtistSelection, IdSelectArtist};
+
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub enum Category {
+    Artist,
+    Album,
+    Track,
+}
+
+#[derive(Clone, Debug, Default)]
+pub struct WidgetState {
+    pub list: ListState,
+    pub height: usize,
+}
+
+impl PartialEq for WidgetState {
+    fn eq(&self, other: &Self) -> bool {
+        self.list.selected().eq(&other.list.selected()) && self.height.eq(&other.height)
+    }
+}
+
+pub struct Selection {
+    pub active: Category,
+    pub artist: ArtistSelection,
+}
+
+pub struct SelectionState<'a, T> {
+    pub list: &'a [T],
+    pub index: usize,
+}
+
+pub enum Delta {
+    Line,
+    Page,
+}
+
+impl Delta {
+    fn as_usize(&self, state: &WidgetState) -> usize {
+        match self {
+            Delta::Line => 1,
+            Delta::Page => state.height.saturating_sub(1),
+        }
+    }
+}
+
+impl Selection {
+    pub fn new(artists: &[Artist]) -> Self {
+        Selection {
+            active: Category::Artist,
+            artist: ArtistSelection::initialise(artists),
+        }
+    }
+
+    pub fn select_by_list(&mut self, selected: ListSelection) {
+        self.artist.state.list = selected.artist;
+        self.artist.album.state.list = selected.album;
+        self.artist.album.track.state.list = selected.track;
+    }
+
+    pub fn select_by_id(&mut self, artists: &[Artist], selected: IdSelection) {
+        self.artist.reinitialise(artists, selected.artist);
+    }
+
+    pub fn increment_category(&mut self) {
+        self.active = match self.active {
+            Category::Artist => Category::Album,
+            Category::Album => Category::Track,
+            Category::Track => Category::Track,
+        };
+    }
+
+    pub fn decrement_category(&mut self) {
+        self.active = match self.active {
+            Category::Artist => Category::Artist,
+            Category::Album => Category::Artist,
+            Category::Track => Category::Album,
+        };
+    }
+
+    pub fn select(&mut self, collection: &Collection, index: Option<usize>) {
+        match self.active {
+            Category::Artist => self.select_artist(collection, index),
+            Category::Album => self.select_album(collection, index),
+            Category::Track => self.select_track(collection, index),
+        }
+    }
+
+    fn select_artist(&mut self, artists: &[Artist], index: Option<usize>) {
+        self.artist.select(artists, index);
+    }
+
+    fn select_album(&mut self, artists: &[Artist], index: Option<usize>) {
+        self.artist.select_album(artists, index);
+    }
+
+    fn select_track(&mut self, artists: &[Artist], index: Option<usize>) {
+        self.artist.select_track(artists, index);
+    }
+
+    pub fn selected(&self) -> Option<usize> {
+        match self.active {
+            Category::Artist => self.selected_artist(),
+            Category::Album => self.selected_album(),
+            Category::Track => self.selected_track(),
+        }
+    }
+
+    fn selected_artist(&self) -> Option<usize> {
+        self.artist.selected()
+    }
+
+    fn selected_album(&self) -> Option<usize> {
+        self.artist.selected_album()
+    }
+
+    fn selected_track(&self) -> Option<usize> {
+        self.artist.selected_track()
+    }
+
+    pub fn state_artist<'a>(&self, coll: &'a Collection) -> Option<SelectionState<'a, Artist>> {
+        self.artist.selection_state(coll)
+    }
+
+    pub fn state_album<'a>(&self, coll: &'a Collection) -> Option<SelectionState<'a, Album>> {
+        self.artist.state_album(coll)
+    }
+
+    pub fn state_track<'a>(&self, coll: &'a Collection) -> Option<SelectionState<'a, Track>> {
+        self.artist.state_track(coll)
+    }
+
+    pub fn reset(&mut self, collection: &Collection) {
+        match self.active {
+            Category::Artist => self.reset_artist(collection),
+            Category::Album => self.reset_album(collection),
+            Category::Track => self.reset_track(collection),
+        }
+    }
+
+    fn reset_artist(&mut self, artists: &[Artist]) {
+        self.artist.reset(artists);
+    }
+
+    fn reset_album(&mut self, artists: &[Artist]) {
+        self.artist.reset_album(artists);
+    }
+
+    fn reset_track(&mut self, artists: &[Artist]) {
+        self.artist.reset_track(artists);
+    }
+
+    pub fn increment_selection(&mut self, collection: &Collection, delta: Delta) {
+        match self.active {
+            Category::Artist => self.increment_artist(collection, delta),
+            Category::Album => self.increment_album(collection, delta),
+            Category::Track => self.increment_track(collection, delta),
+        }
+    }
+
+    fn increment_artist(&mut self, artists: &[Artist], delta: Delta) {
+        self.artist.increment(artists, delta);
+    }
+
+    fn increment_album(&mut self, artists: &[Artist], delta: Delta) {
+        self.artist.increment_album(artists, delta);
+    }
+
+    fn increment_track(&mut self, artists: &[Artist], delta: Delta) {
+        self.artist.increment_track(artists, delta);
+    }
+
+    pub fn decrement_selection(&mut self, collection: &Collection, delta: Delta) {
+        match self.active {
+            Category::Artist => self.decrement_artist(collection, delta),
+            Category::Album => self.decrement_album(collection, delta),
+            Category::Track => self.decrement_track(collection, delta),
+        }
+    }
+
+    fn decrement_artist(&mut self, artists: &[Artist], delta: Delta) {
+        self.artist.decrement(artists, delta);
+    }
+
+    fn decrement_album(&mut self, artists: &[Artist], delta: Delta) {
+        self.artist.decrement_album(artists, delta);
+    }
+
+    fn decrement_track(&mut self, artists: &[Artist], delta: Delta) {
+        self.artist.decrement_track(artists, delta);
+    }
+}
+
+pub struct ListSelection {
+    pub artist: ListState,
+    pub album: ListState,
+    pub track: ListState,
+}
+
+impl ListSelection {
+    pub fn get(selection: &Selection) -> Self {
+        ListSelection {
+            artist: selection.artist.state.list.clone(),
+            album: selection.artist.album.state.list.clone(),
+            track: selection.artist.album.track.state.list.clone(),
+        }
+    }
+}
+
+pub struct IdSelection {
+    artist: Option<IdSelectArtist>,
+}
+
+impl IdSelection {
+    pub fn get(collection: &Collection, selection: &Selection) -> Self {
+        IdSelection {
+            artist: IdSelectArtist::get(collection, &selection.artist),
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tui::testmod::COLLECTION;
+
+    use super::*;
+
+    #[test]
+    fn selection_select() {
+        let mut selection = Selection::new(&COLLECTION);
+
+        selection.select(&COLLECTION, Some(1));
+        selection.increment_category();
+        selection.select(&COLLECTION, Some(1));
+        selection.increment_category();
+        selection.select(&COLLECTION, Some(1));
+
+        assert_eq!(selection.active, Category::Track);
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(1));
+
+        selection.reset(&COLLECTION);
+
+        assert_eq!(selection.active, Category::Track);
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.select(&COLLECTION, Some(1));
+
+        assert_eq!(selection.active, Category::Track);
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(1));
+
+        selection.decrement_category();
+
+        selection.reset(&COLLECTION);
+
+        assert_eq!(selection.active, Category::Album);
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(0));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.select(&COLLECTION, Some(1));
+
+        assert_eq!(selection.active, Category::Album);
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.decrement_category();
+
+        selection.reset(&COLLECTION);
+
+        assert_eq!(selection.active, Category::Artist);
+        assert_eq!(selection.artist.selected(), Some(0));
+        assert_eq!(selection.artist.album.selected(), Some(0));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+    }
+
+    #[test]
+    fn selection_delta() {
+        let mut selection = Selection::new(&COLLECTION);
+
+        assert_eq!(selection.active, Category::Artist);
+        assert_eq!(selection.selected(), Some(0));
+        assert_eq!(selection.artist.selected(), Some(0));
+        assert_eq!(selection.artist.album.selected(), Some(0));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.increment_selection(&COLLECTION, Delta::Line);
+        assert_eq!(selection.active, Category::Artist);
+        assert_eq!(selection.selected(), Some(1));
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(0));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.increment_category();
+        assert_eq!(selection.active, Category::Album);
+        assert_eq!(selection.selected(), Some(0));
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(0));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.increment_selection(&COLLECTION, Delta::Line);
+        assert_eq!(selection.active, Category::Album);
+        assert_eq!(selection.selected(), Some(1));
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.increment_category();
+        assert_eq!(selection.active, Category::Track);
+        assert_eq!(selection.selected(), Some(0));
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.increment_selection(&COLLECTION, Delta::Line);
+        assert_eq!(selection.active, Category::Track);
+        assert_eq!(selection.selected(), Some(1));
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(1));
+
+        selection.increment_category();
+        assert_eq!(selection.active, Category::Track);
+        assert_eq!(selection.selected(), Some(1));
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(1));
+
+        selection.decrement_selection(&COLLECTION, Delta::Line);
+        assert_eq!(selection.active, Category::Track);
+        assert_eq!(selection.selected(), Some(0));
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.increment_selection(&COLLECTION, Delta::Line);
+        selection.decrement_category();
+        assert_eq!(selection.active, Category::Album);
+        assert_eq!(selection.selected(), Some(1));
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(1));
+
+        selection.decrement_selection(&COLLECTION, Delta::Line);
+        assert_eq!(selection.active, Category::Album);
+        assert_eq!(selection.selected(), Some(0));
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(0));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.increment_selection(&COLLECTION, Delta::Line);
+        selection.decrement_category();
+        assert_eq!(selection.active, Category::Artist);
+        assert_eq!(selection.selected(), Some(1));
+        assert_eq!(selection.artist.selected(), Some(1));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.decrement_selection(&COLLECTION, Delta::Line);
+        assert_eq!(selection.active, Category::Artist);
+        assert_eq!(selection.selected(), Some(0));
+        assert_eq!(selection.artist.selected(), Some(0));
+        assert_eq!(selection.artist.album.selected(), Some(0));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+
+        selection.increment_category();
+        selection.increment_selection(&COLLECTION, Delta::Line);
+        selection.decrement_category();
+        selection.decrement_selection(&COLLECTION, Delta::Line);
+        selection.decrement_category();
+        assert_eq!(selection.active, Category::Artist);
+        assert_eq!(selection.selected(), Some(0));
+        assert_eq!(selection.artist.selected(), Some(0));
+        assert_eq!(selection.artist.album.selected(), Some(1));
+        assert_eq!(selection.artist.album.track.selected(), Some(0));
+    }
+}

src/tui/app/selection/track.rs

@@ -0,0 +1,226 @@
+use std::cmp;
+
+use musichoard::collection::track::{Track, TrackId};
+
+use crate::tui::app::selection::{Delta, SelectionState, WidgetState};
+
+#[derive(Clone, Debug, PartialEq)]
+pub struct TrackSelection {
+    pub state: WidgetState,
+}
+
+impl TrackSelection {
+    pub fn initialise(tracks: &[Track]) -> Self {
+        let mut selection = TrackSelection {
+            state: WidgetState::default(),
+        };
+        selection.reinitialise(tracks, None);
+        selection
+    }
+
+    pub fn reinitialise(&mut self, tracks: &[Track], track: Option<IdSelectTrack>) {
+        if let Some(track) = track {
+            let result = tracks.binary_search_by(|t| t.get_sort_key().cmp(&track.track_id));
+            match result {
+                Ok(index) | Err(index) => self.reinitialise_with_index(tracks, index),
+            }
+        } else {
+            self.reinitialise_with_index(tracks, 0)
+        }
+    }
+
+    fn reinitialise_with_index(&mut self, tracks: &[Track], index: usize) {
+        if tracks.is_empty() {
+            self.state.list.select(None);
+        } else if index >= tracks.len() {
+            self.state.list.select(Some(tracks.len() - 1));
+        } else {
+            self.state.list.select(Some(index));
+        }
+    }
+
+    pub fn selected(&self) -> Option<usize> {
+        self.state.list.selected()
+    }
+
+    pub fn select(&mut self, tracks: &[Track], to: Option<usize>) {
+        match to {
+            Some(to) => self.select_to(tracks, to),
+            None => self.state.list.select(None),
+        }
+    }
+
+    fn select_to(&mut self, tracks: &[Track], mut to: usize) {
+        to = cmp::min(to, tracks.len() - 1);
+        self.state.list.select(Some(to));
+    }
+
+    pub fn selection_state<'a>(&self, list: &'a [Track]) -> Option<SelectionState<'a, Track>> {
+        let selected = self.state.list.selected();
+        selected.map(|index| SelectionState { list, index })
+    }
+
+    pub fn reset(&mut self, tracks: &[Track]) {
+        if self.state.list.selected() != Some(0) {
+            self.reinitialise(tracks, None);
+        }
+    }
+
+    pub fn increment(&mut self, tracks: &[Track], delta: Delta) {
+        self.increment_by(tracks, delta.as_usize(&self.state));
+    }
+
+    fn increment_by(&mut self, tracks: &[Track], by: usize) {
+        if let Some(index) = self.state.list.selected() {
+            let mut result = index.saturating_add(by);
+            if result >= tracks.len() {
+                result = tracks.len() - 1;
+            }
+            if self.state.list.selected() != Some(result) {
+                self.state.list.select(Some(result));
+            }
+        }
+    }
+
+    pub fn decrement(&mut self, tracks: &[Track], delta: Delta) {
+        self.decrement_by(tracks, delta.as_usize(&self.state));
+    }
+
+    fn decrement_by(&mut self, _tracks: &[Track], by: usize) {
+        if let Some(index) = self.state.list.selected() {
+            let result = index.saturating_sub(by);
+            if self.state.list.selected() != Some(result) {
+                self.state.list.select(Some(result));
+            }
+        }
+    }
+}
+
+pub struct IdSelectTrack {
+    track_id: TrackId,
+}
+
+impl IdSelectTrack {
+    pub fn get(tracks: &[Track], selection: &TrackSelection) -> Option<Self> {
+        selection.state.list.selected().map(|index| {
+            let track = &tracks[index];
+            IdSelectTrack {
+                track_id: track.get_sort_key().clone(),
+            }
+        })
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::tui::testmod::COLLECTION;
+
+    use super::*;
+
+    #[test]
+    fn track_select() {
+        let tracks = &COLLECTION[0].albums[0].tracks;
+        assert!(tracks.len() > 1);
+
+        let mut sel = TrackSelection::initialise(tracks);
+        assert_eq!(sel.selected(), Some(0));
+
+        sel.select(tracks, None);
+        assert_eq!(sel.selected(), None);
+
+        sel.select(tracks, Some(tracks.len()));
+        assert_eq!(sel.selected(), Some(tracks.len() - 1));
+
+        sel.reset(tracks);
+        assert_eq!(sel.selected(), Some(0));
+    }
+
+    #[test]
+    fn track_delta_line() {
+        let tracks = &COLLECTION[0].albums[0].tracks;
+        assert!(tracks.len() > 1);
+
+        let mut empty = TrackSelection::initialise(&[]);
+        assert_eq!(empty.selected(), None);
+
+        empty.increment(tracks, Delta::Line);
+        assert_eq!(empty.selected(), None);
+
+        empty.decrement(tracks, Delta::Line);
+        assert_eq!(empty.selected(), None);
+
+        let mut sel = TrackSelection::initialise(tracks);
+        assert_eq!(sel.selected(), Some(0));
+
+        sel.decrement(tracks, Delta::Line);
+        assert_eq!(sel.selected(), Some(0));
+
+        sel.increment(tracks, Delta::Line);
+        assert_eq!(sel.selected(), Some(1));
+
+        sel.decrement(tracks, Delta::Line);
+        assert_eq!(sel.selected(), Some(0));
+
+        for _ in 0..(tracks.len() + 5) {
+            sel.increment(tracks, Delta::Line);
+        }
+        assert_eq!(sel.selected(), Some(tracks.len() - 1));
+    }
+
+    #[test]
+    fn track_delta_page() {
+        let tracks = &COLLECTION[0].albums[0].tracks;
+        assert!(tracks.len() > 1);
+
+        let empty = TrackSelection::initialise(&[]);
+        assert_eq!(empty.selected(), None);
+
+        let mut sel = TrackSelection::initialise(tracks);
+        assert_eq!(sel.selected(), Some(0));
+
+        assert!(tracks.len() >= 4);
+        sel.state.height = 3;
+
+        sel.decrement(tracks, Delta::Page);
+        assert_eq!(sel.selected(), Some(0));
+
+        sel.increment(tracks, Delta::Page);
+        assert_eq!(sel.selected(), Some(2));
+
+        sel.decrement(tracks, Delta::Page);
+        assert_eq!(sel.selected(), Some(0));
+
+        for _ in 0..(tracks.len() + 5) {
+            sel.increment(tracks, Delta::Page);
+        }
+        assert_eq!(sel.selected(), Some(tracks.len() - 1));
+    }
+
+    #[test]
+    fn track_reinitialise() {
+        let tracks = &COLLECTION[0].albums[0].tracks;
+        assert!(tracks.len() > 1);
+
+        let mut sel = TrackSelection::initialise(tracks);
+        sel.state.list.select(Some(tracks.len() - 1));
+
+        // Re-initialise.
+        let expected = sel.clone();
+        let active_track = IdSelectTrack::get(tracks, &sel);
+        sel.reinitialise(tracks, active_track);
+        assert_eq!(sel, expected);
+
+        // Re-initialise out-of-bounds.
+        let mut expected = sel.clone();
+        expected.decrement(tracks, Delta::Line);
+        let active_track = IdSelectTrack::get(tracks, &sel);
+        sel.reinitialise(&tracks[..(tracks.len() - 1)], active_track);
+        assert_eq!(sel, expected);
+
+        // Re-initialise empty.
+        let expected = TrackSelection::initialise(&[]);
+        let active_track = IdSelectTrack::get(tracks, &sel);
+        sel.reinitialise(&[], active_track);
+        assert_eq!(sel, expected);
+    }
+}