musichoard/src/tui/ui.rs

use musichoard::{
    collection::{Collection, CollectionManager},
    Album, Artist, Track, TrackFormat,
};
use ratatui::{
    backend::Backend,
    layout::{Alignment, Rect},
    style::{Color, Style},
    widgets::{Block, BorderType, Borders, List, ListItem, ListState, Paragraph},
    Frame,
};

use super::Error;

struct TrackSelection {
    state: ListState,
}

struct AlbumSelection {
    state: ListState,
    track: TrackSelection,
}

struct ArtistSelection {
    state: ListState,
    album: AlbumSelection,
}

impl TrackSelection {
    fn initialise(tracks: Option<&[Track]>) -> Self {
        let mut state = ListState::default();
        if let Some(tracks) = tracks {
            state.select(if !tracks.is_empty() { Some(0) } else { None });
        } else {
            state.select(None);
        };
        TrackSelection { state }
    }

    fn increment(&mut self, tracks: &[Track]) {
        if let Some(index) = self.state.selected() {
            if let Some(result) = index.checked_add(1) {
                if result < tracks.len() {
                    self.state.select(Some(result));
                }
            }
        }
    }

    fn decrement(&mut self, _tracks: &[Track]) {
        if let Some(index) = self.state.selected() {
            if let Some(result) = index.checked_sub(1) {
                self.state.select(Some(result));
            }
        }
    }
}

impl AlbumSelection {
    fn initialise(albums: Option<&[Album]>) -> Self {
        let mut state = ListState::default();
        let track: TrackSelection;
        if let Some(albums) = albums {
            state.select(if !albums.is_empty() { Some(0) } else { None });
            track = TrackSelection::initialise(albums.get(0).map(|a| a.tracks.as_slice()));
        } else {
            state.select(None);
            track = TrackSelection::initialise(None);
        }
        AlbumSelection { state, track }
    }

    fn increment(&mut self, albums: &[Album]) {
        if let Some(index) = self.state.selected() {
            if let Some(result) = index.checked_add(1) {
                if result < albums.len() {
                    self.state.select(Some(result));
                    self.track = TrackSelection::initialise(Some(&albums[result].tracks));
                }
            }
        }
    }

    fn increment_track(&mut self, albums: &[Album]) {
        if let Some(index) = self.state.selected() {
            self.track.increment(&albums[index].tracks);
        }
    }

    fn decrement(&mut self, albums: &[Album]) {
        if let Some(index) = self.state.selected() {
            if let Some(result) = index.checked_sub(1) {
                self.state.select(Some(result));
                self.track = TrackSelection::initialise(Some(&albums[result].tracks));
            }
        }
    }

    fn decrement_track(&mut self, albums: &[Album]) {
        if let Some(index) = self.state.selected() {
            self.track.decrement(&albums[index].tracks);
        }
    }
}

impl ArtistSelection {
    fn initialise(artists: Option<&[Artist]>) -> Self {
        let mut state = ListState::default();
        let album: AlbumSelection;
        if let Some(artists) = artists {
            state.select(if !artists.is_empty() { Some(0) } else { None });
            album = AlbumSelection::initialise(artists.get(0).map(|a| a.albums.as_slice()));
        } else {
            state.select(None);
            album = AlbumSelection::initialise(None);
        }
        ArtistSelection { state, album }
    }

    fn increment(&mut self, artists: &[Artist]) {
        if let Some(index) = self.state.selected() {
            if let Some(result) = index.checked_add(1) {
                if result < artists.len() {
                    self.state.select(Some(result));
                    self.album = AlbumSelection::initialise(Some(&artists[result].albums));
                }
            }
        }
    }

    fn increment_album(&mut self, artists: &[Artist]) {
        if let Some(index) = self.state.selected() {
            self.album.increment(&artists[index].albums);
        }
    }

    fn increment_track(&mut self, artists: &[Artist]) {
        if let Some(index) = self.state.selected() {
            self.album.increment_track(&artists[index].albums);
        }
    }

    fn decrement(&mut self, artists: &[Artist]) {
        if let Some(index) = self.state.selected() {
            if let Some(result) = index.checked_sub(1) {
                self.state.select(Some(result));
                self.album = AlbumSelection::initialise(Some(&artists[result].albums));
            }
        }
    }

    fn decrement_album(&mut self, artists: &[Artist]) {
        if let Some(index) = self.state.selected() {
            self.album.decrement(&artists[index].albums);
        }
    }

    fn decrement_track(&mut self, artists: &[Artist]) {
        if let Some(index) = self.state.selected() {
            self.album.decrement_track(&artists[index].albums);
        }
    }
}

#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum Category {
    Artist,
    Album,
    Track,
}

struct Selection {
    active: Category,
    artist: ArtistSelection,
}

impl Selection {
    fn new(artists: Option<&[Artist]>) -> Self {
        Selection {
            active: Category::Artist,
            artist: ArtistSelection::initialise(artists),
        }
    }

    fn increment_category(&mut self) {
        self.active = match self.active {
            Category::Artist => Category::Album,
            Category::Album => Category::Track,
            Category::Track => Category::Track,
        };
    }

    fn decrement_category(&mut self) {
        self.active = match self.active {
            Category::Artist => Category::Artist,
            Category::Album => Category::Artist,
            Category::Track => Category::Album,
        };
    }

    fn increment_selection(&mut self, collection: &Collection) {
        match self.active {
            Category::Artist => self.increment_artist(collection),
            Category::Album => self.increment_album(collection),
            Category::Track => self.increment_track(collection),
        }
    }

    fn decrement_selection(&mut self, collection: &Collection) {
        match self.active {
            Category::Artist => self.decrement_artist(collection),
            Category::Album => self.decrement_album(collection),
            Category::Track => self.decrement_track(collection),
        }
    }

    fn increment_artist(&mut self, artists: &[Artist]) {
        self.artist.increment(artists);
    }

    fn decrement_artist(&mut self, artists: &[Artist]) {
        self.artist.decrement(artists);
    }

    fn increment_album(&mut self, artists: &[Artist]) {
        self.artist.increment_album(artists);
    }

    fn decrement_album(&mut self, artists: &[Artist]) {
        self.artist.decrement_album(artists);
    }

    fn increment_track(&mut self, artists: &[Artist]) {
        self.artist.increment_track(artists);
    }

    fn decrement_track(&mut self, artists: &[Artist]) {
        self.artist.decrement_track(artists);
    }
}

pub struct MhUi<CM> {
    collection_manager: CM,
    selection: Selection,
    running: bool,
}

struct ArtistArea {
    list: Rect,
}

struct AlbumArea {
    list: Rect,
    info: Rect,
}

struct TrackArea {
    list: Rect,
    info: Rect,
}

struct FrameArea {
    artist: ArtistArea,
    album: AlbumArea,
    track: TrackArea,
}

impl FrameArea {
    fn new(frame: Rect) -> FrameArea {
        let width_one_third = frame.width / 3;
        let height_one_third = frame.height / 3;

        let panel_width = width_one_third;
        let panel_width_last = frame.width - 2 * panel_width;
        let panel_height_top = frame.height - height_one_third;
        let panel_height_bottom = height_one_third;

        let artist_list = Rect {
            x: frame.x,
            y: frame.y,
            width: panel_width,
            height: frame.height,
        };

        let album_list = Rect {
            x: artist_list.x + artist_list.width,
            y: frame.y,
            width: panel_width,
            height: panel_height_top,
        };

        let album_info = Rect {
            x: album_list.x,
            y: album_list.y + album_list.height,
            width: album_list.width,
            height: panel_height_bottom,
        };

        let track_list = Rect {
            x: album_list.x + album_list.width,
            y: frame.y,
            width: panel_width_last,
            height: panel_height_top,
        };

        let track_info = Rect {
            x: track_list.x,
            y: track_list.y + track_list.height,
            width: track_list.width,
            height: panel_height_bottom,
        };

        FrameArea {
            artist: ArtistArea { list: artist_list },
            album: AlbumArea {
                list: album_list,
                info: album_info,
            },
            track: TrackArea {
                list: track_list,
                info: track_info,
            },
        }
    }
}

struct ArtistState<'a, 'b> {
    active: bool,
    list: List<'a>,
    state: &'b mut ListState,
}

impl<'a, 'b> ArtistState<'a, 'b> {
    fn new(active: bool, artists: &'a [Artist], state: &'b mut ListState) -> ArtistState<'a, 'b> {
        let list = List::new(
            artists
                .iter()
                .map(|a| ListItem::new(a.id.name.as_str()))
                .collect::<Vec<ListItem>>(),
        );

        ArtistState {
            active,
            list,
            state,
        }
    }
}

struct AlbumState<'a, 'b> {
    active: bool,
    list: List<'a>,
    state: &'b mut ListState,
    info: Paragraph<'a>,
}

impl<'a, 'b> AlbumState<'a, 'b> {
    fn new(active: bool, albums: &'a [Album], state: &'b mut ListState) -> AlbumState<'a, 'b> {
        let list = List::new(
            albums
                .iter()
                .map(|a| ListItem::new(a.id.title.as_str()))
                .collect::<Vec<ListItem>>(),
        );

        let album = state.selected().map(|i| &albums[i]);
        let info = Paragraph::new(format!(
            "Title: {}\n\
             Year: {}",
            album.map(|a| a.id.title.as_str()).unwrap_or(""),
            album
                .map(|a| a.id.year.to_string())
                .unwrap_or_else(|| "".to_string()),
        ));

        AlbumState {
            active,
            list,
            state,
            info,
        }
    }
}

struct TrackState<'a, 'b> {
    active: bool,
    list: List<'a>,
    state: &'b mut ListState,
    info: Paragraph<'a>,
}

impl<'a, 'b> TrackState<'a, 'b> {
    fn new(active: bool, tracks: &'a [Track], state: &'b mut ListState) -> TrackState<'a, 'b> {
        let list = List::new(
            tracks
                .iter()
                .map(|id| ListItem::new(id.title.as_str()))
                .collect::<Vec<ListItem>>(),
        );

        let track = state.selected().map(|i| &tracks[i]);
        let info = Paragraph::new(format!(
            "Track: {}\n\
             Title: {}\n\
             Artist: {}\n\
             Format: {}",
            track
                .map(|t| t.number.to_string())
                .unwrap_or_else(|| "".to_string()),
            track.map(|t| t.title.as_str()).unwrap_or(""),
            track
                .map(|t| t.artist.join("; "))
                .unwrap_or_else(|| "".to_string()),
            track
                .map(|t| match t.format {
                    TrackFormat::Flac => "FLAC",
                    TrackFormat::Mp3 => "MP3",
                })
                .unwrap_or(""),
        ));

        TrackState {
            active,
            list,
            state,
            info,
        }
    }
}

impl<CM: CollectionManager> MhUi<CM> {
    pub fn new(mut collection_manager: CM) -> Result<Self, Error> {
        collection_manager.rescan_library()?;
        let selection = Selection::new(Some(collection_manager.get_collection()));
        Ok(MhUi {
            collection_manager,
            selection,
            running: true,
        })
    }

    fn style(_active: bool) -> Style {
        Style::default().fg(Color::White).bg(Color::Black)
    }

    fn block_style(active: bool) -> Style {
        Self::style(active)
    }

    fn highlight_style(active: bool) -> Style {
        if active {
            Style::default().fg(Color::White).bg(Color::DarkGray)
        } else {
            Self::style(false)
        }
    }

    fn block<'a>(title: &str, active: bool) -> Block<'a> {
        Block::default()
            .title_alignment(Alignment::Center)
            .borders(Borders::ALL)
            .border_type(BorderType::Rounded)
            .style(Self::block_style(active))
            .title(format!(" {title} "))
    }

    fn render_list_widget<B: Backend>(
        title: &str,
        list: List,
        list_state: &mut ListState,
        active: bool,
        area: Rect,
        frame: &mut Frame<'_, B>,
    ) {
        frame.render_stateful_widget(
            list.highlight_style(Self::highlight_style(active))
                .highlight_symbol(">> ")
                .style(Self::style(active))
                .block(Self::block(title, active)),
            area,
            list_state,
        );
    }

    fn render_info_widget<B: Backend>(
        title: &str,
        paragraph: Paragraph,
        active: bool,
        area: Rect,
        frame: &mut Frame<'_, B>,
    ) {
        frame.render_widget(
            paragraph
                .style(Self::style(active))
                .block(Self::block(title, active)),
            area,
        );
    }

    fn render_artist_column<B: Backend>(st: ArtistState, ar: ArtistArea, fr: &mut Frame<'_, B>) {
        Self::render_list_widget("Artists", st.list, st.state, st.active, ar.list, fr);
    }

    fn render_album_column<B: Backend>(st: AlbumState, ar: AlbumArea, fr: &mut Frame<'_, B>) {
        Self::render_list_widget("Albums", st.list, st.state, st.active, ar.list, fr);
        Self::render_info_widget("Album info", st.info, st.active, ar.info, fr);
    }

    fn render_track_column<B: Backend>(st: TrackState, ar: TrackArea, fr: &mut Frame<'_, B>) {
        Self::render_list_widget("Tracks", st.list, st.state, st.active, ar.list, fr);
        Self::render_info_widget("Track info", st.info, st.active, ar.info, fr);
    }
}

pub trait Ui {
    fn is_running(&self) -> bool;
    fn quit(&mut self);

    fn increment_category(&mut self);
    fn decrement_category(&mut self);

    fn increment_selection(&mut self);
    fn decrement_selection(&mut self);

    fn render<B: Backend>(&mut self, frame: &mut Frame<'_, B>);
}

impl<CM: CollectionManager> Ui for MhUi<CM> {
    fn is_running(&self) -> bool {
        self.running
    }

    fn quit(&mut self) {
        self.running = false;
    }

    fn increment_category(&mut self) {
        self.selection.increment_category();
    }

    fn decrement_category(&mut self) {
        self.selection.decrement_category();
    }

    fn increment_selection(&mut self) {
        self.selection
            .increment_selection(self.collection_manager.get_collection());
    }

    fn decrement_selection(&mut self) {
        self.selection
            .decrement_selection(self.collection_manager.get_collection());
    }

    fn render<B: Backend>(&mut self, frame: &mut Frame<'_, B>) {
        let active = self.selection.active;
        let areas = FrameArea::new(frame.size());

        let artists = self.collection_manager.get_collection();
        let artist_selection = &mut self.selection.artist;
        let artist_state = ArtistState::new(
            active == Category::Artist,
            artists,
            &mut artist_selection.state,
        );

        Self::render_artist_column(artist_state, areas.artist, frame);

        let no_albums: Vec<Album> = vec![];
        let albums = artist_selection
            .state
            .selected()
            .map(|i| &artists[i].albums)
            .unwrap_or_else(|| &no_albums);
        let album_selection = &mut artist_selection.album;
        let album_state = AlbumState::new(
            active == Category::Album,
            albums,
            &mut album_selection.state,
        );

        Self::render_album_column(album_state, areas.album, frame);

        let no_tracks: Vec<Track> = vec![];
        let tracks = album_selection
            .state
            .selected()
            .map(|i| &albums[i].tracks)
            .unwrap_or_else(|| &no_tracks);
        let track_selection = &mut album_selection.track;
        let track_state = TrackState::new(
            active == Category::Track,
            tracks,
            &mut track_selection.state,
        );

        Self::render_track_column(track_state, areas.track, frame);
    }
}

#[cfg(test)]
mod tests {
    use crate::tests::{MockCollectionManager, COLLECTION};
    use crate::tui::tests::{terminal, ui};

    use super::*;

    #[test]
    fn test_track_selection() {
        let tracks = &COLLECTION[0].albums[0].tracks;
        assert!(tracks.len() > 1);

        let empty = TrackSelection::initialise(None);
        assert_eq!(empty.state.selected(), None);

        let empty = TrackSelection::initialise(Some(&vec![]));
        assert_eq!(empty.state.selected(), None);

        let mut sel = TrackSelection::initialise(Some(tracks));
        assert_eq!(sel.state.selected(), Some(0));

        sel.decrement(tracks);
        assert_eq!(sel.state.selected(), Some(0));

        sel.increment(tracks);
        assert_eq!(sel.state.selected(), Some(1));

        sel.decrement(tracks);
        assert_eq!(sel.state.selected(), Some(0));

        for _ in 0..(tracks.len() + 5) {
            sel.increment(tracks);
        }
        assert_eq!(sel.state.selected(), Some(tracks.len() - 1));

        // Artifical test case to verify upper limit.
        sel.state.select(Some(std::usize::MAX));
        assert_eq!(sel.state.selected(), Some(std::usize::MAX));

        sel.increment(&vec![]);
        assert_eq!(sel.state.selected(), Some(std::usize::MAX));
    }

    #[test]
    fn test_album_selection() {
        let albums = &COLLECTION[0].albums;
        assert!(albums.len() > 1);

        let empty = AlbumSelection::initialise(None);
        assert_eq!(empty.state.selected(), None);

        let empty = AlbumSelection::initialise(Some(&vec![]));
        assert_eq!(empty.state.selected(), None);

        let mut sel = AlbumSelection::initialise(Some(albums));
        assert_eq!(sel.state.selected(), Some(0));
        assert_eq!(sel.track.state.selected(), Some(0));

        sel.increment_track(albums);
        assert_eq!(sel.state.selected(), Some(0));
        assert_eq!(sel.track.state.selected(), Some(1));

        // Verify that decrement that doesn't change index does not reset track.
        sel.decrement(albums);
        assert_eq!(sel.state.selected(), Some(0));
        assert_eq!(sel.track.state.selected(), Some(1));

        sel.increment(albums);
        assert_eq!(sel.state.selected(), Some(1));
        assert_eq!(sel.track.state.selected(), Some(0));

        sel.decrement(albums);
        assert_eq!(sel.state.selected(), Some(0));
        assert_eq!(sel.track.state.selected(), Some(0));

        for _ in 0..(albums.len() + 5) {
            sel.increment(albums);
        }
        assert_eq!(sel.state.selected(), Some(albums.len() - 1));
        assert_eq!(sel.track.state.selected(), Some(0));

        sel.increment_track(albums);
        assert_eq!(sel.state.selected(), Some(albums.len() - 1));
        assert_eq!(sel.track.state.selected(), Some(1));

        // Verify that increment that doesn't change index does not reset track.
        sel.increment(albums);
        assert_eq!(sel.state.selected(), Some(albums.len() - 1));
        assert_eq!(sel.track.state.selected(), Some(1));

        // Artifical test case to verify upper limit.
        sel.state.select(Some(std::usize::MAX));
        sel.track.state.select(Some(1));
        assert_eq!(sel.state.selected(), Some(std::usize::MAX));
        assert_eq!(sel.track.state.selected(), Some(1));

        sel.increment(&vec![]);
        assert_eq!(sel.state.selected(), Some(std::usize::MAX));
        assert_eq!(sel.track.state.selected(), Some(1));
    }

    #[test]
    fn test_artist_selection() {
        let artists = &COLLECTION;
        assert!(artists.len() > 1);

        let empty = ArtistSelection::initialise(None);
        assert_eq!(empty.state.selected(), None);

        let empty = ArtistSelection::initialise(Some(&vec![]));
        assert_eq!(empty.state.selected(), None);

        let mut sel = ArtistSelection::initialise(Some(artists));
        assert_eq!(sel.state.selected(), Some(0));
        assert_eq!(sel.album.state.selected(), Some(0));

        sel.increment_album(artists);
        assert_eq!(sel.state.selected(), Some(0));
        assert_eq!(sel.album.state.selected(), Some(1));

        // Verify that decrement that doesn't change index does not reset album.
        sel.decrement(artists);
        assert_eq!(sel.state.selected(), Some(0));
        assert_eq!(sel.album.state.selected(), Some(1));

        sel.increment(artists);
        assert_eq!(sel.state.selected(), Some(1));
        assert_eq!(sel.album.state.selected(), Some(0));

        sel.decrement(artists);
        assert_eq!(sel.state.selected(), Some(0));
        assert_eq!(sel.album.state.selected(), Some(0));

        for _ in 0..(artists.len() + 5) {
            sel.increment(artists);
        }
        assert_eq!(sel.state.selected(), Some(artists.len() - 1));
        assert_eq!(sel.album.state.selected(), Some(0));

        sel.increment_album(artists);
        assert_eq!(sel.state.selected(), Some(artists.len() - 1));
        assert_eq!(sel.album.state.selected(), Some(1));

        // Verify that increment that doesn't change index does not reset album.
        sel.increment(artists);
        assert_eq!(sel.state.selected(), Some(artists.len() - 1));
        assert_eq!(sel.album.state.selected(), Some(1));

        // Artifical test case to verify upper limit.
        sel.state.select(Some(std::usize::MAX));
        sel.album.state.select(Some(1));
        assert_eq!(sel.state.selected(), Some(std::usize::MAX));
        assert_eq!(sel.album.state.selected(), Some(1));

        sel.increment(&vec![]);
        assert_eq!(sel.state.selected(), Some(std::usize::MAX));
        assert_eq!(sel.album.state.selected(), Some(1));
    }

    #[test]
    fn ui_running() {
        let mut collection_manager = MockCollectionManager::new();

        collection_manager
            .expect_rescan_library()
            .times(1)
            .return_once(|| Ok(()));
        collection_manager
            .expect_get_collection()
            .return_const(COLLECTION.to_owned());

        let mut ui = MhUi::new(collection_manager).unwrap();
        assert!(ui.is_running());

        ui.quit();
        assert!(!ui.is_running());
    }

    #[test]
    fn ui_modifiers() {
        let mut collection_manager = MockCollectionManager::new();

        collection_manager
            .expect_rescan_library()
            .times(1)
            .return_once(|| Ok(()));
        collection_manager
            .expect_get_collection()
            .return_const(COLLECTION.to_owned());

        let mut ui = MhUi::new(collection_manager).unwrap();
        assert!(ui.is_running());

        assert_eq!(ui.selection.active, Category::Artist);
        assert_eq!(ui.selection.artist.state.selected(), Some(0));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(0));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(0));

        ui.increment_selection();
        assert_eq!(ui.selection.active, Category::Artist);
        assert_eq!(ui.selection.artist.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(0));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(0));

        ui.increment_category();
        assert_eq!(ui.selection.active, Category::Album);
        assert_eq!(ui.selection.artist.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(0));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(0));

        ui.increment_selection();
        assert_eq!(ui.selection.active, Category::Album);
        assert_eq!(ui.selection.artist.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(0));

        ui.increment_category();
        assert_eq!(ui.selection.active, Category::Track);
        assert_eq!(ui.selection.artist.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(0));

        ui.increment_selection();
        assert_eq!(ui.selection.active, Category::Track);
        assert_eq!(ui.selection.artist.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(1));

        ui.increment_category();
        assert_eq!(ui.selection.active, Category::Track);
        assert_eq!(ui.selection.artist.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(1));

        ui.decrement_selection();
        assert_eq!(ui.selection.active, Category::Track);
        assert_eq!(ui.selection.artist.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(0));

        ui.increment_selection();
        ui.decrement_category();
        assert_eq!(ui.selection.active, Category::Album);
        assert_eq!(ui.selection.artist.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(1));

        ui.decrement_selection();
        assert_eq!(ui.selection.active, Category::Album);
        assert_eq!(ui.selection.artist.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(0));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(0));

        ui.increment_selection();
        ui.decrement_category();
        assert_eq!(ui.selection.active, Category::Artist);
        assert_eq!(ui.selection.artist.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(0));

        ui.decrement_selection();
        assert_eq!(ui.selection.active, Category::Artist);
        assert_eq!(ui.selection.artist.state.selected(), Some(0));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(0));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(0));

        ui.increment_category();
        ui.increment_selection();
        ui.decrement_category();
        ui.decrement_selection();
        ui.decrement_category();
        assert_eq!(ui.selection.active, Category::Artist);
        assert_eq!(ui.selection.artist.state.selected(), Some(0));
        assert_eq!(ui.selection.artist.album.state.selected(), Some(1));
        assert_eq!(ui.selection.artist.album.track.state.selected(), Some(0));
    }

    #[test]
    fn app_no_tracks() {
        let mut collection_manager = MockCollectionManager::new();
        let mut collection = COLLECTION.to_owned();
        collection[0].albums[0].tracks = vec![];

        collection_manager
            .expect_rescan_library()
            .times(1)
            .return_once(|| Ok(()));
        collection_manager
            .expect_get_collection()
            .return_const(collection);

        let mut app = MhUi::new(collection_manager).unwrap();
        assert!(app.is_running());

        assert_eq!(app.selection.active, Category::Artist);
        assert_eq!(app.selection.artist.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.increment_category();
        app.increment_category();

        app.increment_selection();
        assert_eq!(app.selection.active, Category::Track);
        assert_eq!(app.selection.artist.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.decrement_selection();
        assert_eq!(app.selection.active, Category::Track);
        assert_eq!(app.selection.artist.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.track.state.selected(), None);
    }

    #[test]
    fn app_no_albums() {
        let mut collection_manager = MockCollectionManager::new();
        let mut collection = COLLECTION.to_owned();
        collection[0].albums = vec![];

        collection_manager
            .expect_rescan_library()
            .times(1)
            .return_once(|| Ok(()));
        collection_manager
            .expect_get_collection()
            .return_const(collection);

        let mut app = MhUi::new(collection_manager).unwrap();
        assert!(app.is_running());

        assert_eq!(app.selection.active, Category::Artist);
        assert_eq!(app.selection.artist.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.increment_category();

        app.increment_selection();
        assert_eq!(app.selection.active, Category::Album);
        assert_eq!(app.selection.artist.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.decrement_selection();
        assert_eq!(app.selection.active, Category::Album);
        assert_eq!(app.selection.artist.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.increment_category();

        app.increment_selection();
        assert_eq!(app.selection.active, Category::Track);
        assert_eq!(app.selection.artist.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.decrement_selection();
        assert_eq!(app.selection.active, Category::Track);
        assert_eq!(app.selection.artist.state.selected(), Some(0));
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);
    }

    #[test]
    fn app_no_artists() {
        let mut collection_manager = MockCollectionManager::new();
        let collection = vec![];

        collection_manager
            .expect_rescan_library()
            .times(1)
            .return_once(|| Ok(()));
        collection_manager
            .expect_get_collection()
            .return_const(collection);

        let mut app = MhUi::new(collection_manager).unwrap();
        assert!(app.is_running());

        assert_eq!(app.selection.active, Category::Artist);
        assert_eq!(app.selection.artist.state.selected(), None);
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.increment_selection();
        assert_eq!(app.selection.active, Category::Artist);
        assert_eq!(app.selection.artist.state.selected(), None);
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.decrement_selection();
        assert_eq!(app.selection.active, Category::Artist);
        assert_eq!(app.selection.artist.state.selected(), None);
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.increment_category();

        app.increment_selection();
        assert_eq!(app.selection.active, Category::Album);
        assert_eq!(app.selection.artist.state.selected(), None);
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.decrement_selection();
        assert_eq!(app.selection.active, Category::Album);
        assert_eq!(app.selection.artist.state.selected(), None);
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.increment_category();

        app.increment_selection();
        assert_eq!(app.selection.active, Category::Track);
        assert_eq!(app.selection.artist.state.selected(), None);
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);

        app.decrement_selection();
        assert_eq!(app.selection.active, Category::Track);
        assert_eq!(app.selection.artist.state.selected(), None);
        assert_eq!(app.selection.artist.album.state.selected(), None);
        assert_eq!(app.selection.artist.album.track.state.selected(), None);
    }

    // This is UI so the only sensible unit test is to run the code through various app states.

    #[test]
    fn empty() {
        let mut terminal = terminal();
        let mut ui = ui(vec![]);

        terminal.draw(|frame| ui.render(frame)).unwrap();
    }

    #[test]
    fn collection() {
        let mut terminal = terminal();
        let mut ui = ui(COLLECTION.to_owned());

        terminal.draw(|frame| ui.render(frame)).unwrap();

        // Change the track (which has a different track format).
        ui.increment_category();
        ui.increment_category();
        ui.increment_selection();

        terminal.draw(|frame| ui.render(frame)).unwrap();
    }
}