mobile-music/lib/playback/playback_engine.dart

// Named constructor params can't be private, so initializing formals aren't
// possible for the private callback fields below.
// ignore_for_file: prefer_initializing_formals

import 'dart:async';
import 'dart:convert';
import 'dart:io' show File, Platform;

import 'package:flutter/foundation.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:just_audio/just_audio.dart';
import 'package:just_audio_background/just_audio_background.dart';
import 'package:path_provider/path_provider.dart';

import '../subsonic/models.dart';

/// Immutable snapshot of the player, mirroring Timbre's `QueueState` +
/// player-event stream (`timbre-player/src/engine.rs`).
class PlaybackState {
  const PlaybackState({
    this.queue = const [],
    this.currentIndex,
    this.playing = false,
    this.position = Duration.zero,
    this.duration = Duration.zero,
    this.shuffle = false,
    this.loop = LoopMode.off,
    this.supported = true,
  });

  final List<Song> queue;
  final int? currentIndex;
  final bool playing;
  final Duration position;
  final Duration duration;
  final bool shuffle;
  final LoopMode loop;

  /// False on platforms without a just_audio backend (e.g. Linux desktop
  /// without media_kit). The UI still reflects the selected track; only audio
  /// output is unavailable.
  final bool supported;

  Song? get current =>
      (currentIndex != null && currentIndex! >= 0 && currentIndex! < queue.length)
          ? queue[currentIndex!]
          : null;

  double get progress {
    final total = duration.inMilliseconds;
    if (total <= 0) return 0;
    return (position.inMilliseconds / total).clamp(0.0, 1.0);
  }

  PlaybackState copyWith({
    List<Song>? queue,
    int? currentIndex,
    bool? playing,
    Duration? position,
    Duration? duration,
    bool? shuffle,
    LoopMode? loop,
    bool? supported,
  }) {
    return PlaybackState(
      queue: queue ?? this.queue,
      currentIndex: currentIndex ?? this.currentIndex,
      playing: playing ?? this.playing,
      position: position ?? this.position,
      duration: duration ?? this.duration,
      shuffle: shuffle ?? this.shuffle,
      loop: loop ?? this.loop,
      supported: supported ?? this.supported,
    );
  }
}

/// Owns the just_audio player and translates Subsonic songs into a gapless
/// queue. Playback methods no-op where audio is unsupported, but queue/current
/// state and album-art accent extraction still run so the UI is fully alive on
/// the Linux dev target.
class PlaybackController extends StateNotifier<PlaybackState> {
  PlaybackController({
    required Uri? Function(Song) streamUriFor,
    required Uri? Function(Song) coverArtUriFor,
    required String? Function() serverKeyGetter,
    required void Function(Uri artUri) onArt,
    required void Function(Song song) onPlay,
  })  : _streamUriFor = streamUriFor,
        _coverArtUriFor = coverArtUriFor,
        _serverKeyGetter = serverKeyGetter,
        _onArt = onArt,
        _onPlay = onPlay,
        super(PlaybackState(supported: _audioSupported)) {
    if (_audioSupported) {
      _player = AudioPlayer();
      _wireStreams();
    }
    // Persist the queue on any change (throttled) so it survives an app kill.
    addListener((_) => _scheduleSave(), fireImmediately: false);
  }

  final Uri? Function(Song) _streamUriFor;
  final Uri? Function(Song) _coverArtUriFor;
  final String? Function() _serverKeyGetter;
  final void Function(Uri artUri) _onArt;
  final void Function(Song song) _onPlay;

  AudioPlayer? _player;

  /// Coalesces rapid state changes (a position tick every second) into at most
  /// one disk write per window.
  Timer? _saveTimer;

  /// Server key whose queue we've already restored (or adopted). Gates saves so
  /// the empty launch state can't clobber a snapshot before restore runs.
  String? _restoredKey;

  static bool get _audioSupported =>
      !kIsWeb && (Platform.isAndroid || Platform.isIOS || Platform.isMacOS);

  void _wireStreams() {
    final player = _player!;
    player.currentIndexStream.listen((i) {
      if (i == null) return;
      state = state.copyWith(currentIndex: i);
      _notifyCurrent();
    });
    player.playerStateStream.listen((s) {
      state = state.copyWith(playing: s.playing);
    });
    player.positionStream.listen((p) {
      state = state.copyWith(position: p);
    });
    player.durationStream.listen((d) {
      if (d != null) state = state.copyWith(duration: d);
    });
  }

  /// Id of the song we last ran play side effects for. Queue edits shift
  /// `currentIndex` (and re-emit `currentIndexStream`) without changing the
  /// playing track, so we dedupe on song id to avoid re-scrobbling / re-running
  /// accent extraction when the current song hasn't actually changed.
  String? _lastNotifiedId;

  /// Monotonic tag counter — every AudioSource gets a globally-unique MediaItem
  /// id even when the same song appears in the queue twice. just_audio_background
  /// keys its notification off the tag id, so duplicate ids would confuse it.
  int _tagSeq = 0;

  void _notifyCurrent() {
    final song = state.current;
    if (song == null) return;
    if (song.id == _lastNotifiedId) return;
    _lastNotifiedId = song.id;
    final art = _coverArtUriFor(song);
    if (art != null) _onArt(art);
    _onPlay(song);
  }

  AudioSource _sourceFor(Song song) {
    final uri = _streamUriFor(song)!;
    final art = _coverArtUriFor(song);
    return AudioSource.uri(
      uri,
      tag: MediaItem(
        id: '${song.id}#${_tagSeq++}',
        title: song.title ?? 'Unknown',
        album: song.album,
        artist: song.artist,
        duration:
            song.duration != null ? Duration(seconds: song.duration!) : null,
        artUri: art,
      ),
    );
  }

  /// Replace the queue with [songs] and start at [startIndex].
  ///
  /// `state.queue` is set to exactly the *streamable* subset that gets loaded
  /// into the player, so queue index == player source index 1:1. Every later
  /// queue mutation (`playNext` / `addToQueue` / `removeAt`) relies on that
  /// invariant to stay aligned.
  Future<void> playSongs(List<Song> songs, {int startIndex = 0}) async {
    if (songs.isEmpty) return;

    final streamable = songs.where((s) => _streamUriFor(s) != null).toList();
    if (streamable.isEmpty) {
      // Not connected / nothing playable — reflect the selection for the UI
      // only; no player sources exist to mutate.
      state = state.copyWith(
        queue: songs,
        currentIndex: startIndex.clamp(0, songs.length - 1),
        position: Duration.zero,
      );
      _lastNotifiedId = null;
      _notifyCurrent();
      return;
    }

    // Remap the requested start into the filtered list (the chosen song may
    // itself have been unstreamable).
    final target = songs[startIndex.clamp(0, songs.length - 1)];
    final targetIndex = streamable.indexOf(target);
    final start =
        targetIndex >= 0 ? targetIndex : startIndex.clamp(0, streamable.length - 1);

    state = state.copyWith(
      queue: streamable,
      currentIndex: start,
      position: Duration.zero,
    );
    // An explicit play should always (re)scrobble, even if it's the same song.
    _lastNotifiedId = null;

    final player = _player;
    if (player == null) {
      // Linux/desktop: no streams will fire, so reflect the selection (art +
      // history) directly. UI-only, no audio output.
      _notifyCurrent();
      return;
    }
    await player.setAudioSources(
      streamable.map(_sourceFor).toList(),
      initialIndex: start,
    );
    await player.play();
    // currentIndexStream fires _notifyCurrent for the started track.
  }

  /// Insert [song] right after the current track (Timbre's "play next").
  /// Falls back to [playSongs] when nothing is playing.
  Future<void> playNext(Song song) async {
    if (_streamUriFor(song) == null) return;
    final q = state.queue;
    final current = state.currentIndex;
    if (q.isEmpty || current == null) {
      await playSongs([song]);
      return;
    }
    final at = (current + 1).clamp(0, q.length);
    state = state.copyWith(queue: [...q]..insert(at, song));
    await _player?.insertAudioSource(at, _sourceFor(song));
  }

  /// Append [song] to the end of the queue.
  Future<void> addToQueue(Song song) async {
    if (_streamUriFor(song) == null) return;
    final q = state.queue;
    if (q.isEmpty || state.currentIndex == null) {
      await playSongs([song]);
      return;
    }
    state = state.copyWith(queue: [...q, song]);
    await _player?.addAudioSource(_sourceFor(song));
  }

  /// Remove the queue entry at [index], keeping `state.queue` and the player
  /// playlist aligned. On mobile just_audio adjusts its own current index and
  /// re-emits `currentIndexStream`; the id dedupe in [_notifyCurrent] avoids a
  /// spurious re-scrobble when the playing track didn't actually change.
  Future<void> removeAt(int index) async {
    final q = state.queue;
    if (index < 0 || index >= q.length) return;

    final next = [...q]..removeAt(index);
    if (next.isEmpty) {
      await _player?.clearAudioSources();
      state = PlaybackState(
        shuffle: state.shuffle,
        loop: state.loop,
        supported: state.supported,
      );
      _lastNotifiedId = null;
      return;
    }

    final player = _player;
    if (player == null) {
      // Desktop/no-audio: no stream will correct the index for us.
      final current = state.currentIndex;
      var newIndex = current;
      if (current != null) {
        if (index < current) {
          newIndex = current - 1;
        } else if (index == current) {
          // The removed slot now holds the following track.
          newIndex = current.clamp(0, next.length - 1);
        }
      }
      state = state.copyWith(queue: next, currentIndex: newIndex);
      _notifyCurrent();
      return;
    }

    state = state.copyWith(queue: next);
    await player.removeAudioSourceAt(index);
  }

  Future<void> togglePlayPause() async {
    final player = _player;
    if (player == null) return;
    if (player.playing) {
      await player.pause();
    } else {
      await player.play();
    }
  }

  Future<void> next() async => _player?.seekToNext();

  Future<void> previous() async => _player?.seekToPrevious();

  Future<void> seek(Duration position) async => _player?.seek(position);

  Future<void> toggleShuffle() async {
    final enabled = !state.shuffle;
    state = state.copyWith(shuffle: enabled);
    final player = _player;
    if (player != null) {
      await player.setShuffleModeEnabled(enabled);
    }
  }

  /// Cycle off → all → one → off (Timbre's queue-loop toggle, extended with
  /// single-track repeat).
  Future<void> cycleLoop() async {
    final nextMode = switch (state.loop) {
      LoopMode.off => LoopMode.all,
      LoopMode.all => LoopMode.one,
      LoopMode.one => LoopMode.off,
    };
    state = state.copyWith(loop: nextMode);
    await _player?.setLoopMode(nextMode);
  }

  // ---- Persistence --------------------------------------------------------

  /// Per-server queue snapshot file, alongside the playlists/downloads mirrors.
  Future<File> _snapshotFile(String key) async {
    final dir = await getApplicationSupportDirectory();
    return File('${dir.path}/queue_$key.json');
  }

  /// Throttle a save: schedule one write per window, capturing the latest state
  /// when it fires (so continuous position ticks don't hammer the disk).
  void _scheduleSave() {
    if (_saveTimer?.isActive ?? false) return;
    _saveTimer = Timer(const Duration(seconds: 3), _persist);
  }

  Future<void> _persist() async {
    final key = _serverKeyGetter();
    // Only persist once the active server's queue has been restored/adopted.
    if (key == null || key != _restoredKey) return;
    try {
      final file = await _snapshotFile(key);
      final tmp = File('${file.path}.tmp');
      await tmp.writeAsString(jsonEncode({
        'queue': state.queue.map((s) => s.toJson()).toList(),
        'currentIndex': state.currentIndex,
        'positionMs': state.position.inMilliseconds,
        'shuffle': state.shuffle,
        'loop': state.loop.name,
      }));
      await tmp.rename(file.path); // atomic swap
    } catch (_) {
      // Best effort — a failed save just means a slightly staler queue.
    }
  }

  /// Restore the saved queue for the active server (on connect / server switch).
  /// The tracks, shuffle/loop and position are loaded back into the player
  /// **paused**, so the queue auto-populates without surprising the user with
  /// sudden playback. Called from the [serverKeyProvider] listener; a no-op once
  /// the current server has already been restored.
  Future<void> restoreForServer() async {
    final key = _serverKeyGetter();
    if (key == null || key == _restoredKey) return;

    Map<String, dynamic>? snap;
    try {
      final file = await _snapshotFile(key);
      if (await file.exists()) {
        final raw = jsonDecode(await file.readAsString());
        if (raw is Map) snap = raw.cast<String, dynamic>();
      }
    } catch (_) {
      // Missing/corrupt snapshot is non-fatal.
    }

    // Mark restored *after* reading, so saves for this server are now allowed.
    _restoredKey = key;

    // Don't clobber an already-loaded queue (user started playback first).
    if (state.queue.isNotEmpty || snap == null) return;

    final songs = (snap['queue'] as List? ?? const [])
        .whereType<Map>()
        .map((e) => Song.fromJson(e.cast<String, dynamic>()))
        .toList();
    if (songs.isEmpty) return;

    final loop = LoopMode.values.firstWhere(
      (m) => m.name == snap!['loop'],
      orElse: () => LoopMode.off,
    );
    final shuffle = snap['shuffle'] == true;
    final savedIndex = (snap['currentIndex'] as int?) ?? 0;
    final savedPos = Duration(milliseconds: (snap['positionMs'] as int?) ?? 0);

    final streamable = songs.where((s) => _streamUriFor(s) != null).toList();
    if (streamable.isEmpty) {
      // Offline / nothing streamable: reflect the queue for the UI only.
      final start = savedIndex.clamp(0, songs.length - 1);
      _lastNotifiedId = songs[start].id;
      state = state.copyWith(
        queue: songs,
        currentIndex: start,
        position: savedPos,
        shuffle: shuffle,
        loop: loop,
      );
      return;
    }

    // Remap the saved index onto the streamable subset (same invariant as
    // [playSongs]: state.queue == the sources loaded into the player).
    final target = songs[savedIndex.clamp(0, songs.length - 1)];
    final targetIndex = streamable.indexOf(target);
    final start = targetIndex >= 0
        ? targetIndex
        : savedIndex.clamp(0, streamable.length - 1);

    // Suppress a spurious scrobble/history entry for the restored (not actually
    // played) track, but still drive the album-art accent.
    _lastNotifiedId = streamable[start].id;
    final art = _coverArtUriFor(streamable[start]);
    if (art != null) _onArt(art);

    state = state.copyWith(
      queue: streamable,
      currentIndex: start,
      position: savedPos,
      shuffle: shuffle,
      loop: loop,
    );

    final player = _player;
    if (player == null) return; // desktop: UI-only, already reflected above.
    await player.setAudioSources(
      streamable.map(_sourceFor).toList(),
      initialIndex: start,
    );
    await player.setShuffleModeEnabled(shuffle);
    await player.setLoopMode(loop);
    if (savedPos > Duration.zero) await player.seek(savedPos, index: start);
    // Intentionally no play() — restore leaves the queue paused.
  }

  @override
  void dispose() {
    _saveTimer?.cancel();
    _player?.dispose();
    super.dispose();
  }
}