minstrel/flutter_client/lib/player/audio_handler.dart

import 'dart:async';
import 'dart:io';

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

import '../cache/audio_cache_manager.dart';
import '../models/track.dart';
import 'album_cover_cache.dart';

class MinstrelAudioHandler extends BaseAudioHandler with QueueHandler, SeekHandler {
  MinstrelAudioHandler() {
    _player.playbackEventStream.listen(
      _broadcastState,
      // ExoPlayer surfaces stream errors (404, premature EOS, decoder
      // failure, network drop) here. Without an error sink, the
      // player just goes quiet — exactly the "starts then stops"
      // symptom we hit.
      onError: (Object e, StackTrace st) {
        debugPrint('audio_handler: playbackEventStream error: $e\n$st');
      },
    );
    _player.currentIndexStream.listen(_onCurrentIndexChanged);
    // Re-broadcast on shuffle/repeat changes so the PlaybackState's
    // shuffleMode + repeatMode fields stay current for UI subscribers.
    _player.shuffleModeEnabledStream.listen((_) => _broadcastState(null));
    _player.loopModeStream.listen((_) => _broadcastState(null));
    // Watch buffered-position so we can register stream-cached files
    // in the audio cache index once they're fully downloaded. Without
    // this, files written by LockCachingAudioSource never appear in
    // the index and the eviction loop can't reclaim them.
    _player.bufferedPositionStream
        .listen((_) => unawaited(_maybeRegisterStreamCache()));
  }

  final AudioPlayer _player = AudioPlayer();
  String _baseUrl = '';
  String? _token;
  AlbumCoverCache? _coverCache;
  AudioCacheManager? _audioCacheManager;

  /// Trackers to dedupe registration — once we've inserted an index row
  /// for a trackId, don't repeat the work on every buffered-position
  /// emit. Cleared on dispose only; surviving across queue rebuilds is
  /// fine because the index is itself the source of truth.
  final Set<String> _streamCacheRegistered = {};

  /// Cached on first use so we don't hit the platform channel every
  /// time the buffered-position stream emits (~200ms cadence).
  String? _cacheDirPath;

  /// True while _fillRemainingSources is doing backward-fill inserts
  /// at index 0..initialIndex-1. Each insert shifts the player's
  /// currentIndex (it tracks the actively-playing source through
  /// list mutations), and the resulting _onCurrentIndexChanged
  /// callbacks would push the wrong MediaItem onto the stream
  /// (queue.value[shifted_idx] != actively-playing track). When
  /// the fill completes, currentIndex == initialIndex, mediaItem
  /// is already correct, and we re-enable normal listener behavior.
  bool _suppressIndexUpdates = false;

  /// Increments on every setQueueFromTracks call. The background
  /// fill task captures the value at start and bails if the live
  /// counter has moved on — without this, a stale fill will keep
  /// addAudioSource'ing tracks from the previous playlist into the
  /// new queue, leaving the player "locked" to a corrupted state.
  int _queueGeneration = 0;

  /// Tracks the most recent setQueueFromTracks() input so
  /// skipToQueueItem can reconstruct the source list. just_audio
  /// requires every source to be built before it can be a skip
  /// target, but setQueueFromTracks only builds the initial source
  /// and fills the rest in the background — so a skip to an index
  /// past the fill front needs to rebuild from the stored tracks.
  List<TrackRef> _lastTracks = const [];

  /// Volume stream for UI subscribers. Mirrors the just_audio player's
  /// volume directly; set via setVolume(double).
  Stream<double> get volumeStream => _player.volumeStream;
  double get volume => _player.volume;

  /// Position stream for UI subscribers. just_audio emits roughly every
  /// 200ms while playing, which is what makes the seek bar advance
  /// smoothly. PlaybackState.updatePosition only changes on event
  /// transitions (play/pause/buffer), so it's too coarse for live
  /// scrubbing UI.
  Stream<Duration> get positionStream => _player.positionStream;
  Duration get position => _player.position;

  void configure({
    required String baseUrl,
    required String? token,
    AlbumCoverCache? coverCache,
    AudioCacheManager? audioCacheManager,
  }) {
    _baseUrl = baseUrl;
    _token = token;
    if (coverCache != null) _coverCache = coverCache;
    if (audioCacheManager != null) _audioCacheManager = audioCacheManager;
  }

  Future<void> setQueueFromTracks(List<TrackRef> tracks, {int initialIndex = 0}) async {
    if (tracks.isEmpty) return;
    final clampedInitial = initialIndex.clamp(0, tracks.length - 1);

    // Bump the generation FIRST. Any in-flight _fillRemainingSources
    // from a previous play will see the mismatch on its next gen
    // check and stop calling player mutations — important so a stale
    // fill doesn't append old-playlist tracks into the new queue.
    final myGen = ++_queueGeneration;
    // Reset suppress flag in case a prior backward-fill bailed on
    // gen check before reaching its `finally`.
    _suppressIndexUpdates = false;
    _lastTracks = tracks;

    // Pause the old source immediately so the previous track stops
    // audibly the moment the user taps, instead of bleeding through
    // until the new source finishes building. setAudioSources below
    // will swap the source list cleanly; pause is the simplest way
    // to silence the player during the (possibly multi-100ms) build.
    if (_player.playing) {
      await _player.pause();
    }

    // Populate the visible queue + current mediaItem immediately so
    // the player UI reflects the user's tap before any source has
    // been built. Source list at the just_audio layer fills in
    // asynchronously below.
    final items = tracks.map(_toMediaItem).toList();
    queue.add(items);
    mediaItem.add(items[clampedInitial]);

    // Fast path: build only the initial source so the player can
    // start. Remaining sources stream in via _fillRemainingSources()
    // in the background — addAudioSource for next/auto-advance
    // tracks, insertAudioSource for skipPrev tracks.
    final initial = await _buildAudioSource(tracks[clampedInitial]);
    if (myGen != _queueGeneration) {
      debugPrint('audio_handler: superseded before setAudioSources (gen=$myGen)');
      return;
    }

    await _player.setAudioSources([initial], initialIndex: 0);

    unawaited(_loadArtForCurrentItem());
    unawaited(_fillRemainingSources(tracks, clampedInitial, myGen));
  }

  /// Switches playback to the [index]th queue item. The full
  /// just_audio source list isn't necessarily built yet
  /// (_fillRemainingSources runs in the background), so we
  /// reconstruct from the stored TrackRef list rather than calling
  /// _player.seek(index: ...) on a possibly-missing source. Calling
  /// setQueueFromTracks again is the safe path: it bumps the
  /// generation, cancels any in-flight fill, rebuilds source[0] as
  /// the target, and re-fills around. play() restarts playback so
  /// queue taps feel like "jump to this song" rather than "set the
  /// pointer and wait for me to press play."
  @override
  Future<void> skipToQueueItem(int index) async {
    if (index < 0 || index >= _lastTracks.length) return;
    await setQueueFromTracks(_lastTracks, initialIndex: index);
    await play();
  }

  /// Background fill of the rest of the just_audio source list after
  /// the initial source is playing. Forward direction first (most
  /// common skipNext target). Backward inserts shift the player's
  /// currentIndex; we suppress _onCurrentIndexChanged side effects
  /// for those so the mediaItem stream doesn't bounce to the wrong
  /// queue entry.
  ///
  /// `gen` is the queue generation captured when this fill started.
  /// Every loop iteration checks against _queueGeneration; if a
  /// newer setQueueFromTracks has run (user tapped play on something
  /// else), bail immediately so we don't pollute the new queue with
  /// addAudioSource calls from this stale fill.
  Future<void> _fillRemainingSources(
      List<TrackRef> tracks, int initialIndex, int gen) async {
    for (var i = initialIndex + 1; i < tracks.length; i++) {
      if (gen != _queueGeneration) return;
      try {
        final src = await _buildAudioSource(tracks[i]);
        if (gen != _queueGeneration) return;
        await _player.addAudioSource(src);
      } catch (e) {
        debugPrint('audio_handler: forward fill failed for ${tracks[i].id}: $e');
      }
    }
    if (initialIndex > 0) {
      _suppressIndexUpdates = true;
      try {
        for (var i = 0; i < initialIndex; i++) {
          if (gen != _queueGeneration) return;
          final src = await _buildAudioSource(tracks[i]);
          if (gen != _queueGeneration) return;
          await _player.insertAudioSource(i, src);
        }
      } catch (e) {
        debugPrint('audio_handler: backward fill failed: $e');
      } finally {
        // Only release the flag if we're still the active gen — a
        // newer setQueueFromTracks already reset it for itself.
        if (gen == _queueGeneration) _suppressIndexUpdates = false;
      }
    }
  }

  String _resolveStreamUrl(TrackRef t) {
    if (t.streamUrl.isEmpty) {
      return '$_baseUrl/api/tracks/${t.id}/stream';
    }
    final parsed = Uri.tryParse(t.streamUrl);
    if (parsed != null && parsed.hasScheme) {
      return t.streamUrl;
    }
    return '$_baseUrl${t.streamUrl}';
  }

  /// Builds an AudioSource for a track. Cache-aware:
  /// 1. If the track is fully cached on disk, returns a file:// source.
  /// 2. Else returns a LockCachingAudioSource that streams + caches as
  ///    it plays (subsequent plays will hit the cache).
  ///
  /// Without an audio cache manager configured (e.g. in older code paths
  /// that pre-date #357), falls back to a plain network AudioSource.uri.
  Future<AudioSource> _buildAudioSource(TrackRef t) async {
    final headers = _token == null ? null : {'Authorization': 'Bearer $_token'};
    final mgr = _audioCacheManager;

    // 1. Cache hit: play from disk, no headers needed.
    if (mgr != null) {
      final path = await mgr.pathFor(t.id);
      if (path != null) {
        return AudioSource.uri(Uri.file(path));
      }
    }

    final url = _resolveStreamUrl(t);
    final parsed = Uri.parse(url);
    if (!parsed.hasScheme || parsed.host.isEmpty) {
      throw StateError(
        'audio_handler: refused to play scheme-less URL "$url" '
        '(baseUrl="$_baseUrl", track.streamUrl="${t.streamUrl}", '
        'track.id="${t.id}"). configure() must be called with a '
        'non-empty baseUrl before setQueueFromTracks().',
      );
    }

    // 2. Cache miss WITH manager: stream + cache-as-you-play. Future
    // plays of this track will hit the cache. If the cache write
    // completes, we don't currently register an index row — that would
    // require a download-complete hook from just_audio that's not
    // exposed cleanly. Acceptable for v1: prefetcher / explicit
    // pin / Download buttons cover the index path; LockCaching handles
    // the network optimization.
    if (mgr != null) {
      _cacheDirPath ??= (await getApplicationCacheDirectory()).path;
      final cacheFile = File('${_cacheDirPath!}/audio_cache/${t.id}.mp3');
      // ignore: experimental_member_use
      return LockCachingAudioSource(parsed,
          headers: headers, cacheFile: cacheFile);
    }

    // 3. No manager configured: plain network source (legacy path).
    return AudioSource.uri(parsed, headers: headers);
  }

  /// Inserts [track] right after the currently-playing item so it plays
  /// next. If nothing is playing, appends to the end.
  Future<void> playNext(TrackRef track) async {
    final source = await _buildAudioSource(track);
    final item = _toMediaItem(track);
    final currentIdx = _player.currentIndex;
    final insertAt = currentIdx == null ? queue.value.length : currentIdx + 1;
    await _player.insertAudioSource(insertAt, source);
    final current = queue.value;
    queue.add([
      ...current.sublist(0, insertAt),
      item,
      ...current.sublist(insertAt),
    ]);
  }

  /// Appends [track] to the end of the queue.
  Future<void> enqueue(TrackRef track) async {
    final source = await _buildAudioSource(track);
    final item = _toMediaItem(track);
    await _player.addAudioSource(source);
    queue.add([...queue.value, item]);
  }

  MediaItem _toMediaItem(TrackRef t) {
    // Stash album_id + artist_id in extras so widgets reconstructing
    // a TrackRef from the MediaItem (player kebab → "Go to artist",
    // "Go to album") have the IDs they need to navigate. Earlier code
    // only carried album_id which left "Go to artist" pushing
    // /artists/ (empty id, route 404).
    final extras = <String, dynamic>{};
    if (t.albumId.isNotEmpty) extras['album_id'] = t.albumId;
    if (t.artistId.isNotEmpty) extras['artist_id'] = t.artistId;
    return MediaItem(
      id: t.id,
      title: t.title,
      artist: t.artistName,
      album: t.albumTitle,
      duration: Duration(seconds: t.durationSec),
      extras: extras.isEmpty ? null : extras,
    );
  }

  /// Once a track is fully buffered (LockCaching has written the whole
  /// file to disk), insert an audio_cache_index row so the file shows
  /// up to AudioCacheManager.evict() and clearAll(). No-op if the
  /// cache manager isn't configured, no current track, the file isn't
  /// fully buffered yet, the on-disk file is missing, or we already
  /// registered this trackId during this subscription.
  Future<void> _maybeRegisterStreamCache() async {
    final mgr = _audioCacheManager;
    if (mgr == null) return;
    final current = mediaItem.value;
    if (current == null) return;
    final trackId = current.id;
    if (_streamCacheRegistered.contains(trackId)) return;

    final dur = _player.duration;
    if (dur == null) return;
    final buf = _player.bufferedPosition;
    // 200ms slack for header bytes / encoding rounding.
    if (buf < dur - const Duration(milliseconds: 200)) return;

    _cacheDirPath ??= (await getApplicationCacheDirectory()).path;
    final path = '${_cacheDirPath!}/audio_cache/$trackId.mp3';
    final file = File(path);
    if (!await file.exists()) return;
    final size = await file.length();
    if (size <= 0) return;

    _streamCacheRegistered.add(trackId);
    await mgr.registerStreamCache(trackId, path, size);
  }

  void _onCurrentIndexChanged(int? idx) {
    if (idx == null) return;
    if (_suppressIndexUpdates) return;
    // Push the new track's MediaItem onto the mediaItem stream so
    // the player UI rebuilds with the new title/artist/album/cover.
    // Without this, the bar and full player stayed pinned to whichever
    // track was passed via setQueueFromTracks(initialIndex:) regardless
    // of skip/auto-advance.
    final items = queue.value;
    if (idx >= 0 && idx < items.length) {
      mediaItem.add(items[idx]);
    }
    unawaited(_loadArtForCurrentItem());
  }

  /// Async-fetches the cover for whichever item is currently active and
  /// pushes a MediaItem update with artUri set. No-op if no cache is
  /// configured, no current item, the item has no album_id in extras,
  /// or the fetch returns null.
  Future<void> _loadArtForCurrentItem() async {
    final cache = _coverCache;
    if (cache == null) return;
    final current = mediaItem.value;
    if (current == null) return;
    final albumId = current.extras?['album_id'] as String?;
    if (albumId == null || albumId.isEmpty) return;
    if (current.artUri != null) return; // already set
    final path = await cache.getOrFetch(albumId);
    if (path == null) return;
    // Discard if the user advanced to another track while we waited.
    if (mediaItem.value?.id != current.id) return;
    mediaItem.add(current.copyWith(artUri: Uri.file(path)));
  }

  @override
  Future<void> play() => _player.play();

  @override
  Future<void> pause() => _player.pause();

  @override
  Future<void> seek(Duration position) => _player.seek(position);

  @override
  Future<void> skipToNext() => _player.seekToNext();

  @override
  Future<void> skipToPrevious() => _player.seekToPrevious();

  @override
  Future<void> setShuffleMode(AudioServiceShuffleMode shuffleMode) async {
    await _player
        .setShuffleModeEnabled(shuffleMode != AudioServiceShuffleMode.none);
    // _broadcastState picks up the change via shuffleModeEnabledStream.
  }

  @override
  Future<void> setRepeatMode(AudioServiceRepeatMode repeatMode) async {
    final loop = switch (repeatMode) {
      AudioServiceRepeatMode.none => LoopMode.off,
      AudioServiceRepeatMode.one => LoopMode.one,
      AudioServiceRepeatMode.all || AudioServiceRepeatMode.group => LoopMode.all,
    };
    await _player.setLoopMode(loop);
  }

  /// Sets player volume in [0.0, 1.0]. Note: most mobile browsers tie
  /// page audio to system volume — this is the in-app slider for parity
  /// with desktop/web; on mobile the system volume is the real control.
  Future<void> setVolume(double v) async {
    await _player.setVolume(v.clamp(0.0, 1.0));
  }

  // _broadcastState accepts a nullable event because the shuffle/repeat
  // listeners don't have one — we just want to re-emit PlaybackState
  // with up-to-date shuffleMode/repeatMode fields.
  void _broadcastState(PlaybackEvent? event) {
    final playing = _player.playing;
    playbackState.add(PlaybackState(
      controls: [
        MediaControl.skipToPrevious,
        if (playing) MediaControl.pause else MediaControl.play,
        MediaControl.skipToNext,
      ],
      // androidCompactActionIndices tells the system which controls
      // appear in the collapsed/lock-screen view. Without this, some
      // Android versions render the player without working buttons.
      androidCompactActionIndices: const [0, 1, 2],
      // systemActions enumerates which actions the system can invoke
      // on us — without play/pause/skip in here, taps on lock-screen
      // controls don't route back to the handler on Android 13+.
      systemActions: const {
        MediaAction.play,
        MediaAction.pause,
        MediaAction.skipToNext,
        MediaAction.skipToPrevious,
        MediaAction.seek,
      },
      processingState: switch (_player.processingState) {
        ProcessingState.idle => AudioProcessingState.idle,
        ProcessingState.loading => AudioProcessingState.loading,
        ProcessingState.buffering => AudioProcessingState.buffering,
        ProcessingState.ready => AudioProcessingState.ready,
        ProcessingState.completed => AudioProcessingState.completed,
      },
      playing: playing,
      updatePosition: _player.position,
      bufferedPosition: _player.bufferedPosition,
      speed: _player.speed,
      queueIndex: event?.currentIndex ?? _player.currentIndex,
      shuffleMode: _player.shuffleModeEnabled
          ? AudioServiceShuffleMode.all
          : AudioServiceShuffleMode.none,
      repeatMode: switch (_player.loopMode) {
        LoopMode.off => AudioServiceRepeatMode.none,
        LoopMode.one => AudioServiceRepeatMode.one,
        LoopMode.all => AudioServiceRepeatMode.all,
      },
    ));
  }
}