nkbmusic/lib/audio/nk_audio_handler.dart

import 'dart:async';

import 'package:audio_service/audio_service.dart';
import 'package:audio_session/audio_session.dart';
import 'package:just_audio/just_audio.dart';

/// Owns the [AudioPlayer] and exposes it to the OS (lock screen, notification,
/// headset and Bluetooth buttons) through audio_service.
class NkAudioHandler extends BaseAudioHandler with SeekHandler {
  NkAudioHandler() {
    _init();
  }

  /// Sound settings (Android only; iOS has no per-app equalizer in just_audio).
  final equalizer = AndroidEqualizer();
  final loudness = AndroidLoudnessEnhancer();

  late final _player = AudioPlayer(
    audioPipeline: AudioPipeline(androidAudioEffects: [loudness, equalizer]),
  );

  Stream<Duration> get positionStream => _player.positionStream;
  Stream<Duration?> get durationStream => _player.durationStream;

  Future<void> _init() async {
    final session = await AudioSession.instance;
    await session.configure(const AudioSessionConfiguration.music());

    _player.playbackEventStream.listen(
      (_) => playbackState.add(_currentState()),
      onError: (Object e, StackTrace st) => playbackState.add(
        playbackState.value.copyWith(processingState: AudioProcessingState.error, errorMessage: '$e'),
      ),
    );
    _player.playingStream.listen((_) => playbackState.add(_currentState()));
    _player.shuffleModeEnabledStream.listen((_) => playbackState.add(_currentState()));
    _player.loopModeStream.listen((_) => playbackState.add(_currentState()));

    _player.sequenceStateStream.listen((state) {
      final tag = state.currentSource?.tag;
      if (tag is MediaItem) mediaItem.add(tag);
      queue.add([
        for (final s in state.effectiveSequence)
          if (s.tag is MediaItem) s.tag as MediaItem,
      ]);
    });

    // Fill in the real duration once the file is loaded.
    _player.durationStream.listen((d) {
      final item = mediaItem.value;
      if (d != null && item != null && item.duration != d) mediaItem.add(item.copyWith(duration: d));
    });
  }

  /// Replaces the queue with [items] and starts playing at [index].
  Future<void> playQueue(List<MediaItem> items, {int index = 0}) async {
    if (items.isEmpty) return;
    await _player.setAudioSources(
      [for (final item in items) _sourceFor(item)],
      initialIndex: index,
    );
    await _player.play();
  }

  /// Inserts [item] right after the current song.
  Future<void> playNext(MediaItem item) async {
    final source = _sourceFor(item);
    final current = _player.currentIndex;
    if (current == null) return playQueue([item]);
    await _player.insertAudioSource(current + 1, source);
  }

  @override
  Future<void> addQueueItem(MediaItem mediaItem) =>
      _player.addAudioSource(_sourceFor(mediaItem));

  /// Set at startup: returns the downloaded (encrypted) copy of a song, if there is one.
  AudioSource? Function(MediaItem item)? localSource;

  AudioSource _sourceFor(MediaItem item) =>
      localSource?.call(item) ?? AudioSource.uri(Uri.parse(item.extras!['url'] as String), tag: item);

  @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();

  /// Restarts the song when more than 3 s in, like every major player.
  @override
  Future<void> skipToPrevious() async {
    if (_player.position > const Duration(seconds: 3) || !_player.hasPrevious) {
      return _player.seek(Duration.zero);
    }
    return _player.seekToPrevious();
  }

  @override
  Future<void> skipToQueueItem(int index) async {
    final indices = _player.shuffleModeEnabled ? _player.shuffleIndices : null;
    await _player.seek(Duration.zero, index: indices == null ? index : indices[index]);
  }

  @override
  Future<void> setShuffleMode(AudioServiceShuffleMode shuffleMode) async {
    final enable = shuffleMode != AudioServiceShuffleMode.none;
    if (enable) await _player.shuffle();
    await _player.setShuffleModeEnabled(enable);
  }

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

  @override
  Future<void> stop() async {
    await _player.stop();
    return super.stop();
  }

  PlaybackState _currentState() {
    final playing = _player.playing;
    return PlaybackState(
      controls: [
        MediaControl.skipToPrevious,
        if (playing) MediaControl.pause else MediaControl.play,
        MediaControl.skipToNext,
      ],
      systemActions: const {MediaAction.seek, MediaAction.seekForward, MediaAction.seekBackward},
      androidCompactActionIndices: const [0, 1, 2],
      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: _player.currentIndex,
      shuffleMode: _player.shuffleModeEnabled ? AudioServiceShuffleMode.all : AudioServiceShuffleMode.none,
      repeatMode: switch (_player.loopMode) {
        LoopMode.one => AudioServiceRepeatMode.one,
        LoopMode.all => AudioServiceRepeatMode.all,
        LoopMode.off => AudioServiceRepeatMode.none,
      },
    );
  }
}