feat: Add audio_video_progress_bar dependency

lib/features/player/core/audiobook_player.dart

@@ -0,0 +1,119 @@
+/// a wrapper around the audioplayers package to manage the audio player instance
+///
+/// this is needed as audiobook can be a list of audio files instead of a single file
+library;
+
+import 'package:audioplayers/audioplayers.dart';
+import 'package:shelfsdk/audiobookshelf_api.dart';
+
+/// will manage the audio player instance
+class AudiobookPlayer extends AudioPlayer {
+  // constructor which takes in the BookExpanded object
+  AudiobookPlayer(this.token, this.baseUrl, {super.playerId}) : super() {
+    // set the source of the player to the first track in the book
+  }
+
+  /// the [BookExpanded] being played
+  BookExpanded? _book;
+
+  /// the [BookExpanded] being played
+  ///
+  /// to set the book, use [setSourceAudioBook]
+  BookExpanded? get book => _book;
+
+  /// the authentication token to access the [AudioTrack.contentUrl]
+  final String token;
+
+  /// the base url for the audio files
+  final Uri baseUrl;
+
+  // the current index of the audio file in the [book]
+  final int _currentIndex = 0;
+
+  // available audio tracks
+  int? get availableTracks => _book?.tracks.length;
+
+  /// sets the current [AudioTrack] as the source of the player
+  Future<void> setSourceAudioBook(BookExpanded? book) async {
+    // if the book is null, stop the player
+    if (book == null) {
+      _book = null;
+      return stop();
+    }
+
+    // see if the book is the same as the current book
+    if (_book == book) {
+      // if the book is the same, do nothing
+      return;
+    }
+    // first stop the player
+    await stop();
+
+    var track = book.tracks[_currentIndex];
+    var url = '$baseUrl${track.contentUrl}?token=$token';
+    await setSourceUrl(
+      url,
+      mimeType: track.mimeType,
+    );
+    _book = book;
+  }
+
+  /// toggles the player between play and pause
+  Future<void> togglePlayPause() {
+    // check if book is set
+    if (_book == null) {
+      throw StateError('No book is set');
+    }
+    return switch (state) {
+      PlayerState.playing => pause(),
+      PlayerState.paused ||
+      PlayerState.stopped ||
+      PlayerState.completed =>
+        resume(),
+      // do nothing if the player is disposed
+      PlayerState.disposed => throw StateError('Player is disposed'),
+    };
+  }
+
+  /// override resume to set the source if the book is not set
+  @override
+  Future<void> resume() async {
+    if (_book == null) {
+      throw StateError('No book is set');
+    }
+    return super.resume();
+  }
+
+  /// a convenience stream for onPositionEveryXSeconds
+  Stream<Duration> onPositionEvery(Duration duration) => TimerPositionUpdater(
+        getPosition: getCurrentPosition,
+        interval: duration,
+      ).positionStream;
+
+  /// need to override getDuration and getCurrentPosition to return according to the book instead of the current track
+  /// this is because the book can be a list of audio files and the player is only aware of the current track
+  /// so we need to calculate the duration and current position based on the book
+  @override
+  Future<Duration?> getDuration() async {
+    if (_book == null) {
+      return null;
+    }
+    return _book!.tracks.fold<Duration>(
+      Duration.zero,
+      (previousValue, element) => previousValue + element.duration,
+    );
+  }
+
+  @override
+  Future<Duration?> getCurrentPosition() async {
+    if (_book == null) {
+      return null;
+    }
+    var currentTrack = _book!.tracks[_currentIndex];
+    var currentTrackDuration = currentTrack.duration;
+    var currentTrackPosition = await super.getCurrentPosition();
+    return currentTrackPosition != null
+        ? currentTrackPosition + currentTrackDuration
+        : null;
+  }
+}