basic audiobook player

lib/features/player/playlist.dart

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+import 'package:shelfsdk/audiobookshelf_api.dart';
+
+/// will manage the playlist of items
+///
+/// you are responsible for updating the current index and sub index
+class AudiobookPlaylist {
+  /// list of items in the playlist
+  final List<BookExpanded> books;
+
+  /// current index of the item in the playlist
+  int _currentIndex;
+
+  /// current index of the audio file in the current item
+  int _subCurrentIndex;
+
+  // wrappers for adding and removing items
+  void add(BookExpanded item) => books.add(item);
+  void remove(BookExpanded item) => books.remove(item);
+  void clear() {
+    books.clear();
+    _currentIndex = 0;
+    _subCurrentIndex = 0;
+  }
+
+  // move an item from one index to another
+  void move(int from, int to) {
+    final item = books.removeAt(from);
+    books.insert(to, item);
+  }
+
+  /// the book being played
+  BookExpanded? get currentBook {
+    if (_currentIndex >= books.length || _currentIndex < 0 || books.isEmpty) {
+      return null;
+    }
+    return books[_currentIndex];
+  }
+
+  /// of the book in the playlist
+  int get currentIndex => _currentIndex;
+  // every time current index changes, we need to update the sub index
+  set currentIndex(int index) {
+    // if the index is the same, do nothing
+    if (_currentIndex == index) {
+      return;
+    }
+    _currentIndex = index;
+    subCurrentIndex = 0;
+  }
+
+  /// of the audio file in the current book
+  int get subCurrentIndex => _subCurrentIndex;
+
+  set subCurrentIndex(int index) {
+    if (index < 0) {
+      index = 0;
+    }
+    _subCurrentIndex = index;
+  }
+
+  AudiobookPlaylist({
+    this.books = const [],
+    currentIndex = 0,
+    subCurrentIndex = 0,
+  })  : _currentIndex = currentIndex,
+        _subCurrentIndex = subCurrentIndex;
+
+  // most important method, gets the audio file to play
+  // this is needed as a library item is a list of audio files
+  AudioTrack? getAudioTrack() {
+    final book = currentBook;
+    if (book == null) {
+      return null;
+    }
+
+    if (subCurrentIndex > book.tracks.length || book.tracks.isEmpty) {
+      return null;
+    }
+    return book.tracks[subCurrentIndex];
+  }
+
+  bool get isBookFinished => subCurrentIndex >= currentBook!.tracks.length;
+
+  // a method to get the next audio file and advance the sub index
+}