Add player skeleton and playback service

This introduces a dependency on audio_service and implements the
playback service using that package. The UI was adapted to the new
interface.

android/app/build.gradle

@@ -50,6 +50,8 @@ android {
             // TODO: Add your own signing config for the release build.
             // Signing with the debug keys for now, so `flutter run --release` works.
             signingConfig signingConfigs.debug
+            // See https://github.com/ryanheise/audio_service/blob/master/README.md#android-setup
+            shrinkResources false
         }
     }
 }

android/app/src/main/AndroidManifest.xml

@@ -1,6 +1,9 @@
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="de.johrpan.musicus">
 
+    <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
+    <uses-permission android:name="android.permission.WAKE_LOCK" />
+
     <application
         android:name="io.flutter.app.FlutterApplication"
         android:label="Musicus"
@@ -21,6 +24,18 @@
             </intent-filter>
         </activity>
 
+        <service android:name="com.ryanheise.audioservice.AudioService">
+            <intent-filter>
+               <action android:name="android.media.browse.MediaBrowserService" />
+            </intent-filter>
+        </service>
+
+        <receiver android:name="androidx.media.session.MediaButtonReceiver" >
+            <intent-filter>
+               <action android:name="android.intent.action.MEDIA_BUTTON" />
+            </intent-filter>
+        </receiver>
+
         <meta-data
             android:name="flutterEmbedding"
             android:value="2" />

lib/app.dart

@@ -93,13 +93,13 @@ class _ContentState extends State<Content> with SingleTickerProviderStateMixin {
     super.didChangeDependencies();
 
     backend = Backend.of(context);
-    playerBarAnimation.value = backend.playerActive.value ? 1.0 : 0.0;
+    playerBarAnimation.value = backend.player.active.value ? 1.0 : 0.0;
 
     if (playerActiveSubscription != null) {
       playerActiveSubscription.cancel();
     }
 
-    playerActiveSubscription = backend.playerActive.listen((active) =>
+    playerActiveSubscription = backend.player.active.listen((active) =>
         active ? playerBarAnimation.forward() : playerBarAnimation.reverse());
   }
 

lib/backend.dart

@@ -8,10 +8,10 @@ import 'package:moor/moor.dart';
 import 'package:moor_ffi/moor_ffi.dart';
 import 'package:path/path.dart' as p;
 import 'package:path_provider/path_provider.dart' as pp;
-import 'package:rxdart/rxdart.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 
 import 'database.dart';
+import 'player.dart';
 
 // The following code was taken from
 // https://moor.simonbinder.eu/docs/advanced-features/isolates/ and just
@@ -81,9 +81,7 @@ class Backend extends StatefulWidget {
 class BackendState extends State<Backend> {
   static const _platform = MethodChannel('de.johrpan.musicus/platform');
 
-  final playerActive = BehaviorSubject.seeded(false);
+  final player = Player();
-  final playing = BehaviorSubject.seeded(false);
-  final position = BehaviorSubject.seeded(0.0);
 
   BackendStatus status = BackendStatus.loading;
   Database db;
@@ -109,6 +107,7 @@ class BackendState extends State<Backend> {
   Future<void> _load() async {
     _moorIsolate = await _createMoorIsolate();
     final dbConnection = await _moorIsolate.connect();
+    player.setup();
     db = Database.connect(dbConnection);
 
     _shPref = await SharedPreferences.getInstance();
@@ -142,32 +141,6 @@ class BackendState extends State<Backend> {
     }
   }
 
-  void startPlayer() {
-    playerActive.add(true);
-  }
-
-  void playPause() {
-    playing.add(!playing.value);
-    if (playing.value) {
-      simulatePlay();
-    }
-  }
-
-  void seekTo(double pos) {
-    position.add(pos);
-  }
-
-  Future<void> simulatePlay() async {
-    while (playing.value) {
-      await Future.delayed(Duration(milliseconds: 200));
-      if (position.value >= 0.99) {
-        position.add(0.0);
-      } else {
-        position.add(position.value + 0.01);
-      }
-    }
-  }
-
   @override
   void dispose() {
     super.dispose();

lib/main.dart

@@ -1,10 +1,13 @@
+import 'package:audio_service/audio_service.dart';
 import 'package:flutter/widgets.dart';
 
 import 'app.dart';
 import 'backend.dart';
 
 void main() {
-  runApp(Backend(
+  runApp(AudioServiceWidget(
+    child: Backend(
       child: App(),
+    ),
   ));
 }

lib/player.dart

@@ -0,0 +1,249 @@
+import 'dart:async';
+
+import 'package:audio_service/audio_service.dart';
+import 'package:rxdart/rxdart.dart';
+
+/// Entrypoint for the playback service.
+void _playbackServiceEntrypoint() {
+  AudioServiceBackground.run(() => _PlaybackService());
+}
+
+class Player {
+  /// The interval between playback position updates in milliseconds.
+  static const positionUpdateInterval = 250;
+
+  /// Whether the player is active.
+  ///
+  /// This means, that there is at least one item in the queue and the playback
+  /// service is ready to play.
+  final active = BehaviorSubject.seeded(false);
+
+  /// Whether we are currently playing or not.
+  ///
+  /// This will be false, if the player is not active.
+  final playing = BehaviorSubject.seeded(false);
+
+  /// Current playback position.
+  ///
+  /// If the player is not active, this will default to zero.
+  final position = BehaviorSubject.seeded(const Duration());
+
+  /// Duration of the current track.
+  ///
+  /// If the player is not active, the duration will default to 1 s.
+  final duration = BehaviorSubject.seeded(const Duration(seconds: 1));
+
+  /// Playback position normalized to the range from zero to one.
+  final normalizedPosition = BehaviorSubject.seeded(0.0);
+
+  /// The current position in milliseconds.
+  int _positionMs = 0;
+
+  StreamSubscription<PlaybackState> _stateStreamSubscription;
+  StreamSubscription<MediaItem> _mediaItemStreamSubscription;
+
+  /// Update [position] and [normalizedPosition] according to [_positionMs].
+  void _updatePosition() {
+    position.add(Duration(milliseconds: _positionMs));
+    normalizedPosition.add(_positionMs / duration.value.inMilliseconds);
+  }
+
+  /// Set everything to its default because the playback service was stopped.
+  void _stop() {
+    active.add(false);
+    playing.add(false);
+    position.add(const Duration());
+    duration.add(const Duration(seconds: 1));
+    normalizedPosition.add(0.0);
+    _positionMs = 0;
+    _stateStreamSubscription.cancel();
+    _mediaItemStreamSubscription.cancel();
+  }
+
+  /// Start playback service.
+  Future<void> start() async {
+    if (!AudioService.running) {
+      await AudioService.start(
+        backgroundTaskEntrypoint: _playbackServiceEntrypoint,
+        androidNotificationChannelName: 'Musicus playback',
+        androidNotificationChannelDescription:
+            'Keeps Musicus playing in the background',
+        androidNotificationIcon: 'drawable/ic_notification',
+      );
+
+      setup();
+    }
+  }
+
+  /// Connect listeners and initialize streams.
+  void setup() {
+    if (AudioService.running) {
+      active.add(true);
+
+      _stateStreamSubscription =
+          AudioService.playbackStateStream.listen((playbackState) {
+        if (playbackState != null) {
+          if (playbackState.basicState == BasicPlaybackState.stopped) {
+            _stop();
+          } else {
+            if (playbackState.basicState == BasicPlaybackState.playing) {
+              playing.add(true);
+              _play();
+            } else {
+              playing.add(false);
+            }
+
+            _positionMs = playbackState.currentPosition;
+            _updatePosition();
+          }
+        }
+      });
+
+      _mediaItemStreamSubscription =
+          AudioService.currentMediaItemStream.listen((mediaItem) {
+        if (mediaItem?.duration != null) {
+          duration.add(Duration(milliseconds: mediaItem.duration));
+        }
+      });
+    }
+  }
+
+  /// Toggle whether the player is playing or paused.
+  ///
+  /// If the player is not active, this will do nothing.
+  Future<void> playPause() async {
+    if (active.value) {
+      if (playing.value) {
+        await AudioService.pause();
+      } else {
+        await AudioService.play();
+      }
+    }
+  }
+
+  /// Regularly update [_positionMs] while playing.
+  // TODO: Maybe find a better approach on handling this.
+  Future<void> _play() async {
+    while (playing.value) {
+      await Future.delayed(Duration(milliseconds: positionUpdateInterval));
+      _positionMs += positionUpdateInterval;
+      _updatePosition();
+    }
+  }
+
+  /// Seek to [pos], which is a value between (and including) zero and one.
+  ///
+  /// If the player is not active or an invalid value is provided, this will do
+  /// nothing.
+  Future<void> seekTo(double pos) async {
+    if (active.value && pos >= 0.0 && pos <= 1.0) {
+      final durationMs = duration.value.inMilliseconds;
+      await AudioService.seekTo((pos * durationMs).floor());
+    }
+  }
+
+  /// Tidy up.
+  void dispose() {
+    _stateStreamSubscription.cancel();
+    _mediaItemStreamSubscription.cancel();
+
+    active.close();
+    playing.close();
+    position.close();
+    duration.close();
+    normalizedPosition.close();
+  }
+}
+
+class _PlaybackService extends BackgroundAudioTask {
+  static const playControl = MediaControl(
+    androidIcon: 'drawable/ic_play',
+    label: 'Play',
+    action: MediaAction.play,
+  );
+
+  static const pauseControl = MediaControl(
+    androidIcon: 'drawable/ic_pause',
+    label: 'Pause',
+    action: MediaAction.pause,
+  );
+
+  static const stopControl = MediaControl(
+    androidIcon: 'drawable/ic_stop',
+    label: 'Stop',
+    action: MediaAction.stop,
+  );
+
+  static const dummyMediaItem = MediaItem(
+    id: 'dummy',
+    album: 'Johannes Brahms',
+    title: 'Symphony No. 1 in C minor, Op. 68: 1. Un poco sostenuto — Allegro',
+    duration: 10000,
+  );
+
+  final _completer = Completer();
+
+  int _position;
+  int _updateTime;
+  bool _playing = false;
+
+  void _setPosition(int position) {
+    _position = position;
+    _updateTime = DateTime.now().millisecondsSinceEpoch;
+  }
+
+  void _setState() {
+    AudioServiceBackground.setState(
+      controls:
+          _playing ? [pauseControl, stopControl] : [playControl, stopControl],
+      basicState:
+          _playing ? BasicPlaybackState.playing : BasicPlaybackState.paused,
+      position: _position,
+      updateTime: _updateTime,
+    );
+
+    AudioServiceBackground.setMediaItem(dummyMediaItem);
+  }
+
+  @override
+  Future<void> onStart() async {
+    _setPosition(0);
+    _setState();
+    await _completer.future;
+  }
+
+  @override
+  void onPlay() {
+    super.onPlay();
+
+    _playing = true;
+    _setState();
+  }
+
+  @override
+  void onPause() {
+    super.onPause();
+
+    _playing = false;
+    _setState();
+  }
+
+  @override
+  void onSeekTo(int position) {
+    super.onSeekTo(position);
+
+    _setPosition(position);
+    _setState();
+  }
+
+  @override
+  void onStop() {
+    AudioServiceBackground.setState(
+      controls: [],
+      basicState: BasicPlaybackState.stopped,
+    );
+
+    // This will end onStart.
+    _completer.complete();
+  }
+}

lib/screens/home.dart

@@ -34,7 +34,7 @@ class HomeScreen extends StatelessWidget {
             ],
             onSelected: (selected) {
               if (selected == 0) {
-                backend.startPlayer();
+                backend.player.start();
               } else if (selected == 1) {
                 Navigator.push(
                   context,

lib/screens/program.dart

@@ -26,7 +26,7 @@ class _ProgramScreenState extends State<ProgramScreen> {
       positionSubscription.cancel();
     }
 
-    positionSubscription = backend.position.listen((pos) {
+    positionSubscription = backend.player.normalizedPosition.listen((pos) {
       if (!seeking) {
         setState(() {
           position = pos;
@@ -56,7 +56,7 @@ class _ProgramScreenState extends State<ProgramScreen> {
               },
               onChangeEnd: (pos) {
                 seeking = false;
-                backend.seekTo(pos);
+                backend.player.seekTo(pos);
               },
               onChanged: (pos) {
                 setState(() {
@@ -68,7 +68,16 @@ class _ProgramScreenState extends State<ProgramScreen> {
               children: <Widget>[
                 Padding(
                   padding: const EdgeInsets.only(left: 24.0),
-                  child: Text('4:00'),
+                  child: StreamBuilder<Duration>(
+                    stream: backend.player.position,
+                    builder: (context, snapshot) {
+                      if (snapshot.hasData) {
+                        return DurationText(snapshot.data);
+                      } else {
+                        return Container();
+                      }
+                    },
+                  ),
                 ),
                 Spacer(),
                 IconButton(
@@ -83,7 +92,16 @@ class _ProgramScreenState extends State<ProgramScreen> {
                 Spacer(),
                 Padding(
                   padding: const EdgeInsets.only(right: 20.0),
-                  child: Text('10:30'),
+                  child: StreamBuilder<Duration>(
+                    stream: backend.player.duration,
+                    builder: (context, snapshot) {
+                      if (snapshot.hasData) {
+                        return DurationText(snapshot.data);
+                      } else {
+                        return Container();
+                      }
+                    },
+                  ),
                 ),
               ],
             ),
@@ -99,3 +117,19 @@ class _ProgramScreenState extends State<ProgramScreen> {
     positionSubscription.cancel();
   }
 }
+
+class DurationText extends StatelessWidget {
+  final Duration duration;
+
+  DurationText(this.duration);
+
+  @override
+  Widget build(BuildContext context) {
+    final minutes = duration.inMinutes;
+    final seconds = (duration - Duration(minutes: minutes)).inSeconds;
+
+    final secondsString = seconds >= 10 ? seconds.toString() : '0$seconds';
+
+    return Text('$minutes:$secondsString');
+  }
+}

lib/widgets/play_pause_button.dart

@@ -30,13 +30,13 @@ class _PlayPauseButtonState extends State<PlayPauseButton>
     super.didChangeDependencies();
 
     backend = Backend.of(context);
-    playPauseAnimation.value = backend.playing.value ? 1.0 : 0.0;
+    playPauseAnimation.value = backend.player.playing.value ? 1.0 : 0.0;
 
     if (playingSubscription != null) {
       playingSubscription.cancel();
     }
 
-    playingSubscription = backend.playing.listen((playing) =>
+    playingSubscription = backend.player.playing.listen((playing) =>
         playing ? playPauseAnimation.forward() : playPauseAnimation.reverse());
   }
 
@@ -47,7 +47,7 @@ class _PlayPauseButtonState extends State<PlayPauseButton>
         icon: AnimatedIcons.play_pause,
         progress: playPauseAnimation,
       ),
-      onPressed: backend.playPause,
+      onPressed: backend.player.playPause,
     );
   }
 

lib/widgets/player_bar.dart

@@ -16,7 +16,7 @@ class PlayerBar extends StatelessWidget {
           mainAxisSize: MainAxisSize.min,
           children: <Widget>[
             StreamBuilder(
-              stream: backend.position,
+              stream: backend.player.normalizedPosition,
               builder: (context, snapshot) => LinearProgressIndicator(
                 value: snapshot.data,
               ),

pubspec.yaml

@@ -9,6 +9,7 @@ environment:
   sdk: ">=2.3.0 <3.0.0"
 
 dependencies:
+  audio_service:
   flutter:
     sdk: flutter
   moor: