first commit

lib/services/progress_state_stream.dart

@@ -0,0 +1,25 @@
+import 'package:audio_service/audio_service.dart';
+import 'package:get_it/get_it.dart';
+import 'package:rxdart/rxdart.dart';
+
+import 'music_player_background_task.dart';
+
+class ProgressState {
+  final MediaItem? mediaItem;
+  final PlaybackState playbackState;
+  final Duration position;
+
+  ProgressState(this.mediaItem, this.playbackState, this.position);
+}
+
+/// Encapsulate all the different data we're interested in into a single
+/// stream so we don't have to nest StreamBuilders.
+Stream<ProgressState> get progressStateStream {
+  final audioHandler = GetIt.instance<MusicPlayerBackgroundTask>();
+  return Rx.combineLatest3<MediaItem?, PlaybackState, Duration, ProgressState>(
+      audioHandler.mediaItem,
+      audioHandler.playbackState,
+      AudioService.position.startWith(audioHandler.playbackState.value.position),
+      (mediaItem, playbackState, position) =>
+          ProgressState(mediaItem, playbackState, position));
+}