fix: race condition causes multiple songs to play at the same time (#43)

lib/providers/audio_provider.dart

@@ -10,10 +10,12 @@ import 'package:app/utils/preferences.dart' as preferences;
 import 'package:assets_audio_player/assets_audio_player.dart';
 import 'package:flutter/cupertino.dart';
 import 'package:rxdart/rxdart.dart';
+import 'package:mutex/mutex.dart';
 
 class AudioProvider with StreamSubscriber, ChangeNotifier {
   SongProvider _songProvider;
   InteractionProvider _interactionProvider;
+  Mutex _mutex;
 
   late AssetsAudioPlayer _player;
   AssetsAudioPlayer get player => _player;
@@ -22,7 +24,8 @@ class AudioProvider with StreamSubscriber, ChangeNotifier {
     required SongProvider songProvider,
     required InteractionProvider interactionProvider,
   })  : _songProvider = songProvider,
-        _interactionProvider = interactionProvider;
+        _interactionProvider = interactionProvider,
+        _mutex = Mutex();
 
   Future<void> init() async {
     _player = AssetsAudioPlayer.newPlayer();
@@ -72,23 +75,29 @@ class AudioProvider with StreamSubscriber, ChangeNotifier {
   }
 
   Future<void> play({Song? song}) async {
-    if (song == null) {
-      return await _player.play();
-    }
+    await _mutex.acquire();
 
-    int index = await indexInQueue(song);
+    try {
+      if (song == null) {
+        return await _player.play();
+      }
 
-    if (index != -1) {
-      await _player.playlistPlayAtIndex(index);
-    } else {
-      await _player.playlistPlayAtIndex(
-        _player.current.hasValue
-            ? await queueAfterCurrent(song: song)
-            : await queueToTop(song: song),
-      );
-    }
+      int index = await indexInQueue(song);
 
-    await _player.play();
+      if (index != -1) {
+        await _player.playlistPlayAtIndex(index);
+      } else {
+        await _player.playlistPlayAtIndex(
+          _player.current.hasValue
+              ? await queueAfterCurrent(song: song)
+              : await queueToTop(song: song),
+        );
+      }
+
+      await _player.play();
+    } finally {
+      _mutex.release();
+    }
   }
 
   Future<void> stop() async => await _player.stop();

pubspec.lock

@@ -457,6 +457,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "5.0.12"
+  mutex:
+    dependency: "direct main"
+    description:
+      name: mutex
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "3.0.0"
   nested:
     dependency: transitive
     description:

pubspec.yaml

@@ -47,6 +47,7 @@ dependencies:
   uuid: ^3.0.4
   golden_toolkit: ^0.9.0
   fake_async: ^1.2.0
+  mutex: ^3.0.0
 
 dev_dependencies:
   flutter_test: