feat: get duration from audio pool

packages/audioplayers/lib/src/audio_pool.dart

@@ -41,6 +41,9 @@ class AudioPool {
   /// returned to the pool.
   final int maxPlayers;
 
+  @visibleForTesting
+  Duration? duration;
+
   final Lock _lock = Lock();
 
   AudioPool._({
@@ -94,10 +97,7 @@ class AudioPool {
   /// Starts playing the audio, returns a function that can stop the audio.
   Future<StopFunction> start({double volume = 1.0}) async {
     return _lock.synchronized(() async {
-      if (availablePlayers.isEmpty) {
-        availablePlayers.add(await _createNewAudioPlayer());
-      }
-      final player = availablePlayers.removeAt(0);
+      final player = await _createNewOrReserveAnAvailablePlayer();
       currentPlayers[player.playerId] = player;
       await player.setVolume(volume);
       await player.resume();
@@ -125,6 +125,34 @@ class AudioPool {
     });
   }
 
+  /// Returns the duration of the audio.
+  ///
+  /// If the duration is requested for the first time it will use the pool to
+  /// get or create a player and get the duration from it. Subsequent calls will
+  /// return the duration immediately.
+  Future<Duration?> getDuration() async {
+    if (duration != null) {
+      return duration;
+    }
+
+    return _lock.synchronized(() async {
+      final player = await _createNewOrReserveAnAvailablePlayer();
+      currentPlayers[player.playerId] = player;
+      duration = await player.getDuration();
+
+      final removedPlayer = currentPlayers.remove(player.playerId);
+      if (removedPlayer != null) {
+        if (availablePlayers.length >= maxPlayers) {
+          await removedPlayer.dispose();
+        } else {
+          availablePlayers.add(removedPlayer);
+        }
+      }
+
+      return duration;
+    });
+  }
+
   Future<AudioPlayer> _createNewAudioPlayer() async {
     final player = AudioPlayer()..audioCache = audioCache;
     if (audioContext != null) {
@@ -135,6 +163,13 @@ class AudioPool {
     return player;
   }
 
+  Future<AudioPlayer> _createNewOrReserveAnAvailablePlayer() async {
+    if (availablePlayers.isEmpty) {
+      return _createNewAudioPlayer();
+    }
+    return availablePlayers.removeAt(0);
+  }
+
   /// Disposes the audio pool. Then it cannot be used anymore.
   Future<void> dispose() =>
       Future.wait(availablePlayers.map((e) => e.dispose()));

packages/audioplayers/test/audio_pool_test.dart

@@ -79,5 +79,75 @@ void main() {
       expect(pool.availablePlayers.length, 3);
       expect(pool.currentPlayers.isEmpty, isTrue);
     });
+
+    test('gets duration', () async {
+      final pool = await AudioPool.createFromAsset(
+        path: 'audio.mp3',
+        maxPlayers: 3,
+        audioCache: FakeAudioCache(),
+      );
+      final duration = await pool.getDuration();
+      expect(duration, isA<Duration>());
+    });
+
+    test('getDuration adds an available player to the pool', () async {
+      final pool = await AudioPool.createFromAsset(
+        path: 'audio.mp3',
+        maxPlayers: 3,
+        audioCache: FakeAudioCache(),
+      );
+
+      final stop = await pool.start();
+      await Future.wait([
+        pool.getDuration(),
+        stop(),
+      ]);
+
+      expect(pool.availablePlayers.length, 2);
+      expect(pool.currentPlayers.isEmpty, isTrue);
+    });
+
+    test(
+        'Consecutive getDuration returns from cache and does not create player',
+        () async {
+      final pool = await AudioPool.createFromAsset(
+        path: 'audio.mp3',
+        maxPlayers: 3,
+        audioCache: FakeAudioCache(),
+      );
+
+      expect(pool.duration, isNull);
+
+      final durations = await Future.wait([
+        pool.getDuration(),
+        pool.getDuration(),
+      ]);
+
+      final durationFromNewPlayer = durations[0];
+      final durationFromCache = durations[1];
+
+      expect(pool.duration, isNotNull);
+      expect(durationFromNewPlayer, durationFromCache);
+
+      expect(pool.availablePlayers.length, 1);
+      expect(pool.currentPlayers.isEmpty, isTrue);
+    });
+
+    test('getDuration keeps the minPlayers/maxPlayers contract', () async {
+      final pool = await AudioPool.createFromAsset(
+        path: 'audio.mp3',
+        maxPlayers: 3,
+        audioCache: FakeAudioCache(),
+      );
+
+      final stopFunctions =
+          await Future.wait(List.generate(3, (_) => pool.start()));
+
+      await pool.getDuration();
+      await Future.wait(stopFunctions.map((f) => f()));
+
+      expect(pool.availablePlayers.length, 3);
+      expect(pool.currentPlayers.isEmpty, isTrue);
+    });
   });
 }