player: Publish position and duration information

A new method getPosition was introduced and the setUri method returns
the duration of the new track now.

musicus_player/android/src/main/kotlin/de/johrpan/musicus_player/MusicusPlayerPlugin.kt

@@ -40,10 +40,13 @@ public class MusicusPlayerPlugin: FlutterPlugin, MethodCallHandler {
         channel.invokeMethod("onComplete", null)
       }
 
-      result.success(null)
+      result.success(mediaPlayer?.getDuration())
     } else if (call.method == "play") {
       mediaPlayer?.start()
       result.success(null)
+    } else if (call.method == "getPosition") {
+      // TODO: Check, if mediaPlayer is in a valid state.
+      result.success(mediaPlayer?.getCurrentPosition())
     } else if (call.method == "pause") {
       mediaPlayer?.pause()
       result.success(null)

musicus_player/lib/musicus_player.dart

@@ -13,7 +13,9 @@ class MusicusPlayer {
   ///
   /// This will do nothing, until [setUri] was called. If the player reaches
   /// the end of the current audio file, [onComplete] will be called.
-  MusicusPlayer({this.onComplete}) {
+  MusicusPlayer({
+    this.onComplete,
+  }) {
     _channel.setMethodCallHandler(_handleMethodCall);
   }
 
@@ -25,10 +27,11 @@ class MusicusPlayer {
 
   /// Set URI of the audio file to play.
   ///
-  /// If the player will always stop doing, what it did before, and start
-  /// playing from the provided URI if possible.
-  Future<void> setUri(String uri) async {
-    await _channel.invokeMethod('setUri', {'uri': uri});
+  /// The player will always stop doing, what it did before, and start
+  /// playing from the provided URI if possible. The return value is the
+  /// duration of the new track in milliseconds.
+  Future<int> setUri(String uri) async {
+    return await _channel.invokeMethod('setUri', {'uri': uri});
   }
 
   /// Play from the current URI and resume playback if previously paused.
@@ -36,6 +39,11 @@ class MusicusPlayer {
     await _channel.invokeMethod('play');
   }
 
+  /// Get the current playback position in milliseconds.
+  Future<int> getPosition() async {
+    return await _channel.invokeMethod('getPosition');
+  }
+
   /// Pause playback.
   Future<void> pause() async {
     await _channel.invokeMethod('pause');