musicus_player: Add basic playback functionality

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

@@ -1,5 +1,9 @@
 package de.johrpan.musicus_player
 
+import android.content.Context
+import android.media.MediaPlayer
+import android.net.Uri
+
 import androidx.annotation.NonNull;
 
 import io.flutter.embedding.engine.plugins.FlutterPlugin
@@ -11,14 +15,41 @@ import io.flutter.plugin.common.PluginRegistry.Registrar
 
 public class MusicusPlayerPlugin: FlutterPlugin, MethodCallHandler {
   private lateinit var channel: MethodChannel
+  private lateinit var context: Context
+
+  private var uri: Uri? = null
+  private var mediaPlayer: MediaPlayer? = null
 
   override fun onAttachedToEngine(@NonNull flutterPluginBinding: FlutterPlugin.FlutterPluginBinding) {
     channel = MethodChannel(flutterPluginBinding.getFlutterEngine().getDartExecutor(), "de.johrpan.musicus_player/platform")
-    channel.setMethodCallHandler(this);
+    channel.setMethodCallHandler(this)
+    context = flutterPluginBinding.getApplicationContext()
   }
 
   override fun onMethodCall(@NonNull call: MethodCall, @NonNull result: Result) {
-    // TODO: Implement.
+    if (call.method == "setUri") {
+      val newUri = Uri.parse(call.argument<String>("uri"))
+      uri = newUri
+
+      if (mediaPlayer != null) {
+        mediaPlayer?.release()
+      }
+
+      mediaPlayer = MediaPlayer.create(context, uri)
+      mediaPlayer?.setOnCompletionListener {
+        channel.invokeMethod("onComplete", null)
+      }
+
+      result.success(null)
+    } else if (call.method == "play") {
+      mediaPlayer?.start()
+      result.success(null)
+    } else if (call.method == "pause") {
+      mediaPlayer?.pause()
+      result.success(null)
+    } else {
+      result.notImplemented()
+    }
   }
 
   override fun onDetachedFromEngine(@NonNull binding: FlutterPlugin.FlutterPluginBinding) {

musicus_player/lib/musicus_player.dart

@@ -1,13 +1,43 @@
 import 'package:flutter/services.dart';
 
+/// A simple music player.
+/// 
+/// Give it an URI using [setUri] and it will start playing.
 class MusicusPlayer {
+  /// Called, when the player reaches the end of the audio file.
+  final void Function() onComplete;
+
   final _channel = MethodChannel('de.johrpan.musicus_player/platform');
 
-  MusicusPlayer() {
+  /// Create a new player.
+  /// 
+  /// 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}) {
     _channel.setMethodCallHandler(_handleMethodCall);
   }
 
-  Future<void> _handleMethodCall(MethodCall call) {
-    // TODO: Implement.
+  Future<void> _handleMethodCall(MethodCall call) async {
+    if (call.method == 'onComplete' && onComplete != null) {
+      onComplete();
+    }
+  }
+
+  /// 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});
+  }
+
+  /// Play from the current URI and resume playback if previously paused.
+  Future<void> play() async {
+    await _channel.invokeMethod('play');
+  }
+
+  /// Pause playback.
+  Future<void> pause() async {
+    await _channel.invokeMethod('pause');
   }
 }