Simple playback status and controls in Android Auto

Expose a MediaBrowserService from within the existing PlayerService,
and use the existing MediaSession for Auto.

Empty media browser for now.

To test, one needs to enable "Unknown sources" in Android Auto's
developer settings.

Issue: #1758

Author: haggaie

app/src/main/AndroidManifest.xml

@@ -47,11 +47,14 @@
 
         <service
             android:name=".player.PlayerService"
-            android:exported="false"
+            android:exported="true"
             android:foregroundServiceType="mediaPlayback">
             <intent-filter>
                 <action android:name="android.intent.action.MEDIA_BUTTON" />
             </intent-filter>
+            <intent-filter>
+                <action android:name="android.media.browse.MediaBrowserService"/>
+            </intent-filter>
         </service>
 
         <activity

app/src/main/java/org/schabi/newpipe/player/PlayerService.java

@@ -21,21 +21,28 @@
 
 import static org.schabi.newpipe.util.Localization.assureCorrectAppLanguage;
 
-import android.app.Service;
 import android.content.Context;
 import android.content.Intent;
 import android.os.Binder;
+import android.os.Bundle;
 import android.os.IBinder;
+import android.support.v4.media.MediaBrowserCompat.MediaItem;
 import android.util.Log;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
+import androidx.media.MediaBrowserServiceCompat;
+
 import org.schabi.newpipe.player.mediasession.MediaSessionPlayerUi;
 import org.schabi.newpipe.util.ThemeHelper;
 
+import java.util.ArrayList;
+import java.util.List;
 
 /**
  * One service for all players.
  */
-public final class PlayerService extends Service {
+public final class PlayerService extends MediaBrowserServiceCompat {
     private static final String TAG = PlayerService.class.getSimpleName();
     private static final boolean DEBUG = Player.DEBUG;
 
@@ -50,6 +57,8 @@ public final class PlayerService extends Service {
 
     @Override
     public void onCreate() {
+        super.onCreate();
+
         if (DEBUG) {
             Log.d(TAG, "onCreate() called");
         }
@@ -133,6 +142,9 @@ protected void attachBaseContext(final Context base) {
 
     @Override
     public IBinder onBind(final Intent intent) {
+        if (SERVICE_INTERFACE.equals(intent.getAction())) {
+            return super.onBind(intent);
+        }
         return mBinder;
     }
 
@@ -146,4 +158,29 @@ public Player getPlayer() {
             return PlayerService.this.player;
         }
     }
+
+    // MediaBrowserServiceCompat methods
+
+    @NonNull
+    private static final String MY_MEDIA_ROOT_ID = "media_root_id";
+
+    @Nullable
+    @Override
+    public BrowserRoot onGetRoot(@NonNull final String clientPackageName, final int clientUid,
+                                 @Nullable final Bundle rootHints) {
+        Log.d(TAG, String.format("MediaBrowserService.onGetRoot(%s, %s, %s)",
+                                 clientPackageName, clientUid, rootHints));
+
+        return new MediaBrowserServiceCompat.BrowserRoot(MY_MEDIA_ROOT_ID, null);
+    }
+
+    @Override
+    public void onLoadChildren(@NonNull final String parentId,
+                               @NonNull final Result<List<MediaItem>> result) {
+        Log.d(TAG, String.format("MediaBrowserService.onLoadChildren(%s)", parentId));
+
+        final List<MediaItem> mediaItems = new ArrayList<>();
+
+        result.sendResult(mediaItems);
+    }
 }

app/src/main/java/org/schabi/newpipe/player/mediasession/MediaSessionPlayerUi.java

@@ -40,6 +40,7 @@ public void initPlayer() {
 
         mediaSession = new MediaSessionCompat(context, TAG);
         mediaSession.setActive(true);
+        player.getService().setSessionToken(mediaSession.getSessionToken());
 
         sessionConnector = new MediaSessionConnector(mediaSession);
         sessionConnector.setQueueNavigator(new PlayQueueNavigator(mediaSession, player));