Always return empty timeline when wrapped player is empty

In `PlayerWrapper.getCurrentTimelineWithCommandCheck()` we
always return `new CurrentMediaItemOnlyTimeline(this)` in
case the wrapped player doesn't have `COMMAND_GET_TIMELINE`
available but has `COMMAND_GET_CURRENT_MEDIA_ITEM`. This is
emulating a single item timeline with a static window count
of 1 which isn't correct when the wrapped player is empty.

Instead, when the wrapped player is empty we need to return
an empty timeline to match the wrapped player.

Issue: #2320
PiperOrigin-RevId: 746071237

Author: marcbaechinger

RELEASENOTES.md

@@ -68,6 +68,11 @@
         configure this value.
     *   Fix issue where notifications reappear after they have been dismissed by
         the user ([#2302](https://github.com/androidx/media/issues/2302)).
+    *   Fix a bug where the `PlayerWrapper` returned a single-item timeline when
+        the wrapped player is actually empty. This happened when the wrapped
+        player doesn't have `COMMAND_GET_TIMELINE` available while
+        `COMMAND_GET_CURRENT_MEDIA_ITEM` is available and the wrapped player is
+        empty ([#2320](https://github.com/androidx/media/issues/2320)).
 *   UI:
     *   Enable `PlayerSurface` to work with `ExoPlayer.setVideoEffects` and
         `CompositionPlayer`.

libraries/session/src/main/java/androidx/media3/session/PlayerWrapper.java

@@ -670,7 +670,9 @@ public Timeline getCurrentTimelineWithCommandCheck() {
     if (isCommandAvailable(COMMAND_GET_TIMELINE)) {
       return getCurrentTimeline();
     } else if (isCommandAvailable(COMMAND_GET_CURRENT_MEDIA_ITEM)) {
-      return new CurrentMediaItemOnlyTimeline(this);
+      return getCurrentTimeline().isEmpty()
+          ? Timeline.EMPTY
+          : new CurrentMediaItemOnlyTimeline(this);
     }
     return Timeline.EMPTY;
   }

libraries/session/src/test/java/androidx/media3/session/PlayerWrapperTest.java

@@ -22,6 +22,8 @@
 import android.os.Bundle;
 import android.os.Looper;
 import androidx.media3.common.Player;
+import androidx.media3.common.Timeline;
+import androidx.media3.test.utils.FakeTimeline;
 import androidx.test.ext.junit.runners.AndroidJUnit4;
 import com.google.common.collect.ImmutableList;
 import org.junit.Before;
@@ -57,6 +59,52 @@ public void setUp() {
     when(player.getApplicationLooper()).thenReturn(Looper.myLooper());
   }
 
+  @Test
+  public void
+      getCurrentTimelineWithCommandCheck_withoutCommandGetTimelineAndGetCurrentMediaItem_isEmpty() {
+    when(player.isCommandAvailable(Player.COMMAND_GET_TIMELINE)).thenReturn(false);
+    when(player.isCommandAvailable(Player.COMMAND_GET_CURRENT_MEDIA_ITEM)).thenReturn(false);
+    when(player.getCurrentTimeline()).thenReturn(new FakeTimeline(/* windowCount= */ 3));
+
+    Timeline currentTimeline = playerWrapper.getCurrentTimelineWithCommandCheck();
+
+    assertThat(currentTimeline.isEmpty()).isTrue();
+  }
+
+  @Test
+  public void getCurrentTimelineWithCommandCheck_withoutCommandGetTimelineWhenEmpty_isEmpty() {
+    when(player.isCommandAvailable(Player.COMMAND_GET_TIMELINE)).thenReturn(false);
+    when(player.isCommandAvailable(Player.COMMAND_GET_CURRENT_MEDIA_ITEM)).thenReturn(true);
+    when(player.getCurrentTimeline()).thenReturn(Timeline.EMPTY);
+
+    Timeline currentTimeline = playerWrapper.getCurrentTimelineWithCommandCheck();
+
+    assertThat(currentTimeline.isEmpty()).isTrue();
+  }
+
+  @Test
+  public void
+      getCurrentTimelineWithCommandCheck_withoutCommandGetTimelineWhenMultipleItems_hasSingleItemTimeline() {
+    when(player.isCommandAvailable(Player.COMMAND_GET_TIMELINE)).thenReturn(false);
+    when(player.isCommandAvailable(Player.COMMAND_GET_CURRENT_MEDIA_ITEM)).thenReturn(true);
+    when(player.getCurrentTimeline()).thenReturn(new FakeTimeline(/* windowCount= */ 3));
+
+    Timeline currentTimeline = playerWrapper.getCurrentTimelineWithCommandCheck();
+
+    assertThat(currentTimeline.getWindowCount()).isEqualTo(1);
+  }
+
+  @Test
+  public void getCurrentTimelineWithCommandCheck_withCommandGetTimeline_returnOriginalTimeline() {
+    when(player.isCommandAvailable(Player.COMMAND_GET_TIMELINE)).thenReturn(true);
+    when(player.isCommandAvailable(Player.COMMAND_GET_CURRENT_MEDIA_ITEM)).thenReturn(false);
+    when(player.getCurrentTimeline()).thenReturn(new FakeTimeline(/* windowCount= */ 3));
+
+    Timeline currentTimeline = playerWrapper.getCurrentTimelineWithCommandCheck();
+
+    assertThat(currentTimeline.getWindowCount()).isEqualTo(3);
+  }
+
   @Test
   public void createSessionPositionInfoForBundling() {
     int testAdGroupIndex = 12;