add ShuffleOrder.cloneAndSet() to provide startIndex to shuffle order

Shuffle order may want to ensure that the song that's going to be played
(was chosen by user) is also the first song in shuffle playlist, as that
makes sure all other songs will be playing afterwards. If first song gets
random position in shuffled playlist, playback may stop before playing
every song as it will start in the middle of shuffled list.

Author: nift4

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/ExoPlayerImpl.java

@@ -2513,12 +2513,8 @@ private void setMediaSourcesInternal(
     int currentWindowIndex = getCurrentWindowIndexInternal(playbackInfo);
     long currentPositionMs = getCurrentPosition();
     pendingOperationAcks++;
-    if (!mediaSourceHolderSnapshots.isEmpty()) {
-      removeMediaSourceHolders(
-          /* fromIndex= */ 0, /* toIndexExclusive= */ mediaSourceHolderSnapshots.size());
-    }
     List<MediaSourceList.MediaSourceHolder> holders =
-        addMediaSourceHolders(/* index= */ 0, mediaSources);
+        setMediaSourceHolders(mediaSources, startWindowIndex);
     Timeline timeline = createMaskingTimeline();
     if (!timeline.isEmpty() && startWindowIndex >= timeline.getWindowCount()) {
       throw new IllegalSeekPositionException(timeline, startWindowIndex, startPositionMs);
@@ -2564,6 +2560,21 @@ private void setMediaSourcesInternal(
         /* repeatCurrentMediaItem= */ false);
   }
 
+  private List<MediaSourceList.MediaSourceHolder> setMediaSourceHolders(
+      List<MediaSource> mediaSources, int startIndex) {
+    mediaSourceHolderSnapshots.clear();
+    List<MediaSourceList.MediaSourceHolder> holders = new ArrayList<>();
+    for (int i = 0; i < mediaSources.size(); i++) {
+      MediaSourceList.MediaSourceHolder holder =
+          new MediaSourceList.MediaSourceHolder(mediaSources.get(i), useLazyPreparation);
+      holders.add(holder);
+      mediaSourceHolderSnapshots.add(
+          i, new MediaSourceHolderSnapshot(holder.uid, holder.mediaSource));
+    }
+    shuffleOrder = shuffleOrder.cloneAndSet(/* insertionCount= */ holders.size(), startIndex);
+    return holders;
+  }
+
   private List<MediaSourceList.MediaSourceHolder> addMediaSourceHolders(
       int index, List<MediaSource> mediaSources) {
     List<MediaSourceList.MediaSourceHolder> holders = new ArrayList<>();

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/source/ShuffleOrder.java

@@ -284,6 +284,25 @@ default ShuffleOrder cloneAndMove(int indexFrom, int indexToExclusive, int newIn
     return this;
   }
 
+  /**
+   * Returns a copy of the shuffle order with all elements replaced.
+   *
+   * <p>The default implementation uses {@link #cloneAndClear} and {@link #cloneAndInsert(int, int)}
+   * to replace all elements in the shuffle order. Custom implementations can override this method
+   * if the first element in the shuffled order should be set to the one whose index in the
+   * unshuffled order is {@code startIndex}.
+   *
+   * @param insertionCount The number of elements.
+   * @param startIndex The index of the new element in the unshuffled order that should be the first
+   *     in the shuffled order or {@link C#INDEX_UNSET} if the the first element in the shuffled
+   *     order is not specified. It should be ignored if the new list is empty, or if it is larger
+   *     than the last index (inclusive) of the new list.
+   * @return A copy of this {@link ShuffleOrder} with the elements replaced.
+   */
+  default ShuffleOrder cloneAndSet(int insertionCount, int startIndex) {
+    return cloneAndClear().cloneAndInsert(0, insertionCount);
+  }
+
   /**
    * Returns a copy of the shuffle order with a range of elements removed.
    *