Allow moving media source within DynamicConcatenatingMediaSource.

This option allows to move the currently playing media source to another position
and also to move other media source without creating a new MediaSource object.

Issue:#1706

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=161402022

library/core/src/androidTest/java/com/google/android/exoplayer2/source/DynamicConcatenatingMediaSourceTest.java

@@ -85,6 +85,24 @@ public final class DynamicConcatenatingMediaSourceTest extends TestCase {
     TimelineAsserts.assertPeriodCounts(timeline, 2, 4, 1, 5, 6, 7, 3);
     TimelineAsserts.assertWindowIds(timeline, 222, 444, 111, 555, 666, 777, 333);
 
+    // Move sources.
+    mediaSource.moveMediaSource(2, 3);
+    waitForTimelineUpdate();
+    TimelineAsserts.assertPeriodCounts(timeline, 2, 4, 5, 1, 6, 7, 3);
+    TimelineAsserts.assertWindowIds(timeline, 222, 444, 555, 111, 666, 777, 333);
+    mediaSource.moveMediaSource(3, 2);
+    waitForTimelineUpdate();
+    TimelineAsserts.assertPeriodCounts(timeline, 2, 4, 1, 5, 6, 7, 3);
+    TimelineAsserts.assertWindowIds(timeline, 222, 444, 111, 555, 666, 777, 333);
+    mediaSource.moveMediaSource(0, 6);
+    waitForTimelineUpdate();
+    TimelineAsserts.assertPeriodCounts(timeline, 4, 1, 5, 6, 7, 3, 2);
+    TimelineAsserts.assertWindowIds(timeline, 444, 111, 555, 666, 777, 333, 222);
+    mediaSource.moveMediaSource(6, 0);
+    waitForTimelineUpdate();
+    TimelineAsserts.assertPeriodCounts(timeline, 2, 4, 1, 5, 6, 7, 3);
+    TimelineAsserts.assertWindowIds(timeline, 222, 444, 111, 555, 666, 777, 333);
+
     // Remove in the middle.
     mediaSource.removeMediaSource(3);
     waitForTimelineUpdate();
@@ -138,7 +156,9 @@ public final class DynamicConcatenatingMediaSourceTest extends TestCase {
     mediaSource.addMediaSource(childSources[0]);
     mediaSource.addMediaSource(childSources[1]);
     mediaSource.addMediaSource(0, childSources[2]);
-    mediaSource.removeMediaSource(1);
+    mediaSource.moveMediaSource(0, 2);
+    mediaSource.removeMediaSource(0);
+    mediaSource.moveMediaSource(1, 0);
     mediaSource.addMediaSource(1, childSources[3]);
     assertNull(timeline);
 

library/core/src/main/java/com/google/android/exoplayer2/source/DynamicConcatenatingMediaSource.java

@@ -44,6 +44,7 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
   private static final int MSG_ADD = 0;
   private static final int MSG_ADD_MULTIPLE = 1;
   private static final int MSG_REMOVE = 2;
+  private static final int MSG_MOVE = 3;
 
   // Accessed on the app thread.
   private final List<MediaSource> mediaSourcesPublic;
@@ -126,7 +127,8 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
   /**
    * Removes a {@link MediaSource} from the playlist.
    *
-   * @param index The index at which the media source will be removed.
+   * @param index The index at which the media source will be removed. This index must be in the
+   *     range of 0 <= index < {@link #getSize()}.
    */
   public synchronized void removeMediaSource(int index) {
     mediaSourcesPublic.remove(index);
@@ -135,6 +137,25 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
     }
   }
 
+  /**
+   * Moves an existing {@link MediaSource} within the playlist.
+   *
+   * @param currentIndex The current index of the media source in the playlist. This index must be
+   *     in the range of 0 <= index < {@link #getSize()}.
+   * @param newIndex The target index of the media source in the playlist. This index must be in the
+   *     range of 0 <= index < {@link #getSize()}.
+   */
+  public synchronized void moveMediaSource(int currentIndex, int newIndex) {
+    if (currentIndex == newIndex) {
+      return;
+    }
+    mediaSourcesPublic.add(newIndex, mediaSourcesPublic.remove(currentIndex));
+    if (player != null) {
+      player.sendMessages(new ExoPlayerMessage(this, MSG_MOVE,
+          Pair.create(currentIndex, newIndex)));
+    }
+  }
+
   /**
    * Returns the number of media sources in the playlist.
    */
@@ -225,6 +246,11 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
         removeMediaSourceInternal((Integer) message);
         break;
       }
+      case MSG_MOVE: {
+        Pair<Integer, Integer> messageData = (Pair<Integer, Integer>) message;
+        moveMediaSourceInternal(messageData.first, messageData.second);
+        break;
+      }
       default: {
         throw new IllegalStateException();
       }
@@ -304,6 +330,21 @@ public final class DynamicConcatenatingMediaSource implements MediaSource, ExoPl
     holder.mediaSource.releaseSource();
   }
 
+  private void moveMediaSourceInternal(int currentIndex, int newIndex) {
+    int startIndex = Math.min(currentIndex, newIndex);
+    int endIndex = Math.max(currentIndex, newIndex);
+    int windowOffset = mediaSourceHolders.get(startIndex).firstWindowIndexInChild;
+    int periodOffset = mediaSourceHolders.get(startIndex).firstPeriodIndexInChild;
+    mediaSourceHolders.add(newIndex, mediaSourceHolders.remove(currentIndex));
+    for (int i = startIndex; i <= endIndex; i++) {
+      MediaSourceHolder holder = mediaSourceHolders.get(i);
+      holder.firstWindowIndexInChild = windowOffset;
+      holder.firstPeriodIndexInChild = periodOffset;
+      windowOffset += holder.timeline.getWindowCount();
+      periodOffset += holder.timeline.getPeriodCount();
+    }
+  }
+
   private void correctOffsets(int startIndex, int windowOffsetUpdate, int periodOffsetUpdate) {
     windowCount += windowOffsetUpdate;
     periodCount += periodOffsetUpdate;