/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package com.google.android.exoplayer2;

import android.os.Handler;
import android.os.HandlerThread;
import android.os.Message;
import android.os.Process;
import android.os.SystemClock;
import android.util.Log;
import android.util.Pair;
import com.google.android.exoplayer2.ExoPlayer.ExoPlayerMessage;
import com.google.android.exoplayer2.source.MediaPeriod;
import com.google.android.exoplayer2.source.MediaSource;
import com.google.android.exoplayer2.source.SampleStream;
import com.google.android.exoplayer2.trackselection.TrackSelection;
import com.google.android.exoplayer2.trackselection.TrackSelections;
import com.google.android.exoplayer2.trackselection.TrackSelector;
import com.google.android.exoplayer2.util.Assertions;
import com.google.android.exoplayer2.util.MediaClock;
import com.google.android.exoplayer2.util.PriorityHandlerThread;
import com.google.android.exoplayer2.util.StandaloneMediaClock;
import com.google.android.exoplayer2.util.TraceUtil;
import com.google.android.exoplayer2.util.Util;
import java.io.IOException;

/**
 * Implements the internal behavior of {@link ExoPlayerImpl}.
 */
/* package */ final class ExoPlayerImplInternal<T> implements Handler.Callback,
    MediaPeriod.Callback, TrackSelector.InvalidationListener, MediaSource.Listener {

  /**
   * Playback position information which is read on the application's thread by
   * {@link ExoPlayerImpl} and read/written internally on the player's thread.
   */
  public static final class PlaybackInfo {

    public final int periodIndex;
    public final long startPositionUs;

    public volatile long positionUs;
    public volatile long bufferedPositionUs;

    public PlaybackInfo(int periodIndex, long startPositionUs) {
      this.periodIndex = periodIndex;
      this.startPositionUs = startPositionUs;
      positionUs = startPositionUs;
      bufferedPositionUs = startPositionUs;
    }

  }

  private static final String TAG = "ExoPlayerImplInternal";

  // External messages
  public static final int MSG_STATE_CHANGED = 1;
  public static final int MSG_LOADING_CHANGED = 2;
  public static final int MSG_SEEK_ACK = 3;
  public static final int MSG_POSITION_DISCONTINUITY = 4;
  public static final int MSG_SOURCE_INFO_REFRESHED = 5;
  public static final int MSG_ERROR = 6;

  // Internal messages
  private static final int MSG_PREPARE = 0;
  private static final int MSG_SET_PLAY_WHEN_READY = 1;
  private static final int MSG_DO_SOME_WORK = 2;
  private static final int MSG_SEEK_TO = 3;
  private static final int MSG_STOP = 4;
  private static final int MSG_RELEASE = 5;
  private static final int MSG_REFRESH_SOURCE_INFO = 6;
  private static final int MSG_PERIOD_PREPARED = 7;
  private static final int MSG_SOURCE_CONTINUE_LOADING_REQUESTED = 8;
  private static final int MSG_TRACK_SELECTION_INVALIDATED = 9;
  private static final int MSG_CUSTOM = 10;

  private static final int PREPARING_SOURCE_INTERVAL_MS = 10;
  private static final int RENDERING_INTERVAL_MS = 10;
  private static final int IDLE_INTERVAL_MS = 1000;

  /**
   * Limits the maximum number of periods to buffer ahead of the current playing period. The
   * buffering policy normally prevents buffering too far ahead, but the policy could allow too many
   * small periods to be buffered if the period count were not limited.
   */
  private static final int MAXIMUM_BUFFER_AHEAD_PERIODS = 100;

  private final Renderer[] renderers;
  private final RendererCapabilities[] rendererCapabilities;
  private final TrackSelector<T> trackSelector;
  private final LoadControl loadControl;
  private final StandaloneMediaClock standaloneMediaClock;
  private final Handler handler;
  private final HandlerThread internalPlaybackThread;
  private final Handler eventHandler;
  private final Timeline.Window window;
  private final Timeline.Period period;

  private PlaybackInfo playbackInfo;
  private Renderer rendererMediaClockSource;
  private MediaClock rendererMediaClock;
  private MediaSource mediaSource;
  private Renderer[] enabledRenderers;
  private boolean released;
  private boolean playWhenReady;
  private boolean rebuffering;
  private boolean isLoading;
  private int state;
  private int customMessagesSent;
  private int customMessagesProcessed;
  private long elapsedRealtimeUs;

  private long rendererPositionUs;

  private boolean isTimelineReady;
  private boolean isTimelineEnded;
  private int bufferAheadPeriodCount;
  private MediaPeriodHolder<T> playingPeriodHolder;
  private MediaPeriodHolder<T> readingPeriodHolder;
  private MediaPeriodHolder<T> loadingPeriodHolder;

  private Timeline timeline;

  public ExoPlayerImplInternal(Renderer[] renderers, TrackSelector<T> trackSelector,
      LoadControl loadControl, boolean playWhenReady, Handler eventHandler,
      PlaybackInfo playbackInfo) {
    this.renderers = renderers;
    this.trackSelector = trackSelector;
    this.loadControl = loadControl;
    this.playWhenReady = playWhenReady;
    this.eventHandler = eventHandler;
    this.state = ExoPlayer.STATE_IDLE;
    this.playbackInfo = playbackInfo;

    rendererCapabilities = new RendererCapabilities[renderers.length];
    for (int i = 0; i < renderers.length; i++) {
      renderers[i].setIndex(i);
      rendererCapabilities[i] = renderers[i].getCapabilities();
    }
    standaloneMediaClock = new StandaloneMediaClock();
    enabledRenderers = new Renderer[0];
    window = new Timeline.Window();
    period = new Timeline.Period();
    trackSelector.init(this);

    // Note: The documentation for Process.THREAD_PRIORITY_AUDIO that states "Applications can
    // not normally change to this priority" is incorrect.
    internalPlaybackThread = new PriorityHandlerThread("ExoPlayerImplInternal:Handler",
        Process.THREAD_PRIORITY_AUDIO);
    internalPlaybackThread.start();
    handler = new Handler(internalPlaybackThread.getLooper(), this);
  }

  public void prepare(MediaSource mediaSource, boolean resetPosition) {
    handler.obtainMessage(MSG_PREPARE, resetPosition ? 1 : 0, 0, mediaSource)
        .sendToTarget();
  }

  public void setPlayWhenReady(boolean playWhenReady) {
    handler.obtainMessage(MSG_SET_PLAY_WHEN_READY, playWhenReady ? 1 : 0, 0).sendToTarget();
  }

  public void seekTo(int periodIndex, long positionUs) {
    handler.obtainMessage(MSG_SEEK_TO, periodIndex, 0, positionUs).sendToTarget();
  }

  public void stop() {
    handler.sendEmptyMessage(MSG_STOP);
  }

  public void sendMessages(ExoPlayerMessage... messages) {
    if (released) {
      Log.w(TAG, "Ignoring messages sent after release.");
      return;
    }
    customMessagesSent++;
    handler.obtainMessage(MSG_CUSTOM, messages).sendToTarget();
  }

  public synchronized void blockingSendMessages(ExoPlayerMessage... messages) {
    if (released) {
      Log.w(TAG, "Ignoring messages sent after release.");
      return;
    }
    int messageNumber = customMessagesSent++;
    handler.obtainMessage(MSG_CUSTOM, messages).sendToTarget();
    while (customMessagesProcessed <= messageNumber) {
      try {
        wait();
      } catch (InterruptedException e) {
        Thread.currentThread().interrupt();
      }
    }
  }

  public synchronized void release() {
    if (released) {
      return;
    }
    handler.sendEmptyMessage(MSG_RELEASE);
    while (!released) {
      try {
        wait();
      } catch (InterruptedException e) {
        Thread.currentThread().interrupt();
      }
    }
    internalPlaybackThread.quit();
  }

  // MediaSource.Listener implementation.

  @Override
  public void onSourceInfoRefreshed(Timeline timeline, Object manifest) {
    handler.obtainMessage(MSG_REFRESH_SOURCE_INFO, Pair.create(timeline, manifest)).sendToTarget();
  }

  // MediaPeriod.Callback implementation.

  @Override
  public void onPrepared(MediaPeriod source) {
    handler.obtainMessage(MSG_PERIOD_PREPARED, source).sendToTarget();
  }

  @Override
  public void onContinueLoadingRequested(MediaPeriod source) {
    handler.obtainMessage(MSG_SOURCE_CONTINUE_LOADING_REQUESTED, source).sendToTarget();
  }

  // TrackSelector.InvalidationListener implementation.

  @Override
  public void onTrackSelectionsInvalidated() {
    handler.sendEmptyMessage(MSG_TRACK_SELECTION_INVALIDATED);
  }

  // Handler.Callback implementation.

  @Override
  public boolean handleMessage(Message msg) {
    try {
      switch (msg.what) {
        case MSG_PREPARE: {
          prepareInternal((MediaSource) msg.obj, msg.arg1 != 0);
          return true;
        }
        case MSG_SET_PLAY_WHEN_READY: {
          setPlayWhenReadyInternal(msg.arg1 != 0);
          return true;
        }
        case MSG_DO_SOME_WORK: {
          doSomeWork();
          return true;
        }
        case MSG_SEEK_TO: {
          seekToInternal(msg.arg1, (Long) msg.obj);
          return true;
        }
        case MSG_STOP: {
          stopInternal();
          return true;
        }
        case MSG_RELEASE: {
          releaseInternal();
          return true;
        }
        case MSG_PERIOD_PREPARED: {
          handlePeriodPrepared((MediaPeriod) msg.obj);
          return true;
        }
        case MSG_REFRESH_SOURCE_INFO: {
          handleSourceInfoRefreshed((Pair<Timeline, Object>) msg.obj);
          return true;
        }
        case MSG_SOURCE_CONTINUE_LOADING_REQUESTED: {
          handleContinueLoadingRequested((MediaPeriod) msg.obj);
          return true;
        }
        case MSG_TRACK_SELECTION_INVALIDATED: {
          reselectTracksInternal();
          return true;
        }
        case MSG_CUSTOM: {
          sendMessagesInternal((ExoPlayerMessage[]) msg.obj);
          return true;
        }
        default:
          return false;
      }
    } catch (ExoPlaybackException e) {
      Log.e(TAG, "Renderer error.", e);
      eventHandler.obtainMessage(MSG_ERROR, e).sendToTarget();
      stopInternal();
      return true;
    } catch (IOException e) {
      Log.e(TAG, "Source error.", e);
      eventHandler.obtainMessage(MSG_ERROR, ExoPlaybackException.createForSource(e)).sendToTarget();
      stopInternal();
      return true;
    } catch (RuntimeException e) {
      Log.e(TAG, "Internal runtime error.", e);
      eventHandler.obtainMessage(MSG_ERROR, ExoPlaybackException.createForUnexpected(e))
          .sendToTarget();
      stopInternal();
      return true;
    }
  }

  // Private methods.

  private void setState(int state) {
    if (this.state != state) {
      this.state = state;
      eventHandler.obtainMessage(MSG_STATE_CHANGED, state, 0).sendToTarget();
    }
  }

  private void setIsLoading(boolean isLoading) {
    if (this.isLoading != isLoading) {
      this.isLoading = isLoading;
      eventHandler.obtainMessage(MSG_LOADING_CHANGED, isLoading ? 1 : 0, 0).sendToTarget();
    }
  }

  private void prepareInternal(MediaSource mediaSource, boolean resetPosition)
      throws ExoPlaybackException {
    resetInternal();
    loadControl.onPrepared();
    if (resetPosition) {
      playbackInfo = new PlaybackInfo(0, C.TIME_UNSET);
    }
    this.mediaSource = mediaSource;
    mediaSource.prepareSource(this);
    setState(ExoPlayer.STATE_BUFFERING);
    handler.sendEmptyMessage(MSG_DO_SOME_WORK);
  }

  private void setPlayWhenReadyInternal(boolean playWhenReady) throws ExoPlaybackException {
    rebuffering = false;
    this.playWhenReady = playWhenReady;
    if (!playWhenReady) {
      stopRenderers();
      updatePlaybackPositions();
    } else {
      if (state == ExoPlayer.STATE_READY) {
        startRenderers();
        handler.sendEmptyMessage(MSG_DO_SOME_WORK);
      } else if (state == ExoPlayer.STATE_BUFFERING) {
        handler.sendEmptyMessage(MSG_DO_SOME_WORK);
      }
    }
  }

  private void startRenderers() throws ExoPlaybackException {
    rebuffering = false;
    standaloneMediaClock.start();
    for (Renderer renderer : enabledRenderers) {
      renderer.start();
    }
  }

  private void stopRenderers() throws ExoPlaybackException {
    standaloneMediaClock.stop();
    for (Renderer renderer : enabledRenderers) {
      ensureStopped(renderer);
    }
  }

  private void updatePlaybackPositions() throws ExoPlaybackException {
    if (playingPeriodHolder == null) {
      return;
    }

    // Update the playback position.
    long periodPositionUs = playingPeriodHolder.mediaPeriod.readDiscontinuity();
    if (periodPositionUs != C.TIME_UNSET) {
      resetRendererPosition(periodPositionUs);
    } else {
      if (rendererMediaClockSource != null && !rendererMediaClockSource.isEnded()) {
        rendererPositionUs = rendererMediaClock.getPositionUs();
        standaloneMediaClock.setPositionUs(rendererPositionUs);
      } else {
        rendererPositionUs = standaloneMediaClock.getPositionUs();
      }
      periodPositionUs = rendererPositionUs - playingPeriodHolder.rendererPositionOffsetUs;
    }
    playbackInfo.positionUs = periodPositionUs;
    elapsedRealtimeUs = SystemClock.elapsedRealtime() * 1000;

    // Update the buffered position.
    long bufferedPositionUs = enabledRenderers.length == 0 ? C.TIME_END_OF_SOURCE
        : playingPeriodHolder.mediaPeriod.getBufferedPositionUs();
    playbackInfo.bufferedPositionUs = bufferedPositionUs == C.TIME_END_OF_SOURCE
        ? timeline.getPeriod(playingPeriodHolder.index, period).getDurationUs()
        : bufferedPositionUs;
  }

  private void doSomeWork() throws ExoPlaybackException, IOException {
    long operationStartTimeMs = SystemClock.elapsedRealtime();

    updatePeriods();
    if (playingPeriodHolder == null) {
      // We're still waiting for the first period to be prepared.
      maybeThrowPeriodPrepareError();
      scheduleNextWork(operationStartTimeMs, PREPARING_SOURCE_INTERVAL_MS);
      return;
    }

    TraceUtil.beginSection("doSomeWork");

    updatePlaybackPositions();
    boolean allRenderersEnded = true;
    boolean allRenderersReadyOrEnded = true;
    for (Renderer renderer : enabledRenderers) {
      // TODO: Each renderer should return the maximum delay before which it wishes to be called
      // again. The minimum of these values should then be used as the delay before the next
      // invocation of this method.
      renderer.render(rendererPositionUs, elapsedRealtimeUs);
      allRenderersEnded = allRenderersEnded && renderer.isEnded();
      // Determine whether the renderer is ready (or ended). If it's not, throw an error that's
      // preventing the renderer from making progress, if such an error exists.
      boolean rendererReadyOrEnded = renderer.isReady() || renderer.isEnded();
      if (!rendererReadyOrEnded) {
        renderer.maybeThrowStreamError();
      }
      allRenderersReadyOrEnded = allRenderersReadyOrEnded && rendererReadyOrEnded;
    }

    if (!allRenderersReadyOrEnded) {
      maybeThrowPeriodPrepareError();
    }

    long playingPeriodDurationUs = timeline.getPeriod(playingPeriodHolder.index, period)
        .getDurationUs();
    if (allRenderersEnded
        && (playingPeriodDurationUs == C.TIME_UNSET
        || playingPeriodDurationUs <= playbackInfo.positionUs)
        && isTimelineEnded) {
      setState(ExoPlayer.STATE_ENDED);
      stopRenderers();
    } else if (state == ExoPlayer.STATE_BUFFERING) {
      if ((enabledRenderers.length > 0
          ? (allRenderersReadyOrEnded && haveSufficientBuffer(rebuffering)) : isTimelineReady)) {
        setState(ExoPlayer.STATE_READY);
        if (playWhenReady) {
          startRenderers();
        }
      }
    } else if (state == ExoPlayer.STATE_READY
        && (enabledRenderers.length > 0 ? !allRenderersReadyOrEnded : !isTimelineReady)) {
      rebuffering = playWhenReady;
      setState(ExoPlayer.STATE_BUFFERING);
      stopRenderers();
    }

    if (state == ExoPlayer.STATE_BUFFERING) {
      for (Renderer renderer : enabledRenderers) {
        renderer.maybeThrowStreamError();
      }
    }

    if ((playWhenReady && state == ExoPlayer.STATE_READY) || state == ExoPlayer.STATE_BUFFERING) {
      scheduleNextWork(operationStartTimeMs, RENDERING_INTERVAL_MS);
    } else if (enabledRenderers.length != 0) {
      scheduleNextWork(operationStartTimeMs, IDLE_INTERVAL_MS);
    } else {
      handler.removeMessages(MSG_DO_SOME_WORK);
    }

    TraceUtil.endSection();
  }

  private void scheduleNextWork(long thisOperationStartTimeMs, long intervalMs) {
    handler.removeMessages(MSG_DO_SOME_WORK);
    long nextOperationStartTimeMs = thisOperationStartTimeMs + intervalMs;
    long nextOperationDelayMs = nextOperationStartTimeMs - SystemClock.elapsedRealtime();
    if (nextOperationDelayMs <= 0) {
      handler.sendEmptyMessage(MSG_DO_SOME_WORK);
    } else {
      handler.sendEmptyMessageDelayed(MSG_DO_SOME_WORK, nextOperationDelayMs);
    }
  }

  private void seekToInternal(int periodIndex, long periodPositionUs) throws ExoPlaybackException {
    try {
      if (periodPositionUs == C.TIME_UNSET && timeline != null
          && periodIndex < timeline.getPeriodCount()) {
        // We know about the window, so seek to its default initial position now.
        Pair<Integer, Long> defaultPosition = getDefaultPosition(periodIndex);
        periodIndex = defaultPosition.first;
        periodPositionUs = defaultPosition.second;
      }

      if (periodIndex == playbackInfo.periodIndex
          && ((periodPositionUs == C.TIME_UNSET && playbackInfo.positionUs == C.TIME_UNSET)
          || ((periodPositionUs / 1000) == (playbackInfo.positionUs / 1000)))) {
        // Seek position equals the current position. Do nothing.
        return;
      }
      periodPositionUs = seekToPeriodPosition(periodIndex, periodPositionUs);
    } finally {
      playbackInfo = new PlaybackInfo(periodIndex, periodPositionUs);
      eventHandler.obtainMessage(MSG_SEEK_ACK, playbackInfo).sendToTarget();
    }
  }

  private long seekToPeriodPosition(int periodIndex, long periodPositionUs)
      throws ExoPlaybackException {
    if (mediaSource == null) {
      if (periodPositionUs != C.TIME_UNSET) {
        resetRendererPosition(periodPositionUs);
      }
      return periodPositionUs;
    }

    stopRenderers();
    rebuffering = false;
    setState(ExoPlayer.STATE_BUFFERING);

    if (periodPositionUs == C.TIME_UNSET || (readingPeriodHolder != playingPeriodHolder
        && (periodIndex == playingPeriodHolder.index
        || periodIndex == readingPeriodHolder.index))) {
      // Clear the timeline because either the seek position is not known, or a renderer is reading
      // ahead to the next period and the seek is to either the playing or reading period.
      periodIndex = C.INDEX_UNSET;
    }

    MediaPeriodHolder<T> newPlayingPeriodHolder = null;
    if (playingPeriodHolder == null) {
      // We're still waiting for the first period to be prepared.
      if (loadingPeriodHolder != null) {
        loadingPeriodHolder.release();
      }
    } else {
      // Clear the timeline, but keep the requested period if it is already prepared.
      MediaPeriodHolder<T> periodHolder = playingPeriodHolder;
      while (periodHolder != null) {
        if (periodHolder.index == periodIndex && periodHolder.prepared) {
          newPlayingPeriodHolder = periodHolder;
        } else {
          periodHolder.release();
        }
        periodHolder = periodHolder.next;
      }
    }

    // Disable all the renderers if the period is changing.
    if (newPlayingPeriodHolder != playingPeriodHolder) {
      for (Renderer renderer : enabledRenderers) {
        renderer.disable();
      }
      enabledRenderers = new Renderer[0];
      rendererMediaClock = null;
      rendererMediaClockSource = null;
    }

    // Update loaded periods.
    bufferAheadPeriodCount = 0;
    if (newPlayingPeriodHolder != null) {
      newPlayingPeriodHolder.next = null;
      setPlayingPeriodHolder(newPlayingPeriodHolder);
      updateTimelineState();
      readingPeriodHolder = playingPeriodHolder;
      loadingPeriodHolder = playingPeriodHolder;
      if (playingPeriodHolder.hasEnabledTracks) {
        periodPositionUs = playingPeriodHolder.mediaPeriod.seekToUs(periodPositionUs);
      }
      resetRendererPosition(periodPositionUs);
      maybeContinueLoading();
    } else {
      playingPeriodHolder = null;
      readingPeriodHolder = null;
      loadingPeriodHolder = null;
      if (periodPositionUs != C.TIME_UNSET) {
        resetRendererPosition(periodPositionUs);
      }
    }
    updatePlaybackPositions();
    handler.sendEmptyMessage(MSG_DO_SOME_WORK);
    return periodPositionUs;
  }

  private void resetRendererPosition(long periodPositionUs) throws ExoPlaybackException {
    long periodOffsetUs = playingPeriodHolder == null ? 0
        : playingPeriodHolder.rendererPositionOffsetUs;
    rendererPositionUs = periodOffsetUs + periodPositionUs;
    standaloneMediaClock.setPositionUs(rendererPositionUs);
    for (Renderer renderer : enabledRenderers) {
      renderer.resetPosition(rendererPositionUs);
    }
  }

  private void stopInternal() {
    resetInternal();
    loadControl.onStopped();
    setState(ExoPlayer.STATE_IDLE);
  }

  private void releaseInternal() {
    resetInternal();
    loadControl.onReleased();
    setState(ExoPlayer.STATE_IDLE);
    synchronized (this) {
      released = true;
      notifyAll();
    }
  }

  private void resetInternal() {
    handler.removeMessages(MSG_DO_SOME_WORK);
    rebuffering = false;
    standaloneMediaClock.stop();
    rendererMediaClock = null;
    rendererMediaClockSource = null;
    for (Renderer renderer : enabledRenderers) {
      try {
        ensureStopped(renderer);
        renderer.disable();
      } catch (ExoPlaybackException | RuntimeException e) {
        // There's nothing we can do.
        Log.e(TAG, "Stop failed.", e);
      }
    }
    enabledRenderers = new Renderer[0];
    releasePeriodHoldersFrom(playingPeriodHolder != null ? playingPeriodHolder
        : loadingPeriodHolder);
    if (mediaSource != null) {
      mediaSource.releaseSource();
      mediaSource = null;
    }
    isTimelineReady = false;
    isTimelineEnded = false;
    playingPeriodHolder = null;
    readingPeriodHolder = null;
    loadingPeriodHolder = null;
    timeline = null;
    bufferAheadPeriodCount = 0;
    setIsLoading(false);
  }

  private void sendMessagesInternal(ExoPlayerMessage[] messages) throws ExoPlaybackException {
    try {
      for (ExoPlayerMessage message : messages) {
        message.target.handleMessage(message.messageType, message.message);
      }
      if (mediaSource != null) {
        // The message may have caused something to change that now requires us to do work.
        handler.sendEmptyMessage(MSG_DO_SOME_WORK);
      }
    } finally {
      synchronized (this) {
        customMessagesProcessed++;
        notifyAll();
      }
    }
  }

  private void ensureStopped(Renderer renderer) throws ExoPlaybackException {
    if (renderer.getState() == Renderer.STATE_STARTED) {
      renderer.stop();
    }
  }

  private void reselectTracksInternal() throws ExoPlaybackException {
    if (playingPeriodHolder == null) {
      // We don't have tracks yet, so we don't care.
      return;
    }
    // Reselect tracks on each period in turn, until the selection changes.
    MediaPeriodHolder<T> periodHolder = playingPeriodHolder;
    boolean selectionsChangedForReadPeriod = true;
    while (true) {
      if (periodHolder == null || !periodHolder.prepared) {
        // The reselection did not change any prepared periods.
        return;
      }
      if (periodHolder.selectTracks()) {
        // Selected tracks have changed for this period.
        break;
      }
      if (periodHolder == readingPeriodHolder) {
        // The track reselection didn't affect any period that has been read.
        selectionsChangedForReadPeriod = false;
      }
      periodHolder = periodHolder.next;
    }

    if (selectionsChangedForReadPeriod) {
      // Update streams and rebuffer for the new selection, recreating all streams if reading ahead.
      boolean recreateStreams = readingPeriodHolder != playingPeriodHolder;
      releasePeriodHoldersFrom(playingPeriodHolder.next);
      playingPeriodHolder.next = null;
      readingPeriodHolder = playingPeriodHolder;
      loadingPeriodHolder = playingPeriodHolder;
      bufferAheadPeriodCount = 0;

      boolean[] streamResetFlags = new boolean[renderers.length];
      long periodPositionUs = playingPeriodHolder.updatePeriodTrackSelection(
          playbackInfo.positionUs, loadControl, recreateStreams, streamResetFlags);
      if (periodPositionUs != playbackInfo.positionUs) {
        playbackInfo.positionUs = periodPositionUs;
        resetRendererPosition(periodPositionUs);
      }

      int enabledRendererCount = 0;
      boolean[] rendererWasEnabledFlags = new boolean[renderers.length];
      for (int i = 0; i < renderers.length; i++) {
        Renderer renderer = renderers[i];
        rendererWasEnabledFlags[i] = renderer.getState() != Renderer.STATE_DISABLED;
        SampleStream sampleStream = playingPeriodHolder.sampleStreams[i];
        if (sampleStream != null) {
          enabledRendererCount++;
        }
        if (rendererWasEnabledFlags[i]) {
          if (sampleStream != renderer.getStream()) {
            // We need to disable the renderer.
            if (renderer == rendererMediaClockSource) {
              // The renderer is providing the media clock.
              if (sampleStream == null) {
                // The renderer won't be re-enabled. Sync standaloneMediaClock so that it can take
                // over timing responsibilities.
                standaloneMediaClock.setPositionUs(rendererMediaClock.getPositionUs());
              }
              rendererMediaClock = null;
              rendererMediaClockSource = null;
            }
            ensureStopped(renderer);
            renderer.disable();
          } else if (streamResetFlags[i]) {
            // The renderer will continue to consume from its current stream, but needs to be reset.
            renderer.resetPosition(playbackInfo.positionUs);
          }
        }
      }
      trackSelector.onSelectionActivated(playingPeriodHolder.trackSelections);
      enableRenderers(rendererWasEnabledFlags, enabledRendererCount);
    } else {
      // Release and re-prepare/buffer periods after the one whose selection changed.
      loadingPeriodHolder = periodHolder;
      periodHolder = loadingPeriodHolder.next;
      while (periodHolder != null) {
        periodHolder.release();
        periodHolder = periodHolder.next;
        bufferAheadPeriodCount--;
      }
      loadingPeriodHolder.next = null;
      long loadingPeriodPositionUs = Math.max(0,
          rendererPositionUs - loadingPeriodHolder.rendererPositionOffsetUs);
      loadingPeriodHolder.updatePeriodTrackSelection(loadingPeriodPositionUs, loadControl, false);
    }
    maybeContinueLoading();
    updatePlaybackPositions();
    handler.sendEmptyMessage(MSG_DO_SOME_WORK);
  }

  private boolean haveSufficientBuffer(boolean rebuffering) {
    if (loadingPeriodHolder == null) {
      return false;
    }
    long loadingPeriodPositionUs = rendererPositionUs
        - loadingPeriodHolder.rendererPositionOffsetUs;
    long loadingPeriodBufferedPositionUs =
        !loadingPeriodHolder.prepared ? 0 : loadingPeriodHolder.mediaPeriod.getBufferedPositionUs();
    if (loadingPeriodBufferedPositionUs == C.TIME_END_OF_SOURCE) {
      if (loadingPeriodHolder.isLast) {
        return true;
      }
      loadingPeriodBufferedPositionUs = timeline.getPeriod(loadingPeriodHolder.index, period)
          .getDurationUs();
    }
    return loadControl.shouldStartPlayback(
        loadingPeriodBufferedPositionUs - loadingPeriodPositionUs, rebuffering);
  }

  private void maybeThrowPeriodPrepareError() throws IOException {
    if (loadingPeriodHolder != null && !loadingPeriodHolder.prepared
        && (readingPeriodHolder == null || readingPeriodHolder.next == loadingPeriodHolder)) {
      for (Renderer renderer : enabledRenderers) {
        if (!renderer.hasReadStreamToEnd()) {
          return;
        }
      }
      loadingPeriodHolder.mediaPeriod.maybeThrowPrepareError();
    }
  }

  private void handleSourceInfoRefreshed(Pair<Timeline, Object> timelineAndManifest)
      throws ExoPlaybackException, IOException {
    eventHandler.obtainMessage(MSG_SOURCE_INFO_REFRESHED, timelineAndManifest).sendToTarget();
    Timeline oldTimeline = this.timeline;
    this.timeline = timelineAndManifest.first;

    // Update the loaded periods to take into account the new timeline.
    if (playingPeriodHolder != null) {
      int index = timeline.getIndexOfPeriod(playingPeriodHolder.uid);
      if (index == C.INDEX_UNSET) {
        attemptRestart(timeline, oldTimeline, playingPeriodHolder.index);
        return;
      }

      // The playing period is also in the new timeline. Update the index for each loaded period
      // until a period is found that does not match the old timeline.
      timeline.getPeriod(index, period, true);
      playingPeriodHolder.setIndex(timeline, timeline.getWindow(period.windowIndex, window),
          index);

      MediaPeriodHolder<T> previousPeriodHolder = playingPeriodHolder;
      boolean seenReadingPeriod = false;
      bufferAheadPeriodCount = 0;
      while (previousPeriodHolder.next != null) {
        MediaPeriodHolder<T> periodHolder = previousPeriodHolder.next;
        index++;
        timeline.getPeriod(index, period, true);
        if (!periodHolder.uid.equals(period.uid)) {
          if (!seenReadingPeriod) {
            // Renderers may have read a period that has been removed, so release all loaded periods
            // and seek to the current position of the playing period index.
            index = playingPeriodHolder.index;
            releasePeriodHoldersFrom(playingPeriodHolder);
            playingPeriodHolder = null;
            readingPeriodHolder = null;
            loadingPeriodHolder = null;
            long newPositionUs = seekToPeriodPosition(index, playbackInfo.positionUs);
            if (newPositionUs != playbackInfo.positionUs) {
              playbackInfo = new PlaybackInfo(index, newPositionUs);
              eventHandler.obtainMessage(MSG_POSITION_DISCONTINUITY, playbackInfo).sendToTarget();
            }
            return;
          }

          // Update the loading period to be the latest period that is still valid.
          loadingPeriodHolder = previousPeriodHolder;
          loadingPeriodHolder.next = null;

          // Release the rest of the timeline.
          releasePeriodHoldersFrom(periodHolder);
          break;
        }

        bufferAheadPeriodCount++;
        int windowIndex = timeline.getPeriod(index, period).windowIndex;
        periodHolder.setIndex(timeline, timeline.getWindow(windowIndex, window), index);
        if (periodHolder == readingPeriodHolder) {
          seenReadingPeriod = true;
        }
        previousPeriodHolder = periodHolder;
      }
    } else if (loadingPeriodHolder != null) {
      Object uid = loadingPeriodHolder.uid;
      int index = timeline.getIndexOfPeriod(uid);
      if (index == C.INDEX_UNSET) {
        attemptRestart(timeline, oldTimeline, loadingPeriodHolder.index);
        return;
      } else {
        int windowIndex = timeline.getPeriod(index, this.period).windowIndex;
        loadingPeriodHolder.setIndex(timeline, timeline.getWindow(windowIndex, window),
            index);
      }
    }

    // TODO[playlists]: Signal the identifier discontinuity, even if the index hasn't changed.
    if (oldTimeline != null) {
      int newPlayingIndex = playingPeriodHolder != null ? playingPeriodHolder.index
          : loadingPeriodHolder != null ? loadingPeriodHolder.index : C.INDEX_UNSET;
      if (newPlayingIndex != C.INDEX_UNSET
          && newPlayingIndex != playbackInfo.periodIndex) {
        playbackInfo = new PlaybackInfo(newPlayingIndex, playbackInfo.positionUs);
        updatePlaybackPositions();
        eventHandler.obtainMessage(MSG_POSITION_DISCONTINUITY, playbackInfo).sendToTarget();
      }
    }
  }

  private void attemptRestart(Timeline newTimeline, Timeline oldTimeline,
      int oldPeriodIndex) throws ExoPlaybackException {
    int newPeriodIndex = C.INDEX_UNSET;
    while (newPeriodIndex == C.INDEX_UNSET
        && oldPeriodIndex < oldTimeline.getPeriodCount() - 1) {
      newPeriodIndex =
          newTimeline.getIndexOfPeriod(oldTimeline.getPeriod(++oldPeriodIndex, period, true).uid);
    }
    if (newPeriodIndex == C.INDEX_UNSET) {
      // We failed to find a replacement period. Stop the player.
      stopInternal();
      return;
    }

    // Release all loaded periods.
    releasePeriodHoldersFrom(playingPeriodHolder != null ? playingPeriodHolder
        : loadingPeriodHolder);
    bufferAheadPeriodCount = 0;
    playingPeriodHolder = null;
    readingPeriodHolder = null;
    loadingPeriodHolder = null;

    // Find the default initial position in the window and seek to it.
    Pair<Integer, Long> defaultPosition = getDefaultPosition(newPeriodIndex);
    newPeriodIndex = defaultPosition.first;
    long newPlayingPositionUs = defaultPosition.second;

    playbackInfo = new PlaybackInfo(newPeriodIndex, newPlayingPositionUs);
    eventHandler.obtainMessage(MSG_POSITION_DISCONTINUITY, playbackInfo).sendToTarget();
  }

  private Pair<Integer, Long> getDefaultPosition(int periodIndex) {
    timeline.getPeriod(periodIndex, period);
    timeline.getWindow(period.windowIndex, window);
    periodIndex = window.firstPeriodIndex;
    long periodPositionUs = window.getPositionInFirstPeriodUs()
        + window.getDefaultPositionUs();
    timeline.getPeriod(periodIndex, period);
    while (periodIndex < window.lastPeriodIndex
        && periodPositionUs > period.getDurationMs()) {
      periodPositionUs -= period.getDurationUs();
      timeline.getPeriod(periodIndex++, period);
    }
    return Pair.create(periodIndex, periodPositionUs);
  }

  private void updatePeriods() throws ExoPlaybackException, IOException {
    if (timeline == null) {
      // We're waiting to get information about periods.
      mediaSource.maybeThrowSourceInfoRefreshError();
      return;
    }

    if (loadingPeriodHolder == null
        || (loadingPeriodHolder.isFullyBuffered() && !loadingPeriodHolder.isLast
        && bufferAheadPeriodCount < MAXIMUM_BUFFER_AHEAD_PERIODS)) {
      // We don't have a loading period or it's fully loaded, so try and create the next one.
      int newLoadingPeriodIndex = loadingPeriodHolder == null ? playbackInfo.periodIndex
          : loadingPeriodHolder.index + 1;
      if (newLoadingPeriodIndex >= timeline.getPeriodCount()) {
        // The period is not available yet.
        mediaSource.maybeThrowSourceInfoRefreshError();
      } else {
        int windowIndex = timeline.getPeriod(newLoadingPeriodIndex, period).windowIndex;
        boolean isFirstPeriodInWindow = newLoadingPeriodIndex
            == timeline.getWindow(windowIndex, window).firstPeriodIndex;
        long periodStartPositionUs = loadingPeriodHolder == null ? playbackInfo.positionUs
            : (isFirstPeriodInWindow ? C.TIME_UNSET : 0);
        if (periodStartPositionUs == C.TIME_UNSET) {
          // This is the first period of a new window or we don't have a start position, so seek to
          // the default position for the window.
          Pair<Integer, Long> defaultPosition = getDefaultPosition(newLoadingPeriodIndex);
          newLoadingPeriodIndex = defaultPosition.first;
          periodStartPositionUs = defaultPosition.second;
        }
        Object newPeriodUid = timeline.getPeriod(newLoadingPeriodIndex, period, true).uid;
        MediaPeriod newMediaPeriod = mediaSource.createPeriod(newLoadingPeriodIndex,
            loadControl.getAllocator(), periodStartPositionUs);
        newMediaPeriod.prepare(this);
        MediaPeriodHolder<T> newPeriodHolder = new MediaPeriodHolder<>(renderers,
            rendererCapabilities, trackSelector, mediaSource, newMediaPeriod, newPeriodUid,
            periodStartPositionUs);
        timeline.getWindow(windowIndex, window);
        newPeriodHolder.setIndex(timeline, window, newLoadingPeriodIndex);
        if (loadingPeriodHolder != null) {
          loadingPeriodHolder.setNext(newPeriodHolder);
          newPeriodHolder.rendererPositionOffsetUs = loadingPeriodHolder.rendererPositionOffsetUs
              + timeline.getPeriod(loadingPeriodHolder.index, period).getDurationUs();
        }
        bufferAheadPeriodCount++;
        loadingPeriodHolder = newPeriodHolder;
        setIsLoading(true);
      }
    }

    if (loadingPeriodHolder == null || loadingPeriodHolder.isFullyBuffered()) {
      setIsLoading(false);
    } else if (loadingPeriodHolder != null && loadingPeriodHolder.needsContinueLoading) {
      maybeContinueLoading();
    }

    if (playingPeriodHolder == null) {
      // We're waiting for the first period to be prepared.
      return;
    }

    // Update the playing and reading periods.
    while (playingPeriodHolder != readingPeriodHolder && playingPeriodHolder.next != null
        && rendererPositionUs >= playingPeriodHolder.next.rendererPositionOffsetUs) {
      // All enabled renderers' streams have been read to the end, and the playback position reached
      // the end of the playing period, so advance playback to the next period.
      playingPeriodHolder.release();
      setPlayingPeriodHolder(playingPeriodHolder.next);
      bufferAheadPeriodCount--;
      playbackInfo = new PlaybackInfo(playingPeriodHolder.index,
          playingPeriodHolder.startPositionUs);
      updatePlaybackPositions();
      eventHandler.obtainMessage(MSG_POSITION_DISCONTINUITY, playbackInfo).sendToTarget();
    }
    updateTimelineState();

    if (readingPeriodHolder.isLast) {
      // The renderers have their final SampleStreams.
      for (Renderer renderer : enabledRenderers) {
        renderer.setCurrentStreamIsFinal();
      }
      return;
    }

    for (Renderer renderer : enabledRenderers) {
      if (!renderer.hasReadStreamToEnd()) {
        return;
      }
    }
    if (readingPeriodHolder.next != null && readingPeriodHolder.next.prepared) {
      TrackSelections<T> oldTrackSelections = readingPeriodHolder.trackSelections;
      readingPeriodHolder = readingPeriodHolder.next;
      TrackSelections<T> newTrackSelections = readingPeriodHolder.trackSelections;
      for (int i = 0; i < renderers.length; i++) {
        Renderer renderer = renderers[i];
        TrackSelection oldSelection = oldTrackSelections.get(i);
        TrackSelection newSelection = newTrackSelections.get(i);
        if (oldSelection != null) {
          if (newSelection != null) {
            // Replace the renderer's SampleStream so the transition to playing the next period can
            // be seamless.
            Format[] formats = new Format[newSelection.length()];
            for (int j = 0; j < formats.length; j++) {
              formats[j] = newSelection.getFormat(j);
            }
            renderer.replaceStream(formats, readingPeriodHolder.sampleStreams[i],
                readingPeriodHolder.rendererPositionOffsetUs);
          } else {
            // The renderer will be disabled when transitioning to playing the next period. Mark the
            // SampleStream as final to play out any remaining data.
            renderer.setCurrentStreamIsFinal();
          }
        }
      }
    }
  }

  private void handlePeriodPrepared(MediaPeriod period) throws ExoPlaybackException {
    if (loadingPeriodHolder == null || loadingPeriodHolder.mediaPeriod != period) {
      // Stale event.
      return;
    }
    loadingPeriodHolder.handlePrepared(loadingPeriodHolder.startPositionUs, loadControl);
    if (playingPeriodHolder == null) {
      // This is the first prepared period, so start playing it.
      readingPeriodHolder = loadingPeriodHolder;
      setPlayingPeriodHolder(readingPeriodHolder);
      if (playbackInfo.startPositionUs == C.TIME_UNSET) {
        // Update the playback info when seeking to a default position.
        playbackInfo = new PlaybackInfo(playingPeriodHolder.index,
            playingPeriodHolder.startPositionUs);
        resetRendererPosition(playbackInfo.startPositionUs);
        updatePlaybackPositions();
        eventHandler.obtainMessage(MSG_POSITION_DISCONTINUITY, playbackInfo).sendToTarget();
      }
      updateTimelineState();
    }
    maybeContinueLoading();
  }

  private void handleContinueLoadingRequested(MediaPeriod period) {
    if (loadingPeriodHolder == null || loadingPeriodHolder.mediaPeriod != period) {
      return;
    }
    maybeContinueLoading();
  }

  private void maybeContinueLoading() {
    long nextLoadPositionUs = loadingPeriodHolder.mediaPeriod.getNextLoadPositionUs();
    if (nextLoadPositionUs != C.TIME_END_OF_SOURCE) {
      long loadingPeriodPositionUs = rendererPositionUs
          - loadingPeriodHolder.rendererPositionOffsetUs;
      long bufferedDurationUs = nextLoadPositionUs - loadingPeriodPositionUs;
      boolean continueLoading = loadControl.shouldContinueLoading(bufferedDurationUs);
      setIsLoading(continueLoading);
      if (continueLoading) {
        loadingPeriodHolder.needsContinueLoading = false;
        loadingPeriodHolder.mediaPeriod.continueLoading(loadingPeriodPositionUs);
      } else {
        loadingPeriodHolder.needsContinueLoading = true;
      }
    } else {
      setIsLoading(false);
    }
  }

  private void releasePeriodHoldersFrom(MediaPeriodHolder<T> periodHolder) {
    while (periodHolder != null) {
      periodHolder.release();
      periodHolder = periodHolder.next;
    }
  }

  private void setPlayingPeriodHolder(MediaPeriodHolder<T> periodHolder)
      throws ExoPlaybackException {
    int enabledRendererCount = 0;
    boolean[] rendererWasEnabledFlags = new boolean[renderers.length];
    for (int i = 0; i < renderers.length; i++) {
      Renderer renderer = renderers[i];
      rendererWasEnabledFlags[i] = renderer.getState() != Renderer.STATE_DISABLED;
      TrackSelection newSelection = periodHolder.trackSelections.get(i);
      if (newSelection != null) {
        // The renderer should be enabled when playing the new period.
        enabledRendererCount++;
      } else if (rendererWasEnabledFlags[i]) {
        // The renderer should be disabled when playing the new period.
        if (renderer == rendererMediaClockSource) {
          // Sync standaloneMediaClock so that it can take over timing responsibilities.
          standaloneMediaClock.setPositionUs(rendererMediaClock.getPositionUs());
          rendererMediaClock = null;
          rendererMediaClockSource = null;
        }
        ensureStopped(renderer);
        renderer.disable();
      }
    }

    trackSelector.onSelectionActivated(periodHolder.trackSelections);
    playingPeriodHolder = periodHolder;
    enableRenderers(rendererWasEnabledFlags, enabledRendererCount);
  }

  private void updateTimelineState() {
    long playingPeriodDurationUs = timeline.getPeriod(playingPeriodHolder.index, period)
        .getDurationUs();
    isTimelineReady = playingPeriodDurationUs == C.TIME_UNSET
        || playbackInfo.positionUs < playingPeriodDurationUs
        || (playingPeriodHolder.next != null && playingPeriodHolder.next.prepared);
    isTimelineEnded = playingPeriodHolder.isLast;
  }

  private void enableRenderers(boolean[] rendererWasEnabledFlags, int enabledRendererCount)
      throws ExoPlaybackException {
    enabledRenderers = new Renderer[enabledRendererCount];
    enabledRendererCount = 0;
    for (int i = 0; i < renderers.length; i++) {
      Renderer renderer = renderers[i];
      TrackSelection newSelection = playingPeriodHolder.trackSelections.get(i);
      if (newSelection != null) {
        enabledRenderers[enabledRendererCount++] = renderer;
        if (renderer.getState() == Renderer.STATE_DISABLED) {
          // The renderer needs enabling with its new track selection.
          boolean playing = playWhenReady && state == ExoPlayer.STATE_READY;
          // Consider as joining only if the renderer was previously disabled.
          boolean joining = !rendererWasEnabledFlags[i] && playing;
          // Build an array of formats contained by the selection.
          Format[] formats = new Format[newSelection.length()];
          for (int j = 0; j < formats.length; j++) {
            formats[j] = newSelection.getFormat(j);
          }
          // Enable the renderer.
          renderer.enable(formats, playingPeriodHolder.sampleStreams[i], rendererPositionUs,
              joining, playingPeriodHolder.rendererPositionOffsetUs);
          MediaClock mediaClock = renderer.getMediaClock();
          if (mediaClock != null) {
            if (rendererMediaClock != null) {
              throw ExoPlaybackException.createForUnexpected(
                  new IllegalStateException("Multiple renderer media clocks enabled."));
            }
            rendererMediaClock = mediaClock;
            rendererMediaClockSource = renderer;
          }
          // Start the renderer if playing.
          if (playing) {
            renderer.start();
          }
        }
      }
    }
  }

  /**
   * Holds a {@link MediaPeriod} with information required to play it as part of a timeline.
   */
  private static final class MediaPeriodHolder<T> {

    public final MediaPeriod mediaPeriod;
    public final Object uid;

    public final SampleStream[] sampleStreams;
    public final boolean[] mayRetainStreamFlags;

    public int index;
    public long startPositionUs;
    public boolean isLast;
    public boolean prepared;
    public boolean hasEnabledTracks;
    public long rendererPositionOffsetUs;
    public MediaPeriodHolder<T> next;
    public boolean needsContinueLoading;

    private final Renderer[] renderers;
    private final RendererCapabilities[] rendererCapabilities;
    private final TrackSelector<T> trackSelector;
    private final MediaSource mediaSource;

    private TrackSelections<T> trackSelections;
    private TrackSelections<T> periodTrackSelections;

    public MediaPeriodHolder(Renderer[] renderers, RendererCapabilities[] rendererCapabilities,
        TrackSelector<T> trackSelector, MediaSource mediaSource, MediaPeriod mediaPeriod,
        Object uid, long positionUs) {
      this.renderers = renderers;
      this.rendererCapabilities = rendererCapabilities;
      this.trackSelector = trackSelector;
      this.mediaSource = mediaSource;
      this.mediaPeriod = mediaPeriod;
      this.uid = Assertions.checkNotNull(uid);
      sampleStreams = new SampleStream[renderers.length];
      mayRetainStreamFlags = new boolean[renderers.length];
      startPositionUs = positionUs;
    }

    public void setNext(MediaPeriodHolder<T> next) {
      this.next = next;
    }

    public void setIndex(Timeline timeline, Timeline.Window window, int periodIndex) {
      this.index = periodIndex;
      isLast = index == timeline.getPeriodCount() - 1 && !window.isDynamic;
    }

    public boolean isFullyBuffered() {
      return prepared
          && (!hasEnabledTracks || mediaPeriod.getBufferedPositionUs() == C.TIME_END_OF_SOURCE);
    }

    public void handlePrepared(long positionUs, LoadControl loadControl)
        throws ExoPlaybackException {
      prepared = true;
      selectTracks();
      startPositionUs = updatePeriodTrackSelection(positionUs, loadControl, false);
    }

    public boolean selectTracks() throws ExoPlaybackException {
      TrackSelections<T> newTrackSelections = trackSelector.selectTracks(rendererCapabilities,
          mediaPeriod.getTrackGroups());
      if (newTrackSelections.equals(periodTrackSelections)) {
        return false;
      }
      trackSelections = newTrackSelections;
      return true;
    }

    public long updatePeriodTrackSelection(long positionUs, LoadControl loadControl,
        boolean forceRecreateStreams) throws ExoPlaybackException {
      return updatePeriodTrackSelection(positionUs, loadControl, forceRecreateStreams,
          new boolean[renderers.length]);
    }

    public long updatePeriodTrackSelection(long positionUs, LoadControl loadControl,
        boolean forceRecreateStreams, boolean[] streamResetFlags) throws ExoPlaybackException {
      for (int i = 0; i < trackSelections.length; i++) {
        mayRetainStreamFlags[i] = !forceRecreateStreams
            && Util.areEqual(periodTrackSelections == null ? null : periodTrackSelections.get(i),
            trackSelections.get(i));
      }

      // Disable streams on the period and get new streams for updated/newly-enabled tracks.
      positionUs = mediaPeriod.selectTracks(trackSelections.getAll(), mayRetainStreamFlags,
          sampleStreams, streamResetFlags, positionUs);
      periodTrackSelections = trackSelections;

      // Update whether we have enabled tracks and sanity check the expected streams are non-null.
      hasEnabledTracks = false;
      for (int i = 0; i < sampleStreams.length; i++) {
        if (sampleStreams[i] != null) {
          Assertions.checkState(trackSelections.get(i) != null);
          hasEnabledTracks = true;
        } else {
          Assertions.checkState(trackSelections.get(i) == null);
        }
      }

      // The track selection has changed.
      loadControl.onTracksSelected(renderers, mediaPeriod.getTrackGroups(), trackSelections);
      return positionUs;
    }

    public void release() {
      try {
        mediaSource.releasePeriod(mediaPeriod);
      } catch (RuntimeException e) {
        // There's nothing we can do.
        Log.e(TAG, "Period release failed.", e);
      }
    }

  }

}