/*
 * Copyright (C) 2014 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.exoplayer;

import com.google.android.exoplayer.ExoPlayer.ExoPlayerMessage;
import com.google.android.exoplayer.TrackSelector.InvalidationListener;
import com.google.android.exoplayer.util.PriorityHandlerThread;
import com.google.android.exoplayer.util.TraceUtil;
import com.google.android.exoplayer.util.Util;

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 java.io.IOException;
import java.util.ArrayList;

/**
 * Implements the internal behavior of {@link ExoPlayerImpl}.
 */
// TODO[REFACTOR]: Make sure renderer errors that will prevent prepare from being called again are
// always propagated properly.
/* package */ final class ExoPlayerImplInternal implements Handler.Callback, InvalidationListener {

  /**
   * 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 sourceIndex;

    public volatile long positionUs;
    public volatile long bufferedPositionUs;
    public volatile long durationUs;

    public PlaybackInfo(int sourceIndex) {
      this.sourceIndex = sourceIndex;
      durationUs = C.UNSET_TIME_US;
    }

  }

  private static final String TAG = "ExoPlayerImplInternal";

  // External messages
  public static final int MSG_STATE_CHANGED = 1;
  public static final int MSG_SET_PLAY_WHEN_READY_ACK = 2;
  public static final int MSG_SET_SOURCE_PROVIDER_ACK = 3;
  public static final int MSG_SEEK_ACK = 4;
  public static final int MSG_SOURCE_CHANGED = 5;
  public static final int MSG_ERROR = 6;

  // Internal messages
  private static final int MSG_SET_SOURCE_PROVIDER = 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_TRACK_SELECTION_INVALIDATED = 6;
  private static final int MSG_CUSTOM = 7;

  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 sources to buffer ahead of the current source in the timeline. The
   * source buffering policy normally prevents buffering too far ahead, but the policy could allow
   * too many very small sources to be buffered if the buffered source count were not limited.
   */
  private static final int MAXIMUM_BUFFER_AHEAD_SOURCES = 100;

  private final TrackSelector trackSelector;
  private final StandaloneMediaClock standaloneMediaClock;
  private final long minBufferUs;
  private final long minRebufferUs;
  private final Handler handler;
  private final HandlerThread internalPlaybackThread;
  private final Handler eventHandler;
  private final Timeline timeline;

  private PlaybackInfo playbackInfo;
  private TrackRenderer rendererMediaClockSource;
  private MediaClock rendererMediaClock;
  private SampleSourceProvider sampleSourceProvider;
  private TrackRenderer[] enabledRenderers;
  private boolean released;
  private boolean playWhenReady;
  private boolean rebuffering;
  private int state;
  private int customMessagesSent;
  private int customMessagesProcessed;
  private long elapsedRealtimeUs;

  private long sourceOffsetUs;
  private long internalPositionUs;

  public ExoPlayerImplInternal(TrackRenderer[] renderers, TrackSelector trackSelector,
      int minBufferMs, int minRebufferMs, boolean playWhenReady, Handler eventHandler) {
    this.trackSelector = trackSelector;
    this.minBufferUs = minBufferMs * 1000L;
    this.minRebufferUs = minRebufferMs * 1000L;
    this.playWhenReady = playWhenReady;
    this.eventHandler = eventHandler;
    this.state = ExoPlayer.STATE_IDLE;

    for (int i = 0; i < renderers.length; i++) {
      renderers[i].setIndex(i);
    }

    standaloneMediaClock = new StandaloneMediaClock();
    enabledRenderers = new TrackRenderer[0];
    timeline = new Timeline(renderers);
    playbackInfo = new PlaybackInfo(0);

    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 setSourceProvider(SampleSourceProvider sourceProvider) {
    handler.obtainMessage(MSG_SET_SOURCE_PROVIDER, sourceProvider).sendToTarget();
  }

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

  public void seekTo(int sourceIndex, long positionUs) {
    handler.obtainMessage(MSG_SEEK_TO, sourceIndex, -1, 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();
  }

  // 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_SET_SOURCE_PROVIDER: {
          setSourceProviderInternal((SampleSourceProvider) msg.obj);
          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_CUSTOM: {
          sendMessagesInternal((ExoPlayerMessage[]) msg.obj);
          return true;
        }
        case MSG_TRACK_SELECTION_INVALIDATED: {
          reselectTracksInternal();
          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 boolean isReadyOrEnded(TrackRenderer renderer) {
    return renderer.isReady() || renderer.isEnded();
  }

  private boolean haveSufficientBuffer() {
    // TODO[playlists]: Take into account the buffered position in the timeline.
    long minBufferDurationUs = rebuffering ? minRebufferUs : minBufferUs;
    return minBufferDurationUs <= 0
        || playbackInfo.bufferedPositionUs == C.END_OF_SOURCE_US
        || playbackInfo.bufferedPositionUs >= playbackInfo.positionUs + minBufferDurationUs
        || (playbackInfo.durationUs != C.UNSET_TIME_US
            && playbackInfo.bufferedPositionUs >= playbackInfo.durationUs);
  }

  private void setSourceProviderInternal(SampleSourceProvider sourceProvider) {
    try {
      resetInternal();
      sampleSourceProvider = sourceProvider;
      setState(ExoPlayer.STATE_BUFFERING);
      handler.sendEmptyMessage(MSG_DO_SOME_WORK);
    } finally {
      eventHandler.sendEmptyMessage(MSG_SET_SOURCE_PROVIDER_ACK);
    }
  }

  private void setPlayWhenReadyInternal(boolean playWhenReady) throws ExoPlaybackException {
    try {
      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);
        }
      }
    } finally {
      eventHandler.sendEmptyMessage(MSG_SET_PLAY_WHEN_READY_ACK);
    }
  }

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

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

  private void updatePlaybackPositions() throws ExoPlaybackException {
    SampleSource sampleSource = timeline.getSampleSource();
    if (sampleSource == null) {
      return;
    }

    // Update the duration.
    if (playbackInfo.durationUs == C.UNSET_TIME_US) {
      playbackInfo.durationUs = sampleSource.getDurationUs();
    }

    // Update the playback position.
    long positionUs = sampleSource.readDiscontinuity();
    if (positionUs != C.UNSET_TIME_US) {
      resetInternalPosition(positionUs);
    } else {
      if (rendererMediaClockSource != null && !rendererMediaClockSource.isEnded()) {
        internalPositionUs = rendererMediaClock.getPositionUs();
        standaloneMediaClock.setPositionUs(internalPositionUs);
      } else {
        internalPositionUs = standaloneMediaClock.getPositionUs();
      }
      positionUs = internalPositionUs - sourceOffsetUs;
    }
    playbackInfo.positionUs = positionUs;
    elapsedRealtimeUs = SystemClock.elapsedRealtime() * 1000;

    // Update the buffered position.
    long bufferedPositionUs;
    if (enabledRenderers.length == 0) {
      bufferedPositionUs = C.END_OF_SOURCE_US;
    } else {
      bufferedPositionUs = sampleSource.getBufferedPositionUs();
      if (bufferedPositionUs == C.END_OF_SOURCE_US && playbackInfo.durationUs != C.UNSET_TIME_US) {
        bufferedPositionUs = playbackInfo.durationUs;
      }
    }
    playbackInfo.bufferedPositionUs = bufferedPositionUs;
  }

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

    timeline.updateSources();
    if (timeline.getSampleSource() == null) {
      // We're still waiting for the source to be prepared.
      scheduleNextOperation(MSG_DO_SOME_WORK, operationStartTimeMs, PREPARING_SOURCE_INTERVAL_MS);
      return;
    }

    TraceUtil.beginSection("doSomeWork");

    updatePlaybackPositions();
    boolean allRenderersEnded = true;
    boolean allRenderersReadyOrEnded = true;
    for (TrackRenderer renderer : enabledRenderers) {
      // TODO: Each renderer should return the maximum delay before which it wishes to be invoked
      // again. The minimum of these values should then be used as the delay before the next
      // invocation of this method.
      renderer.render(internalPositionUs, 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 = isReadyOrEnded(renderer);
      if (!rendererReadyOrEnded) {
        renderer.maybeThrowStreamError();
      }
      allRenderersReadyOrEnded = allRenderersReadyOrEnded && rendererReadyOrEnded;
    }

    // TODO: Have timeline.updateSources() above return whether the timeline is ready, and remove
    // timeline.isReady(). This will avoid any inconsistencies that could arise due to the playback
    // position update. We could probably return [ENDED|READY|BUFFERING] and get rid of isEnded too.
    if (allRenderersEnded && (playbackInfo.durationUs == C.UNSET_TIME_US
        || playbackInfo.durationUs <= playbackInfo.positionUs) && timeline.isEnded()) {
      setState(ExoPlayer.STATE_ENDED);
      stopRenderers();
    } else if (state == ExoPlayer.STATE_BUFFERING) {
      if ((enabledRenderers.length > 0 ? allRenderersReadyOrEnded : timeline.isReady())
          && haveSufficientBuffer()) {
        setState(ExoPlayer.STATE_READY);
        if (playWhenReady) {
          startRenderers();
        }
      }
    } else if (state == ExoPlayer.STATE_READY) {
      if (enabledRenderers.length > 0 ? !allRenderersReadyOrEnded : !timeline.isReady()) {
        rebuffering = playWhenReady;
        setState(ExoPlayer.STATE_BUFFERING);
        stopRenderers();
      }
    }

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

    TraceUtil.endSection();
  }

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

  private void seekToInternal(int sourceIndex, long seekPositionUs) throws ExoPlaybackException {
    try {
      if (sourceIndex == playbackInfo.sourceIndex
          && (seekPositionUs / 1000) == (playbackInfo.positionUs / 1000)) {
        // Seek position equals the current position to the nearest millisecond. Do nothing.
        return;
      }

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

      timeline.seekToSource(sourceIndex);
      SampleSource sampleSource = timeline.getSampleSource();
      if (sampleSource != null && enabledRenderers.length > 0) {
        seekPositionUs = sampleSource.seekToUs(seekPositionUs);
      }
      resetInternalPosition(seekPositionUs);

      if (sourceIndex != playbackInfo.sourceIndex) {
        playbackInfo = new PlaybackInfo(sourceIndex);
        playbackInfo.positionUs = seekPositionUs;
        updatePlaybackPositions();
        eventHandler.obtainMessage(MSG_SOURCE_CHANGED, playbackInfo).sendToTarget();
      }

      if (sampleSourceProvider != null) {
        handler.sendEmptyMessage(MSG_DO_SOME_WORK);
      }
    } finally {
      eventHandler.sendEmptyMessage(MSG_SEEK_ACK);
    }
  }

  private void resetInternalPosition(long sourcePositionUs) throws ExoPlaybackException {
    internalPositionUs = sourceOffsetUs + sourcePositionUs;
    standaloneMediaClock.setPositionUs(internalPositionUs);
    for (TrackRenderer renderer : enabledRenderers) {
      renderer.reset(internalPositionUs);
    }
  }

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

  private void releaseInternal() {
    resetInternal();
    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 (TrackRenderer 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 TrackRenderer[0];
    sampleSourceProvider = null;
    timeline.reset();
  }

  private void sendMessagesInternal(ExoPlayerMessage[] messages) throws ExoPlaybackException {
    try {
      for (ExoPlayerMessage message : messages) {
        message.target.handleMessage(message.messageType, message.message);
      }
      if (sampleSourceProvider != 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(TrackRenderer renderer) throws ExoPlaybackException {
    if (renderer.getState() == TrackRenderer.STATE_STARTED) {
      renderer.stop();
    }
  }

  private void reselectTracksInternal() throws ExoPlaybackException {
    if (timeline.getSampleSource() == null) {
      // We don't have tracks yet, so we don't care.
      return;
    }
    timeline.reselectTracks();
    updatePlaybackPositions();
    handler.sendEmptyMessage(MSG_DO_SOME_WORK);
  }

  /**
   * Keeps track of the {@link Source}s of media being played in the timeline.
   */
  private final class Timeline {

    private final TrackRenderer[] renderers;

    // Used during track reselection.
    private final boolean[] rendererWasEnabledFlags;
    private final ArrayList<TrackStream> oldStreams;
    private final ArrayList<TrackSelection> newSelections;

    private Source playingSource;
    private Source readingSource;
    private Source bufferingSource;

    private int pendingSourceIndex;
    private long playingSourceEndPositionUs;
    private long bufferingSourceOffsetUs;

    public Timeline(TrackRenderer[] renderers) {
      this.renderers = renderers;
      rendererWasEnabledFlags = new boolean[renderers.length];
      oldStreams = new ArrayList<>();
      newSelections = new ArrayList<>();
      playingSourceEndPositionUs = C.UNSET_TIME_US;
    }

    public SampleSource getSampleSource() throws ExoPlaybackException {
      return playingSource == null ? null : playingSource.sampleSource;
    }

    public boolean isEnded() {
      if (playingSource == null) {
        return false;
      }
      int sourceCount = sampleSourceProvider.getSourceCount();
      return sourceCount != SampleSourceProvider.UNKNOWN_SOURCE_COUNT
          && playingSource.index == sourceCount - 1;
    }

    public boolean isReady() {
      return playingSourceEndPositionUs == C.UNSET_TIME_US
          || internalPositionUs < playingSourceEndPositionUs
          || (playingSource.nextSource != null && playingSource.nextSource.prepared);
    }

    public void updateSources() throws ExoPlaybackException, IOException {
      // TODO[playlists]: Let sample source providers invalidate sources that are already buffering.

      int sourceCount = sampleSourceProvider.getSourceCount();
      if (bufferingSource == null
          || (bufferingSource.isFullyBuffered() && bufferingSource.index
              - (playingSource != null ? playingSource.index : 0) < MAXIMUM_BUFFER_AHEAD_SOURCES)) {
        // Try and obtain the next source to start buffering.
        int sourceIndex = bufferingSource == null ? pendingSourceIndex : bufferingSource.index + 1;
        if (sourceCount == SampleSourceProvider.UNKNOWN_SOURCE_COUNT || sourceIndex < sourceCount) {
          // Attempt to create the next source.
          SampleSource sampleSource = sampleSourceProvider.createSource(sourceIndex);
          if (sampleSource != null) {
            Source newSource = new Source(sampleSource, sourceIndex, renderers.length);
            if (bufferingSource != null) {
              bufferingSource.nextSource = newSource;
              bufferingSourceOffsetUs += bufferingSource.sampleSource.getDurationUs();
            }
            bufferingSource = newSource;
          }
        }
      }

      if (bufferingSource != null) {
        if (!bufferingSource.prepared) {
          // Continue preparation.
          // TODO[playlists]: Add support for setting the start position to play in a source.
          long startPositionUs = playingSource == null ? playbackInfo.positionUs : 0;
          if (bufferingSource.prepare(startPositionUs)) {
            Pair<TrackSelectionArray, Object> result = trackSelector.selectTracks(renderers,
                bufferingSource.sampleSource.getTrackGroups());
            bufferingSource.selectTracks(result.first, result.second, startPositionUs);
            if (playingSource == null) {
              // This is the first prepared source, so start playing it.
              setPlayingSource(bufferingSource, 0);
            }
          }
        }

        if (bufferingSource.hasEnabledTracks) {
          long sourcePositionUs = internalPositionUs - bufferingSourceOffsetUs;
          bufferingSource.sampleSource.continueBuffering(sourcePositionUs);
        }
      }

      if (playingSource == null) {
        return;
      }

      if (readingSource != playingSource) {
        if (playingSourceEndPositionUs != C.UNSET_TIME_US
            && internalPositionUs >= playingSourceEndPositionUs) {
          playingSource.release();
          setPlayingSource(readingSource, playingSourceEndPositionUs);
          playbackInfo = new PlaybackInfo(playingSource.index);
          updatePlaybackPositions();
          eventHandler.obtainMessage(MSG_SOURCE_CHANGED, playbackInfo).sendToTarget();
        } else {
          // We're reading ahead, but it's not time to update the playing source yet.
          return;
        }
      }

      // Check whether all enabled renderers have read to the end of their TrackStreams.
      for (TrackRenderer renderer : enabledRenderers) {
        if (!renderer.hasReadStreamToEnd()) {
          return;
        }
      }
      // TODO: Is playingSourceEndPositionUs equivalent to playbackInfo.durationUs?
      if (playingSourceEndPositionUs == C.UNSET_TIME_US) {
        playingSourceEndPositionUs = sourceOffsetUs + playingSource.sampleSource.getDurationUs();
      }
      if (sourceCount != SampleSourceProvider.UNKNOWN_SOURCE_COUNT
          && readingSource.index == sourceCount - 1) {
        // This is the last source, so signal the renderers to read the end of the stream.
        for (TrackRenderer renderer : enabledRenderers) {
          renderer.setCurrentTrackStreamIsFinal();
        }
        readingSource = null;
        playingSourceEndPositionUs = C.UNSET_TIME_US;
      } else if (playingSource.nextSource != null && playingSource.nextSource.prepared) {
        readingSource = playingSource.nextSource;
        TrackSelectionArray newTrackSelections = readingSource.trackSelections;
        TrackGroupArray groups = readingSource.sampleSource.getTrackGroups();
        for (int i = 0; i < renderers.length; i++) {
          TrackRenderer renderer = renderers[i];
          TrackSelection selection = newTrackSelections.get(i);
          if (renderer.getState() != TrackRenderer.STATE_DISABLED) {
            if (selection != null) {
              // Replace the renderer's TrackStream so the transition to playing the next source can
              // be seamless.
              Format[] formats = new Format[selection.length];
              for (int j = 0; j < formats.length; j++) {
                formats[j] = groups.get(selection.group).getFormat(selection.getTrack(j));
              }
              renderer.replaceTrackStream(formats, readingSource.trackStreams[i],
                  playingSourceEndPositionUs);
            } else {
              // The renderer will be disabled when transitioning to playing the next source. Send
              // end-of-stream to play out any remaining data.
              renderer.setCurrentTrackStreamIsFinal();
            }
          }
        }
      }
    }

    public void seekToSource(int sourceIndex) throws ExoPlaybackException {
      // Clear the timeline, but keep the requested source if it is already prepared.
      Source source = playingSource;
      Source newPlayingSource = null;
      while (source != null) {
        if (source.index == sourceIndex && source.prepared) {
          newPlayingSource = source;
        } else {
          source.release();
        }
        source = source.nextSource;
      }

      if (newPlayingSource != null) {
        newPlayingSource.nextSource = null;
        setPlayingSource(newPlayingSource, sourceOffsetUs);
        bufferingSource = playingSource;
        bufferingSourceOffsetUs = sourceOffsetUs;
      } else {
        // TODO[REFACTOR]: We need to disable the renderers somewhere in here?
        playingSource = null;
        readingSource = null;
        bufferingSource = null;
        bufferingSourceOffsetUs = 0;
        pendingSourceIndex = sourceIndex;
      }
    }

    public void reselectTracks() throws ExoPlaybackException {
      if (readingSource != null && readingSource != playingSource) {
        // Newly enabled tracks in playingSource can increase the calculated start timestamp for the
        // next source, so we have to discard the reading source. Reset TrackStreams for renderers
        // that are reading the next source already back to the playing source.
        TrackSelectionArray newTrackSelections = readingSource.trackSelections;
        TrackGroupArray groups = readingSource.sampleSource.getTrackGroups();
        for (int i = 0; i < renderers.length; i++) {
          TrackRenderer renderer = renderers[i];
          TrackSelection selection = newTrackSelections.get(i);
          if (selection != null && renderer.getState() != TrackRenderer.STATE_DISABLED) {
            // The renderer is enabled and will continue to be enabled after the transition.
            Format[] formats = new Format[selection.length];
            for (int j = 0; j < formats.length; j++) {
              formats[j] = groups.get(selection.group).getFormat(selection.getTrack(j));
            }
            renderer.replaceTrackStream(formats, playingSource.trackStreams[i], sourceOffsetUs);
          }
        }
      }

      // Discard the rest of the timeline after the playing source, as the player may need to
      // rebuffer after track selection.
      Source source = playingSource.nextSource;
      while (source != null) {
        source.release();
        source = source.nextSource;
      }
      playingSource.nextSource = null;
      readingSource = playingSource;
      bufferingSource = playingSource;
      playingSourceEndPositionUs = C.UNSET_TIME_US;
      bufferingSourceOffsetUs = sourceOffsetUs;

      // Update the track selection for the playing source.
      Pair<TrackSelectionArray, Object> result =
          trackSelector.selectTracks(renderers, playingSource.sampleSource.getTrackGroups());
      TrackSelectionArray newTrackSelections = result.first;
      Object trackSelectionData = result.second;
      if (newTrackSelections.equals(playingSource.trackSelections)) {
        trackSelector.onSelectionActivated(trackSelectionData);
        return;
      }

      int enabledRendererCount = disableRenderers(false, newTrackSelections);
      TrackStream[] newStreams = playingSource.sampleSource.selectTracks(oldStreams, newSelections,
          playbackInfo.positionUs);
      playingSource.updateTrackStreams(newTrackSelections, newSelections, newStreams);
      trackSelector.onSelectionActivated(trackSelectionData);

      // Update the stored TrackStreams.
      for (int i = 0; i < renderers.length; i++) {
        TrackRenderer renderer = renderers[i];
        TrackSelection newSelection = newTrackSelections.get(i);
        if (newSelection != null && renderer.getState() == TrackRenderer.STATE_DISABLED) {
          int newStreamIndex = newSelections.indexOf(newSelection);
          playingSource.trackStreams[i] = newStreams[newStreamIndex];
        }
      }

      enableRenderers(newTrackSelections, enabledRendererCount);
    }

    public void reset() {
      Source source = playingSource != null ? playingSource : bufferingSource;
      while (source != null) {
        source.release();
        source = source.nextSource;
      }
      playingSource = null;
      readingSource = null;
      bufferingSource = null;
      playingSourceEndPositionUs = C.UNSET_TIME_US;
      pendingSourceIndex = 0;
      sourceOffsetUs = 0;
      bufferingSourceOffsetUs = 0;
      playbackInfo = new PlaybackInfo(0);
      eventHandler.obtainMessage(MSG_SOURCE_CHANGED, playbackInfo).sendToTarget();
    }

    private void setPlayingSource(Source source, long offsetUs) throws ExoPlaybackException {
      sourceOffsetUs = offsetUs;
      // Disable/enable renderers for the new source.
      int enabledRendererCount = disableRenderers(true, source.trackSelections);
      if (playingSource != source) {
        trackSelector.onSelectionActivated(source.trackSelectionData);
      }
      readingSource = source;
      playingSource = source;
      playingSourceEndPositionUs = C.UNSET_TIME_US;
      enableRenderers(source.trackSelections, enabledRendererCount);
    }

    private int disableRenderers(boolean sourceTransition, TrackSelectionArray newTrackSelections)
        throws ExoPlaybackException {
      // Disable any renderers whose selections have changed, adding the corresponding TrackStream
      // instances to oldStreams. Where we need to obtain a new TrackStream instance for a renderer,
      // we add the corresponding TrackSelection to newSelections.
      oldStreams.clear();
      newSelections.clear();
      int enabledRendererCount = 0;
      for (int i = 0; i < renderers.length; i++) {
        TrackRenderer renderer = renderers[i];
        rendererWasEnabledFlags[i] = renderer.getState() != TrackRenderer.STATE_DISABLED;
        TrackSelection oldSelection = playingSource == null ? null
            : playingSource.trackSelections.get(i);
        TrackSelection newSelection = newTrackSelections.get(i);
        if (newSelection != null) {
          enabledRendererCount++;
        }
        // If the player is transitioning to a new source, disable renderers that are not used when
        // playing the new source. Otherwise, disable renderers whose selections are changing.
        if ((sourceTransition && oldSelection != null && newSelection == null)
            || (!sourceTransition && !Util.areEqual(oldSelection, newSelection))) {
          // Either this is a source transition and the renderer is not needed any more, or the
          if (rendererWasEnabledFlags[i]) {
            // We need to disable the renderer so that we can enable it with its new selection.
            if (renderer == rendererMediaClockSource) {
              // The renderer is providing the media clock.
              if (newSelection == 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();
            oldStreams.add(playingSource.trackStreams[i]);
          }
          if (newSelection != null) {
            newSelections.add(newSelection);
          }
        }
      }
      return enabledRendererCount;
    }

    private void enableRenderers(TrackSelectionArray newTrackSelections, int enabledRendererCount)
        throws ExoPlaybackException {
      playingSource.trackSelections = newTrackSelections;
      enabledRenderers = new TrackRenderer[enabledRendererCount];
      enabledRendererCount = 0;
      TrackGroupArray trackGroups = playingSource.sampleSource.getTrackGroups();
      for (int i = 0; i < renderers.length; i++) {
        TrackRenderer renderer = renderers[i];
        TrackSelection newSelection = playingSource.trackSelections.get(i);
        if (newSelection != null) {
          enabledRenderers[enabledRendererCount++] = renderer;
          if (renderer.getState() == TrackRenderer.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 new selection.
            Format[] formats = new Format[newSelection.length];
            for (int j = 0; j < formats.length; j++) {
              formats[j] = trackGroups.get(newSelection.group).getFormat(newSelection.getTrack(j));
            }
            // Enable the renderer.
            renderer.enable(formats, playingSource.trackStreams[i], internalPositionUs, joining,
                sourceOffsetUs);
            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();
            }
          }
        }
      }
    }

  }

  /**
   * Represents a {@link SampleSource} with information required to play it as part of a timeline.
   */
  private static final class Source {

    public final SampleSource sampleSource;
    public final int index;
    public final TrackStream[] trackStreams;

    public boolean prepared;
    public boolean hasEnabledTracks;
    public TrackSelectionArray trackSelections;
    public Object trackSelectionData;

    public Source nextSource;

    public Source(SampleSource sampleSource, int index, int rendererCount) {
      this.sampleSource = sampleSource;
      this.index = index;
      trackStreams = new TrackStream[rendererCount];
    }

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

    public boolean prepare(long startPositionUs) throws IOException {
      if (sampleSource.prepare(startPositionUs)) {
        prepared = true;
        return true;
      } else {
        return false;
      }
    }

    public void selectTracks(TrackSelectionArray newTrackSelections, Object trackSelectionData,
        long positionUs) throws ExoPlaybackException {
      this.trackSelectionData = trackSelectionData;
      if (newTrackSelections.equals(trackSelections)) {
        return;
      }

      ArrayList<TrackStream> oldStreams = new ArrayList<>();
      ArrayList<TrackSelection> newSelections = new ArrayList<>();
      for (int i = 0; i < newTrackSelections.length; i++) {
        TrackSelection oldSelection = trackSelections == null ? null : trackSelections.get(i);
        TrackSelection newSelection = newTrackSelections.get(i);
        if (!Util.areEqual(oldSelection, newSelection)) {
          if (oldSelection != null) {
            oldStreams.add(trackStreams[i]);
          }
          if (newSelection != null) {
            newSelections.add(newSelection);
          }
        }
      }
      TrackStream[] newStreams = sampleSource.selectTracks(oldStreams, newSelections, positionUs);
      updateTrackStreams(newTrackSelections, newSelections, newStreams);
    }

    public void updateTrackStreams(TrackSelectionArray newTrackSelections,
        ArrayList<TrackSelection> newSelections, TrackStream[] newStreams) {
      hasEnabledTracks = false;
      for (int i = 0; i < newTrackSelections.length; i++) {
        TrackSelection selection = newTrackSelections.get(i);
        if (selection != null) {
          hasEnabledTracks = true;
          int index = newSelections.indexOf(selection);
          if (index != -1) {
            trackStreams[i] = newStreams[index];
          } else {
            // This selection/stream is unchanged.
          }
        } else {
          trackStreams[i] = null;
        }
      }
      trackSelections = newTrackSelections;
    }

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

  }

}