/*
 * 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 com.google.android.exoplayer2.audio.MediaCodecAudioRenderer;
import com.google.android.exoplayer2.metadata.MetadataRenderer;
import com.google.android.exoplayer2.source.ConcatenatingMediaSource;
import com.google.android.exoplayer2.source.ExtractorMediaSource;
import com.google.android.exoplayer2.source.MediaSource;
import com.google.android.exoplayer2.source.MergingMediaSource;
import com.google.android.exoplayer2.source.SingleSampleMediaSource;
import com.google.android.exoplayer2.source.TrackGroupArray;
import com.google.android.exoplayer2.source.dash.DashMediaSource;
import com.google.android.exoplayer2.source.hls.HlsMediaSource;
import com.google.android.exoplayer2.source.smoothstreaming.SsMediaSource;
import com.google.android.exoplayer2.text.TextRenderer;
import com.google.android.exoplayer2.trackselection.DefaultTrackSelector;
import com.google.android.exoplayer2.trackselection.TrackSelectionArray;
import com.google.android.exoplayer2.trackselection.TrackSelector;
import com.google.android.exoplayer2.upstream.DataSource;
import com.google.android.exoplayer2.video.MediaCodecVideoRenderer;

/**
 * An extensible media player exposing traditional high-level media player functionality, such as
 * the ability to buffer media, play, pause and seek. Instances can be obtained from
 * {@link ExoPlayerFactory}.
 *
 * <h3>Player composition</h3>
 * <p>ExoPlayer is designed to make few assumptions about (and hence impose few restrictions on) the
 * type of the media being played, how and where it is stored, and how it is rendered. Rather than
 * implementing the loading and rendering of media directly, ExoPlayer implementations delegate this
 * work to components that are injected when a player is created or when it's prepared for playback.
 * Components common to all ExoPlayer implementations are:
 * <ul>
 *   <li>A <b>{@link MediaSource}</b> that defines the media to be played, loads the media, and from
 *   which the loaded media can be read. A MediaSource is injected via {@link #prepare} at the start
 *   of playback. The library provides default implementations for regular media files
 *   ({@link ExtractorMediaSource}), DASH ({@link DashMediaSource}), SmoothStreaming
 *   ({@link SsMediaSource}) and HLS ({@link HlsMediaSource}), implementations for merging
 *   ({@link MergingMediaSource}) and concatenating ({@link ConcatenatingMediaSource}) other
 *   MediaSources, and an implementation for loading single samples
 *   ({@link SingleSampleMediaSource}) most often used for side-loaded subtitle and closed
 *   caption files.</li>
 *   <li><b>{@link Renderer}</b>s that render individual components of the media. The library
 *   provides default implementations for common media types ({@link MediaCodecVideoRenderer},
 *   {@link MediaCodecAudioRenderer}, {@link TextRenderer} and {@link MetadataRenderer}). A Renderer
 *   consumes media of its corresponding type from the MediaSource being played. Renderers are
 *   injected when the player is created.</li>
 *   <li>A <b>{@link TrackSelector}</b> that selects tracks provided by the MediaSource to be
 *   consumed by each of the available Renderers. The library provides a default implementation
 *   ({@link DefaultTrackSelector}) suitable for most use cases. A TrackSelector is injected when
 *   the player is created.</li>
 *   <li>A <b>{@link LoadControl}</b> that controls when the MediaSource buffers more media, and how
 *   much media is buffered. The library provides a default implementation
 *   ({@link DefaultLoadControl}) suitable for most use cases. A LoadControl is injected when the
 *   player is created.</li>
 * </ul>
 * <p>An ExoPlayer can be built using the default components provided by the library, but may also
 * be built using custom implementations if non-standard behaviors are required. For example a
 * custom LoadControl could be injected to change the player's buffering strategy, or a custom
 * Renderer could be injected to use a video codec not supported natively by Android.
 *
 * <p>The concept of injecting components that implement pieces of player functionality is present
 * throughout the library. The default component implementations listed above delegate work to
 * further injected components. This allows many sub-components to be individually replaced with
 * custom implementations. For example the default MediaSource implementations require one or more
 * {@link DataSource} factories to be injected via their constructors. By providing a custom factory
 * it's possible to load data from a non-standard source or through a different network stack.
 *
 * <h3>Threading model</h3>
 * <p>The figure below shows ExoPlayer's threading model.</p>
 * <p align="center">
 *   <img src="doc-files/exoplayer-threading-model.svg" alt="ExoPlayer's threading model">
 * </p>
 *
 * <ul>
 * <li>It is recommended that ExoPlayer instances are created and accessed from a single application
 * thread. The application's main thread is ideal. Accessing an instance from multiple threads is
 * discouraged, however if an application does wish to do this then it may do so provided that it
 * ensures accesses are synchronized.</li>
 * <li>Registered listeners are called on the thread that created the ExoPlayer instance.</li>
 * <li>An internal playback thread is responsible for playback. Injected player components such as
 * Renderers, MediaSources, TrackSelectors and LoadControls are called by the player on this
 * thread.</li>
 * <li>When the application performs an operation on the player, for example a seek, a message is
 * delivered to the internal playback thread via a message queue. The internal playback thread
 * consumes messages from the queue and performs the corresponding operations. Similarly, when a
 * playback event occurs on the internal playback thread, a message is delivered to the application
 * thread via a second message queue. The application thread consumes messages from the queue,
 * updating the application visible state and calling corresponding listener methods.</li>
 * <li>Injected player components may use additional background threads. For example a MediaSource
 * may use a background thread to load data. These are implementation specific.</li>
 * </ul>
 */
public interface ExoPlayer {

  /**
   * Listener of changes in player state.
   */
  interface EventListener {

    /**
     * Called when the available or selected tracks change.
     *
     * @param trackGroups The available tracks. Never null, but may be of length zero.
     * @param trackSelections The track selections for each {@link Renderer}. Never null and always
     *     of length {@link #getRendererCount()}, but may contain null elements.
     */
    void onTracksChanged(TrackGroupArray trackGroups, TrackSelectionArray trackSelections);

    /**
     * Called when the player starts or stops loading the source.
     *
     * @param isLoading Whether the source is currently being loaded.
     */
    void onLoadingChanged(boolean isLoading);

    /**
     * Called when the value returned from either {@link #getPlayWhenReady()} or
     * {@link #getPlaybackState()} changes.
     *
     * @param playWhenReady Whether playback will proceed when ready.
     * @param playbackState One of the {@code STATE} constants defined in the {@link ExoPlayer}
     *     interface.
     */
    void onPlayerStateChanged(boolean playWhenReady, int playbackState);

    /**
     * Called when timeline and/or manifest has been refreshed.
     *
     * @param timeline The latest timeline, or null if the timeline is being cleared.
     * @param manifest The latest manifest, or null if the manifest is being cleared.
     */
    void onTimelineChanged(Timeline timeline, Object manifest);

    /**
     * Called when an error occurs. The playback state will transition to {@link #STATE_IDLE}
     * immediately after this method is called. The player instance can still be used, and
     * {@link #release()} must still be called on the player should it no longer be required.
     *
     * @param error The error.
     */
    void onPlayerError(ExoPlaybackException error);

    /**
     * Called when a position discontinuity occurs. Position discontinuities occur when seeks are
     * performed, when playbacks transition from one period in the timeline to the next, and when
     * the player introduces discontinuities internally.
     */
    void onPositionDiscontinuity();

  }

  /**
   * A component of an {@link ExoPlayer} that can receive messages on the playback thread.
   * <p>
   * Messages can be delivered to a component via {@link #sendMessages} and
   * {@link #blockingSendMessages}.
   */
  interface ExoPlayerComponent {

    /**
     * Handles a message delivered to the component. Called on the playback thread.
     *
     * @param messageType The message type.
     * @param message The message.
     * @throws ExoPlaybackException If an error occurred whilst handling the message.
     */
    void handleMessage(int messageType, Object message) throws ExoPlaybackException;

  }

  /**
   * Defines a message and a target {@link ExoPlayerComponent} to receive it.
   */
  final class ExoPlayerMessage {

    /**
     * The target to receive the message.
     */
    public final ExoPlayerComponent target;
    /**
     * The type of the message.
     */
    public final int messageType;
    /**
     * The message.
     */
    public final Object message;

    /**
     * @param target The target of the message.
     * @param messageType The message type.
     * @param message The message.
     */
    public ExoPlayerMessage(ExoPlayerComponent target, int messageType, Object message) {
      this.target = target;
      this.messageType = messageType;
      this.message = message;
    }

  }

  /**
   * The player does not have a source to play, so it is neither buffering nor ready to play.
   */
  int STATE_IDLE = 1;
  /**
   * The player not able to immediately play from the current position. The cause is
   * {@link Renderer} specific, but this state typically occurs when more data needs to be
   * loaded to be ready to play, or more data needs to be buffered for playback to resume.
   */
  int STATE_BUFFERING = 2;
  /**
   * The player is able to immediately play from the current position. The player will be playing if
   * {@link #getPlayWhenReady()} returns true, and paused otherwise.
   */
  int STATE_READY = 3;
  /**
   * The player has finished playing the media.
   */
  int STATE_ENDED = 4;

  /**
   * Register a listener to receive events from the player. The listener's methods will be called on
   * the thread that was used to construct the player.
   *
   * @param listener The listener to register.
   */
  void addListener(EventListener listener);

  /**
   * Unregister a listener. The listener will no longer receive events from the player.
   *
   * @param listener The listener to unregister.
   */
  void removeListener(EventListener listener);

  /**
   * Returns the current state of the player.
   *
   * @return One of the {@code STATE} constants defined in this interface.
   */
  int getPlaybackState();

  /**
   * Prepares the player to play the provided {@link MediaSource}. Equivalent to
   * {@code prepare(mediaSource, true, true)}.
   */
  void prepare(MediaSource mediaSource);

  /**
   * Prepares the player to play the provided {@link MediaSource}, optionally resetting the playback
   * position the default position in the first {@link Timeline.Window}.
   *
   * @param mediaSource The {@link MediaSource} to play.
   * @param resetPosition Whether the playback position should be reset to the default position in
   *     the first {@link Timeline.Window}. If false, playback will start from the position defined
   *     by {@link #getCurrentWindowIndex()} and {@link #getCurrentPosition()}.
   * @param resetState Whether the timeline, manifest, tracks and track selections should be reset.
   *     Should be true unless the player is being prepared to play the same media as it was playing
   *     previously (e.g. if playback failed and is being retried).
   */
  void prepare(MediaSource mediaSource, boolean resetPosition, boolean resetState);

  /**
   * Sets whether playback should proceed when {@link #getPlaybackState()} == {@link #STATE_READY}.
   * <p>
   * If the player is already in the ready state then this method can be used to pause and resume
   * playback.
   *
   * @param playWhenReady Whether playback should proceed when ready.
   */
  void setPlayWhenReady(boolean playWhenReady);

  /**
   * Whether playback will proceed when {@link #getPlaybackState()} == {@link #STATE_READY}.
   *
   * @return Whether playback will proceed when ready.
   */
  boolean getPlayWhenReady();

  /**
   * Whether the player is currently loading the source.
   *
   * @return Whether the player is currently loading the source.
   */
  boolean isLoading();

  /**
   * Seeks to the default position associated with the current window. The position can depend on
   * the type of source passed to {@link #prepare(MediaSource)}. For live streams it will typically
   * be the live edge of the window. For other streams it will typically be the start of the window.
   */
  void seekToDefaultPosition();

  /**
   * Seeks to the default position associated with the specified window. The position can depend on
   * the type of source passed to {@link #prepare(MediaSource)}. For live streams it will typically
   * be the live edge of the window. For other streams it will typically be the start of the window.
   *
   * @param windowIndex The index of the window whose associated default position should be seeked
   *     to.
   */
  void seekToDefaultPosition(int windowIndex);

  /**
   * Seeks to a position specified in milliseconds in the current window.
   *
   * @param windowPositionMs The seek position in the current window.
   */
  void seekTo(long windowPositionMs);

  /**
   * Seeks to a position specified in milliseconds in the specified window.
   *
   * @param windowIndex The index of the window.
   * @param windowPositionMs The seek position in the specified window.
   */
  void seekTo(int windowIndex, long windowPositionMs);

  /**
   * Stops playback. Use {@code setPlayWhenReady(false)} rather than this method if the intention
   * is to pause playback.
   * <p>
   * Calling this method will cause the playback state to transition to {@link #STATE_IDLE}. The
   * player instance can still be used, and {@link #release()} must still be called on the player if
   * it's no longer required.
   * <p>
   * Calling this method does not reset the playback position.
   */
  void stop();

  /**
   * Releases the player. This method must be called when the player is no longer required. The
   * player must not be used after calling this method.
   */
  void release();

  /**
   * Sends messages to their target components. The messages are delivered on the playback thread.
   * If a component throws an {@link ExoPlaybackException} then it is propagated out of the player
   * as an error.
   *
   * @param messages The messages to be sent.
   */
  void sendMessages(ExoPlayerMessage... messages);

  /**
   * Variant of {@link #sendMessages(ExoPlayerMessage...)} that blocks until after the messages have
   * been delivered.
   *
   * @param messages The messages to be sent.
   */
  void blockingSendMessages(ExoPlayerMessage... messages);

  /**
   * Returns the number of renderers.
   */
  int getRendererCount();

  /**
   * Returns the track type that the renderer at a given index handles.
   *
   * @see Renderer#getTrackType()
   * @param index The index of the renderer.
   * @return One of the {@code TRACK_TYPE_*} constants defined in {@link C}.
   */
  int getRendererType(int index);

  /**
   * Returns the available track groups.
   */
  TrackGroupArray getCurrentTrackGroups();

  /**
   * Returns the current track selections for each renderer.
   */
  TrackSelectionArray getCurrentTrackSelections();

  /**
   * Returns the current manifest. The type depends on the {@link MediaSource} passed to
   * {@link #prepare}.
   */
  Object getCurrentManifest();

  /**
   * Returns the current {@link Timeline}, or {@code null} if there is no timeline.
   */
  Timeline getCurrentTimeline();

  /**
   * Returns the index of the period currently being played, or {@link C#INDEX_UNSET} if unknown.
   */
  int getCurrentPeriodIndex();

  /**
   * Returns the index of the window currently being played.
   */
  int getCurrentWindowIndex();

  /**
   * Returns the duration of the current window in milliseconds, or {@link C#TIME_UNSET} if the
   * duration is not known.
   */
  long getDuration();

  /**
   * Returns the playback position in the current window, in milliseconds.
   */
  long getCurrentPosition();

  /**
   * Returns an estimate of the position in the current window up to which data is buffered, in
   * milliseconds.
   */
  long getBufferedPosition();

  /**
   * Returns an estimate of the percentage in the current window up to which data is buffered, or 0
   * if no estimate is available.
   */
  int getBufferedPercentage();

}