# All files / src/controller subtitle-track-controller.js

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     /*
     * subtitle track controller
    */

    import Event from '../events';
    import EventHandler from '../event-handler';
    import {logger} from '../utils/logger';

    function filterSubtitleTracks(textTrackList) {
      let tracks = [];
      for (let i = 0; i < textTrackList.length; i++) {
        if (textTrackList[i].kind === 'subtitles') {
          tracks.push(textTrackList[i]);
        }
      }
      return tracks;
    }

    class SubtitleTrackController extends EventHandler {

      constructor(hls) {
        super(hls,
                   Event.MEDIA_ATTACHED,
                   Event.MEDIA_DETACHING,
                   Event.MANIFEST_LOADING,
                   Event.MANIFEST_LOADED,
                   Event.SUBTITLE_TRACK_LOADED);
        this.tracks = [];
        this.trackId = -1;
        this.media = undefined;
        this.subtitleDisplay = false;
      }

      _onTextTracksChanged() {
        // Media is undefined when switching streams via loadSource()
        if (!this.media) {
          return;
        }

        let trackId = -1;
        let tracks = filterSubtitleTracks(this.media.textTracks);
        for (let id = 0; id < tracks.length; id++) {
          if (tracks[id].mode === 'showing') {
            trackId = id;
          }
        }

        // Setting current subtitleTrack will invoke code.
        this.subtitleTrack = trackId;
      }

      destroy() {
        EventHandler.prototype.destroy.call(this);
      }

      // Listen for subtitle track change, then extract the current track ID.
      onMediaAttached(data) {
        this.media = data.media;
        if (!this.media) {
          return;
        }

        this.trackChangeListener = this._onTextTracksChanged.bind(this);

        this.useTextTrackPolling = !(this.media.textTracks && 'onchange' in this.media.textTracks);
        if (this.useTextTrackPolling) {
          this.subtitlePollingInterval = setInterval(() => {
            this.trackChangeListener();
          }, 500);
        } else {
          this.media.textTracks.addEventListener('change', this.trackChangeListener);
        }
      }

      onMediaDetaching() {
        if (!this.media) {
          return;
        }
        if (this.useTextTrackPolling) {
          clearInterval(this.subtitlePollingInterval);
        } else {
          this.media.textTracks.removeEventListener('change', this.trackChangeListener);
        }

        this.media = undefined;
      }

      // Reset subtitle tracks on manifest loading
      onManifestLoading() {
        this.tracks = [];
        this.trackId = -1;
      }

      // Fired whenever a new manifest is loaded.
      onManifestLoaded(data) {
        let tracks = data.subtitles || [];
        let defaultFound = false;
        this.tracks = tracks;
        this.trackId = -1;
        this.hls.trigger(Event.SUBTITLE_TRACKS_UPDATED, {subtitleTracks : tracks});

        // loop through available subtitle tracks and autoselect default if needed
        // TODO: improve selection logic to handle forced, etc
        tracks.forEach(track => {
          if (track.default) {
            this.subtitleTrack = track.id;
            defaultFound = true;
          }
        });
      }

      // Trigger subtitle track playlist reload.
      onTick() {
        const trackId = this.trackId;
        const subtitleTrack = this.tracks[trackId];
        if (!subtitleTrack) {
          return;
        }

        const details = subtitleTrack.details;
        // check if we need to load playlist for this subtitle Track
        if (details === undefined || details.live === true) {
          // track not retrieved yet, or live playlist we need to (re)load it
          logger.log(`(re)loading playlist for subtitle track ${trackId}`);
          this.hls.trigger(Event.SUBTITLE_TRACK_LOADING, {url: subtitleTrack.url, id: trackId});
        }
      }

      onSubtitleTrackLoaded(data) {
        if (data.id < this.tracks.length) {
          logger.log(`subtitle track ${data.id} loaded`);
          this.tracks[data.id].details = data.details;
          // check if current playlist is a live playlist
          if (data.details.live && !this.timer) {
            // if live playlist we will have to reload it periodically
            // set reload period to playlist target duration
            this.timer = setInterval(() => {
              this.onTick();
            }, 1000 * data.details.targetduration, this);
          }
          if (!data.details.live && this.timer) {
            // playlist is not live and timer is armed : stopping it
            clearInterval(this.timer);
            this.timer = null;
          }
        }
      }

      /** get alternate subtitle tracks list from playlist **/
      get subtitleTracks() {
        return this.tracks;
      }

      /** get index of the selected subtitle track (index in subtitle track lists) **/
      get subtitleTrack() {
       return this.trackId;
      }

      /** select a subtitle track, based on its index in subtitle track lists**/
      set subtitleTrack(subtitleTrackId) {
        if (this.trackId !== subtitleTrackId) {// || this.tracks[subtitleTrackId].details === undefined) {
          this.setSubtitleTrackInternal(subtitleTrackId);
        }
      }

     setSubtitleTrackInternal(newId) {
        // check if level idx is valid
        if (newId < -1 || newId >= this.tracks.length) {
          return;
        }

        // stopping live reloading timer if any
        if (this.timer) {
          clearInterval(this.timer);
          this.timer = null;
        }

        let textTracks = filterSubtitleTracks(this.media.textTracks);

        // hide currently enabled subtitle track
        if (this.trackId !== -1 && this.subtitleDisplay) {
          textTracks[this.trackId].mode = 'hidden';
        }

        this.trackId = newId;
        logger.log(`switching to subtitle track ${newId}`);
        this.hls.trigger(Event.SUBTITLE_TRACK_SWITCH, {id: newId});

        if (newId === -1) {
          return;
        }

        let subtitleTrack = this.tracks[newId];
        if (this.subtitleDisplay) {
          textTracks[newId].mode = 'showing';
        }

        // check if we need to load playlist for this subtitle Track
        let details = subtitleTrack.details;
        if (details === undefined || details.live === true) {
          // track not retrieved yet, or live playlist we need to (re)load it
          logger.log(`(re)loading playlist for subtitle track ${newId}`);
          this.hls.trigger(Event.SUBTITLE_TRACK_LOADING, {url: subtitleTrack.url, id: newId});
        }
      }
    }

    export default SubtitleTrackController;