@videojs/http-streaming/src/rendition-mixin.js

import { isIncompatible, isEnabled, isAudioOnly } from './playlist.js';
import { codecsForPlaylist } from './util/codecs.js';

/**
 * Returns a function that acts as the Enable/disable playlist function.
 *
 * @param {PlaylistLoader} loader - The master playlist loader
 * @param {string} playlistID - id of the playlist
 * @param {Function} changePlaylistFn - A function to be called after a
 * playlist's enabled-state has been changed. Will NOT be called if a
 * playlist's enabled-state is unchanged
 * @param {boolean=} enable - Value to set the playlist enabled-state to
 * or if undefined returns the current enabled-state for the playlist
 * @return {Function} Function for setting/getting enabled
 */
const enableFunction = (loader, playlistID, changePlaylistFn) => (enable) => {
  const playlist = loader.master.playlists[playlistID];
  const incompatible = isIncompatible(playlist);
  const currentlyEnabled = isEnabled(playlist);

  if (typeof enable === 'undefined') {
    return currentlyEnabled;
  }

  if (enable) {
    delete playlist.disabled;
  } else {
    playlist.disabled = true;
  }

  if (enable !== currentlyEnabled && !incompatible) {
    // Ensure the outside world knows about our changes
    changePlaylistFn();
    if (enable) {
      loader.trigger('renditionenabled');
    } else {
      loader.trigger('renditiondisabled');
    }
  }
  return enable;
};

/**
 * The representation object encapsulates the publicly visible information
 * in a media playlist along with a setter/getter-type function (enabled)
 * for changing the enabled-state of a particular playlist entry
 *
 * @class Representation
 */
class Representation {
  constructor(vhsHandler, playlist, id) {
    const {
      masterPlaylistController_: mpc,
      options_: { smoothQualityChange }
    } = vhsHandler;
    // Get a reference to a bound version of the quality change function
    const changeType = smoothQualityChange ? 'smooth' : 'fast';
    const qualityChangeFunction = mpc[`${changeType}QualityChange_`].bind(mpc);

    // some playlist attributes are optional
    if (playlist.attributes) {
      const resolution = playlist.attributes.RESOLUTION;

      this.width = resolution && resolution.width;
      this.height = resolution && resolution.height;

      this.bandwidth = playlist.attributes.BANDWIDTH;
    }

    this.codecs = codecsForPlaylist(mpc.master(), playlist);

    this.playlist = playlist;

    // The id is simply the ordinality of the media playlist
    // within the master playlist
    this.id = id;

    // Partially-apply the enableFunction to create a playlist-
    // specific variant
    this.enabled = enableFunction(
      vhsHandler.playlists,
      playlist.id,
      qualityChangeFunction
    );
  }
}

/**
 * A mixin function that adds the `representations` api to an instance
 * of the VhsHandler class
 *
 * @param {VhsHandler} vhsHandler - An instance of VhsHandler to add the
 * representation API into
 */
const renditionSelectionMixin = function(vhsHandler) {

  // Add a single API-specific function to the VhsHandler instance
  vhsHandler.representations = () => {
    const master = vhsHandler.masterPlaylistController_.master();
    const playlists = isAudioOnly(master) ?
      vhsHandler.masterPlaylistController_.getAudioTrackPlaylists_() :
      master.playlists;

    if (!playlists) {
      return [];
    }
    return playlists
      .filter((media) => !isIncompatible(media))
      .map((e, i) => new Representation(vhsHandler, e, e.id));
  };
};

export default renditionSelectionMixin;