text: /**
   * @license
   * Copyright 2016 Google Inc.
   *
   * 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.
   */
  
  goog.provide('shaka.media.TextEngine');
  
  goog.require('goog.asserts');
  goog.require('shaka.util.IDestroyable');
  
  
  
  /**
   * Manages text parsers and cues.
   *
   * @struct
   * @constructor
   * @param {TextTrack} track
   * @param {string} mimeType
   * @implements {shaka.util.IDestroyable}
   */
  shaka.media.TextEngine = function(track, mimeType) {
    /** @private {?shaka.media.TextEngine.TextParser} */
    this.parser_ = shaka.media.TextEngine.parserMap_[mimeType];
  
    // This should not happen if type negotiation is working as it should.
    goog.asserts.assert(this.parser_,
                        'Text type negotiation should have happened already');
  
    /** @private {TextTrack} */
    this.track_ = track;
  
    /** @private {number} */
    this.timestampOffset_ = 0;
  
    /** @private {number} */
    this.appendWindowEnd_ = Number.POSITIVE_INFINITY;
  
    /** @private {?number} */
    this.bufferStart_ = null;
  
    /** @private {?number} */
    this.bufferEnd_ = null;
  };
  
  
  /**
   * Parses a text buffer into an array of cues.
   *
   * @typedef {function((ArrayBuffer|ArrayBufferView)):!Array.<!TextTrackCue>}
   * @exportDoc
   */
  shaka.media.TextEngine.TextParser;
  
  
  /** @private {!Object.<string, !shaka.media.TextEngine.TextParser>} */
  shaka.media.TextEngine.parserMap_ = {};
  
  
  /**
   * @param {string} mimeType
   * @param {!shaka.media.TextEngine.TextParser} parser
   * @export
   */
  shaka.media.TextEngine.registerParser = function(mimeType, parser) {
    shaka.media.TextEngine.parserMap_[mimeType] = parser;
  };
  
  
  /**
   * @param {string} mimeType
   * @export
   */
  shaka.media.TextEngine.unregisterParser = function(mimeType) {
    delete shaka.media.TextEngine.parserMap_[mimeType];
  };
  
  
  /**
   * @param {string} mimeType
   * @return {boolean}
   */
  shaka.media.TextEngine.isTypeSupported = function(mimeType) {
    return !!shaka.media.TextEngine.parserMap_[mimeType];
  };
  
  
  /** @override */
  shaka.media.TextEngine.prototype.destroy = function() {
    if (this.track_) {
      this.removeWhere_(function(cue) { return true; });
    }
  
    this.parser_ = null;
    this.track_ = null;
  
    return Promise.resolve();
  };
  
  
  /**
   * @param {ArrayBuffer|ArrayBufferView} buffer
   * @param {number} startTime
   * @param {number} endTime
   * @return {!Promise}
   */
  shaka.media.TextEngine.prototype.appendBuffer =
      function(buffer, startTime, endTime) {
    var offset = this.timestampOffset_;
  
    startTime += offset;
    endTime += offset;
  
    // Start the operation asynchronously to avoid blocking the caller.
    return Promise.resolve().then(function() {
      // Parse the buffer and add the new cues.
      var cues = this.parser_(buffer);
  
      for (var i = 0; i < cues.length; ++i) {
        cues[i].startTime += offset;
        cues[i].endTime += offset;
        if (cues[i].startTime >= this.appendWindowEnd_) break;
        this.track_.addCue(cues[i]);
      }
  
      // NOTE: We update the buffered range from the start and end times passed
      // down from the segment reference, not with the start and end times of the
      // parsed cues.  This is important because some segments may contain no
      // cues, but we must still consider those ranges buffered.
      if (this.bufferStart_ == null) {
        this.bufferStart_ = startTime;
      } else {
        // We already had something in buffer, and we assume we are extending the
        // range from the end.
        goog.asserts.assert((startTime - this.bufferEnd_) <= 1,
                            'There should not be a gap in text references >1s');
      }
      this.bufferEnd_ = Math.min(endTime, this.appendWindowEnd_);
    }.bind(this));
  };
  
  
  /**
   * @param {number} start
   * @param {number} end
   * @return {!Promise}
   */
  shaka.media.TextEngine.prototype.remove = function(start, end) {
    // Start the operation asynchronously to avoid blocking the caller.
    return Promise.resolve().then(function() {
      this.removeWhere_(function(cue) {
        if (cue.startTime >= end || cue.endTime <= start) {
          // Outside the remove range.  Hang on to it.
          return false;
        }
        return true;
      });
  
      if (this.bufferStart_ == null) {
        goog.asserts.assert(this.bufferEnd_ == null,
                            'end must be null if start is null');
      } else {
        goog.asserts.assert(this.bufferEnd_ != null,
                            'end must be non-null if start is non-null');
  
        // Update buffered range.
        if (end <= this.bufferStart_ || start >= this.bufferEnd_) {
          // No intersection.  Nothing was removed.
        } else if (start <= this.bufferStart_ && end >= this.bufferEnd_) {
          // We wiped out everything.
          goog.asserts.assert(
              this.track_.cues.length == 0, 'should be no cues left');
          this.bufferStart_ = this.bufferEnd_ = null;
        } else if (start <= this.bufferStart_ && end < this.bufferEnd_) {
          // We removed from the beginning of the range.
          this.bufferStart_ = end;
        } else if (start > this.bufferStart_ && end >= this.bufferEnd_) {
          // We removed from the end of the range.
          this.bufferEnd_ = start;
        } else {
          // We removed from the middle?  StreamingEngine isn't supposed to.
          goog.asserts.assert(
              false, 'removal from the middle is not supported by TextEngine');
        }
      }
    }.bind(this));
  };
  
  
  /** @param {number} timestampOffset */
  shaka.media.TextEngine.prototype.setTimestampOffset =
      function(timestampOffset) {
    this.timestampOffset_ = timestampOffset;
  };
  
  
  /** @param {number} windowEnd */
  shaka.media.TextEngine.prototype.setAppendWindowEnd =
      function(windowEnd) {
    this.appendWindowEnd_ = windowEnd;
  };
  
  
  /**
   * @return {?number} Time in seconds of the beginning of the buffered range,
   *   or null if nothing is buffered.
   */
  shaka.media.TextEngine.prototype.bufferStart = function() {
    return this.bufferStart_;
  };
  
  
  /**
   * @return {?number} Time in seconds of the end of the buffered range,
   *   or null if nothing is buffered.
   */
  shaka.media.TextEngine.prototype.bufferEnd = function() {
    return this.bufferEnd_;
  };
  
  
  /**
   * @param {number} t A timestamp
   * @return {number} Number of seconds ahead of 't' we have buffered
   */
  shaka.media.TextEngine.prototype.bufferedAheadOf = function(t) {
    if (this.bufferEnd_ == null || this.bufferEnd_ < t) return 0;
  
    goog.asserts.assert(
        this.bufferStart_ != null, 'start should not be null if end is not null');
  
    if (t < this.bufferStart_) return 0;
  
    return this.bufferEnd_ - t;
  };
  
  
  /**
   * Remove all cues for which the matching function returns true.
   *
   * @param {function(!TextTrackCue):boolean} predicate
   * @private
   */
  shaka.media.TextEngine.prototype.removeWhere_ = function(predicate) {
    var cues = this.track_.cues;
    var removeMe = [];
  
    // Remove these in another loop to avoid mutating the TextTrackCueList
    // while iterating over it.  This allows us to avoid making assumptions
    // about whether or not this.track_.remove() will alter that list.
    for (var i = 0; i < cues.length; ++i) {
      if (predicate(cues[i])) {
        removeMe.push(cues[i]);
      }
    }
  
    for (var i = 0; i < removeMe.length; ++i) {
      this.track_.removeCue(removeMe[i]);
    }
  };
  