# All files / src/utils buffer-helper.ts

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     /**
     * @module BufferHelper
     *
     * Providing methods dealing with buffer length retrieval for example.
     *
     * In general, a helper around HTML5 MediaElement TimeRanges gathered from `buffered` property.
     *
     * Also @see https://developer.mozilla.org/en-US/docs/Web/API/HTMLMediaElement/buffered
    */

    type BufferTimeRange = {
      start: number
      end: number
    };

    type Bufferable = {
      buffered: TimeRanges
    };

    export class BufferHelper {
      /**
       * Return true if `media`'s buffered include `position`
       * @param {Bufferable} media
       * @param {number} position
       * @returns {boolean}
       */
      static isBuffered (media: Bufferable, position: number): boolean {
        try {
          if (media) {
            let buffered = media.buffered;
            for (let i = 0; i < buffered.length; i++) {
              if (position >= buffered.start(i) && position <= buffered.end(i)) {
                return true;
              }
            }
          }
        } catch (error) {
          // this is to catch
          // InvalidStateError: Failed to read the 'buffered' property from 'SourceBuffer':
          // This SourceBuffer has been removed from the parent media source
        }
        return false;
      }

      static bufferInfo (
        media: Bufferable,
        pos: number,
        maxHoleDuration: number
      ): {
        len: number,
        start: number,
        end: number,
        nextStart?: number,
      } {
        try {
          if (media) {
            let vbuffered = media.buffered;
            let buffered: BufferTimeRange[] = [];
            let i: number;
            for (i = 0; i < vbuffered.length; i++) {
              buffered.push({ start: vbuffered.start(i), end: vbuffered.end(i) });
            }

            return this.bufferedInfo(buffered, pos, maxHoleDuration);
          }
        } catch (error) {
          // this is to catch
          // InvalidStateError: Failed to read the 'buffered' property from 'SourceBuffer':
          // This SourceBuffer has been removed from the parent media source
        }
        return { len: 0, start: pos, end: pos, nextStart: undefined };
      }

      static bufferedInfo (
        buffered: BufferTimeRange[],
        pos: number,
        maxHoleDuration: number
      ): {
        len: number,
        start: number,
        end: number,
        nextStart?: number,
      } {
        // sort on buffer.start/smaller end (IE does not always return sorted buffered range)
        buffered.sort(function (a, b) {
          let diff = a.start - b.start;
          if (diff) {
            return diff;
          } else {
            return b.end - a.end;
          }
        });

        let buffered2: BufferTimeRange[] = [];
        if (maxHoleDuration) {
          // there might be some small holes between buffer time range
          // consider that holes smaller than maxHoleDuration are irrelevant and build another
          // buffer time range representations that discards those holes
          for (let i = 0; i < buffered.length; i++) {
            let buf2len = buffered2.length;
            if (buf2len) {
              let buf2end = buffered2[buf2len - 1].end;
              // if small hole (value between 0 or maxHoleDuration ) or overlapping (negative)
              if ((buffered[i].start - buf2end) < maxHoleDuration) {
                // merge overlapping time ranges
                // update lastRange.end only if smaller than item.end
                // e.g.  [ 1, 15] with  [ 2,8] => [ 1,15] (no need to modify lastRange.end)
                // whereas [ 1, 8] with  [ 2,15] => [ 1,15] ( lastRange should switch from [1,8] to [1,15])
                if (buffered[i].end > buf2end) {
                  buffered2[buf2len - 1].end = buffered[i].end;
                }
              } else {
                // big hole
                buffered2.push(buffered[i]);
              }
            } else {
              // first value
              buffered2.push(buffered[i]);
            }
          }
        } else {
          buffered2 = buffered;
        }

        let bufferLen = 0;

        // bufferStartNext can possibly be undefined based on the conditional logic below
        let bufferStartNext: number | undefined;

        // bufferStart and bufferEnd are buffer boundaries around current video position
        let bufferStart: number = pos;
        let bufferEnd: number = pos;
        for (let i = 0; i < buffered2.length; i++) {
          let start = buffered2[i].start,
            end = buffered2[i].end;
          // logger.log('buf start/end:' + buffered.start(i) + '/' + buffered.end(i));
          if ((pos + maxHoleDuration) >= start && pos < end) {
            // play position is inside this buffer TimeRange, retrieve end of buffer position and buffer length
            bufferStart = start;
            bufferEnd = end;
            bufferLen = bufferEnd - pos;
          } else if ((pos + maxHoleDuration) < start) {
            bufferStartNext = start;
            break;
          }
        }
        return { len: bufferLen, start: bufferStart, end: bufferEnd, nextStart: bufferStartNext };
      }
    }