jsmediatags/build2/ChunkedFileData.js

Media Tags Reader (ID3, MP4)

/**
 * This class represents a file that might not have all its data loaded yet.
 * It is used when loading the entire file is not an option because it's too
 * expensive. Instead, parts of the file are loaded and added only when needed.
 * From a reading point of view is as if the entire file is loaded. The
 * exception is when the data is not available yet, an error will be thrown.
 * This class does not load the data, it just manages it. It provides operations
 * to add and read data from the file.
 *
 * 
 */
'use strict';

function _classCallCheck(instance, Constructor) { if (!(instance instanceof Constructor)) { throw new TypeError("Cannot call a class as a function"); } }

function _defineProperties(target, props) { for (var i = 0; i < props.length; i++) { var descriptor = props[i]; descriptor.enumerable = descriptor.enumerable || false; descriptor.configurable = true; if ("value" in descriptor) descriptor.writable = true; Object.defineProperty(target, descriptor.key, descriptor); } }

function _createClass(Constructor, protoProps, staticProps) { if (protoProps) _defineProperties(Constructor.prototype, protoProps); if (staticProps) _defineProperties(Constructor, staticProps); return Constructor; }

function _defineProperty(obj, key, value) { if (key in obj) { Object.defineProperty(obj, key, { value: value, enumerable: true, configurable: true, writable: true }); } else { obj[key] = value; } return obj; }

var NOT_FOUND = -1;

var ChunkedFileData = /*#__PURE__*/function () {
  function ChunkedFileData() {
    _classCallCheck(this, ChunkedFileData);

    _defineProperty(this, "_fileData", void 0);

    this._fileData = [];
  }
  /**
   * Adds data to the file storage at a specific offset.
   */


  _createClass(ChunkedFileData, [{
    key: "addData",
    value: function addData(offset, data) {
      var offsetEnd = offset + data.length - 1;

      var chunkRange = this._getChunkRange(offset, offsetEnd);

      if (chunkRange.startIx === NOT_FOUND) {
        this._fileData.splice(chunkRange.insertIx || 0, 0, {
          offset: offset,
          data: data
        });
      } else {
        // If the data to add collides with existing chunks we prepend and
        // append data from the half colliding chunks to make the collision at
        // 100%. The new data can then replace all the colliding chunkes.
        var firstChunk = this._fileData[chunkRange.startIx];
        var lastChunk = this._fileData[chunkRange.endIx];
        var needsPrepend = offset > firstChunk.offset;
        var needsAppend = offsetEnd < lastChunk.offset + lastChunk.data.length - 1;
        var chunk = {
          offset: Math.min(offset, firstChunk.offset),
          data: data
        };

        if (needsPrepend) {
          var slicedData = this._sliceData(firstChunk.data, 0, offset - firstChunk.offset);

          chunk.data = this._concatData(slicedData, data);
        }

        if (needsAppend) {
          // Use the lastChunk because the slice logic is easier to handle.
          var slicedData = this._sliceData(chunk.data, 0, lastChunk.offset - chunk.offset);

          chunk.data = this._concatData(slicedData, lastChunk.data);
        }

        this._fileData.splice(chunkRange.startIx, chunkRange.endIx - chunkRange.startIx + 1, chunk);
      }
    }
  }, {
    key: "_concatData",
    value: function _concatData(dataA, dataB) {
      // TypedArrays don't support concat.
      if (typeof ArrayBuffer !== "undefined" && ArrayBuffer.isView && ArrayBuffer.isView(dataA)) {
        // $FlowIssue - flow thinks dataAandB is a string but it's not
        var dataAandB = new dataA.constructor(dataA.length + dataB.length); // $FlowIssue - flow thinks dataAandB is a string but it's not

        dataAandB.set(dataA, 0); // $FlowIssue - flow thinks dataAandB is a string but it's not

        dataAandB.set(dataB, dataA.length);
        return dataAandB;
      } else {
        // $FlowIssue - flow thinks dataAandB is a TypedArray but it's not
        return dataA.concat(dataB);
      }
    }
  }, {
    key: "_sliceData",
    value: function _sliceData(data, begin, end) {
      // Some TypeArray implementations do not support slice yet.
      if (data.slice) {
        return data.slice(begin, end);
      } else {
        // $FlowIssue - flow thinks data is a string but it's not
        return data.subarray(begin, end);
      }
    }
    /**
     * Finds the chunk range that overlaps the [offsetStart-1,offsetEnd+1] range.
     * When a chunk is adjacent to the offset we still consider it part of the
     * range (this is the situation of offsetStart-1 or offsetEnd+1).
     * When no chunks are found `insertIx` denotes the index where the data
     * should be inserted in the data list (startIx == NOT_FOUND and endIX ==
     * NOT_FOUND).
     */

  }, {
    key: "_getChunkRange",
    value: function _getChunkRange(offsetStart, offsetEnd) {
      var startChunkIx = NOT_FOUND;
      var endChunkIx = NOT_FOUND;
      var insertIx = 0; // Could use binary search but not expecting that many blocks to exist.

      for (var i = 0; i < this._fileData.length; i++, insertIx = i) {
        var chunkOffsetStart = this._fileData[i].offset;
        var chunkOffsetEnd = chunkOffsetStart + this._fileData[i].data.length;

        if (offsetEnd < chunkOffsetStart - 1) {
          // This offset range doesn't overlap with any chunks.
          break;
        } // If it is adjacent we still consider it part of the range because
        // we're going end up with a single block with all contiguous data.


        if (offsetStart <= chunkOffsetEnd + 1 && offsetEnd >= chunkOffsetStart - 1) {
          startChunkIx = i;
          break;
        }
      } // No starting chunk was found, meaning that the offset is either before
      // or after the current stored chunks.


      if (startChunkIx === NOT_FOUND) {
        return {
          startIx: NOT_FOUND,
          endIx: NOT_FOUND,
          insertIx: insertIx
        };
      } // Find the ending chunk.


      for (var i = startChunkIx; i < this._fileData.length; i++) {
        var chunkOffsetStart = this._fileData[i].offset;
        var chunkOffsetEnd = chunkOffsetStart + this._fileData[i].data.length;

        if (offsetEnd >= chunkOffsetStart - 1) {
          // Candidate for the end chunk, it doesn't mean it is yet.
          endChunkIx = i;
        }

        if (offsetEnd <= chunkOffsetEnd + 1) {
          break;
        }
      }

      if (endChunkIx === NOT_FOUND) {
        endChunkIx = startChunkIx;
      }

      return {
        startIx: startChunkIx,
        endIx: endChunkIx
      };
    }
  }, {
    key: "hasDataRange",
    value: function hasDataRange(offsetStart, offsetEnd) {
      for (var i = 0; i < this._fileData.length; i++) {
        var chunk = this._fileData[i];

        if (offsetEnd < chunk.offset) {
          return false;
        }

        if (offsetStart >= chunk.offset && offsetEnd < chunk.offset + chunk.data.length) {
          return true;
        }
      }

      return false;
    }
  }, {
    key: "getByteAt",
    value: function getByteAt(offset) {
      var dataChunk;

      for (var i = 0; i < this._fileData.length; i++) {
        var dataChunkStart = this._fileData[i].offset;
        var dataChunkEnd = dataChunkStart + this._fileData[i].data.length - 1;

        if (offset >= dataChunkStart && offset <= dataChunkEnd) {
          dataChunk = this._fileData[i];
          break;
        }
      }

      if (dataChunk) {
        return dataChunk.data[offset - dataChunk.offset];
      }

      throw new Error("Offset " + offset + " hasn't been loaded yet.");
    }
  }], [{
    key: "NOT_FOUND",
    get: // $FlowIssue - get/set properties not yet supported
    function get() {
      return NOT_FOUND;
    }
  }]);

  return ChunkedFileData;
}();

module.exports = ChunkedFileData;