mapping-list.js

/* -*- Mode: js; js-indent-level: 2; -*- */
/*
 * Copyright 2014 Mozilla Foundation and contributors
 * Licensed under the New BSD license. See LICENSE or:
 * http://opensource.org/licenses/BSD-3-Clause
 */
if (typeof define !== 'function') {
    var define = require('amdefine')(module, require);
}
define(function (require, exports, module) {

  var util = require('./util');

  /**
   * Determine whether mappingB is after mappingA with respect to generated
   * position.
   */
  function generatedPositionAfter(mappingA, mappingB) {
    // Optimized for most common case
    var lineA = mappingA.generatedLine;
    var lineB = mappingB.generatedLine;
    var columnA = mappingA.generatedColumn;
    var columnB = mappingB.generatedColumn;
    return lineB > lineA || lineB == lineA && columnB >= columnA ||
           util.compareByGeneratedPositions(mappingA, mappingB) <= 0;
  }

  /**
   * A data structure to provide a sorted view of accumulated mappings in a
   * performance conscious manner. It trades a neglibable overhead in general
   * case for a large speedup in case of mappings being added in order.
   */
  function MappingList() {
    this._array = [];
    this._sorted = true;
    // Serves as infimum
    this._last = {generatedLine: -1, generatedColumn: 0};
  }

  /**
   * Iterate through internal items. This method takes the same arguments that
   * `Array.prototype.forEach` takes.
   *
   * NOTE: The order of the mappings is NOT guaranteed.
   */
  MappingList.prototype.unsortedForEach =
    function MappingList_forEach(aCallback, aThisArg) {
      this._array.forEach(aCallback, aThisArg);
    };

  /**
   * Add the given source mapping.
   *
   * @param Object aMapping
   */
  MappingList.prototype.add = function MappingList_add(aMapping) {
    var mapping;
    if (generatedPositionAfter(this._last, aMapping)) {
      this._last = aMapping;
      this._array.push(aMapping);
    } else {
      this._sorted = false;
      this._array.push(aMapping);
    }
  };

  /**
   * Returns the flat, sorted array of mappings. The mappings are sorted by
   * generated position.
   *
   * WARNING: This method returns internal data without copying, for
   * performance. The return value must NOT be mutated, and should be treated as
   * an immutable borrow. If you want to take ownership, you must make your own
   * copy.
   */
  MappingList.prototype.toArray = function MappingList_toArray() {
    if (!this._sorted) {
      this._array.sort(util.compareByGeneratedPositions);
      this._sorted = true;
    }
    return this._array;
  };

  exports.MappingList = MappingList;

});