char-props.js

/* -*- Mode: js; js-indent-level: 2; -*- */
/*
 * char-props from https://github.com/twolfson/char-props
 * with slimmed down for source-map
 */
define(function (require, exports, module) {
  /**
   * Indexer constructor (takes index and performs pre-emptive caching)
   * @constructor
   * @param {String} input Content to index
   */
  function Indexer(input) {
    this.input = input;

    // Break up lines by line breaks
    var lines = input.split('\n');

    // Iterate over the lines until we reach the end or we hit our index
    var i = 0,
        len = lines.length,
        line,
        lineStart = 0,
        lineEnd,
        lineMap = {'length': len};
    for (; i < len; i++) {
      // Grab the line
      line = lines[i];

      // Calculate the line end (includes \n we removed)
      lineEnd = lineStart + line.length + 1;

      // Save the line to its map
      lineMap[i] = {'start': lineStart, 'end': lineEnd};

      // Overwrite lineStart with lineEnd
      lineStart = lineEnd;
    }

    // Save the lineMap to this
    this.lineMap = lineMap;
  }
  Indexer.prototype = {
    /**
     * Get the line of the character at a certain index
     * @param {Number} index Index of character to retrieve line of
     * @param {Object} [options] Options to use for search
     * @param {Number} [options.minLine=0] Minimum line for us to search on
     * TODO: The following still have to be built/implemented
     * @param {Number} [options.maxLine=lines.length] Maximum line for us to search on
     * @param {String} [options.guess="average"] Affects searching pattern -- can be "high", "low", or "average" (linear top-down, linear bottom-up, or binary)
     * @returns {Number} Line number of character
     */
    'lineAt': function (index, options) {
      // Fallback options
      options = options || {};

      // TODO: We can binary search here
      // Grab the line map and iterate over it
      var lineMap = this.lineMap,
          i = options.minLine || 0,
          len = lineMap.length,
          lineItem;

      for (; i < len; i++) {
        // TODO: If binary searching, this requires both above and below
        // If the index is under end of the lineItem, stop
        lineItem = lineMap[i];
        if (index < lineItem.end) {
          break;
        }
      }

      // Return the line we stopped on
      return i;
    },
    /**
     * Get the column of the character at a certain index
     * @param {Number} index Index of character to retrieve column of
     * @returns {Number} Column number of character
     */
    'columnAt': function (index) {
      // Start at the index - 1
      var input = this.input,
          char,
          i = index - 1;

      // If the index is negative, return now
      if (index < 0) {
        return 0;
      }

      // Continue left until index < 0 or we hit a line break
      for (; i >= 0; i--) {
        char = input.charAt(i);
        if (char === '\n') {
          break;
        }
      }

      // Return the col of our index - 1 (line break is not in the column count)
      var col = index - i - 1;
      return col;
    }
  };

  function charProps(input) {
    // Create and return a new Indexer with the content
    var indexer = new Indexer(input);
    return indexer;
  }

  // Expose Indexer to charProps
  charProps.Indexer = Indexer;

  // Export charProps
  exports['char-props'] = charProps;

});