import Utils from '../core/Utils';

/**
 * Unicode operations.
 *
 * @author n1474335 [n1474335@gmail.com]
 * @copyright Crown Copyright 2016
 * @license Apache-2.0
 *
 * @namespace
 */
const Unicode = {

    /**
     * @constant
     * @default
     */
  PREFIXES: ['\\u', '%u', 'U+'],

    /**
     * Unescape Unicode Characters operation.
     *
     * @param {string} input
     * @param {Object[]} args
     * @returns {string}
     */
  run_unescape(input, args) {
    let prefix = Unicode._prefix_to_regex[args[0]],
      regex = new RegExp(`${prefix}([a-f\\d]{4,6})`, 'ig'),
      output = '',
      m,
      i = 0;

    while (m = regex.exec(input)) {
            // Add up to match
      output += input.slice(i, m.index);
      i = m.index;

            // Add match
      output += Utils.chr(parseInt(m[1], 16));

      i = regex.lastIndex;
    }

        // Add all after final match
    output += input.slice(i, input.length);

    return output;
  },


    /**
     * Lookup table to add prefixes to unicode delimiters so that they can be used in a regex.
     *
     * @private
     * @constant
     */
  _prefix_to_regex: {
    '\\u': '\\\\u',
    '%u': '%u',
    'U+': 'U\\+',
  },

};

export default Unicode;