'use strict';

var extend = require('extend-shallow');
var regexCache = {};
var all;

var charSets = {
  default: {
    '"': '"',
    '"': '"',

    ''': '\'',
    ''': '\'',

    '&': '&',
    '&': '&',

    '>': '>',
    '>': '>',

    '&lt;': '<',
    '&#60;': '<'
  },
  extras: {
    '&cent;': '¢',
    '&#162;': '¢',

    '&copy;': '©',
    '&#169;': '©',

    '&euro;': '€',
    '&#8364;': '€',

    '&pound;': '£',
    '&#163;': '£',

    '&reg;': '®',
    '&#174;': '®',

    '&yen;': '¥',
    '&#165;': '¥'
  }
};

// don't merge char sets unless "all" is explicitly called
Object.defineProperty(charSets, 'all', {
  get: function() {
    return all || (all = extend({}, charSets.default, charSets.extras));
  }
});

/**
 * Convert HTML entities to HTML characters.
 *
 * @param  {String} `str` String with HTML entities to un-escape.
 * @return {String}
 */

function unescape(str, type) {
  if (!isString(str)) return '';
  var chars = charSets[type || 'default'];
  var regex = toRegex(type, chars);
  return str.replace(regex, function(m) {
    return chars[m];
  });
}

function toRegex(type, chars) {
  if (regexCache[type]) {
    return regexCache[type];
  }
  var keys = Object.keys(chars).join('|');
  var regex = new RegExp('(?=(' + keys + '))\\1', 'g');
  regexCache[type] = regex;
  return regex;
}

/**
 * Returns true if str is a non-empty string
 */

function isString(str) {
  return str && typeof str === 'string';
}

/**
 * Expose charSets
 */

unescape.chars = charSets.default;
unescape.extras = charSets.extras;
// don't trip the "charSets" getter unless it's explicitly called
Object.defineProperty(unescape, 'all', {
  get: function() {
    return charSets.all;
  }
});

/**
 * Expose `unescape`
 */

module.exports = unescape;