/**
 * Escapes a property value of a CSS selector
 * @see https://github.com/mathiasbynens/CSS.escape/
 * @see http://dev.w3.org/csswg/cssom/#serialize-an-identifier
 * @param  {String} value The piece of the selector to escape
 * @return {String}        The escaped selector
 */
function escapeSelector(value) {
  /*eslint no-bitwise: 0, eqeqeq: 0, one-var: 0 */
  const string = String(value);
  const length = string.length;
  let index = -1;
  let codeUnit;
  let result = '';
  const firstCodeUnit = string.charCodeAt(0);
  while (++index < length) {
    codeUnit = string.charCodeAt(index);
    // Note: there’s no need to special-case astral symbols, surrogate
    // pairs, or lone surrogates.

    // If the character is NULL (U+0000), then the REPLACEMENT CHARACTER
    // (U+FFFD).
    if (codeUnit == 0x0000) {
      result += '\uFFFD';
      continue;
    }

    if (
      // If the character is in the range [\1-\1F] (U+0001 to U+001F) or is
      // U+007F, […]
      (codeUnit >= 0x0001 && codeUnit <= 0x001f) ||
      codeUnit == 0x007f ||
      // If the character is the first character and is in the range [0-9]
      // (U+0030 to U+0039), […]
      (index == 0 && codeUnit >= 0x0030 && codeUnit <= 0x0039) ||
      // If the character is the second character and is in the range [0-9]
      // (U+0030 to U+0039) and the first character is a `-` (U+002D), […]
      (index == 1 &&
        codeUnit >= 0x0030 &&
        codeUnit <= 0x0039 &&
        firstCodeUnit == 0x002d)
    ) {
      // https://drafts.csswg.org/cssom/#escape-a-character-as-code-point
      result += '\\' + codeUnit.toString(16) + ' ';
      continue;
    }

    // If the character is the first character and is a `-` (U+002D), and
    // there is no second character, […]
    if (index == 0 && length == 1 && codeUnit == 0x002d) {
      result += '\\' + string.charAt(index);
      continue;
    }

    // If the character is not handled by one of the above rules and is
    // greater than or equal to U+0080, is `-` (U+002D) or `_` (U+005F), or
    // is in one of the ranges [0-9] (U+0030 to U+0039), [A-Z] (U+0041 to
    // U+005A), or [a-z] (U+0061 to U+007A), […]
    if (
      codeUnit >= 0x0080 ||
      codeUnit == 0x002d ||
      codeUnit == 0x005f ||
      (codeUnit >= 0x0030 && codeUnit <= 0x0039) ||
      (codeUnit >= 0x0041 && codeUnit <= 0x005a) ||
      (codeUnit >= 0x0061 && codeUnit <= 0x007a)
    ) {
      // the character itself
      result += string.charAt(index);
      continue;
    }

    // Otherwise, the escaped character.
    // https://drafts.csswg.org/cssom/#escape-a-character
    result += '\\' + string.charAt(index);
  }
  return result;
}

export default escapeSelector;
