class Uuidv4 {


  /// v4() Generates a RNG version 4 UUID
  ///
  /// By default it will generate a string based mathRNG, and will return
  /// a string. If you wish to use crypto-strong RNG, pass in UuidUtil.cryptoRNG
  ///
  /// The first argument is an options map that takes various configuration
  /// options detailed in the readme.
  ///
  /// http://tools.ietf.org/html/rfc4122.html#section-4.4
  String v4({Map<String, dynamic> options}) {
    options = (options != null) ? options : new Map<String, dynamic>();

    // Use the built-in RNG or a custom provided RNG
    var positionalArgs =
        (options['positionalArgs'] != null) ? options['positionalArgs'] : [];
    var namedArgs = (options['namedArgs'] != null)
        ? options['namedArgs'] as Map<Symbol, dynamic>
        : const <Symbol, dynamic>{};
    var rng = (options['rng'] != null)
        ? Function.apply(options['rng'], positionalArgs, namedArgs)
        : _globalRNG();

    // Use provided values over RNG
    var rnds = (options['random'] != null) ? options['random'] : rng;

    // per 4.4, set bits for version and clockSeq high and reserved
    rnds[6] = (rnds[6] & 0x0f) | 0x40;
    rnds[8] = (rnds[8] & 0x3f) | 0x80;

    return unparse(rnds);
  }

}