let rng: any;

// Unique ID creation requires a high quality random # generator.  In the
// browser this is a little complicated due to unknown quality of Math.random()
// and inconsistent support for the `crypto` API.  We do the best we can via
// feature-detection

// getRandomValues needs to be invoked in a context where "this" is a Crypto implementation.
var getRandomValues = (typeof(crypto) != 'undefined' && crypto.getRandomValues.bind(crypto));

if (getRandomValues) {
  // WHATWG crypto RNG - http://wiki.whatwg.org/wiki/Crypto
  var rnds8 = new Uint8Array(16); // eslint-disable-line no-undef

  rng = function whatwgRNG() {
    getRandomValues(rnds8);
    return rnds8;
  };
} else {
  // Math.random()-based (RNG)
  //
  // If all else fails, use Math.random().  It's fast, but is of unspecified
  // quality.
  var rnds = new Array(16);

  rng = function mathRNG() {
    for (var i = 0, r; i < 16; i++) {
      if ((i & 0x03) === 0) r = Math.random() * 0x100000000;
      rnds[i] = r >>> ((i & 0x03) << 3) & 0xff;
    }

    return rnds;
  };
}

/**
 * Convert array of 16 byte values to UUID string format of the form:
 * XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXXX
 */
var byteToHex: any = [];
for (var i = 0; i < 256; ++i) {
  byteToHex[i] = (i + 0x100).toString(16).substr(1);
}

function bytesToUuid(buf: any, offset: any) {
  var i = offset || 0;
  var bth = byteToHex;
  return bth[buf[i++]] + bth[buf[i++]] +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] + '-' +
          bth[buf[i++]] + bth[buf[i++]] +
          bth[buf[i++]] + bth[buf[i++]] +
          bth[buf[i++]] + bth[buf[i++]];
}

export function uuidIonic(options: any = {}, buf: any = null, offset: any = null) {
  var i = buf && offset || 0;

  if (typeof(options) == 'string') {
    buf = options === 'binary' ? new Array(16) : null;
    options = null;
  }
  options = options || {};

  var rnds = options.random || (options.rng || rng)();

  // Per 4.4, set bits for version and `clock_seq_hi_and_reserved`
  rnds[6] = (rnds[6] & 0x0f) | 0x40;
  rnds[8] = (rnds[8] & 0x3f) | 0x80;

  // Copy bytes to buffer, if provided
  if (buf) {
    for (var ii = 0; ii < 16; ++ii) {
      buf[i + ii] = rnds[ii];
    }
  }

  return buf || bytesToUuid(rnds, null);
}