generate method

String generate({ V1Options? options, })

v1() Generates a time-based version 1 UUID

By default it will generate a string based off current Gregorian epoch time, and will return a string.

The first argument is an options map that takes various configuration options detailed in the readme.

http://tools.ietf.org/html/rfc4122.html#section-4.2.2

Implementation

String generate({V1Options? options}) {
  _init();
  var i = 0;
  var buf = Uint8List(16);

  int clockSeq = options?.clockSeq ?? V1State.clockSeq ?? 0;

  // UUID timestamps are 100 nano-second units since the Gregorian epoch,
  // (1582-10-15 00:00). Time is handled internally as 'msecs' (integer
  // milliseconds) and 'nsecs' (100-nanoseconds offset from msecs) since unix
  // epoch, 1970-01-01 00:00.
  int mSecs = options?.mSecs ?? DateTime.timestamp().millisecondsSinceEpoch;

  // Per 4.2.1.2, use count of uuid's generated during the current clock
  // cycle to simulate higher resolution clock
  int nSecs = options?.nSecs ?? V1State.nSecs + 1;

  // Time since last uuid creation (in msecs)
  var dt = (mSecs - V1State.mSecs) + (nSecs - V1State.nSecs) / 10000;

  // Per 4.2.1.2, Bump clockseq on clock regression
  if (dt < 0 && options?.clockSeq == null) {
    clockSeq = clockSeq + 1 & 0x3fff;
  }

  // Reset nsecs if clock regresses (new clockseq) or we've moved onto a new
  // time interval
  if ((dt < 0 || mSecs > V1State.mSecs) && options?.nSecs == null) {
    nSecs = 0;
  }

  // Per 4.2.1.2 Throw error if too many uuids are requested
  if (nSecs >= 10000) {
    throw Exception('uuid.v1(): Can\'t create more than 10M uuids/sec');
  }

  V1State.mSecs = mSecs;
  V1State.nSecs = nSecs;
  V1State.clockSeq = clockSeq;

  // Per 4.1.4 - Convert from unix epoch to Gregorian epoch
  mSecs += 12219292800000;

  // time Low
  var tl = ((mSecs & 0xfffffff) * 10000 + nSecs) % 0x100000000;
  buf[i++] = tl >> 24 & 0xff;
  buf[i++] = tl >> 16 & 0xff;
  buf[i++] = tl >> 8 & 0xff;
  buf[i++] = tl & 0xff;

  // time mid
  var tmh = (mSecs / 0x100000000 * 10000).floor() & 0xfffffff;
  buf[i++] = tmh >> 8 & 0xff;
  buf[i++] = tmh & 0xff;

  // time high and version
  buf[i++] = tmh >> 24 & 0xff; // | 0x10; // include version
  buf[i++] = tmh >> 16 & 0xff;

  // clockSeq high and reserved (Per 4.2.2 - include variant)
  buf[i++] = (clockSeq & 0x3F00) >> 8;

  // clockSeq low
  buf[i++] = clockSeq & 0xff;

  // set version
  buf[6] = buf[6] & 0xf | 0x10;
  buf[8] = buf[8] | 0x80;
  // node
  List<int> node = options?.node ?? V1State.nodeId ?? [0, 0, 0, 0, 0, 0];
  for (var n = 0; n < 6; n++) {
    buf[i + n] = node[n];
  }

  return UuidParsing.unparse(buf);
}