generate method

String generate({ V6Options? options, })

v6() Generates a time-based version 6 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.

https://datatracker.ietf.org/doc/html/draft-ietf-uuidrev-rfc4122bis#name-uuid-version-7

Implementation

String generate({V6Options? options}) {
  _init();
  var buf = Uint8List(16);

  int clockSeq = options?.clockSeq ?? V6State.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 ?? V6State.nSecs + 1;

  // Time since last uuid creation (in msecs)
  var dt = (mSecs - V6State.mSecs) + (nSecs - V6State.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 > V6State.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.v6(): Can\'t create more than 10M uuids/sec');
  }

  V6State.mSecs = mSecs;
  V6State.nSecs = nSecs;
  V6State.clockSeq = clockSeq;

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

  var uuidTime = Int64(mSecs) * Int64(10000) + Int64(nSecs);

  var high = uuidTime ~/ pow(2, 28);
  var mid = uuidTime * pow(2, 4);
  var low = uuidTime & 0x0fff | 0x6000;
  var clock = (clockSeq & 0x3fff) | 0x8000;

  buf..buffer.asByteData().setUint32(0, high.toInt());
  buf..buffer.asByteData().setUint32(4, mid.toInt());
  buf..buffer.asByteData().setUint16(6, low.toInt());
  buf..buffer.asByteData().setUint16(8, clock);

  var node =
      options?.node ?? V6State.nodeId ?? [0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
  buf.setAll(10, node);
  return UuidParsing.unparse(buf);
}