# generate method

String generate({

1. 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);
    }