generate method Null safety
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-peabody-dispatch-new-uuid-format#section-4.3
Implementation
String generate({Map<String, dynamic>? options}) {
var buf = Uint8List(16);
options ??= const {};
int clockSeq = options['clockSeq'] ?? this.clockSeq;
// 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.now()).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'] ?? this.nSecs + 1;
// Time since last uuid creation (in msecs)
var dt = (mSecs - this.mSecs) + (nSecs - this.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 > this.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');
}
this.mSecs = mSecs;
this.nSecs = nSecs;
this.clockSeq = clockSeq;
// Per 4.1.4 - Convert from unix epoch to Gregorian epoch
mSecs += 12219292800000;
var uuid_time = mSecs * 10000 + nSecs;
var high = uuid_time << 4;
var low = uuid_time & 0x0fff | 0x6000;
var clock = (clockSeq & 0x3fff) | 0x8000;
buf..buffer.asByteData().setUint64(0, high);
buf..buffer.asByteData().setUint16(6, low);
buf..buffer.asByteData().setUint16(8, clock);
var node = (options['node'] != null) ? options['node'] : nodeId;
buf.setAll(10, node);
return UuidParsing.unparse(buf);
}