const hexdigit = (c: number) => '0123456789abcdef'[c & 15];
export function uuid(): string {
    // https://datatracker.ietf.org/doc/html/rfc4122#section-4.4
    const bs = new Uint8Array(16);
    crypto.getRandomValues(bs);
    bs[6] = (bs[6] & 15) | 0x40;
    bs[8] = (bs[8] & 63) | 0x80;
    const result: string[] = [];
    bs.forEach(b => result.push(hexdigit(b >> 4), hexdigit(b)));
    const s = result.join('');
    return [s.slice(0,8), s.slice(8,12), s.slice(12,16), s.slice(16,20), s.slice(20)].join('-');
}