UUID v4 Generator

function generateUUIDv4() {
  const bytes = new Uint8Array(16);
  crypto.getRandomValues(bytes);

  // Set version (4) and variant (10xx) bits per RFC 4122
  bytes[6] = (bytes[6] & 0x0f) | 0x40; // Version 4
  bytes[8] = (bytes[8] & 0x3f) | 0x80; // Variant 1

  const hex = Array.from(bytes, b => b.toString(16).padStart(2, '0')).join('');
  return `${hex.slice(0,8)}-${hex.slice(8,12)}-${hex.slice(12,16)}-${hex.slice(16,20)}-${hex.slice(20)}`;
}

// Generate 5 UUIDs
for (let i = 0; i < 5; i++) {
  console.log(generateUUIDv4());
}

async function generateUUIDv5(namespace, name) {
  const NS = '6ba7b810-9dad-11d1-80b4-00c04fd430c8'; // DNS namespace
  const nsBytes = hexToBytes(namespace || NS);
  const nameBytes = new TextEncoder().encode(name);

  const buffer = new Uint8Array(nsBytes.length + nameBytes.length);
  buffer.set(nsBytes);
  buffer.set(nameBytes, nsBytes.length);

  const hash = await crypto.subtle.digest('SHA-1', buffer);
  const bytes = new Uint8Array(hash).slice(0, 16);

  bytes[6] = (bytes[6] & 0x0f) | 0x50; // Version 5
  bytes[8] = (bytes[8] & 0x3f) | 0x80; // Variant 1

  const hex = Array.from(bytes, b => b.toString(16).padStart(2, '0')).join('');
  return `${hex.slice(0,8)}-${hex.slice(8,12)}-${hex.slice(12,16)}-${hex.slice(16,20)}-${hex.slice(20)}`;
}

function hexToBytes(hex) {
  return Uint8Array.from(hex.replace(/-/g, ''), c => parseInt(c, 16));
}

// Deterministic UUID — same input always produces same output
const uuid = await generateUUIDv5(null, 'example.com');
console.log(uuid); // Always: 9073926b-929f-31c2-abc9-fad77ae3e8eb