function guidv4($data = null) {
  $data = $data ?? random_bytes(16);
  assert(strlen($data) == 16);
  $data[6] = chr(ord($data[6]) & 0x0f | 0x40); // set version to 0100
  $data[8] = chr(ord($data[8]) & 0x3f | 0x80); // set bits 6-7 to 10
  return vsprintf('%s%s-%s-%s-%s-%s%s%s', str_split(bin2hex($data), 4));
}

$data = openssl_random_pseudo_bytes(16);
echo guidv4($data) . "\n";
echo guidv4() . "\n";