trait VariantTrait

trait VariantTrait {
    
    /**
     * Returns the bytes that comprise the fields
     */
    public abstract function getBytes() : string;
    
    /**
     * Returns the variant identifier, according to RFC 4122, for the given bytes
     *
     * The following values may be returned:
     *
     * - `0` -- Reserved, NCS backward compatibility.
     * - `2` -- The variant specified in RFC 4122.
     * - `6` -- Reserved, Microsoft Corporation backward compatibility.
     * - `7` -- Reserved for future definition.
     *
     * @link https://tools.ietf.org/html/rfc4122#section-4.1.1 RFC 4122, § 4.1.1: Variant
     *
     * @return int The variant identifier, according to RFC 4122
     */
    public function getVariant() : int {
        if (strlen($this->getBytes()) !== 16) {
            throw new InvalidBytesException('Invalid number of bytes');
        }
        if ($this->isMax() || $this->isNil()) {
            // RFC 4122 defines these special types of UUID, so we will consider
            // them as belonging to the RFC 4122 variant.
            return Uuid::RFC_4122;
        }
        
        /** @var int[] $parts */
        $parts = unpack('n*', $this->getBytes());
        // $parts[5] is a 16-bit, unsigned integer containing the variant bits
        // of the UUID. We convert this integer into a string containing a
        // binary representation, padded to 16 characters. We analyze the first
        // three characters (three most-significant bits) to determine the
        // variant.
        $binary = str_pad(decbin($parts[5]), 16, '0', STR_PAD_LEFT);
        $msb = substr($binary, 0, 3);
        if ($msb === '111') {
            return Uuid::RESERVED_FUTURE;
        }
        elseif ($msb === '110') {
            return Uuid::RESERVED_MICROSOFT;
        }
        elseif (str_starts_with($msb, '10')) {
            return Uuid::RFC_4122;
        }
        return Uuid::RESERVED_NCS;
    }

}