DragonBe\Vies\Validator\ValidatorDE::validate PHP Method

    public function validate($vatNumber)
    {
        if (strlen($vatNumber) != 9) {
            return false;
        }
        $prod = 10;
        $checksum = (int) substr($vatNumber, -1);
        for ($i = 0; $i < 8; $i++) {
            $checkval = ((int) $vatNumber[$i] + $prod) % 10;
            $checkval = $checkval == 0 ? 10 : $checkval;
            $prod = $checkval * 2 % 11;
        }
        $prod = $prod == 1 ? 11 : $prod;
        if (11 - $prod != $checksum) {
            return false;
        }
        return true;
    }