Jyxo\Input\Validator\IsCompanyId::isValid PHP Method

    public function isValid($value) : bool
    {
        // Removes spaces
        $companyId = preg_replace('~\\s+~', '', (string) $value);
        // Only numbers
        if (!preg_match('~^\\d{8}$~', $companyId)) {
            return false;
        }
        // Checksum
        $a = 0;
        for ($i = 0; $i < 7; $i++) {
            $a += $companyId[$i] * (8 - $i);
        }
        $a = $a % 11;
        if (0 === $a) {
            $c = 1;
        } elseif (10 === $a) {
            $c = 1;
        } elseif (1 === $a) {
            $c = 0;
        } else {
            $c = 11 - $a;
        }
        if ((int) $companyId[7] !== $c) {
            return false;
        }
        return true;
    }