class IsbnValidator

class IsbnValidator extends ConstraintValidator {
    public function validate(mixed $value, Constraint $constraint) : void {
        if (!$constraint instanceof Isbn) {
            throw new UnexpectedTypeException($constraint, Isbn::class);
        }
        if (null === $value || '' === $value) {
            return;
        }
        if (!\is_scalar($value) && !$value instanceof \Stringable) {
            throw new UnexpectedValueException($value, 'string');
        }
        $value = (string) $value;
        $canonical = str_replace('-', '', $value);
        // Explicitly validate against ISBN-10
        if (Isbn::ISBN_10 === $constraint->type) {
            if (true !== ($code = $this->validateIsbn10($canonical))) {
                $this->context
                    ->buildViolation($this->getMessage($constraint, $constraint->type))
                    ->setParameter('{{ value }}', $this->formatValue($value))
                    ->setCode($code)
                    ->addViolation();
            }
            return;
        }
        // Explicitly validate against ISBN-13
        if (Isbn::ISBN_13 === $constraint->type) {
            if (true !== ($code = $this->validateIsbn13($canonical))) {
                $this->context
                    ->buildViolation($this->getMessage($constraint, $constraint->type))
                    ->setParameter('{{ value }}', $this->formatValue($value))
                    ->setCode($code)
                    ->addViolation();
            }
            return;
        }
        // Try both ISBNs
        // First, try ISBN-10
        $code = $this->validateIsbn10($canonical);
        // The ISBN can only be an ISBN-13 if the value was too long for ISBN-10
        if (Isbn::TOO_LONG_ERROR === $code) {
            // Try ISBN-13 now
            $code = $this->validateIsbn13($canonical);
            // If too short, this means we have 11 or 12 digits
            if (Isbn::TOO_SHORT_ERROR === $code) {
                $code = Isbn::TYPE_NOT_RECOGNIZED_ERROR;
            }
        }
        if (true !== $code) {
            $this->context
                ->buildViolation($this->getMessage($constraint))
                ->setParameter('{{ value }}', $this->formatValue($value))
                ->setCode($code)
                ->addViolation();
        }
    }
    protected function validateIsbn10(string $isbn) : string|bool {
        // Choose an algorithm so that ERROR_INVALID_CHARACTERS is preferred
        // over ERROR_TOO_SHORT/ERROR_TOO_LONG
        // Otherwise "0-45122-5244" passes, but "0-45122_5244" reports
        // "too long"
        // Error priority:
        // 1. ERROR_INVALID_CHARACTERS
        // 2. ERROR_TOO_SHORT/ERROR_TOO_LONG
        // 3. ERROR_CHECKSUM_FAILED
        $checkSum = 0;
        for ($i = 0; $i < 10; ++$i) {
            // If we test the length before the loop, we get an ERROR_TOO_SHORT
            // when actually an ERROR_INVALID_CHARACTERS is wanted, e.g. for
            // "0-45122_5244" (typo)
            if (!isset($isbn[$i])) {
                return Isbn::TOO_SHORT_ERROR;
            }
            if ('X' === $isbn[$i]) {
                $digit = 10;
            }
            elseif (ctype_digit($isbn[$i])) {
                $digit = $isbn[$i];
            }
            else {
                return Isbn::INVALID_CHARACTERS_ERROR;
            }
            $checkSum += $digit * (10 - $i);
        }
        if (isset($isbn[$i])) {
            return Isbn::TOO_LONG_ERROR;
        }
        return 0 === $checkSum % 11 ? true : Isbn::CHECKSUM_FAILED_ERROR;
    }
    protected function validateIsbn13(string $isbn) : string|bool {
        // Error priority:
        // 1. ERROR_INVALID_CHARACTERS
        // 2. ERROR_TOO_SHORT/ERROR_TOO_LONG
        // 3. ERROR_CHECKSUM_FAILED
        if (!ctype_digit($isbn)) {
            return Isbn::INVALID_CHARACTERS_ERROR;
        }
        $length = \strlen($isbn);
        if ($length < 13) {
            return Isbn::TOO_SHORT_ERROR;
        }
        if ($length > 13) {
            return Isbn::TOO_LONG_ERROR;
        }
        $checkSum = 0;
        for ($i = 0; $i < 13; $i += 2) {
            $checkSum += $isbn[$i];
        }
        for ($i = 1; $i < 12; $i += 2) {
            $checkSum += $isbn[$i] * 3;
        }
        return 0 === $checkSum % 10 ? true : Isbn::CHECKSUM_FAILED_ERROR;
    }
    protected function getMessage(Isbn $constraint, ?string $type = null) : string {
        if (null !== $constraint->message) {
            return $constraint->message;
        }
        elseif (Isbn::ISBN_10 === $type) {
            return $constraint->isbn10Message;
        }
        elseif (Isbn::ISBN_13 === $type) {
            return $constraint->isbn13Message;
        }
        return $constraint->bothIsbnMessage;
    }

}