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<?php
namespace Faker\Calculator;
/**
* Utility class for validating ISBN-10
*/
class Isbn
{
/**
* @var string ISBN-10 validation pattern
*/
public const PATTERN = '/^\d{9}[0-9X]$/';
/**
* ISBN-10 check digit
*
* @see http://en.wikipedia.org/wiki/International_Standard_Book_Number#ISBN-10_check_digits
*
* @param string $input ISBN without check-digit
*
* @throws \LengthException When wrong input length passed
*/
public static function checksum(string $input): string
{
// We're calculating check digit for ISBN-10
// so, the length of the input should be 9
$length = 9;
if (strlen($input) !== $length) {
throw new \LengthException(sprintf('Input length should be equal to %d', $length));
}
$digits = str_split($input);
array_walk(
$digits,
static function (&$digit, $position): void {
$digit = (10 - $position) * $digit;
},
);
$result = (11 - array_sum($digits) % 11) % 11;
// 10 is replaced by X
return ($result < 10) ? (string) $result : 'X';
}
/**
* Checks whether the provided number is a valid ISBN-10 number
*
* @param string $isbn ISBN to check
*/
public static function isValid(string $isbn): bool
{
if (!preg_match(self::PATTERN, $isbn)) {
return false;
}
return self::checksum(substr($isbn, 0, -1)) === substr($isbn, -1);
}
}
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