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