cnp-validation

cnp-validation.php

<?php

function isCnpValid (string $cnp) : bool {
    if (empty($cnp) || (preg_match('/^[1-9]{1}[0-9]{12}$/', $cnp) !== 1)) {
        return false;
    }

    $birthMonth = (int) ($cnp[3] . $cnp[4]);

    if (!$birthMonth || ($birthMonth > 12)) {
        return false;
    }

    $birthDay = (int) ($cnp[5] . $cnp[6]);
    $birthYear = '19';

    if (($cnp[0] === '3') || ($cnp[0] === '4')) {
        $birthYear = '18';
    } elseif (($cnp[0] === '5') || ($cnp[0] === '6')) {
        $birthYear = '20';
    }

    $birthYear = (int) ($birthYear . $cnp[1] . $cnp[2]);

    // check if the birth day doesn't exceed the number of days in the birth month
    if (!$birthDay || ($birthDay > (int) date('t', strtotime($birthYear . '-' . $birthMonth . '-01')))) {
        return false;
    }

    $birthPlace = (int) ($cnp[7] . $cnp[8]);

    if (
        !$birthPlace ||
        (($birthPlace > 46) && ($birthPlace < 51)) ||
        ($birthPlace > 52)
    ) {
        return false;
    }

    // the number formed by the 9th, 10th, and 11th digits (0-indexed) must be between 1 and 999
    if (($cnp[9] === '0') && ($cnp[10] === '0') && ($cnp[11] === '0')) {
        return false;
    }

    $controlNumber = (($cnp[0] * 2) + ($cnp[1] * 7) + ($cnp[2] * 9) + ($cnp[3] * 1) + ($cnp[4] * 4) + ($cnp[5] * 6) + ($cnp[6] * 3) + ($cnp[7] * 5) + ($cnp[8] * 8) + ($cnp[9] * 2) + ($cnp[10] * 7) + ($cnp[11] * 9)) % 11;
    $controlNumber = $controlNumber === 10 ? 1 : $controlNumber;

    if ((int) $cnp[12] !== $controlNumber) {
        return false;
    }

    return true;
}