Iranian National Code Validation - PHP

iranian-national-code-validation.php

/**
 * Check the validity of an Iranian national code
 *
 * @param string $code The national code to be validated.
 * @return bool True if the code is valid, false otherwise.
 */
function check_national_code($code)
{
    // Check if the input code is a 10-digit number
    if (!preg_match('/^[0-9]{10}$/', $code)) {
        return false;
    }

    // Check for repetitive patterns like "0000000000"
    for ($i = 0; $i < 10; $i++) {
        if (preg_match('/^'.$i.'{10}$/', $code)) {
            return false;
        }
    }

    // Calculate the sum based on the algorithm
    for ($i = 0, $sum = 0; $i < 9; $i++) {
        $sum += ((10 - $i) * intval(substr($code, $i, 1)));
    }

    // Validate the code using modulus operation
    $ret = $sum % 11;
    $parity = intval(substr($code, 9, 1));

    if (($ret < 2 && $ret == $parity) || ($ret >= 2 && $ret == 11 - $parity)) {
        return true;
    }

    return false;
}