LuhnValidator.php

<?php

/*
 * This file is part of the Symfony package.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *
 * For the full copyright and license information, please view the LICENSE
 * file that was distributed with this source code.
 */
namespace Symfony\Component\Validator\Constraints;

use Symfony\Component\Validator\Constraint;
use Symfony\Component\Validator\ConstraintValidator;

/**
 * Validates a PAN using the LUHN Algorithm
 *
 * For a list of example card numbers that are used to test this
 * class, please see the LuhnValidatorTest class.
 *
 * @see    http://en.wikipedia.org/wiki/Luhn_algorithm
 * @author Tim Nagel <t.nagel@infinite.net.au>
 * @author Greg Knapp http://gregk.me/2011/php-implementation-of-bank-card-luhn-algorithm/
 */
class LuhnValidator extends ConstraintValidator {

  /**
   * Validates a creditcard number with the Luhn algorithm.
   *
   * @param mixed      $value
   * @param Constraint $constraint
   */
  public function validate($value, Constraint $constraint) {
    if (null === $value || '' === $value) {
      return;
    }
    if (!is_numeric($value)) {
      $this->context
        ->addViolation($constraint->message);
      return;
    }
    $length = strlen($value);
    $oddLength = $length % 2;
    for ($sum = 0, $i = $length - 1; $i >= 0; $i--) {
      $digit = (int) $value[$i];
      $sum += $i % 2 === $oddLength ? array_sum(str_split($digit * 2)) : $digit;
    }
    if ($sum === 0 || $sum % 10 !== 0) {
      $this->context
        ->addViolation($constraint->message);
    }
  }

}