Not luhn compliant

[fedeisas]

Hi guys, I noticed the credit cards numbers generated by this library won't pass a luhn validator. Is this by design?

[ulrikjohansson]

From a 5-second googling it seems like all the major credit card providers all use the same checksum validation algorithm (Luhn). There are also personal identification numbers that use this algorithm for their checksums.
Perhaps it would be a good idea to pull this checksum calculator into core, and let the providers use it as a utility function? That way we don't end up with copies everywhere in the different providers, which seems to be the way it's done in the localized versions today (I did this myself for the sv_SE translation).

[nineinchnick]

I think it's also used for IBANs. If it were available in the core I'd update those generators.

[fedeisas]

Many PHP Validation libraries have luhn validation. I don't think it's possible to generate luhn-valid numbers. Instead, we could wrap the creditCardNumber() method do..while using that checksum validator?

Taken from the lithium validation class:

<?php

function isValidLuhn($value) {
  if (empty($value) || !is_string($value)) {
    return false;
  }
  $sum = 0;
  $length = strlen($value);

  for ($position = 1 - ($length % 2); $position < $length; $position += 2) {
    $sum += $value[$position];
  }
  for ($position = ($length % 2); $position < $length; $position += 2) {
    $number = $value[$position] * 2;
    $sum += ($number < 10) ? $number : $number - 9;
  }
  return ($sum % 10 === 0);
}

[fzaninotto]

Fixed in #414

[fedeisas]

@fzaninotto amazing! Thanks 😃

[ulrikjohansson]

Great work! Much better implementation now.

I noticed one little naming thing in the rewritten tests in test/Faker/Provider/sv_SE/PersonTest.php. I've written a comment here: https://github.com/fzaninotto/Faker/pull/414/files#r17042304