<?php

/**
 * Implements hook_vat_info().
 */
function vat_validators_vat_info() {
  return array(
    'be' => array(
      'country' => t('Belgium'),
      'demonym' => t('belgian'),
      'validator' => '_is_valid_be_vat',
    ),
    'nl' => array(
      'country' => t('Netherlands'),
      'demonym' => t('dutch'),
      'validator' => '_is_valid_nl_vat',
    ),
  );
}

/**
 * BE VAT Validator callback function
 */
function _is_valid_be_vat($vat = NULL) {
  $matches = array();
  if (!preg_match('/BE(\d{8})(\d{2})/', $vat, $matches)) {
    return FALSE;
  }
  return (97 - ($matches[1] % 97)) == $matches[2];
}

/**
 * NL VAT Validator callback function
 */
function _is_valid_nl_vat($vat) {
  $matches = array();
  if (!preg_match('/NL(\d{9})B\d{2}/', $vat, $matches)) {
    return FALSE;
  }
  $sum = 0;
  for ($i = 0; $i < 8; $i++) {
    $sum += (9 - $i) * $matches[1][$i];
  }
  $sum %= 11;
  return $sum == $matches[1][8];
}