Coupon/ReferralCode Tracking / auto-apply in Zen Cart

config.referral_tracking.php

<?php
  $autoLoadConfig[100][] = array('autoType'=>'init_script',
                                 'loadFile'=> 'init_referral_tracking.php');

init_referral_tracking.php

<?php
/**
 * initialize referral-tracking-system variables
 *
 * Determines which referral code the customer came in on 
 *
 */
  if (!defined('IS_ADMIN_FLAG')) {
   die('Illegal Access');
  }

// REFERRALS SYSTEM (c/f modules/checkout_process.php and tpl_checkout_success_default.php)
if (isset($_GET['ref']) && $_GET['ref'] != '') {
  $_SESSION['referral_code'] = $_GET['ref'];

  if ($_GET['ref'] == 'vt') {
    $_SESSION['referral_code'] = 'vtarget';
    $_SESSION['cc_id']='vtarget';
  }
}

// TESTING - the following dumps the referral-code for this session into the page-headers as a comment, which is invisible to customers. It only shows up for administrators' PC's whose IP address is in the down-for-maint list.
if (strstr(EXCLUDE_ADMIN_IP_FOR_MAINTENANCE, $_SERVER['REMOTE_ADDR'])) {
  if (isset($_SESSION['referral_code'])) $debug_message .= '<!-- ref=' . $_SESSION['referral_code'] . ' -->';
//	print_r($_COOKIE);
}