Vendo A/B testing script

<?php
//NATS' tracker url (with a trailing slash)
$natsTrackUrl = 'http://natsv4.staging.vend-o.com/track/';
//NATS' signup url
$natsSignupUrl = 'http://natsv4.staging.vend-o.com/signup/signup.php';

$configuration = array(
    //maps all current tours of SiteID 11 to the new tour (88) configured for the Vendo A/B test
    '11.*' => '88',
    //The A/B split will occur between all the current tours (A) and the new one configured for Vendo (B)
);

$abTester = new VendoABTester($configuration, $natsTrackUrl, $natsSignupUrl);
$abTester->performTest();

class VendoABTester
{
    protected $_config;
    protected $_testAvailable;
    protected $_natsUrl;
    protected $_currentNatsCode;
    protected $_newNatsCode;
    protected $_requestType;

    public function __construct(array $config, $trackUrl, $signupUrl)
    {
        $this->_config = $config;
        $this->_testAvailable = false;
        $this->_natsUrl = $natsUrl;
        $this->dectectSiteAndTour();
        /**
         * We need to identify where the traffic is coming from:
         * /track/(.+) ?
         * or /signup/signup.php ?
         */
        if (empty($_GET['signup'])) {//the apache rule appends this
            $this->_requestType = 'track';
            $this->_natsUrl = $trackUrl;
        } else {
            $this->_requestType = 'signup';
            $this->_natsUrl = $signupUrl;
        }
        $this->_requestType = empty($_GET['signup']) ? 'track' : 'signup';
    }

    /**
     * Decodes the NATS code and checks whether the site+tour combination is configured to be A/B tested or not.
     * Check http://nats.yourdomain.com/admin_codes.php to get the details on how the NATS codes get generated.
     */
    public function dectectSiteAndTour()
    {
        $this->_testAvailable = false;
        if (!empty($_GET['nats'])) {
            //we need to decode the code that NATS generated (see http://nats.yourdomain.com/admin_codes.php)
            $this->_currentNatsCode = base64_decode($_GET['nats']);
            @list($affId, $programId, $siteId, $tourId, $other1, $other2, $other3, $other4, $other5) = explode('.', $this->_currentNatsCode);
            if (!empty($siteId) && !empty($tourId)) {
                //do we have a specific rule for the current siteId and tourId?
                if (isset($this->_config[$siteId . '.' . $tourId])) {
                    $newTourId = $this->_config[$siteId . '.' . $tourId];
                    $this->_testAvailable = true;
                //do we have a catch-all rule for this siteId?
                } elseif (isset($this->_config[$siteId . '.*'])
                         //this condition prevents to A/B on a previous A/B
                          &&  $this->_config[$siteId . '.*'] != $tourId
                ) {
                    $newTourId = $this->_config[$siteId . '.*'];
                    $this->_testAvailable = true;
                }
                if ($this->_testAvailable) {
                    $this->_newNatsCode = implode('.', array(
                        $affId, $programId, $siteId, $newTourId,
                        $other1, $other2, $other3, $other4, $other5,
                    ));
                }
            } else {
                //something is not OK in the NATS code. We'll have to ignore this request.
                $this->_testAvailable = false;
            }
        }
    }

    /**
     * Tells whether the site+tour combination is configured to be A/B tested or not
     */
    public function testAvailable()
    {
        return $this->_testAvailable;
    }

    /**
     * Flips a coin and picks the nats code that will take the user to Vendo or to the other biller
     * Redirects the user back to NATS
     */
    public function performTest()
    {
        $url = '';
        $natsCode = base64_encode($this->_currentNatsCode);

        if ($this->_testAvailable) {
            //flip the coin
            $random = mt_rand(1, 100);
            if ($random > 50) {
                //process with Vendo
                $natsCode = base64_encode($this->_newNatsCode);
            }
        }

        if ($this->_requestType == 'track') {
            $url = $this->_natsUrl . $natsCode . '?vendoab=1';
        } else {
            $queryString = parse_str($_SERVER['QUERY_STRING']);
            unset($queryString['signup']);
            $queryString['nats'] = $natsCode;
            $queryString['vendoab'] = 1;
            $url = $this->_natsUrl . '?' . http_build_query($queryString);
        }

        //We use the vendoab=1 parameter to tell apache to take the user to the original tour's flow
        //(i.e. apache won't redirect the user to this script again)
        header('Location: ' . $url);
        exit;
    }
}