<?php

function returnImage()
{
    $path = 'image/pixel.png';
	// finally return the image
	header('Content-Type: image/png');
	header('Content-Length: ' . filesize( $path ));
	readfile($path);
	exit;
}

// If cookie exists or there is no url referrer 
// => return the image
if( isset($_COOKIE['linxo_attr']) || !isset($_SERVER['HTTP_REFERER']))
{
	returnImage();
	return;
}

// lookup and parse the referrer's host to make sure we're on linxo.com
$url_components = parse_url($_SERVER['HTTP_REFERER']);
$host = $url_components['host'];
$domain_pos = strripos($host,"linxo.com");
if($domain_pos === false || $domain_pos != (strlen($host) - strlen("linxo.com"))) 
{
	// not on linxo.com => return the image directly
//	error_log("Not on linxo.com domain");
	returnImage();
	return;
}


// lookup and parse the referrer's query string for utm_** parameters
if(!isset($url_components['query']))
{
	// No Query string => return the image directly
//	error_log("No query string in referer");
	returnImage();
	return;
}


$query_params = array();
parse_str($url_components['query'], $query_params);
if(! isset($query_params['utm_source']) ||
   ! isset($query_params['utm_medium']) || 
   ! isset($query_params['utm_campaign']))
{
	// At least one of the expected params is not available
	// => return the image
//	error_log("Not all three items in query string of referer [".$url_components['query']."]");
	returnImage();
	return;
}

// At this point, we have no cookie set and all the params are 
// in the query string of the referrer URL.
//
// So we can set the cookie with the value of the query string
// => set the cookie linxo_attr with the encoded query string
// name: "linxo_attr"
// value : referrer's query string + "click_time=".time()
// expire in 30 days
// path : /
// domain: .linxo.com
$cookie_value = $url_components['query'] . '&click_time=' .time();
setcookie("linxo_attr", $cookie_value, time()+60*60*24*30, "/", ".linxo.com");
returnImage();

?>