<?php

/**
 * 
 * @author Cerion Morgauin
 * @version $Id$
 * @copyright Enrico Marongiu (cerion hide@address.com tiscali _._ it) - 2004
*  linkObfuscator manages a simple way of validating links: starting from a session, an user can browse exclusively those links that are performed by this page. to do this, a random seed is generated and a special code (named go) is attached to each link.
* each page that has to be obfuscated needs this class and a $linkObfuscator::check() to validate the user.
 **/

class linkObfuscator
{
	var $seed=0;
	var $referralSeed=0;
	function linkObfuscator($referralSeed=false)
	{
		// new seed, to obfuscate new pages
   		srand();
		$this->seed= rand();
		// old seed, to check access
		if($referralSeed===false or !is_numeric($referralSeed)) {
			$this->referralSeed=$referralSeed;
		} else if(is_numeric($_SESSION['referralSeed'])) {
			$this->referralSeed=$_SESSION['referralSeed'];
			$_SESSION['referralSeed']=$this->seed;
		}	
	}

	function _obfuscate($aLink,$aSeed)
	{
		$sep=(strpos('?',$aLink)===false)?'?':'&';
		return $aLink. $sep ."go=".md5($aSeed .$aLink);
	}
	
	function obfuscate($aLink)
	{
		return $this->_obfuscate($aLink,$this->seed);
	}
	
	function check($anObfuscatedLink)
	{
		$theLink=preg_replace('/(&|\?)go=(\w)+/','',$anObfuscatedLink);
		if($this->_obfuscate($theLink,$this->referralSeed)==$anObfuscatedLink)
			return true;
			
		return false;
	}
}
?>