khosb/modules/checkout/classes/Checkout/Plugin.php

<?php defined('SYSPATH') or die('No direct access allowed.');

/**
 * This class provides CHECKOUT Plugin Support
 *
 * @package    Checkout
 * @category   Plugins
 * @author     Deon George
 * @copyright  (c) 2009-2013 Open Source Billing
 * @license    http://dev.osbill.net/license.html
 * @todo Does this need to be Serializable?
 */
abstract class Checkout_Plugin implements Serializable {
	protected $co; // Our Checkout Object
	protected $_object;

        // Our required abstract classes
	public function serialize() {
		return (string)$this->_object;
	}
	public function unserialize($s) {
		$this->_object = XML::factory(NULL,NULL,$s);
	}

	// Required abstract classes
	// Present pre-plugin processing information
	abstract public function before(Cart $co);
	abstract public function notify(Model_Checkout_Notify $cno);

	public function __construct(Model_Checkout $co) {
		$this->co = $co;
	}
}
?>