Observer.php

<?php
/**
 *
 * NOTICE OF LICENSE
 *
 * This source file is subject to the Open Software License (OSL 3.0)
 * that is bundled with this package in the file LICENSE.txt.
 * It is also available through the world-wide-web at this URL:
 * http://opensource.org/licenses/osl-3.0.php
 * If you did not receive a copy of the license and are unable to
 * obtain it through the world-wide-web, please send an email
 * to license@magentocommerce.com so we can send you a copy immediately.
 *
 * DISCLAIMER
 *
 * Do not edit or add to this file if you wish to upgrade this extension
 * to newer versions in the future.
 *
 * @category   Hackathon
 * @package    Hackathon_PromoCodeMessages
 * @license    http://opensource.org/licenses/osl-3.0.php  Open Software License (OSL 3.0)
 */

class Hackathon_PromoCodeMessages_Model_Observer
{
    /**
     * Called on sales_quote_collect_totals_after. Ensure that the action is couponPost before continuing.
     *
     * @param Varien_Event_Observer $observer
     */
    public function validateCode(Varien_Event_Observer $observer)
    {
        if (!Mage::getStoreConfigFlag('checkout/promocodemessages/enabled')) {
            return;
        }

        if (Mage::app()->getRequest()->getActionName() !== 'couponPost') {
            return;
        }

        if ((int)Mage::app()->getRequest()->getParam('remove') === 1) {
            return;
        }

        $quote      = $observer->getQuote();
        $couponCode = $quote->getCouponCode();

        if (!$couponCode) {
            // parent validation has failed
            $couponCode = (string)Mage::app()->getRequest()->getParam('coupon_code');
            try {
                Mage::getModel('hackathon_promocodemessages/validator')->validate($couponCode, $quote);
            } catch (Mage_Core_Exception $e) {
                $msg = Mage::helper('hackathon_promocodemessages')
                    ->__('Your coupon "%s" could not be redeemed.', $couponCode);
                $msg = "<p class=\"promo_error_intro\">$msg</p>";
                $msg .= $e->getMessage();
                throw new Mage_Core_Exception($msg, 0, $e);
            }
        }
    }
}