Magento - apply coupon code automatically

applyCouponCodeAction.php

public function indexAction() {    
    $coupon_code = $this->getRequest()->getParam('coupon_code');
    
    if ($coupon_code != '') {
        Mage::getSingleton("checkout/session")->setData("coupon_code",$coupon_code);
        Mage::getSingleton('checkout/cart')->getQuote()->setCouponCode($coupon_code)->save();
	Mage::getSingleton('core/session')->addSuccess($this->__('Coupon was automatically applied'));
    }
    else {
        Mage::getSingleton("checkout/session")->setData("coupon_code","");
	$cart = Mage::getSingleton('checkout/cart');
	foreach( Mage::getSingleton('checkout/session')->getQuote()->getItemsCollection() as $item ) {
	    $cart->removeItem( $item->getId() );
	}
	$cart->save();
    }

    if ($this->getRequest()->getParam('url')) {
	//using raw header instead of _redirect because _redirect appends a /
	header('HTTP/1.1 301 Moved Permanently');
	$gclid = $this->getRequest()->getParam('gclid');
	$url = $this->getRequest()->getParam('url');
        header('Location: /' . $url . '?gclid=' . $gclid);
	die();
    } else {
        $this->_redirect("/");
    }
}