custom plugin for coupon

-- HikaShop version -- : 2.2.3
-- Joomla version -- : 2.5.18
-- PHP version -- : 5

Hi,

I need to write a custom plugin for coupons. I have seen the "developer documentation" describing how to create a custom plugin and indeed i have written a custom plugin for hikashop before (albeit a long time ago). Ok so what i want to do is write a custom plugin for coupons - so im thinking of adding that custom plugin as follows:-

/plugins/hikashop/coupon/coupon.php

(for the above: is this the correct folder/file path for adding a coupon plugin?)

and then im thinking of adding code like so (to the coupon.php plugin file):-

class plgHikashopCoupon extends JPlugin {
	function plgHikashopCoupon(&$subject, $config) {
		parent::__construct($subject, $config);
	}

	function onBeforeCouponLoad(&$coupon,&$do) {

	}
}