Multiple Gift Vouchers 2.0.2.0 Almost, some help needed

Hi Guys,

I'm keen to change Opencart to allow customers who have more than one gift voucher the ability to combine them to make a purchase (currently not possible as standard in Opencart strangely!?). Would have thought this is the way gift vouchers should work e.g as your store's own kind of currency.

Found a great article that explains most of how to achieve Multiple Gift Vouchers but the controller file (catalog/controller/checkout/cart.php) in Opencart 2.0.2.0 is quite different to that of Opencart 2.0 which is the example in the article. Has anybody got any tips on the changes needed for the new Controller file (catalog/controller/checkout/cart.php)

The article is here;

http://code.tutsplus.com/articles/quick ... -cms-24405

and I have attached the up to date version of the (catalog/controller/checkout/cart.php) file to this message.
Any help would be really appreciated.

Stu