How can I design a Promo code engine?

I am trying to design an promo code engine which will validate the promocode and applies discount depending on the items in the cart, promocode and User.

I was thinking that the I can have many strategies for the promocode say,

NewUserPromocodeStrategy checks the user is performing the transaction for first time. If yes then provide discount 10% discount FreqUserPromocodeStrategy checks the user is freq user and if the cart value is more than a certain value provide 5% discount

And I will have a Strategy factory for which will provide me the respective strategy class.

So I can have business logic now to calculate the discount depending on the cart, user and Strategy object I got from the factory.

Strategy st = StrategyFactory.get("NEWUSER")

if (st == null) 
   invalid promo code
else
   calculateDiscount(user,cart,st)

Is this a good design ?