Adjust woocommerce discount code behaviour

Normally discount codes are off the product price, or when there is one, of the sales price. Because I have a lot of sales prices, I do not want my discount codes to behave always this way. I want to be able to select if a discount code goes off the normal price or off sale price. So I can get customers 25% discount code of the normal price and give 10 sale price for a period of time also. If you could write me so software for woocommerce for me, that would be nice. I think you could sell this plugin later too ;-)