Woocommerce add sort by discount percentage low to high and high to low

I am using discount pricing and rules pro by Asana plugins in a woocommerce site. I need in woocommerce category page inside the sort by drop down to add 2 options: by discount percentage low to high and by discount percentage high to low and of course each option to be functional.
I know how to add the option via hooks, but I need the functionality inside the function to calculate the discount using regular and sales price and sort products by it.