[rules-users] Drools calculation of a date function

I am new to drools. I want to write a function that accepts two strings and returns a date. The two strings are one for the payment frequency and the other for the payment day. Following are my requirements: 1.If the payment frequency is daily, return current date 2.If the payment frequency is weekly and the payment day is let's say Monday, and the current day is Monday, then return current date. If the current day is Monday and the payment day is Tuesday, return current date + 1. Likewise, if the payment day is Wednesday, return current date + 2. 3.If the payment frequency is monthly and payment day is 15, retrieve the current month and current year and return MM-15-YYYY. Please help me write a function for this. Thank you so much in advance.