Develop a catalog for a company. Assume that this company sells three different Items. The seller can sell individual items or a combination of any two items. A gift pack is a special combination that contains all three items. Here are some special considerations: If a customer purchases individual items, he does not receive any discount. If a customer purchases a combo pack with two unique items, he gets a 10% discount. If the customer purchases a gift pack, he gets a 25% discount. Write a function for the above scenario. Perform the calculations in code wherever applicable.