SBC Games wrote a series of tutorials on building games that are easy to maintain: "Many tutorials show you how to build a game. Let’s say, you already have one. And because it is good and catchy, sponsors are interested in it. Your nice and clean code is step by step polluted with sponsor specific APIs.
Today we will continue on managing different sponsor APIs. Last time in part 1 we build solid base for handling different events by different sponsors. We also created system for loading external config file for each sponsor, that overrides default config values. Today we will add more examples, how to use it."