Personally, I split code into two parts. The business logic and actually implementation. The business logic may be duplicated due to its nature, but it should n

Personally, I split code into two parts. The business logic and actually implementation. The business logic may be duplicated due to its nature, but it should not have too many duplicated technical details in it. While the business logic can be as shitty as you want as long as you do not handle business logic directly in it and keep it application independent. In that way. If you know things messed up and don't go too well. You have the option to wipe the implementation as a whole instead of forced to fix it and try to find out the actual spec from implementation.