So here's the problem- I'm writing my own engine library, and it works fine with stuff like menus and the actual game screen. The thing is, I can't really figure out how to integrate something like an intro or dialogue preceding certain levels into this system. Let's look at another example- say I have a game-specific engine which gets a Level object and runs it. Engine would have its own collision and physics system, all hard coded. Now, what if at some point in a level, I want the player to enter a mini-game with different rules? How do I morph the Engine class to support these sub-systems without having to deal with their code all the time (as in: if(regular game) ... else if(mini game) ...)?

And what if I want an intro animation at the start of a level, and I want the player to be able to assume control of his character once the animation ends, do I implement the animation into the Engine class itself? Or maybe I need to run another class, CutScene, and when it ends, it calls Engine and starts the level? What if I want to add a dialogue system, where at the start of each level there's a short dialogue and the player can't control his character, and once it ends, he can? Would I then run the dialogue code inside the Engine code?

Maybe these sub-systems should all be scripted? I don't know anything about scripting, is it necessary for this kind of situation? Any help would be appreciated.