Architectural refactoring

[WildWeazel]

This is a big one. Following #261 refactor the code to follow the proposed layered architecture: cleanly separate Godot scripts, game logic, data types, C7 & Civ3 file IO, and anything else so that each layer depends only on the one(s) below it. See also #132

[QuintillusCFC]

One of the things that has occasionally come up, and is a bit awkward currently, is the AI, and AI data. Right now, the AI behavior is in C7Engine, but the data classes that stored AI data (which can thus be persisted across a save game, important if we want the AI to have long-term planning) live in C7GameData. This is consistent with wanting C7GameData to contain what can be written out, but means the AI is somewhat split.

There may be a better way to do this, especially one that considers the potential for pluggable AI components, including those that may include data written as part of the save file. That's a longer-term thing I want to consider (but before that there are things like teaching the AI how to arbitrate among potential strategies). Still, it's something that there's been some pushback on (mainly suggesting putting the data in with the C7Engine). I haven't seen pushback with what I'd consider a better alternative being put forward at the same time. But FYI, while I support the general separation of concerns, I see why the AI split in particular has garnered a few PR questions.

[rchoffardet]

Just stopping by to write here some curiosities I found while scanning the repository:

I'm not sure the messaging pattern is appropriate with C7 (as a Civ3 remake) because Civ3 is very sequential (make an action, watch it being rendered, then make another action, watch it being rendered, ...) while messaging is async by nature and thus requires the workaround with the mutex.

In a similar idea, C7Engine hosts the responsibility of "waiting" for an animation to finish or not. It shouldn't have to. In Civ3, units in the fog of war aren't animated (obviously), but units outside are, by default. IMHO, the fog of war handling is a rendering responsibility and should be handled by the rendering part. Determining to animate and wait for the end of the animation, should be done in the rendering part.

C7Engine / C7GameData separation seems a bit artificial to me. It's like separating behavior and data, which is odd in the OOP paradigm. Even if you want to keep the separation, I don't think having two separate projects is necessary (my 2cts).
However, having no separation between live data (units, cities, ...) and constant data (unit prototypes, techs, strength bonuses, ...) is odd to me.

I'm willing to contribute if you're interested by my remarks :)