Implemented IDifficultyCalculatorBeatmap to move diffcalc-specific functions into specific classes

[Givikap120]

Part of this PR - #29482

Calculation of MaxCombo and ObjectsCount time complexity is changed from O(t^2) to O(t) for progressive calculation.
This significantly cuts the time of TimedDifficultyAttributes calculation.

[bdach]

With this sort of thing and #28473 I do worry a bit if IBeatmap isn't growing out of control. But I haven't been able to get a conclusion on that other one so...

[smoogipoo]

I agree with @bdach, maybe difficulty calculators shouldn't use IBeatmap, and provide their own interface instead?

[Givikap120]

I agree with @bdach, maybe difficulty calculators shouldn't use IBeatmap, and provide their own interface instead?

Does this mean that I should remade it to add something like IDiffucultyCalculationBeatmap?
Or this still needs some discussion.

[bdach]

I agree with @bdach, maybe difficulty calculators shouldn't use IBeatmap, and provide their own interface instead?

Last I tried this avenue (exactly when exploring solutions to #28473, mind) I ended up with a bunch of generic badness. The primary problem here is WorkingBeatmap.GetBeatmap(), which firmly chains itself to IBeatmap. After which point it's rather difficult to do any lateral movement wrt interface separation without either ugly yolo casting, or sprinkling in generic badness (WorkingBeatmap.GetBeatmap<TBeatmap>()....????) Then there's also beatmap conversion which is another level of the same...

[smoogipoo]

@bdach I don't think that's going to be relevant here because the IBeatmap in this case is post-WorkingBeatmap.GetPlayableBeatmap(). I just see it wrapping whatever IBeatmap results from the former, as:

// Difficulty calculators internally will use this
interface IDifficultyCalculatorBeatmap : IBeatmap
{
}

// Private implementation, could either house stuff to do with progressive difficulty, or be overridden to do as such.
private class DifficultyCalculatorBeatmap : IDifficultyCalculatorBeatmap
{
    public DifficultyCalculatorBeatmap(IBeatmap baseBeatmap) { }
    // Delegations to baseBeatmap, or custom implementation for progressive difficulty.
}

At least, I can't see why this wouldn't work in principle. I suggest you try going down this route and see if anything blocking comes up - if it does then it needs more discussion because I would hope things to be this simple.

[bdach]

If I understand your proposal correctly this sort of decorator pattern probably works. If it does, then sure I guess. I might have overlooked that.

[Givikap120]

BIG WARNING
this will most likely break all the custom rulesets, as DifficultyCalculator.CreateDifficultyAttributes signature is changed and now has IDifficultyCalculationBeatmap instead of IBeatmap