Engine-Pong/Platforms/Desktop/KeyboardInputsBehaviour.cs

using System;
using System.Collections.Generic;

using Microsoft.Xna.Framework.Input;

using Syntriax.Engine.Core;
using Syntriax.Engine.Systems.Input;

namespace Pong.Platforms.Desktop;

public class KeyboardInputsBehaviour : Behaviour, IButtonInputs<Keys>
{
    public Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments> OnAnyButtonPressed { get; } = new();
    public Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments> OnAnyButtonReleased { get; } = new();

    private readonly Dictionary<Keys, Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>> OnPressed = new(256);
    private readonly Dictionary<Keys, Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>> OnReleased = new(256);

    private int cachePressedCurrentlyCount = 0;
    private readonly Keys[] cachePressedCurrently = new Keys[256];

    private int cachePressedPreviouslyCount = 0;
    private readonly Keys[] cachePressedPreviously = new Keys[256];

    public void RegisterOnPress(Keys key, Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>.EventHandler callback)
    {
        if (!OnPressed.TryGetValue(key, out Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>? delegateCallback))
        {
            delegateCallback = new();
            OnPressed.Add(key, delegateCallback);
        }

        delegateCallback.AddListener(callback);
    }

    public void UnregisterOnPress(Keys key, Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>.EventHandler callback)
    {
        if (OnPressed.TryGetValue(key, out Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>? delegateCallback))
            delegateCallback.RemoveListener(callback);
    }

    public void RegisterOnRelease(Keys key, Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>.EventHandler callback)
    {
        if (!OnReleased.TryGetValue(key, out Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>? delegateCallback))
        {
            delegateCallback = new();
            OnReleased.Add(key, delegateCallback);
        }

        delegateCallback.AddListener(callback);
    }

    public void UnregisterOnRelease(Keys key, Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>.EventHandler callback)
    {
        if (OnReleased.TryGetValue(key, out Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>? delegateCallback))
            delegateCallback.RemoveListener(callback);
    }

    protected override void OnUpdate()
    {
        KeyboardState keyboardState = Keyboard.GetState();
        keyboardState.GetPressedKeys(cachePressedCurrently);
        cachePressedCurrentlyCount = keyboardState.GetPressedKeyCount();

        for (int i = 0; i < cachePressedCurrentlyCount; i++)
        {
            Keys currentlyPressedKey = cachePressedCurrently[i];

            if (WasPressed(currentlyPressedKey))
                continue;

            if (OnPressed.TryGetValue(currentlyPressedKey, out Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>? callback))
                callback?.Invoke(this, new(currentlyPressedKey));

            OnAnyButtonPressed?.Invoke(this, new(currentlyPressedKey));
        }

        for (int i = 0; i < cachePressedPreviouslyCount; i++)
        {
            Keys previouslyPressedKey = cachePressedPreviously[i];

            if (IsPressed(previouslyPressedKey))
                continue;

            if (OnReleased.TryGetValue(previouslyPressedKey, out Event<IButtonInputs<Keys>, IButtonInputs<Keys>.ButtonCallbackArguments>? callback))
                callback?.Invoke(this, new(previouslyPressedKey));

            OnAnyButtonReleased?.Invoke(this, new(previouslyPressedKey));
        }

        Array.Copy(cachePressedCurrently, cachePressedPreviously, cachePressedCurrentlyCount);
        cachePressedPreviouslyCount = cachePressedCurrentlyCount;
    }

    public bool IsPressed(Keys key)
    {
        for (int i = 0; i < cachePressedCurrentlyCount; i++)
            if (cachePressedCurrently[i] == key)
                return true;
        return false;
    }

    private bool WasPressed(Keys key)
    {
        for (int i = 0; i < cachePressedPreviouslyCount; i++)
            if (cachePressedPreviously[i] == key)
                return true;
        return false;
    }
}