Syntriax.Engine/Engine.Core/Systems/UpdateManager.cs

using System.Collections.Generic;

namespace Engine.Core;

public class UpdateManager : Behaviour, IEnterUniverse, IExitUniverse
{
    // We use Ascending order because we are using reverse for loop to call them
    private static Comparer<int> SortByAscendingPriority() => Comparer<int>.Create((x, y) => x.CompareTo(y));
    private static System.Func<IBehaviour, int> GetPriority() => (b) => b.Priority;

    private readonly ActiveBehaviourCollectorOrdered<int, IFirstFrameUpdate> firstFrameUpdates = new(GetPriority(), SortByAscendingPriority());
    private readonly ActiveBehaviourCollector<ILastFrameUpdate> lastFrameUpdates = new();
    private readonly ActiveBehaviourCollectorOrdered<int, IPreUpdate> preUpdateEntities = new(GetPriority(), SortByAscendingPriority());
    private readonly ActiveBehaviourCollectorOrdered<int, IUpdate> updateEntities = new(GetPriority(), SortByAscendingPriority());
    private readonly ActiveBehaviourCollectorOrdered<int, IPostUpdate> postUpdateEntities = new(GetPriority(), SortByAscendingPriority());

    private readonly List<IFirstFrameUpdate> toCallFirstFrameUpdates = new(32);

    public void EnterUniverse(IUniverse universe)
    {
        firstFrameUpdates.Assign(universe);
        lastFrameUpdates.Assign(universe);
        preUpdateEntities.Assign(universe);
        updateEntities.Assign(universe);
        postUpdateEntities.Assign(universe);

        universe.OnPreUpdate.AddListener(OnFirstUpdate, int.MaxValue);
        universe.OnPreUpdate.AddListener(OnPreUpdate);
        universe.OnUpdate.AddListener(OnUpdate);
        universe.OnPostUpdate.AddListener(OnPostUpdate);
    }

    public void ExitUniverse(IUniverse universe)
    {
        firstFrameUpdates.Unassign();
        lastFrameUpdates.Unassign();
        preUpdateEntities.Unassign();
        updateEntities.Unassign();
        postUpdateEntities.Unassign();

        universe.OnPreUpdate.RemoveListener(OnFirstUpdate);
        universe.OnPreUpdate.RemoveListener(OnPreUpdate);
        universe.OnUpdate.RemoveListener(OnUpdate);
        universe.OnPostUpdate.RemoveListener(OnPostUpdate);
    }

    private void OnFirstUpdate(IUniverse sender, IUniverse.UpdateArguments args)
    {
        for (int i = toCallFirstFrameUpdates.Count - 1; i >= 0; i--)
        {
            toCallFirstFrameUpdates[i].FirstActiveFrame();
            toCallFirstFrameUpdates.RemoveAt(i);
        }
    }

    private void OnPreUpdate(IUniverse sender, IUniverse.UpdateArguments args)
    {
        for (int i = preUpdateEntities.Count - 1; i >= 0; i--)
            preUpdateEntities[i].PreUpdate();
    }

    private void OnUpdate(IUniverse sender, IUniverse.UpdateArguments args)
    {
        for (int i = updateEntities.Count - 1; i >= 0; i--)
            updateEntities[i].Update();
    }

    private void OnPostUpdate(IUniverse sender, IUniverse.UpdateArguments args)
    {
        for (int i = postUpdateEntities.Count - 1; i >= 0; i--)
            postUpdateEntities[i].PostUpdate();
    }

    private void OnFirstFrameCollected(IBehaviourCollector<IFirstFrameUpdate> sender, IBehaviourCollector<IFirstFrameUpdate>.BehaviourCollectedArguments args)
    {
        toCallFirstFrameUpdates.Add(args.BehaviourCollected);
    }

    private void OnLastFrameRemoved(IBehaviourCollector<ILastFrameUpdate> sender, IBehaviourCollector<ILastFrameUpdate>.BehaviourRemovedArguments args)
    {
        args.BehaviourRemoved.LastActiveFrame();
    }

    private void CallLastFramesBeforeExit(object? sender, System.EventArgs e)
    {
        for (int i = lastFrameUpdates.Count - 1; i >= 0; i--)
            lastFrameUpdates[i].LastActiveFrame();
    }

    public UpdateManager()
    {
        firstFrameUpdates.OnCollected.AddListener(OnFirstFrameCollected);
        lastFrameUpdates.OnRemoved.AddListener(OnLastFrameRemoved);
        System.AppDomain.CurrentDomain.ProcessExit += CallLastFramesBeforeExit;
    }
}