Syntriax.Engine/Engine.Core/BehaviourCollector.cs

using System;
using System.Collections.Generic;

namespace Syntriax.Engine.Core;

public class BehaviourCollector<T> : IBehaviourCollector<T> where T : class
{
    public Event<IBehaviourCollector<T>, IBehaviourCollector<T>.BehaviourCollectedArguments> OnCollected { get; } = new();
    public Event<IBehaviourCollector<T>, IBehaviourCollector<T>.BehaviourRemovedArguments> OnRemoved { get; } = new();
    public Event<IHasUniverse> OnUniverseAssigned { get; } = new();
    public Event<IAssignable>? OnUnassigned { get; } = new();

    private readonly Event<IBehaviourController, IBehaviourController.BehaviourAddedArguments>.EventHandler cachedOnBehaviourAdded = null!;
    private readonly Event<IBehaviourController, IBehaviourController.BehaviourRemovedArguments>.EventHandler cachedOnBehaviourRemoved = null!;
    private readonly Event<IUniverse, IUniverse.UniverseObjectRegisteredArguments>.EventHandler cachedOnUniverseObjectRegistered = null!;
    private readonly Event<IUniverse, IUniverse.UniverseObjectUnRegisteredArguments>.EventHandler cachedOnUniverseObjectUnregistered = null!;

    protected readonly List<T> behaviours = new(32);

    public IUniverse Universe { get; private set; } = null!;

    private void OnUniverseObjectRegistered(IUniverse manager, IUniverse.UniverseObjectRegisteredArguments arguments)
    {
        IUniverseObject universeObject = arguments.UniverseObjectRegistered;

        universeObject.BehaviourController.OnBehaviourAdded.AddListener(cachedOnBehaviourAdded);
        universeObject.BehaviourController.OnBehaviourRemoved.AddListener(cachedOnBehaviourRemoved);

        for (int i = 0; i < universeObject.BehaviourController.Count; i++)
            OnBehaviourAdded(universeObject.BehaviourController, new(universeObject.BehaviourController[i]));
    }

    private void OnUniverseObjectUnregistered(IUniverse manager, IUniverse.UniverseObjectUnRegisteredArguments arguments)
    {
        IUniverseObject universeObject = arguments.UniverseObjectUnregistered;

        universeObject.BehaviourController.OnBehaviourAdded.RemoveListener(cachedOnBehaviourAdded);
        universeObject.BehaviourController.OnBehaviourRemoved.RemoveListener(cachedOnBehaviourRemoved);

        for (int i = 0; i < universeObject.BehaviourController.Count; i++)
            OnBehaviourRemoved(universeObject.BehaviourController, new(universeObject.BehaviourController[i]));
    }

    protected virtual void OnBehaviourAdd(IBehaviour behaviour) { }
    private void OnBehaviourAdded(IBehaviourController controller, IBehaviourController.BehaviourAddedArguments arguments)
    {
        if (arguments.BehaviourAdded is not T tBehaviour)
            return;

        behaviours.Add(tBehaviour);
        OnBehaviourAdd(arguments.BehaviourAdded);
        OnCollected?.Invoke(this, new(tBehaviour));
    }

    protected virtual void OnBehaviourRemove(IBehaviour behaviour) { }
    private void OnBehaviourRemoved(IBehaviourController controller, IBehaviourController.BehaviourRemovedArguments arguments)
    {
        if (arguments.BehaviourRemoved is not T tBehaviour)
            return;

        if (!behaviours.Remove(tBehaviour))
            return;

        OnBehaviourRemove(arguments.BehaviourRemoved);
        OnRemoved?.Invoke(this, new(tBehaviour));
    }

    protected virtual void OnAssign(IUniverse universe) { }
    public bool Assign(IUniverse universe)
    {
        if (Universe is not null)
            return false;

        foreach (IUniverseObject universeObject in universe.UniverseObjects)
            OnUniverseObjectRegistered(universe, new(universeObject));

        universe.OnUniverseObjectRegistered.AddListener(cachedOnUniverseObjectRegistered);
        universe.OnUniverseObjectUnRegistered.AddListener(cachedOnUniverseObjectUnregistered);

        Universe = universe;
        OnAssign(universe);
        OnUniverseAssigned?.Invoke(this);

        return true;
    }

    public bool Unassign()
    {
        if (Universe is null)
            return false;

        foreach (IUniverseObject universeObject in Universe.UniverseObjects)
            OnUniverseObjectUnregistered(Universe, new(universeObject));

        Universe.OnUniverseObjectRegistered.RemoveListener(cachedOnUniverseObjectRegistered);
        Universe.OnUniverseObjectUnRegistered.RemoveListener(cachedOnUniverseObjectUnregistered);

        Universe = null!;
        OnUnassigned?.Invoke(this);
        return true;
    }

    public int Count => behaviours.Count;
    public T this[Index index] => behaviours[index];

    public BehaviourCollector()
    {
        cachedOnBehaviourAdded = OnBehaviourAdded;
        cachedOnBehaviourRemoved = OnBehaviourRemoved;
        cachedOnUniverseObjectRegistered = OnUniverseObjectRegistered;
        cachedOnUniverseObjectUnregistered = OnUniverseObjectUnregistered;
    }
}