Syntriax.Engine/Engine.Core/BehaviourCollector.cs

using System;
using System.Collections;
using System.Collections.Generic;

using Syntriax.Engine.Core.Abstract;

namespace Syntriax.Engine.Core;

public class BehaviourCollector<T> : IAssignableGameManager, IEnumerable<T>
{
    public event IAssignable.OnUnassignedDelegate? OnUnassigned = null;
    public event IAssignableGameManager.OnGameManagerAssignedDelegate? OnGameManagerAssigned = null;

    public event OnCollectedDelegate? OnCollected = null;
    public event OnRemovedDelegate? OnRemoved = null;

    private readonly List<T> _behaviours = new(32);

    public IReadOnlyList<T> Behaviours => _behaviours;
    public IGameManager GameManager { get; private set; } = null!;

    public T this[Index index] => _behaviours[index];

    public BehaviourCollector() { }
    public BehaviourCollector(IGameManager gameManager) => Assign(gameManager);

    private void OnGameObjectRegistered(IGameManager manager, IGameObject gameObject)
    {
        gameObject.BehaviourController.OnBehaviourAdded += OnBehaviourAdded;
        gameObject.BehaviourController.OnBehaviourRemoved += OnBehaviourRemoved;

        foreach (IBehaviour item in gameObject.BehaviourController)
            OnBehaviourAdded(gameObject.BehaviourController, item);
    }

    private void OnGameObjectUnregistered(IGameManager manager, IGameObject gameObject)
    {
        gameObject.BehaviourController.OnBehaviourAdded -= OnBehaviourAdded;
        gameObject.BehaviourController.OnBehaviourRemoved -= OnBehaviourRemoved;

        foreach (IBehaviour item in gameObject.BehaviourController)
            OnBehaviourRemoved(gameObject.BehaviourController, item);
    }

    private void OnBehaviourAdded(IBehaviourController controller, IBehaviour behaviour)
    {
        if (behaviour is not T tBehaviour)
            return;

        _behaviours.Add(tBehaviour);
        OnCollected?.Invoke(this, tBehaviour);
    }

    private void OnBehaviourRemoved(IBehaviourController controller, IBehaviour behaviour)
    {
        if (behaviour is not T tBehaviour)
            return;

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

        OnRemoved?.Invoke(this, tBehaviour);
    }

    public bool Assign(IGameManager gameManager)
    {
        if (GameManager is not null)
            return false;

        foreach (IGameObject gameObject in gameManager.GameObjects)
            OnGameObjectRegistered(gameManager, gameObject);

        gameManager.OnGameObjectRegistered += OnGameObjectRegistered;
        gameManager.OnGameObjectUnRegistered += OnGameObjectUnregistered;

        GameManager = gameManager;
        OnGameManagerAssigned?.Invoke(this);

        return true;
    }

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

        foreach (IGameObject gameObject in GameManager.GameObjects)
            OnGameObjectUnregistered(GameManager, gameObject);

        GameManager.OnGameObjectRegistered -= OnGameObjectRegistered;
        GameManager.OnGameObjectUnRegistered -= OnGameObjectUnregistered;

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

    public IEnumerator<T> GetEnumerator() => _behaviours.GetEnumerator();
    IEnumerator IEnumerable.GetEnumerator() => _behaviours.GetEnumerator();


    public delegate void OnCollectedDelegate(BehaviourCollector<T> sender, T behaviourCollected);
    public delegate void OnRemovedDelegate(BehaviourCollector<T> sender, T behaviourRemoved);
}