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

using Syntriax.Engine.Core.Abstract;

namespace Syntriax.Engine.Core;

public class BehaviourCollector<T> : IBehaviourCollector<T> where T : class
{
    public event IAssignable.UnassignEventHandler? OnUnassigned = null;
    public event IHasUniverse.UniverseAssignedEventHandler? OnUniverseAssigned = null;

    public event IBehaviourCollector<T>.CollectedEventHandler? OnCollected = null;
    public event IBehaviourCollector<T>.RemovedEventHandler? OnRemoved = null;

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

    public IReadOnlyList<T> Behaviours => behaviours;
    public IUniverse Universe { get; private set; } = null!;

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

    public BehaviourCollector() { }
    public BehaviourCollector(IUniverse universe) => Assign(universe);

    private void OnUniverseObjectRegistered(IUniverse manager, IUniverseObject universeObject)
    {
        universeObject.BehaviourController.OnBehaviourAdded += OnBehaviourAdded;
        universeObject.BehaviourController.OnBehaviourRemoved += OnBehaviourRemoved;

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

    private void OnUniverseObjectUnregistered(IUniverse manager, IUniverseObject universeObject)
    {
        universeObject.BehaviourController.OnBehaviourAdded -= OnBehaviourAdded;
        universeObject.BehaviourController.OnBehaviourRemoved -= OnBehaviourRemoved;

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

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

        behaviours.Add(tBehaviour);
        OnBehaviourAdd(behaviour);
        OnCollected?.InvokeSafe(this, tBehaviour);
    }

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

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

        OnBehaviourRemove(behaviour);
        OnRemoved?.InvokeSafe(this, 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, universeObject);

        universe.OnUniverseObjectRegistered += OnUniverseObjectRegistered;
        universe.OnUniverseObjectUnRegistered += OnUniverseObjectUnregistered;

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

        return true;
    }

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

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

        Universe.OnUniverseObjectRegistered -= OnUniverseObjectRegistered;
        Universe.OnUniverseObjectUnRegistered -= OnUniverseObjectUnregistered;

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

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