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

using Syntriax.Engine.Core.Abstract;

namespace Syntriax.Engine.Core;

[System.Diagnostics.DebuggerDisplay("Name: {Name}, Initialized: {Initialized}")]
public class HierarchyObject : BaseEntity, IHierarchyObject
{
    public event IHierarchyObject.EnteredHierarchyEventHandler? OnEnteredHierarchy = null;
    public event IHierarchyObject.ExitedHierarchyEventHandler? OnExitedHierarchy = null;
    public event IHierarchyObject.ParentChangedEventHandler? OnParentChanged = null;
    public event IHierarchyObject.ChildrenAddedEventHandler? OnChildrenAdded = null;
    public event IHierarchyObject.ChildrenRemovedEventHandler? OnChildrenRemoved = null;
    public event IHasBehaviourController.BehaviourControllerAssignedEventHandler? OnBehaviourControllerAssigned = null;
    public event INameable.NameChangedEventHandler? OnNameChanged = null;
    public event IActive.ActiveChangedEventHandler? OnActiveChanged = null;

    private string _name = nameof(HierarchyObject);
    private IGameManager _gameManager = null!;
    private IBehaviourController _behaviourController = null!;
    private bool _isActive = false;
    private readonly List<IHierarchyObject> _children = [];

    public IHierarchyObject? Parent { get; private set; } = null;
    public IReadOnlyList<IHierarchyObject> Children => _children;
    public IBehaviourController BehaviourController => _behaviourController;
    public IGameManager GameManager => _gameManager;
    public bool IsInHierarchy => _gameManager is not null;
    public bool IsActive => _isActive;

    public string Name
    {
        get => _name;
        set
        {
            if (value == _name) return;

            string previousName = _name;
            _name = value;
            OnNameChanged?.Invoke(this, previousName);
        }
    }

    protected virtual void OnEnteringHierarchy(IGameManager gameManager) { }
    bool IHierarchyObject.EnterHierarchy(IGameManager gameManager)
    {
        if (IsInHierarchy)
            return false;

        _gameManager = gameManager;
        UpdateActive();
        OnEnteringHierarchy(gameManager);
        OnEnteredHierarchy?.Invoke(this, gameManager);
        return true;
    }

    protected virtual void OnExitingHierarchy(IGameManager gameManager) { }
    bool IHierarchyObject.ExitHierarchy()
    {
        if (!IsInHierarchy || _gameManager is not IGameManager gameManager)
            return false;

        _gameManager = null!;
        OnExitingHierarchy(gameManager);
        OnExitedHierarchy?.Invoke(this, gameManager);
        return true;
    }

    public void SetParent(IHierarchyObject? parent)
    {
        if (parent == this || Parent == parent)
            return;

        IHierarchyObject? previousParent = Parent;
        if (previousParent is not null)
        {
            previousParent.RemoveChild(this);
            previousParent.OnParentChanged -= NotifyChildrenOnParentChange;
            previousParent.OnActiveChanged -= OnParentActiveChanged;
        }

        Parent = parent;

        if (parent is not null)
        {
            parent.AddChild(this);
            parent.OnParentChanged += NotifyChildrenOnParentChange;
            parent.OnActiveChanged += OnParentActiveChanged;
        }

        UpdateActive();
        OnParentChanged?.Invoke(this, previousParent, parent);
    }

    public void AddChild(IHierarchyObject parent)
    {
        if (_children.Contains(parent))
            return;

        _children.Add(parent);
        parent.SetParent(this);
        OnChildrenAdded?.Invoke(this, parent);
    }

    public void RemoveChild(IHierarchyObject parent)
    {
        if (!_children.Remove(parent))
            return;

        parent.SetParent(null);
        OnChildrenRemoved?.Invoke(this, parent);
    }

    private void NotifyChildrenOnParentChange(IHierarchyObject sender, IHierarchyObject? previousParent, IHierarchyObject? newParent)
    {
        // TODO No idea how logical this is to propagate this to the children the way I'm doing right now.
        // I was originally gonna just call `child.OnParentChanged?.Invoke(child, child.parentTransform);` but seems an unnecessary call too?
        foreach (IHierarchyObject child in Children) // TODO CHECK ERRORS
            child.SetParent(this);
    }

    protected virtual void OnAssign(IBehaviourController behaviourController) { }
    public bool Assign(IBehaviourController behaviourController)
    {
        if (IsInitialized)
            return false;

        _behaviourController = behaviourController;
        OnAssign(behaviourController);
        OnBehaviourControllerAssigned?.Invoke(this);
        return true;
    }

    protected override void OnAssign(IStateEnable stateEnable)
    {
        base.OnAssign(stateEnable);

        stateEnable.OnEnabledChanged += OnStateEnabledChanged;
    }

    private void OnParentActiveChanged(IActive sender, bool previousState) => UpdateActive();
    private void OnStateEnabledChanged(IStateEnable sender, bool previousState) => UpdateActive();

    private void UpdateActive()
    {
        bool previousActive = IsActive;
        _isActive = StateEnable.Enabled && (Parent?.IsActive ?? true);

        if (previousActive != IsActive)
            OnActiveChanged?.Invoke(this, previousActive);
    }

    protected override void UnassignInternal()
    {
        base.UnassignInternal();
        StateEnable.OnEnabledChanged -= OnStateEnabledChanged;
    }

    protected override void InitializeInternal()
    {
        base.InitializeInternal();
        _behaviourController ??= Factory.BehaviourControllerFactory.Instantiate(this);
    }

    public IEnumerator<IHierarchyObject> GetEnumerator() => _children.GetEnumerator();
    IEnumerator IEnumerable.GetEnumerator() => _children.GetEnumerator();
}