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 UniverseObject : BaseEntity, IUniverseObject
{
    public event IUniverseObject.EnteredUniverseEventHandler? OnEnteredUniverse = null;
    public event IUniverseObject.ExitedUniverseEventHandler? OnExitedUniverse = null;
    public event IUniverseObject.ParentChangedEventHandler? OnParentChanged = null;
    public event IUniverseObject.ChildrenAddedEventHandler? OnChildrenAdded = null;
    public event IUniverseObject.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(UniverseObject);
    private IUniverse _universe = null!;
    private IBehaviourController _behaviourController = null!;
    private bool _isActive = false;
    private readonly List<IUniverseObject> _children = [];

    public IUniverseObject? Parent { get; private set; } = null;
    public IReadOnlyList<IUniverseObject> Children => _children;
    public IBehaviourController BehaviourController => _behaviourController;
    public IUniverse Universe => _universe;
    public bool IsInUniverse => _universe is not null;
    public bool IsActive => _isActive;

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

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

    protected virtual void OnEnteringUniverse(IUniverse universe) { }
    bool IUniverseObject.EnterUniverse(IUniverse universe)
    {
        if (IsInUniverse)
            return false;

        _universe = universe;
        UpdateActive();
        OnEnteringUniverse(universe);
        OnEnteredUniverse?.InvokeSafe(this, universe);
        return true;
    }

    protected virtual void OnExitingUniverse(IUniverse universe) { }
    bool IUniverseObject.ExitUniverse()
    {
        if (!IsInUniverse || _universe is not IUniverse universe)
            return false;

        OnExitingUniverse(universe);
        _universe = null!;
        OnExitedUniverse?.InvokeSafe(this, universe);
        return true;
    }

    public void SetParent(IUniverseObject? parent)
    {
        if (parent == this)
            throw new Exceptions.AssignFailedException($"{Name} can not parent itself");

        if (Parent == parent)
            return;

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

        Parent = parent;

        if (parent is not null)
        {
            if (parent.IsInUniverse && !IsInUniverse)
                parent.Universe.Register(this);

            parent.AddChild(this);
            parent.OnActiveChanged += OnParentActiveChanged;
        }

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

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

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

    public void RemoveChild(IUniverseObject child)
    {
        if (!_children.Remove(child))
            return;

        child.SetParent(null);
        OnChildrenRemoved?.InvokeSafe(this, child);
    }

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

        _behaviourController = behaviourController;
        OnAssign(behaviourController);
        OnBehaviourControllerAssigned?.InvokeSafe(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?.InvokeSafe(this, previousActive);
    }

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

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

    public UniverseObject()
    {
        _name = GetType().Name;
    }

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