Syntriax.Engine/Engine.Core/UniverseObject.cs

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

namespace Syntriax.Engine.Core;

[System.Diagnostics.DebuggerDisplay("Name: {Name}, Initialized: {Initialized}")]
public class UniverseObject : BaseEntity, IUniverseObject
{
    public Event<IUniverseObject, IUniverseObject.EnteredUniverseArguments> OnEnteredUniverse { get; } = new();
    public Event<IUniverseObject, IUniverseObject.ExitedUniverseArguments> OnExitedUniverse { get; } = new();
    public Event<IUniverseObject, IUniverseObject.ParentChangedArguments> OnParentChanged { get; } = new();
    public Event<IUniverseObject, IUniverseObject.ChildrenAddedArguments> OnChildrenAdded { get; } = new();
    public Event<IUniverseObject, IUniverseObject.ChildrenRemovedArguments> OnChildrenRemoved { get; } = new();

    public Event<IActive, IActive.ActiveChangedArguments> OnActiveChanged { get; } = new();
    public Event<INameable, INameable.NameChangedArguments> OnNameChanged { get; } = new();
    public Event<IHasBehaviourController> OnBehaviourControllerAssigned { get; } = new();

    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?.Invoke(this, new(previousName));
        }
    }

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

        _universe = universe;
        UpdateActive();
        OnEnteringUniverse(universe);
        OnEnteredUniverse?.Invoke(this, new(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?.Invoke(this, new(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.RemoveListener(OnParentActiveChanged);
        }

        Parent = parent;

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

            parent.AddChild(this);
            parent.OnActiveChanged.AddListener(OnParentActiveChanged);
        }

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

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

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

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

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

    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.AddListener(OnStateEnabledChanged);
    }

    private void OnParentActiveChanged(IActive sender, IActive.ActiveChangedArguments arguments) => UpdateActive();
    private void OnStateEnabledChanged(IStateEnable sender, IStateEnable.EnabledChangedArguments arguments) => UpdateActive();

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

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

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

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

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

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