Syntriax.Engine/Engine.Core/UniverseObject.cs

using System.Collections.Generic;

namespace 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 readonly FastList<IUniverseObject> _children = [];

    public IBehaviourController BehaviourController { get; private set; } = null!;
    public IUniverse Universe { get; private set; } = null!;
    public bool IsActive { get; private set; } = false;

    public IReadOnlyList<IUniverseObject> Children => _children;
    public bool IsInUniverse => Universe is not null;

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

            string previousName = field;
            field = value;
            OnNameChanged?.Invoke(this, new(previousName));
        }
    } = nameof(UniverseObject);

    public IUniverseObject? Parent
    {
        get;
        set
        {
            if (value == this)
                throw new Exceptions.AssignFailedException($"{Name} can not parent itself");

            if (field == value)
                return;

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

            field = value;

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

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

            UpdateActive();
            OnParentChanged?.Invoke(this, new(previousParent, value));
        }
    } = null;

    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 AddChild(IUniverseObject child)
    {
        if (_children.Contains(child))
            return;

        _children.Add(child);
        child.Parent = this;
        OnChildrenAdded?.Invoke(this, new(child));
    }

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

        child.Parent = 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);
        UpdateActive();
    }

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