Syntriax.Engine/Engine.Core/Behaviour.cs

namespace Engine.Core;

[System.Diagnostics.DebuggerDisplay("{GetType().Name, nq}, Priority: {Priority}, Initialized: {Initialized}")]
public abstract class Behaviour : BaseEntity, IBehaviour
{
    public Event<IBehaviour, IBehaviour.PriorityChangedArguments> OnPriorityChanged { get; } = new();
    public Event<IActive, IActive.ActiveChangedArguments> OnActiveChanged { get; } = new();
    public Event<IHasBehaviourController> OnBehaviourControllerAssigned { get; } = new();

    private readonly Event<IHasUniverseObject>.EventHandler delegateOnUniverseObjectAssigned = null!;
    private readonly Event<IActive, IActive.ActiveChangedArguments>.EventHandler delegateOnUniverseObjectActiveChanged = null!;
    private readonly Event<IStateEnable, IStateEnable.EnabledChangedArguments>.EventHandler delegateOnStateEnabledChanged = null!;

    public IUniverse Universe => BehaviourController.UniverseObject.Universe;
    public IUniverseObject UniverseObject => BehaviourController.UniverseObject;

    private IBehaviourController _behaviourController = null!;
    public IBehaviourController BehaviourController => _behaviourController;

    private int _priority = 0;
    public int Priority
    {
        get => _priority;
        set
        {
            if (value == _priority)
                return;

            int previousPriority = _priority;
            _priority = value;
            OnPriorityChanged?.Invoke(this, new(previousPriority));
        }
    }

    private bool _isActive = false;
    public bool IsActive => _isActive;

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

        _behaviourController = behaviourController;
        OnAssign(behaviourController);
        behaviourController.OnUniverseObjectAssigned.AddListener(delegateOnUniverseObjectAssigned);
        behaviourController.StateEnable.OnEnabledChanged.AddListener(delegateOnStateEnabledChanged);
        if (behaviourController.UniverseObject is not null)
            OnUniverseObjectAssigned(behaviourController);
        OnBehaviourControllerAssigned?.Invoke(this);
        return true;
    }

    private void OnUniverseObjectAssigned(IHasUniverseObject sender)
    {
        sender.UniverseObject.OnActiveChanged.AddListener(delegateOnUniverseObjectActiveChanged);
        UpdateActive();
    }

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

        stateEnable.OnEnabledChanged.AddListener(delegateOnStateEnabledChanged);
    }

    protected override void UnassignInternal()
    {
        BehaviourController.UniverseObject.OnActiveChanged.RemoveListener(delegateOnUniverseObjectActiveChanged);
        StateEnable.OnEnabledChanged.RemoveListener(delegateOnStateEnabledChanged);
        BehaviourController.OnUniverseObjectAssigned.RemoveListener(delegateOnUniverseObjectAssigned);
        BehaviourController.StateEnable.OnEnabledChanged.RemoveListener(delegateOnStateEnabledChanged);
        base.UnassignInternal();
        _behaviourController = null!;
    }

    protected override void InitializeInternal()
    {
        Debug.Assert.AssertBehaviourControllerAssigned(this);
        Debug.Assert.AssertStateEnableAssigned(this);

        UpdateActive();
    }

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

    private void UpdateActive()
    {
        bool previousActive = IsActive;
        _isActive = StateEnable.Enabled && _behaviourController.StateEnable.Enabled && _behaviourController.UniverseObject.IsActive;

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

    protected Behaviour()
    {
        delegateOnUniverseObjectAssigned = OnUniverseObjectAssigned;
        delegateOnUniverseObjectActiveChanged = OnUniverseObjectActiveChanged;
        delegateOnStateEnabledChanged = OnStateEnabledChanged;
    }
}