cirnogodot/Scripts/Components/FSM/StateMachineBase.cs

#nullable enable
using System.Collections.Generic;
using Godot;

namespace Cirno.Scripts.Components.FSM;

public abstract partial class StateMachineBase<TKey, TType> : Node, IStateMachine<TKey, TType>
    where TKey : notnull
    where TType : Node
{
    [Signal]
    public delegate void StateChangedEventHandler(Variant from, Variant to);

    public Dictionary<TKey, IState<TKey, TType>> States { get; set; } = new();
    public TKey CurrentStateIndex { get; set; }
    public TKey PreviousStateIndex { get; private set; }
    public IState<TKey, TType> CurrentState => States[CurrentStateIndex];
    public abstract TKey InitialState { get; protected set; }

    private TType _mainObject = default!;
    public TType MainObject => _mainObject;

    // Internal flag to indicate if a state has been set previously
    private bool _hasState;

    public override void _Ready()
    {
        _mainObject = this.GetParent<TType>();
        var children = GetChildren();

        foreach (var child in children)
        {
            if (child is IState<TKey, TType> state)
            {
                States.Add(state.StateId, state);
                state.Init(this);
            }
        }
        SetState(InitialState);
    }

    public TKey GetState()
    {
        return CurrentState.StateId;
    }

    public void SetState(TKey stateId)
    {
        if (_hasState)
        {
            PreviousStateIndex = CurrentStateIndex;
            CurrentState.ExitState();
        }

        var from = _hasState ? CurrentStateIndex.ToString() : string.Empty;
        CurrentStateIndex = stateId;
        var to = CurrentStateIndex.ToString();
        CurrentState.EnterState();
        _hasState = true;
        EmitSignal(nameof(StateChanged), from, to);
    }

    /// <summary>
    /// Returns the first descendant under the main object (root node that owns this state machine)
    /// that matches the requested type T, or null if none found. This lets states fetch
    /// modules attached to the actor without per-state editor wiring.
    /// </summary>
    public T? GetModule<T>() where T : Node
    {
        if (MainObject is null) return default;
        return FindInChildren<T>(MainObject);
    }

    private static T? FindInChildren<T>(Node parent) where T : Node
    {
        foreach (var obj in parent.GetChildren())
        {
            if (obj is T t) return t;
            if (obj is Node node)
            {
                var found = FindInChildren<T>(node);
                if (found is not null) return found;
            }
        }
        return default;
    }

    public override void _Process(double delta)
    {
        if (!_hasState) return;
        CurrentState.ProcessState(delta);
    }

    public override void _PhysicsProcess(double delta)
    {
        if (!_hasState) return;
        CurrentState.PhysicsProcessState(delta);
    }
}