Syntriax.Engine/Engine.Systems/StateMachine/StateMachine.cs

using Syntriax.Engine.Core;

namespace Syntriax.Engine.StateMachine;

public class StateMachine : Behaviour
{
    public event StateChangedEventHandler? OnStateChanged = null;

    private IState _state = new State();
    public IState State
    {
        get => _state;
        set
        {
            if (_state == value)
                return;

            IState previousState = _state;
            previousState.OnStateTransitionReady -= OnStateTransitionReady;

            _state = value;
            previousState.TransitionFrom(value);
            value.TransitionTo(_state);
            OnStateChanged?.Invoke(this, previousState, value);

            value.OnStateTransitionReady += OnStateTransitionReady;
        }
    }

    private void OnStateTransitionReady(IState sender, IState toState)
    {
        State = toState;
        while (State.GetNextState() is IState nextState)
            State = nextState;
    }

    protected override void OnUpdate()
    {
        if (State is null)
            return;

        while (State.GetNextState() is IState nextState)
            State = nextState;

        State.Update();
    }

    public delegate void StateChangedEventHandler(StateMachine sender, IState previousState, IState newState);
}