SupaLidlGame/State/StateMachine.cs

using Godot;

namespace SupaLidlGame.State
{
    public abstract partial class StateMachine<T> : Node where T : IState<T>
    {
        public T CurrentState { get; protected set; }

        public abstract T InitialState { get; set; }

        public override void _Ready()
        {
            ChangeState(InitialState);
        }

        public virtual bool ChangeState(T nextState, bool isProxied = false)
        {
            if (nextState is null)
            {
                return false;
            }

            if (CurrentState != null)
            {
                CurrentState.Exit(nextState);
            }

            CurrentState = nextState;

            // if the next state decides it should enter a different state,
            // then we enter that different state instead
            var nextNextState = nextState.Enter(CurrentState);
            if (nextNextState is T t)
            {
                return ChangeState(t, true);
            }

            return true;
        }
    }
}