public interface IState
{
    void OnEnter();

    void OnExecute();

    void OnExit();
}

public class StateMachine
{
    private IState currentState;
    private IState previousState;

    // call OnUpdate in actor OnUpdate class, which is called by ActorManager which is called by GameManager xD
    // trying to make this whole thing explicit, otherwise running game logic on a different thread will be hard
    // with different thread, I mean a different CPUthread, not Coroutine
    public void OnUpdate()
    {
        if (currentState != null)
        {
            currentState.OnExecute();
        }
    }

    public void ChangeState(IState state)
    {
        if (currentState != null)
        {
            currentState.OnExit();
        }

        previousState = currentState;
        currentState = state;

        currentState.OnEnter();
    }

    public IState GetState()
    {
        return currentState;
    }

    public void RevertToPreviousState()
    {
        if (currentState != null)
        {
            currentState = previousState;
        }
    }
}