sneak/Shared/FSM.cs

using System;
using System.Collections.Generic;

namespace SemiColinGames {
  public interface IState<T> {
    public void Enter();
    public string? Update(T obj, float modelTime, World world);
  }

  public class FSM<T> {
    float timeInState = 0f;
    Dictionary<string, IState<T>> states;
    IState<T> state;

    public FSM(Dictionary<string, IState<T>> states, string initial) {
      this.states = states;
      StateName = initial;
      Transition(StateName);
    }

    public string StateName { get; private set; }

    public void Update(T obj, float modelTime, World world) {
      timeInState += modelTime;
      string? newState = state.Update(obj, modelTime, world);
      if (newState != null) {
        Transition(newState);
      }
    }

    void Transition(string state) {
      Debug.WriteLine("{0} -> {1} @ {2}", StateName, state, timeInState);
      timeInState = 0f;
      StateName = state;
      IState<T> newState = states[state];
      this.state = newState;
      this.state.Enter();
    }
  }
}