sneak/Shared/FSM.cs

using System.Collections.Generic;

namespace SemiColinGames {
  public interface IState<T> {
    public void Enter();

    // Returns the name of the new state, or null if we should stay in the same state.
    public string Update(T obj, float modelTime, World world);
  }

  public class FSM<T> {
    readonly 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) {
      string newState = state.Update(obj, modelTime, world);
      if (newState != null) {
        Transition(newState);
      }
    }

    void Transition(string state) {
      StateName = state;
      IState<T> newState = states[state];
      this.state = newState;
      this.state.Enter();
    }
  }
}