sneak/Shared/FSM.cs

using System.Collections.Generic;

namespace SemiColinGames {
  public interface IState<T> {
    // Called automatically whenever this state is transitioned to. Should reset whichever
    // state-specific variables need resetting.
    public void Enter();

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

  public class FSM<T> {
    readonly Dictionary<string, IState<T>> states;

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

    public string StateName { get; private set; }

    public IState<T> State { get; private set; }

    public void Update(float modelTime, World world, T input) {
      string newState = State.Update(modelTime, world, input);
      if (newState != null) {
        Transition(newState);
      }
    }

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