Generic Finite State Machine

FiniteStateMachine.cs

public class FiniteStateMachine<T_Data, T_Id>
{
    protected T_Data data;
    protected FSMState<T_Data, T_Id> globalState;
    protected FSMState<T_Data, T_Id> activeState;
    protected Dictionary<T_Id, FSMState<T_Data, T_Id>> states;

    public FiniteStateMachine(T_Data data)
    {
        this.data = data;
        states = new Dictionary<T_Id, FSMState<T_Data, T_Id>>();
    }

    public virtual void SetGlobalState(FSMState<T_Data, T_Id> state)
    {
        globalState = state;
    }

    public virtual void AddState(FSMState<T_Data, T_Id> state)
    {
        if (states.ContainsKey(state.id))
            throw new Exception("State machine already contains state with id {0}", state.id); 
        
        states.Add(state.id, state);
        if (activeState == null) TransitionToState(state.id);
    }

    public virtual void RemoveState(FSMState<T_Data, T_Id> state)
    {
        if (states.ContainsKey(state.id)) states.Remove(state.id);
    }

    public virtual void Update()
    {
        if (globalState != null) globalState.OnUpdate(data);
        if (activeState != null) activeState.OnUpdate(data);
    }

    public virtual void TransitionToState(T_Id id)
    {
        if (!states.ContainsKey(id)) return;
        var targetState = states[id];

        if (activeState != null)
        {
            activeState.TransitionEvent -= TransitionToState;
            activeState.OnExit(data);
        }

        activeState = targetState;
        activeState.TransitionEvent += TransitionToState;
        activeState.OnEnter(data);
    }
}

FSMState.cs

public abstract class FSMState<T_Data, T_Id>
{
    public abstract T_Id id { get; protected set; }

    public virtual void OnEnter(T_Data data) { }
    public virtual void OnUpdate(T_Data data) { }
    public virtual void OnExit(T_Data data) { }

    public delegate void TransitionEventHandler(T_Id id);
    public event TransitionEventHandler TransitionEvent;

    protected virtual void FireTransition(T_Id targetId)
    {
        if (TransitionEvent != null) TransitionEvent(targetId);
    }
}