NewFSM create a new FSM object then registers transitions and callbacks to it.

NewState create a State object with current state set to initState.

Entry/Exit event are defined by fsm package.

Entry/Exit event are defined by fsm package.

State is a thread-safe structure that represents the state of a object and it can be used for FSM.

Transition defines a transition that a Event is triggered at From state, and transfer to To state after the Event.