Finite state machine (FSM) builder. FSMs are commonly needed for protocol implementation. While fjåge provides a FSMBehavior class to help with making FSMs, this class adds some Groovy functionality to make it simpler to describe FSMs in Groovy.

The usage of this class is best described through an example FSM:

 enum State { TICK, TOCK }
 enum Event { RESET }

 FSMBehavior fsm = FSMBuilder.build {

   long count = 0

   state(State.TICK) {
     onEnter {
       println 'TICK'
     }
     after(1.seconds) {             // every time we enter the TICK state,
       setNextState(State.TOCK)     //   switch to TOCK after 1 second
     }
     action {
       println "CLOCK says $count seconds"
       block()
     }
     onEvent(Event.RESET) {         // reset count if RESET trigger received
       count = 0
     }
   }

   state(State.TOCK) {
     onEnter {
       println 'TOCK'
       after(1.second) {           // in this form, the delay is recomputed every
         setNextState(State.TICK)  //   time the TOCK state is entered
       }
     }
     onEvent(Event.RESET) {         // reset count if RESET trigger received
       count = 0                    //   and also go back to TICK state
       setNextState(State.TICK)
     }
     onExit {                       // increment count every time we leave
       count++                      //   the TICK state
     }
   }

 }