transition.go

package fsm

// transition is to go from a state to an other
// It will check the current state to ensure that the transition is
// allowed execute the handler and then change the current state to
// a new state
type transition struct {
	// from represent the state needed for allowing the transition
	from string
	// to represente the state of the fsm after the transition
	to string
	// handler to call if the transition is allowed
	handler func()
}

// AddTransition will add to the fsm a new transition.
func (fsm *Fsm) AddTransition(name string, from string, to string, handler func()) error {
	if isValideState(fsm.states, from) == false {
		return ErrUnknowState
	}

	if isValideState(fsm.states, to) == false {
		return ErrUnknowState
	}

	fsm.transitions[name] = transition{from, to, handler}
	return nil
}

// HandleTransition will check if the transition is possible.
// Check if the current state is the state require, call the handler and
// change the current state to the new state.
func (fsm *Fsm) HandleTransition(name string) (string, error) {
	transition, exist := fsm.transitions[name]
	if exist == false {
		return fsm.current, ErrUnknowTransition
	}

	fsm.mutex.Lock()
	defer fsm.mutex.Unlock()

	if transition.from == fsm.current {
		transition.handler()
		fsm.current = transition.to
		return fsm.current, nil
	}
	return fsm.current, ErrBadState
}