state_machine_with_guards.rb

module DataMapper
  module Is
    module StateMachine

      # hook may be either a Proc or symbol
      def run_hook_if_present(hook)
        return true unless hook
        if hook.respond_to?(:call)
          hook.call(self)
        else
          self.send(hook)
        end
      end

      module EventDsl
        def transition(options)
          unless state_machine_context?(:event)
            raise InvalidContext, "Valid only in 'event' block"
          end
          event_name   = @is_state_machine[:event][:name]
          event_object = @is_state_machine[:event][:object]

          from  = options[:from]
          to    = options[:to]
          guard = options[:guard]
          event_object.add_transition(from, to, guard)
        end
      end

      module Data
        class Event
          def add_transition(from, to, guard)
            @transitions << { :from => from, :to => to, :guard => guard }
          end
        end

        class Machine
          def fire_event(event_name, resource)
            unless event = find_event(event_name)
              raise InvalidEvent, "Could not find event (#{event_name.inspect})"
            end
            transition = event.transitions.find do |t|
               t[:from].to_s == @current_state_name.to_s
            end
            unless transition
              raise InvalidEvent, "Event (#{event_name.inspect}) does not" +
              "exist for current state (#{@current_state_name.inspect})"
            end
            
            # == Run transition :guard hook (if present) ==
            return unless resource.run_hook_if_present(transition[:guard])

            # == Run :exit hook (if present) ==
            resource.run_hook_if_present current_state.options[:exit]

            # == Change the current_state ==
            @current_state_name = transition[:to]

            # == Run :enter hook (if present) ==
            resource.run_hook_if_present current_state.options[:enter]
          end
        end
      end # module Data
    end # module StateMachine
  end
end