reactor.clj

(defprotocol ReactorStateRef
  (restore-state! [this]
    "Restore the referenced state to the most recent snapshot if available
     or to the initial state. Update the version to reflect the new state.")
  (reset-state! [this]
    "Reset the referenced state to the initial state. Update the version to 0.")
  (apply-event! [this event version]
    "Apply the supplied event to the referenced state and update the version.
     Nil events are considered to be no-op and only update the version. If the
     version is nil, apply the event but do not update the version.")
  (current-version [this]
    "Return the current version represented by the refernced state."))

(defn make-reactor
  "Create a reactor with the supplied name and handler componenets.
     - connection should be an open RabbitMQ connection.
     - name is arbitrary but should be valid as a queue name and routing
       selector since it is used to direct commands and control messages
       to this router.
     - state-ref should implement ReactorStateRef. it is responsible for managing
       the state affected by this router's event stream
     - event-handler is a function from state-ref and event to a pair of
       sequences [commands events]. Commands is a possibly empty sequence of
       [destination command] pairs. Events is a possibly empty sequence of
       events to apply to the state of this handler.
       event-handler MUST not have any side effects.
     - command-handler is a function from state-ref and command to a pair as
       returned by event-handler. command-handler may have external side effects
       as needed to complete the requested command. If a command needs to do
       long running processing it should spawn a worker task and return the
       result as a followup command.

   After calling the event and command handlers the reactor will apply any
   returned events to the state of this reactor and publish them to the remainder
   of the system. After event processing has completed commands returned are
   routed to their requested destinations."
  [connection name state-ref event-handler command-handler])