Reorganized infrastructure code, particularly event buses, so that li…

…bzeromq is not required unless EventBus::Zero is used

Gemfile

@@ -4,9 +4,10 @@ gem 'rails', '3.0.0'
 
 gem 'uuidtools'
 gem 'ohm'
-gem 'carrot'
-gem 'ffi-rzmq'
-gem 'amqp', :require => 'mq'
+
+gem 'carrot',   :require => false
+gem 'ffi-rzmq', :require => false
+gem 'amqp',     :require => false
 
 group :development, :test do
   gem 'rspec-rails'

README.md

@@ -16,10 +16,6 @@ For persistence the app uses [Redis](http://code.google.com/p/redis/). So a Redi
 
     $ brew install redis
     $ redis-server
-
-You also need libzeromq:
-
-    $ brew install zeromq
 
 With all that set, the test suite should pass by just running:
 
@@ -59,9 +55,11 @@ This is the equivalent to the missing `app/models` and you'll find the entities
 
 Reports are subscribed to events from the domain model and update themselves according to those events. That way they are always in sync but totally uncoupled from the domain model. The reporting repository is denormalized and persisted with Redis.
 
-**app/infrastructure**
+**lib/infrastructure**
+
+Infrastructure libraries. Most of the magic is here. Including implementations of the Event Bus using different technologies (ZeroMQ, AMQP, Redis…)
 
-Typically the contents of this directory would be inside `lib` (or a plugin or gem) but, for development purposes, it turned out more convenient to put them in directory added to the `load_path`
+Configuration and initialization can be found at `config/initializers/infrastructure.rb` (if you want to try alternative Event Buses you should look here)
 
 **spec/acceptance**
 

config/application.rb

@@ -17,7 +17,7 @@ class Application < Rails::Application
     # -- all .rb files in that directory are automatically loaded.
 
     # Custom directories with classes and modules you want to be autoloadable.
-    # config.autoload_paths += %W(#{config.root}/extras)
+    config.autoload_paths += %W(#{config.root}/lib/infrastructure)
 
     # Only load the plugins named here, in the order given (default is alphabetical).
     # :all can be used as a placeholder for all plugins not explicitly named.

config/initializers/infrastructure.rb

@@ -1,5 +1,5 @@
 Rails.application.class.configure do
-  config.event_bus = 'RedisEventBus'
+  config.event_bus = 'EventBus::Redis'
   config.event_subscribers = %w{ClientReport ClientDetailsReport AccountDetailsReport MoneyTransferSaga}
   config.to_prepare { EventBus.init }
 end

lib/infrastructure/event_bus.rb

@@ -0,0 +1,11 @@
+module EventBus  
+  class << self
+    attr_accessor :current
+    delegate :publish, :subscribe, :wait_for_events, :start, :purge, :stop, :to => :current
+
+    def init
+      EventBus.current = Rails.configuration.event_bus.constantize.new
+      Rails.configuration.event_subscribers.each(&:constantize)
+    end
+  end
+end

lib/infrastructure/event_bus/amqp.rb

@@ -0,0 +1,41 @@
+require 'carrot'
+require 'mq'
+
+class EventBus::AMQP
+  def publish(event)
+    Carrot.queue('events').publish(event.id)
+  end
+
+  def subscriptions(event_name)
+    @subscriptions ||= Hash.new
+    @subscriptions[event_name.to_s] ||= Set.new
+  end
+
+  def subscribe(event_name, &handler)
+    subscriptions(event_name.to_s) << handler
+  end
+
+  def wait_for_events
+    sleep(0.15) # next_tick 
+  end
+
+  def purge
+    Carrot.queue("events").purge
+  end
+
+  def start
+    AMQP.start do
+      MQ.new.queue("events").subscribe do |event_id|
+        event = Event[event_id]
+        subscriptions(event.name).each do |subscription|
+          subscription.call(event)
+        end
+      end
+    end
+  end
+
+  def stop
+    AMQP.stop { EM.stop }
+    wait_for_events
+  end
+end

lib/infrastructure/event_bus/in_process.rb

@@ -0,0 +1,21 @@
+class EventBus::InProcess
+  def publish(event)
+    subscriptions(event.name).each do |subscription|
+      subscription.call(event)
+    end
+  end
+
+  def subscriptions(event_name)
+    @subscriptions ||= Hash.new
+    @subscriptions[event_name] ||= Set.new
+  end
+
+  def subscribe(event_name, &handler)
+    subscriptions(event_name) << handler
+  end
+
+  def wait_for_events; end
+  def purge; end
+  def start; end
+  def stop; end
+end

lib/infrastructure/event_bus/redis.rb

@@ -0,0 +1,35 @@
+class EventBus::Redis
+  def publish(event)
+    Redis.new.publish "events", event.id
+  end
+
+  def subscriptions(event_name)
+    @subscriptions ||= Hash.new
+    @subscriptions[event_name.to_s] ||= Set.new
+  end
+
+  def subscribe(event_name, &handler)
+    subscriptions(event_name.to_s) << handler
+  end
+
+  def wait_for_events
+    sleep(0.05) # next_tick 
+  end
+
+  def purge
+    Redis.new.del "events"
+  end
+
+  def start
+    Redis.new.subscribe("events") do |on|
+      on.message do |channel, event_id|
+        event = Event[event_id]
+        subscriptions(event.name).each do |subscription|
+          subscription.call(event)
+        end
+      end
+    end
+  end
+
+  def stop; end
+end