pub/sub with ActiveSupport::Notifications

emitter.rb

module Eventable
  module Emitter
    extend ActiveSupport::Concern

    included do
      def emit(event_name, payload = {})
        full_event = "#{self.class.to_s.underscore}:#{event_name}"
        Eventable.emit full_event, self, payload
      end
    end
  end
end

eventable.rb

module Eventable
  extend self

  def emit(event_name, instance = nil, payload = {})
    ActiveSupport::Notifications.publish(event_name, instance, payload)
  end
end

subscriber.rb

module Eventable
  module Subscriber
    extend ActiveSupport::Concern

    included do
      @queue = :eventable

      attr_accessor :event, :instance, :payload

      def self.perform(event, instance, payload, callback)
        self.new(event, instance, payload.with_indifferent_access).send(callback)
      end

      def self.on(klass, event_name, callback, options = {})
        full_event = /^#{klass.to_s.underscore}:#{event_name}$/

        ActiveSupport::Notifications.subscribe(full_event) do |event, instance, payload|
          payload[:_class] = instance.class.name
          payload[:_id] = instance.id if instance.is_a?(ActiveRecord::Base)

          if options[:async]
            Resque.enqueue(self, event, nil, payload, callback)
          else
            self.new(event, instance, payload).send(callback)
          end
        end
      end

      def initialize(event, instance, payload)
        self.event = event
        self.instance = instance
        self.payload = payload
      end
    end
  end
end