slurper_notification_example.rb

# setting up and running a slurp
slurper = Slurpeee::Slurper.new
slurper.on(:progress) { |data| do_something_with(data) }
slurper.on(:some_other_known_event) { |data| do_something_with(data) }
slurp = slurper.slurp(url_to_slurp)

# slurper.rb
module Slurpeee
  class Slurper
    def initialize
      @notifier = Notifier.instance
    end
  
    def slurp(url)
      # misc code here
      @notifier.broadcast(:progress, "The slurp is starting")
      @notifier.broadcast(:progress, complex: "data structures", foo: "bar")
      # other code to kick off slurp
    end
  end
end

# notifier.rb
require "singleton"

module Slurpeee
  class Notifier
    include Singleton

    def initialize
      @events = {}
    end

    def subscribe(event, &handler)
      @events[event] ||= []
      @events[event] << handler
    end

    def broadcast(event, data)
      @events[event].each do |handler|
        handler.call(data)
      end
    end
  end
end