Latest thoughts on service implementation

services.rb

# Inspired by this thread:
# https://groups.google.com/forum/?fromgroups=#!msg/rubyparley/Rnm2tC0Ry8g/xoyIfH4Qb_AJ
# 
# "My habit is to pass all the data for the operation in the constructor, and then have a generic `run` method to make it go.
# That way I can separate creation from execution should I want to, just as you can with a block." - Martin Fowler

class CheckoutController
  def purchase
    purchase_order
  end

  private

  def purchase_order
    PurchaseOrder.call(order)
  end

  def order
    @order ||= Order.find_by_number(params[:id])
  end    
end

class PurchaseOrder

  def self.call(order)
    purchase_order       = PurchaseOrder.new
    redeem_store_credits = RedeemStoreCredits.new
    prepare_payout       = PreparePayout.new
    
    purchase_order.addListener(redeem_store_credits)
    purchase_order.addListener(prepare_payout)

    purchase_order.call(order)
  end

  attr_reader :order

  def add_listener(listener)
    @listener ||= []
    @listener << listener
  end

  def call
    @order = order

    # do stuff
    notify_listeners
  end

  private

  def notify_listeners
    @listeners.each { |listener| listener.call(order) }
  end
end

class RedeemStoreCredits

 attr_reader :order, :store_credits

 def initialize(store_credits=nil)
   @store_credits = store_credits
 end

 def call(order)
   # do stuff
 end

 private

 def store_credits
   @store_credits ||= StoreCredit.redeemable_for_user(order.user)
 end
end