Reliable presenter code with monadic

monadic.rb

class MonadicHotelBookingPresenter
  def initialize(booking)
    @booking = Maybe(booking)
  end

  def hotel_name
    hotel_details['name'].fetch.to_s
  end

  def hotel_category
    hotel_details['category'].fetch(0)
  end

  def consumer_price
    prices.detect { |p| p['type'] == 'CONSUMER' }.or({ 'currency' => 'YYY', 'value' => 0.0 }).fetch
  end

  private
  def hotel
    services.map {|e| e.detect { |svc| svc['product'] == 'HOTEL' } }
  end

  def hotel_details
    hotel['details']
  end

  def prices
    @booking['prices']
  end  

  def services
    @booking['services']
  end
end

original.rb

class HotelBookingPresenter
  def initialize(booking)
    @booking = booking
  end

  def hotel_name
    hotel_details.fetch('name', 'Nothing')
  end

  def hotel_category
    hotel_details.fetch('category', 0)
  end

  def consumer_price
    prices.detect { |p| p['type'] == 'CONSUMER' } || { 'currency' => 'YYY', 'value' => 0.0 }
  end

  private 
  def hotel
    services.detect { |svc| svc['product'] == 'HOTEL' } || {}
  end

  def hotel_details
    hotel.fetch('details', {})
  end

  def prices
    @booking.fetch('prices', [])
  end

  def services
    @booking.fetch('services', [])
  end
end

presenter_spec.rb

require 'monadic'
require './monadic'
require './original'

shared_examples 'presenter' do
  describe 'for an empty booking' do
    subject { presenter.new({}) }

    its(:hotel_name)     { should == 'Nothing' }
    its(:hotel_category) { should == 0 }
    its(:consumer_price) { should == {'currency' => 'YYY', 'value' => 0.0 } }
  end

  describe 'for a complete booking' do
    let(:booking) do
      {
        "prices" => [
          { 
            "type" => "CONSUMER",
            "currency" => "EUR",
            "value" => 119.78
          }
        ],

        "services" => [
          {
            "product" => "HOTEL",
            "details" => {
              "name" => "Hotel Wroclaw",
              "category" => 3
            }
          }
        ]
      }
    end

    subject { presenter.new(booking) }

    its(:hotel_name) { should == 'Hotel Wroclaw' }
    its(:hotel_category) { should == 3 }
  end
end

describe MonadicHotelBookingPresenter do
  it_behaves_like 'presenter' do 
    let(:presenter) { MonadicHotelBookingPresenter }
  end  
end


describe HotelBookingPresenter do
  it_behaves_like 'presenter' do
    let(:presenter) { HotelBookingPresenter }
  end
end