Sage: DDD

booker.ex

defmodule BookingApp.Booker do
  alias BookingApp.{Billing, Users, Hotels, Cars, Flights, Repo}

  def create_booking(attrs) do
    Sage.new()
    |> Billing.authorize_card(attrs)
    |> Hotels.maybe_book_hotel(attrs)
    |> Cars.maybe_book_car(attrs)
    |> Flights.maybe_book_flight(attrs)
    |> Users.sign_up()
    |> Billing.charge_card()
    |> Sage.transaction(Repo, attrs)
  end
end

hotels.ex

defmodule BookingApp.Hotels do
  def maybe_book_hotel(%Sage{} = sage, %{"hotel" => hotel}) do
    Sage.run_async(sage, :book_hotel, &book/2, &cancel_booking/4)  
  end
  
  def maybe_book_hotel(%Sage{} = sage, _attrs) do
    sage
  end
  
  # ...
end