Sage: Handle charge failure when we are booking a trip

booking_sage_handle_charge_failure.ex

def book_trip(attrs) do
  with {:ok, exchange_rates} <- BillingAPI.fetch_currency_exchange_rates(attrs),
       {:ok, card_authorization} <- BillingAPI.authorize_card(exchange_rates, attrs),
       {:ok, hotel_booking} <- HotelsBookingAPI.book_hotel(attrs),
       :ok <- Mailer.send_email_confirmation(card_authorization, hotel_booking, attrs),
       {:charge, {:ok, charge}, _} <- {:charge, BillingAPI.charge_card(card_authorization), [hotel_booking]} do
    {:ok, %{charge: charge, bookings: [hotel_booking]}}
  else
    {:charge, {:error, reason], [hotel_booking]} ->
      :ok = send_excuse_email(authorization)
      :ok = cancel_booking(hotel_booking)
      {:error, reason}

    other ->
      other
  end
end