Extract checkout params adaptation logic into a service class

app/controllers/checkout_controller.rb

@@ -40,13 +40,12 @@ class CheckoutController < Spree::StoreController
   end
 
   def update
-    shipping_method_id = object_params.delete(:shipping_method_id)
-
-    return update_failed unless @order.update_attributes(object_params)
+    params_adapter = CheckoutFormDataAdapter.new(params)
+    return update_failed unless @order.update_attributes(params_adapter.order_params)
 
     fire_event('spree.checkout.update')
 
-    checkout_workflow(shipping_method_id)
+    checkout_workflow(params_adapter.shipping_method_id)
   rescue Spree::Core::GatewayError => e
     rescue_from_spree_gateway_error(e)
   rescue StandardError => e
@@ -150,56 +149,6 @@ class CheckoutController < Spree::StoreController
     end
   end
 
-  def object_params
-    move_payment_source_to_payment_attributes!
-
-    set_amount_in_payments_attributes
-
-    construct_saved_card_attributes if params[:order][:existing_card_id]
-
-    params[:order]
-  end
-
-  # For payment step, filter order parameters to produce the expected
-  #   nested attributes for a single payment and its source,
-  #   discarding attributes for payment methods other than the one selected
-  def move_payment_source_to_payment_attributes!
-    return unless params[:payment_source].present? &&
-                  payment_source_params = delete_payment_source_params!
-
-    params[:order][:payments_attributes].first[:source_attributes] = payment_source_params
-  end
-
-  def delete_payment_source_params!
-    params.delete(:payment_source)[
-      params[:order][:payments_attributes].first[:payment_method_id].underscore
-    ]
-  end
-
-  def set_amount_in_payments_attributes
-    if params[:order][:payments_attributes]
-      params[:order][:payments_attributes].first[:amount] = @order.total
-    end
-  end
-
-  def construct_saved_card_attributes
-    existing_card_id = params[:order].delete(:existing_card_id)
-    return if existing_card_id.blank?
-
-    move_to_payment_attributes(existing_card_id)
-
-    params[:order][:payments_attributes].first.delete :source_attributes
-  end
-
-  def move_to_payment_attributes(existing_card_id)
-    credit_card = Spree::CreditCard.find(existing_card_id)
-    if credit_card.try(:user_id).blank? || credit_card.user_id != spree_current_user.try(:id)
-      raise Spree::Core::GatewayError, I18n.t(:invalid_credit_card)
-    end
-
-    params[:order][:payments_attributes].first[:source] = credit_card
-  end
-
   def checkout_workflow(shipping_method_id)
     while @order.state != "complete"
       if @order.state == "payment"

app/services/checkout_form_data_adapter.rb

@@ -0,0 +1,64 @@
+# frozen_string_literal: true
+
+# Adapts checkout form data (params) so that the order can be directly saved to the database
+class CheckoutFormDataAdapter
+  attr_reader :shipping_method_id
+
+  def initialize(params)
+    @params = params
+
+    move_payment_source_to_payment_attributes!
+
+    set_amount_in_payments_attributes
+
+    construct_saved_card_attributes if @params[:order][:existing_card_id]
+
+    @shipping_method_id = @params[:order].delete(:shipping_method_id)
+  end
+
+  def order_params
+    @params[:order]
+  end
+
+  private
+
+  # For payment step, filter order parameters to produce the expected
+  #   nested attributes for a single payment and its source,
+  #   discarding attributes for payment methods other than the one selected
+  def move_payment_source_to_payment_attributes!
+    return unless @params[:payment_source].present? &&
+                  payment_source_params = delete_payment_source_params!
+
+    @params[:order][:payments_attributes].first[:source_attributes] = payment_source_params
+  end
+
+  def delete_payment_source_params!
+    params.delete(:payment_source)[
+      @params[:order][:payments_attributes].first[:payment_method_id].underscore
+    ]
+  end
+
+  def set_amount_in_payments_attributes
+    return unless @params[:order][:payments_attributes]
+
+    @params[:order][:payments_attributes].first[:amount] = @order.total
+  end
+
+  def construct_saved_card_attributes
+    existing_card_id = @params[:order].delete(:existing_card_id)
+    return if existing_card_id.blank?
+
+    move_to_payment_attributes(existing_card_id)
+
+    @params[:order][:payments_attributes].first.delete :source_attributes
+  end
+
+  def move_to_payment_attributes(existing_card_id)
+    credit_card = Spree::CreditCard.find(existing_card_id)
+    if credit_card.try(:user_id).blank? || credit_card.user_id != spree_current_user.try(:id)
+      raise Spree::Core::GatewayError, I18n.t(:invalid_credit_card)
+    end
+
+    @params[:order][:payments_attributes].first[:source] = credit_card
+  end
+end