MAke more code just use the single shipment of the order even if the …

…DB still supports multiple shipments per order

app/models/spree/order.rb

@@ -231,7 +231,7 @@ def item_count
     end
 
     def backordered?
-      shipments.any?(&:backordered?)
+      shipment&.backordered?
     end
 
     # Returns the relevant zone (if any) to be used for taxation purposes.
@@ -443,10 +443,8 @@ def finalize!
 
       # update payment and shipment(s) states, and save
       updater.update_payment_state
-      shipments.each do |shipment|
-        shipment.update!(self)
-        shipment.finalize!
-      end
+      shipment&.update!(self)
+      shipment&.finalize!
 
       updater.update_shipment_state
       updater.before_save_hook
@@ -561,20 +559,52 @@ def state_changed(name)
       )
     end
 
+    # The Spree 2 db model we use supports multiple shipments per order,
+    #   in OFN we have only one shipment per order.
+    # A shipment is associated to a shipping_method through a selected shipping_rate.
+    def shipment
+      return if shipments.blank?
+
+      shipments.first
+    end
+
+    # The shipping method of the shipment in the order
+    def shipping_method
+      return if shipment.blank?
+
+      shipment.shipping_method
+    end
+
+    # Finds the shipment's shipping_rate for the given shipping_method_id and selects that shipping_rate.
+    # If the selection is successful, it persists it in the database by saving the shipment.
+    # If it fails, it does not clear the current shipping_method selection.
+    #
+    # @return [ShippingMethod] the selected shipping method, or nil if the given shipping_method_id is
+    #   empty or if it cannot find the given shipping_method_id in the order
+    def select_shipping_method(shipping_method_id)
+      return if shipping_method_id.blank? || shipment.blank?
+
+      shipment = shipments.first
+
+      shipping_rate = shipment.shipping_rates.find_by(shipping_method_id: shipping_method_id)
+      return unless shipping_rate
+
+      shipment.selected_shipping_rate_id = shipping_rate.id
+      shipment.shipping_method
+    end
+
     def shipped?
       %w(partial shipped).include?(shipment_state)
     end
 
     # Does this order have shipments that can be shipped?
     def ready_to_ship?
-      shipments.any?(&:can_ship?)
+      shipment&.can_ship?
     end
 
     # Ship all pending orders
     def ship
-      shipments.each do |s|
-        s.ship if s.can_ship?
-      end
+      shipment.ship if ready_to_ship?
     end
 
     def line_item_variants
@@ -610,14 +640,14 @@ def create_proposed_shipments
     # to delivery again so that proper updated shipments are created.
     # e.g. customer goes back from payment step and changes order items
     def ensure_updated_shipments
-      return unless shipments.any?
+      return if shipment.blank?
 
       shipments.destroy_all
       update_column(:state, "address")
     end
 
     def refresh_shipment_rates
-      shipments.map(&:refresh_rates)
+      shipment.refresh_rates
     end
 
     # Check that line_items in the current order are available from a newly selected distribution
@@ -636,12 +666,10 @@ def disallow_guest_order
 
     # After changing line items of a completed order
     def update_shipping_fees!
-      shipments.each do |shipment|
-        next if shipment.shipped?
+      return if shipment.blank? || shipment.shipped?
 
-        update_adjustment! shipment.adjustment if shipment.adjustment
-        save_or_rescue_shipment(shipment)
-      end
+      update_adjustment!(shipment.adjustment) if shipment.adjustment
+      save_or_rescue_shipment(shipment)
     end
 
     def save_or_rescue_shipment(shipment)
@@ -800,7 +828,7 @@ def has_available_shipment
     end
 
     def ensure_available_shipping_rates
-      return unless shipments.empty? || shipments.any? { |shipment| shipment.shipping_rates.blank? }
+      return unless shipment.blank? || shipment.shipping_rates.blank?
 
       errors.add(:base, Spree.t(:items_cannot_be_shipped)) && (return false)
     end
@@ -811,14 +839,14 @@ def has_available_payment
     end
 
     def after_cancel
-      shipments.each(&:cancel!)
+      shipment&.cancel!
 
       OrderMailer.cancel_email(id).deliver
       self.payment_state = 'credit_owed' unless shipped?
     end
 
     def after_resume
-      shipments.each(&:resume!)
+      shipment&.resume!
     end
 
     def use_billing?