Refactor shipping_rate calculation upon selecting different rates

app/decorators/models/solidus_easypost/spree/shipment_decorator.rb

@@ -29,8 +29,41 @@ def easypost_postage_label_url
         easypost_shipment&.postage_label&.label_url
       end
 
+      def select_shipping_method(shipping_method)
+        # Selects the specified shipping method for the shipment.
+        # This method fetches available shipping rates using the estimator and
+        # marks the selected shipping rate while deselecting all others.
+        estimator = ::Spree::Config.stock.estimator_class.new
+        rates = estimator.shipping_rates(to_package, false)
+
+        # Find the rate that matches the provided shipping method
+        rate = rates.detect { |detected| detected.shipping_method_id == shipping_method.id }
+
+        # Mark the selected shipping method as true and deselect others
+        deselect_other_shipping_rates(rate.id)
+        rate.update(selected: true)
+      end
+
+      def update_amounts
+        # NOTE: Reload the shipment to reflect any updates to the selected shipping rate.
+        # Updates the shipment amounts by reloading the selected shipping rate.
+        # This ensures that the shipment cost is recalculated based on the latest
+        # selected shipping rate.
+        reload
+
+        # Call the parent method from solidus_core to ensure proper cost recalculations.
+        super
+      end
+
       private
 
+      def deselect_other_shipping_rates(selected_rate_id)
+        # Deselects all shipping rates except the one selected by the user.
+        # This ensures that only one shipping rate remains marked as selected.
+        # Update all other shipping rates, setting `selected` to false.
+        shipping_rates.where.not(id: selected_rate_id).update_all(selected: false)
+      end
+
       def buy_easypost_rate
         # Skip label purchase if tracking information already exists.
         return if tracking

lib/solidus_easypost/estimator.rb

@@ -3,10 +3,22 @@
 module SolidusEasypost
   class Estimator
     def shipping_rates(package, _frontend_only = true)
-      easypost_rates = ShipmentBuilder.from_package(package).rates.sort_by(&:rate)
-
-      shipping_rates = easypost_rates.map { |rate| build_shipping_rate(rate) }.compact
-      shipping_rates.min_by(&:cost)&.selected = true
+      # NOTE: The easypost_shipments were being created again when retrieving shipping_rates
+      # Hence this method has been updated to check if an EasyPost shipment has already been created for the shipment.
+      # If it exists, it fetches the stored shipping rates instead of creating a new EasyPost shipment.
+      shipment = package.shipment
+
+      if shipment.easypost_shipment
+        shipping_rates = shipment.shipping_rates
+      else
+        easypost_rates = ShipmentBuilder.from_package(package).rates.sort_by(&:rate)
+
+        # Build shipping rate objects from EasyPost rates.
+        shipping_rates = easypost_rates.map { |rate| build_shipping_rate(rate) }.compact
+
+        # Automatically select the shipping rate with the lowest cost.
+        shipping_rates.min_by(&:cost)&.selected = true
+      end
 
       shipping_rates
     end