Fall back to given product w/o wholesale variant

The class is moving to providing all data with several methods instead
of a data class containing the information. That should be more
flexible. Still some work to do.

app/services/fdc_offer_broker.rb

@@ -11,16 +11,31 @@ class FdcOfferBroker
   end
 
   def best_offer(product_id)
-    consumption_flow = catalog_item("#{product_id}/AsPlannedConsumptionFlow")
+    Solution.new(
+      wholesale_product(product_id),
+      contained_quantity(product_id),
+      offer_of(wholesale_product(product_id))
+    )
+  end
+
+  def wholesale_product(product_id)
     production_flow = catalog_item("#{product_id}/AsPlannedProductionFlow")
 
-    contained_quantity = consumption_flow.quantity.value.to_i
-    wholesale_product_id = production_flow.product
-    wholesale_product = catalog_item(wholesale_product_id)
+    if production_flow
+      wholesale_product_id = production_flow.product
+      catalog_item(wholesale_product_id)
+    else
+      # We didn't find a wholesale variant, falling back to the given product.
+      catalog_item(product_id)
+    end
+  end
 
-    offer = offer_of(wholesale_product)
+  def contained_quantity(product_id)
+    consumption_flow = catalog_item("#{product_id}/AsPlannedConsumptionFlow")
 
-    Solution.new(wholesale_product, contained_quantity, offer)
+    # If we don't find a transformation, we return the original product,
+    # which contains exactly one of itself (identity).
+    consumption_flow&.quantity&.value&.to_i || 1
   end
 
   def wholesale_to_retail(wholesale_product_id)

spec/services/fdc_offer_broker_spec.rb

@@ -24,5 +24,15 @@ RSpec.describe FdcOfferBroker do
       expect(solution.factor).to eq 12
       expect(solution.offer.offeredItem).to eq solution.product
     end
+
+    it "falls back to the original product offer", vcr: true do
+      solution = subject.best_offer(product.semanticId)
+      fallback_solution = subject.best_offer(solution.product.semanticId)
+
+      # These values depend on the test data but are a good sanity check:
+      expect(fallback_solution.product.name).to eq "Baked British Beans - Case, 12 x 400g (can)"
+      expect(fallback_solution.factor).to eq 1
+      expect(fallback_solution.offer.offeredItem).to eq fallback_solution.product
+    end
   end
 end