Fix import of zero-weight products

We don't allow variants to have zero weight or volume. But a DFC import
in production showed that some catalogs list products with zero weight.
Despite the products having a weight, it's simpler to treat these as
items.

engines/dfc_provider/app/services/quantitative_value_builder.rb

@@ -29,11 +29,18 @@ class QuantitativeValueBuilder < DfcBuilder
 
   def self.apply(quantity, product)
     measure, unit_name, unit_scale = map_unit(quantity.unit)
+    value = quantity.value.to_f * unit_scale
+
+    if measure.in?(%w(weight volume)) && value <= 0
+      measure = "items"
+      unit_name = "items"
+      value = 1
+    end
 
     product.variant_unit = measure
     product.variant_unit_name = unit_name if measure == "items"
     product.variant_unit_scale = unit_scale
-    product.unit_value = quantity.value.to_f * unit_scale
+    product.unit_value = value
   end
 
   # Map DFC units to OFN fields:

engines/dfc_provider/spec/fixtures/files/product.GET.json

@@ -0,0 +1,38 @@
+{
+  "@context": "https://www.datafoodconsortium.org",
+  "@graph": [
+    {
+      "@id": "_:b433",
+      "@type": "dfc-b:QuantitativeValue",
+      "dfc-b:hasUnit": "dfc-m:Kilogram",
+      "dfc-b:value": "0"
+    },
+    {
+      "@id": "_:b434",
+      "@type": "dfc-b:Price",
+      "dfc-b:VATrate": "1",
+      "dfc-b:hasUnit": "dfc-m:Euro",
+      "dfc-b:value": "12.06"
+    },
+    {
+      "@id": "https://example-producer.jcloud-ver-jpe.ik-server.com/api/dfc/Enterprises/5c21b9-95/SuppliedProducts/49055026544964",
+      "@type": "dfc-b:SuppliedProduct",
+      "dfc-b:hasQuantity": "_:b433",
+      "dfc-b:name": "Fillet Steak - 201g x 1 Steak",
+      "dfc-b:referencedBy": "https://example-producer.jcloud-ver-jpe.ik-server.com/api/dfc/Enterprises/5c21b9-95/SuppliedProducts/49055026544964/CatalogItem"
+    },
+    {
+      "@id": "https://example-producer.jcloud-ver-jpe.ik-server.com/api/dfc/Enterprises/5c21b9-95/SuppliedProducts/49055026544964/CatalogItem",
+      "@type": "dfc-b:CatalogItem",
+      "dfc-b:offeredThrough": "https://example-producer.jcloud-ver-jpe.ik-server.com/api/dfc/Enterprises/5c21b9-95/SuppliedProducts/49055026544964/Offer",
+      "dfc-b:stockLimitation": "11"
+    },
+    {
+      "@id": "https://example-producer.jcloud-ver-jpe.ik-server.com/api/dfc/Enterprises/5c21b9-95/SuppliedProducts/49055026544964/Offer",
+      "@type": "dfc-b:Offer",
+      "dfc-b:hasPrice": {
+        "@id": "_:b434"
+      }
+    }
+  ]
+}

engines/dfc_provider/spec/services/supplied_product_builder_spec.rb

@@ -84,6 +84,33 @@ RSpec.describe SuppliedProductBuilder do
     end
   end
 
+  describe ".store_product" do
+    let(:subject) { builder.store_product(product, supplier) }
+    let(:product) {
+      DfcIo.import(product_json).find do |subject|
+        subject.is_a? DataFoodConsortium::Connector::SuppliedProduct
+      end
+    }
+    let(:product_json) { ExampleJson.read("product.GET") }
+
+    before do
+      taxon.save!
+    end
+
+    it "stores a new Spree Product and Variant" do
+      expect { subject }.to change {
+        Spree::Product.count
+      }.by(1)
+
+      expect(subject).to be_a(Spree::Variant)
+      expect(subject).to be_valid
+      expect(subject).to be_persisted
+      expect(subject.name).to eq("Fillet Steak - 201g x 1 Steak")
+      expect(subject.variant_unit).to eq("items")
+      expect(subject.unit_value).to eq(1)
+    end
+  end
+
   describe ".import_product" do
     let(:supplied_product) do
       DfcProvider::SuppliedProduct.new(