Import on-demand stock setting in DFC import

app/models/spree/variant.rb

@@ -240,6 +240,8 @@ def set_cost_currency
     end
 
     def create_stock_items
+      return unless stock_items.empty?
+
       StockLocation.find_each do |stock_location|
         stock_location.propagate_variant(self)
       end

engines/dfc_provider/app/services/catalog_item_builder.rb

@@ -0,0 +1,22 @@
+# frozen_string_literal: true
+
+class CatalogItemBuilder < DfcBuilder
+  def self.apply_stock(item, variant)
+    limit = item&.stockLimitation
+
+    return if limit.blank?
+
+    # Negative stock means "on demand".
+    # And we are only interested in that for now.
+    return unless limit.to_i.negative?
+
+    if variant.stock_items.empty?
+      variant.stock_items << Spree::StockItem.new(
+        stock_location: DefaultStockLocation.find_or_create,
+        variant:,
+      )
+    end
+
+    variant.stock_items[0].backorderable = true
+  end
+end

engines/dfc_provider/app/services/supplied_product_builder.rb

@@ -43,6 +43,7 @@ def self.import_variant(supplied_product, supplier)
     end.tap do |variant|
       link = supplied_product.semanticId
       variant.semantic_links.new(semantic_id: link) if link.present?
+      CatalogItemBuilder.apply_stock(supplied_product&.catalogItems&.first, variant)
     end
   end
 

engines/dfc_provider/spec/services/supplied_product_builder_spec.rb

@@ -147,11 +147,23 @@
           value: 2,
         ),
         productType: product_type,
+        catalogItems: [catalog_item],
       )
     end
     let(:product_type) { DfcLoader.connector.PRODUCT_TYPES.VEGETABLE.NON_LOCAL_VEGETABLE }
+    let(:catalog_item) {
+      DataFoodConsortium::Connector::CatalogItem.new(
+        nil,
+        # On-demand is expressed as negative stock.
+        # And some APIs send strings instead of numbers...
+        stockLimitation: "-1",
+      )
+    }
 
     it "creates a new Spree::Product and variant" do
+      # We need this to save stock:
+      DefaultStockLocation.find_or_create
+
       create(:taxon)
 
       expect(imported_variant).to be_a(Spree::Variant)
@@ -169,6 +181,11 @@
       expect(imported_product.name).to eq("Tomato")
       expect(imported_product.description).to eq("Awesome tomato")
       expect(imported_product.variant_unit).to eq("weight")
+
+      # Stock can only be checked when persisted:
+      imported_product.save!
+      expect(imported_variant.on_demand).to eq true
+      expect(imported_variant.on_hand).to eq 0
     end
 
     context "with spree_product_id supplied" do