Changing quantity and deleting line_items of completed orders works with inventory where present

app/models/spree/line_item_decorator.rb

@@ -94,8 +94,41 @@ Spree::LineItem.class_eval do
     (final_weight_volume || 0) / quantity
   end
 
+  # MONKEYPATCH of Spree method
+  # Enables scoping of variant to hub/shop, stock drawn down from inventory
+  def update_inventory
+    return true unless order.completed?
+
+    scoper.scope(variant) # this line added
+
+    if new_record?
+      Spree::InventoryUnit.increase(order, variant, quantity)
+    elsif old_quantity = self.changed_attributes['quantity']
+      if old_quantity < quantity
+        Spree::InventoryUnit.increase(order, variant, (quantity - old_quantity))
+      elsif old_quantity > quantity
+        Spree::InventoryUnit.decrease(order, variant, (old_quantity - quantity))
+      end
+    end
+  end
+
+  # MONKEYPATCH of Spree method
+  # Enables scoping of variant to hub/shop, stock replaced to inventory
+  def remove_inventory
+    return true unless order.completed?
+
+    scoper.scope(variant) # this line added
+
+    Spree::InventoryUnit.decrease(order, variant, quantity)
+  end
+
   private
 
+  def scoper
+	  return @scoper unless @scoper.nil?
+	  @scoper = OpenFoodNetwork::ScopeVariantToHub.new(order.distributor)
+	end
+
   def calculate_final_weight_volume
     if final_weight_volume.present? && quantity_was > 0
       self.final_weight_volume = final_weight_volume * quantity / quantity_was

spec/models/spree/line_item_spec.rb

@@ -77,6 +77,56 @@ module Spree
       end
     end
 
+    describe "tracking stock when quantity is changed" do
+      context "when the order is already complete" do
+        let(:shop) { create(:distributor_enterprise)}
+        let(:order) { create(:completed_order_with_totals, distributor: shop) }
+        let!(:line_item) { order.reload.line_items.first }
+        let!(:variant) { line_item.variant }
+
+        context "when a variant override applies" do
+          let!(:vo) { create(:variant_override, hub: shop, variant: variant, count_on_hand: 3 ) }
+
+          it "draws stock from the variant override" do
+            expect(vo.reload.count_on_hand).to eq 3
+            expect{line_item.increment!(:quantity)}.to_not change{Spree::Variant.find(variant.id).on_hand}
+            expect(vo.reload.count_on_hand).to eq 2
+          end
+        end
+
+        context "when a variant override does not apply" do
+          it "draws stock from the variant" do
+            expect{line_item.increment!(:quantity)}.to change{Spree::Variant.find(variant.id).on_hand}.by(-1)
+          end
+        end
+      end
+    end
+
+    describe "tracking stock when a line item is destroyed" do
+      context "when the order is already complete" do
+        let(:shop) { create(:distributor_enterprise)}
+        let(:order) { create(:completed_order_with_totals, distributor: shop) }
+        let!(:line_item) { order.reload.line_items.first }
+        let!(:variant) { line_item.variant }
+
+        context "when a variant override applies" do
+          let!(:vo) { create(:variant_override, hub: shop, variant: variant, count_on_hand: 3 ) }
+
+          it "restores stock to the variant override" do
+            expect(vo.reload.count_on_hand).to eq 3
+            expect{line_item.destroy}.to_not change{Spree::Variant.find(variant.id).on_hand}
+            expect(vo.reload.count_on_hand).to eq 4
+          end
+        end
+
+        context "when a variant override does not apply" do
+          it "restores stock to the variant" do
+            expect{line_item.destroy}.to change{Spree::Variant.find(variant.id).on_hand}.by(1)
+          end
+        end
+      end
+    end
+
     describe "calculating price with adjustments" do
       it "does not return fractional cents" do
         li = LineItem.new