Fix errors found in testing

app/events/event_types/inventory.rb

@@ -30,6 +30,14 @@ def set_item_quantity(item_id:, quantity:, location:)
     # @param to_location [Integer]
     # @param validate [Boolean]
     def move_item(item_id:, quantity:, from_location: nil, to_location: nil, validate: true)
+      if quantity.negative?
+        move_item(item_id: item_id,
+          quantity: -quantity,
+          from_location: to_location,
+          to_location: from_location,
+          validate: validate)
+        return
+      end
       if from_location
         if storage_locations[from_location].nil? && validate
           raise "Storage location #{from_location} not found!"

app/models/view/inventory.rb

@@ -82,7 +82,7 @@ def quantity_for(storage_location: nil, item_id: nil)
 
       if storage_location
         if item_id
-          @inventory.storage_locations[storage_location.to_i].items[item_id.to_i]&.quantity || 0
+          @inventory.storage_locations[storage_location.to_i]&.items&.dig(item_id.to_i)&.quantity || 0
         else
           @inventory.storage_locations[storage_location.to_i]&.items&.values&.map(&:quantity)&.sum || 0
         end
@@ -100,6 +100,7 @@ def storage_locations_for_item(item_id)
     # @param storage_location [Integer]
     # @return [Float]
     def total_value_in_dollars(storage_location: nil)
+      return 0.0 if @inventory.storage_locations[storage_location].nil?
       total = @inventory.storage_locations[storage_location].items.values
         .map { |i| i.value_in_cents ? i.quantity * i.value_in_cents : 0 }.sum
       total.to_f / 100

spec/events/inventory_aggregate_spec.rb

@@ -709,6 +709,19 @@
     end
 
     context "subsequent event is incorrect" do
+      it "should handle negative quantities" do
+        next unless Event.read_events?(organization) # only relevant if flag is on
+
+        donation = FactoryBot.create(:donation, organization: organization, storage_location: storage_location1)
+        donation.line_items << build(:line_item, quantity: 100, item: item1)
+        DonationEvent.publish(donation)
+        distribution = FactoryBot.create(:distribution, organization: organization, storage_location: storage_location1)
+        distribution.line_items << build(:line_item, quantity: 90, item: item1)
+        DistributionEvent.publish(distribution)
+        donation.line_items.first.quantity = 20
+        expect { DonationEvent.publish(donation) }.to raise_error(InventoryError)
+      end
+
       it "should add the event to the message" do
         next unless Event.read_events?(organization) # only relevant if flag is on