Handle backorder cancellations

app/jobs/complete_backorder_job.rb

@@ -34,16 +34,23 @@ class CompleteBackorderJob < ApplicationJob
     broker = FdcOfferBroker.new(BackorderJob.load_catalog(user))
 
     order.lines.each do |line|
+      line.quantity = line.quantity.to_i
       wholesale_product_id = line.offer.offeredItem.semanticId
       transformation = broker.wholesale_to_retail(wholesale_product_id)
       linked_variant = variants.linked_to(transformation.retail_product_id)
 
       # Note that a division of integers dismisses the remainder, like `floor`:
       wholesale_items_contained_in_stock = linked_variant.on_hand / transformation.factor
-      line.quantity = line.quantity.to_i - wholesale_items_contained_in_stock
 
-      retail_stock_changes = wholesale_items_contained_in_stock * transformation.factor
+      # But maybe we didn't actually order that much:
+      deductable_quantity = [line.quantity, wholesale_items_contained_in_stock].min
+      line.quantity -= deductable_quantity
+
+      retail_stock_changes = deductable_quantity * transformation.factor
       linked_variant.on_hand -= retail_stock_changes
     end
+
+    # Clean up empty lines:
+    order.lines.reject! { |line| line.quantity.zero? }
   end
 end

app/services/fdc_backorderer.rb

@@ -56,9 +56,7 @@ class FdcBackorderer
   end
 
   def find_order(semantic_id)
-    import(semantic_id).find do |o|
-      o.semanticType == "dfc-b:Order"
-    end
+    find_subject(import(semantic_id), "dfc-b:Order")
   end
 
   def find_or_build_order_line(order, offer)
@@ -88,6 +86,14 @@ class FdcBackorderer
     end
   end
 
+  def find_subject(object_or_graph, type)
+    if object_or_graph.is_a?(Array)
+      object_or_graph.find { |i| i.semanticType == type }
+    else
+      object_or_graph
+    end
+  end
+
   def import(url)
     api = DfcRequest.new(user)
     json = api.call(url)
@@ -110,7 +116,7 @@ class FdcBackorderer
              end
 
     result = api.call(backorder.semanticId, json, method:)
-    DfcIo.import(result).find { |i| i.semanticType == "dfc-b:Order" }
+    find_subject(DfcIo.import(result), "dfc-b:Order")
   end
 
   def complete_order(backorder)

spec/jobs/complete_backorder_job_spec.rb

@@ -32,11 +32,6 @@ RSpec.describe CompleteBackorderJob do
       variant.semantic_links << SemanticLink.new(
         semantic_id: retail_product.semanticId
       )
-
-      # We are assuming 12 cans in a slab.
-      # We got more stock than we need.
-      variant.on_hand = 13
-
       ofn_order.order_cycle = create(
         :simple_order_cycle,
         distributors: [distributor],
@@ -45,6 +40,10 @@ RSpec.describe CompleteBackorderJob do
     end
 
     it "completes an order", vcr: true do
+      # We are assuming 12 cans in a slab.
+      # We got more stock than we need.
+      variant.on_hand = 13
+
       current_order = order
 
       expect {
@@ -60,5 +59,28 @@ RSpec.describe CompleteBackorderJob do
           variant.on_hand
         }.from(13).to(1)
     end
+
+    it "removes line items", vcr: true do
+      # We are assuming 12 cans in a slab.
+      # We backordered 3 slabs, which is 36 cans.
+      # And now we would have more than 4 slabs (4*12 + 1 = 49)
+      # We got more stock than we need.
+      variant.on_hand = 49
+
+      current_order = order
+
+      expect {
+        subject.perform(user, distributor, order_cycle, order.semanticId)
+        current_order = orderer.find_order(order.semanticId)
+      }.to change {
+        current_order.orderStatus[:path]
+      }.from("Held").to("Complete")
+        .and change {
+          current_order.lines.count
+        }.from(1).to(0)
+        .and change {
+          variant.on_hand
+        }.from(49).to(13) # minus 3 backordered slabs (3 * 12 = 36)
+    end
   end
 end