Show a nice error message instead of 500 error when deleting a referenced order cycle

app/controllers/admin/order_cycles_controller.rb

@@ -7,6 +7,8 @@ module Admin
 
     before_filter :load_data_for_index, :only => :index
     before_filter :require_coordinator, only: :new
+    around_filter :protect_invalid_destroy, only: :destroy
+
 
     def show
       respond_to do |format|
@@ -106,5 +108,14 @@ module Admin
         render :set_coordinator
       end
     end
+
+    def protect_invalid_destroy
+      begin
+        yield
+      rescue ActiveRecord::InvalidForeignKey
+        redirect_to main_app.admin_order_cycles_url
+        flash[:error] = "That order cycle has been selected by a customer and cannot be deleted. To prevent customers from accessing it, please close it instead."
+      end
+    end
   end
 end

spec/controllers/admin/order_cycles_controller_spec.rb

@@ -56,5 +56,21 @@ module Admin
         end
       end
     end
+
+    describe "destroy" do
+      let!(:distributor) { create(:distributor_enterprise, owner: distributor_owner) }
+
+      describe "when an order cycle becomes non-deletable, and we attempt to delete it" do
+        let!(:oc)    { create(:simple_order_cycle, coordinator: distributor) }
+        let!(:order) { create(:order, order_cycle: oc) }
+
+        before { spree_get :destroy, id: oc.id }
+
+        it "displays an error message" do
+          expect(response).to redirect_to admin_order_cycles_path
+          expect(flash[:error]).to eq "That order cycle has been selected by a customer and cannot be deleted. To prevent customers from accessing it, please close it instead."
+        end
+      end
+    end
   end
 end