Validate deleting a shipping method or switching it to backoffice only doesn't invalidate any order cycles

app/models/spree/shipping_method.rb

@@ -30,8 +30,11 @@ module Spree
     validates :name, presence: true
     validate :distributor_validation
     validate :at_least_one_shipping_category
+    validate :switching_to_backoffice_only_wont_leave_order_cycles_without_shipping_methods
     validates :display_on, inclusion: { in: DISPLAY_ON_OPTIONS.values }, allow_nil: true
 
+    before_destroy :check_destroy_wont_leave_order_cycles_without_shipping_methods
+
     after_save :touch_distributors
 
     scope :managed_by, lambda { |user|
@@ -112,6 +115,20 @@ module Spree
 
     private
 
+    def no_active_or_upcoming_non_simple_order_cycles_with_only_one_shipping_method?
+      return true if new_record?
+
+      OrderCycle.active.or(OrderCycle.upcoming).joins(:coordinator, :shipping_methods).where("
+        sells != 'own' AND
+        spree_shipping_methods.id = ? AND
+        NOT EXISTS(
+          SELECT 1
+          FROM order_cycle_shipping_methods
+          WHERE order_cycle_id = order_cycles.id AND
+          shipping_method_id != ?
+        )", id, id).none?
+    end
+
     def at_least_one_shipping_category
       return unless shipping_categories.empty?
 
@@ -127,5 +144,19 @@ module Spree
     def distributor_validation
       validates_with DistributorsValidator
     end
+
+    def check_destroy_wont_leave_order_cycles_without_shipping_methods
+      return if no_active_or_upcoming_non_simple_order_cycles_with_only_one_shipping_method?
+
+      errors.add(:base, :destroy_leaves_order_cycles_without_shipping_methods)
+      throw :abort
+    end
+
+    def switching_to_backoffice_only_wont_leave_order_cycles_without_shipping_methods
+      return if frontend? ||
+                no_active_or_upcoming_non_simple_order_cycles_with_only_one_shipping_method?
+
+      errors.add(:base, :switching_to_backoffice_only_leaves_order_cycles_without_shipping_methods)
+    end
   end
 end

config/locales/en.yml

@@ -73,6 +73,11 @@ en:
           attributes:
             base:
               card_expired: "has expired"
+        spree/shipping_method:
+          attributes:
+            base:
+              switching_to_backoffice_only_leaves_order_cycles_without_shipping_methods: Unable to switch to backoffice only, some open or upcoming order cycles would be left without any shipping methods
+              destroy_leaves_order_cycles_without_shipping_methods: Unable to delete, some open or upcoming order cycles would be left without any shipping methods
         order_cycle:
           attributes:
             base:

spec/models/spree/shipping_method_spec.rb

@@ -180,6 +180,31 @@ module Spree
           it { expect(shipping_method).to be_valid }
         end
       end
+
+      context "when it is being changed to backoffice only" do
+        let!(:order_cycle) { create(:distributor_order_cycle, with_distributor_and_shipping_method: true) }
+        let(:distributor) { order_cycle.distributors.first }
+        let(:shipping_method) { order_cycle.shipping_methods.first }
+
+        context "when the shipping method is the only shipping method on a distributor order cycle" do
+          it "should not be valid" do
+            shipping_method.display_on = "back_end"
+
+            expect(shipping_method).not_to be_valid
+            expect(shipping_method.errors.to_a).to eq ["Unable to switch to backoffice only, some open or upcoming order cycles would be left without any shipping methods"]
+          end
+        end
+
+        context "when the order cycles the shipping method is attached to has other valid shipping methods" do
+          it "is is valid" do
+            order_cycle.shipping_methods << create(:shipping_method, distributors: [distributor])
+
+            shipping_method.display_on = "back_end"
+
+            expect(shipping_method).to be_valid
+          end
+        end
+      end
     end
 
     # Regression test for Spree #4320
@@ -213,5 +238,49 @@ module Spree
         expect(shipping_method.shipments).to include(shipment)
       end
     end
+
+    context "#destroy" do
+      let(:shipping_method) { create(:shipping_method) }
+      let(:distributor) { create(:distributor_enterprise, shipping_methods: [shipping_method]) }
+      let!(:order_cycle) { create(:distributor_order_cycle, distributors: [distributor], shipping_methods: [shipping_method]) }
+
+      context "when the shipping method is the only shipping method on a distributor order cycle" do
+        it "can be deleted if the order cycle is closed" do
+          order_cycle.update!(orders_close_at: 1.minute.ago)
+
+          shipping_method.destroy
+
+          expect(shipping_method).to be_deleted
+        end
+
+        it "cannot be deleted if the order cycle is active" do
+          order_cycle.update!(orders_open_at: 1.day.ago, orders_close_at: 1.week.from_now)
+
+          shipping_method.destroy
+
+          expect(shipping_method).not_to be_deleted
+          expect(shipping_method.errors.to_a).to eq ["Unable to delete, some open or upcoming order cycles would be left without any shipping methods"]
+        end
+
+        it "cannot be deleted if the order cycle is upcoming" do
+          order_cycle.update!(orders_open_at: 1.day.from_now, orders_close_at: 1.week.from_now)
+
+          shipping_method.destroy
+
+          expect(shipping_method).not_to be_deleted
+          expect(shipping_method.errors.to_a).to eq ["Unable to delete, some open or upcoming order cycles would be left without any shipping methods"]
+        end
+      end
+
+      context "when the order cycles the shipping method is attached to has other valid shipping methods" do
+        it "can be deleted" do
+          order_cycle.shipping_methods << create(:shipping_method, distributors: [distributor])
+
+          shipping_method.destroy
+
+          expect(shipping_method).to be_deleted
+        end
+      end
+    end
   end
 end