Disallow to modify the end date for an ended poll

app/models/poll.rb

@@ -40,6 +40,7 @@ class Poll < ApplicationRecord
   validate :start_date_is_not_past_date, on: :create
   validate :start_date_change, on: :update
   validate :end_date_is_not_past_date, on: :update
+  validate :end_date_change, on: :update
   validate :only_one_active, unless: :public?
 
   accepts_nested_attributes_for :questions, reject_if: :all_blank, allow_destroy: true
@@ -168,6 +169,12 @@ class Poll < ApplicationRecord
     end
   end
 
+  def end_date_change
+    if will_save_change_to_ends_at? && ends_at_in_database < Time.current
+      errors.add(:ends_at, I18n.t("errors.messages.cannot_change_date.poll_ended"))
+    end
+  end
+
   def generate_slug?
     slug.nil?
   end

config/locales/en/general.yml

@@ -140,6 +140,7 @@ en:
       past_date: "Must not be a past date"
       cannot_change_date:
         poll_started: "Cannot be changed if voting has already started"
+        poll_ended: "Cannot be changed if voting has already ended"
   form:
     accept_terms: I agree to the %{policy} and the %{conditions}
     accept_terms_title: I agree to the Privacy Policy and the Terms and conditions of use

config/locales/es/general.yml

@@ -140,6 +140,7 @@ es:
       past_date: "No puede ser una fecha pasada"
       cannot_change_date:
         poll_started: "No puede ser cambiada si la votación ha comenzado"
+        poll_ended: "No puede ser cambiada si la votación ha acabado"
   form:
     accept_terms: Acepto la %{policy} y las %{conditions}
     accept_terms_title: Acepto la Política de privacidad y las Condiciones de uso

spec/models/poll/poll_spec.rb

@@ -70,7 +70,7 @@ describe Poll do
         expect(poll).not_to be_valid
       end
 
-      it "is valid if changing the end date to a future date" do
+      it "is valid if changing the end date for a non-expired poll to a future date" do
         poll.ends_at = 1.day.from_now
         expect(poll).to be_valid
       end
@@ -81,6 +81,20 @@ describe Poll do
         poll.ends_at = 1.day.ago
         expect(poll).not_to be_valid
       end
+
+      it "is valid if the past end date is the same as it was" do
+        poll = create(:poll, starts_at: 3.days.ago, ends_at: 2.days.ago)
+        poll.ends_at = poll.ends_at
+
+        expect(poll).to be_valid
+      end
+
+      it "is not valid if changing the end date for an expired poll" do
+        poll = create(:poll, :expired)
+
+        poll.ends_at = 1.day.from_now
+        expect(poll).not_to be_valid
+      end
     end
   end