FEATURE: Topic slow mode. (#10904)

Adds a new slow mode for topics that are heating up. Users will have to wait for a period of time before being able to post again.

We store this interval inside the topics table and track the last time a user posted using the last_posted_at datetime in the TopicUser relation.

spec/requests/topics_controller_spec.rb

@@ -3047,6 +3047,58 @@ RSpec.describe TopicsController do
     end
   end
 
+  describe '#set_slow_mode' do
+    context 'when not logged in' do
+      it 'returns a forbidden response' do
+        put "/t/#{topic.id}/slow_mode.json", params: {
+          seconds: '3600'
+        }
+
+        expect(response.status).to eq(403)
+      end
+    end
+
+    context 'logged in as an admin' do
+      it 'allows admins to set the slow mode interval' do
+        sign_in(admin)
+
+        put "/t/#{topic.id}/slow_mode.json", params: {
+          seconds: '3600'
+        }
+
+        topic.reload
+        expect(response.status).to eq(200)
+        expect(topic.slow_mode_seconds).to eq(3600)
+      end
+    end
+
+    context 'logged in as a regular user' do
+      it 'does nothing if the user is not TL4' do
+        user.update!(trust_level: TrustLevel[3])
+        sign_in(user)
+
+        put "/t/#{topic.id}/slow_mode.json", params: {
+          seconds: '3600'
+        }
+
+        expect(response.status).to eq(403)
+      end
+
+      it 'allows TL4 users to set the slow mode interval' do
+        user.update!(trust_level: TrustLevel[4])
+        sign_in(user)
+
+        put "/t/#{topic.id}/slow_mode.json", params: {
+          seconds: '3600'
+        }
+
+        topic.reload
+        expect(response.status).to eq(200)
+        expect(topic.slow_mode_seconds).to eq(3600)
+      end
+    end
+  end
+
   describe '#invite' do
     describe 'when not logged in' do
       it "should return the right response" do