FEATURE: add composer warning when user haven't been seen in a long time (#18340)

* FEATURE: add composer warning when user haven't been seen in a long time

When a user creates a PM and adds a recipient that hasn't been seen in a
long time then we'll now show a warning in composer indicating that the
user hasn't been seen in a long time.

spec/requests/composer_messages_controller_spec.rb

@@ -30,4 +30,45 @@ RSpec.describe ComposerMessagesController do
       end
     end
   end
+
+  describe '#user_not_seen_in_a_while' do
+    fab!(:user_1) { Fabricate(:user, last_seen_at: 3.years.ago) }
+    fab!(:user_2) { Fabricate(:user, last_seen_at: 2.years.ago) }
+    fab!(:user_3) { Fabricate(:user, last_seen_at: 6.months.ago) }
+
+    it 'requires you to be logged in' do
+      get '/composer_messages/user_not_seen_in_a_while.json', params: { usernames: [user_1.username, user_2.username, user_3.username] }
+      expect(response.status).to eq(403)
+    end
+
+    context 'when logged in' do
+      let!(:user) { sign_in(Fabricate(:user)) }
+
+      before do
+        SiteSetting.pm_warn_user_last_seen_months_ago = 24
+      end
+
+      it 'requires usernames parameter to be present' do
+        get '/composer_messages/user_not_seen_in_a_while.json'
+        expect(response.status).to eq(400)
+      end
+
+      it 'returns users that have not been seen recently' do
+        get '/composer_messages/user_not_seen_in_a_while.json', params: { usernames: [user_1.username, user_2.username, user_3.username] }
+        expect(response.status).to eq(200)
+        json = response.parsed_body
+        expect(json["user_count"]).to eq(2)
+        expect(json["usernames"]).to contain_exactly(user_1.username, user_2.username)
+      end
+
+      it 'accounts for pm_warn_user_last_seen_months_ago site setting' do
+        SiteSetting.pm_warn_user_last_seen_months_ago = 30
+        get '/composer_messages/user_not_seen_in_a_while.json', params: { usernames: [user_1.username, user_2.username, user_3.username] }
+        expect(response.status).to eq(200)
+        json = response.parsed_body
+        expect(json["user_count"]).to eq(1)
+        expect(json["usernames"]).to contain_exactly(user_1.username)
+      end
+    end
+  end
 end