Add system note when escalating to users

Creates a system note after an escalation event to
show which users and on-call polices were escalated to.

Changelog: added
EE: true

ee/app/models/incident_management/pending_escalations/alert.rb

@@ -28,6 +28,7 @@ module IncidentManagement
       validates :rule_id, presence: true, uniqueness: { scope: [:alert_id] }
 
       delegate :project, to: :alert
+      delegate :policy, to: :rule
     end
   end
 end

ee/app/services/ee/system_note_service.rb

@@ -112,6 +112,10 @@ module EE
       issuables_service(noteable, project, author).publish_issue_to_status_page
     end
 
+    def alert_via_escalation(noteable, project, recipients, escalation_policy)
+      escalations_service(noteable, project).alert_via_escalation(recipients, escalation_policy)
+    end
+
     private
 
     def issuables_service(noteable, project, author)
@@ -129,5 +133,9 @@ module EE
     def vulnerabilities_service(noteable, project, author)
       ::SystemNotes::VulnerabilitiesService.new(noteable: noteable, project: project, author: author)
     end
+
+    def escalations_service(noteable, project)
+      ::SystemNotes::EscalationsService.new(noteable: noteable, project: project)
+    end
   end
 end

ee/app/services/incident_management/pending_escalations/process_service.rb

@@ -3,6 +3,8 @@
 module IncidentManagement
   module PendingEscalations
     class ProcessService < BaseService
+      include Gitlab::Utils::StrongMemoize
+
       def initialize(escalation)
         @escalation = escalation
         @project = escalation.project
@@ -17,6 +19,7 @@ module IncidentManagement
         return if target_status_exceeded_rule?
 
         notify_recipients
+        create_system_notes
         destroy_escalation!
       end
 
@@ -42,11 +45,17 @@ module IncidentManagement
         NotificationService
           .new
           .async
-          .notify_oncall_users_of_alert(oncall_notification_recipients.to_a, target)
+          .notify_oncall_users_of_alert(oncall_notification_recipients, target)
+      end
+
+      def create_system_notes
+        SystemNoteService.alert_via_escalation(target, project, oncall_notification_recipients, escalation.policy)
       end
 
       def oncall_notification_recipients
-        ::IncidentManagement::OncallUsersFinder.new(project, schedule: oncall_schedule).execute
+        strong_memoize(:oncall_notification_recipients) do
+          ::IncidentManagement::OncallUsersFinder.new(project, schedule: oncall_schedule).execute.to_a
+        end
       end
 
       def destroy_escalation!

ee/app/services/system_notes/escalations_service.rb

+# frozen_string_literal: true
+
+module SystemNotes
+  class EscalationsService < ::SystemNotes::BaseService
+    def initialize(noteable: nil, project: nil)
+      @noteable = noteable
+      @project = project
+      @author = User.alert_bot
+    end
+
+    def alert_via_escalation(recipients, escalation_policy)
+      body = "notified #{recipients.map(&:to_reference).to_sentence} of this alert via escalation policy **#{escalation_policy.name}**"
+
+      create_note(NoteSummary.new(noteable, project, author, body, action: 'new_alert_added'))
+    end
+  end
+end

ee/spec/services/incident_management/pending_escalations/process_service_spec.rb

@@ -49,6 +49,14 @@ RSpec.describe IncidentManagement::PendingEscalations::ProcessService do
       it_behaves_like 'sends on-call notification'
       it_behaves_like 'deletes the escalation'
 
+      it 'creates a system note' do
+        expect(SystemNoteService)
+          .to receive(:alert_via_escalation).with(alert, project, [a_kind_of(User)], escalation_policy)
+          .and_call_original
+
+        expect { execute }.to change(Note, :count).by(1)
+      end
+
       context 'feature flag is off' do
         before do
           stub_feature_flags(escalation_policies_mvc: false)

ee/spec/services/system_notes/escalations_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe SystemNotes::EscalationsService do
+  let_it_be(:project) { create(:project) }
+  let_it_be(:user) { create(:user) }
+  let_it_be(:user_2) { create(:user) }
+  let_it_be(:author) { User.alert_bot }
+
+  describe '#alert_via_escalation' do
+    subject { described_class.new(noteable: noteable, project: project).alert_via_escalation([user, user_2], escalation_policy) }
+
+    let_it_be(:escalation_policy) { create(:incident_management_escalation_policy, project: project) }
+    let_it_be(:noteable) { create(:alert_management_alert, project: project) }
+
+    it_behaves_like 'a system note' do
+      let(:action) { 'new_alert_added' }
+    end
+
+    it 'posts the correct text to the system note' do
+      expect(subject.note).to match("notified #{user.to_reference} and #{user_2.to_reference} of this alert via escalation policy **#{escalation_policy.name}**")
+    end
+  end
+end