DeleteService for deleting self monitoring project

Create a DeleteService which can be used to delete the self monitoring
project.

lib/gitlab/database_importers/self_monitoring/project/delete_service.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module DatabaseImporters
+    module SelfMonitoring
+      module Project
+        class DeleteService < ::BaseService
+          include Stepable
+          include SelfMonitoring::Helpers
+
+          steps :validate_self_monitoring_project_exists,
+            :destroy_project_owner,
+            :delete_project_id
+
+          def initialize
+            super(nil)
+          end
+
+          def execute
+            execute_steps
+          end
+
+          private
+
+          def validate_self_monitoring_project_exists(result)
+            unless project_created? || self_monitoring_project_id.present?
+              return error(_('Self monitoring project does not exist'))
+            end
+
+            success(result)
+          end
+
+          def destroy_project_owner(result)
+            return success(result) unless project_created?
+
+            if self_monitoring_project.owner.destroy
+              success(result)
+            else
+              log_error(self_monitoring_project.errors.full_messages)
+              error(_('Error deleting project. Check logs for error details.'))
+            end
+          end
+
+          def delete_project_id(result)
+            update_result = application_settings.update(
+              instance_administration_project_id: nil
+            )
+
+            if update_result
+              success(result)
+            else
+              log_error("Could not delete self monitoring project ID, errors: %{errors}" % { errors: application_settings.errors.full_messages })
+              error(_('Could not delete project ID'))
+            end
+          end
+        end
+      end
+    end
+  end
+end

locale/gitlab.pot

@@ -5121,6 +5121,9 @@ msgstr ""
 msgid "Could not delete chat nickname %{chat_name}."
 msgstr ""
 
+msgid "Could not delete project ID"
+msgstr ""
+
 msgid "Could not fetch projects"
 msgstr ""
 
@@ -7122,6 +7125,9 @@ msgstr ""
 msgid "Error deleting  %{issuableType}"
 msgstr ""
 
+msgid "Error deleting project. Check logs for error details."
+msgstr ""
+
 msgid "Error details"
 msgstr ""
 
@@ -16262,6 +16268,9 @@ msgstr ""
 msgid "Selecting a GitLab user will add a link to the GitLab user in the descriptions of issues and comments (e.g. \"By <a href=\"#\">@johnsmith</a>\"). It will also associate and/or assign these issues and comments with the selected user."
 msgstr ""
 
+msgid "Self monitoring project does not exist"
+msgstr ""
+
 msgid "Self-monitoring is not enabled on this GitLab server, contact your administrator."
 msgstr ""
 

spec/lib/gitlab/database_importers/self_monitoring/project/delete_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::DatabaseImporters::SelfMonitoring::Project::DeleteService do
+  describe '#execute' do
+    let(:result) { subject.execute }
+    let(:application_setting) { Gitlab::CurrentSettings.current_application_settings }
+
+    before do
+      allow(ApplicationSetting).to receive(:current_without_cache) { application_setting }
+    end
+
+    context 'when project does not exist' do
+      it 'returns error' do
+        expect(result).to eq(
+          status: :error,
+          message: 'Self monitoring project does not exist',
+          last_step: :validate_self_monitoring_project_exists
+        )
+      end
+    end
+
+    context 'with project destroyed but ID still present in application settings' do
+      before do
+        application_setting.instance_administration_project_id = 1
+      end
+
+      it 'deletes project ID from application settings' do
+        subject.execute
+
+        expect(application_setting.instance_administration_project_id).to be_nil
+      end
+    end
+
+    context 'when self monitoring project exists' do
+      let(:group) { create(:group) }
+      let(:project) { create(:project, namespace: group) }
+
+      before do
+        application_setting.instance_administration_project = project
+      end
+
+      it 'destroys project' do
+        subject.execute
+
+        expect { project.reload }.to raise_error(ActiveRecord::RecordNotFound)
+      end
+
+      it 'deletes project ID from application settings' do
+        subject.execute
+
+        expect(application_setting.instance_administration_project_id).to be_nil
+      end
+    end
+  end
+end