Find admin integration with group-level integrations

After adding the group_id column to the services table
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/38499, we can now
save integrations that belongs to a group
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/39959.

Integrations can inherit the admin integration from the UI selector.
Now, having group-level integration we need to find the right
integration to inherit the values from.

We have to find the closest group integration or instance-level
integration.

app/controllers/groups/settings/integrations_controller.rb

@@ -12,7 +12,7 @@ module Groups
       end
 
       def edit
-        @admin_integration = Service.instance_for(integration.type)
+        @admin_integration = Service.default_integration(integration.type, group)
 
         super
       end

app/controllers/projects/services_controller.rb

@@ -20,7 +20,7 @@ class Projects::ServicesController < Projects::ApplicationController
   layout "project_settings"
 
   def edit
-    @admin_integration = Service.instance_for(service.type)
+    @admin_integration = Service.default_integration(service.type, project)
   end
 
   def update

app/models/group.rb

@@ -33,6 +33,7 @@ class Group < Namespace
 
   has_many :milestones
   has_many :iterations
+  has_many :services
   has_many :shared_group_links, foreign_key: :shared_with_group_id, class_name: 'GroupGroupLink'
   has_many :shared_with_group_links, foreign_key: :shared_group_id, class_name: 'GroupGroupLink'
   has_many :shared_groups, through: :shared_group_links, source: :shared_group

app/models/service.rb

@@ -46,6 +46,7 @@ class Service < ApplicationRecord
   after_commit :cache_project_has_external_wiki
 
   belongs_to :project, inverse_of: :services
+  belongs_to :group, inverse_of: :services
   has_one :service_hook
 
   validates :project_id, presence: true, unless: -> { template? || instance? || group_id }
@@ -236,10 +237,25 @@ class Service < ApplicationRecord
     exists?(instance: true, type: type)
   end
 
-  def self.instance_for(type)
-    find_by(instance: true, type: type)
+  def self.default_integration(type, scope)
+    closest_group_integration(type, scope) || instance_level_integration(type)
   end
 
+  def self.closest_group_integration(type, scope)
+    group_ids = scope.ancestors.select(:id)
+    array = group_ids.to_sql.present? ? "array(#{group_ids.to_sql})" : 'ARRAY[]'
+
+    where(type: type, group_id: group_ids)
+      .order(Arel.sql("array_position(#{array}::bigint[], services.group_id)"))
+      .first
+  end
+  private_class_method :closest_group_integration
+
+  def self.instance_level_integration(type)
+    find_by(type: type, instance: true)
+  end
+  private_class_method :instance_level_integration
+
   def activated?
     active
   end

spec/models/concerns/id_in_ordered_spec.rb

@@ -14,7 +14,7 @@ RSpec.describe IdInOrdered do
 
         expect(Issue.id_in_ordered([issue3.id, issue1.id, issue4.id, issue5.id, issue2.id])).to eq([
           issue3, issue1, issue4, issue5, issue2
-])
+        ])
       end
 
       context 'when the ids are not an array of integers' do

spec/models/group_spec.rb

@@ -27,6 +27,7 @@ RSpec.describe Group do
     it { is_expected.to have_many(:milestones) }
     it { is_expected.to have_many(:iterations) }
     it { is_expected.to have_many(:group_deploy_keys) }
+    it { is_expected.to have_many(:services) }
 
     describe '#members & #requesters' do
       let(:requester) { create(:user) }

spec/models/service_spec.rb

@@ -8,6 +8,7 @@ RSpec.describe Service do
 
   describe "Associations" do
     it { is_expected.to belong_to :project }
+    it { is_expected.to belong_to :group }
     it { is_expected.to have_one :service_hook }
     it { is_expected.to have_one :jira_tracker_data }
     it { is_expected.to have_one :issue_tracker_data }
@@ -419,29 +420,49 @@ RSpec.describe Service do
     end
   end
 
-  describe 'instance' do
-    describe '.instance_for' do
-      let_it_be(:jira_service) { create(:jira_service, :instance) }
-      let_it_be(:slack_service) { create(:slack_service, :instance) }
+  describe '.default_integration' do
+    context 'with an instance-level service' do
+      let_it_be(:instance_service) { create(:jira_service, :instance) }
 
-      subject { described_class.instance_for(type) }
-
-      context 'Hipchat serivce' do
-        let(:type) { 'HipchatService' }
+      it 'returns the instance service' do
+        expect(described_class.default_integration('JiraService', project)).to eq(instance_service)
+      end
 
-        it { is_expected.to eq(nil) }
+      it 'returns nil for nonexistent service type' do
+        expect(described_class.default_integration('HipchatService', project)).to eq(nil)
       end
 
-      context 'Jira serivce' do
-        let(:type) { 'JiraService' }
+      context 'with a group service' do
+        let_it_be(:group_service) { create(:jira_service, group_id: group.id, project_id: nil) }
 
-        it { is_expected.to eq(jira_service) }
-      end
+        it 'returns the group service for a project' do
+          expect(described_class.default_integration('JiraService', project)).to eq(group_service)
+        end
+
+        it 'returns the instance service for a group' do
+          expect(described_class.default_integration('JiraService', group)).to eq(instance_service)
+        end
 
-      context 'Slack serivce' do
-        let(:type) { 'SlackService' }
+        context 'with a subgroup' do
+          let_it_be(:subgroup) { create(:group, parent: group) }
+          let!(:project) { create(:project, group: subgroup) }
 
-        it { is_expected.to eq(slack_service) }
+          it 'returns the closest group service for a project' do
+            expect(described_class.default_integration('JiraService', project)).to eq(group_service)
+          end
+
+          it 'returns the closest group service for a subgroup' do
+            expect(described_class.default_integration('JiraService', subgroup)).to eq(group_service)
+          end
+
+          context 'having a service' do
+            let!(:subgroup_service) { create(:jira_service, group_id: subgroup.id, project_id: nil) }
+
+            it 'returns the closest group service for a project' do
+              expect(described_class.default_integration('JiraService', project)).to eq(subgroup_service)
+            end
+          end
+        end
       end
     end
   end