Add service to create Oncall-rotation

Add specs too

ee/app/policies/incident_management/oncall_rotation_policy.rb

+# frozen_string_literal: true
+
+module IncidentManagement
+  class OncallRotationPolicy < ::BasePolicy
+    delegate :project
+  end
+end

ee/app/services/incident_management/oncall_rotations/create_service.rb

+# frozen_string_literal: true
+
+module IncidentManagement
+  module OncallRotations
+    class CreateService
+      # @param schedule [IncidentManagement::OncallSchedule]
+      # @param project [Project]
+      # @param user [User]
+      # @param params [Hash<Symbol,Any>]
+      # @param params - name [String] The name of the on-call rotation.
+      # @param params - length [Integer] The length of the rotation.
+      # @param params - length_unit [String] The unit of the rotation length. (One of 'hours', days', 'weeks')
+      # @param params - starts_at [DateTime] The datetime the rotation starts on.
+      # @param params - participants [Array<hash>] An array of hashes defining participants of the on-call rotations.
+      #                 - participant [User] The user who is part of the rotation
+      #                 - color_palette [String] The color palette to assign to the on-call user, for example: "blue".
+      #                 - color_weight [String] The color weight to assign to for the on-call user, for example "500". Max 4 chars.
+      def initialize(schedule, project, user, params)
+        @schedule = schedule
+        @project = project
+        @current_user = user
+        @params = params
+      end
+
+      def execute
+        return error_no_license unless available?
+        return error_no_permissions unless allowed?
+
+        oncall_rotation = schedule.oncall_rotations.create(params.except(:participants))
+
+        return error_in_create(oncall_rotation) unless oncall_rotation.persisted?
+
+        new_participants = Array(params[:participants]).map do |participant|
+          OncallParticipant.new(
+            oncall_rotation: oncall_rotation,
+            participant: participant[:user],
+            color_palette:  participant[:color_palette],
+            color_weight: participant[:color_weight]
+          )
+        end
+
+        OncallParticipant.bulk_insert!(new_participants)
+
+        success(oncall_rotation)
+      end
+
+      private
+
+      attr_reader :schedule, :project, :current_user, :params, :participants
+
+      def allowed?
+        Ability.allowed?(current_user, :admin_incident_management_oncall_schedule, project)
+      end
+
+      def available?
+        Feature.enabled?(:oncall_schedules_mvc, project) &&
+          project.feature_available?(:oncall_schedules)
+      end
+
+      def error(message)
+        ServiceResponse.error(message: message)
+      end
+
+      def success(oncall_rotation)
+        ServiceResponse.success(payload: { oncall_rotation: oncall_rotation })
+      end
+
+      def error_no_permissions
+        error('You have insufficient permissions to create an on-call rotation for this project')
+      end
+
+      def error_no_license
+        error('Your license does not support on-call rotations')
+      end
+
+      def error_in_create(oncall_rotation)
+        error(oncall_rotation.errors.full_messages.to_sentence)
+      end
+    end
+  end
+end

ee/spec/policies/incident_management/oncall_rotation_policy_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe IncidentManagement::OncallRotationPolicy do
+  let_it_be(:project) { create(:project) }
+  let_it_be(:user) { create(:user) }
+  let_it_be(:oncall_schedule) { create(:incident_management_oncall_schedule, project: project) }
+  let_it_be(:oncall_schedule) { create(:incident_management_oncall_rotation, oncall_schedule: oncall_schedule) }
+
+  subject(:policy) { described_class.new(user, oncall_schedule) }
+
+  describe 'rules' do
+    it { is_expected.to be_disallowed :read_incident_management_oncall_schedule }
+
+    context 'when maintainer' do
+      before do
+        project.add_maintainer(user)
+      end
+
+      it { is_expected.to be_allowed :read_incident_management_oncall_schedule }
+    end
+  end
+end

ee/spec/services/incident_management/oncall_rotations/create_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe IncidentManagement::OncallRotations::CreateService do
+  let_it_be_with_refind(:project) { create(:project) }
+  let_it_be(:schedule) { create(:incident_management_oncall_schedule, project: project) }
+
+  let_it_be(:user_with_permissions) { create(:user) }
+  let_it_be(:user_without_permissions) { create(:user) }
+  let_it_be(:current_user) { user_with_permissions }
+
+  let(:participants) do
+    [
+      {
+        user: current_user,
+        color_palette: 'black',
+        color_weight: '500'
+      }
+    ]
+  end
+
+  let(:params) { { name: 'On-call rotation', starts_at: Time.current, length: '1', length_unit: 'days' }.merge(participants: participants) }
+  let(:service) { described_class.new(schedule, project, current_user, params) }
+
+  before_all do
+    project.add_maintainer(user_with_permissions)
+  end
+
+  before do
+    stub_licensed_features(oncall_schedules: true)
+  end
+
+  describe '#execute' do
+    shared_examples 'error response' do |message|
+      it 'has an informative message' do
+        expect(execute).to be_error
+        expect(execute.message).to eq(message)
+      end
+    end
+
+    subject(:execute) { service.execute }
+
+    context 'when the current_user is anonymous' do
+      let(:current_user) { nil }
+
+      it_behaves_like 'error response', 'You have insufficient permissions to create an on-call rotation for this project'
+    end
+
+    context 'when the current_user does not have permissions to create on-call schedules' do
+      let(:current_user) { user_without_permissions }
+
+      it_behaves_like 'error response', 'You have insufficient permissions to create an on-call rotation for this project'
+    end
+
+    context 'when feature is not available' do
+      before do
+        stub_licensed_features(oncall_schedules: false)
+      end
+
+      it_behaves_like 'error response', 'Your license does not support on-call rotations'
+    end
+
+    context 'when feature flag is disabled' do
+      before do
+        stub_feature_flags(oncall_schedules_mvc: false)
+      end
+
+      it_behaves_like 'error response', 'Your license does not support on-call rotations'
+    end
+
+    context 'when an on-call rotation already exists' do
+      let!(:oncall_schedule) { create(:incident_management_oncall_rotation, oncall_schedule: schedule, name: 'On-call rotation') }
+
+      it_behaves_like 'error response', 'Name has already been taken'
+    end
+
+    context 'with valid params' do
+      it 'successfully creates an on-call rotation' do
+        expect(execute).to be_success
+
+        oncall_schedule = execute.payload[:oncall_rotation]
+        expect(oncall_schedule).to be_a(::IncidentManagement::OncallRotation)
+        expect(oncall_schedule.name).to eq('On-call rotation')
+        expect(oncall_schedule.length).to eq('1')
+        expect(oncall_schedule.length_unit).to eq('days')
+      end
+    end
+  end
+end