Add metrics starred dashboards finder service

To provide unified and performan fetch interface
we need to add finder for metrics_users_starred_dashboards
records.

app/finders/metrics/users_starred_dashboards_finder.rb

+# frozen_string_literal: true
+
+module Metrics
+  class UsersStarredDashboardsFinder
+    def initialize(user:, project:, params: {})
+      @user, @project, @params = user, project, params
+    end
+
+    def execute
+      return ::Metrics::UsersStarredDashboard.none unless Ability.allowed?(user, :read_metrics_user_starred_dashboard, project)
+
+      items = starred_dashboards
+      items = by_project(items)
+      by_dashboard(items)
+    end
+
+    private
+
+    attr_reader :user, :project, :params
+
+    def by_project(items)
+      items.for_project(project)
+    end
+
+    def by_dashboard(items)
+      return items unless params[:dashboard_path]
+
+      items.merge(starred_dashboards.for_project_dashboard(project, params[:dashboard_path]))
+    end
+
+    def starred_dashboards
+      @starred_dashboards ||= user.metrics_users_starred_dashboards
+    end
+  end
+end

app/models/metrics/users_starred_dashboard.rb

@@ -11,5 +11,8 @@ module Metrics
     validates :project_id, presence: true
     validates :dashboard_path, presence: true, length: { maximum: 255 }
     validates :dashboard_path, uniqueness: { scope: %i[user_id project_id] }
+
+    scope :for_project, ->(project) { where(project: project) }
+    scope :for_project_dashboard, ->(project, path) { for_project(project).where(dashboard_path: path) }
   end
 end

spec/finders/metrics/users_starred_dashboards_finder_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Metrics::UsersStarredDashboardsFinder do
+  describe '#execute' do
+    subject(:starred_dashboards) { described_class.new(user: user, project: project, params: params).execute }
+
+    let_it_be(:user) { create(:user) }
+    let(:project) { create(:project) }
+    let(:dashboard_path) { 'config/prometheus/common_metrics.yml' }
+    let(:params) { {} }
+
+    context 'there are no starred dashboard records' do
+      it 'returns empty array' do
+        expect(starred_dashboards).to be_empty
+      end
+    end
+
+    context 'with annotation records' do
+      let!(:starred_dashboard_1) { create(:metrics_users_starred_dashboard, user: user, project: project) }
+      let!(:starred_dashboard_2) { create(:metrics_users_starred_dashboard, user: user, project: project, dashboard_path: dashboard_path) }
+      let!(:other_project_dashboard) { create(:metrics_users_starred_dashboard, user: user, dashboard_path: dashboard_path) }
+      let!(:other_user_dashboard) { create(:metrics_users_starred_dashboard, project: project, dashboard_path: dashboard_path) }
+
+      context 'user without read access to project' do
+        it 'returns empty relation' do
+          expect(starred_dashboards).to be_empty
+        end
+      end
+
+      context 'user with read access to project' do
+        before do
+          project.add_reporter(user)
+        end
+
+        it 'loads starred dashboards' do
+          expect(starred_dashboards).to contain_exactly starred_dashboard_1, starred_dashboard_2
+        end
+
+        context 'when the dashboard_path filter is present' do
+          let(:params) do
+            {
+              dashboard_path: dashboard_path
+            }
+          end
+
+          it 'loads filtered starred dashboards' do
+            expect(starred_dashboards).to contain_exactly starred_dashboard_2
+          end
+        end
+      end
+    end
+  end
+end

spec/models/metrics/users_starred_dashboard_spec.rb

@@ -17,4 +17,23 @@ describe Metrics::UsersStarredDashboard do
     it { is_expected.to validate_length_of(:dashboard_path).is_at_most(255) }
     it { is_expected.to validate_uniqueness_of(:dashboard_path).scoped_to(%i[user_id project_id]) }
   end
+
+  context 'scopes' do
+    let_it_be(:project) { create(:project) }
+    let_it_be(:starred_dashboard_a) { create(:metrics_users_starred_dashboard, project: project, dashboard_path: 'path_a') }
+    let_it_be(:starred_dashboard_b) { create(:metrics_users_starred_dashboard, project: project, dashboard_path: 'path_b') }
+    let_it_be(:starred_dashboard_c) { create(:metrics_users_starred_dashboard, dashboard_path: 'path_b') }
+
+    describe '#for_project' do
+      it 'selects only starred dashboards belonging to project' do
+        expect(described_class.for_project(project)).to contain_exactly starred_dashboard_a, starred_dashboard_b
+      end
+    end
+
+    describe '#for_project_dashboard' do
+      it 'selects only starred dashboards belonging to project with given dashboard path' do
+        expect(described_class.for_project_dashboard(project, 'path_b')).to contain_exactly starred_dashboard_b
+      end
+    end
+  end
 end