Implement dummy report pages API endpoints

This change adds two API endpoints, both of them return dummy data
for now.

ee/lib/api/analytics/reports.rb

+# frozen_string_literal: true
+
+module API
+  module Analytics
+    class Reports < Grape::API::Instance
+      DESCRIPTION_DETAIL =
+        'This feature is experimental and gated by the `:report_pages`'\
+        ' feature flag, introduced in GitLab 13.2.'
+
+      helpers do
+        def api_endpoints_available?
+          # This will be scoped to a project or a group
+          Feature.enabled?(:report_pages) && ::License.feature_available?(:group_activity_analytics)
+        end
+      end
+
+      params do
+        requires :report_id, type: String, desc: 'The ID of the report'
+      end
+
+      resource :analytics do
+        resource :reports do
+          route_param :report_id do
+            resource :chart do
+              get do
+                not_found! unless api_endpoints_available?
+
+                # Dummy response
+                {
+                  id: params[:report_id],
+                  title: 'Recent Issues (90 days)',
+                  chart: {
+                    type: 'bar',
+                    series: [
+                      {
+                        id: 'open_merge_requests',
+                        title: 'Merge requests'
+                      }
+                    ]
+                  }
+                }
+              end
+            end
+          end
+        end
+
+        resource :series do
+          params do
+            requires :series_id, type: String, desc: 'The ID of the series'
+          end
+          route_param :report_id do
+            route_param :series_id do
+              get do
+                not_found! unless api_endpoints_available?
+
+                # Dummy response
+                {
+                  labels: %w[label1 label2 label3],
+                  datasets: [
+                    {
+                      label: "Series 1",
+                      data: [
+                        1,
+                        2,
+                        3
+                      ]
+                    }
+                  ]
+                }
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

ee/lib/ee/api/api.rb

@@ -58,6 +58,7 @@ module EE
         mount ::API::VisualReviewDiscussions
         mount ::API::Analytics::CodeReviewAnalytics
         mount ::API::Analytics::GroupActivityAnalytics
+        mount ::API::Analytics::Reports
         mount ::API::ProtectedEnvironments
         mount ::API::ResourceWeightEvents
 

ee/spec/requests/api/analytics/reports_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe API::Analytics::Reports do
+  let_it_be(:user) { create(:user) }
+  let_it_be(:report_id) { 'some_report_id' }
+
+  shared_examples 'error response examples' do
+    context 'when `report_pages` feature flag is off' do
+      before do
+        stub_feature_flags(report_pages: false)
+      end
+
+      it 'returns 404, not found' do
+        api_call
+
+        expect(response).to have_gitlab_http_status(:not_found)
+      end
+    end
+
+    context 'when `report_pages` license is missing' do
+      before do
+        stub_feature_flags(report_pages: true)
+        stub_licensed_features(group_activity_analytics: false)
+      end
+
+      it 'returns 404, not found' do
+        api_call
+
+        expect(response).to have_gitlab_http_status(:not_found)
+      end
+    end
+  end
+
+  describe 'GET /analytics/reports/:id/chart' do
+    subject(:api_call) do
+      get api("/analytics/reports/#{report_id}/chart", user)
+    end
+
+    before do
+      stub_licensed_features(group_activity_analytics: true)
+    end
+
+    it 'is successful' do
+      api_call
+
+      expect(response).to have_gitlab_http_status(:ok)
+      expect(response.parsed_body["id"]).to eq(report_id)
+    end
+
+    include_examples 'error response examples'
+  end
+
+  describe 'GET /analytics/series/:report_id/:series_id' do
+    let_it_be(:series_id) { 'some_series_id' }
+
+    subject(:api_call) do
+      get api("/analytics/series/#{report_id}/#{series_id}", user)
+    end
+
+    it 'is successful' do
+      api_call
+
+      expect(response).to have_gitlab_http_status(:ok)
+      expect(response.parsed_body["datasets"].size).to eq(1)
+    end
+
+    include_examples 'error response examples'
+  end
+end