Add PanelIdsInserter stage for dashboards

When processing metrics dashboard structure from yml files
we need to insert id property to each panel.

lib/gitlab/metrics/dashboard/stages/base_stage.rb

@@ -37,10 +37,8 @@ module Gitlab
           def for_metrics
             missing_panel_groups! unless dashboard[:panel_groups].is_a?(Array)
 
-            dashboard[:panel_groups].each do |panel_group|
-              missing_panels! unless panel_group[:panels].is_a?(Array)
-
-              panel_group[:panels].each do |panel|
+            for_panel_groups do |panel_group|
+              for_panels_in(panel_group) do |panel|
                 missing_metrics! unless panel[:metrics].is_a?(Array)
 
                 panel[:metrics].each do |metric|
@@ -49,6 +47,20 @@ module Gitlab
               end
             end
           end
+
+          def for_panel_groups
+            dashboard[:panel_groups].each do |panel_group|
+              yield panel_group
+            end
+          end
+
+          def for_panels_in(panel_group)
+            missing_panels! unless panel_group[:panels].is_a?(Array)
+
+            panel_group[:panels].each do |panel|
+              yield panel
+            end
+          end
         end
       end
     end

lib/gitlab/metrics/dashboard/stages/panel_ids_inserter.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Metrics
+    module Dashboard
+      module Stages
+        class PanelIdsInserter < BaseStage
+          # For each panel within given dashboard inserts panel_id unique in scope of the dashboard
+          def transform!
+            missing_panel_groups! unless dashboard[:panel_groups]
+
+            for_panels_group_with_panels do |panel_group, panel|
+              id = generate_panel_id(panel_group, panel)
+              remove_panel_ids! && break if duplicated_panel_id?(id)
+
+              insert_panel_id(id, panel)
+            end
+          end
+
+          private
+
+          def generate_panel_id(group, panel)
+            ::PerformanceMonitoring::PrometheusPanel.new(panel.with_indifferent_access).id(group[:group])
+          end
+
+          def insert_panel_id(id, panel)
+            track_inserted_panel_ids(id, panel)
+            panel[:id] = id
+          end
+
+          def track_inserted_panel_ids(id, panel)
+            panel_ids[id] = panel
+          end
+
+          def duplicated_panel_id?(id)
+            panel_ids.key?(id)
+          end
+
+          def remove_panel_ids!
+            panel_ids.each_value { |panel| panel.delete(:id) }
+          end
+
+          def panel_ids
+            @_panel_ids ||= {}
+          end
+
+          def for_panels_group_with_panels
+            for_panel_groups do |panel_group|
+              for_panels_in(panel_group) do |panel|
+                yield panel_group, panel
+              end
+            end
+          end
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/metrics/dashboard/stages/panel_ids_inserter_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Metrics::Dashboard::Stages::PanelIdsInserter do
+  let(:project) { build_stubbed(:project) }
+
+  def fetch_panel_ids(dashboard_hash)
+    dashboard_hash[:panel_groups].flat_map { |group| group[:panels].flat_map { |panel| panel[:id] } }
+  end
+
+  describe '#transform!' do
+    subject(:transform!) { described_class.new(project, dashboard, nil).transform! }
+
+    let(:dashboard) { YAML.safe_load(fixture_file('lib/gitlab/metrics/dashboard/sample_dashboard.yml')).deep_symbolize_keys }
+
+    context 'when dashboard panels are present' do
+      it 'assigns unique ids to each panel using PerformanceMonitoring::PrometheusPanel', :aggregate_failures do
+        dashboard.fetch(:panel_groups).each do |group|
+          group.fetch(:panels).each do |panel|
+            panel_double = instance_double(::PerformanceMonitoring::PrometheusPanel)
+
+            expect(::PerformanceMonitoring::PrometheusPanel).to receive(:new).with(panel).and_return(panel_double)
+            expect(panel_double).to receive(:id).with(group[:group]).and_return(FFaker::Lorem.unique.characters(125))
+          end
+        end
+
+        transform!
+
+        expect(fetch_panel_ids(dashboard)).not_to include nil
+      end
+    end
+
+    context 'when dashboard panels has duplicated ids' do
+      it 'no panel has assigned id' do
+        panel_double = instance_double(::PerformanceMonitoring::PrometheusPanel)
+        allow(::PerformanceMonitoring::PrometheusPanel).to receive(:new).and_return(panel_double)
+        allow(panel_double).to receive(:id).and_return('duplicated id')
+
+        transform!
+
+        expect(fetch_panel_ids(dashboard)).to all be_nil
+        expect(fetch_panel_ids(dashboard)).not_to include 'duplicated id'
+      end
+    end
+
+    context 'when there are no panels in the dashboard' do
+      it 'raises a processing error' do
+        dashboard[:panel_groups][0].delete(:panels)
+
+        expect { transform! }.to(
+          raise_error(::Gitlab::Metrics::Dashboard::Errors::DashboardProcessingError)
+        )
+      end
+    end
+
+    context 'when there are no panel_groups in the dashboard' do
+      it 'raises a processing error' do
+        dashboard.delete(:panel_groups)
+
+        expect { transform! }.to(
+          raise_error(::Gitlab::Metrics::Dashboard::Errors::DashboardProcessingError)
+        )
+      end
+    end
+  end
+end