1 files changed, 123 insertions, 0 deletions
diff --git a/app/services/metrics/dashboard/custom_metric_embed_service.rb b/app/services/metrics/dashboard/custom_metric_embed_service.rb
new file mode 100644
index 00000000000..50f070989fc
--- /dev/null
+++ b/app/services/metrics/dashboard/custom_metric_embed_service.rb
@@ -0,0 +1,123 @@
+# frozen_string_literal: true
+
+# Responsible for returning a dashboard containing specified
+# custom metrics. Creates panels based on the matching metrics
+# stored in the database.
+#
+# Use Gitlab::Metrics::Dashboard::Finder to retrive dashboards.
+module Metrics
+  module Dashboard
+    class CustomMetricEmbedService < ::Metrics::Dashboard::BaseEmbedService
+      extend ::Gitlab::Utils::Override
+      include Gitlab::Utils::StrongMemoize
+      include Gitlab::Metrics::Dashboard::Defaults
+
+      class << self
+        # Determines whether the provided params are sufficient
+        # to uniquely identify a panel composed of user-defined
+        # custom metrics from the DB.
+        def valid_params?(params)
+          [
+            params[:embedded],
+            valid_dashboard?(params[:dashboard_path]),
+            valid_group_title?(params[:group]),
+            params[:title].present?,
+            params.has_key?(:y_label)
+          ].all?
+        end
+
+        private
+
+        # A group title is valid if it is one of the limited
+        # options the user can select in the UI.
+        def valid_group_title?(group)
+          PrometheusMetricEnums
+            .custom_group_details
+            .map { |_, details| details[:group_title] }
+            .include?(group)
+        end
+
+        # All custom metrics are displayed on the system dashboard.
+        # Nil is acceptable as we'll default to the system dashboard.
+        def valid_dashboard?(dashboard)
+          dashboard.nil? || SystemDashboardService.system_dashboard?(dashboard)
+        end
+      end
+
+      # Returns a new dashboard with only the matching
+      # metrics from the system dashboard, stripped of
+      # group info.
+      #
+      # Note: This overrides the method #raw_dashboard,
+      # which means the result will not be cached. This
+      # is because we are inserting DB info into the
+      # dashboard before post-processing. This ensures
+      # we aren't acting on deleted or out-of-date metrics.
+      #
+      # @return [Hash]
+      override :raw_dashboard
+      def raw_dashboard
+        panels_not_found!(identifiers) if panels.empty?
+
+        { 'panel_groups' => [{ 'panels' => panels }] }
+      end
+
+      private
+
+      # Generated dashboard panels for each metric which
+      # matches the provided input.
+      # @return [Array<Hash>]
+      def panels
+        strong_memoize(:panels) do
+          metrics.map { |metric| panel_for_metric(metric) }
+        end
+      end
+
+      # Metrics which match the provided inputs.
+      # There may be multiple metrics, but they should be
+      # displayed in a single panel/chart.
+      # @return [ActiveRecord::AssociationRelation<PromtheusMetric>]
+      # rubocop: disable CodeReuse/ActiveRecord
+      def metrics
+        project.prometheus_metrics.where(
+          group: group_key,
+          title: title,
+          y_label: y_label
+        )
+      end
+      # rubocop: enable CodeReuse/ActiveRecord
+
+      # Returns a symbol representing the group that
+      # the dashboard's group title belongs to.
+      # It will be one of the keys found under
+      # PrometheusMetricEnums.custom_groups.
+      #
+      # @return [String]
+      def group_key
+        strong_memoize(:group_key) do
+          PrometheusMetricEnums
+            .group_details
+            .find { |_, details| details[:group_title] == group }
+            .first
+            .to_s
+        end
+      end
+
+      # Returns a representation of a PromtheusMetric
+      # as a dashboard panel. As the panel is generated
+      # on the fly, we're using default values for info
+      # not represented in the DB.
+      #
+      # @return [Hash]
+      def panel_for_metric(metric)
+        {
+          type: DEFAULT_PANEL_TYPE,
+          weight: DEFAULT_PANEL_WEIGHT,
+          title: metric.title,
+          y_label: metric.y_label,
+          metrics: [metric.to_metric_hash]
+        }
+      end
+    end
+  end
+end