Inject dashboard response with db info

app/services/metrics_dashboard_processing_service.rb

+# frozen_string_literal: true
+
+class MetricsDashboardProcessingService
+  DEFAULT_PANEL_TYPE = 'area-chart'
+
+  def initialize(dashboard, project)
+    @dashboard = dashboard.deep_transform_keys(&:to_sym)
+    @project = project
+  end
+
+  def process
+    insert_persisted_metrics!
+    insert_metric_ids!
+    @dashboard.to_json
+  end
+
+  private
+
+  # Inserts project-specific metrics into the dashboard config.
+  # If there are no project-specific metrics, this will have no effect.
+  def insert_persisted_metrics!
+    @project.prometheus_metrics.each do |persisted_metric|
+      group = find_or_create_group(@dashboard[:panel_groups], persisted_metric)
+      panel = find_or_create_panel(group[:panels], persisted_metric)
+      find_or_create_metric(panel[:metrics], persisted_metric)
+    end
+  end
+
+  # For each metric in the dashboard config, attempts to find a corresponding
+  # persisted record. If found, includes the record id in the config.
+  def insert_metric_ids!
+    @dashboard[:panel_groups].each do |group|
+      group[:panels].each do |panel|
+        panel[:metrics].each do |metric|
+          metric_record = common_metrics.find {|m| m.identifier == metric[:id] }
+          metric[:metric_id] = metric_record.id if metric_record
+        end
+      end
+    end
+  end
+
+  def common_metrics
+    @common_metrics ||= ::PrometheusMetric.common
+  end
+
+  def find_or_create_group(panel_groups, metric)
+    target_group = panel_groups.find { |group| group[:group] == metric.group_title }
+
+    unless target_group
+      target_group = {
+        group: metric.group_title,
+        priority: metric.priority,
+        panels: []
+      }
+      panel_groups << target_group
+    end
+
+    target_group
+  end
+
+  def find_or_create_panel(panels, metric)
+    panel_identifiers = [DEFAULT_PANEL_TYPE, metric.title, metric.y_label]
+    target_panel = panels.find { |panel| panel.values_at(:type, :title, :y_label) == panel_identifiers }
+
+    unless target_panel
+      target_panel = {
+        type: DEFAULT_PANEL_TYPE,
+        title: metric.title,
+        y_label: metric.y_label,
+        metrics: []
+      }
+      panels << target_panel
+    end
+
+    target_panel
+  end
+
+  def find_or_create_metric(metrics, metric)
+    target_metric = metrics.find { |m| m[:id] == metric.identifier }
+
+    unless target_metric
+      target_metric = metric.queries.first.merge(metric_id: metric.id)
+      metrics << target_metric
+    end
+
+    target_metric
+  end
+end

app/services/metrics_dashboard_service.rb

@@ -3,7 +3,11 @@
 # Fetches the metrics dashboard layout and supplemented the output with DB info.
 class MetricsDashboardService
   SYSTEM_DASHBOARD_NAME = 'system_dashboard'
-  SYSTEM_DASHBOARD_PATH = Rails.root.join("config/prometheus", "#{SYSTEM_DASHBOARD_NAME}.yml")
+  SYSTEM_DASHBOARD_PATH = Rails.root.join('config', 'prometheus', "#{SYSTEM_DASHBOARD_NAME}.yml")
+
+  def initialize(project)
+    @project = project
+  end
 
   # Returns a DB-supplemented json representation of a dashboard config file.
   def get_dashboard
@@ -26,6 +30,6 @@ class MetricsDashboardService
   # TODO: "Processing" the dashboard needs to include several steps such as
   # inserting metric ids and alert information.
   def process_dashboard(dashboard)
-    dashboard.to_json
+    MetricsDashboardProcessingService.new(dashboard, @project).process
   end
 end