Support dashboard params for metrics dashboard

https://gitlab.com/gitlab-org/gitlab-ce/issues/62971

Adds support to EnvironmentsController#metrics_dashboard
for the following params: group, title, y_label
These params are used to uniquely identify a panel on
the metrics dashboard.

Metrics are stored in several places, so this adds
utilities to find a specific panel from the database
or filesystem depending on the metric specified.

Also moves some shared utilities into separate classes,
notably default values and errors.

2 files changed, 18 insertions, 6 deletions

diff --git a/app/models/prometheus_metric.rb b/app/models/prometheus_metric.rb
index b8e7673dcf5..c7786500c5c 100644
--- a/app/models/prometheus_metric.rb
+++ b/app/models/prometheus_metric.rb
@@ -32,6 +32,10 @@ class PrometheusMetric < ApplicationRecord
     Gitlab::Prometheus::Metric.new(id: id, title: title, required_metrics: required_metrics, weight: 0, y_label: y_label, queries: queries)
   end
 
+  def to_metric_hash
+    queries.first.merge(metric_id: id)
+  end
+
   def queries
     [
       {
diff --git a/app/models/prometheus_metric_enums.rb b/app/models/prometheus_metric_enums.rb
index 6cb22cc69cd..d58f825f222 100644
--- a/app/models/prometheus_metric_enums.rb
+++ b/app/models/prometheus_metric_enums.rb
@@ -9,13 +9,17 @@ module PrometheusMetricEnums
       aws_elb: -3,
       nginx: -4,
       kubernetes: -5,
-      nginx_ingress: -6,
+      nginx_ingress: -6
+    }.merge(custom_groups).freeze
+  end
 
-      # custom/user groups
+  # custom/user groups
+  def self.custom_groups
+    {
       business: 0,
       response: 1,
       system: 2
-    }
+    }.freeze
   end
 
   def self.group_details
@@ -50,16 +54,20 @@ module PrometheusMetricEnums
         group_title: _('System metrics (Kubernetes)'),
         required_metrics: %w(container_memory_usage_bytes container_cpu_usage_seconds_total),
         priority: 5
-      }.freeze,
+      }.freeze
+    }.merge(custom_group_details).freeze
+  end
 
-      # custom/user groups
+  # custom/user groups
+  def self.custom_group_details
+    {
       business: {
         group_title: _('Business metrics (Custom)'),
         priority: 0
       }.freeze,
       response: {
         group_title: _('Response metrics (Custom)'),
-      priority: -5
+        priority: -5
       }.freeze,
       system: {
         group_title: _('System metrics (Custom)'),