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.

8 files changed, 272 insertions, 21 deletions

diff --git a/app/controllers/projects/environments_controller.rb b/app/controllers/projects/environments_controller.rb
index ccd54b369fa..07eb689d031 100644
--- a/app/controllers/projects/environments_controller.rb
+++ b/app/controllers/projects/environments_controller.rb
@@ -165,7 +165,8 @@ class Projects::EnvironmentsController < Projects::ApplicationController
         project,
         current_user,
         environment,
-        embedded: params[:embedded]
+        dashboard_path: params[:dashboard],
+        **dashboard_params.to_h.symbolize_keys
       )
     elsif Feature.enabled?(:environment_metrics_show_multiple_dashboards, project)
       result = dashboard_finder.find(
@@ -233,6 +234,10 @@ class Projects::EnvironmentsController < Projects::ApplicationController
     params.require([:start, :end])
   end
 
+  def dashboard_params
+    params.permit(:embedded, :group, :title, :y_label)
+  end
+
   def dashboard_finder
     Gitlab::Metrics::Dashboard::Finder
   end
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)'),
diff --git a/app/services/metrics/dashboard/base_embed_service.rb b/app/services/metrics/dashboard/base_embed_service.rb
new file mode 100644
index 00000000000..8bb5f4892cb
--- /dev/null
+++ b/app/services/metrics/dashboard/base_embed_service.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+# Base class for embed services. Contains a few basic helper
+# methods that the embed services share.
+module Metrics
+  module Dashboard
+    class BaseEmbedService < ::Metrics::Dashboard::BaseService
+      def cache_key
+        "dynamic_metrics_dashboard_#{identifiers}"
+      end
+
+      protected
+
+      def dashboard_path
+        params[:dashboard_path].presence ||
+          ::Metrics::Dashboard::SystemDashboardService::SYSTEM_DASHBOARD_PATH
+      end
+
+      def group
+        params[:group]
+      end
+
+      def title
+        params[:title]
+      end
+
+      def y_label
+        params[:y_label]
+      end
+
+      def identifiers
+        [dashboard_path, group, title, y_label].join('|')
+      end
+    end
+  end
+end
diff --git a/app/services/metrics/dashboard/base_service.rb b/app/services/metrics/dashboard/base_service.rb
index b331bf51874..8a42675c66d 100644
--- a/app/services/metrics/dashboard/base_service.rb
+++ b/app/services/metrics/dashboard/base_service.rb
@@ -5,17 +5,14 @@
 module Metrics
   module Dashboard
     class BaseService < ::BaseService
-      PROCESSING_ERROR = Gitlab::Metrics::Dashboard::Stages::BaseStage::DashboardProcessingError
-      NOT_FOUND_ERROR = Gitlab::Template::Finders::RepoTemplateFinder::FileNotFoundError
+      include Gitlab::Metrics::Dashboard::Errors
 
       def get_dashboard
         return error('Insufficient permissions.', :unauthorized) unless allowed?
 
         success(dashboard: process_dashboard)
-      rescue NOT_FOUND_ERROR
-        error("#{dashboard_path} could not be found.", :not_found)
-      rescue PROCESSING_ERROR => e
-        error(e.message, :unprocessable_entity)
+      rescue StandardError => e
+        handle_errors(e)
       end
 
       # Summary of all known dashboards for the service.
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
diff --git a/app/services/metrics/dashboard/default_embed_service.rb b/app/services/metrics/dashboard/default_embed_service.rb
index 8b01b44fc98..e1bd98bd5c2 100644
--- a/app/services/metrics/dashboard/default_embed_service.rb
+++ b/app/services/metrics/dashboard/default_embed_service.rb
@@ -1,9 +1,9 @@
 # frozen_string_literal: true
 
 # Responsible for returning a filtered system dashboard
-# containing only the default embedded metrics. In future,
-# this class may be updated to support filtering to
-# alternate metrics/panels.
+# containing only the default embedded metrics. This class
+# operates by selecting metrics directly from the system
+# dashboard.
 #
 # Why isn't this filtering in a processing stage? By filtering
 # here, we ensure the dynamically-determined dashboard is cached.
@@ -11,7 +11,7 @@
 # Use Gitlab::Metrics::Dashboard::Finder to retrive dashboards.
 module Metrics
   module Dashboard
-    class DefaultEmbedService < ::Metrics::Dashboard::BaseService
+    class DefaultEmbedService < ::Metrics::Dashboard::BaseEmbedService
       # For the default filtering for embedded metrics,
       # uses the 'id' key in dashboard-yml definition for
       # identification.
@@ -33,10 +33,6 @@ module Metrics
         { 'panel_groups' => [{ 'panels' => panels }] }
       end
 
-      def cache_key
-        "dynamic_metrics_dashboard_#{metric_identifiers.join('_')}"
-      end
-
       private
 
       # Returns an array of the panels groups on the
@@ -58,6 +54,10 @@ module Metrics
       def metric_identifiers
         DEFAULT_EMBEDDED_METRICS_IDENTIFIERS
       end
+
+      def identifiers
+        metric_identifiers.join('|')
+      end
     end
   end
 end
diff --git a/app/services/metrics/dashboard/dynamic_embed_service.rb b/app/services/metrics/dashboard/dynamic_embed_service.rb
new file mode 100644
index 00000000000..db5b7c9e32a
--- /dev/null
+++ b/app/services/metrics/dashboard/dynamic_embed_service.rb
@@ -0,0 +1,78 @@
+# frozen_string_literal: true
+
+# Responsible for returning a filtered project dashboard
+# containing only the request-provided metrics. The result
+# is then cached for future requests. Metrics are identified
+# based on a combination of identifiers for now, but the ideal
+# would be similar to the approach in DefaultEmbedService, but
+# a single unique identifier is not currently available across
+# all metric types (custom, project-defined, cluster, or system).
+#
+# Use Gitlab::Metrics::Dashboard::Finder to retrive dashboards.
+module Metrics
+  module Dashboard
+    class DynamicEmbedService < ::Metrics::Dashboard::BaseEmbedService
+      include Gitlab::Utils::StrongMemoize
+
+      class << self
+        # Determines whether the provided params are sufficient
+        # to uniquely identify a panel from a yml-defined dashboard.
+        #
+        # See https://docs.gitlab.com/ee/user/project/integrations/prometheus.html#defining-custom-dashboards-per-project
+        # for additional info on defining custom dashboards.
+        def valid_params?(params)
+          [
+            params[:embedded],
+            params[:group].present?,
+            params[:title].present?,
+            params[:y_label]
+          ].all?
+        end
+      end
+
+      # Returns a new dashboard with only the matching
+      # metrics from the system dashboard, stripped of groups.
+      # @return [Hash]
+      def get_raw_dashboard
+        not_found! if panels.empty?
+
+        { 'panel_groups' => [{ 'panels' => panels }] }
+      end
+
+      private
+
+      def panels
+        strong_memoize(:panels) do
+          not_found! unless base_dashboard
+          not_found! unless groups = base_dashboard['panel_groups']
+          not_found! unless matching_group = find_group(groups)
+          not_found! unless all_panels = matching_group['panels']
+
+          find_panels(all_panels)
+        end
+      end
+
+      def base_dashboard
+        strong_memoize(:base_dashboard) do
+          Gitlab::Metrics::Dashboard::Finder.find_raw(project, dashboard_path: dashboard_path)
+        end
+      end
+
+      def find_group(groups)
+        groups.find do |candidate_group|
+          candidate_group['group'] == group
+        end
+      end
+
+      def find_panels(all_panels)
+        all_panels.select do |panel|
+          panel['title'] == title && panel['y_label'] == y_label
+        end
+      end
+
+      def not_found!
+        panels_not_found!(identifiers)
+      end
+    end
+  end
+end