Add a Cluster Metric Embed Banzai Filter

Part of the work to, embed cluster health metrics charts in any
Notable (comment, issue description) via adding a url to the gitlab
chart in a field that supports Gilab Flafored Markdown(GFM).
This MR adds a div with a distinctive class name related to metrics to
a Gitlab Flavored Markdown field. The field is redacted by default based
on its class name because permissions are not yet added to
permissions_by_route in this MR.

ee/lib/banzai/filter/inline_cluster_metrics_filter.rb

+# frozen_string_literal: true
+
+module Banzai
+  module Filter
+    class InlineClusterMetricsFilter < ::Banzai::Filter::InlineEmbedsFilter
+      include ::Gitlab::Utils::StrongMemoize
+
+      def create_element(params)
+        doc.document.create_element(
+          'div',
+          class: 'js-render-metrics',
+          'data-dashboard-url': metrics_dashboard_url(params)
+        )
+      end
+
+      def embed_params(node)
+        url = node['href']
+
+        return unless [:group, :title, :y_label].all? do |param|
+          query_params(url).include?(param)
+        end
+
+        link_pattern.match(url) { |m| m.named_captures }.symbolize_keys
+      end
+
+      def xpath_search
+        "descendant-or-self::a[contains(@href,'clusters') and \
+          starts-with(@href, '#{::Gitlab.config.gitlab.url}')]"
+      end
+
+      def link_pattern
+        ::Gitlab::Metrics::Dashboard::Url.clusters_regex
+      end
+
+      def metrics_dashboard_url(params)
+        ::Gitlab::Routing.url_helpers.metrics_dashboard_namespace_project_cluster_url(
+          params[:namespace],
+          params[:project],
+          params[:cluster_id],
+          # Only Project clusters are supported for now
+          # admin and group cluster types may be supported in the future
+          cluster_type: 'project',
+          embedded: true,
+          format: :json,
+          **query_params(params['url'])
+        )
+      end
+    end
+  end
+end

ee/lib/ee/banzai/pipeline/gfm_pipeline.rb

@@ -14,6 +14,13 @@ module EE
               *super
             ]
           end
+
+          def metrics_filters
+            [
+              ::Banzai::Filter::InlineClusterMetricsFilter,
+              *super
+            ]
+          end
         end
       end
     end

ee/spec/lib/banzai/filter/inline_cluster_metrics_filter_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Banzai::Filter::InlineClusterMetricsFilter do
+  include FilterSpecHelper
+
+  let!(:cluster) { create(:cluster) }
+  let!(:project) { create(:project) }
+  let(:params) { [project.path, project.namespace.path, cluster.id] }
+  let(:query_params) { { group: 'Food metrics', title: 'Pizza Consumption', y_label: 'Slice Count' } }
+
+  let(:trigger_url) { urls.metrics_namespace_project_cluster_url(*params, **query_params) }
+  let(:dashboard_url) do
+    urls.metrics_dashboard_namespace_project_cluster_url(
+      *params,
+      **{
+        embedded: true,
+        cluster_type: 'project',
+        format: :json
+      }.merge(query_params)
+    )
+  end
+
+  it_behaves_like 'a metrics embed filter'
+end

lib/banzai/filter/inline_embeds_filter.rb

@@ -6,6 +6,7 @@ module Banzai
     # a given link format. To transform references to DB
     # resources in place, prefer to inherit from AbstractReferenceFilter.
     class InlineEmbedsFilter < HTML::Pipeline::Filter
+      include Gitlab::Utils::StrongMemoize
       # Find every relevant link, create a new node based on
       # the link, and insert this node after any html content
       # surrounding the link.
@@ -60,6 +61,16 @@ module Banzai
 
         link_pattern.match(url) { |m| m.named_captures }
       end
+
+      # Parses query params out from full url string into hash.
+      #
+      # Ex) 'https://<root>/<project>/<environment>/metrics?title=Title&group=Group'
+      #       --> { title: 'Title', group: 'Group' }
+      def query_params(url)
+        strong_memoize(:query_params) do
+          Gitlab::Metrics::Dashboard::Url.parse_query(url)
+        end
+      end
     end
   end
 end