Expose metrics element for FE consumption

Adds GFM Pipline filters to insert a placeholder in the generated
HTML from GFM based on the presence of a metrics dashboard link.

The front end should look for the class 'js-render-metrics' to
determine if it should replace the element with metrics charts.
The data element 'data-dashboard-url' should be the endpoint
the front end should hit in order to obtain a dashboard layout
in order to appropriately render the charts.

3 files changed, 169 insertions, 0 deletions

diff --git a/spec/lib/banzai/filter/inline_metrics_filter_spec.rb b/spec/lib/banzai/filter/inline_metrics_filter_spec.rb
new file mode 100644
index 00000000000..772c94e3180
--- /dev/null
+++ b/spec/lib/banzai/filter/inline_metrics_filter_spec.rb
@@ -0,0 +1,55 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Banzai::Filter::InlineMetricsFilter do
+  include FilterSpecHelper
+
+  let(:input) { %(<a href="#{url}">example</a>) }
+  let(:doc) { filter(input) }
+
+  context 'when the document has an external link' do
+    let(:url) { 'https://foo.com' }
+
+    it 'leaves regular non-metrics links unchanged' do
+      expect(doc.to_s).to eq input
+    end
+  end
+
+  context 'when the document has a metrics dashboard link' do
+    let(:params) { ['foo', 'bar', 12] }
+    let(:url) { urls.metrics_namespace_project_environment_url(*params) }
+
+    it 'leaves the original link unchanged' do
+      expect(doc.at_css('a').to_s).to eq input
+    end
+
+    it 'appends a metrics charts placeholder with dashboard url after metrics links' do
+      node = doc.at_css('.js-render-metrics')
+      expect(node).to be_present
+
+      dashboard_url = urls.metrics_dashboard_namespace_project_environment_url(*params, embedded: true)
+      expect(node.attribute('data-dashboard-url').to_s).to eq dashboard_url
+    end
+
+    context 'when the metrics dashboard link is part of a paragraph' do
+      let(:paragraph) { %(This is an <a href="#{url}">example</a> of metrics.) }
+      let(:input) { %(<p>#{paragraph}</p>) }
+
+      it 'appends the charts placeholder after the enclosing paragraph' do
+        expect(doc.at_css('p').to_s).to include paragraph
+        expect(doc.at_css('.js-render-metrics')).to be_present
+      end
+
+      context 'when the feature is disabled' do
+        before do
+          stub_feature_flags(gfm_embedded_metrics: false)
+        end
+
+        it 'does nothing' do
+          expect(doc.to_s).to eq input
+        end
+      end
+    end
+  end
+end
diff --git a/spec/lib/banzai/filter/inline_metrics_redactor_filter_spec.rb b/spec/lib/banzai/filter/inline_metrics_redactor_filter_spec.rb
new file mode 100644
index 00000000000..fb2186e9d12
--- /dev/null
+++ b/spec/lib/banzai/filter/inline_metrics_redactor_filter_spec.rb
@@ -0,0 +1,58 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Banzai::Filter::InlineMetricsRedactorFilter do
+  include FilterSpecHelper
+
+  set(:project) { create(:project) }
+
+  let(:url) { urls.metrics_dashboard_project_environment_url(project, 1, embedded: true) }
+  let(:input) { %(<a href="#{url}">example</a>) }
+  let(:doc) { filter(input) }
+
+  context 'when the feature is disabled' do
+    before do
+      stub_feature_flags(gfm_embedded_metrics: false)
+    end
+
+    it 'does nothing' do
+      expect(doc.to_s).to eq input
+    end
+  end
+
+  context 'without a metrics charts placeholder' do
+    it 'leaves regular non-metrics links unchanged' do
+      expect(doc.to_s).to eq input
+    end
+  end
+
+  context 'with a metrics charts placeholder' do
+    let(:input) { %(<div class="js-render-metrics" data-dashboard-url="#{url}"></div>) }
+
+    context 'no user is logged in' do
+      it 'redacts the placeholder' do
+        expect(doc.to_s).to be_empty
+      end
+    end
+
+    context 'the user does not have permission do see charts' do
+      let(:doc) { filter(input, current_user: build(:user)) }
+
+      it 'redacts the placeholder' do
+        expect(doc.to_s).to be_empty
+      end
+    end
+
+    context 'the user has requisite permissions' do
+      let(:user) { create(:user) }
+      let(:doc) { filter(input, current_user: user) }
+
+      it 'leaves the placeholder' do
+        project.add_maintainer(user)
+
+        expect(doc.to_s).to eq input
+      end
+    end
+  end
+end
diff --git a/spec/lib/gitlab/metrics/dashboard/url_spec.rb b/spec/lib/gitlab/metrics/dashboard/url_spec.rb
new file mode 100644
index 00000000000..34bc6359414
--- /dev/null
+++ b/spec/lib/gitlab/metrics/dashboard/url_spec.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Metrics::Dashboard::Url do
+  describe '#regex' do
+    it 'returns a regular expression' do
+      expect(described_class.regex).to be_a Regexp
+    end
+
+    it 'matches a metrics dashboard link with named params' do
+      url = Gitlab::Routing.url_helpers.metrics_namespace_project_environment_url('foo', 'bar', 1, start: 123345456, anchor: 'title')
+
+      expected_params = {
+        'url' => url,
+        'namespace' => 'foo',
+        'project' => 'bar',
+        'environment' => '1',
+        'query' => '?start=123345456',
+        'anchor' => '#title'
+      }
+
+      expect(described_class.regex).to match url
+
+      described_class.regex.match(url) do |m|
+        expect(m.named_captures).to eq expected_params
+      end
+    end
+
+    it 'does not match other gitlab urls that contain the term metrics' do
+      url = Gitlab::Routing.url_helpers.active_common_namespace_project_prometheus_metrics_url('foo', 'bar', :json)
+
+      expect(described_class.regex).not_to match url
+    end
+
+    it 'does not match other gitlab urls' do
+      url = Gitlab.config.gitlab.url
+
+      expect(described_class.regex).not_to match url
+    end
+
+    it 'does not match non-gitlab urls' do
+      url = 'https://www.super_awesome_site.com/'
+
+      expect(described_class.regex).not_to match url
+    end
+  end
+
+  describe '#build_dashboard_url' do
+    it 'builds the url for the dashboard endpoint' do
+      url = described_class.build_dashboard_url('foo', 'bar', 1)
+
+      expect(url).to match described_class.regex
+    end
+  end
+end