1 files changed, 96 insertions, 0 deletions
diff --git a/lib/banzai/filter/label_reference_filter.rb b/lib/banzai/filter/label_reference_filter.rb
new file mode 100644
index 00000000000..07bac2dd7fd
--- /dev/null
+++ b/lib/banzai/filter/label_reference_filter.rb
@@ -0,0 +1,96 @@
+require 'banzai'
+
+module Banzai
+  module Filter
+    # HTML filter that replaces label references with links.
+    class LabelReferenceFilter < ReferenceFilter
+      # Public: Find label references in text
+      #
+      #   LabelReferenceFilter.references_in(text) do |match, id, name|
+      #     "<a href=...>#{Label.find(id)}</a>"
+      #   end
+      #
+      # text - String text to search.
+      #
+      # Yields the String match, an optional Integer label ID, and an optional
+      # String label name.
+      #
+      # Returns a String replaced with the return of the block.
+      def self.references_in(text)
+        text.gsub(Label.reference_pattern) do |match|
+          yield match, $~[:label_id].to_i, $~[:label_name]
+        end
+      end
+
+      def self.referenced_by(node)
+        { label: LazyReference.new(Label, node.attr("data-label")) }
+      end
+
+      def call
+        replace_text_nodes_matching(Label.reference_pattern) do |content|
+          label_link_filter(content)
+        end
+
+        replace_link_nodes_with_href(Label.reference_pattern) do |link, text|
+          label_link_filter(link, link_text: text)
+        end
+      end
+
+      # Replace label references in text with links to the label specified.
+      #
+      # text - String text to replace references in.
+      #
+      # Returns a String with label references replaced with links. All links
+      # have `gfm` and `gfm-label` class names attached for styling.
+      def label_link_filter(text, link_text: nil)
+        project = context[:project]
+
+        self.class.references_in(text) do |match, id, name|
+          params = label_params(id, name)
+
+          if label = project.labels.find_by(params)
+            url = url_for_label(project, label)
+            klass = reference_class(:label)
+            data = data_attribute(
+              original: link_text || match,
+              project: project.id,
+              label: label.id
+            )
+
+            text = link_text || render_colored_label(label)
+
+            %(<a href="#{url}" #{data}
+                 class="#{klass}">#{text}</a>)
+          else
+            match
+          end
+        end
+      end
+
+      def url_for_label(project, label)
+        h = Gitlab::Application.routes.url_helpers
+        h.namespace_project_issues_url( project.namespace, project, label_name: label.name,
+                                                                    only_path:  context[:only_path])
+      end
+
+      def render_colored_label(label)
+        LabelsHelper.render_colored_label(label)
+      end
+
+      # Parameters to pass to `Label.find_by` based on the given arguments
+      #
+      # id   - Integer ID to pass. If present, returns {id: id}
+      # name - String name to pass. If `id` is absent, finds by name without
+      #        surrounding quotes.
+      #
+      # Returns a Hash.
+      def label_params(id, name)
+        if name
+          { name: name.tr('"', '') }
+        else
+          { id: id }
+        end
+      end
+    end
+  end
+end