1 files changed, 100 insertions, 0 deletions
diff --git a/lib/gitlab/markdown/abstract_reference_filter.rb b/lib/gitlab/markdown/abstract_reference_filter.rb
new file mode 100644
index 00000000000..fd5b7eb9332
--- /dev/null
+++ b/lib/gitlab/markdown/abstract_reference_filter.rb
@@ -0,0 +1,100 @@
+require 'gitlab/markdown'
+
+module Gitlab
+  module Markdown
+    # Issues, Snippets and Merge Requests shares similar functionality in refernce filtering.
+    # All this functionality moved to this class
+    class AbstractReferenceFilter < ReferenceFilter
+      include CrossProjectReference
+
+      def self.object_class
+        # Implement in child class
+        # Example: MergeRequest
+      end
+
+      def self.object_name
+        object_class.name.underscore
+      end
+
+      def self.object_sym
+        object_name.to_sym
+      end
+
+      def self.data_reference
+        "data-#{object_name.dasherize}"
+      end
+
+      # Public: Find references in text (like `!123` for merge requests)
+      #
+      #   AnyReferenceFilter.references_in(text) do |match, object|
+      #     "<a href=...>PREFIX#{object}</a>"
+      #   end
+      #
+      # PREFIX - symbol that detects reference (like ! for merge requests)
+      # object - reference object (snippet, merget request etc)
+      # text - String text to search.
+      #
+      # Yields the String match, the Integer referenced object ID, and an optional String
+      # of the external project reference.
+      #
+      # Returns a String replaced with the return of the block.
+      def self.references_in(text)
+        text.gsub(object_class.reference_pattern) do |match|
+          yield match, $~[object_sym].to_i, $~[:project]
+        end
+      end
+
+      def self.referenced_by(node)
+        { object_sym => LazyReference.new(object_class, node.attr(data_reference)) }
+      end
+
+      delegate :object_class, :object_sym, :references_in, to: :class
+
+      def find_object(project, id)
+        # Implement in child class
+        # Example: project.merge_requests.find
+      end
+
+      def url_for_object(object, project)
+        # Implement in child class
+        # Example: project_merge_request_url
+      end
+
+      def call
+        replace_text_nodes_matching(object_class.reference_pattern) do |content|
+          object_link_filter(content)
+        end
+      end
+
+      # Replace references (like `!123` for merge requests) in text with links
+      # to the referenced object's details page.
+      #
+      # text - String text to replace references in.
+      #
+      # Returns a String with references replaced with links. All links
+      # have `gfm` and `gfm-OBJECT_NAME` class names attached for styling.
+      def object_link_filter(text)
+        references_in(text) do |match, id, project_ref|
+          project = project_from_ref(project_ref)
+
+          if project && object = find_object(project, id)
+            title = escape_once("#{object_title}: #{object.title}")
+            klass = reference_class(object_sym)
+            data  = data_attribute(project: project.id, object_sym => object.id)
+            url = url_for_object(object, project)
+
+            %(<a href="#{url}" #{data}
+                 title="#{title}"
+                 class="#{klass}">#{match}</a>)
+          else
+            match
+          end
+        end
+      end
+
+      def object_title
+        object_class.name.titleize
+      end
+    end
+  end
+end