FEATURE: Add githubfolder engine (#440)

* FEATURE: Add an engine for deep linking to folders in Github repos

* DEV: add favicon

lib/onebox/engine.rb

@@ -152,6 +152,7 @@ def always_https?
 require_relative "engine/github_issue_onebox"
 require_relative "engine/github_blob_onebox"
 require_relative "engine/github_commit_onebox"
+require_relative "engine/github_folder_onebox"
 require_relative "engine/github_gist_onebox"
 require_relative "engine/github_pullrequest_onebox"
 require_relative "engine/google_calendar_onebox"

lib/onebox/engine/github_folder_onebox.rb

@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+module Onebox
+  module Engine
+    class GithubFolderOnebox
+      include Engine
+      include StandardEmbed
+      include LayoutSupport
+
+      matches_regexp Regexp.new(/^https?:\/\/(?:www\.)?(?:(?:\w)+\.)?(github)\.com[\:\d]*(\/\w*){2}\/tree/)
+      always_https
+
+      private
+
+      def data
+        og = get_opengraph
+
+        max_length = 250
+
+        display_path = extract_path(og.url, max_length)
+        display_description = clean_description(og.description, og.title, max_length)
+
+        {
+          link: og.url,
+          path_link: url,
+          image: og.image,
+          title: og.title,
+          path: display_path,
+          description: display_description,
+          favicon: get_favicon
+        }
+      end
+
+      def extract_path(root, max_length)
+        path = url.split('#')[0].split('?')[0]
+        path = path["#{root}/tree/".length..-1]
+        path.length > max_length ? path[-max_length..-1] : path
+      end
+
+      def clean_description(description, title, max_length)
+        return unless description
+
+        desc_end = " - #{title}"
+        if description[-desc_end.length..-1] == desc_end
+          description = description[0...-desc_end.length]
+        end
+
+        Onebox::Helpers.truncate(description, max_length)
+      end
+    end
+  end
+end