#399

backend/app/services/preview/known_site_extractor.rb

@@ -4,6 +4,15 @@ module Preview
       youtube_thumbnail(uri)
     end
 
+    def self.youtube_video_id(uri)
+      case uri.host&.downcase
+      when 'youtu.be'
+        uri.path.split('/').reject(&:blank?).first
+      when 'www.youtube.com', 'youtube.com', 'm.youtube.com'
+        uri.path == '/watch' ? URI.decode_www_form(uri.query.to_s).to_h['v'] : nil
+      end&.then { _1 if _1.match?(/\A[A-Za-z0-9_-]{6,20}\z/) }
+    end
+
     def self.niconico_video_id(uri)
       case uri.host&.downcase
       when 'www.nicovideo.jp', 'nicovideo.jp'
@@ -14,14 +23,8 @@ module Preview
     end
 
     def self.youtube_thumbnail(uri)
-      id =
-          case uri.host&.downcase
-          when 'youtu.be'
-            uri.path.split('/').reject(&:blank?).first
-          when 'www.youtube.com', 'youtube.com', 'm.youtube.com'
-            uri.path == '/watch' ? URI.decode_www_form(uri.query.to_s).to_h['v'] : nil
-          end
-      return unless id&.match?(/\A[A-Za-z0-9_-]{6,20}\z/)
+      id = youtube_video_id(uri)
+      return unless id
 
       "https://i.ytimg.com/vi/#{ id }/hqdefault.jpg"
     end