FEATURE: Remap group mentions when group name has been changed.

app/services/group_mentions_updater.rb

@@ -0,0 +1,14 @@
+class GroupMentionsUpdater
+  def self.update(current_name, previous_name)
+    Post.where(
+      "cooked LIKE '%class=\"mention-group\"%' AND raw LIKE :previous_name",
+      previous_name: "%@#{previous_name}%"
+    ).find_in_batches do |posts|
+
+      posts.each do |post|
+        post.raw.gsub!(/(^|\s)(@#{previous_name})(\s|$)/, "\\1@#{current_name}\\3")
+        post.save!
+      end
+    end
+  end
+end