public function addParticipants($userIds)
    {
        if (is_array($userIds)) {
            foreach ($userIds as $id) {
                $this->users()->attach($id);
            }
        } else {
            $this->users()->attach($userIds);
        }

        if (Chat::makeThreeOrMoreUsersPublic() && $this->fresh()->users->count() > 2) {
            $this->private = false;
            $this->save();
        }

        return $this;
    }