public string addSubForum(string forumName, string subForumName, List <Tuple <string, string, int> > moderators,
                                  string requestingUser)
        {
            if (moderators == null)
            {
                return(Constants.INVALID_INPUT);
            }
            List <string> input = new List <string>()
            {
                forumName, subForumName
            };

            foreach (Tuple <string, string, int> t in moderators)
            {
                input.Add(t.Item1);
                //input.Add(t.Item2);
            }
            if (Constants.isValidInput(input))
            {
                lock (o)
                {
                    int maxNumOfModerators = _fm.getForumMaxModerators(forumName);
                    if (maxNumOfModerators == -1)
                    {
                        return(Constants.forumDoesntExist(forumName));
                    }
                    if (moderators.Count > maxNumOfModerators)
                    {
                        return(Constants.ILLEGAL_ACTION);
                    }
                    int    seniority = _fm.getForumSeniorityLimit(forumName);
                    string res       = _um.addSubForum(forumName, subForumName, moderators, requestingUser, seniority);
                    if (res.Equals(Constants.SUCCESS))
                    {
                        return(_fm.addSubForum(forumName, subForumName));
                    }
                    return(res);
                }
            }
            return(Constants.INVALID_INPUT);
        }