public async Task <ICollection <HistoryData> > GetUserHistory(string username)
        {
            ICollection <IHistory> history = await marketUsers.GetUserHistory(username);

            ICollection <HistoryData> ret = new HashSet <HistoryData>();

            foreach (var h in history)
            {
                ret.Add(new HistoryData(h));
            }
            return(ret);
        }