private void DeleteUserHistoryAsync(TLChannel channel, TLInputUserBase userId, Action <TLAffectedHistory> callback, Action <TLRPCError> faultCallback = null)
 {
     MTProtoService.DeleteUserHistoryAsync(channel, userId,
                                           result =>
     {
         if (result.Offset.Value > 0)
         {
             DeleteUserHistoryAsync(channel, userId, callback, faultCallback);
         }
         else
         {
             callback.SafeInvoke(result);
         }
     },
                                           error =>
     {
         Telegram.Api.Helpers.Execute.ShowDebugMessage("channels.deleteUserHistory error " + error);
     });
 }