public string UploadFiles(int respondentId)
        {
            var result = "";

            if (Request == null || Request.Files == null || Request.Files.Count == 0)
            {
                return("Не выбрано ни одного файла");
            }

            if (SM.CurrentUserIsNull)
            {
                return("Для загрузки файлов необходимо авторизоваться на сайте");
            }

            var files  = new List <UserFile>();
            var userId = SM.CurrentUserId;

            var message = new Message
            {
                SenderId    = userId,
                RecipientId = respondentId,
                Text        = "Прикрепленные файлы:",
                Files       = new List <UserFile>()
            };
            var messageId = UserHelper.AddMessage(message);

            message.Id = messageId;

            foreach (string upload in Request.Files)
            {
                var uploadFile = Request.Files[upload];
                if (uploadFile == null || uploadFile.ContentLength == 0)
                {
                    continue;
                }

                var byteCount = uploadFile.ContentLength;
                if (byteCount > 50 * 1024 * 1024)
                {
                    result += "error,0,0";
                    continue;
                }

                string filename  = uploadFile.FileName;
                var    extension = Path.GetExtension(filename);
                if (extension != null)
                {
                    extension = extension.Replace(".", "");
                    filename  = filename.Substring(0, filename.IndexOf(extension) - 1);
                }

                var deniedExtensions = new List <string>()
                {
                    "exe", "js"
                };
                if (deniedExtensions.Contains(extension))
                {
                    return("Запрещено загружать файлы с расширением " + extension);
                }

                //var isImage = new List<string>() { "jpg", "jpeg", "png" }.Contains(extension);

                var file = new UserFile()
                {
                    UserId         = userId,
                    MessageId      = 0,
                    Name           = filename,
                    Extension      = extension,
                    ModerateResult = ModerateResults.NotChecked,
                    Added          = DateTime.Now.ToUniversalTime(),
                    Changed        = DateTime.Now.ToUniversalTime()
                };
                message.Files.Add(file);
                file.MessageId = messageId;

                try
                {
                    var folder = GetFileDirectoryForFiles(file);
                    if (!Directory.Exists(folder))
                    {
                        Directory.CreateDirectory(folder);
                    }
                    uploadFile.SaveAs(file.FullPath);
                    files.Add(file);
                    result += $"ok,{file.NameWithExtension},{file.Url}|";
                }
                catch (Exception ex)
                {
                    result = "error";
                    LogsDAL.AddError("in UserController.UploadFile(): userId = " + file.UserId + ", exception: " + ex);
                    return(result);
                }
            }

            SM.AddMessageToCurrentDialogs(message);

            FilesDAL.AddFiles(files);

            return(result);
        }