拷贝文件的一点问题

先判断文件夹有没有存在，不存在则先建文件夹，反之则copy
if (!Directory.Exists(FolderPath))
            {
                //文件夹不存在则创建
                Directory.CreateDirectory(FolderPath);
                //写入日志
                string FilePath = Server.MapPath("/LoginLog/" + DateTime.Now.ToString("yyyy-MM") + "/" + DateTime.Now.ToString("yyyy-MM-dd"));
                if (!Directory.Exists(FilePath))
                {
                    //如果文件存在则写入日志
                    using (StreamWriter writer = File.AppendText(FilePath + ".txt"))
                    {
                        writer.WriteLine("[登录成功！][用户IP]：" + ip + "； [登录时间]：" + DateTime.Now);
                        writer.Flush();
                        writer.Close();
                    }
                }
                else
                {
                    //如果文件不存在当前目录下创建一个文本文件  
                    StreamWriter writer = new StreamWriter(FilePath + ".txt");                    writer.WriteLine("[登录成功！][用户IP]：" + ip + "； [登录时间]：" + DateTime.Now);
                    writer.Flush();
                    writer.Close();
                }
            }
            else
            {
                //文件夹存在则写入日志
                string FilePath = Server.MapPath("/LoginLog/" + DateTime.Now.ToString("yyyy-MM") + "/" + DateTime.Now.ToString("yyyy-MM-dd"));
                if (!Directory.Exists(FilePath))
                {
                    //如果文件存在则写入日志
                    using (StreamWriter writer = File.AppendText(FilePath + ".txt"))
                    {
                        writer.WriteLine("[登录成功！][用户IP]：" + ip + "； [登录时间]：" + DateTime.Now);
                        writer.Flush();
                        writer.Close();
                    }
                }
                else
                {
                    //如果文件不存在当前目录下创建一个文本文件  
                    StreamWriter writer = new StreamWriter(FilePath + ".txt");                    writer.WriteLine("[登录成功！][用户IP]：" + ip + "； [登录时间]：" + DateTime.Now);
                    writer.Flush();
                    writer.Close();
                }
            }
            Response.Redirect("ManageLogin/");
        }