SendNotify/Log.cs

namespace SendNotify
{
    internal class Log
    {
        private static object obj = new object();
        public static void Logger(string str)
        {
            lock (obj)
            {
                string outdir = Environment.CurrentDirectory + @"\logs\";
                if (!Directory.Exists(outdir)) Directory.CreateDirectory(outdir);
                string filename = $"{DateTime.Now.Day}_{DateTime.Now.Month}_{DateTime.Now.Year}_SendNotify";

                foreach (FileInfo file in new DirectoryInfo(outdir).GetFiles())
                {
                    if (Convert.ToDateTime(file.LastWriteTime) < DateTime.Now.AddDays(-30))
                        file.Delete();
                }

                using (FileStream aFile = new FileStream($@"{outdir}\{filename}.log", FileMode.Append, FileAccess.Write))
                using (StreamWriter sw = new StreamWriter(aFile))
                {
                    sw.WriteLine(DateTime.Now + " - " + str);
                }
            }
        }
    }
}