A time logger

using System;
using System.IO;

namespace Microsoft.Dnx.Testing
{
    public class TimeLogger
    {
        private readonly string _file;

        private TimeLogger()
        {
            _file = $@"C:\code\playground\wow\time{DateTime.Now.ToString("yyyyMMdd-hhmmss")}.log";

            using (File.CreateText(_file)) ;
        }

        public static TimeLogger Instance = new TimeLogger();
        public void Log(DateTime beginning, string category)
        {
            Log(beginning, category, null);
        }

        public void Log(DateTime beginning, string category, string remark)
        {
            var elapsed = (DateTime.Now - beginning).TotalMilliseconds;
            File.AppendAllLines(_file, new string[] { $"{elapsed}, {category}, {remark ?? string.Empty}" });
        }
    }
}