using System;

using DaleNewman;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string test = ReplaceDateMath("__DATEMATH(now-1M/M)__");

        Console.WriteLine(test);

        string test2 = ReplaceDateMath("__DATEMATH(now-1M/M):o__");

        Console.WriteLine(test2);

        string test3 = ReplaceDateMath("__TODAY:F__");

        Console.WriteLine(test3);

        string test4 = ReplaceDateMath("__TODAY__");

        Console.WriteLine(test4);

        string test5 = ReplaceDateMath("someurl");

        Console.WriteLine(test5);

        string test6 = ReplaceDateMath("someurl with __TODAY:F__");

        Console.WriteLine(test6);

    }

​

    public static string ReplaceDateMath(string input)

    {

        if (input == "__THISYEAR__")

            return DateTime.UtcNow.Year.ToString();

        var retVal = input;

        string dateMathPattern = "__DATEMATH\\((.+?)\\):{0,1}(.*?)__";

        string todayPattern = "__TODAY:{0,1}(.*?)__";

        if (Regex.IsMatch(input, dateMathPattern))

        {

            var match = Regex.Match(input, dateMathPattern);

            var dateMathExpression = match.Groups[1].Value;

            var dateFormat = !string.IsNullOrEmpty(match.Groups[2].Value) ? match.Groups[2].Value : "yyyyMMdd";

            DateTime date;

            if (DateMath.TryParse(dateMathExpression, out date))

            {

                retVal = Regex.Replace(input, dateMathPattern, date.ToString(dateFormat));

            }

        }

        else if (Regex.IsMatch(input, todayPattern))

        {

            var match = Regex.Match(input, todayPattern);

            var dateFormat = !string.IsNullOrEmpty(match.Groups[1].Value) ? match.Groups[1].Value : "yyyyMMdd";

            retVal = Regex.Replace(input, todayPattern, DateTime.UtcNow.ToString(dateFormat));

​

        }

​

        return retVal;

​

    }

}