using System;using System.Linq;

public static class Program

{ 

    private static string seperator = "~"; //must be single character string, tilde is a valid filename char, may want to use a non-valid char for filenames.

    private const int leadingnumbers = 5;  //number of leading characters to build up to

    /// <summary>

    /// Format filename to a length (maxFileLen), by splitting filename into 1/3rd leading and 2/3rds ending until max leadingnumbers is reached. Used for toast nofications less than 41 characters by metadataconsulting.blogspot.com

    /// </summary>

    /// <param name="filename"></param>

    /// <param name="maxFileLen"></param>

    /// <returns></returns>

    public static string TrimMidFileNameFormat(this string filename, int maxFileLen)

    {

         Console.Write(string.Format("{0,5:###}", maxFileLen)+" "); //remove line when using in your library

​

         string ext = filename.GetFileNameExtension(); 

         int extLen = ext.Length;  //includes dot in length 

         string filenamelessext = filename.Substring(0, filename.Length - extLen);

         int filenamelessextLen = filenamelessext.Length;

         int maxroom = Math.Min(leadingnumbers * 2 - 1, filenamelessextLen); 

         int minLen  = 2 + 1 + extLen; //1st char + tilde.length(1) + last char + extLen(min 4) => 7 ie s~p.exe

         int lastLen = 1 + extLen; // last char + extLen(min 4) ie p.exe

​

         if (filename.Length <= maxFileLen)

            return filename;

         else if (filename.Length < minLen)

             return filename;

         else if (maxFileLen < minLen) //implied && filename.Length > maxFileLen) 

             return filename.Substring(0, 1) + seperator + filename.Substring(filename.Length-lastLen, lastLen);

         else if (maxFileLen >= minLen && maxFileLen < (maxroom + minLen)) //implied && filename.Length > maxFileLen) { //middle

         {

              int room = (maxFileLen - lastLen);         

              int one3rd = (3 + room - 1) / 3; //integer division with round up, old room/3 rounds down.

              int two3rds = room - one3rd;  

              return filename.Substring(0, one3rd) + seperator + filename.Substring(filename.Length-(two3rds + lastLen), (two3rds + lastLen));

         }

         else if (filename.Length > maxFileLen + leadingnumbers + 1) // > 2  + 1 + extLen (min 4)  

             return filename.Substring(0, leadingnumbers) + seperator + filename.Substring(filename.Length - maxFileLen, maxFileLen);

         else

             return filename;

    }

    private static Random random = new Random(); //not cryptographically secure

    public static string RandomString(int length) 

    {

        const string chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789!@#$%^*-.";

        return new string(Enumerable.Repeat(chars, length)

          .Select(s => s[random.Next(s.Length)]).ToArray());

    }

    /// <summary>

    /// Get filename extension, not ext of . only returns empty string, mirrors Path.GetExtension not try/catch issues by metadataconsulting.blogspot.com

    /// </summary>

    /// <param name="s"></param>

    /// <returns></returns>

    public static string GetFileNameExtension(this string s)

    {

        string ext = "";

        int fileExtPos = s.LastIndexOf('.');

        if (fileExtPos > s.LastIndexOf('\\'))

        {

            ext = s.Substring(fileExtPos, s.Length - fileExtPos);

            if (ext.Length <= 1) ext = "";

        }

        else

            ext = "";

        return ext;

    }  

​

    public static void Main()

    {

     string filename = ""; 

     for (int j = 1; j < 41; j++) {

         filename = RandomString(j) + ".exe";

         Console.WriteLine(filename); Console.WriteLine("Length=" + filename.Length); Console.WriteLine();

         for (int i = -1; i < filename.Length+3; i++)

            Console.WriteLine(filename.TrimMidFileNameFormat(i)); //7 min length viable name for shrinked name

         Console.WriteLine();

     }

    }

}