using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var billId = "bill-f71b7ec9-0ac7-4f73-a9eb-c81ef20ccb4f";

        var guidString = billId.Replace("bill-", "");

        Console.WriteLine("Getting shortId from {0}", guidString);

        // var shortId = GetShortId(billId);

        var shortGuid = new ShortGuid(Guid.Parse(guidString));

        Console.WriteLine($"The ShortGuid, \"{shortGuid}\", has {shortGuid.ToString().Length} characters." );

​

        var guidFromShortGuid = shortGuid.ToGuid();

        Console.WriteLine($"The original Guid:              {guidString}");

        Console.WriteLine($"Guid translated from ShortGuid: {guidFromShortGuid}");

    }

    public static string GetShortId(string billId)

    {

        var myGuidString = billId.Replace("bill-", "");

        return myGuidString.ToString();

    }

​

    public static Guid GetGuidFromShortId(string id)

    {

        return Guid.Parse(id);

    }

}

​

public class ShortGuid

{

    private readonly Guid guid;

    private readonly string value;

    /// <summary>Create a 22-character case-sensitive short GUID.</summary>

    public ShortGuid(Guid guid)

    {

        if (guid == null)

        {

            throw new ArgumentNullException("guid");

        }

        this.guid = guid;

        this.value = Convert.ToBase64String(guid.ToByteArray())

            .Substring(0, 22)

            .Replace("/", "_")

            .Replace("+", "-");

    }

    /// <summary>Get the short GUID as a string.</summary>

    public override string ToString()

    {

        return this.value;

    }

    /// <summary>Get the Guid object from which the short GUID was created.</summary>

    public Guid ToGuid()

    {

        return this.guid;

    }

    /// <summary>Get a short GUID as a Guid object.</summary>

    /// <exception cref="System.ArgumentNullException"></exception>

    /// <exception cref="System.FormatException"></exception>

    public static ShortGuid Parse(string shortGuid)

    {

        if (shortGuid == null)

        {

            throw new ArgumentNullException("shortGuid");

        }

        else if (shortGuid.Length != 22)

        {

            throw new FormatException("Input string was not in a correct format.");

        }

        return new ShortGuid(new Guid(Convert.FromBase64String

            (shortGuid.Replace("_", "/").Replace("-", "+") + "==")));

    }

    public static implicit operator String(ShortGuid guid)

    {

        return guid.ToString();

    }

    public static implicit operator Guid(ShortGuid shortGuid)

    {

        return shortGuid.guid;

    }

}