using System;

using System.Linq;

using System.Runtime.Serialization;

using System.Security.Cryptography;

using System.Text;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        var url = "https://i-ngoisao.vnecdn.net/2020/02/06/quynh-nga-1580947647-6340-1580948393_r_460x0.jpg";

        Console.WriteLine(KeyForUrl(url));

        Console.WriteLine(PartitionKeyForId(KeyForUrl(url)));

    }

    private static readonly HashAlgorithm HASH_PROVIDER = MD5.Create();

​

    public static string PartitionKeyForId(string id)

    {

        byte[] hash = HASH_PROVIDER.ComputeHash(Encoding.UTF8.GetBytes(id));

​

        // Return only first 4 symbols.

        return string.Join("", hash.Take(2).Select(x => x.ToString("x2")));

    }

​

    private static Regex KeyValidator = new Regex(@"[^a-zA-Z0-9\-_\.]");

​

    public static string KeyForUrl(string url)

    {

        var uri = new Uri(url);

        var key = uri.Host + KeyValidator.Replace(uri.PathAndQuery, "_");

        return key.Substring(0, Math.Min(key.Length, 254));

    }

}