using System;

using System.Net;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        string[] ipAddresses = {"50.212.80.65/29",};

        var result = ValidateAndCorrectIpAddresses(ipAddresses);

        Console.WriteLine();

    }

        private static List<string> ValidateAndCorrectIpAddresses(string[] ipAddressesList)

    {

        List<string> result = new(); 

        foreach(string iPAddress in ipAddressesList)

        {

            Console.Write("original ip address: " + iPAddress);

            var correctedIPAddress = CorrectCidrFormat(iPAddress);

            result.Add(correctedIPAddress);

            Console.Write("corrected ip address: " + correctedIPAddress);

            //convert iPAddress value to type long

            //long ip = BitConverter.ToInt32(iPAddress.GetAddressBytes(), 0);

            //var newValue = ip & 0b11111111111111111111111111111100;

        }

​

        return result;

    }

​

    private static string CorrectCidrFormat(string cidrInput)

    {

        Console.Write("cidrInput: " + cidrInput);

        var cidrParts= cidrInput.Split('/');

        if(cidrParts.Length == 2)

        {

            var ipAddress = IPAddress.Parse(cidrParts[0]);

            Console.Write("ipAddres: " + ipAddress);

            var subnetMask = int.Parse(cidrParts[1]);

            Console.Write("subnetMask: " + subnetMask);

            var networkAddress = GetNetworkAddress(ipAddress, subnetMask);

            Console.Write("networkAddress: " + networkAddress);

​

            return $"{networkAddress}/{subnetMask}";

        }

​

        return cidrInput;

    }

    static IPAddress GetNetworkAddress(IPAddress ipAddress, int prefixLength)

    {

        byte[] ipBytes = ipAddress.GetAddressBytes();

        byte[] mask = GetSubnetMask(prefixLength);

​

        for (int i = 0; i < ipBytes.Length; i++)

        {

            ipBytes[i] &= mask[i];

        }

​

        return new IPAddress(ipBytes);

    }

​

    static byte[] GetSubnetMask(int prefixLength)

    {

        int fullBytes = prefixLength / 8;

        int remainingBits = prefixLength % 8;

​

        byte[] mask = new byte[4];

        for (int i = 0; i < fullBytes; i++)

        {

            mask[i] = 255;

        }

​

        if (remainingBits > 0)

        {

            mask[fullBytes] = (byte)(255 << (8 - remainingBits));

        }

​

        return mask;

    }

​

    /*

    private static int GetNetWorkAddress(Byte[] addressBytes, int subnetMask)

    {

        int fullBytes = subnetMask / 8;

    int remainingBits = subnetMask % 8;

​

    for (int i = fullBytes; i < 4; i++)

    {

        addressBytes[i] = 0;

    }

​

    if (remainingBits > 0)

    {

        int mask = (byte)(255 << (8 - remainingBits));

        addressBytes[fullBytes] &= (byte)mask;

    }

​

    return BitConverter.ToInt32(addressBytes, 0);

    }

    */

}