using System;

using System.Collections.Generic;

using System.IO;

using System.Security.Cryptography;

using System.Text;

public class Program

{

    public static void Main()

    {

        int Code=DateTime.Now.Millisecond;

        Console.WriteLine("Survey config code:"+Code);

        Console.WriteLine(DistributionShorteningUrlEncryptV2('A',"91",57,164,Code,null,null ));

        Console.WriteLine(DistributionShorteningUrlDecryptV2(DistributionShorteningUrlEncryptV2('A',"91",57,164,Code,null,null )));

        Console.WriteLine(DistributionShorteningUrlEncryptV2('A',"91",57,10000,Code,null,null ));

        Console.WriteLine(DistributionShorteningUrlDecryptV2(DistributionShorteningUrlEncryptV2('A',"91",57,10000,Code,null,null )));

        int Code2=DateTime.Now.Millisecond;

        Console.WriteLine("contact code:"+Code2);

        Console.WriteLine(DistributionShorteningUrlEncryptV2('I', "91", 57, 164,Code, 590,Code2));

        Console.WriteLine(DistributionShorteningUrlDecryptV2(DistributionShorteningUrlEncryptV2('I', "91", 57, 164,Code, 590,Code2)));

        Console.WriteLine(DistributionShorteningUrlEncryptV2('I', "91", 57, 10000,Code, 999999,Code2));

        Console.WriteLine(DistributionShorteningUrlDecryptV2(DistributionShorteningUrlEncryptV2('I', "91", 57, 10000,Code, 999999,Code2)));

        Console.WriteLine(DistributionShorteningUrlDecryptV2("Jpx31yrMRMzmv5sNBmufKTaMAddx2ZtC55Aqr3kwRrBkctLXVS9HkD2v5AeQ"));

    }

    static byte[] DistributionShorteningUrlV2Key { get { return Convert.FromBase64String("Z3P0t9jzMxKPIQck6W4P7W1eEeCB97K3oURRHGwG0SE="); } }

    class DistributionShorteningUrlV2Payload

    {

        /// <summary>

        /// UrlPrefixCode - distribution type

        /// </summary>

        public char D { get; set; }

        /// <summary>

        /// ISDCode - zone

        /// </summary>

        public string Z { get; set; }

        /// <summary>

        /// TimeZoneId - time

        /// </summary>

        public int T { get; set; }

        /// <summary>

        /// SurveyConfigId - survey instance

        /// </summary>

        public int I { get; set; }

        /// <summary>

        /// SurveyConfigIdCode - survey instance code

        /// </summary>

        public int IC { get; set; }

        /// <summary>

        /// DistContactId - contact

        /// </summary>

        public int? C { get; set; }

        /// <summary>

        /// DistContactIdCode - contact code

        /// </summary>

        public int? CC { get; set; }

    }

    private static string Base64UrlEncode(byte[] data)

    {

        return Convert.ToBase64String(data)

            .TrimEnd('=')

            .Replace('+', '-')

            .Replace('/', '_');

    }

    private static byte[] Base64UrlDecode(string base64Url)

    {

        string padded = base64Url.Replace('-', '+').Replace('_', '/');

        switch (padded.Length % 4)

        {

            case 2: padded += "=="; break;

            case 3: padded += "="; break;

            case 1: padded += "==="; break;

        }

        return Convert.FromBase64String(padded);

    }

    private static byte[] SerializeToCompactBytesMinified(DistributionShorteningUrlV2Payload payload)

    {

        using var ms = new MemoryStream();

        using var writer = new BinaryWriter(ms);

​

        writer.Write((byte)payload.D); // 1 byte for char

        writer.Write((byte)payload.Z.Length); // 1 byte

        writer.Write(Encoding.ASCII.GetBytes(payload.Z)); // n bytes

        writer.Write(payload.T);  // 4 bytes

        writer.Write(payload.I);  // 4 bytes

        writer.Write(payload.IC); // 4 bytes

​

        byte flags = 0;

        if (payload.C.HasValue) flags |= 1;

        if (payload.CC.HasValue) flags |= 2;

        writer.Write(flags); // 1 byte

​

        if (payload.C.HasValue)

            writer.Write(payload.C.Value); // 4 bytes

​

        if (payload.CC.HasValue)

            writer.Write(payload.CC.Value); // 4 bytes

​

        return ms.ToArray();

    }

    private static DistributionShorteningUrlV2Payload DeserializeFromCompactBytesMinified(byte[] data)

    {

        using var ms = new MemoryStream(data);

        using var reader = new BinaryReader(ms);

​

        var payload = new DistributionShorteningUrlV2Payload();

​

        payload.D = (char)reader.ReadByte();

​

        int isdLen = reader.ReadByte();

        payload.Z = Encoding.ASCII.GetString(reader.ReadBytes(isdLen));

​

        payload.T = reader.ReadInt32();

        payload.I = reader.ReadInt32();

        payload.IC = reader.ReadInt32();

​

        var flags = reader.ReadByte();

​

        if ((flags & 1) != 0)

            payload.C = reader.ReadInt32();

​

        if ((flags & 2) != 0)

            payload.CC = reader.ReadInt32();

​

        return payload;

    }

    public static string DistributionShorteningUrlEncryptV2(char UrlPrefixCode, string ISDCode, int TimeZoneId, int SurveyConfigId, int SurveyConfigIdCode, int? DistContactId, int? DistContactIdCode)

    {

        byte[] key = DistributionShorteningUrlV2Key;

        var payload = new DistributionShorteningUrlV2Payload

        {

            D = UrlPrefixCode,

            Z = ISDCode.Trim(),

            T = TimeZoneId,

            I = SurveyConfigId,

            IC = SurveyConfigIdCode,

            C = DistContactId,

            CC = DistContactIdCode

        };

​

        var json = Newtonsoft.Json.JsonConvert.SerializeObject(payload);

        var plaintextBytes = SerializeToCompactBytesMinified(payload);

​

        using var aes = new AesGcm(key);

​

        byte[] nonce = new byte[12]; // 256-bit key

        RandomNumberGenerator.Fill(nonce);

​

        var ciphertext = new byte[plaintextBytes.Length];

        var tag = new byte[16]; // GCM tag

​

        aes.Encrypt(nonce, plaintextBytes, ciphertext, tag);

​

        var result = new byte[nonce.Length + ciphertext.Length + tag.Length];

        Buffer.BlockCopy(nonce, 0, result, 0, nonce.Length);

        Buffer.BlockCopy(ciphertext, 0, result, nonce.Length, ciphertext.Length);

        Buffer.BlockCopy(tag, 0, result, nonce.Length + ciphertext.Length, tag.Length);

        return Base64UrlEncode(result);

    }

    public static (char DistType, string IsdCode, int TimezoneId, int SurveyConfigId, int SurveyConfigTimeMM, int? ContactId, int? ContactTimeMM) DistributionShorteningUrlDecryptV2(string Code)

    {

        byte[] key = DistributionShorteningUrlV2Key;

        var data = Base64UrlDecode(Code);

​

        var nonce = data[..12];

        var tag = data[^16..];

        var ciphertext = data[12..^16];

        var plaintext = new byte[ciphertext.Length];

​

        using var aes = new AesGcm(key);

        aes.Decrypt(nonce, ciphertext, tag, plaintext);

​

        var payload = DeserializeFromCompactBytesMinified(plaintext);

​

        return (payload.D, payload.Z, payload.T, payload.I, payload.IC, (int?)payload.C, payload.CC);

    }   

}