using System;

using System.IO;

using System.Security.Cryptography;

using System.Text;

using System;

public class Program

{

    public class TripAdvisorRentalsHeader

    {

        private readonly Uri _uri;

        private readonly string _requestBody;

        private readonly string _client;

        private readonly string _secret;

        private readonly string _requestMethod;

        private readonly string _timestamp;

        private string _bodyDigest;

        private string _requestDigest;

        private string _signature;

        private const string Algorithm = "VRS-HMAC-SHA512";

​

​

        /// <summary>

        /// Constructor for TripAdvisorRentalsHeader

        /// </summary>

        /// <param name="url">The url to send to request on</param>

        /// <param name="requestBody">The request body</param>

        /// <param name="requestMethod">The HTTP verb</param>

        /// <param name="client">The TAR client</param>

        /// <param name="secret">The TAR secret</param>

        public TripAdvisorRentalsHeader(string url, string requestBody, string requestMethod, string client, string secret)

        {

            _uri = new Uri(url);

            _requestBody = requestBody;

            _client = client;

            _secret = secret;

            _requestMethod = requestMethod.ToUpper();

            _timestamp = GetFormattedTimeStamp();

        }

​

        /// <summary>

        /// Generate the value part of the request Header required by TripAdvisor Rentals to authenticate

        /// </summary>

        /// <returns>Header as a string</returns>

        public string GetHeader()

        {

            var header = $"{Algorithm} timestamp={_timestamp},client={_client},signature={GetSignedHashFormatted(_uri, _timestamp, _requestBody, _secret, _requestMethod)}";

            return header;

        }

​

        private string GetSignedHashFormatted(Uri uri, string timestamp, string requestBody, string secret,

            string requestMethod)

        {

            var urlPath = uri.AbsolutePath;

            var query = uri.Query.TrimStart('?');

            _bodyDigest = GetSha512Hash(requestBody);

            var requestData = $"{requestMethod}\n{urlPath}\n{query}\n{timestamp}\n{_bodyDigest}";

            _requestDigest = GetSha512Hash(requestData);

            var keyByte = Encoding.UTF8.GetBytes(secret);

​

            using (var shaM = new HMACSHA512(keyByte))

            {

                using (var stream = new MemoryStream())

                {

                    var signedHash = shaM.ComputeHash(GenerateStreamFromString(_requestDigest, stream));

                    _signature = FormatToHexadecimalString(signedHash);

                }

            }

​

            return _signature;

        }

​

        private string FormatToHexadecimalString(byte[] hash)

        {

            return new StringBuilder(BitConverter.ToString(hash))

                .Replace("-", "")

                .ToString()

                .ToLower();

        }

​

        private string GetFormattedTimeStamp()

        {

            return $"{DateTime.UtcNow.ToString("s")}Z";

        }

​

        private string GetSha512Hash(string toHash)

        {

            using (SHA512 shaM = new SHA512Managed())

            {

                using (var stream = new MemoryStream())

                {

                    var hash = shaM.ComputeHash(GenerateStreamFromString(toHash, stream));

​

                    return FormatToHexadecimalString(hash);

                }

            }

        }

​

        private Stream GenerateStreamFromString(string s, MemoryStream memoryStream)

        {

            // this StreamWriter is left to be garbage collected when it goes out of scope

            var writer = new StreamWriter(memoryStream);

​

            writer.Write(s);

            writer.Flush();

            memoryStream.Position = 0;

​

            return memoryStream;

        }

    }

    public static void Main()

    {

        var tarHeader = new TripAdvisorRentalsHeader("https://rentals.tripadvisor.com/api/property/v1/4103393/eviivo_Greenhill_57092", null, "GET", "Eviivo",

                                                     "e5M6rvJTe9HM2vRjp0xFkcj0VpBn17Fxq3v7nqCiFUmNWTcq42YaIWPvVCqm5dMkeSB6NNX14NT9h5CJGPf4ZQ==");

        var header = tarHeader.GetHeader();

        Console.WriteLine("Hello World");

        Console.WriteLine(header);

    }

}