using System.Security.Cryptography;
using System.Text;

namespace ServiceShared.Crypto
{
    public static class SHA512
    {
        /// <summary>
        /// Encrypts a string value in SHA512 hash
        /// </summary>
        /// <param name="value">string value that should be encrypted in SHA512 hash</param>
        /// <returns>Returns SHA512 hash</returns>
        public static string Encrypt(string value)
        {
            string result = null;

            try
            {
                byte[] bytes = Encoding.UTF8.GetBytes(value);

                using (System.Security.Cryptography.SHA512 hash = System.Security.Cryptography.SHA512.Create())
                {
                    byte[] hashedInputBytes = hash.ComputeHash(bytes);

                    StringBuilder hashedInputStringBuilder = new StringBuilder(128);

                    foreach (var b in hashedInputBytes)
                    {
                        hashedInputStringBuilder.Append(b.ToString("X2"));
                    }

                    result = hashedInputStringBuilder.ToString().ToLower();
                }
            }
            catch
            {
                result = null;
            }

            return result;
        }

        /// <summary>
        /// Generates SHA512 HMAC Hash with key
        /// </summary>
        /// <param name="message">message that should be signed by sha512 hmac</param>
        /// <param name="key">key that should be used for signing</param>
        /// <returns>SHA512 HMAC</returns>
        public static string HMAC(string message, byte[] key)
        {
            string result = null;

            try
            {
                StringBuilder hash = new StringBuilder();

                byte[] messageBytes = Encoding.UTF8.GetBytes(message);

                using (HMACSHA512 hmac = new HMACSHA512(key))
                {
                    byte[] hashValue = hmac.ComputeHash(messageBytes);

                    foreach (var theByte in hashValue)
                    {
                        hash.Append(theByte.ToString("x2"));
                    }
                }

                return hash.ToString();
            }
            catch
            {
                result = null;
            }

            return result;
        }

        /// <summary>
        /// Validates HMAC with message and key
        /// </summary>
        /// <param name="hmac">HMAC from the partner</param>
        /// <param name="message">message that should be signed by sha512 hmac</param>
        /// <param name="key">key that should be used for signing</param>
        /// <returns>returns true if success</returns>
        public static bool isValidAuthenticationCode(string hmac, string message, byte[] key)
        {
            return (hmac != null && HMAC(message, key) == hmac);
        }
    }
}