using System;
using System.Text;
using Xylem.Common.Cryptology.Security;

namespace Xylem.ServiceFwUpdate.Common.FwUpdateSafe
{
    /// <summary>
    /// Class for FW-Update specific cryptology.
    /// </summary>
    [Serializable]
    public static class FwUpdateCrypt
    {
        /// <summary>
        /// Separator for domain to user login name
        /// </summary>
        private const String StrDomainSeparator = "\\";

        /// <summary>
        /// Separator for key fields
        /// </summary>
        private const String StrKeyFieldSeparator = ":";

        /// <summary>
        /// Nonce size
        /// </summary>
        private const Int32 NonceSize = 16;

        /// <summary>
        /// Key size
        /// </summary>
        private const Int32 KeySize = 16;

        /// <summary>
        /// Salt size for en- and decryption key
        /// </summary>
        private const Int32 SaltSize = 8;

        /// <summary>
        /// Build primary key sources to byte array from input
        /// </summary>
        /// <returns> byte array containing primary key </returns>
        /// <remarks date="2021-Feb-03" author="Thomas Wiedebusch">
        /// - Initial.
        /// </remarks>
        public static Byte[] BuildPrimaryKey(String hardwareId, String domain, String userLoginName, 
            String userPwdHash)
        {
            var strPrimaryKey = hardwareId + StrKeyFieldSeparator + 
                                domain + StrDomainSeparator + 
                                userLoginName + StrKeyFieldSeparator +
                                userPwdHash;
            return Encoding.ASCII.GetBytes(strPrimaryKey);
        }

        /// <summary>
        /// FW-Update specific encryption of raw data buffer
        /// </summary>
        /// <param name="rawData"> raw data buffer needed to be encrypted </param>
        /// <param name="primaryKey">primary key</param>
        /// <returns> encrypted data buffer </returns>
        /// <remarks date="2020-Dec-02" author="Thomas Wiedebusch">
        /// - Initial Dummy implementation as base for FW-Update SW password extraction.
        /// </remarks>
        /// <remarks date="2021-Jan-21" author="Thomas Wiedebusch">
        /// - AES-GCM Encryption using bouncy Castle nuget package based on code snipped from Ray Savarda.
        /// </remarks>
        /// <remarks date="2021-Feb-03" author="Thomas Wiedebusch">
        /// - Primary key as optional input, if this is null, the key is going to be build locally.
        /// </remarks>
        /// <remarks date="2021-Mar-15" author="Thomas Wiedebusch">
        /// - Primary key is not optional anymore.
        /// </remarks>
        public static Byte[] Encrypt(Byte[] rawData, Byte[] primaryKey)
        {
            var encryptedData = Cryptology.AesGcmEncryption(SaltSize, NonceSize, KeySize, primaryKey, rawData);

            return encryptedData;
        }

        /// <summary>
        /// FW-Update specific decryption of encrypted data buffer
        /// </summary>
        /// <param name="encryptedData"> encrypted data buffer = nonce | salt | Cipher text </param>
        /// <param name="primaryKey">optional primary key</param>
        /// <returns> decrypted raw data buffer </returns>
        /// <remarks date="2020-Dec-02" author="Thomas Wiedebusch">
        /// - Initial Dummy implementation as base for FW-Update SW password extraction.
        /// </remarks>
        /// <remarks date="2021-Jan-21" author="Thomas Wiedebusch">
        /// - AES-GCM Decryption using bouncy Castle nuget package based on code snipped from Ray Savarda.
        /// </remarks>
        /// <remarks date="2021-Mar-15" author="Thomas Wiedebusch">
        /// - Primary key is not optional anymore.
        /// </remarks>
        public static Byte[] Decrypt(Byte[] encryptedData, Byte[] primaryKey)
        {
            var rawData = Cryptology.AesGcmDecryption(SaltSize, NonceSize, KeySize, primaryKey, encryptedData);

            return rawData;
        }
    }
}