/*
 * Created by SharpDevelop.
 * User: Doug.Macintosh
 * Date: 2023-02-05
 * Time: 9:52 AM
 * 
 * To change this template use Tools | Options | Coding | Edit Standard Headers.
 */
using System;
using System.Collections.Generic;
using System.IO;
using System.IO.Compression;
using System.Runtime.ConstrainedExecution;
using System.Security.Cryptography;
using System.Text;

using Newtonsoft.Json;


namespace cdrtool
{
    class License
    {

        public static string validate(string filename)
        {
            string license;
            if ( (!File.Exists(filename)) || ( new FileInfo(filename).Length == 0))
                throw new FileNotFoundException("License file missing or corrupt.");

            if (cdrtool.company.Length < 6) 
                throw new InvalidDataException("User account missing or corrupt.");

            try
            {
                license = License.getLicense(filename, makeHash(cdrtool.company + cdrtool.product + cdrtool.version.Substring(0, 3)).Substring(0, 32));
                Logger.Log(5, "Decrypted License Key: {0}", license);
            }
            catch (Exception)
            {
                throw new InvalidDataException("Unable to decrypt license file, please contact Support.");
            }

            return license;

        }

        private static string getLicense(string filename, string secretKey)
        {
            return Decrypt(File.ReadAllText(filename), secretKey);
        }

        private static string Decrypt(string encryptedText, string secretKey)
        {
            byte[] encryptedTextBytes = Convert.FromBase64String(encryptedText);
            using (Aes aes = Aes.Create())
            {
                aes.Key = Encoding.UTF8.GetBytes(secretKey);
                byte[] iv = new byte[aes.BlockSize / 8];
                byte[] encrypted = new byte[encryptedTextBytes.Length - iv.Length];

                Array.Copy(encryptedTextBytes, 0, iv, 0, iv.Length);
                Array.Copy(encryptedTextBytes, iv.Length, encrypted, 0, encrypted.Length);

                aes.IV = iv;

                using (ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV))
                {
                    byte[] decryptedBytes = decryptor.TransformFinalBlock(encrypted, 0, encrypted.Length);
                    return Encoding.UTF8.GetString(decryptedBytes);
                }
            }
        }

        private static string makeHash(string InputString)
        {
            using (SHA256 sha256Hash = SHA256.Create())
            {
                byte[] bytes = sha256Hash.ComputeHash(System.Text.Encoding.UTF8.GetBytes(InputString));
                return Convert.ToBase64String(bytes);
            }
        }


    }
}