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

namespace Landmark.OLA.Application.Common.Security
{
    public static class CookieCryptor
    {
        private static byte[] RandomBytes(int len)
        {
            var b = new byte[len];
            RandomNumberGenerator.Fill(b);
            return b;
        }

        private static byte[] DeriveKey(string pass, byte[] salt, int keyBytes = 32, int iterations = 100_000)
            => new Rfc2898DeriveBytes(pass, salt, iterations, HashAlgorithmName.SHA256).GetBytes(keyBytes);


        public static string EncryptJwt(string jwt, string key)
        {
            var salt = RandomBytes(32);

            using var aes = Aes.Create();
            aes.KeySize = 256;
            aes.BlockSize = 128;
            aes.Mode = CipherMode.CBC;
            aes.Padding = PaddingMode.PKCS7;

            aes.GenerateIV();
            aes.Key = DeriveKey(key, salt, 32);

            using var ms = new MemoryStream();

            ms.Write(salt, 0, salt.Length);
            ms.Write(aes.IV, 0, aes.IV.Length);

            using (var crypto = new CryptoStream(ms, aes.CreateEncryptor(), CryptoStreamMode.Write))
            using (var writer = new StreamWriter(crypto, Encoding.UTF8))
            {
                writer.Write(jwt);
                writer.Flush();
                crypto.FlushFinalBlock();
            }

            return Convert.ToBase64String(ms.ToArray());
        }

        public static string DecryptJwt(string cipherText, string passPhrase)
        {
            var all = Convert.FromBase64String(cipherText);

            var saltLen = 32;
            var ivLen = 16;

            if (all.Length < saltLen + ivLen)
                throw new CryptographicException("Ciphertext too short.");

            var salt = new byte[saltLen];
            Buffer.BlockCopy(all, 0, salt, 0, saltLen);

            var iv = new byte[ivLen];
            Buffer.BlockCopy(all, saltLen, iv, 0, ivLen);

            var cipher = new byte[all.Length - saltLen - ivLen];
            Buffer.BlockCopy(all, saltLen + ivLen, cipher, 0, cipher.Length);

            using var aes = Aes.Create();
            aes.KeySize = 256;
            aes.BlockSize = 128;
            aes.Mode = CipherMode.CBC;
            aes.Padding = PaddingMode.PKCS7;
            aes.Key = DeriveKey(passPhrase, salt, 32);
            aes.IV = iv;

            using var ms = new MemoryStream(cipher);
            using var crypto = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Read);
            using var reader = new StreamReader(crypto, Encoding.UTF8);

            return reader.ReadToEnd();
        }
    }
}