using System;
using System.IO;
using System.Security.Cryptography;

namespace artem_laba_2
{
    class Program
    {

        public static byte[] StringToByteArray(string hex) {
            byte[] bytes = new byte[hex.Length / 2];
            for (int i = 0; i < hex.Length; i += 2)
                bytes[i / 2] = Convert.ToByte(hex.Substring(i, 2), 16);

            return bytes;
        }

        private static byte[] EncryptAES(string input, byte[] Key, byte[] IV)
        {
            if (input == null || input.Length <= 0)
                throw new ArgumentNullException("cipherText");
            if (Key == null || Key.Length <= 0)
                throw new ArgumentNullException("Key");
            if (IV == null || IV.Length <= 0)
                throw new ArgumentNullException("Key");
            byte[] encrypted;
            using var aes = Aes.Create();
            aes.Key = Key;
            aes.IV = IV;
            var encrypt = aes.CreateEncryptor(aes.Key, aes.IV); // ICryptoTransform
            using var msEncrypt = new MemoryStream();
            using var csEncrypt = new CryptoStream(msEncrypt, encrypt, CryptoStreamMode.Write);
            using (var swEncrypt = new StreamWriter(csEncrypt))
            {
                swEncrypt.Write(input);
            }
            encrypted = msEncrypt.ToArray();

            return encrypted;
        }

        private static string DecryptAES(byte[] cipherText, byte[] Key, byte[] IV)
        {
            if (cipherText == null || cipherText.Length <= 0)
                throw new ArgumentNullException("cipherText");
            if (Key == null || Key.Length <= 0)
                throw new ArgumentNullException("Key");
            if (IV == null || IV.Length <= 0)
                throw new ArgumentNullException("Key");
            var output = string.Empty;
            using var aes = Aes.Create();
            aes.Key = Key;
            aes.IV = IV;
            var decrypt = aes.CreateDecryptor(aes.Key, aes.IV); // ICryptoTransform
            using var msDecrypt = new MemoryStream(cipherText);
            using var csDecrypt = new CryptoStream(msDecrypt, decrypt, CryptoStreamMode.Read);
            using var srDecrypt = new StreamReader(csDecrypt);
            output = srDecrypt.ReadToEnd();

            return output;
        }

        static void Main(string[] args)
        {
            Console.Write("1. Encrypt\n2. Decrypt\n");
            Console.WriteLine("Choose: ");
            int choice = int.Parse(Console.ReadLine()); // может быть null
            byte[] aesKey, aesIV;
            Console.Write("Enter key: ");
            aesKey = StringToByteArray(Console.ReadLine());
            Console.Write("Enter IV: ");
            aesIV = StringToByteArray(Console.ReadLine());
            string path;
            do
            {
                Console.Write("Enter path: ");
                path = Console.ReadLine();
                path = path.Trim();
            } while (path == "");

            // проверка абсолютный или относительный путь
            bool absolute = path.Contains('\\');
            if (!absolute)
                path = Path.GetFullPath(path).ToString();
            Console.WriteLine(path);
            // читаем из файла
            try
            {
                // шифруем
                switch (choice)
                {
                    case 1:
                    {
                        using StreamReader sr = new StreamReader(path);
                        string context = sr.ReadToEnd();
                        byte[] encBytes = EncryptAES(context, aesKey, aesIV);
                        string output = Path.GetFullPath("out.txt");
                        Console.WriteLine($"File has been saved in {output}");
                        File.WriteAllBytes(output, encBytes);
                        string encrypted = BitConverter.ToString(encBytes);
                        Console.WriteLine(encrypted);
                    }
                        break;
                    case 2:
                    {
                        byte[] rd = File.ReadAllBytes(path);
                        string decrypted = DecryptAES(rd,aesKey,aesIV);
                        Console.WriteLine(decrypted);
                    }
                        break;
                }
            }
            catch (Exception e)
            {
                Console.WriteLine(e.Message);
            }
        }
    }
}