using System;
using System.Numerics;
using System.Security.Cryptography;

namespace CipherTest
{
    static class Program
    {
        const long KeySize = 64;

        // OpenSSL DH Parameters
        static readonly BigInteger Generator = new BigInteger(2);
        static readonly BigInteger Prime = BigInteger.Parse("11435638110073884015312138951374632602058080675070521707579703088370446597672067452229024566834732449017970455481029703480957707976441965258194321262569523");

        static void Main()
        {
            RNGCryptoServiceProvider provider = new RNGCryptoServiceProvider();

            byte[] bytes = new byte[KeySize];
            provider.GetBytes(bytes);

            BigInteger priv = new BigInteger(bytes, true);
            BigInteger pub = BigInteger.ModPow(Generator, priv, Prime);

            Console.WriteLine($"Your public key is:\n{pub}");

            string input;

            BigInteger other;

            while (true)
            {
                Console.WriteLine("\nEnter other public key:");
                input = Console.ReadLine();

                if (input.Length == 0)
                {
                    Console.WriteLine("\nProgram terminated!");
                    return;
                }
                else if (BigInteger.TryParse(input, out other))
                {
                    break;
                }
                else
                {
                    Console.WriteLine("\nCould not parse input!");
                }
            }

            BigInteger key = BigInteger.ModPow(other, priv, Prime);
            Cipher cipher = new Cipher(provider, key);

            Console.WriteLine("\nSetup complete!");

            string output;

            while (true)
            {
                Console.WriteLine("\nAwaiting input...");
                input = Console.ReadLine();

                if (input.Length == 0)
                {
                    Console.WriteLine("\nProgram terminated!");
                    return;
                }
                else if (input.StartsWith('~'))
                {
                    input = input.Substring(1);
                    if (Helpers.IsHexString(input))
                    {
                        output = cipher.Decrypt(input);
                        if (output != null)
                        {
                            Console.WriteLine($"\n{output}");
                        }
                        else
                        {
                            Console.WriteLine("\nCould not parse input!");
                        }
                    }
                    else
                    {
                        Console.WriteLine("\nCould not parse input!");
                    }
                }
                else if (Helpers.IsValidString(input))
                {
                    output = cipher.Encrypt(input);
                    if (output != null)
                    {
                        Console.WriteLine($"\n{output}");
                    }
                    else
                    {
                        Console.WriteLine("\nCould not parse input!");
                    }
                }
                else
                {
                    Console.WriteLine("\nCould not parse input!");
                }
            }
        }
    }
}