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

using HISP.Server;
using System;
using HISP.Util;

namespace HISP.Security
{
    public class Authentication
    {

        public const string ROTPOOL = "bl7Jgk61IZdnY mfDN5zjM2XLqTCty4WSEoKR3BFVQsaUhHOAx0rPwp9uc8iGve";
        public const string POSPOOL = "DQc3uxiGsKZatMmOS5qYveN71zoPTk8yU0H2w9VjprBXWn l4FJd6IRbhgACfEL";

        public static string EncryptLogin(string plainpass)
        {
            string encrypt = "";

            int i = 0;
            while (i < plainpass.Length)
            {
                int rotation = GameServer.RandomNumberGenerator.Next(0, ROTPOOL.Length);
                int position = ROTPOOL.IndexOf(plainpass[i]);

                position = position + (rotation + i);
                while (position >= ROTPOOL.Length)
                    position -= ROTPOOL.Length;
                encrypt += ROTPOOL[rotation];
                encrypt += POSPOOL[position];

                i++;
            }
            return encrypt;

        }
        public static string DecryptLogin(string encpass)
        {
            string decrypt = "";

            int i = 0;
            int rotationCycle = 0;
            while (i < encpass.Length)
            {
                int rotation = ROTPOOL.IndexOf(encpass[i].ToString());
                int position = POSPOOL.IndexOf(encpass[i + 1].ToString());
                position -= (rotation + rotationCycle);
                if (position < 0)
                {
                    position = (position / -1) - 1;

                    while (position >= ROTPOOL.Length)
                        position -= ROTPOOL.Length;

                    decrypt += Helper.ReverseString(ROTPOOL)[position];
                }
                else
                {
                    while (position >= ROTPOOL.Length)
                        position -= ROTPOOL.Length;

                    decrypt += ROTPOOL[position];
                }

                i += 2;
                rotationCycle++;
            }
            return decrypt.Replace(" ", "");
        }

        public static byte[] Sha1Digest(byte[] message)
        {
            using (SHA1 sha1 = SHA1.Create())
                return sha1.ComputeHash(message);
        }


        public static byte[] Sha512Digest(byte[] message)
        {
            using (SHA512 sha512 = SHA512.Create())
                return sha512.ComputeHash(message);
        }

        public static byte[] XorBytes(byte[] plaintext, byte[] key)
        {
            int length = Math.Min(plaintext.Length, key.Length);

            byte[] ciphertext = new byte[length];
            for(int i = 0; i < length; i++)
                ciphertext[i] = Convert.ToByte(plaintext[i] ^ key[i]);

            return ciphertext;
        }

        public static byte[] HashAndSalt(string plaintext, byte[] salt)
        {
            byte[] plaintextBytes = Encoding.UTF8.GetBytes(plaintext);

            byte[] hash = Sha512Digest(plaintextBytes);
            byte[] saltedHash = XorBytes(hash, salt);
            byte[] finalHash = Sha512Digest(saltedHash);

            return finalHash;
        }

        public static bool CheckPassword(string username, string password)
        {
            if(Database.CheckUserExist(username))
            {
                byte[] expectedPassword = Database.GetPasswordHash(username);
                byte[] salt = Database.GetPasswordSalt(username);
                byte[] hashedPassword = HashAndSalt(password, salt);

                if (Enumerable.SequenceEqual(expectedPassword, hashedPassword))
                    return true;
            }
            return false;
        }

        public static int CreateAccount(string username, string password, string gender, bool admin, bool moderator)
        {
            // Get a free user id
            int userId = Database.GetNextFreeUserId();

            // Generate salt value
            byte[] salt = new byte[64];
            GameServer.RandomNumberGenerator.NextBytes(salt);
            string saltText = BitConverter.ToString(salt).Replace("-", "");
            string hashsalt = BitConverter.ToString(Authentication.HashAndSalt(password, salt)).Replace("-", "");

            // Add user to database
            Database.CreateUser(userId, username, hashsalt, saltText, gender, admin, moderator);

            return userId;
        }


    }
}