using System;
using System.Security.Cryptography;
using Microsoft.AspNetCore.Cryptography.KeyDerivation;

namespace SecureCore
{
    public class Authentication
    {
        private static int Iterations { get; set; } = 100000;
        private static KeyDerivationPrf KeyType { get; } = KeyDerivationPrf.HMACSHA512;
        private static int KeySize { get; } = 512 / 8;
        private static int SaltSize { get; } = 128 / 8; //128 bit salt
        private static int SessionKeySize { get; } = 32; //32 bytes

        public static string CreateSessionToken()
        {
            var token = new byte[SessionKeySize];

            GetRandomBytes(ref token);

            return Convert.ToBase64String(token);
        }

        public static (string Hash, string Salt) HashPassword(string password)
        {
            var salt = new byte[SaltSize];

            GetRandomBytes(ref salt);

            return (GetPasswordHash(password, salt), Convert.ToBase64String(salt));
        }

        public static bool PasswordIsValid(string password, string salt, string passwordHash)
        {
            var saltBytes = Convert.FromBase64String(salt);

            return passwordHash == GetPasswordHash(password, saltBytes);
        }

        private static string GetPasswordHash(string password, byte[] salt)
        {
            return Convert.ToBase64String(KeyDerivation.Pbkdf2(password, salt, KeyType, Iterations, KeySize));
        }

        private static void GetRandomBytes(ref byte[] bytes)
        {
            using var rng = RandomNumberGenerator.Create();
            rng.GetBytes(bytes);
        }
    }

    public class LoginInfo
    {
        public string UserName { get; set; }
        public string Password { get; set; }
    }
}