// Method for validating the e-mail
    public bool ValidateEmail(string emailaddress)
    {
        string email = emailaddress;
        Regex regex = new Regex(@"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,4}$", RegexOptions.IgnoreCase);
        Match match = regex.Match(email);
        if (match.Success)
            return true;
        else
            return false;
    }

    // Method for creating the password key
    private string key()
    {
        var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        var stringChars = new char[10];
        var random = new Random();

        for (int i = 0; i < stringChars.Length; i++)
        {
            stringChars[i] = chars[random.Next(chars.Length)];
        }

        var key = new String(stringChars);

        return key;
    }

    // Method for hashing the password
    private string GetHashedString(string pass, string salt)
    {
        string hashedPass;
        SHA512 sha = new SHA512CryptoServiceProvider();
        byte[] result;
        StringBuilder strBuilder = new StringBuilder();

        // Hashes the password along with the random salt
        sha.ComputeHash(ASCIIEncoding.ASCII.GetBytes(pass + salt));
        result = sha.Hash;

        for (int i = 0; i < result.Length; i++)
        {
            strBuilder.Append(result[i].ToString("x2"));
        }

        hashedPass = strBuilder.ToString();
        return hashedPass;
    }

public void btnRegister_Click(object sender, EventArgs e)
    {
        using (conn = new SqlConnection(ConfigurationManager.ConnectionStrings["DBConn"].ToString()))
        {
            string Name = txtName.Text;
            string Email = txtEmail.Text;
            string Pass = txtPass.Text;
            string RePass = txtPassRepeat.Text;

            if(Name != string.Empty && Email != string.Empty && Pass != string.Empty && RePass != string.Empty)
            {
                if (ValidateEmail(Email))
                {
                    if (Pass == RePass)
                    {
                        // Tjek om mailen allerede er brugt
                        using (SqlCommand CheckEmail = new SqlCommand("SELECT * FROM users WHERE userEmail = @mail", conn))
                        {
                            CheckEmail.Parameters.AddWithValue("@mail", Email);

                            conn.Open();
                            SqlDataReader reader = CheckEmail.ExecuteReader();
                            if (!reader.HasRows)
                            {
                                reader.Close();

                                using (SqlCommand registerUser = new SqlCommand("INSERT INTO users (userName, userEmail, userPass, userKey) VALUES ()", conn))
                                {
                                    string keyCollection = key();
                                    string hashedPass = GetHashedString(Pass, keyCollection);

                                    registerUser.Parameters.AddWithValue("@name", Name);
                                    registerUser.Parameters.AddWithValue("@mail", Email);
                                    registerUser.Parameters.AddWithValue("@pass", hashedPass);
                                    registerUser.Parameters.AddWithValue("@key", keyCollection);
                                    
                                    registerUser.ExecuteNonQuery();
                                }
                            }
                            else
                            {
                                litAlert.Text = "This e-mail is allready in use";
                                panAlert.Visible = true;
                            }
                            conn.Close();
                        }
                    }
                    else
                    {
                        litAlert.Text = "The passwords doesn't match";
                        panAlert.Visible = true;
                    }
                }
                else
                {
                    litAlert.Text = "Please type your real e-mail adress";
                    panAlert.Visible = true;
                }
            }
            else
            {
                litAlert.Text = "Please fill all the fields.";
                panAlert.Visible = true;
            }
        }
    }