using System.Net.Mail;
using System.Text.RegularExpressions;

namespace QuestionsApi.Services;

public static partial class AuthValidation
{
    [GeneratedRegex("^[A-Za-z0-9_]{3,24}$", RegexOptions.CultureInvariant)]
    private static partial Regex UsernamePattern();

    public static string NormalizeEmail(string email) => email.Trim().ToLowerInvariant();

    public static bool ValidEmail(string email)
    {
        var normalized = NormalizeEmail(email);
        var domain = normalized.Split('@').LastOrDefault() ?? "";
        return MailAddress.TryCreate(normalized, out _) && domain.Contains('.');
    }

    public static string? ValidateNewAccount(string username, string email, string password)
    {
        if (!UsernamePattern().IsMatch(username.Trim()))
            return "Username must be 3-24 characters using only letters, numbers, or underscores.";
        if (password.Length < 8)
            return "Password must be at least 8 characters.";
        if (!ValidEmail(email))
            return "A valid email address is required.";
        return null;
    }
}