/// 登录 / 注册页的表单状态与提交逻辑。
///
/// 校验规则与后端一致（邮箱格式、密码 8-64 位且含字母数字），本地先拦一次是为了少一次网络往返、
/// 也让用户立刻看到哪个字段不合格；后端仍会再校验一遍（前端校验不作为安全边界）。
class AuthLogic {
  bool signUpMode;
  String email = '';
  String password = '';
  bool busy = false;
  String? errorMessage;
  AuthFieldError? fieldError;

  AuthLogic({this.signUpMode = false, this.errorMessage});

  void toggleMode() {
    signUpMode = !signUpMode;
    errorMessage = null;
    fieldError = null;
  }

  /// 返回 null 表示校验通过，否则返回错误文案（由视图用 l10n 映射）
  AuthFieldError? validate() {
    final mail = email.trim();
    if (mail.isEmpty) return _record(AuthFieldError.emailRequired);
    if (!_emailPattern.hasMatch(mail)) {
      return _record(AuthFieldError.emailInvalid);
    }
    if (password.isEmpty) return _record(AuthFieldError.passwordRequired);
    if (password.length < 8 || password.length > 64) {
      return _record(AuthFieldError.passwordLength);
    }
    if (!_hasLetter.hasMatch(password) || !_hasDigit.hasMatch(password)) {
      return _record(AuthFieldError.passwordWeak);
    }
    fieldError = null;
    return null;
  }

  /// 清除当前字段错误；输入变化时由页面调用。
  void clearFieldError() {
    fieldError = null;
  }

  AuthFieldError _record(AuthFieldError error) {
    fieldError = error;
    return error;
  }

  String get normalizedEmail => email.trim().toLowerCase();

  static final _emailPattern = RegExp(
    r'^[A-Za-z0-9._%+\-]{1,64}@[A-Za-z0-9]([A-Za-z0-9\-]{0,61}[A-Za-z0-9])?'
    r'(\.[A-Za-z0-9]([A-Za-z0-9\-]{0,61}[A-Za-z0-9])?)*\.[A-Za-z]{2,}$',
  );
  static final _hasLetter = RegExp('[A-Za-z]');
  static final _hasDigit = RegExp('[0-9]');
}

enum AuthFieldError {
  emailRequired,
  emailInvalid,
  passwordRequired,
  passwordLength,
  passwordWeak,
}