String formatPhoneForDisplay(String? rawPhone) {
  final normalized = _normalizePhone(rawPhone);
  if (normalized == null) {
    return rawPhone?.trim() ?? '';
  }

  if (normalized.startsWith('+86') && normalized.length == 14) {
    final local = normalized.substring(3);
    return '${local.substring(0, 3)}****${local.substring(7)}';
  }

  if (!normalized.startsWith('+')) {
    return normalized;
  }
  final digits = normalized.substring(1);
  final countryCode = _detectCountryCode(digits);
  if (countryCode == null) {
    return normalized;
  }
  final localNumber = digits.substring(countryCode.length);
  if (localNumber.length <= 4) {
    return '+$countryCode $localNumber';
  }
  final tail = localNumber.substring(localNumber.length - 4);
  return '+$countryCode ****$tail';
}

String? _normalizePhone(String? rawPhone) {
  if (rawPhone == null) {
    return null;
  }
  var phone = rawPhone.trim();
  for (final separator in const [' ', '-', '(', ')']) {
    phone = phone.replaceAll(separator, '');
  }
  if (phone.isEmpty) {
    return null;
  }
  if (phone.startsWith('00') && phone.length > 2) {
    phone = '+${phone.substring(2)}';
  }
  if (!phone.startsWith('+') && RegExp(r'^\d+$').hasMatch(phone)) {
    phone = '+$phone';
  }
  return phone;
}

String? _detectCountryCode(String digits) {
  const knownCodes = ['86', '1', '44', '81', '65', '33'];
  for (final code in knownCodes) {
    if (digits.startsWith(code) && digits.length > code.length + 3) {
      return code;
    }
  }
  for (int length = 3; length >= 1; length--) {
    if (length >= digits.length) {
      continue;
    }
    final candidate = digits.substring(0, length);
    if (candidate.startsWith('0')) {
      continue;
    }
    if (digits.length - length >= 4) {
      return candidate;
    }
  }
  return null;
}