class WhatsAppSharePayload {
  const WhatsAppSharePayload({
    required this.messageText,
    this.sourceDisplayName,
    this.sourceUserId,
    this.sourceThreadId,
  });

  final String messageText;
  final String? sourceDisplayName;
  final String? sourceUserId;
  final String? sourceThreadId;
}

/// Parses raw shared text from WhatsApp into normalized fields.
class WhatsAppShareParser {
  const WhatsAppShareParser._();

  static final RegExp _datePrefixPattern = RegExp(
    r'^\[[^\]]+\]\s*([^:\n]{2,80}):\s*(.+)$',
    dotAll: true,
  );

  static final RegExp _namePrefixPattern = RegExp(
    r'^([^:\n]{2,80}):\s*(.+)$',
    dotAll: true,
  );

  static WhatsAppSharePayload parse(String raw) {
    final String input = raw.trim();
    if (input.isEmpty) {
      return const WhatsAppSharePayload(messageText: '');
    }

    String? senderName;
    String messageText = input;

    final RegExpMatch? dateMatch = _datePrefixPattern.firstMatch(input);
    if (dateMatch != null) {
      senderName = _cleanSender(dateMatch.group(1));
      messageText = dateMatch.group(2)?.trim() ?? input;
    } else {
      final RegExpMatch? nameMatch = _namePrefixPattern.firstMatch(input);
      if (nameMatch != null) {
        senderName = _cleanSender(nameMatch.group(1));
        messageText = nameMatch.group(2)?.trim() ?? input;
      }
    }

    final String? sourceUserId = _normalizedKey(senderName);
    return WhatsAppSharePayload(
      messageText: messageText,
      sourceDisplayName: senderName,
      sourceUserId: sourceUserId,
      sourceThreadId: null,
    );
  }

  static bool looksLikeWhatsAppMessage(String raw) {
    final String input = raw.trim();
    if (input.isEmpty) {
      return false;
    }
    return _datePrefixPattern.hasMatch(input) ||
        _namePrefixPattern.hasMatch(input);
  }

  static String? _cleanSender(String? input) {
    if (input == null) {
      return null;
    }
    final String cleaned = input.trim();
    return cleaned.isEmpty ? null : cleaned;
  }

  static String? _normalizedKey(String? input) {
    if (input == null) {
      return null;
    }
    final String key = input
        .toLowerCase()
        .replaceAll(RegExp(r'[^a-z0-9]+'), ' ')
        .trim()
        .replaceAll(RegExp(r'\s+'), ' ');
    return key.isEmpty ? null : 'wa:$key';
  }
}