class FollowUpMessage {
  const FollowUpMessage({
    required this.id,
    required this.seq,
    required this.role,
    required this.content,
    required this.timestamp,
  });

  final String id;
  final int seq;
  final String role;
  final String content;
  final DateTime timestamp;

  factory FollowUpMessage.fromJson(Map<String, dynamic> json) {
    return FollowUpMessage(
      id: _requiredString(json, 'id'),
      seq: _requiredInt(json, 'seq'),
      role: _requiredString(json, 'role'),
      content: _requiredStringAllowEmpty(json, 'content'),
      timestamp: DateTime.parse(_requiredString(json, 'timestamp')).toLocal(),
    );
  }
}

String _requiredString(Map<String, dynamic> json, String key) {
  final value = json[key];
  if (value is! String || value.isEmpty) {
    throw FormatException('Missing required string: $key');
  }
  return value;
}

String _requiredStringAllowEmpty(Map<String, dynamic> json, String key) {
  final value = json[key];
  if (value is! String) {
    throw FormatException('Missing required string: $key');
  }
  return value;
}

int _requiredInt(Map<String, dynamic> json, String key) {
  final value = json[key];
  if (value is int) {
    return value;
  }
  if (value is num) {
    return value.toInt();
  }
  throw FormatException('Missing required int: $key');
}