/// 单据附件模型（对应 MgrServer MongoDB erp_bill_atts 文档）
class BillAttachment {
  final String id;
  final String bilId;
  final String bilNo;
  final int srcItm; // 0=表头附件, >0=表身行号
  final int itm; // 附件序号
  final String fileName;
  final String ext;
  final String fileId; // GridFS 文件 ID
  final int tag;
  final String effDd;
  final String usr;

  const BillAttachment({
    required this.id,
    required this.bilId,
    required this.bilNo,
    required this.srcItm,
    required this.itm,
    required this.fileName,
    required this.ext,
    required this.fileId,
    required this.tag,
    required this.effDd,
    required this.usr,
  });

  factory BillAttachment.fromJson(Map<String, dynamic> json) {
    return BillAttachment(
      id: (json['_id'] is Map<String, dynamic>
              ? (json['_id']['\$oid'] as String?)
              : json['_id'] as String?) ??
          '',
      bilId: json['BIL_ID'] as String? ?? '',
      bilNo: json['BIL_NO'] as String? ?? '',
      srcItm: json['SRCITM'] as int? ?? 0,
      itm: json['ITM'] as int? ?? 1,
      fileName: json['FILENAME'] as String? ?? '',
      ext: json['EXT'] as String? ?? '',
      fileId: (json['FILEID'] is Map<String, dynamic>
              ? (json['FILEID']['\$oid'] as String?)
              : json['FILEID'] as String?) ??
          '',
      tag: json['TAG'] as int? ?? 1,
      effDd: json['EFF_DD'] as String? ?? '',
      usr: json['USR'] as String? ?? '',
    );
  }

  /// 是否是表头附件
  bool get isHeader => srcItm == 0;

  /// 是否是表身附件
  bool get isBody => srcItm > 0;

  /// 文件图标（根据扩展名）
  String get fileIcon {
    switch (ext.toLowerCase()) {
      case 'pdf':
        return 'pdf';
      case 'doc':
      case 'docx':
        return 'doc';
      case 'xls':
      case 'xlsx':
        return 'xls';
      case 'jpg':
      case 'jpeg':
      case 'png':
      case 'gif':
      case 'bmp':
        return 'image';
      default:
        return 'file';
    }
  }
}