/// 出/入库 KPI 汇总（本月 + 上月同期供环比 + 待审核）。
/// 对应后端 `GET /stock-in/summary`、`/stock-out/summary`。
class StockSummary {
  final int monthCount;
  final double monthAmount;
  final int pendingCount;
  final int draftCount;
  final int lastMonthCount;
  final double lastMonthAmount;

  const StockSummary({
    this.monthCount = 0,
    this.monthAmount = 0,
    this.pendingCount = 0,
    this.draftCount = 0,
    this.lastMonthCount = 0,
    this.lastMonthAmount = 0,
  });

  factory StockSummary.fromJson(Map<String, dynamic> j) => StockSummary(
        monthCount: (j['month_count'] as num?)?.toInt() ?? 0,
        monthAmount: (j['month_amount'] as num?)?.toDouble() ?? 0,
        pendingCount: (j['pending_count'] as num?)?.toInt() ?? 0,
        draftCount: (j['draft_count'] as num?)?.toInt() ?? 0,
        lastMonthCount: (j['last_month_count'] as num?)?.toInt() ?? 0,
        lastMonthAmount: (j['last_month_amount'] as num?)?.toDouble() ?? 0,
      );

  /// 笔数环比（%）；上月为 0 时返回 null（无从比较）。
  double? get countDeltaPct => lastMonthCount == 0
      ? null
      : (monthCount - lastMonthCount) / lastMonthCount * 100;

  /// 金额环比（%）；上月为 0 时返回 null。
  double? get amountDeltaPct => lastMonthAmount == 0
      ? null
      : (monthAmount - lastMonthAmount) / lastMonthAmount * 100;
}