import '../models/bill.dart';

/// 按日期分组的账单
class BillDayGroup {
  final String date; // yyyy-MM-dd
  final List<Bill> bills;
  final double expenseTotal; // type==1 的合计
  final double incomeTotal; // type==2 的合计

  const BillDayGroup({
    required this.date,
    required this.bills,
    required this.expenseTotal,
    required this.incomeTotal,
  });
}

/// 按 billDate 分组，并分别累计当日支出/收入。
///
/// 后端已按 `billDate DESC, createTime DESC` 排序，Dart 的 Map 保持插入顺序，
/// 因此直接顺序遍历累积即可，不要再次排序（否则会打乱同日内的时间顺序）。
List<BillDayGroup> groupBillsByDate(List<Bill> bills) {
  final grouped = <String, List<Bill>>{};
  for (final bill in bills) {
    grouped.putIfAbsent(bill.billDate, () => []).add(bill);
  }

  return grouped.entries.map((entry) {
    var expense = 0.0;
    var income = 0.0;
    for (final bill in entry.value) {
      if (bill.isExpense) {
        expense += bill.absAmount;
      } else {
        income += bill.absAmount;
      }
    }
    return BillDayGroup(
      date: entry.key,
      bills: entry.value,
      expenseTotal: expense,
      incomeTotal: income,
    );
  }).toList();
}