/// یه کپسول کارخانه که داده ورودی رو بعد از یه تأخیر کوتاه برمی‌گردونه.  
/// این همچنین یه مثال از یه کپسول عمومیه.  
Future<T> Function(T) delayedEchoFactory<T>(CapsuleHandle _) {
  return (data) => Future.delayed(const Duration(seconds: 1), () => data);
}

class InfiniteList extends StatelessWidget {
  const InfiniteList({super.key});

  @override
  Widget build(BuildContext context) {
    return ListView.builder(
      itemBuilder: (context, index) => InfiniteScrollItem(index: index),
    );
  }
}

class InfiniteScrollItem extends RearchConsumer {
  const InfiniteScrollItem({required this.index, super.key});

  /// شاخص این آیتم.  
  final int index;

  @override
  Widget build(BuildContext context, WidgetHandle use) {
    final (keepAlive, setKeepAlive) = use.state(false);
    use.automaticKeepAlive(keepAlive: keepAlive);

    final factory = use(delayedEchoFactory<int>);
    final echoFuture = use.memo(() => factory(index), [factory, index]);
    final echoState = use.future(echoFuture);

    return ListTile(
      selected: keepAlive,
      onTap: () => setKeepAlive(!keepAlive),
      leading: Icon(
        keepAlive
            ? Icons.task_alt_rounded
            : Icons.radio_button_unchecked_rounded,
      ),
      title: switch (echoState) {
        AsyncData(:final data) => Text('$data'),
        AsyncLoading() => const Align(
            alignment: Alignment.centerLeft,
            child: CircularProgressIndicator.adaptive(),
          ),
        AsyncError(:final error) => Text('$error'),
      },
    );
  }
}