Get index of the widget at the top visible of a list view builder

Question

I would like to know the index of the top visible widget in my ListViewBuilder

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At this point I should get index 12

At this point I should get index 21

class XXX extends StatelessWidget {
  const XXX({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Test')),
      body: ListView.builder(
          reverse: true,
          itemCount: 50,
          itemBuilder: (context, index) {
            return Container(
              color: index.isEven ? Colors.amber : Colors.yellow,
              padding: EdgeInsets.all(12),
              child: Text("HELLO $index"),
            );
          }),
    );
  }
}