import 'dart:ui';

import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      scrollBehavior: const MaterialScrollBehavior().copyWith(
        physics: const ClampingScrollPhysics(),
        scrollbars: false,
        dragDevices: {
          PointerDeviceKind.mouse,
          PointerDeviceKind.touch,
          PointerDeviceKind.stylus,
          PointerDeviceKind.unknown
        },
      ),
      debugShowCheckedModeBanner: false,
      home: const Scaffold(
        body: NewsScreen(),
      ),
    ),
  );
}

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

  static const List<String> _tabs = <String>['Featured', 'Popular', 'Latest'];

  static final List<Widget> _tabViews = <Widget>[
    for (final String name in _tabs)
      SafeArea(
        top: false,
        bottom: false,
        child: Builder(builder: (BuildContext context) {
          final handle =
              NestedScrollView.sliverOverlapAbsorberHandleFor(context);

          return NotificationListener<ScrollNotification>(
            onNotification: (ScrollNotification notification) => true,
            child: CustomScrollView(
              key: PageStorageKey<String>(name),
              slivers: <Widget>[
                SliverOverlapInjector(handle: handle),
                SliverPadding(
                  padding: const EdgeInsets.all(8.0),
                  sliver: SliverList(
                    delegate: SliverChildBuilderDelegate(
                      childCount: 30,
                      (BuildContext context, int index) => Container(
                        margin: const EdgeInsets.only(bottom: 8),
                        width: double.infinity,
                        height: 150,
                        color: const Color(0xFFB0A4C8),
                        alignment: Alignment.center,
                        child: Text(
                          '$name $index',
                          style: const TextStyle(fontWeight: FontWeight.w600),
                        ),
                      ),
                    ),
                  ),
                ),
              ],
            ),
          );
        }),
      ),
  ];

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
      length: _tabs.length,
      child: NestedScrollView(
        headerSliverBuilder: (BuildContext context, bool innerBoxIsScrolled) =>
            <Widget>[
          SliverOverlapAbsorber(
            handle: NestedScrollView.sliverOverlapAbsorberHandleFor(context),
            sliver: SliverSafeArea(
              top: false,
              sliver: SliverAppBar(
                title: const Text('Tab Demo'),
                floating: true,
                pinned: true,
                snap: true,
                forceElevated: innerBoxIsScrolled,
                bottom: TabBar(
                  tabs: _tabs.map((String name) => Tab(text: name)).toList(),
                ),
              ),
            ),
          ),
        ],
        body: TabBarView(children: _tabViews),
      ),
    );
  }
}

  testWidgets('Maintains scroll position of inactive tab #2', (WidgetTester tester) async {
    await tester.pumpWidget(const example.NestedScrollViewExampleApp());

    final Finder finderItemAny = find.byType(ListTile, skipOffstage: false).first;
    final Finder finderItem11 = find.text('Item 11', skipOffstage: false);
    final Finder finderItem6 = find.text('Item 6', skipOffstage: false);
    final Finder finderItem4 = find.text('Item 4', skipOffstage: false);

    final Finder finderTab1 = find.text('Tab 1');
    final Finder finderTab2 = find.text('Tab 2');

    double getScrollPosition() {
      return Scrollable.of(tester.element(finderItemAny)).position.pixels;
    }

    expect(getScrollPosition(), 0.0);

    await tester.ensureVisible(finderItem11);
    await tester.pumpAndSettle();

    await tester.tap(finderTab2);
    await tester.pumpAndSettle();

    await tester.ensureVisible(finderItem6);
    await tester.pumpAndSettle();

    await tester.tap(finderTab1);
    await tester.pumpAndSettle();

    final tab1Position = getScrollPosition();

    await tester.tap(finderTab2);
    await tester.pumpAndSettle();

    // Without these two lines, the test passes
    await tester.ensureVisible(finderItem4);
    await tester.pumpAndSettle();

    await tester.tap(finderTab1);
    await tester.pumpAndSettle();

    expect(getScrollPosition(), tab1Position);
  });

  testWidgets('Maintains scroll position of inactive tab #2', (WidgetTester tester) async {
    await tester.pumpWidget(const example.NestedScrollViewExampleApp());

    final Finder finderItemAny = find.byType(ListTile, skipOffstage: false).first;
    final Finder finderItem11 = find.text('Item 11', skipOffstage: false);
    final Finder finderItem6 = find.text('Item 6', skipOffstage: false);
    final Finder finderItem4 = find.text('Item 4', skipOffstage: false);

    final Finder finderTab1 = find.text('Tab 1');
    final Finder finderTab2 = find.text('Tab 2');

    double getScrollPosition() {
      return Scrollable.of(tester.element(finderItemAny)).position.pixels;
    }

    expect(getScrollPosition(), 0.0);

    await tester.ensureVisible(finderItem11);
    await tester.pumpAndSettle();

    await tester.tap(finderTab2);
    await tester.pumpAndSettle();

    await tester.ensureVisible(finderItem6);
    await tester.pumpAndSettle();

    await tester.tap(finderTab1);
    await tester.pumpAndSettle();

    final double tab1Position = getScrollPosition();

    await tester.tap(finderTab2);
    await tester.pumpAndSettle();
    expect(getScrollPosition(), 416);

    await tester.ensureVisible(finderItem4);
    await tester.pumpAndSettle();
    expect(getScrollPosition(), 0); // passes

    // await tester.tap(finderTab1);
    // await tester.pumpAndSettle();

    // expect(getScrollPosition(), tab1Position);
  });