import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:krow_worker_app/main.dart';

/// A list whose content is shorter than the viewport, so there is nothing to
/// scroll to.
Widget shortList() => MaterialApp(
  scrollBehavior: const KrowScrollBehavior(),
  home: Scaffold(
    body: ListView(
      children: const [SizedBox(height: 100, child: Text('only item'))],
    ),
  ),
);

Widget longList() => MaterialApp(
  scrollBehavior: const KrowScrollBehavior(),
  home: Scaffold(
    body: ListView(
      children: [
        for (var i = 0; i < 40; i++) SizedBox(height: 100, child: Text('$i')),
      ],
    ),
  ),
);

ScrollPosition positionOf(WidgetTester tester) =>
    tester.state<ScrollableState>(find.byType(Scrollable)).position;

void main() {
  // TargetPlatformVariant sets and restores the override around each test;
  // assigning it by hand trips the framework's debug-variable invariant check.
  final android = TargetPlatformVariant.only(TargetPlatform.android);
  final ios = TargetPlatformVariant.only(TargetPlatform.iOS);

  group('on Android', () {
    testWidgets('content that already fits does not move when dragged', (
      tester,
    ) async {
      await tester.pumpWidget(shortList());
      final position = positionOf(tester);

      // Every vertical list without a controller is handed an
      // AlwaysScrollableScrollPhysics by ScrollView itself, so the drag is
      // accepted whatever the content. Clamping is what pins it to the
      // boundary. Forcing bouncing globally instead let a one-item list be
      // dragged hundreds of pixels down, leaving a gap under the header.
      await tester.drag(find.text('only item'), const Offset(0, 300));
      await tester.pump();

      expect(position.pixels, 0);
    }, variant: android);

    testWidgets('a list that overflows still scrolls', (tester) async {
      await tester.pumpWidget(longList());
      final position = positionOf(tester);

      await tester.drag(find.text('0'), const Offset(0, -200));
      await tester.pump();

      expect(position.pixels, greaterThan(0));
    }, variant: android);

    testWidgets('and does not overscroll past the top', (tester) async {
      await tester.pumpWidget(longList());
      final position = positionOf(tester);

      await tester.drag(find.byType(Scrollable), const Offset(0, 400));
      await tester.pump();

      expect(position.pixels, 0);
    }, variant: android);
  });

  group('on iOS', () {
    testWidgets('short content rubber-bands, which is the convention there', (
      tester,
    ) async {
      await tester.pumpWidget(shortList());
      final position = positionOf(tester);

      await tester.drag(find.text('only item'), const Offset(0, 300));
      await tester.pump();
      expect(position.pixels, lessThan(0));

      // And springs back on release, rather than leaving the gap behind.
      await tester.pumpAndSettle();
      expect(position.pixels, 0);
    }, variant: ios);
  });
}