// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/cupertino.dart';
import 'package:flutter_test/flutter_test.dart';

import '../painting/mocks_for_image_cache.dart';
import '../rendering/rendering_tester.dart';

List<int> selectedTabs;

class MockCupertinoTabController extends CupertinoTabController {
  MockCupertinoTabController({ int initialIndex }): super(initialIndex: initialIndex);

  bool isDisposed = false;
  int numOfListeners = 0;

  @override
  void addListener(VoidCallback listener) {
    numOfListeners++;
    super.addListener(listener);
  }

  @override
  void removeListener(VoidCallback listener) {
    numOfListeners--;
    super.removeListener(listener);
  }

  @override
  void dispose() {
    isDisposed = true;
    super.dispose();
  }
}

void main() {
  setUp(() {
    selectedTabs = <int>[];
  });

  BottomNavigationBarItem tabGenerator(int index) {
    return BottomNavigationBarItem(
      icon: const ImageIcon(TestImageProvider(24, 24)),
      title: Text('Tab ${index + 1}'),
    );
  }

  testWidgets('Tab switching', (WidgetTester tester) async {
    final List<int> tabsPainted = <int>[];

    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: _buildTabBar(),
          tabBuilder: (BuildContext context, int index) {
            return CustomPaint(
              child: Text('Page ${index + 1}'),
              painter: TestCallbackPainter(
                onPaint: () { tabsPainted.add(index); }
              ),
            );
          },
        ),
      ),
    );

    expect(tabsPainted, <int>[0]);
    RichText tab1 = tester.widget(find.descendant(
      of: find.text('Tab 1'),
      matching: find.byType(RichText),
    ));
    expect(tab1.text.style.color, CupertinoColors.activeBlue);
    RichText tab2 = tester.widget(find.descendant(
      of: find.text('Tab 2'),
      matching: find.byType(RichText),
    ));
    expect(tab2.text.style.color, CupertinoColors.inactiveGray);

    await tester.tap(find.text('Tab 2'));
    await tester.pump();

    expect(tabsPainted, <int>[0, 1]);
    tab1 = tester.widget(find.descendant(
      of: find.text('Tab 1'),
      matching: find.byType(RichText),
    ));
    expect(tab1.text.style.color, CupertinoColors.inactiveGray);
    tab2 = tester.widget(find.descendant(
      of: find.text('Tab 2'),
      matching: find.byType(RichText),
    ));
    expect(tab2.text.style.color, CupertinoColors.activeBlue);

    await tester.tap(find.text('Tab 1'));
    await tester.pump();

    expect(tabsPainted, <int>[0, 1, 0]);
    // CupertinoTabBar's onTap callbacks are passed on.
    expect(selectedTabs, <int>[1, 0]);
  });

  testWidgets('Tabs are lazy built and moved offstage when inactive', (WidgetTester tester) async {
    final List<int> tabsBuilt = <int>[];

    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: _buildTabBar(),
          tabBuilder: (BuildContext context, int index) {
            tabsBuilt.add(index);
            return Text('Page ${index + 1}');
          },
        ),
      ),
    );

    expect(tabsBuilt, <int>[0]);
    expect(find.text('Page 1'), findsOneWidget);
    expect(find.text('Page 2'), findsNothing);

    await tester.tap(find.text('Tab 2'));
    await tester.pump();

    // Both tabs are built but only one is onstage.
    expect(tabsBuilt, <int>[0, 0, 1]);
    expect(find.text('Page 1', skipOffstage: false), isOffstage);
    expect(find.text('Page 2'), findsOneWidget);

    await tester.tap(find.text('Tab 1'));
    await tester.pump();

    expect(tabsBuilt, <int>[0, 0, 1, 0, 1]);
    expect(find.text('Page 1'), findsOneWidget);
    expect(find.text('Page 2', skipOffstage: false), isOffstage);
  });

  testWidgets('Last tab gets focus', (WidgetTester tester) async {
    // 2 nodes for 2 tabs
    final List<FocusNode> focusNodes = <FocusNode>[
      FocusNode(debugLabel: 'Node 1'),
      FocusNode(debugLabel: 'Node 2'),
    ];

    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: _buildTabBar(),
          tabBuilder: (BuildContext context, int index) {
            return CupertinoTextField(
              focusNode: focusNodes[index],
              autofocus: true,
            );
          },
        ),
      ),
    );

    expect(focusNodes[0].hasFocus, isTrue);

    await tester.tap(find.text('Tab 2'));
    await tester.pump();

    expect(focusNodes[0].hasFocus, isFalse);
    expect(focusNodes[1].hasFocus, isTrue);

    await tester.tap(find.text('Tab 1'));
    await tester.pump();

    expect(focusNodes[0].hasFocus, isTrue);
    expect(focusNodes[1].hasFocus, isFalse);
  });

  testWidgets('Do not affect focus order in the route', (WidgetTester tester) async {
    final List<FocusNode> focusNodes = <FocusNode>[
      FocusNode(debugLabel: 'Node 1'),
      FocusNode(debugLabel: 'Node 2'),
      FocusNode(debugLabel: 'Node 3'),
      FocusNode(debugLabel: 'Node 4'),
    ];

    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: _buildTabBar(),
          tabBuilder: (BuildContext context, int index) {
            return Column(
              children: <Widget>[
                CupertinoTextField(
                  focusNode: focusNodes[index * 2],
                  placeholder: 'TextField 1',
                ),
                CupertinoTextField(
                  focusNode: focusNodes[index * 2 + 1],
                  placeholder: 'TextField 2',
                ),
              ],
            );
          },
        ),
      ),
    );

    expect(
      focusNodes.any((FocusNode node) => node.hasFocus),
      isFalse,
    );

    await tester.tap(find.widgetWithText(CupertinoTextField, 'TextField 2'));

    expect(
      focusNodes.indexOf(focusNodes.singleWhere((FocusNode node) => node.hasFocus)),
      1,
    );

    await tester.tap(find.text('Tab 2'));
    await tester.pump();

    await tester.tap(find.widgetWithText(CupertinoTextField, 'TextField 1'));

    expect(
      focusNodes.indexOf(focusNodes.singleWhere((FocusNode node) => node.hasFocus)),
      2,
    );

    await tester.tap(find.text('Tab 1'));
    await tester.pump();

    // Upon going back to tab 1, the item it tab 1 that previously had the focus
    // (TextField 2) gets it back.
    expect(
      focusNodes.indexOf(focusNodes.singleWhere((FocusNode node) => node.hasFocus)),
      1,
    );
  });

  testWidgets('Programmatic tab switching by changing the index of an existing controller', (WidgetTester tester) async {
    final CupertinoTabController controller = CupertinoTabController(initialIndex: 1);
    final List<int> tabsPainted = <int>[];

    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: _buildTabBar(),
          controller: controller,
          tabBuilder: (BuildContext context, int index) {
            return CustomPaint(
              child: Text('Page ${index + 1}'),
              painter: TestCallbackPainter(
                onPaint: () { tabsPainted.add(index); }
              ),
            );
          },
        ),
      ),
    );

    expect(tabsPainted, <int>[1]);

    controller.index = 0;
    await tester.pump();

    expect(tabsPainted, <int>[1, 0]);
    // onTap is not called when changing tabs programmatically.
    expect(selectedTabs, isEmpty);

    // Can still tap out of the programmatically selected tab.
    await tester.tap(find.text('Tab 2'));
    await tester.pump();

    expect(tabsPainted, <int>[1, 0, 1]);
    expect(selectedTabs, <int>[1]);
  });

  testWidgets('Programmatic tab switching by passing in a new controller', (WidgetTester tester) async {
    final List<int> tabsPainted = <int>[];

    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: _buildTabBar(),
          tabBuilder: (BuildContext context, int index) {
            return CustomPaint(
              child: Text('Page ${index + 1}'),
              painter: TestCallbackPainter(
                onPaint: () { tabsPainted.add(index); }
              ),
            );
          },
        ),
      ),
    );

    expect(tabsPainted, <int>[0]);

    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: _buildTabBar(),
          controller: CupertinoTabController(initialIndex: 1), // Programmatically change the tab now.
          tabBuilder: (BuildContext context, int index) {
            return CustomPaint(
              child: Text('Page ${index + 1}'),
              painter: TestCallbackPainter(
                onPaint: () { tabsPainted.add(index); }
              ),
            );
          },
        ),
      ),
    );

    expect(tabsPainted, <int>[0, 1]);
    // onTap is not called when changing tabs programmatically.
    expect(selectedTabs, isEmpty);

    // Can still tap out of the programmatically selected tab.
    await tester.tap(find.text('Tab 1'));
    await tester.pump();

    expect(tabsPainted, <int>[0, 1, 0]);
    expect(selectedTabs, <int>[0]);
  });

  testWidgets('Tab bar respects themes', (WidgetTester tester) async {
    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: _buildTabBar(),
          tabBuilder: (BuildContext context, int index) {
            return const Placeholder();
          },
        ),
      ),
    );

    BoxDecoration tabDecoration = tester.widget<DecoratedBox>(find.descendant(
      of: find.byType(CupertinoTabBar),
      matching: find.byType(DecoratedBox),
    )).decoration;

    expect(tabDecoration.color, const Color(0xCCF8F8F8));

    await tester.tap(find.text('Tab 2'));
    await tester.pump();

    // Pump again but with dark theme.
    await tester.pumpWidget(
      CupertinoApp(
        theme: const CupertinoThemeData(
          brightness: Brightness.dark,
          primaryColor: CupertinoColors.destructiveRed,
        ),
        home: CupertinoTabScaffold(
          tabBar: _buildTabBar(),
          tabBuilder: (BuildContext context, int index) {
            return const Placeholder();
          },
        ),
      ),
    );

    tabDecoration = tester.widget<DecoratedBox>(find.descendant(
      of: find.byType(CupertinoTabBar),
      matching: find.byType(DecoratedBox),
    )).decoration;

    expect(tabDecoration.color, const Color(0xB7212121));

    final RichText tab1 = tester.widget(find.descendant(
      of: find.text('Tab 1'),
      matching: find.byType(RichText),
    ));
    // Tab 2 should still be selected after changing theme.
    expect(tab1.text.style.color, CupertinoColors.inactiveGray);
    final RichText tab2 = tester.widget(find.descendant(
      of: find.text('Tab 2'),
      matching: find.byType(RichText),
    ));
    expect(tab2.text.style.color, CupertinoColors.destructiveRed);
  });

  testWidgets('Tab contents are padded when there are view insets', (WidgetTester tester) async {
    BuildContext innerContext;

    await tester.pumpWidget(
      CupertinoApp(
        home: MediaQuery(
          data: const MediaQueryData(
            viewInsets: EdgeInsets.only(bottom: 200),
          ),
          child: CupertinoTabScaffold(
            tabBar: _buildTabBar(),
            tabBuilder: (BuildContext context, int index) {
              innerContext = context;
              return const Placeholder();
            },
          ),
        ),
      ),
    );

    expect(tester.getRect(find.byType(Placeholder)), const Rect.fromLTWH(0, 0, 800, 400));
    // Don't generate more media query padding from the translucent bottom
    // tab since the tab is behind the keyboard now.
    expect(MediaQuery.of(innerContext).padding.bottom, 0);
  });

  testWidgets('Tab contents are not inset when resizeToAvoidBottomInset overriden', (WidgetTester tester) async {
    BuildContext innerContext;

    await tester.pumpWidget(
      CupertinoApp(
        home: MediaQuery(
          data: const MediaQueryData(
            viewInsets: EdgeInsets.only(bottom: 200),
          ),
          child: CupertinoTabScaffold(
            resizeToAvoidBottomInset: false,
            tabBar: _buildTabBar(),
            tabBuilder: (BuildContext context, int index) {
              innerContext = context;
              return const Placeholder();
            },
          ),
        ),
      ),
    );

    expect(tester.getRect(find.byType(Placeholder)), const Rect.fromLTWH(0, 0, 800, 600));
    // Media query padding shows up in the inner content because it wasn't masked
    // by the view inset.
    expect(MediaQuery.of(innerContext).padding.bottom, 50);
  });

  testWidgets('Tab and page scaffolds do not double stack view insets', (WidgetTester tester) async {
    BuildContext innerContext;

    await tester.pumpWidget(
      CupertinoApp(
        home: MediaQuery(
          data: const MediaQueryData(
            viewInsets: EdgeInsets.only(bottom: 200),
          ),
          child: CupertinoTabScaffold(
            tabBar: _buildTabBar(),
            tabBuilder: (BuildContext context, int index) {
              return CupertinoPageScaffold(
                child: Builder(
                  builder: (BuildContext context) {
                    innerContext = context;
                    return const Placeholder();
                  },
                ),
              );
            },
          ),
        ),
      ),
    );

    expect(tester.getRect(find.byType(Placeholder)), const Rect.fromLTWH(0, 0, 800, 400));
    expect(MediaQuery.of(innerContext).padding.bottom, 0);
  });

  testWidgets('Deleting tabs after selecting them should switch to the last available tab', (WidgetTester tester) async {
    final List<int> tabsBuilt = <int>[];

    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: CupertinoTabBar(
            items: List<BottomNavigationBarItem>.generate(4, tabGenerator),
            onTap: (int newTab) => selectedTabs.add(newTab),
          ),
          tabBuilder: (BuildContext context, int index) {
            tabsBuilt.add(index);
            return Text('Page ${index + 1}');
          },
        ),
      ),
    );

    expect(tabsBuilt, <int>[0]);
    // selectedTabs list is appended to on onTap callbacks. We didn't tap
    // any tabs yet.
    expect(selectedTabs, <int>[]);
    tabsBuilt.clear();

    await tester.tap(find.text('Tab 4'));
    await tester.pump();

    // Tabs 1 and 4 are built but only one is onstage.
    expect(tabsBuilt, <int>[0, 3]);
    expect(selectedTabs, <int>[3]);
    expect(find.text('Page 1', skipOffstage: false), isOffstage);
    expect(find.text('Page 4'), findsOneWidget);
    tabsBuilt.clear();

    // Delete 2 tabs while Page 4 is still selected.
    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: CupertinoTabBar(
            items: List<BottomNavigationBarItem>.generate(2, tabGenerator),
            onTap: (int newTab) => selectedTabs.add(newTab),
          ),
          tabBuilder: (BuildContext context, int index) {
            tabsBuilt.add(index);
            // Change the builder too.
            return Text('Different page ${index + 1}');
          },
        ),
      )
    );

    expect(tabsBuilt, <int>[0, 1]);
    // We didn't tap on any additional tabs to invoke the onTap callback. We
    // just deleted a tab.
    expect(selectedTabs, <int>[3]);
    // Tab 1 was previously built so it's rebuilt again, albeit offstage.
    expect(find.text('Different page 1', skipOffstage: false), isOffstage);
    // Since all the tabs after tab 2 are deleted, tab 2 is now the last tab and
    // the actively shown tab.
    expect(find.text('Different page 2'), findsOneWidget);
    // No more tab 4 since it's deleted.
    expect(find.text('Different page 4', skipOffstage: false), findsNothing);
    // We also changed the builder so no tabs should be built with the old
    // builder.
    expect(find.text('Page 1', skipOffstage: false), findsNothing);
    expect(find.text('Page 2', skipOffstage: false), findsNothing);
    expect(find.text('Page 4', skipOffstage: false), findsNothing);
  });

  testWidgets('If a controller is initially provided then the parent stops doing so for rebuilds, '
              'a new instance of CupertinoTabController should be created and used by the widget, '
              "while preserving the previous controller's tab index",
    (WidgetTester tester) async {
      final List<int> tabsPainted = <int>[];
      final CupertinoTabController oldController = CupertinoTabController(initialIndex: 0);

      await tester.pumpWidget(
        CupertinoApp(
          home: CupertinoTabScaffold(
            tabBar: CupertinoTabBar(
              items: List<BottomNavigationBarItem>.generate(10, tabGenerator),
            ),
            controller: oldController,
            tabBuilder: (BuildContext context, int index) {
              return CustomPaint(
                child: Text('Page ${index + 1}'),
                painter: TestCallbackPainter(
                  onPaint: () { tabsPainted.add(index); }
                ),
              );
            }
          ),
        )
      );

      expect(tabsPainted, <int> [0]);

      await tester.pumpWidget(
        CupertinoApp(
          home: CupertinoTabScaffold(
            tabBar: CupertinoTabBar(
              items: List<BottomNavigationBarItem>.generate(10, tabGenerator),
            ),
            controller: null,
            tabBuilder:
            (BuildContext context, int index) {
              return CustomPaint(
                child: Text('Page ${index + 1}'),
                painter: TestCallbackPainter(
                  onPaint: () { tabsPainted.add(index); }
                ),
              );
            }
          ),
        )
      );

      expect(tabsPainted, <int> [0, 0]);

      await tester.tap(find.text('Tab 2'));
      await tester.pump();

      // Tapping the tabs should still work.
      expect(tabsPainted, <int>[0, 0, 1]);

      oldController.index = 10;
      await tester.pump();

      // Changing [index] of the oldController should not work.
      expect(tabsPainted, <int> [0, 0, 1]);
  });

  testWidgets('Do not call dispose on a controller that we do not own'
              'but do remove from its listeners when done listening to it',
    (WidgetTester tester) async {
      final MockCupertinoTabController mockController = MockCupertinoTabController(initialIndex: 0);

      await tester.pumpWidget(
        CupertinoApp(
          home: CupertinoTabScaffold(
            tabBar: CupertinoTabBar(
              items: List<BottomNavigationBarItem>.generate(2, tabGenerator),
            ),
            controller: mockController,
            tabBuilder: (BuildContext context, int index) => const Placeholder(),
          ),
        )
      );

      expect(mockController.numOfListeners, 1);
      expect(mockController.isDisposed, isFalse);

      await tester.pumpWidget(
        CupertinoApp(
          home: CupertinoTabScaffold(
            tabBar: CupertinoTabBar(
              items: List<BottomNavigationBarItem>.generate(2, tabGenerator),
            ),
            controller: null,
            tabBuilder: (BuildContext context, int index) => const Placeholder(),
          ),
        )
      );

      expect(mockController.numOfListeners, 0);
      expect(mockController.isDisposed, isFalse);
  });

  testWidgets('The owner can dispose the old controller', (WidgetTester tester) async {
    CupertinoTabController controller = CupertinoTabController(initialIndex: 2);

    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: CupertinoTabBar(
            items: List<BottomNavigationBarItem>.generate(3, tabGenerator),
          ),
          controller: controller,
          tabBuilder: (BuildContext context, int index) => const Placeholder()
        ),
      )
    );
    expect(find.text('Tab 1'), findsOneWidget);
    expect(find.text('Tab 2'), findsOneWidget);
    expect(find.text('Tab 3'), findsOneWidget);

    controller.dispose();
    controller = CupertinoTabController(initialIndex: 0);
    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: CupertinoTabBar(
            items: List<BottomNavigationBarItem>.generate(2, tabGenerator),
          ),
          controller: controller,
          tabBuilder: (BuildContext context, int index) => const Placeholder()
        ),
      )
    );

    // Should not crash here.
    expect(find.text('Tab 1'), findsOneWidget);
    expect(find.text('Tab 2'), findsOneWidget);
    expect(find.text('Tab 3'), findsNothing);
  });

  testWidgets('A controller can control more than one CupertinoTabScaffold,'
    'removal of listeners does not break the controller',
    (WidgetTester tester) async {
      final List<int> tabsPainted0 = <int>[];
      final List<int> tabsPainted1 = <int>[];
      MockCupertinoTabController controller = MockCupertinoTabController(initialIndex: 2);

      await tester.pumpWidget(
        CupertinoApp(
          home: CupertinoPageScaffold(
            child: Stack(
              children: <Widget>[
                CupertinoTabScaffold(
                  tabBar: CupertinoTabBar(
                    items: List<BottomNavigationBarItem>.generate(3, tabGenerator),
                  ),
                  controller: controller,
                  tabBuilder: (BuildContext context, int index) {
                    return CustomPaint(
                      painter: TestCallbackPainter(
                        onPaint: () => tabsPainted0.add(index)
                      )
                    );
                  }
                ),
                CupertinoTabScaffold(
                  tabBar: CupertinoTabBar(
                    items: List<BottomNavigationBarItem>.generate(3, tabGenerator),
                  ),
                  controller: controller,
                  tabBuilder: (BuildContext context, int index) {
                    return CustomPaint(
                      painter: TestCallbackPainter(
                        onPaint: () => tabsPainted1.add(index)
                      )
                    );
                  }
                ),
              ]
            )
          )
        )
      );
      expect(tabsPainted0, const <int>[2]);
      expect(tabsPainted1, const <int>[2]);
      expect(controller.numOfListeners, 2);

      controller.index = 0;
      await tester.pump();
      expect(tabsPainted0, const <int>[2, 0]);
      expect(tabsPainted1, const <int>[2, 0]);

      controller.index = 1;
      // Removing one of the tabs works.
      await tester.pumpWidget(
        CupertinoApp(
          home: CupertinoPageScaffold(
            child: Stack(
              children: <Widget>[
                CupertinoTabScaffold(
                  tabBar: CupertinoTabBar(
                    items: List<BottomNavigationBarItem>.generate(3, tabGenerator),
                  ),
                  controller: controller,
                  tabBuilder: (BuildContext context, int index) {
                    return CustomPaint(
                      painter: TestCallbackPainter(
                        onPaint: () => tabsPainted0.add(index)
                      )
                    );
                  }
                ),
              ]
            )
          )
        )
      );

      expect(tabsPainted0, const <int>[2, 0, 1]);
      expect(tabsPainted1, const <int>[2, 0]);
      expect(controller.numOfListeners, 1);

      // Replacing controller works.
      controller = MockCupertinoTabController(initialIndex: 2);
      await tester.pumpWidget(
        CupertinoApp(
          home: CupertinoPageScaffold(
            child: Stack(
              children: <Widget>[
                CupertinoTabScaffold(
                  tabBar: CupertinoTabBar(
                    items: List<BottomNavigationBarItem>.generate(3, tabGenerator),
                  ),
                  controller: controller,
                  tabBuilder: (BuildContext context, int index) {
                    return CustomPaint(
                      painter: TestCallbackPainter(
                        onPaint: () => tabsPainted0.add(index)
                      )
                    );
                  }
                ),
              ]
            )
          )
        )
      );
      expect(tabsPainted0, const <int>[2, 0, 1, 2]);
      expect(tabsPainted1, const <int>[2, 0]);
      expect(controller.numOfListeners, 1);
    });

  testWidgets('Assert when current tab index >= number of tabs', (WidgetTester tester) async {
    final CupertinoTabController controller = CupertinoTabController(initialIndex: 2);

    try {
      await tester.pumpWidget(
        CupertinoApp(
          home: CupertinoTabScaffold(
            tabBar: CupertinoTabBar(
              items: List<BottomNavigationBarItem>.generate(2, tabGenerator),
            ),
            controller: controller,
            tabBuilder: (BuildContext context, int index) => Text('Different page ${index + 1}'),
          ),
        )
      );
    } on AssertionError catch (e) {
      expect(e.toString(), contains('controller.index < tabBar.items.length'));
    }

    await tester.pumpWidget(
      CupertinoApp(
        home: CupertinoTabScaffold(
          tabBar: CupertinoTabBar(
            items: List<BottomNavigationBarItem>.generate(3, tabGenerator),
          ),
          controller: controller,
          tabBuilder: (BuildContext context, int index) => Text('Different page ${index + 1}'),
        ),
      )
    );

    expect(tester.takeException(), null);

    controller.index = 10;
    await tester.pump();

    final String message = tester.takeException().toString();
    expect(message, contains('current index ${controller.index}'));
    expect(message, contains('with 3 tabs'));
  });

  testWidgets('Current tab index cannot go below zero or be null', (WidgetTester tester) async {
    void expectAssertionError(VoidCallback callback, String errorMessage) {
      try {
        callback();
      } on AssertionError catch (e) {
        expect(e.toString(), contains(errorMessage));
      }
    }

    expectAssertionError(() => CupertinoTabController(initialIndex: -1), '>= 0');
    expectAssertionError(() => CupertinoTabController(initialIndex: null), '!= null');

    final CupertinoTabController controller = CupertinoTabController();

    expectAssertionError(() => controller.index = -1, '>= 0');
    expectAssertionError(() => controller.index = null, '!= null');
  });

  testWidgets('Does not lose state when focusing on text input', (WidgetTester tester) async {
    // Regression testing for https://github.com/flutter/flutter/issues/28457.

    await tester.pumpWidget(
      MediaQuery(
        data: const MediaQueryData(
          viewInsets:  EdgeInsets.only(bottom: 0),
        ),
        child: CupertinoApp(
          home: CupertinoTabScaffold(
            tabBar: _buildTabBar(),
            tabBuilder: (BuildContext context, int index) {
              return const CupertinoTextField();
            },
          ),
        ),
      ),
    );

    final EditableTextState editableState = tester.state<EditableTextState>(find.byType(EditableText));

    await tester.enterText(find.byType(CupertinoTextField), "don't lose me");

    await tester.pumpWidget(
      MediaQuery(
        data: const MediaQueryData(
          viewInsets:  EdgeInsets.only(bottom: 100),
        ),
        child: CupertinoApp(
          home: CupertinoTabScaffold(
            tabBar: _buildTabBar(),
            tabBuilder: (BuildContext context, int index) {
              return const CupertinoTextField();
            },
          ),
        ),
      ),
    );

    // The exact same state instance is still there.
    expect(tester.state<EditableTextState>(find.byType(EditableText)), editableState);
    expect(find.text("don't lose me"), findsOneWidget);
  });
}

CupertinoTabBar _buildTabBar({ int selectedTab = 0 }) {
  return CupertinoTabBar(
    items: const <BottomNavigationBarItem>[
      BottomNavigationBarItem(
        icon: ImageIcon(TestImageProvider(24, 24)),
        title: Text('Tab 1'),
      ),
      BottomNavigationBarItem(
        icon: ImageIcon(TestImageProvider(24, 24)),
        title: Text('Tab 2'),
      ),
    ],
    currentIndex: selectedTab,
    onTap: (int newTab) => selectedTabs.add(newTab),
  );
}