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

import 'package:miler/widget/Bottom_page.dart';

/// The shell keeps every tab alive in an `IndexedStack`: all four pages are
/// built at launch and switching tabs only changes which one is painted. So a
/// page that loads in `initState` shows whatever was true before the rider did
/// anything — which is exactly how a completed stop failed to appear on
/// Activity. Pages re-read when their index comes forward, so the notifier that
/// tells them has to actually change.
void main() {
  testWidgets('an IndexedStack builds every child up front', (tester) async {
    final built = <int>[];

    Widget page(int i) => Builder(builder: (_) {
          built.add(i);
          return SizedBox(key: ValueKey('page$i'));
        });

    await tester.pumpWidget(
      MaterialApp(
        home: IndexedStack(index: 0, children: [page(0), page(1), page(2)]),
      ),
    );

    expect(
      built,
      containsAll(<int>[0, 1, 2]),
      reason: 'this is why initState cannot be a page\'s only load',
    );
  });

  test('the shell publishes the tab on screen', () {
    // Starts on Home and is a broadcast point a page can listen to.
    var heard = <int>[];
    void listener() => heard.add(BottomPage.currentTab.value);

    BottomPage.currentTab.addListener(listener);
    addTearDown(() => BottomPage.currentTab.removeListener(listener));

    BottomPage.currentTab.value = 2;
    BottomPage.currentTab.value = 1;

    expect(heard, [2, 1]);
  });
}