import 'package:flutter/material.dart';

void main() async {
  runApp(const _MyApp());
}

class _MyApp extends StatelessWidget {
  const _MyApp();

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        useMaterial3: false,
        pageTransitionsTheme: const PageTransitionsTheme(
          builders: <TargetPlatform, PageTransitionsBuilder>{
            TargetPlatform.android: PredictiveBackPageTransitionsBuilder(),
          },
        ),
      ),
      title: 'Flutter Demo',
      routes: {
        '/': (BuildContext context) {
          return _NestedNavigatorPage();
        },
        'nav1leaf': (BuildContext context) {
          return const _Nav1LeafPage();
        },
      },
    );
  }
}

class _NestedNavigatorPage extends StatelessWidget {
  _NestedNavigatorPage();

  final GlobalKey<NavigatorState> _nestedNavigatorKey = GlobalKey<NavigatorState>();

  @override
  Widget build(BuildContext context) {
    return Navigator(
      key: _nestedNavigatorKey,
      initialRoute: 'nav2home',
      onGenerateRoute: (RouteSettings settings) {
        return switch (settings.name) {
          'nav2home' => MaterialPageRoute(
            builder: (BuildContext context) => const _Nav2HomePage(),
          ),
          'nav2leaf' => MaterialPageRoute(
            builder: (BuildContext context) => const _Nav2LeafPage(),
          ),
          _ => MaterialPageRoute(
            builder: (BuildContext context) => const Text('404'),
          ),
        };
      },
    );
  }
}

class _Nav2HomePage extends StatelessWidget {
  const _Nav2HomePage();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.blueAccent,
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text('Home page of Navigator 2'),
            const SizedBox(height: 16, width: double.infinity),
            ElevatedButton(
              child: const Text('Open nav 2 leaf page'),
              onPressed: () => Navigator.of(context).pushNamed('nav2leaf'),
            ),
          ],
        ),
      ),
    );
  }
}

class _Nav2LeafPage extends StatelessWidget {
  const _Nav2LeafPage();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.blue,
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            const Text('Leaf page of Navigator 2'),
            const SizedBox(height: 16, width: double.infinity),
            ElevatedButton(
              child: const Text('Open nav 1 leaf page'),
              onPressed: () => Navigator.of(context, rootNavigator: true).pushNamed('nav1leaf'),
            ),
          ],
        ),
      ),
    );
  }
}

class _Nav1LeafPage extends StatelessWidget {
  const _Nav1LeafPage();

  @override
  Widget build(BuildContext context) {
    return const Scaffold(
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.center,
        children: [
          Text('Leaf of Navigator 1'),
        ],
      ),
    );
  }
}