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

void main() {
  runApp(const MyApp());
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key});

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int index = 0;

  @override
  Widget build(BuildContext context) {
    return PopScope(
      canPop: false,
      onPopInvokedWithResult: (didPop, result) {
        if (index != 0) {
          setState(() {
            index = 0;
          });
        } else {
          SystemNavigator.pop();
        }
      },
      child: Scaffold(
        appBar: AppBar(
          title: const Text('Flutter Demo'),
        ),
        body: Center(
          child: Text(
            index.toString(),
            style: const TextStyle(fontSize: 25),
          ),
        ),
        bottomNavigationBar: NavigationBar(
          onDestinationSelected: (value) {
            setState(() {
              index = value;
            });
          },
          selectedIndex: index,
          destinations: const [
            NavigationDestination(
              icon: Icon(Icons.home),
              label: 'Home',
            ),
            NavigationDestination(
              icon: Icon(Icons.settings),
              label: 'Settings',
            ),
          ],
        ),
      ),
    );
  }
}