Traffic Light

main.dart

import 'dart:async';
import 'package:flutter/material.dart';
import 'package:flutter_bloc/flutter_bloc.dart';
import 'package:equatable/equatable.dart';

void main() => runApp(const MyApp());

sealed class TrafficLightState extends Equatable {
  @override
  List<Object?> get props => [];
}

final class TrafficLightGo extends TrafficLightState {}

final class TrafficLightGetReady extends TrafficLightState {}

final class TrafficLightStopIfSafe extends TrafficLightState {}

final class TrafficLightStop extends TrafficLightState {}

class TrafficLightCubit extends Cubit<TrafficLightState> {
  TrafficLightCubit() : super(TrafficLightGo()) {
    Timer.periodic(const Duration(milliseconds: 1000), (_) {
      if (state is TrafficLightGo) {
        emit(TrafficLightStopIfSafe());
      } else if (state is TrafficLightStopIfSafe) {
        emit(TrafficLightStop());
      } else if (state is TrafficLightStop) {
        emit(TrafficLightGetReady());
      } else if (state is TrafficLightGetReady) {
        emit(TrafficLightGo());
      }
    });
  }
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Counter App',
      debugShowCheckedModeBanner: false,
      theme: ThemeData(colorSchemeSeed: Colors.blue),
      home: BlocProvider(
        create: (context) => TrafficLightCubit(),
        child: const MyHomePage(title: 'Traffic Light'),
      ),
    );
  }
}

class MyHomePage extends StatelessWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(title)),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            BlocBuilder<TrafficLightCubit, TrafficLightState>(
              builder: (context, state) {
                return Column(
                  children: [                    
                    CircleAvatar(
                      radius: 30,
                      backgroundColor: (state is TrafficLightStop || state is TrafficLightGetReady) ? Colors.red : Color(0xff999999)
                    ),
                    CircleAvatar(
                      radius: 30,
                      backgroundColor: (state is TrafficLightGetReady || state is TrafficLightStopIfSafe) ? Colors.amber : Color(0xff999999),
                    ),       
                    CircleAvatar(
                      radius: 30,
                      backgroundColor: (state is TrafficLightGo) ? Colors.green : Color(0xff999999)
                    ),
                  ]
                ); 
              },
            ),
          ],
        ),
      ),
     );                 
  }
}