TrafficLights.dart

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

final Color darkBlue = Color.fromARGB(255, 18, 32, 47);

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: Crossing(),
      ),
    );
  }
}

class Crossing extends StatefulWidget {
  @override
  CrossingState createState() => CrossingState();
}

class CrossingState extends State<Crossing> {
  TrafficStatus trafficStatus = TrafficStatus.go;

  void onPressed() {
    trafficPrepareToStop();
  }

  void trafficPrepareToStop() {
    setState(() {
      trafficStatus = TrafficStatus.prepareToStop;
    });

    Timer(Duration(seconds: 2), trafficStop);
  }

  void trafficStop() {
    setState(() {
      trafficStatus = TrafficStatus.stop;
    });

    Timer(Duration(seconds: 5), trafficPrepareToGo);
  }

  void trafficPrepareToGo() {
    setState(() {
      trafficStatus = TrafficStatus.prepareToGo;
    });

    Timer(Duration(seconds: 2), trafficGo);
  }

  void trafficGo() {
    setState(() {
      trafficStatus = TrafficStatus.go;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Row(
      crossAxisAlignment: CrossAxisAlignment.start,
      children: [
        Padding(
          padding: EdgeInsets.all(32),
          child: TrafficLight(trafficStatus),
        ),
        Padding(
          padding: EdgeInsets.all(32),
          child:
              PedestrianLight(trafficStatus == TrafficStatus.stop, onPressed),
        ),
      ],
    );
  }
}

class PedestrianLight extends StatelessWidget {
  PedestrianLight(this.isSafeToCross, this.onPressed);

  final VoidCallback onPressed;
  final isSafeToCross;

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Container(
          color: Colors.black54,
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: <Widget>[
              Container(
                height: 30,
                width: 30,
                margin: EdgeInsets.all(8),
                decoration: BoxDecoration(
                  color: Colors.grey,
                  shape: BoxShape.circle,
                ),
                child: !isSafeToCross
                    ? Icon(Icons.person, color: Colors.red)
                    : null,
              ),
              Container(
                height: 30,
                width: 30,
                margin: EdgeInsets.all(8),
                decoration: BoxDecoration(
                  color: Colors.grey,
                  shape: BoxShape.circle,
                ),
                child: isSafeToCross
                    ? Icon(Icons.person, color: Colors.green)
                    : null,
              )
            ],
          ),
        ),
        RaisedButton(
          onPressed: () {
            onPressed();
          },
          child: Text('I want to cross'),
        ),
      ],
    );
  }
}

class TrafficLight extends StatelessWidget {
  TrafficLight(this.trafficStatus);

  final TrafficStatus trafficStatus;

  @override
  Widget build(BuildContext context) {
    return Container(
      color: Colors.black54,
      child: Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          Container(
            height: 30,
            width: 30,
            margin: EdgeInsets.all(8),
            decoration: BoxDecoration(
              color: trafficStatus == TrafficStatus.stop ||
                      trafficStatus == TrafficStatus.prepareToGo
                  ? Colors.red
                  : Colors.grey,
              shape: BoxShape.circle,
            ),
          ),
          Container(
            height: 30,
            width: 30,
            margin: EdgeInsets.all(8),
            decoration: BoxDecoration(
              color: trafficStatus == TrafficStatus.prepareToGo ||
                      trafficStatus == TrafficStatus.prepareToStop
                  ? Colors.amber
                  : Colors.grey,
              shape: BoxShape.circle,
            ),
          ),
          Container(
            height: 30,
            width: 30,
            margin: EdgeInsets.all(8),
            decoration: BoxDecoration(
              color: trafficStatus == TrafficStatus.go
                  ? Colors.green
                  : Colors.grey,
              shape: BoxShape.circle,
            ),
          )
        ],
      ),
    );
  }
}

enum TrafficStatus { go, prepareToStop, stop, prepareToGo }