Flutter puzzle (I)

main.dart

import 'dart:math';

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);
  
  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  late int _counter;
  late bool _reversed;

  @override
  void initState() {
    super.initState();
    _counter = 0;
    _reversed = false;
  }

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  void _decrementCounter() {
    setState(() {
      _counter--;
    });
  }

  void _resetCounter() {
    setState(() {
      _counter = 0;
      _swap();
    });
  }

  void _swap() {
    setState(() {
      _reversed = !_reversed;
    });
  }

  @override
  Widget build(BuildContext context) {
    final incrementButton = FancyButton(
        onPressed: () => _incrementCounter(), child: const Text("Increment"));

    final decrementButton = FancyButton(
        onPressed: _decrementCounter, child: const Text("Decrement"));

    List<Widget> buttons = <Widget>[incrementButton, decrementButton];
    if (_reversed) {
      buttons = buttons.reversed.toList();
    }

    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[            
            const Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.headline4,
            ),
            Row(
                mainAxisAlignment: MainAxisAlignment.spaceAround,
                crossAxisAlignment: CrossAxisAlignment.center,
                children: buttons)
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _resetCounter,
        tooltip: 'Reset',
        child: const Icon(Icons.refresh),
      ), 
    );
  }
}

class FancyButton extends StatefulWidget {
  final VoidCallback onPressed;
  final Widget child;

  const FancyButton({Key? key, required this.onPressed, required this.child})
      : super(key: key);

  @override
  State<FancyButton> createState() => _FancyButtonState();
}

class _FancyButtonState extends State<FancyButton> {
  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      style: ElevatedButton.styleFrom(primary: _getColors()),
      onPressed: widget.onPressed,
      child: widget.child,
    );
  }

  Color _getColors() {
    return _buttonColors.putIfAbsent(
        this, () => colors[next(0, colors.length - 1)]);
  }

  final Map<_FancyButtonState, Color> _buttonColors = {};
  final _random = Random();

  int next(int min, int max) => min + _random.nextInt(max - min);
  List<Color> colors = [
    Colors.blue,
    Colors.green,
    Colors.orange,
    Colors.purple,
    Colors.amber,
    Colors.lightBlue,
    Colors.teal,
    Colors.yellow,
    Colors.deepOrange,
    Colors.greenAccent,
  ];
}