import 'package:flutter/material.dart';

/// roughly a frame at 60 fps
const _microsecondsPerFrameAt60fps = 16333;
const _arbitraryScrollDuration = Duration(seconds: 5);
const _itemCount = 10000;
const _sixtyFPSDuration = Duration(
  microseconds: _microsecondsPerFrameAt60fps * _itemCount,
);

void main() => runApp(
      const MaterialApp(
        showPerformanceOverlay: true,
        home: MyHomePage(),
      ),
    );

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

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

class _MyHomePageState extends State<MyHomePage> {
  var _hasIcon = false;
  late final ScrollController _controller;

  @override
  void initState() {
    super.initState();
    _controller = ScrollController();
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  void _toggleIcon() => setState(() => _hasIcon = !_hasIcon);

  @override
  Widget build(context) => Scaffold(
        body: ListView.builder(
          controller: _controller,
          itemCount: _itemCount,
          itemBuilder: (context, index) {
            final textWidget = Expanded(
              flex: 1,
              child: Text('$index', textAlign: TextAlign.center),
            );
            return Row(
              mainAxisAlignment: MainAxisAlignment.spaceAround,
              children: [
                textWidget,
                for (var i = 0; i < 5; i++) ...[
                  _hasIcon
                      ? const Expanded(
                          flex: 1,
                          child: FlutterLogo(),
                        )
                      : textWidget,
                ]
              ],
            );
          },
        ),
        floatingActionButton: Row(
          mainAxisAlignment: MainAxisAlignment.spaceAround,
          children: [
            FloatingActionButton(
              onPressed: () => _controller.jumpTo(0),
              child: const Text('reset'),
            ),
            TimerButton(
              controller: _controller,
              duration: _arbitraryScrollDuration,
            ),
            TimerButton(
              controller: _controller,
              duration: _sixtyFPSDuration,
            ),
            FloatingActionButton(
              onPressed: _toggleIcon,
              child: _hasIcon
                  ? const Icon(Icons.text_increase_outlined)
                  : const FlutterLogo(),
            ),
          ],
        ),
      );
}

class TimerButton extends StatelessWidget {
  final ScrollController controller;
  final Duration duration;
  const TimerButton({
    super.key,
    required this.controller,
    required this.duration,
  });

  @override
  Widget build(context) => FloatingActionButton(
        onPressed: () async {
          final start = DateTime.now();

          await controller.animateTo(
            controller.position.maxScrollExtent,
            duration: duration,
            curve: Curves.linear,
          );

          if (!context.mounted) {
            return;
          }

          final actualDuration = DateTime.now().difference(start);
          ScaffoldMessenger.of(context).showSnackBar(
            SnackBar(
              content: Text('expected duration: ${duration.inMilliseconds} ms\n'
                  'actual duration: ${actualDuration.inMilliseconds}'),
            ),
          );
        },
        child: Text('~${duration.inSeconds} s'),
      );
}