import 'dart:async';
import 'dart:ui';

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

/// falling points
void main() {
  runApp(MaterialApp(
    home: Scaffold(body: Board()),
    debugShowCheckedModeBanner: false,
  ));
}

final size = window.physicalSize / window.devicePixelRatio;

const maxPoints = 99;

const force = Offset(0, 1);

const acceleration = 1.1;

const fillColor = Colors.grey;

const strokeColor = Colors.grey;

class Point {
  final Offset offset;
  final Offset force;

  final bool active;

  static const zero = Point(Offset.zero, Offset.zero, false);

  const Point(this.offset, this.force, [this.active = true]);

  Point update() => active
      ? Point(offset + force, force * acceleration, offset.dy < size.height)
      : zero;

  @override
  bool operator ==(Object other) =>
      identical(this, other) ||
      other is Point &&
          runtimeType == other.runtimeType &&
          offset == other.offset &&
          force == other.force &&
          active == other.active;

  @override
  int get hashCode => offset.hashCode ^ force.hashCode ^ active.hashCode;
}

class Segment {
  final Point point1;

  final Point point2;

  final Color strokeColor;

  final Color fillColor;

  Offset get offset1 => point1.offset;

  Offset get offset2 => point2.offset;

  const Segment(this.point1, this.point2, {this.strokeColor, this.fillColor});

  bool get active => point1.active && point2.active;

  Segment update() => Segment(
        point1.update(),
        point2.update(),
        strokeColor: strokeColor,
        fillColor: fillColor,
      );
}

class Board extends StatefulWidget {
  @override
  _BoardState createState() => _BoardState();
}

class _BoardState extends State<Board> with SingleTickerProviderStateMixin {
  List<Segment> _segments = [];

  StreamController<List<Segment>> _streamer;

  Stream<List<Segment>> get _segment$ => _streamer.stream;

  @override
  void initState() {
    _streamer = StreamController<List<Segment>>()..add(<Segment>[]);
    AnimationController.unbounded(vsync: this, duration: Duration(seconds: 1))
      ..repeat()
      ..addListener(_updateSegments);
    super.initState();
  }

  @override
  Widget build(BuildContext context) => MouseRegion(
        onHover: (details) => _addSegment(details.position),
        child: StreamBuilder<List<Segment>>(
          initialData: <Segment>[],
          stream: _segment$,
          builder: (_, stream) =>
              CustomPaint(size: size, painter: Painter(stream.data)),
        ),
      );

  void _addSegment(Offset offset) {
    _segments
      ..add(
        Segment(
          _segments.isEmpty ? Point(offset, force) : _segments.last.point2,
          Point(offset, force),
          strokeColor: strokeColor,
          fillColor: fillColor,
        ),
      );
  }

  void _updateSegments() {
    _segments = _segments
        .where((element) => element.active)
        .map((element) => element.update())
        .toList();
    _streamer.add(_segments);
  }
}

class Painter extends CustomPainter {
  static const radius = 2.0;

  static const offsetTop = Offset(0, -50);

  static const offsetBottom = Offset(0, 50);

  static final fill = Paint()..color = fillColor;

  static final stroke = Paint()
    ..color = Colors.grey
    ..style = PaintingStyle.stroke;

  final List<Segment> segments;

  const Painter(this.segments);

  @override
  void paint(Canvas canvas, Size size) {
    if (segments.isEmpty) return;

    for (final segment in segments) {
      canvas.drawCircle(segment.point1.offset, radius, fill);

      canvas.drawLine(
        segment.point1.offset - offsetTop,
        segment.point1.offset - offsetBottom,
        stroke,
      );
      canvas.drawLine(
        segment.point1.offset - offsetTop,
        segment.point2.offset - offsetTop,
        stroke,
      );
      canvas.drawLine(
        segment.point1.offset - offsetBottom,
        segment.point2.offset - offsetBottom,
        stroke,
      );
      canvas.drawLine(
        segment.point2.offset - offsetTop,
        segment.point2.offset - offsetBottom,
        stroke,
      );
    }

    for (int i = 0; i < segments.length; i++) {
      canvas.drawLine(
          segments[i].point1.offset, segments[i].point2.offset, stroke);
    }
  }

  @override
  bool shouldRepaint(Painter oldDelegate) =>
      segments.isNotEmpty && !listEquals(segments, oldDelegate.segments);
}