import 'package:flutter/material.dart';import 'package:flutter/animation.dart';import 'dart:ui' show lerpDouble;import 'dart:math';import 'color_palette.dart';import 'tween.dart';class BarChart { BarChart(this.groups); final List<BarGroup> groups; factory BarChart.empty(Size size) { return new BarChart(<BarGroup>[]); } factory BarChart.random(Size size, Random random) { const groupWidthFraction = 0.75; const barWidthFraction = 0.9; final groupRanks = _selectRanks(random, 5); final groupCount = groupRanks.length; final groupDistance = size.width / (1+groupCount); final groupWidth = groupDistance * groupWidthFraction; final startX = groupDistance - groupWidth/2; final barRanks = _selectRanks(random, ColorPalette.primary.length ~/ 2); final barCount = barRanks.length; final barDistance = groupWidth / barCount; final barWidth = barDistance * barWidthFraction; final groups = new List.generate(  groupCount,  (i) {  final bars = new List.generate(   barCount,   (j) => new Bar(   barRanks[j],   startX + i * groupDistance + j * barDistance,   barWidth,   random.nextDouble() * size.height,   ColorPalette.primary[barRanks[j]],   )  );  return new BarGroup(   groupRanks[i],   bars  );  } ); return new BarChart(groups); } static List<int> _selectRanks(Random random, int cap) { final ranks = <int>[]; var rank = 0; while(true) {  rank += random.nextInt(2);  if(cap <= rank) break;  ranks.add(rank);  rank++; } return ranks; }}class BarChartTween extends Tween<BarChart> { BarChartTween(BarChart begin, BarChart end) : _groupsTween = new MergeTween<BarGroup>(begin.groups, end.groups), super(begin: begin, end: end); final MergeTween<BarGroup> _groupsTween; @override BarChart lerp(double t) => new BarChart(_groupsTween.lerp(t));}class BarGroup implements MergeTweenable<BarGroup> { BarGroup(this.rank, this.bars); final int rank; final List<Bar> bars; @override BarGroup get empty => new BarGroup(rank, <Bar>[]); @override bool operator <(BarGroup other) => rank < other.rank; @override Tween<BarGroup> tweenTo(BarGroup other) => new BarGroupTween(this, other);}class BarGroupTween extends Tween<BarGroup> { BarGroupTween(BarGroup begin, BarGroup end) : _barsTween = new MergeTween<Bar>(begin.bars, end.bars), super(begin: begin, end: end) {  assert(begin.rank == end.rank); } final MergeTween<Bar> _barsTween; @override BarGroup lerp(double t) => new BarGroup( begin.rank, _barsTween.lerp(t) );}class Bar extends MergeTweenable<Bar> { Bar(this.rank, this.x, this.width, this.height, this.color); final int rank; final double x; final double width; final double height; final Color color; @override Bar get empty => new Bar(rank, x, 0.0, 0.0, color); @override bool operator <(Bar other) => rank < other.rank; @override Tween<Bar> tweenTo(Bar other) => new BarTween(this, other); static Bar lerp(Bar begin, Bar end, double t) { assert(begin.rank == end.rank); return new Bar(  begin.rank,  lerpDouble(begin.x, end.x, t),  lerpDouble(begin.width, end.width, t),  lerpDouble(begin.height, end.height, t),  Color.lerp(begin.color, end.color, t) ); }}class BarTween extends Tween<Bar> { BarTween(Bar begin, Bar end) : super(begin: begin, end: end) { assert(begin.rank == end.rank); } @override Bar lerp(double t) => Bar.lerp(begin, end, t);}class BarChartPainter extends CustomPainter { BarChartPainter(Animation<BarChart> animation)  : animation = animation,  super(repaint: animation); final Animation<BarChart> animation; @override void paint(Canvas canvas, Size size) { final paint = new Paint()..style = PaintingStyle.fill; final chart = animation.value; for(final stack in chart.groups) {  for(final bar in stack.bars) {  paint.color = bar.color;  canvas.drawRect(   new Rect.fromLTWH(   bar.x,   size.height - bar.height,   bar.width,   bar.height   ),   paint,  );  } } } @override bool shouldRepaint(BarChartPainter old) => false;}