samples/material_studies/rally/lib/charts/pie_chart.dart

// Copyright 2019-present the Flutter authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

import 'dart:math';

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';

import 'package:rally/colors.dart';
import 'package:rally/data.dart';
import 'package:rally/formatters.dart';

/// A colored piece of the [RallyPieChart].
class RallyPieChartSegment {
  final Color color;
  final double value;

  const RallyPieChartSegment({this.color, this.value});
}

List<RallyPieChartSegment> buildSegmentsFromAccountItems(
    List<AccountData> items) {
  return List<RallyPieChartSegment>.generate(
    items.length,
    (i) => RallyPieChartSegment(
      color: RallyColors.accountColor(i),
      value: items[i].primaryAmount,
    ),
  );
}

List<RallyPieChartSegment> buildSegmentsFromBillItems(List<BillData> items) {
  return List<RallyPieChartSegment>.generate(
    items.length,
    (i) => RallyPieChartSegment(
      color: RallyColors.billColor(i),
      value: items[i].primaryAmount,
    ),
  );
}

List<RallyPieChartSegment> buildSegmentsFromBudgetItems(
    List<BudgetData> items) {
  return List<RallyPieChartSegment>.generate(
    items.length,
    (i) => RallyPieChartSegment(
      color: RallyColors.budgetColor(i),
      value: items[i].primaryAmount - items[i].amountUsed,
    ),
  );
}

/// An animated circular pie chart to represent pieces of a whole, which can
/// have empty space.
class RallyPieChart extends StatefulWidget {
  RallyPieChart(
      {this.heroLabel, this.heroAmount, this.wholeAmount, this.segments});

  final String heroLabel;
  final double heroAmount;
  final double wholeAmount;
  final List<RallyPieChartSegment> segments;

  _RallyPieChartState createState() => _RallyPieChartState();
}

class _RallyPieChartState extends State<RallyPieChart>
    with SingleTickerProviderStateMixin {
  AnimationController controller;
  Animation<double> animation;

  @override
  initState() {
    super.initState();
    controller = AnimationController(
        duration: const Duration(milliseconds: 600), vsync: this);
    animation = CurvedAnimation(
        parent: TweenSequence(<TweenSequenceItem<double>>[
          TweenSequenceItem(tween: Tween(begin: 0.0, end: 0.0), weight: 1.0),
          TweenSequenceItem(tween: Tween(begin: 0.0, end: 1.0), weight: 1.5),
        ]).animate(controller),
        curve: Curves.decelerate);
    controller.forward();
  }

  dispose() {
    controller.dispose();
    super.dispose();
  }

  Widget build(BuildContext context) {
    return _AnimatedRallyPieChart(
      animation: animation,
      centerLabel: widget.heroLabel,
      centerAmount: widget.heroAmount,
      total: widget.wholeAmount,
      segments: widget.segments,
    );
  }
}

class _AnimatedRallyPieChart extends AnimatedWidget {
  _AnimatedRallyPieChart({
    Key key,
    this.animation,
    this.centerLabel,
    this.centerAmount,
    this.total,
    this.segments,
  }) : super(key: key, listenable: animation);

  final Animation<double> animation;
  final String centerLabel;
  final double centerAmount;
  final double total;
  final List<RallyPieChartSegment> segments;

  Widget build(BuildContext context) {
    final labelTextStyle = Theme.of(context)
        .textTheme
        .body1
        .copyWith(fontSize: 14.0, letterSpacing: 0.5);

    return DecoratedBox(
      decoration: _RallyPieChartOutlineDecoration(
          maxFraction: animation.value, total: total, segments: segments),
      child: SizedBox(
        height: 300.0,
        child: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              Text(
                centerLabel,
                style: labelTextStyle,
              ),
              Text(
                Formatters.usdWithSign.format(centerAmount),
                style: Theme.of(context).textTheme.headline,
              ),
            ],
          ),
        ),
      ),
    );
  }
}

class _RallyPieChartOutlineDecoration extends Decoration {
  _RallyPieChartOutlineDecoration(
      {this.maxFraction, this.total, this.segments});

  final double maxFraction;
  final double total;
  final List<RallyPieChartSegment> segments;

  @override
  BoxPainter createBoxPainter([onChanged]) {
    return _RallyPieChartOutlineBoxPainter(
      maxFraction: maxFraction,
      wholeAmount: total,
      segments: segments,
    );
  }
}

class _RallyPieChartOutlineBoxPainter extends BoxPainter {
  _RallyPieChartOutlineBoxPainter(
      {this.maxFraction, this.wholeAmount, this.segments});

  final double maxFraction;
  final double wholeAmount;
  final List<RallyPieChartSegment> segments;

  @override
  void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) {
    // Create two padded rects to draw arcs in: one for colored arcs and one for
    // inner bg arc.
    const double strokeWidth = 4.0;
    final outerRadius =
        min(configuration.size.width, configuration.size.height) / 2;
    final outerRect = Rect.fromCircle(
        center: configuration.size.center(Offset.zero),
        radius: outerRadius - strokeWidth * 3.0);
    final innerRect = Rect.fromCircle(
        center: configuration.size.center(Offset.zero),
        radius: outerRadius - strokeWidth * 4.0);

    // Paint each arc with spacing.
    double cummulativeSpace = 0.0;
    double cummulativeTotal = 0.0;
    const double wholeRadians = (2.0 * pi);
    const double spaceRadians = wholeRadians / 180.0;
    final wholeMinusSpacesRadians =
        wholeRadians - (segments.length * spaceRadians);
    for (RallyPieChartSegment segment in segments) {
      final paint = Paint()..color = segment.color;
      final start = maxFraction *
              ((cummulativeTotal / wholeAmount * wholeMinusSpacesRadians) +
                  cummulativeSpace) -
          pi / 2.0;
      final sweep =
          maxFraction * (segment.value / wholeAmount * wholeMinusSpacesRadians);
      canvas.drawArc(outerRect, start, sweep, true, paint);
      cummulativeTotal += segment.value;
      cummulativeSpace += spaceRadians;
    }

    // Paint any remaining space black (e.g. budget amount remaining).
    double remaining = wholeAmount - cummulativeTotal;
    if (remaining > 0) {
      final paint = Paint()..color = Colors.black;
      final start = maxFraction *
              ((cummulativeTotal / wholeAmount * wholeMinusSpacesRadians) +
                  spaceRadians * segments.length) -
          pi / 2.0;
      final sweep = maxFraction *
          (remaining / wholeAmount * wholeMinusSpacesRadians - spaceRadians);
      canvas.drawArc(outerRect, start, sweep, true, paint);
    }

    // Paint a smaller inner circle to cover the painted arcs, so they are
    // display as segments.
    Paint bgPaint = Paint()..color = RallyColors.primaryBackground;
    canvas.drawArc(innerRect, 0.0, 2.0 * pi, true, bgPaint);
  }
}