import 'dart:math' as math;
import 'dart:ui' as ui;
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> {
  final GlobalKey _paragraphKey = GlobalKey();
  List<String> _lineMetricData = <String>[];

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text(widget.title)),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.start,
        children: <Widget>[
          Paragraph(
            key: _paragraphKey,
            inlineSpan: const TextSpan(
              text: 'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do '
                'eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim '
                'ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut '
                'aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit '
                'in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur '
                'sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt '
                'mollit anim id est laborum.',
              style: TextStyle(fontSize: 16.0, color: Colors.black),
            ),
          ),
          const SizedBox(height: 50.0),
          for (String metricData in _lineMetricData) Text(metricData),
        ],
      ),
      floatingActionButton: FloatingActionButton(
        child: const Icon(Icons.abc),
        onPressed: _getLineMetrics,
      ),
    );
  }

  void _getLineMetrics() {
    RenderParagraph renderParagraph = _paragraphKey.currentContext!.findRenderObject()! as RenderParagraph;
    List<ui.LineMetrics> lineMetrics = renderParagraph.lineMetrics;
    _lineMetricData = lineMetrics.map((metrics) => '#${metrics.lineNumber} baseLine=${metrics.baseline}').toList();
    _lineMetricData.add('Total text height: ${renderParagraph.height}');
    setState(() {  });
  }
}

class Paragraph extends SingleChildRenderObjectWidget {
  const Paragraph({Key? key, required this.inlineSpan}) : super(key: key);

  final InlineSpan inlineSpan;

  @override
  RenderParagraph createRenderObject(BuildContext context) {
    return RenderParagraph(inlineSpan: inlineSpan);
  }
}

class RenderParagraph extends RenderBox {
  RenderParagraph({required this.inlineSpan})
    : _textPainter = TextPainter(
      text: inlineSpan,
      textDirection: TextDirection.ltr,
    );

  final InlineSpan inlineSpan;
  final TextPainter _textPainter;

  List<ui.LineMetrics> get lineMetrics => _textPainter.computeLineMetrics();
  double get height => _textPainter.height;

  @override
  double computeMinIntrinsicWidth(double height) {
    _layoutText();
    return _textPainter.minIntrinsicWidth;
  }

  @override
  double computeMaxIntrinsicWidth(double height) {
    _layoutText();
    return _textPainter.maxIntrinsicWidth;
  }

  @override
  Size computeDryLayout(BoxConstraints constraints) {
    _layoutText(minWidth: constraints.minWidth, maxWidth: constraints.maxWidth);
    return Size(constraints.maxWidth, _textPainter.height);
  }

  @override
  void performLayout() {
    final BoxConstraints constraints = this.constraints;
    _layoutText(minWidth: constraints.minWidth, maxWidth: constraints.maxWidth);
    size = Size(math.min(_textPainter.width, constraints.maxWidth), _textPainter.height);
  }

  void _layoutText({double minWidth = 0.0, double maxWidth = double.infinity}) {
    final double availableMaxWidth = math.max(0.0, maxWidth);
    _textPainter.layout(minWidth: availableMaxWidth, maxWidth: availableMaxWidth);
  }

  @override
  void paint(PaintingContext context, Offset offset) {
    _textPainter.paint(context.canvas, offset);
  }
}