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

final loremIpsum =
    "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.";

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Welcome to Flutter',
      home: Scaffold(
        appBar: AppBar(
          title: Text('Welcome to Flutter'),
        ),
        body: Center(
          child: Container(
            width: 350,
            color: Color.fromARGB(100, 0, 0, 0),
            child: SelectText(),
          ),
        ),
      ),
    );
  }
}

class SelectText extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final double sidebar = 20;
    final InlineSpan zeText =
        TextSpan(text: loremIpsum, style: TextStyle(fontSize: 15), children: [
      TextSpan(
          text: loremIpsum,
          style: TextStyle(
              fontWeight: FontWeight
                  .bold) // offending line, comment it out and web will work too
          )
    ]);
    return LayoutBuilder(
        builder: (BuildContext context, BoxConstraints constraints) {
      final textPainter = RenderParagraph(
        zeText,
        textDirection: TextDirection.ltr,
      );
      final width = constraints.maxWidth - sidebar;
      textPainter.layout(constraints);
      final height = textPainter.computeMaxIntrinsicHeight(width);

      return Container(
          width: width,
          height: height,
          color: Colors.yellow,
          child: GestureDetector(
            onTapDown: (details) {
              var pos = textPainter.getPositionForOffset(details.localPosition);
              var offset = textPainter.getOffsetForCaret(
                  pos, Rect.fromLTWH(1.0, 1.0, 1.0, 1.0));
              print("Selection pos: $pos");
              print("Selection pos: $offset");
            },
            child: Text.rich(
              zeText,
              textDirection: TextDirection.ltr,
            ),
          ));
    });
  }
}