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 WidgetSpanTextEditingController _controller =
      WidgetSpanTextEditingController(text: '...\n' * 5 + 'Lazy \uffff dog.' + '...\n' * 5);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Container(
          constraints: const BoxConstraints.expand(),
          child: TextField(
            controller: _controller,
            maxLines: 1000000,
          ),
        ),
      ),
    );
  }
}

class WidgetSpanTextEditingController extends TextEditingController {
  WidgetSpanTextEditingController({String? text})
      : super.fromValue(text == null ? TextEditingValue.empty : TextEditingValue(text: text));

  @override
  TextSpan buildTextSpan(
      {required BuildContext context,
      TextStyle? style,
      required bool withComposing}) {

    TextRange? matchedRange;

    if (text.contains('\uffff')) {
      matchedRange = _findMatchedRange(text);
    }

    if (matchedRange != null) {
      return TextSpan(
        children: [
          TextSpan(text: matchedRange.textBefore(text)),
          WidgetSpan(
            child: IconButton(
              onPressed: () => ScaffoldMessenger.of(context)
                  .showSnackBar(const SnackBar(content: Text('Pressed!'), duration: Durations.short2)),
              icon: const Icon(Icons.bug_report_outlined),
            ),
          ),
          TextSpan(text: matchedRange.textAfter(text)),
        ],
        style: style,
      );
    }

    return TextSpan(text: text, style: style);
  }

  TextRange _findMatchedRange(String text) {
    final RegExp matchPattern = RegExp(RegExp.escape('\uffff'));
    late TextRange matchedRange;
    
    for (final Match match in matchPattern.allMatches(text)) {
      matchedRange = TextRange(start: match.start, end: match.end);
    }

    return matchedRange;
  }
}