import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);
  @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 ScrollController _scrollController = ScrollController();

  Widget _list() {
    return Container(
      height: 5 * 40,
      child: Scrollbar(
          controller: _scrollController,
          thumbVisibility: true,
          child: ListView.builder(
              controller: _scrollController,
              padding: EdgeInsets.zero,
              itemCount: 20,
              itemBuilder: (context, index) => ListTile(
                    title: Text('item $index'),
                  ))),
    );
  }

  final LayerLink _layerLink = LayerLink();

  OverlayEntry _createOverlayEntry() {
    return OverlayEntry(
        builder: (context) => Positioned(
              left: searchFieldDimensions.offset!.dx,
              width: searchFieldDimensions.width,
              child: CompositedTransformFollower(
                  offset: Offset(0, 50),
                  link: _layerLink,
                  child: Material(color: Colors.red, child: _list())),
            ));
  }

  @override
  void initState() {
    WidgetsBinding.instance.addPostFrameCallback((_) {
      if (mounted) {
        _calculateDimensions();
      }
    });
    super.initState();
  }

  @override
  void didChangeDependencies() {
    // update overlay dimensions on mediaQuery change
    _calculateDimensions();
    if (_overlayEntry != null && _overlayEntry!.mounted) {
      WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
        if (mounted) {
          _overlayEntry!.markNeedsBuild();
        }
      });
    }
    super.didChangeDependencies();
  }

  void _calculateDimensions() {
    if (!mounted || key.currentContext == null) {
      return;
    }

    try {
      final MediaQueryData mediaQuery = MediaQuery.of(context);
      final RenderBox? textFieldRenderBox =
          key.currentContext!.findRenderObject() as RenderBox?;

      if (textFieldRenderBox == null || !textFieldRenderBox.hasSize) {
        return;
      }

      final textFieldsize = textFieldRenderBox.size;
      final offset = textFieldRenderBox.localToGlobal(Offset.zero);

      searchFieldDimensions = SearchFieldDimensions(
        offset: offset,
        height: textFieldsize.height,
        width: textFieldsize.width,
        bottom: mediaQuery.size.height - offset.dy - textFieldsize.height,
        top: offset.dy,
      );
    } catch (e) {
      debugPrint('Error calculating SearchField dimensions: $e');
    }
  }

  OverlayEntry? _overlayEntry;

  var searchFieldDimensions = SearchFieldDimensions();
  final GlobalKey key = GlobalKey();
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            CompositedTransformTarget(
              link: _layerLink,
              child: TextFormField(
                key: key,
                decoration: InputDecoration(
                  focusedBorder: OutlineInputBorder(
                    borderSide: BorderSide(
                      color: Colors.black.withOpacity(0.8),
                    ),
                  ),
                  border: OutlineInputBorder(
                    borderSide: BorderSide(color: Colors.red),
                  ),
                ),
                onTapOutside: (event) {
                  if (_overlayEntry != null && _overlayEntry!.mounted) {
                    _overlayEntry!.remove();
                    _overlayEntry = null;
                    FocusScope.of(context).unfocus();
                  }
                },
                onTap: () {
                  _overlayEntry?.remove();
                  _overlayEntry = _createOverlayEntry();
                  Overlay.of(context)!.insert(_overlayEntry!);
                },
                onChanged: (query) {},
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class SearchFieldDimensions {
  /// height of the searchfield
  final double? height;

  /// width of the searchfield
  final double? width;

  /// offset of the searchfield
  final Offset? offset;

  /// Space Above the searchfield
  final double? top;

  /// Space Below the searchfield
  ///
  final double? bottom;

  SearchFieldDimensions({
    this.height,
    this.width,
    this.offset,
    this.top,
    this.bottom,
  });
}