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

void main() {
  runApp(
    const MaterialApp(
      home: Scaffold(
        body: TextInputExample(),
      ),
    ),
  );
}

class TextInputExample extends StatefulWidget {
  const TextInputExample({Key? key}) : super(key: key);

  @override
  State<TextInputExample> createState() => _TextInputExampleState();
}

class _TextInputExampleState extends State<TextInputExample> implements DeltaTextInputClient {
  TextInputConnection? _inputConnection;

  TextEditingValue _currentEditingValue = TextEditingValue(
    text: '',
    selection: TextSelection.collapsed(offset: 0),
  );

  FocusNode _focusNode = FocusNode();

  @override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
      _attach();
    });
  }

  @override
  void dispose() {
    _focusNode.dispose();
    super.dispose();
  }

  @override
  void updateEditingValueWithDeltas(List<TextEditingDelta> textEditingDeltas) {
    TextEditingValue newEditingValue = _currentEditingValue;

    for (final delta in textEditingDeltas) {
      newEditingValue = delta.apply(newEditingValue);
    }

    setState(() {
      _currentEditingValue = newEditingValue;
    });
  }

  void _attach() {
    if (_inputConnection != null) {
      return;
    }
    _inputConnection = TextInput.attach(
      this,
      const TextInputConfiguration(
        enableDeltaModel: true,
        inputType: TextInputType.multiline,
        textCapitalization: TextCapitalization.sentences,
        inputAction: TextInputAction.newline,
        keyboardAppearance: Brightness.light,
      ),
    );

    final renderBox = context.findRenderObject() as RenderBox;

    _inputConnection!
      ..show()
      ..setEditingState(_currentEditingValue)
      ..setEditableSizeAndTransform(renderBox.size, renderBox.getTransformTo(null))
      ..setCaretRect(
        Rect.fromCenter(center: renderBox.size.center(Offset.zero), width: 50, height: 50),
      );
  }

  @override
  Widget build(BuildContext context) {
    return Actions(
      actions: {
        // Prevent Flutter from using the arrow keys to perform focus traversal.
        DoNothingAndStopPropagationTextIntent: DoNothingAction(consumesKey: false),
      },
      child: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            Text(
              'Press and hold "a"',
              style: TextStyle(fontSize: 18),
            ),
            Focus(
              focusNode: _focusNode,
              autofocus: true,
              child: Text(
                _currentEditingValue.text,
                textAlign: TextAlign.center,
                style: TextStyle(
                  fontSize: 18,
                  fontWeight: FontWeight.bold,
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }

  @override
  void connectionClosed() {}

  @override
  AutofillScope? get currentAutofillScope => null;

  @override
  TextEditingValue? get currentTextEditingValue => null;

  @override
  void insertTextPlaceholder(Size size) {}

  @override
  void performAction(TextInputAction action) {}

  @override
  void performPrivateCommand(String action, Map<String, dynamic> data) {}

  @override
  void removeTextPlaceholder() {}

  @override
  void showAutocorrectionPromptRect(int start, int end) {}

  @override
  void showToolbar() {}

  @override
  void updateEditingValue(TextEditingValue value) {}

  @override
  void updateFloatingCursor(RawFloatingCursorPoint point) {}

  @override
  void didChangeInputControl(TextInputControl? oldControl, TextInputControl? newControl) {}

  @override
  void insertContent(KeyboardInsertedContent content) {}

  @override
  void performSelector(String selectorName) {}
}