Address autocomplete form

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

class AddressSuggestion {
  const AddressSuggestion({required this.label, required this.street, required this.city, required this.postcode});
  final String label, street, city, postcode;
  @override
  String toString() => label;
}

typedef AddressLookup = Future<List<AddressSuggestion>> Function(String query);

class AddressForm extends StatefulWidget {
  const AddressForm({super.key, required this.lookup});
  final AddressLookup lookup;
  @override
  State<AddressForm> createState() => _AddressFormState();
}

class _AddressFormState extends State<AddressForm> {
  final _street = TextEditingController();
  final _city = TextEditingController();
  final _postcode = TextEditingController();
  Timer? _debounce;
  int _ticket = 0;

  @override
  void dispose() {
    _debounce?.cancel();
    for (final c in [_street, _city, _postcode]) { c.dispose(); }
    super.dispose();
  }

  /// Autocomplete wants a Future per keystroke; wait for a pause and drop stale answers.
  Future<Iterable<AddressSuggestion>> _options(TextEditingValue v) {
    final completer = Completer<Iterable<AddressSuggestion>>();
    _debounce?.cancel();
    final mine = ++_ticket;
    if (v.text.trim().length < 3) return Future.value(const []);
    _debounce = Timer(const Duration(milliseconds: 300), () async {
      try {
        final rows = await widget.lookup(v.text.trim());
        completer.complete(mine == _ticket ? rows : const []);
      } catch (_) {
        completer.complete(const []);
      }
    });
    return completer.future;
  }

  void _fill(AddressSuggestion s) {
    _street.text = s.street;
    _city.text = s.city;
    _postcode.text = s.postcode;
  }

  @override
  Widget build(BuildContext context) {
    return Column(children: [
      Autocomplete<AddressSuggestion>(
        optionsBuilder: (v) async => await _options(v),
        onSelected: _fill,
        fieldViewBuilder: (context, controller, focus, onSubmit) => TextField(
          controller: controller,
          focusNode: focus,
          decoration: const InputDecoration(labelText: 'Search address', prefixIcon: Icon(Icons.search)),
        ),
      ),
      const SizedBox(height: 12),
      TextField(controller: _street, decoration: const InputDecoration(labelText: 'Street')),
      Row(children: [
        Expanded(child: TextField(controller: _city, decoration: const InputDecoration(labelText: 'City'))),
        const SizedBox(width: 12),
        SizedBox(width: 120, child: TextField(controller: _postcode, decoration: const InputDecoration(labelText: 'Postcode'))),
      ]),
    ]);
  }
}