SendTrain/lib/widgets/generic/elements/form_search_input.dart

import 'dart:async';

import 'package:flutter/material.dart';
import 'package:sendtrain/widgets/generic/elements/form_text_input.dart';

class FormSearchInput extends StatefulWidget {
  const FormSearchInput({super.key, required this.sessionController});

  final TextEditingController sessionController;

  @override
  State<FormSearchInput> createState() => _FormSearchInputState();
}

class _FormSearchInputState extends State<FormSearchInput> {
  String? _currentQuery;

  // The most recent suggestions received from the API.
  late Iterable<Widget> _lastOptions = <Widget>[];

  late final _Debounceable<Iterable<String>?, String> _debouncedSearch;

  // Calls the "remote" API to search with the given query. Returns null when
  // the call has been made obsolete.
  Future<Iterable<String>?> _search(String query) async {
    _currentQuery = query;

    // In a real application, there should be some error handling here.
    final Iterable<String> options = await _FakeAPI.search(_currentQuery!);

    // If another search happened after this one, throw away these options.
    if (_currentQuery != query) {
      return null;
    }
    _currentQuery = null;

    return options;
  }

  @override
  void initState() {
    super.initState();
    _debouncedSearch = _debounce<Iterable<String>?, String>(_search);
  }

  @override
  Widget build(BuildContext context) {
    return SearchAnchor(
            builder: (BuildContext context, SearchController controller) {
          return FormTextInput(
              controller: widget.sessionController,
              title: 'Location (optional)',
              icon: Icon(Icons.search_rounded),
              maxLines: 2,
              onTap: () {
                controller.openView();
              });
        }, suggestionsBuilder:
                (BuildContext context, SearchController controller) async {
          final List<String>? options =
              (await _debouncedSearch(controller.text))?.toList();
          if (options == null) {
            return _lastOptions;
          }
          _lastOptions = List<ListTile>.generate(options.length, (int index) {
            final String item = options[index];
            return ListTile(
              title: Text(item),
              onTap: () {
                if (item.isNotEmpty) {
                  widget.sessionController.text = item;
                }
                controller.closeView(item);
                // debugPrint('You just selected $item');
                // Navigator.of(context).pop();
              },
            );
          });

          return _lastOptions;
        });
  }
}

const Duration fakeAPIDuration = Duration(seconds: 1);
const Duration debounceDuration = Duration(milliseconds: 500);

class _FakeAPI {
  static const List<String> _kOptions = <String>[
    'aardvark',
    'bobcat',
    'chameleon',
  ];

  // Searches the options, but injects a fake "network" delay.
  static Future<Iterable<String>> search(String query) async {
    await Future<void>.delayed(fakeAPIDuration); // Fake 1 second delay.
    if (query == '') {
      return const Iterable<String>.empty();
    }
    return _kOptions.where((String option) {
      return option.contains(query.toLowerCase());
    });
  }
}

typedef _Debounceable<S, T> = Future<S?> Function(T parameter);

/// Returns a new function that is a debounced version of the given function.
///
/// This means that the original function will be called only after no calls
/// have been made for the given Duration.
_Debounceable<S, T> _debounce<S, T>(_Debounceable<S?, T> function) {
  _DebounceTimer? debounceTimer;

  return (T parameter) async {
    if (debounceTimer != null && !debounceTimer!.isCompleted) {
      debounceTimer!.cancel();
    }
    debounceTimer = _DebounceTimer();
    try {
      await debounceTimer!.future;
    } on _CancelException {
      return null;
    }
    return function(parameter);
  };
}

// A wrapper around Timer used for debouncing.
class _DebounceTimer {
  _DebounceTimer() {
    _timer = Timer(debounceDuration, _onComplete);
  }

  late final Timer _timer;
  final Completer<void> _completer = Completer<void>();

  void _onComplete() {
    _completer.complete();
  }

  Future<void> get future => _completer.future;

  bool get isCompleted => _completer.isCompleted;

  void cancel() {
    _timer.cancel();
    _completer.completeError(const _CancelException());
  }
}

// An exception indicating that the timer was canceled.
class _CancelException implements Exception {
  const _CancelException();
}