Barcode scan pick list

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

class PickLine {
  PickLine({required this.barcode, required this.name, required this.needed});
  final String barcode;
  final String name;
  final int needed;
  int picked = 0;
  bool get complete => picked >= needed;
}

enum ScanResult { picked, alreadyComplete, unknown }

class PickList extends ChangeNotifier {
  PickList(List<PickLine> lines) : lines = List.unmodifiable(lines);
  final List<PickLine> lines;

  bool get allDone => lines.every((l) => l.complete);

  ScanResult scan(String code) {
    final match = lines.where((l) => l.barcode == code);
    if (match.isEmpty) return ScanResult.unknown;
    final line = match.first;
    if (line.complete) return ScanResult.alreadyComplete;
    line.picked++;
    notifyListeners();
    return ScanResult.picked;
  }
}

class PickScreen extends StatefulWidget {
  const PickScreen({super.key, required this.list});
  final PickList list;

  @override
  State<PickScreen> createState() => _PickScreenState();
}

class _PickScreenState extends State<PickScreen> {
  String? _last;
  DateTime _lastAt = DateTime(0);

  void _onDetect(BarcodeCapture capture) {
    final code = capture.barcodes.firstOrNull?.rawValue;
    if (code == null) return;
    final now = DateTime.now();
    // The camera reports the same code many times per second; ignore repeats.
    if (code == _last && now.difference(_lastAt) < const Duration(seconds: 2)) return;
    _last = code;
    _lastAt = now;
    final r = widget.list.scan(code);
    ScaffoldMessenger.of(context).showSnackBar(SnackBar(
      duration: const Duration(seconds: 1),
      content: Text(switch (r) {
        ScanResult.picked => 'Picked',
        ScanResult.alreadyComplete => 'Line already complete',
        ScanResult.unknown => 'Not on this list',
      }),
    ));
  }

  @override
  Widget build(BuildContext context) {
    return Column(children: [
      SizedBox(height: 220, child: MobileScanner(onDetect: _onDetect)),
      Expanded(
        child: ListenableBuilder(
          listenable: widget.list,
          builder: (context, _) => ListView(children: [
            for (final l in widget.list.lines)
              CheckboxListTile(
                value: l.complete,
                onChanged: null,
                title: Text(l.name),
                subtitle: Text('${l.picked} of ${l.needed}'),
              ),
          ]),
        ),
      ),
    ]);
  }
}