import 'dart:async';

import 'package:flutter/foundation.dart';
import 'package:sentry_flutter/sentry_flutter.dart';

import '../models/app_error.dart';
import '../models/product.dart';
import '../services/product_service.dart';

/// The app-wide product list, kept in sync with the database. Stock changes
/// from tabs show up here automatically.
class InventoryViewModel extends ChangeNotifier {
  final ProductService productService;

  InventoryViewModel({required this.productService});

  StreamSubscription<List<Product>>? _subscription;
  List<Product> _products = [];
  bool _hasLoaded = false;
  AppError? _loadError;

  List<Product> get products => _products;

  bool get hasLoaded => _hasLoaded;

  bool get isLoading => !_hasLoaded;

  AppError? get loadError => _loadError;

  void ensureLoaded() {
    if (_subscription != null) return;

    _subscription = productService.watchProducts().listen(
      _onProducts,
      onError: _onLoadError,
    );
  }

  /// Starts watching again after a load error.
  void retry() {
    unawaited(_subscription?.cancel());
    _subscription = null;
    _hasLoaded = false;
    _loadError = null;
    notifyListeners();
    ensureLoaded();
  }

  void _onProducts(List<Product> products) {
    _products = products;
    _hasLoaded = true;
    _loadError = null;
    notifyListeners();
  }

  void _onLoadError(Object error, StackTrace stack) {
    debugPrint('InventoryViewModel: load error: $error');
    unawaited(Sentry.captureException(error, stackTrace: stack));

    _hasLoaded = true;
    _loadError = AppError.loadProducts;
    notifyListeners();
  }

  @override
  void dispose() {
    _subscription?.cancel();
    super.dispose();
  }
}