thesis_shop/lib/store/cart_store.dart

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:thesis_shop/models/cart_item.dart';
import 'package:thesis_shop/models/product.dart';
import 'package:thesis_shop/models/remote_resource.dart';
import 'package:thesis_shop/store/product_store.dart';

class CartStore extends ChangeNotifier {
  List<CartItem> _cart = [];
  List<CartItem> get cart => _cart;

  int get numberOfProducts => _cart.length;
  double get totalPrice => _cart.fold<double>(
        0.0,
        (value, item) => value + item.product.price * item.amount,
      );

  int amountOfProduct(Product product) => cart
      .firstWhere((item) => product == item.product,
          orElse: () => CartItem(product: product, amount: 0))
      .amount;

  void updateProductList(RemoteResource<List<Product>> remoteProducts) {
    if (remoteProducts is LoadingRemoteResource) {
      return;
    }
    late final List<Product> products;
    if (remoteProducts is ErrorRemoteResource) {
      products = [];
    } else {
      products = remoteProducts.asFinished().value;
    }
    final productsByKey = {
      for (final product in products) product.title: product,
    };
    _cart = _cart
        .where((item) => productsByKey.containsKey(item.product.title))
        .map((item) => CartItem(
            product: productsByKey[item.product.title]!, amount: item.amount))
        .toList();
    notifyListeners();
  }

  void _addAmount(Product product, int amount) {
    final old = _cart.cast<CartItem?>().firstWhere(
        (item) => item?.product.title == product.title,
        orElse: () => null);
    if (old == null) {
      if (amount <= 0) return;
      _cart = _cart..add(CartItem(product: product, amount: amount));
      notifyListeners();
      return;
    }
    if (old.amount + amount < 0) return;
    final newItem = CartItem(product: product, amount: old.amount + amount);
    _cart = _cart
        .map(
          (item) => item.product.title == product.title ? newItem : item,
        )
        .toList();
    notifyListeners();
  }

  void increaseAmount(Product product) => _addAmount(product, 1);
  void decreaseAmount(Product product) => _addAmount(product, -1);
}

class CartStoreProvider
    extends ChangeNotifierProxyProvider<ProductStore, CartStore> {
  CartStoreProvider({Key? key, Widget? child})
      : super(
            key: key,
            child: child,
            create: (context) => CartStore(),
            update: (context, productStore, cartStore) =>
                cartStore!..updateProductList(productStore.products));
}