OnlineStore v4

Good iPhone12 = new Good("IPhone 12");
Good iPhone11 = new Good("IPhone 11");

Warehouse warehouse = new Warehouse();

Shop shop = new Shop(warehouse);

warehouse.Delive(iPhone12, 10);
warehouse.Delive(iPhone11, 1);

//Вывод всех товаров на складе с их остатком

Cart cart = shop.Cart();
cart.Add(iPhone12, 4);
cart.Add(iPhone11, 3); //при такой ситуации возникает ошибка так, как нет нужного количества товара на складе

//Вывод всех товаров в корзине

Console.WriteLine(cart.Order().Paylink);

cart.Add(iPhone12, 9); //Ошибка, после заказа со склада убираются заказанные товары


public class Warehouse : IDeliveryWarehouse
{
    private readonly Dictionary<Good, int> _goods;

    public Warehouse() =>
        _goods = new(new GoodEqualityCompare());


    public void Delive(Good good, int countGoods)
    {
        good = good ?? throw new ArgumentNullException();

        if (countGoods < 0)
            throw new ArgumentOutOfRangeException();

        if (_goods.ContainsKey(good) == false)
            _goods[good] = 0;

        _goods[good] += countGoods;
    }

    public bool CanIssue(Good good, int countGoods)
    {
        good = good ?? throw new ArgumentNullException();

        if (countGoods < 0)
            throw new ArgumentOutOfRangeException();

        if (_goods.TryGetValue(good, out int count) == false)
            return false;

        return count >= countGoods;
    }

    public void TransferForDelivery(Good good, int countGoods)
    {
        good = good ?? throw new ArgumentNullException();

        if (countGoods < 0)
            throw new ArgumentOutOfRangeException();

        if (_goods.ContainsKey(good) == false || _goods[good] < countGoods)
            throw new ArgumentOutOfRangeException();

        _goods[good] -= countGoods;
    }
}

public class Shop
{
    private readonly Warehouse _warehouse;

    public Shop(Warehouse warehouse) =>
        _warehouse = warehouse ?? throw new ArgumentNullException();

    public Cart Cart() =>
         new Cart(_warehouse);
}

public class Cart
{
    private readonly Dictionary<Good, int> _goods;
    private readonly IDeliveryWarehouse _warehouse;

    public Cart(IDeliveryWarehouse warehouse)
    {
        _warehouse = warehouse ?? throw new ArgumentNullException();

        GoodEqualityCompare goodEqualityCompare = new();
        _goods = new(goodEqualityCompare);
    }

    public void Add(Good good, int countGoods)
    {
        good = good ?? throw new ArgumentNullException();

        if (countGoods < 0)
            throw new ArgumentOutOfRangeException();

        if (_warehouse.CanIssue(good, countGoods) == false)
            throw new InvalidOperationException();

        if (_goods.ContainsKey(good) == false)
            _goods[good] = 0;

        _goods[good] += countGoods;
    }

    public PayOrder Order()
    {
        foreach(var goods in _goods)
        {
            _warehouse.TransferForDelivery(goods.Key, goods.Value);
        }

        _goods.Clear();

        return new PayOrder();
    }
}

public class Good
{
    public Good(string name)
    {
        if (string.IsNullOrEmpty(name))
            throw new ArgumentNullException();

        Name = name;
    }

    public string Name { get; }
}

public class PayOrder
{
    public PayOrder() { }

    public string Paylink { get; }
}

public interface IDeliveryWarehouse
{
    public bool CanIssue(Good good, int countGoods);

    public void TransferForDelivery(Good good, int countGoods);
}

public class GoodEqualityCompare : IEqualityComparer<Good>
{
    public bool Equals(Good? good1, Good? good2)
    {
        if (ReferenceEquals(good1, good2))
            return true;

        if (good1 == null || good2 == null)
            return false;

        return good1.Name == good2.Name;
    }

    public int GetHashCode(Good good) =>
        good.Name.GetHashCode();
}