OnlineStore

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 List<Cell> _cells;

    public Warehouse()
    {
        _cells = new List<Cell>();
    }

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

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

        Cell newCell = new Cell(good, countGoods);

        int cellIndex = _cells.FindIndex(cell => cell.Good == good);

        if (cellIndex < 0)
            _cells.Add(newCell);
        else
            _cells[cellIndex].Merge(newCell);
    }

    public bool CanIssue(IReadOnlyCell issuedCell)
    {
        issuedCell = issuedCell ?? throw new ArgumentNullException();

        int cellIndex = _cells.FindIndex(cell => cell.Good == issuedCell.Good);

        return (cellIndex > -1 && _cells[cellIndex].CountGoods >= issuedCell.CountGoods) == false;
    }

    public void TransferForDelivery(IReadOnlyCell issuedCell)
    {
        issuedCell = issuedCell ?? throw new ArgumentNullException();

        int cellIndex = _cells.FindIndex(cell => cell.Good == issuedCell.Good);

        if (cellIndex > -1 && _cells[cellIndex].CountGoods >= issuedCell.CountGoods)
            _cells[cellIndex].Issue(issuedCell);
    }
}

public class Shop
{
    private Warehouse _warehouse;

    public Shop(Warehouse warehouse)
    {
        if (_warehouse == null)
            throw new ArgumentNullException();

        _warehouse = warehouse;
    }

    public Cart Cart()
    {
        return new Cart(_warehouse);
    }
}

public class Cart
{
    private List<Cell> _cells;
    private IDeliveryWarehouse _warehouse;

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

        _cells = new List<Cell>();
    }

    public IReadOnlyList<IReadOnlyCell> Cells => _cells;

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

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

        Cell newCell = new Cell(good, countGoods);

        if (_warehouse.CanIssue(newCell) == false)
            throw new ArgumentOutOfRangeException();

        int cellIndex = _cells.FindIndex(cell => cell.Good == good);

        if (cellIndex < 0)
            _cells.Add(newCell);
        else
            _cells[cellIndex].Merge(newCell);
    }

    public PayOrder Order()
    {
        foreach (Cell cell in _cells)
            _warehouse.TransferForDelivery(cell);

        _cells.Clear();
        return new PayOrder();
    }
}

public class Cell : IReadOnlyCell
{
    public Cell(Good good, int countGoods)
    {
        if (good == null)
            throw new ArgumentNullException();

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

        Good = good;
        CountGoods = countGoods;
    }

    public Good Good {get; private set;}
    public int CountGoods { get; private set;}

    public void Merge(Cell newCell)
    {
        if (newCell.Good != Good)
            throw new InvalidOperationException();

        if (newCell.CountGoods < 0)
            throw new ArgumentOutOfRangeException();

        CountGoods += newCell.CountGoods;
    }

    public void Issue(IReadOnlyCell newCell)
    {
        if(newCell.Good != Good)
            throw new InvalidOperationException();

        if (newCell.CountGoods < 0 || newCell.CountGoods > CountGoods)
            throw new ArgumentOutOfRangeException();

        CountGoods -= newCell.CountGoods;
    }
}

public class Good
{
    public Good(string name)
    {
        if (name == null)
            throw new ArgumentNullException();

        Name = name;
    }

    public string Name { get; private set; }
}

public class PayOrder
{
    public PayOrder() { }

    public string Paylink { get; private set; }
}

public interface IReadOnlyCell
{
    public Good Good { get; }
    public int CountGoods { get;}
}

public interface IDeliveryWarehouse
{
    public bool CanIssue(IReadOnlyCell cell);

    public void TransferForDelivery(IReadOnlyCell cell);
}