AddCartItem

class AddCartItem(View):
    """Добавление товара в карзину"""

    def check_cart(self, request):
        if request.user.is_authenticated:
            cart = Cart.objects.get(user=request.user, accepted=False)
        else:
            session_cart = request.session.get('cart')
            if not session_cart:
                SessionStore = import_module(settings.SESSION_ENGINE).SessionStore
                session = SessionStore()
                session.create()
                session_cart = session.session_key
                request.session['cart'] = session_cart
            cart, add = Cart.objects.get_or_create(session=session_cart, accepted=False)
        return cart

    def post(self, request, slug, pk):
        quantity = request.POST.get("quantity", None)
        if quantity is not None and int(quantity) > 0:
            cart = self.check_cart(request)
            try:
                item = CartItem.objects.get(
                    cart_id=cart.id,
                    product_id=pk,
                    cart__accepted=False)
                item.quantity += int(quantity)
            except CartItem.DoesNotExist:
                item = CartItem(
                    cart_id=cart.id,
                    product_id=pk,
                    quantity=int(quantity)
                )
            item.save()
            messages.add_message(request, settings.MY_INFO, "Товар добавлен")
            return redirect("/detail/{}/".format(slug))
        else:
            messages.add_message(request, settings.MY_INFO, "Значение не может быть 0")
            return redirect("/detail/{}/".format(slug))