def _items(self, cart_status, category=None):

            Q(productitem__cart__status=cart_status)

    def items_purchased(self, category=None):

        ''' Aggregates the items that this user has purchased.

        Arguments:

            category (Optional[models.inventory.Category]): the category

                of items to restrict to.

        Returns:

            [ProductAndQuantity, ...]: A list of product-quantity pairs,

                aggregating like products from across multiple invoices.

        '''

        return self._items(commerce.Cart.STATUS_PAID)

        return self._items(commerce.Cart.STATUS_ACTIVE)

    def items_released(self):

        ''' Gets all of the items that the user previously paid for, but has

        since refunded.

        Returns:

            [ProductAndQuantity, ...]: A list of product-quantity pairs for the

                items that the user has not yet paid for.

        '''

        return self._items(commerce.Cart.STATUS_RELEASED)

from registrasion.controllers.product import ProductController

def staff_products_form_factory(user):

    ''' Creates a StaffProductsForm that restricts the available products to

    those that are available to a user. '''

    products = inventory.Product.objects.all()

    products = ProductController.available_products(user, products=products)

    product_ids = [product.id for product in products]

    product_set = inventory.Product.objects.filter(id__in=product_ids)

    class StaffProductsForm(forms.Form):

        ''' Form for allowing staff to add an item to a user's cart. '''

        product = forms.ModelChoiceField(

            widget=forms.Select,

            queryset=product_set,

        )

        quantity = forms.IntegerField(

            min_value=0,

        )

    return StaffProductsForm

def staff_products_formset_factory(user):

    ''' Creates a formset of StaffProductsForm for the given user. '''

    form_type = staff_products_form_factory(user)

    return forms.formset_factory(form_type)

def attendee(request, form, user_id=None):

    if user_id is None and not form.has_changed():

        user_id = form.cleaned_data["user"]

    attendee = people.Attendee.objects.get(user__id=user_id)

            attendee.user.id,

    amend_registration,

    url(r"^amend/([0-9]+)$", amend_registration, name="amend_registration"),

    url(r"^checkout/([0-9]+)$", checkout, name="checkout"),

from registrasion.controllers.item import ItemController

from django.contrib.auth.models import User

def checkout(request, user_id=None):

    Arguments:

        user_id (castable to int):

            If the requesting user is staff, then the user ID can be used to

            run checkout for another user.

    if user_id is not None:

        if request.user.is_staff:

            user = User.objects.get(id=int(user_id))

        else:

            raise Http404()

    else:

        user = request.user

    current_cart = CartController.for_user(user)

@user_passes_test(_staff_only)

def amend_registration(request, user_id):

    ''' Allows staff to amend a user's current registration cart, and etc etc.

    '''

    user = User.objects.get(id=int(user_id))

    current_cart = CartController.for_user(user)

    items = commerce.ProductItem.objects.filter(

        cart=current_cart.cart,

    ).select_related("product")

    initial = [{"product": i.product, "quantity": i.quantity} for i in items]

    StaffProductsFormSet = forms.staff_products_formset_factory(user)

    formset = StaffProductsFormSet(

        request.POST or None,

        initial=initial,

        prefix="products",

    )

    voucher_form = forms.VoucherForm(

        request.POST or None,

        prefix="voucher",

    )

    if request.POST and formset.is_valid():

        pq = [

            (f.cleaned_data["product"], f.cleaned_data["quantity"])

            for f in formset

            if "product" in f.cleaned_data and

            f.cleaned_data["product"] is not None

        ]

        try:

            current_cart.set_quantities(pq)

            return redirect(amend_registration, user_id)

        except ValidationError as ve:

            for ve_field in ve.error_list:

                product, message = ve_field.message

                for form in formset:

                    if form.cleaned_data["product"] == product:

                        form.add_error("quantity", message)

    if request.POST and voucher_form.is_valid():

        try:

            current_cart.apply_voucher(voucher_form.cleaned_data["voucher"])

            return redirect(amend_registration, user_id)

        except ValidationError as ve:

            voucher_form.add_error(None, ve)

    ic = ItemController(user)

    data = {

        "user": user,

        "paid": ic.items_purchased(),

        "cancelled": ic.items_released(),

        "form": formset,

        "voucher_form": voucher_form,

    }

    return render(request, "registrasion/amend_registration.html", data)