def __init__(self, discount, clause, quantity):

        self.discount = discount

        self.clause = clause

        self.quantity = quantity

    def __repr__(self):

            self.discount, self.clause, self.quantity,

        )

def available_discounts(user, categories, products):

    ''' Returns all discounts available to this user for the given categories

    # discounts that match categories for provided products

    product_category_discounts = rego.DiscountForCategory.objects.filter(

        category__in=(product.category for product in products)

    )

    # (Not relevant: discounts that match products in provided categories)

    # The set of all potential discounts

    potential_discounts = set(itertools.chain(

        product_discounts,

    ))

    discounts = []

    # Markers so that we don't need to evaluate given conditions more than once

    accepted_discounts = set()

    failed_discounts = set()

    for discount in potential_discounts:

        real_discount = rego.DiscountBase.objects.get_subclass(

            pk=discount.discount.pk,

        )

        cond = ConditionController.for_condition(real_discount)

        # If this user has exceeded the limit for the clause, this clause

        # is not available any more.

        past_uses = rego.DiscountItem.objects.filter(

            cart__user=user,

            cart__active=False,  # Only past carts count

            cart__released=False,  # You can reuse refunded discounts

        )

        agg = past_uses.aggregate(Sum("quantity"))

        past_use_count = agg["quantity__sum"]

        if past_use_count is None:

            past_use_count = 0