import itertools from conditions import ConditionController from registrasion import models as rego from django.db.models import Sum class DiscountAndQuantity(object): def __init__(self, discount, clause, quantity): self.discount = discount self.clause = clause self.quantity = quantity def available_discounts(user, categories, products): ''' Returns all discounts available to this user for the given categories and products. The discounts also list the available quantity for this user, not including products that are pending purchase. ''' # discounts that match provided categories category_discounts = rego.DiscountForCategory.objects.filter( category__in=categories ) # discounts that match provided products product_discounts = rego.DiscountForProduct.objects.filter( product__in=products ) # 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, category_discounts, product_category_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) # Count the past uses of the given discount item. # 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 discount=discount.discount, ) agg = past_uses.aggregate(Sum("quantity")) past_use_count = agg["quantity__sum"] if past_use_count is None: past_use_count = 0 if past_use_count >= discount.quantity: # This clause has exceeded its use count pass elif real_discount not in failed_discounts: # This clause is still available if real_discount in accepted_discounts or cond.is_met(user, 0): # This clause is valid for this user discounts.append(DiscountAndQuantity( discount=real_discount, clause=discount, quantity=discount.quantity - past_use_count, )) accepted_discounts.add(real_discount) else: # This clause is not valid for this user failed_discounts.add(real_discount) return discounts