symposion_app/registrasion/controllers/discount.py

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import itertools
from .batch import BatchController
from .conditions import ConditionController
from registrasion.models import commerce
from registrasion.models import conditions
from django.db.models import Case
from django.db.models import F, Q
from django.db.models import Sum
from django.db.models import Value
from django.db.models import When
class DiscountAndQuantity(object):
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''' Represents a discount that can be applied to a product or category
for a given user.
Attributes:
discount (conditions.DiscountBase): The discount object that the
clause arises from. A given DiscountBase can apply to multiple
clauses.
clause (conditions.DiscountForProduct|conditions.DiscountForCategory):
A clause describing which product or category this discount item
applies to. This casts to ``str()`` to produce a human-readable
version of the clause.
quantity (int): The number of times this discount item can be applied
for the given user.
'''
def __init__(self, discount, clause, quantity):
self.discount = discount
self.clause = clause
self.quantity = quantity
def __repr__(self):
return "(discount=%s, clause=%s, quantity=%d)" % (
self.discount, self.clause, self.quantity,
)
class DiscountController(object):
@classmethod
def available_discounts(cls, user, categories, products):
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''' 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. '''
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filtered_clauses = cls._filtered_clauses(user)
# clauses that match provided categories
categories = set(categories)
# clauses that match provided products
products = set(products)
# clauses that match categories for provided products
product_categories = set(product.category for product in products)
# (Not relevant: clauses that match products in provided categories)
all_categories = categories | product_categories
filtered_clauses = (
clause for clause in filtered_clauses
if hasattr(clause, 'product') and clause.product in products or
hasattr(clause, 'category') and clause.category in all_categories
)
discounts = []
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# Markers so that we don't need to evaluate given conditions
# more than once
accepted_discounts = set()
failed_discounts = set()
for clause in filtered_clauses:
discount = clause.discount
cond = ConditionController.for_condition(discount)
past_use_count = clause.past_use_count
if past_use_count >= clause.quantity:
# This clause has exceeded its use count
pass
elif discount not in failed_discounts:
# This clause is still available
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is_accepted = discount in accepted_discounts
if is_accepted or cond.is_met(user, filtered=True):
# This clause is valid for this user
discounts.append(DiscountAndQuantity(
discount=discount,
clause=clause,
quantity=clause.quantity - past_use_count,
))
accepted_discounts.add(discount)
else:
# This clause is not valid for this user
failed_discounts.add(discount)
return discounts
@classmethod
@BatchController.memoise
def _filtered_clauses(cls, user):
'''
Returns:
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Sequence[DiscountForProduct | DiscountForCategory]: All clauses
that passed the filter function.
'''
types = list(ConditionController._controllers())
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discounttypes = [
i for i in types if issubclass(i, conditions.DiscountBase)
]
product_clauses = conditions.DiscountForProduct.objects.all()
product_clauses = product_clauses.select_related(
"discount",
"product",
"product__category",
)
category_clauses = conditions.DiscountForCategory.objects.all()
category_clauses = category_clauses.select_related(
"category",
"discount",
)
valid_discounts = conditions.DiscountBase.objects.all()
all_subsets = []
for discounttype in discounttypes:
discounts = discounttype.objects.filter(id__in=valid_discounts)
ctrl = ConditionController.for_type(discounttype)
discounts = ctrl.pre_filter(discounts, user)
all_subsets.append(discounts)
filtered_discounts = list(itertools.chain(*all_subsets))
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# Map from discount key to itself
# (contains annotations needed in the future)
from_filter = dict((i.id, i) for i in filtered_discounts)
clause_sets = (
product_clauses.filter(discount__in=filtered_discounts),
category_clauses.filter(discount__in=filtered_discounts),
)
clause_sets = (
cls._annotate_with_past_uses(i, user) for i in clause_sets
)
# The set of all potential discount clauses
discount_clauses = set(itertools.chain(*clause_sets))
# Replace discounts with the filtered ones
# These are the correct subclasses (saves query later on), and have
# correct annotations from filters if necessary.
for clause in discount_clauses:
clause.discount = from_filter[clause.discount.id]
return discount_clauses
@classmethod
def _annotate_with_past_uses(cls, queryset, user):
''' Annotates the queryset with a usage count for that discount claus
by the given user. '''
if queryset.model == conditions.DiscountForCategory:
matches = (
Q(category=F('discount__discountitem__product__category'))
)
elif queryset.model == conditions.DiscountForProduct:
matches = (
Q(product=F('discount__discountitem__product'))
)
in_carts = (
Q(discount__discountitem__cart__user=user) &
Q(discount__discountitem__cart__status=commerce.Cart.STATUS_PAID)
)
past_use_quantity = When(
in_carts & matches,
then="discount__discountitem__quantity",
)
past_use_quantity_or_zero = Case(
past_use_quantity,
default=Value(0),
)
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queryset = queryset.annotate(
past_use_count=Sum(past_use_quantity_or_zero)
)
return queryset