import collections import datetime import discount import itertools from django.core.exceptions import ObjectDoesNotExist from django.core.exceptions import ValidationError from django.db import transaction from django.db.models import Max from django.utils import timezone from registrasion import models as rego from category import CategoryController from conditions import ConditionController from product import ProductController class CartController(object): def __init__(self, cart): self.cart = cart @classmethod def for_user(cls, user): ''' Returns the user's current cart, or creates a new cart if there isn't one ready yet. ''' try: existing = rego.Cart.objects.get(user=user, active=True) except ObjectDoesNotExist: existing = rego.Cart.objects.create( user=user, time_last_updated=timezone.now(), reservation_duration=datetime.timedelta(), ) existing.save() return cls(existing) def extend_reservation(self): ''' Updates the cart's time last updated value, which is used to determine whether the cart has reserved the items and discounts it holds. ''' reservations = [datetime.timedelta()] # If we have vouchers, we're entitled to an hour at minimum. if len(self.cart.vouchers.all()) >= 1: reservations.append(rego.Voucher.RESERVATION_DURATION) # Else, it's the maximum of the included products items = rego.ProductItem.objects.filter(cart=self.cart) agg = items.aggregate(Max("product__reservation_duration")) product_max = agg["product__reservation_duration__max"] if product_max is not None: reservations.append(product_max) self.cart.time_last_updated = timezone.now() self.cart.reservation_duration = max(reservations) def end_batch(self): ''' Performs operations that occur occur at the end of a batch of product changes/voucher applications etc. THIS SHOULD BE PRIVATE ''' self.recalculate_discounts() self.extend_reservation() self.cart.revision += 1 self.cart.save() @transaction.atomic def set_quantities(self, product_quantities): ''' Sets the quantities on each of the products on each of the products specified. Raises an exception (ValidationError) if a limit is violated. `product_quantities` is an iterable of (product, quantity) pairs. ''' items_in_cart = rego.ProductItem.objects.filter(cart=self.cart) product_quantities = list(product_quantities) # n.b need to add have the existing items first so that the new # items override the old ones. all_product_quantities = dict(itertools.chain( ((i.product, i.quantity) for i in items_in_cart.all()), product_quantities, )).items() # Validate that the limits we're adding are OK self._test_limits(all_product_quantities) for product, quantity in product_quantities: try: product_item = rego.ProductItem.objects.get( cart=self.cart, product=product, ) product_item.quantity = quantity product_item.save() except ObjectDoesNotExist: rego.ProductItem.objects.create( cart=self.cart, product=product, quantity=quantity, ) items_in_cart.filter(quantity=0).delete() self.end_batch() def _test_limits(self, product_quantities): ''' Tests that the quantity changes we intend to make do not violate the limits and enabling conditions imposed on the products. ''' # Test each product limit here for product, quantity in product_quantities: if quantity < 0: # TODO: batch errors raise ValidationError("Value must be zero or greater.") prod = ProductController(product) limit = prod.user_quantity_remaining(self.cart.user) if quantity > limit: # TODO: batch errors raise ValidationError( "You may only have %d of product: %s" % ( limit, product.name, ) ) # Collect by category by_cat = collections.defaultdict(list) for product, quantity in product_quantities: by_cat[product.category].append((product, quantity)) # Test each category limit here for cat in by_cat: ctrl = CategoryController(cat) limit = ctrl.user_quantity_remaining(self.cart.user) # Get the amount so far in the cart to_add = sum(i[1] for i in by_cat[cat]) if to_add > limit: # TODO: batch errors raise ValidationError( "You may only have %d items in category: %s" % ( limit, cat.name, ) ) # Test the enabling conditions errs = ConditionController.test_enabling_conditions( self.cart.user, product_quantities=product_quantities, ) if errs: # TODO: batch errors raise ValidationError("An enabling condition failed") def apply_voucher(self, voucher_code): ''' Applies the voucher with the given code to this cart. ''' # Is voucher exhausted? active_carts = rego.Cart.reserved_carts() # Try and find the voucher voucher = rego.Voucher.objects.get(code=voucher_code.upper()) # It's invalid for a user to enter a voucher that's exhausted carts_with_voucher = active_carts.filter(vouchers=voucher) if len(carts_with_voucher) >= voucher.limit: raise ValidationError("This voucher is no longer available") # It's not valid for users to re-enter a voucher they already have user_carts_with_voucher = rego.Cart.objects.filter( user=self.cart.user, released=False, vouchers=voucher, ) if len(user_carts_with_voucher) > 0: raise ValidationError("You have already entered this voucher.") # If successful... self.cart.vouchers.add(voucher) self.end_batch() def validate_cart(self): ''' Determines whether the status of the current cart is valid; this is normally called before generating or paying an invoice ''' # TODO: validate vouchers items = rego.ProductItem.objects.filter(cart=self.cart) product_quantities = list((i.product, i.quantity) for i in items) self._test_limits(product_quantities) # Validate the discounts discount_items = rego.DiscountItem.objects.filter(cart=self.cart) seen_discounts = set() for discount_item in discount_items: discount = discount_item.discount if discount in seen_discounts: continue seen_discounts.add(discount) real_discount = rego.DiscountBase.objects.get_subclass( pk=discount.pk) cond = ConditionController.for_condition(real_discount) if not cond.is_met(self.cart.user): raise ValidationError("Discounts are no longer available") def recalculate_discounts(self): ''' Calculates all of the discounts available for this product. NB should be transactional, and it's terribly inefficient. ''' # Delete the existing entries. rego.DiscountItem.objects.filter(cart=self.cart).delete() product_items = self.cart.productitem_set.all() products = [i.product for i in product_items] discounts = discount.available_discounts(self.cart.user, [], products) # The highest-value discounts will apply to the highest-value # products first. product_items = self.cart.productitem_set.all() product_items = product_items.order_by('product__price') product_items = reversed(product_items) for item in product_items: self._add_discount(item.product, item.quantity, discounts) def _add_discount(self, product, quantity, discounts): ''' Applies the best discounts on the given product, from the given discounts.''' def matches(discount): ''' Returns True if and only if the given discount apples to our product. ''' if isinstance(discount.clause, rego.DiscountForCategory): return discount.clause.category == product.category else: return discount.clause.product == product def value(discount): ''' Returns the value of this discount clause as applied to this product ''' if discount.clause.percentage is not None: return discount.clause.percentage * product.price else: return discount.clause.price discounts = [i for i in discounts if matches(i)] discounts.sort(key=value) for candidate in reversed(discounts): if quantity == 0: break elif candidate.quantity == 0: # This discount clause has been exhausted by this cart continue # Get a provisional instance for this DiscountItem # with the quantity set to as much as we have in the cart discount_item = rego.DiscountItem.objects.create( product=product, cart=self.cart, discount=candidate.discount, quantity=quantity, ) # Truncate the quantity for this DiscountItem if we exceed quantity ours = discount_item.quantity allowed = candidate.quantity if ours > allowed: discount_item.quantity = allowed # Update the remaining quantity. quantity = ours - allowed else: quantity = 0 candidate.quantity -= discount_item.quantity discount_item.save()