import collections import contextlib import datetime import functools 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.db.models import Q from django.utils import timezone from registrasion.exceptions import CartValidationError from registrasion.models import commerce from registrasion.models import conditions from registrasion.models import inventory from .category import CategoryController from .discount import DiscountController from .flag import FlagController from .product import ProductController def _modifies_cart(func): ''' Decorator that makes the wrapped function raise ValidationError if we're doing something that could modify the cart. It also wraps the execution of this function in a database transaction, and marks the boundaries of a cart operations batch. ''' @functools.wraps(func) def inner(self, *a, **k): self._fail_if_cart_is_not_active() with transaction.atomic(): with CartController.operations_batch(self.cart.user) as mark: mark.mark = True # Marker that we've modified the cart return func(self, *a, **k) return inner 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 = commerce.Cart.objects.get( user=user, status=commerce.Cart.STATUS_ACTIVE, ) except ObjectDoesNotExist: existing = commerce.Cart.objects.create( user=user, time_last_updated=timezone.now(), reservation_duration=datetime.timedelta(), ) return cls(existing) # Marks the carts that are currently in batches _FOR_USER = {} _BATCH_COUNT = collections.defaultdict(int) _MODIFIED_CARTS = set() class _ModificationMarker(object): pass @classmethod @contextlib.contextmanager def operations_batch(cls, user): ''' Marks the boundary for a batch of operations on a user's cart. These markers can be nested. Only on exiting the outermost marker will a batch be ended. When a batch is ended, discounts are recalculated, and the cart's revision is increased. ''' if user not in cls._FOR_USER: _ctrl = cls.for_user(user) cls._FOR_USER[user] = (_ctrl, _ctrl.cart.id) ctrl, _id = cls._FOR_USER[user] cls._BATCH_COUNT[_id] += 1 try: success = False marker = cls._ModificationMarker() yield marker if hasattr(marker, "mark"): cls._MODIFIED_CARTS.add(_id) success = True finally: cls._BATCH_COUNT[_id] -= 1 # Only end on the outermost batch marker, and only if # it excited cleanly, and a modification occurred modified = _id in cls._MODIFIED_CARTS outermost = cls._BATCH_COUNT[_id] == 0 if modified and outermost and success: ctrl._end_batch() cls._MODIFIED_CARTS.remove(_id) # Clear out the cache on the outermost operation if outermost: del cls._FOR_USER[user] def _fail_if_cart_is_not_active(self): self.cart.refresh_from_db() if self.cart.status != commerce.Cart.STATUS_ACTIVE: raise ValidationError("You can only amend active carts.") def _autoextend_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(inventory.Voucher.RESERVATION_DURATION) # Else, it's the maximum of the included products items = commerce.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. You need to call this after you've finished modifying the user's cart. This is normally done by wrapping a block of code using ``operations_batch``. ''' self.cart.refresh_from_db() self._recalculate_discounts() self._autoextend_reservation() self.cart.revision += 1 self.cart.save() @_modifies_cart 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 = commerce.ProductItem.objects.filter(cart=self.cart) items_in_cart = items_in_cart.select_related( "product", "product__category", ) 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) new_items = [] products = [] for product, quantity in product_quantities: products.append(product) if quantity == 0: continue item = commerce.ProductItem( cart=self.cart, product=product, quantity=quantity, ) new_items.append(item) to_delete = ( Q(quantity=0) | Q(product__in=products) ) items_in_cart.filter(to_delete).delete() commerce.ProductItem.objects.bulk_create(new_items) def _test_limits(self, product_quantities): ''' Tests that the quantity changes we intend to make do not violate the limits and flag conditions imposed on the products. ''' errors = [] # Pre-annotate products products = [p for (p, q) in product_quantities] r = ProductController.attach_user_remainders(self.cart.user, products) with_remainders = dict((p, p) for p in r) # Test each product limit here for product, quantity in product_quantities: if quantity < 0: errors.append((product, "Value must be zero or greater.")) limit = with_remainders[product].remainder if quantity > limit: errors.append(( product, "You may only have %d of product: %s" % ( limit, product, ) )) # Collect by category by_cat = collections.defaultdict(list) for product, quantity in product_quantities: by_cat[product.category].append((product, quantity)) # Pre-annotate categories r = CategoryController.attach_user_remainders(self.cart.user, by_cat) with_remainders = dict((cat, cat) for cat in r) # Test each category limit here for category in by_cat: limit = with_remainders[category].remainder # Get the amount so far in the cart to_add = sum(i[1] for i in by_cat[category]) if to_add > limit: errors.append(( category, "You may only have %d items in category: %s" % ( limit, category.name, ) )) # Test the flag conditions errs = FlagController.test_flags( self.cart.user, product_quantities=product_quantities, ) if errs: for error in errs: errors.append(error) if errors: raise CartValidationError(errors) @_modifies_cart def apply_voucher(self, voucher_code): ''' Applies the voucher with the given code to this cart. ''' # Try and find the voucher voucher = inventory.Voucher.objects.get(code=voucher_code.upper()) # Re-applying vouchers should be idempotent if voucher in self.cart.vouchers.all(): return self._test_voucher(voucher) # If successful... self.cart.vouchers.add(voucher) def _test_voucher(self, voucher): ''' Tests whether this voucher is allowed to be applied to this cart. Raises ValidationError if not. ''' # Is voucher exhausted? active_carts = commerce.Cart.reserved_carts() # It's invalid for a user to enter a voucher that's exhausted carts_with_voucher = active_carts.filter(vouchers=voucher) carts_with_voucher = carts_with_voucher.exclude(pk=self.cart.id) if carts_with_voucher.count() >= voucher.limit: raise ValidationError( "Voucher %s is no longer available" % voucher.code) # It's not valid for users to re-enter a voucher they already have user_carts_with_voucher = carts_with_voucher.filter( user=self.cart.user, ) if user_carts_with_voucher.count() > 0: raise ValidationError("You have already entered this voucher.") def _test_vouchers(self, vouchers): ''' Tests each of the vouchers against self._test_voucher() and raises the collective ValidationError. Future work will refactor _test_voucher in terms of this, and save some queries. ''' errors = [] for voucher in vouchers: try: self._test_voucher(voucher) except ValidationError as ve: errors.append(ve) if errors: raise(ValidationError(ve)) def _test_required_categories(self): ''' Makes sure that the owner of this cart has satisfied all of the required category constraints in the inventory (be it in this cart or others). ''' required = set(inventory.Category.objects.filter(required=True)) items = commerce.ProductItem.objects.filter( product__category__required=True, cart__user=self.cart.user, ).exclude( cart__status=commerce.Cart.STATUS_RELEASED, ) for item in items: required.remove(item.product.category) errors = [] for category in required: msg = "You must have at least one item from: %s" % category errors.append((None, msg)) if errors: raise ValidationError(errors) def _append_errors(self, errors, ve): for error in ve.error_list: errors.append(error.message[1]) def validate_cart(self): ''' Determines whether the status of the current cart is valid; this is normally called before generating or paying an invoice ''' cart = self.cart user = self.cart.user errors = [] try: self._test_vouchers(self.cart.vouchers.all()) except ValidationError as ve: errors.append(ve) items = commerce.ProductItem.objects.filter(cart=cart) items = items.select_related("product", "product__category") product_quantities = list((i.product, i.quantity) for i in items) try: self._test_limits(product_quantities) except ValidationError as ve: self._append_errors(errors, ve) try: self._test_required_categories() except ValidationError as ve: self._append_errors(errors, ve) # Validate the discounts # TODO: refactor in terms of available_discounts # why aren't we doing that here?! # def available_discounts(cls, user, categories, products): products = [i.product for i in items] discounts_with_quantity = DiscountController.available_discounts( user, [], products, ) discounts = set(i.discount.id for i in discounts_with_quantity) discount_items = commerce.DiscountItem.objects.filter(cart=cart) for discount_item in discount_items: discount = discount_item.discount if discount.id not in discounts: errors.append( ValidationError("Discounts are no longer available") ) if errors: raise ValidationError(errors) @_modifies_cart def fix_simple_errors(self): ''' This attempts to fix the easy errors raised by ValidationError. This includes removing items from the cart that are no longer available, recalculating all of the discounts, and removing voucher codes that are no longer available. ''' # Fix vouchers first (this affects available discounts) to_remove = [] for voucher in self.cart.vouchers.all(): try: self._test_voucher(voucher) except ValidationError: to_remove.append(voucher) for voucher in to_remove: self.cart.vouchers.remove(voucher) # Fix products and discounts items = commerce.ProductItem.objects.filter(cart=self.cart) items = items.select_related("product") products = set(i.product for i in items) available = set(ProductController.available_products( self.cart.user, products=products, )) not_available = products - available zeros = [(product, 0) for product in not_available] self.set_quantities(zeros) @transaction.atomic def _recalculate_discounts(self): ''' Calculates all of the discounts available for this product.''' # Delete the existing entries. commerce.DiscountItem.objects.filter(cart=self.cart).delete() product_items = self.cart.productitem_set.all().select_related( "product", "product__category", "product__price" ) products = [i.product for i in product_items] discounts = DiscountController.available_discounts( self.cart.user, [], products, ) # The highest-value discounts will apply to the highest-value # products first. 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, conditions.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 = commerce.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 discount_item.save() # Update the remaining quantity. quantity = ours - allowed else: quantity = 0 candidate.quantity -= discount_item.quantity