Cross selling (#4185)

Product categories can now be marked as "cross-selling categories", causing them to 
appear in the add-on checkout step as additional recommendations, depending on 
their cross-selling visibility (always, only if certain products are already in the cart, or 
only if they qualify for a discount according to discount rules).

---------

Co-authored-by: Raphael Michel <michel@rami.io>
Co-authored-by: Richard Schreiber <schreiber@rami.io>

src/pretix/base/services/cart.py

@@ -1542,10 +1542,9 @@ def add_items_to_cart(self, event: int, items: List[dict], cart_id: str=None, lo
 @app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(CartError,))
 def apply_voucher(self, event: Event, voucher: str, cart_id: str=None, locale='en', sales_channel='web', override_now_dt: datetime=None) -> None:
     """
-    Removes a list of items from a user's cart.
     :param event: The event ID in question
     :param voucher: A voucher code
-    :param session: Session ID of a guest
+    :param cart_id: The cart ID of the cart to modify
     """
     with language(locale), time_machine_now_assigned(override_now_dt):
         try:
@@ -1566,10 +1565,10 @@ def apply_voucher(self, event: Event, voucher: str, cart_id: str=None, locale='e
 @app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(CartError,))
 def remove_cart_position(self, event: Event, position: int, cart_id: str=None, locale='en', sales_channel='web', override_now_dt: datetime=None) -> None:
     """
-    Removes a list of items from a user's cart.
+    Removes an item specified by its position ID from a user's cart.
     :param event: The event ID in question
     :param position: A cart position ID
-    :param session: Session ID of a guest
+    :param cart_id: The cart ID of the cart to modify
     """
     with language(locale), time_machine_now_assigned(override_now_dt):
         try:
@@ -1590,9 +1589,9 @@ def remove_cart_position(self, event: Event, position: int, cart_id: str=None, l
 @app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(CartError,))
 def clear_cart(self, event: Event, cart_id: str=None, locale='en', sales_channel='web', override_now_dt: datetime=None) -> None:
     """
-    Removes a list of items from a user's cart.
+    Removes all items from a user's cart.
     :param event: The event ID in question
-    :param session: Session ID of a guest
+    :param cart_id: The cart ID of the cart to modify
     """
     with language(locale), time_machine_now_assigned(override_now_dt):
         try:
@@ -1611,13 +1610,15 @@ def clear_cart(self, event: Event, cart_id: str=None, locale='en', sales_channel
 
 
 @app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(CartError,))
-def set_cart_addons(self, event: Event, addons: List[dict], cart_id: str=None, locale='en',
+def set_cart_addons(self, event: Event, addons: List[dict], add_to_cart_items: List[dict], cart_id: str=None, locale='en',
                     invoice_address: int=None, sales_channel='web', override_now_dt: datetime=None) -> None:
     """
-    Removes a list of items from a user's cart.
+    Assigns addons to eligible products in a user's cart, adding and removing the addon products as necessary to
+    ensure the requested addon state.
     :param event: The event ID in question
     :param addons: A list of dicts with the keys addon_to, item, variation
-    :param session: Session ID of a guest
+    :param add_to_cart_items: A list of dicts with the keys item, variation, count, custom_price, voucher, seat ID
+    :param cart_id: The cart ID of the cart to modify
     """
     with language(locale), time_machine_now_assigned(override_now_dt):
         ia = False
@@ -1635,6 +1636,7 @@ def set_cart_addons(self, event: Event, addons: List[dict], cart_id: str=None, l
             try:
                 cm = CartManager(event=event, cart_id=cart_id, invoice_address=ia, sales_channel=sales_channel)
                 cm.set_addons(addons)
+                cm.add_new_items(add_to_cart_items)
                 cm.commit()
             except LockTimeoutException:
                 self.retry()

src/pretix/base/services/cross_selling.py

@@ -0,0 +1,232 @@
+#
+# This file is part of pretix (Community Edition).
+#
+# Copyright (C) 2014-2020 Raphael Michel and contributors
+# Copyright (C) 2020-2021 rami.io GmbH and contributors
+#
+# This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General
+# Public License as published by the Free Software Foundation in version 3 of the License.
+#
+# ADDITIONAL TERMS APPLY: Pursuant to Section 7 of the GNU Affero General Public License, additional terms are
+# applicable granting you additional permissions and placing additional restrictions on your usage of this software.
+# Please refer to the pretix LICENSE file to obtain the full terms applicable to this work. If you did not receive
+# this file, see <https://pretix.eu/about/en/license>.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied
+# warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Affero General Public License for more
+# details.
+#
+# You should have received a copy of the GNU Affero General Public License along with this program.  If not, see
+# <https://www.gnu.org/licenses/>.
+#
+
+from collections import defaultdict
+from decimal import Decimal
+from itertools import groupby
+from math import inf
+from typing import List
+
+from django.utils.functional import cached_property
+
+from pretix.base.models import CartPosition, ItemCategory, SalesChannel
+from pretix.presale.views.event import get_grouped_items
+
+
+class DummyCategory:
+    """
+    Used to create fake category objects for displaying the same cross-selling category multiple times,
+    once for each subevent
+    """
+
+    def __init__(self, category: ItemCategory, subevent):
+        self.id = category.id
+        self.name = str(category.name)
+        self.subevent_name = str(subevent)
+        self.description = category.description
+
+
+class CrossSellingService:
+    def __init__(self, event, sales_channel: SalesChannel, cartpositions: List[CartPosition], customer):
+        self.event = event
+        self.sales_channel = sales_channel
+        self.cartpositions = cartpositions
+        self.customer = customer
+
+    def get_data(self):
+        if self.event.has_subevents:
+            subevents = set(pos.subevent for pos in self.cartpositions)
+            result = (
+                (DummyCategory(category, subevent),
+                 self._prepare_items(subevent, items_qs, discount_info),
+                 f'subevent_{subevent.pk}_')
+                for subevent in subevents
+                for (category, items_qs, discount_info) in self._applicable_categories(subevent.pk)
+            )
+        else:
+            result = (
+                (category,
+                 self._prepare_items(None, items_qs, discount_info),
+                 '')
+                for (category, items_qs, discount_info) in self._applicable_categories(0)
+            )
+        result = [(category, items, form_prefix) for (category, items, form_prefix) in result if len(items) > 0]
+        for category, items, form_prefix in result:
+            category.category_has_discount = any(item.original_price for item in items)
+        return result
+
+    def _applicable_categories(self, subevent_id):
+        return [
+            (c, products_qs, discount_info) for (c, products_qs, discount_info) in
+            (
+                (c, *self._get_visible_items_for_category(subevent_id, c))
+                for c in self.event.categories.filter(cross_selling_mode__isnull=False).prefetch_related('items')
+            )
+            if products_qs is not None
+        ]
+
+    def _get_visible_items_for_category(self, filter_subevent_id, category: ItemCategory):
+        """
+        If this category should be visible in the cross-selling step for a given cart and sales_channel, this method
+        returns a queryset of the items that should be displayed, as well as a dict giving additional information on them.
+
+        :returns: (QuerySet<Item>, dict<(subevent_id, item_pk): (max_count, discount_rule)>)
+            max_count is `inf` if the item should not be limited
+            discount_rule is None if the item will not be discounted
+        """
+        if category.cross_selling_mode is None:
+            return None, {}
+        if category.cross_selling_condition == 'always':
+            return category.items.all(), {}
+        if category.cross_selling_condition == 'products':
+            match = set(match.pk for match in category.cross_selling_match_products.only('pk'))  # TODO prefetch this
+            return (category.items.all(), {}) if any(pos.item.pk in match for pos in self.cartpositions) else (None, {})
+        if category.cross_selling_condition == 'discounts':
+            my_item_pks = [item.id for item in category.items.all()]
+            potential_discount_items = {
+                item.pk: (max_count, discount_rule)
+                for subevent_id, item, max_count, discount_rule in self._potential_discounts_by_subevent_and_item_for_current_cart
+                if max_count > 0 and item.pk in my_item_pks and item.is_available() and (subevent_id == filter_subevent_id or subevent_id is None)
+            }
+            return category.items.filter(pk__in=potential_discount_items), potential_discount_items
+
+    @cached_property
+    def _potential_discounts_by_subevent_and_item_for_current_cart(self):
+        potential_discounts_by_cartpos = defaultdict(list)
+
+        from ..services.pricing import apply_discounts
+        self._discounted_prices = apply_discounts(
+            self.event,
+            self.sales_channel,
+            [
+                (cp.item_id, cp.subevent_id, cp.line_price_gross, bool(cp.addon_to), cp.is_bundled,
+                 cp.listed_price - cp.price_after_voucher)
+                for cp in self.cartpositions
+            ],
+            collect_potential_discounts=potential_discounts_by_cartpos
+        )
+
+        # flatten potential_discounts_by_cartpos (a dict of lists of potential discounts) into a set of potential discounts
+        # (which is technically stored as a dict, but we use it as an OrderedSet here)
+        potential_discount_set = dict.fromkeys(
+            info for lst in potential_discounts_by_cartpos.values() for info in lst)
+
+        # sum up the max_counts and pass them on (also pass on the discount_rules so we can calculate actual discounted prices later):
+        # group by benefit product
+        # - max_count for product: sum up max_counts
+        # - discount_rule for product: take first discount_rule
+
+        def discount_info(subevent_id, item, infos_for_item):
+            infos_for_item = list(infos_for_item)
+            return (
+                subevent_id,
+                item,
+                sum(max_count for (subevent_id, item, discount_rule, max_count, i) in infos_for_item),
+                next(discount_rule for (subevent_id, item, discount_rule, max_count, i) in infos_for_item),
+            )
+
+        return [
+            discount_info(subevent_id, item, infos_for_item) for (subevent_id, item), infos_for_item in
+            groupby(
+                sorted(
+                    (
+                        (subevent_id, item, discount_rule, max_count, i)
+                        for (discount_rule, max_count, i, subevent_id) in potential_discount_set.keys()
+                        for item in discount_rule.benefit_limit_products.all()
+                    ),
+                    key=lambda tup: (tup[0], tup[1].pk)
+                ),
+                lambda tup: (tup[0], tup[1]))
+        ]
+
+    def _prepare_items(self, subevent, items_qs, discount_info):
+        items, _btn = get_grouped_items(
+            self.event,
+            subevent=subevent,
+            voucher=None,
+            channel=self.sales_channel,
+            base_qs=items_qs,
+            allow_addons=False,
+            allow_cross_sell=True,
+            memberships=(
+                self.customer.usable_memberships(
+                    for_event=subevent or self.event,
+                    testmode=self.event.testmode
+                )
+                if self.customer else None
+            ),
+        )
+        new_items = list()
+        for item in items:
+            max_count = inf
+            if item.pk in discount_info:
+                (max_count, discount_rule) = discount_info[item.pk]
+
+                # only benefit_only_apply_to_cheapest_n_matches discounted items have a max_count, all others get 'inf'
+                if not max_count:
+                    max_count = inf
+
+                # calculate discounted price
+                if discount_rule and discount_rule.benefit_discount_matching_percent > 0:
+                    if not item.has_variations:
+                        item.original_price = item.original_price or item.display_price
+                        previous_price = item.display_price
+                        new_price = (
+                            previous_price * (
+                                (Decimal('100.00') - discount_rule.benefit_discount_matching_percent) / Decimal('100.00'))
+                        )
+                        item.display_price = new_price
+                    else:
+                        # discounts always match "whole" items, not specific variations -> we apply the discount to all
+                        # available variations of the item
+                        for var in item.available_variations:
+                            var.original_price = var.original_price or var.display_price
+                            previous_price = var.display_price
+                            new_price = (
+                                previous_price * (
+                                    (Decimal('100.00') - discount_rule.benefit_discount_matching_percent) / Decimal('100.00'))
+                            )
+                            var.display_price = new_price
+
+            if not item.has_variations:
+                # reduce order_max by number of items already in cart (prevent recommending a product the user can't add anyway)
+                item.order_max = min(
+                    item.order_max - sum(1 for pos in self.cartpositions if pos.item_id == item.pk),
+                    max_count
+                )
+                if item.order_max > 0:
+                    new_items.append(item)
+            else:
+                new_vars = list()
+                for var in item.available_variations:
+                    # reduce order_max by number of items already in cart (prevent recommending a product the user can't add anyway)
+                    var.order_max = min(
+                        var.order_max - sum(1 for pos in self.cartpositions if pos.item_id == item.pk and pos.variation_id == var.pk),
+                        max_count
+                    )
+                    if var.order_max > 0:
+                        new_vars.append(var)
+                if len(new_vars):
+                    item.available_variations = new_vars
+                    new_items.append(item)
+
+        return new_items

src/pretix/base/services/pricing.py

@@ -20,8 +20,9 @@
 # <https://www.gnu.org/licenses/>.
 #
 import re
+from collections import defaultdict
 from decimal import Decimal
-from typing import List, Optional, Tuple
+from typing import List, Optional, Tuple, Union
 
 from django import forms
 from django.db.models import Q
@@ -31,6 +32,7 @@ from pretix.base.models import (
     AbstractPosition, InvoiceAddress, Item, ItemAddOn, ItemVariation,
     SalesChannel, Voucher,
 )
+from pretix.base.models.discount import Discount, PositionInfo
 from pretix.base.models.event import Event, SubEvent
 from pretix.base.models.tax import TAXED_ZERO, TaxedPrice, TaxRule
 from pretix.base.timemachine import time_machine_now
@@ -155,14 +157,22 @@ def get_line_price(price_after_voucher: Decimal, custom_price_input: Decimal, cu
     return price
 
 
-def apply_discounts(event: Event, sales_channel: str,
-                    positions: List[Tuple[int, Optional[int], Decimal, bool, bool]]) -> List[Decimal]:
+def apply_discounts(event: Event, sales_channel: Union[str, SalesChannel],
+                    positions: List[Tuple[int, Optional[int], Decimal, bool, bool, Decimal]],
+                    collect_potential_discounts: Optional[defaultdict]=None) -> List[Tuple[Decimal, Optional[Discount]]]:
     """
     Applies any dynamic discounts to a cart
 
     :param event: Event the cart belongs to
     :param sales_channel: Sales channel the cart was created with
     :param positions: Tuple of the form ``(item_id, subevent_id, line_price_gross, is_addon_to, is_bundled, voucher_discount)``
+    :param collect_potential_discounts: If a `defaultdict(list)` is supplied, all discounts that could be applied to the cart
+    based on the "consumed" items, but lack matching "benefitting" items will be collected therein.
+    The dict will contain a mapping from index in the `positions` list of the item that could be consumed, to a list
+    of tuples describing the discounts that could be applied in the form `(discount, max_count, grouping_id)`.
+    `max_count` is either the maximum number of benefitting items that the discount would apply to, or `inf` if that number
+    is not limited. The `grouping_id` can be used to distinguish several occurrences of the same discount.
+
     :return: A list of ``(new_gross_price, discount)`` tuples in the same order as the input
     """
     if isinstance(sales_channel, SalesChannel):
@@ -177,10 +187,10 @@ def apply_discounts(event: Event, sales_channel: str,
     ).prefetch_related('condition_limit_products', 'benefit_limit_products').order_by('position', 'pk')
     for discount in discount_qs:
         result = discount.apply({
-            idx: (item_id, subevent_id, line_price_gross, is_addon_to, voucher_discount)
+            idx: PositionInfo(item_id, subevent_id, line_price_gross, is_addon_to, voucher_discount)
             for idx, (item_id, subevent_id, line_price_gross, is_addon_to, is_bundled, voucher_discount) in enumerate(positions)
             if not is_bundled and idx not in new_prices
-        })
+        }, collect_potential_discounts)
         for k in result.keys():
             result[k] = (result[k], discount)
         new_prices.update(result)