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/models/discount.py

@@ -20,11 +20,11 @@
 # <https://www.gnu.org/licenses/>.
 #
 
-from collections import defaultdict
+from collections import defaultdict, namedtuple
 from decimal import Decimal
 from itertools import groupby
-from math import ceil
-from typing import Dict, Optional, Tuple
+from math import ceil, inf
+from typing import Dict
 
 from django.core.exceptions import ValidationError
 from django.core.validators import MinValueValidator
@@ -36,6 +36,8 @@ from django_scopes import ScopedManager
 from pretix.base.decimal import round_decimal
 from pretix.base.models.base import LoggedModel
 
+PositionInfo = namedtuple('PositionInfo', ['item_id', 'subevent_id', 'line_price_gross', 'is_addon_to', 'voucher_discount'])
+
 
 class Discount(LoggedModel):
     SUBEVENT_MODE_MIXED = 'mixed'
@@ -245,22 +247,26 @@ class Discount(LoggedModel):
             return False
         return True
 
-    def _apply_min_value(self, positions, condition_idx_group, benefit_idx_group, result):
-        if self.condition_min_value and sum(positions[idx][2] for idx in condition_idx_group) < self.condition_min_value:
+    def _apply_min_value(self, positions, condition_idx_group, benefit_idx_group, result, collect_potential_discounts, subevent_id):
+        if self.condition_min_value and sum(positions[idx].line_price_gross for idx in condition_idx_group) < self.condition_min_value:
             return
 
         if self.condition_min_count or self.benefit_only_apply_to_cheapest_n_matches:
             raise ValueError('Validation invariant violated.')
 
         for idx in benefit_idx_group:
-            previous_price = positions[idx][2]
+            previous_price = positions[idx].line_price_gross
             new_price = round_decimal(
                 previous_price * (Decimal('100.00') - self.benefit_discount_matching_percent) / Decimal('100.00'),
                 self.event.currency,
             )
             result[idx] = new_price
 
-    def _apply_min_count(self, positions, condition_idx_group, benefit_idx_group, result):
+        if collect_potential_discounts is not None:
+            for idx in condition_idx_group:
+                collect_potential_discounts[idx] = [(self, inf, -1, subevent_id)]
+
+    def _apply_min_count(self, positions, condition_idx_group, benefit_idx_group, result, collect_potential_discounts, subevent_id):
         if len(condition_idx_group) < self.condition_min_count:
             return
 
@@ -268,23 +274,53 @@ class Discount(LoggedModel):
             raise ValueError('Validation invariant violated.')
 
         if self.benefit_only_apply_to_cheapest_n_matches:
-            if not self.condition_min_count:
-                raise ValueError('Validation invariant violated.')
-
-            condition_idx_group = sorted(condition_idx_group, key=lambda idx: (positions[idx][2], -idx))  # sort by line_price
-            benefit_idx_group = sorted(benefit_idx_group, key=lambda idx: (positions[idx][2], -idx))  # sort by line_price
+            # sort by line_price
+            condition_idx_group = sorted(condition_idx_group, key=lambda idx: (positions[idx].line_price_gross, -idx))
+            benefit_idx_group = sorted(benefit_idx_group, key=lambda idx: (positions[idx].line_price_gross, -idx))
 
             # Prevent over-consuming of items, i.e. if our discount is "buy 2, get 1 free", we only
             # want to match multiples of 3
-            n_groups = min(len(condition_idx_group) // self.condition_min_count, ceil(len(benefit_idx_group) / self.benefit_only_apply_to_cheapest_n_matches))
+
+            # how many discount applications are allowed according to condition products in cart
+            possible_applications_cond = len(condition_idx_group) // self.condition_min_count
+
+            # how many discount applications are possible according to benefitting products in cart
+            possible_applications_benefit = ceil(len(benefit_idx_group) / self.benefit_only_apply_to_cheapest_n_matches)
+
+            n_groups = min(possible_applications_cond, possible_applications_benefit)
             consume_idx = condition_idx_group[:n_groups * self.condition_min_count]
             benefit_idx = benefit_idx_group[:n_groups * self.benefit_only_apply_to_cheapest_n_matches]
+
+            if collect_potential_discounts is not None:
+                if n_groups * self.benefit_only_apply_to_cheapest_n_matches > len(benefit_idx_group):
+                    # partially used discount ("for each 1 ticket you buy, get 50% on 2 t-shirts", cart content: 1 ticket
+                    # but only 1 t-shirt) -> 1 shirt definitiv potential discount
+                    for idx in consume_idx:
+                        collect_potential_discounts[idx] = [
+                            (self, n_groups * self.benefit_only_apply_to_cheapest_n_matches - len(benefit_idx_group), -1, subevent_id)
+                        ]
+
+                if possible_applications_cond * self.benefit_only_apply_to_cheapest_n_matches > len(benefit_idx_group):
+                    # unused discount ("for each 1 ticket you buy, get 50% on 2 t-shirts", cart content: 1 ticket
+                    # but 0 t-shirts) -> 2 shirt maybe potential discount (if the 1 ticket is not consumed by a later discount)
+                    for i, idx in enumerate(condition_idx_group[
+                                            n_groups * self.condition_min_count:
+                                            possible_applications_cond * self.condition_min_count
+                                            ]):
+                        collect_potential_discounts[idx] += [
+                            (self, self.benefit_only_apply_to_cheapest_n_matches, i // self.condition_min_count, subevent_id)
+                        ]
+
         else:
             consume_idx = condition_idx_group
             benefit_idx = benefit_idx_group
 
+            if collect_potential_discounts is not None:
+                for idx in consume_idx:
+                    collect_potential_discounts[idx] = [(self, inf, -1, subevent_id)]
+
         for idx in benefit_idx:
-            previous_price = positions[idx][2]
+            previous_price = positions[idx].line_price_gross
             new_price = round_decimal(
                 previous_price * (Decimal('100.00') - self.benefit_discount_matching_percent) / Decimal('100.00'),
                 self.event.currency,
@@ -292,15 +328,16 @@ class Discount(LoggedModel):
             result[idx] = new_price
 
         for idx in consume_idx:
-            result.setdefault(idx, positions[idx][2])
+            result.setdefault(idx, positions[idx].line_price_gross)
 
-    def apply(self, positions: Dict[int, Tuple[int, Optional[int], Decimal, bool, Decimal]]) -> Dict[int, Decimal]:
+    def apply(self, positions: Dict[int, PositionInfo],
+              collect_potential_discounts=None) -> Dict[int, Decimal]:
         """
         Tries to apply this discount to a cart
 
-        :param positions: Dictionary mapping IDs to tuples of the form
-                          ``(item_id, subevent_id, line_price_gross, is_addon_to, voucher_discount)``.
+        :param positions: Dictionary mapping IDs to PositionInfo tuples.
                           Bundled positions may not be included.
+        :param collect_potential_discounts: For detailed description, see pretix.base.services.pricing.apply_discounts
 
         :return: A dictionary mapping keys from the input dictionary to new prices. All positions
                  contained in this dictionary are considered "consumed" and should not be considered
@@ -342,13 +379,13 @@ class Discount(LoggedModel):
 
         if self.subevent_mode == self.SUBEVENT_MODE_MIXED:  # also applies to non-series events
             if self.condition_min_count:
-                self._apply_min_count(positions, condition_candidates, benefit_candidates, result)
+                self._apply_min_count(positions, condition_candidates, benefit_candidates, result, collect_potential_discounts, None)
             else:
-                self._apply_min_value(positions, condition_candidates, benefit_candidates, result)
+                self._apply_min_value(positions, condition_candidates, benefit_candidates, result, collect_potential_discounts, None)
 
         elif self.subevent_mode == self.SUBEVENT_MODE_SAME:
             def key(idx):
-                return positions[idx][1] or 0  # subevent_id
+                return positions[idx].subevent_id or 0
 
             # Build groups of candidates with the same subevent, then apply our regular algorithm
             # to each group
@@ -357,11 +394,11 @@ class Discount(LoggedModel):
             candidate_groups = [(k, list(g)) for k, g in _groups]
 
             for subevent_id, g in candidate_groups:
-                benefit_g = [idx for idx in benefit_candidates if positions[idx][1] == subevent_id]
+                benefit_g = [idx for idx in benefit_candidates if positions[idx].subevent_id == subevent_id]
                 if self.condition_min_count:
-                    self._apply_min_count(positions, g, benefit_g, result)
+                    self._apply_min_count(positions, g, benefit_g, result, collect_potential_discounts, subevent_id)
                 else:
-                    self._apply_min_value(positions, g, benefit_g, result)
+                    self._apply_min_value(positions, g, benefit_g, result, collect_potential_discounts, subevent_id)
 
         elif self.subevent_mode == self.SUBEVENT_MODE_DISTINCT:
             if self.condition_min_value or not self.benefit_same_products:
@@ -377,9 +414,9 @@ class Discount(LoggedModel):
             # Build a list of subevent IDs in descending order of frequency
             subevent_to_idx = defaultdict(list)
             for idx, p in positions.items():
-                subevent_to_idx[p[1]].append(idx)
+                subevent_to_idx[p.subevent_id].append(idx)
             for v in subevent_to_idx.values():
-                v.sort(key=lambda idx: positions[idx][2])
+                v.sort(key=lambda idx: positions[idx].line_price_gross)
             subevent_order = sorted(list(subevent_to_idx.keys()), key=lambda s: len(subevent_to_idx[s]), reverse=True)
 
             # Build groups of exactly condition_min_count distinct subevents
@@ -394,7 +431,7 @@ class Discount(LoggedModel):
                     l = [ll for ll in l if ll in condition_candidates and ll not in current_group]
                     if cardinality and len(l) != cardinality:
                         continue
-                    if se not in {positions[idx][1] for idx in current_group}:
+                    if se not in {positions[idx].subevent_id for idx in current_group}:
                         candidates += l
                         cardinality = len(l)
 
@@ -403,7 +440,7 @@ class Discount(LoggedModel):
 
                 # Sort the list by prices, then pick one. For "buy 2 get 1 free" we apply a "pick 1 from the start
                 # and 2 from the end" scheme to optimize price distribution among groups
-                candidates = sorted(candidates, key=lambda idx: positions[idx][2])
+                candidates = sorted(candidates, key=lambda idx: positions[idx].line_price_gross)
                 if len(current_group) < (self.benefit_only_apply_to_cheapest_n_matches or 0):
                     candidate = candidates[0]
                 else:
@@ -415,14 +452,14 @@ class Discount(LoggedModel):
                 if len(current_group) >= max(self.condition_min_count, 1):
                     candidate_groups.append(current_group)
                     for c in current_group:
-                        subevent_to_idx[positions[c][1]].remove(c)
+                        subevent_to_idx[positions[c].subevent_id].remove(c)
                     current_group = []
 
             # Distribute "leftovers"
             for se in subevent_order:
                 if subevent_to_idx[se]:
                     for group in candidate_groups:
-                        if se not in {positions[idx][1] for idx in group}:
+                        if se not in {positions[idx].subevent_id for idx in group}:
                             group.append(subevent_to_idx[se].pop())
                             if not subevent_to_idx[se]:
                                 break
@@ -432,6 +469,8 @@ class Discount(LoggedModel):
                     positions,
                     [idx for idx in g if idx in condition_candidates],
                     [idx for idx in g if idx in benefit_candidates],
-                    result
+                    result,
+                    None,
+                    None
                 )
         return result

src/pretix/base/models/event.py

@@ -870,10 +870,12 @@ class Event(EventMixin, LoggedModel):
         for i in Item.objects.filter(event=other).prefetch_related(
             'variations', 'limit_sales_channels', 'require_membership_types',
             'variations__limit_sales_channels', 'variations__require_membership_types',
+            'matched_by_cross_selling_categories',
         ):
             vars = list(i.variations.all())
             require_membership_types = list(i.require_membership_types.all())
             limit_sales_channels = list(i.limit_sales_channels.all())
+            matched_by_cross_selling_categories = list(i.matched_by_cross_selling_categories.all())
             item_map[i.pk] = i
             i.pk = None
             i.event = self
@@ -911,6 +913,9 @@ class Event(EventMixin, LoggedModel):
                 if not v.all_sales_channels:
                     v.limit_sales_channels.set(self.organizer.sales_channels.filter(identifier__in=[s.identifier for s in limit_sales_channels]))
 
+            if matched_by_cross_selling_categories:
+                i.matched_by_cross_selling_categories.set([category_map[c.pk] for c in matched_by_cross_selling_categories])
+
         for i in self.items.filter(hidden_if_item_available__isnull=False):
             i.hidden_if_item_available = item_map[i.hidden_if_item_available_id]
             i.save()

src/pretix/base/models/items.py

@@ -63,14 +63,13 @@ from django_countries.fields import Country
 from django_scopes import ScopedManager
 from i18nfield.fields import I18nCharField, I18nTextField
 
+from pretix.base.media import MEDIA_TYPES
+from pretix.base.models import Event, SubEvent
 from pretix.base.models.base import LoggedModel
 from pretix.base.models.fields import MultiStringField
 from pretix.base.models.tax import TaxedPrice
 from pretix.base.timemachine import time_machine_now
-
-from ...helpers.images import ImageSizeValidator
-from ..media import MEDIA_TYPES
-from .event import Event, SubEvent
+from pretix.helpers.images import ImageSizeValidator
 
 
 class ItemCategory(LoggedModel):
@@ -111,6 +110,33 @@ class ItemCategory(LoggedModel):
                     'only be bought in combination with a product that has this category configured as a possible '
                     'source for add-ons.')
     )
+    CROSS_SELLING_MODES = (
+        (None, _('Normal category')),
+        ('both', _('Normal + cross-selling category')),
+        ('only', _('Cross-selling category')),
+    )
+    cross_selling_mode = models.CharField(
+        choices=CROSS_SELLING_MODES,
+        null=True,
+        max_length=5
+    )
+    CROSS_SELLING_CONDITION = (
+        ('always', _('Always show in cross-selling step')),
+        ('discounts', _('Only show products that qualify for a discount according to discount rules')),
+        ('products', _('Only show if the cart contains one of the following products')),
+    )
+    cross_selling_condition = models.CharField(
+        verbose_name=_("Cross-selling condition"),
+        choices=CROSS_SELLING_CONDITION,
+        null=True,
+        max_length=10,
+    )
+    cross_selling_match_products = models.ManyToManyField(
+        'pretixbase.Item',
+        blank=True,
+        verbose_name=_("Cross-selling condition products"),
+        related_name="matched_by_cross_selling_categories",
+    )
 
     class Meta:
         verbose_name = _("Product category")
@@ -119,19 +145,31 @@ class ItemCategory(LoggedModel):
 
     def __str__(self):
         name = self.internal_name or self.name
-        if self.is_addon:
-            return _('{category} (Add-On products)').format(category=str(name))
+        category_type = self.get_category_type_display()
+        if category_type:
+            return _('{category} ({category_type})').format(category=str(name), category_type=category_type)
         return str(name)
 
     def get_category_type_display(self):
         if self.is_addon:
-            return _('Add-On products')
+            return _('Add-on category')
+        elif self.cross_selling_mode:
+            return self.get_cross_selling_mode_display()
         else:
             return None
 
     @property
     def category_type(self):
-        return 'addon' if self.is_addon else 'normal'
+        return 'addon' if self.is_addon else self.cross_selling_mode or 'normal'
+
+    @category_type.setter
+    def category_type(self, new_value):
+        if new_value == 'addon':
+            self.is_addon = True
+            self.cross_selling_mode = None
+        else:
+            self.is_addon = False
+            self.cross_selling_mode = None if new_value == 'normal' else new_value
 
     def delete(self, *args, **kwargs):
         super().delete(*args, **kwargs)
@@ -270,7 +308,7 @@ class SubEventItemVariation(models.Model):
         return True
 
 
-def filter_available(qs, channel='web', voucher=None, allow_addons=False):
+def filter_available(qs, channel='web', voucher=None, allow_addons=False, allow_cross_sell=False):
     # Channel can currently be a SalesChannel or a str, since we need that compatibility, but a SalesChannel
     # makes the query SIGNIFICANTLY faster
     from .organizer import SalesChannel
@@ -291,6 +329,8 @@ def filter_available(qs, channel='web', voucher=None, allow_addons=False):
 
     if not allow_addons:
         q &= Q(Q(category__isnull=True) | Q(category__is_addon=False))
+    if not allow_cross_sell:
+        q &= Q(Q(category__isnull=True) | ~Q(category__cross_selling_mode='only'))
 
     if voucher:
         if voucher.item_id:
@@ -304,8 +344,8 @@ def filter_available(qs, channel='web', voucher=None, allow_addons=False):
 
 
 class ItemQuerySet(models.QuerySet):
-    def filter_available(self, channel='web', voucher=None, allow_addons=False):
-        return filter_available(self, channel, voucher, allow_addons)
+    def filter_available(self, channel='web', voucher=None, allow_addons=False, allow_cross_sell=False):
+        return filter_available(self, channel, voucher, allow_addons, allow_cross_sell)
 
 
 class ItemQuerySetManager(ScopedManager(organizer='event__organizer').__class__):
@@ -313,8 +353,8 @@ class ItemQuerySetManager(ScopedManager(organizer='event__organizer').__class__)
         super().__init__()
         self._queryset_class = ItemQuerySet
 
-    def filter_available(self, channel='web', voucher=None, allow_addons=False):
-        return filter_available(self.get_queryset(), channel, voucher, allow_addons)
+    def filter_available(self, channel='web', voucher=None, allow_addons=False, allow_cross_sell=False):
+        return filter_available(self.get_queryset(), channel, voucher, allow_addons, allow_cross_sell)
 
 
 class Item(LoggedModel):