Fix #1001 -- Add product bundles (#1041)

* Data model + Editor

* Cart and order management

* Rebase migrations

* Fix typos, add tests on cart handling

* Add tests for checkout and quotas

* Add API endpoints

* Validation of settings

* Front page tax display

* Voucher handling

* Widget foo

* Show correct net pricing

* Front page tests

* reverse charge foo

* Allow to require bundling

* Fix test failure on postgres

src/pretix/base/services/cart.py

@@ -13,7 +13,8 @@ from django.utils.translation import pgettext_lazy, ugettext as _
 
 from pretix.base.i18n import language
 from pretix.base.models import (
-    CartPosition, Event, InvoiceAddress, Item, ItemVariation, Voucher,
+    CartPosition, Event, InvoiceAddress, Item, ItemBundle, ItemVariation,
+    Voucher,
 )
 from pretix.base.models.event import SubEvent
 from pretix.base.models.orders import OrderFee
@@ -87,12 +88,13 @@ error_messages = {
     'addon_min_count': _('You need to select at least %(min)s add-ons from the category %(cat)s for the '
                          'product %(base)s.'),
     'addon_only': _('One of the products you selected can only be bought as an add-on to another project.'),
+    'bundled_only': _('One of the products you selected can only be bought part of a bundle.'),
 }
 
 
 class CartManager:
     AddOperation = namedtuple('AddOperation', ('count', 'item', 'variation', 'price', 'voucher', 'quotas',
-                                               'addon_to', 'subevent', 'includes_tax'))
+                                               'addon_to', 'subevent', 'includes_tax', 'bundled'))
     RemoveOperation = namedtuple('RemoveOperation', ('position',))
     ExtendOperation = namedtuple('ExtendOperation', ('position', 'count', 'item', 'variation', 'price', 'voucher',
                                                      'quotas', 'subevent'))
@@ -162,7 +164,7 @@ class CartManager:
         self._items_cache.update({
             i.pk: i
             for i in self.event.items.select_related('category').prefetch_related(
-                'addons', 'addons__addon_category', 'quotas'
+                'addons', 'bundles', 'addons__addon_category', 'quotas'
             ).filter(
                 id__in=[i for i in item_ids if i and i not in self._items_cache]
             )
@@ -215,9 +217,12 @@ class CartManager:
                 raise CartError(error_messages['ended'])
 
         if isinstance(op, self.AddOperation):
-            if op.item.category and op.item.category.is_addon and not op.addon_to:
+            if op.item.category and op.item.category.is_addon and not (op.addon_to and op.addon_to != 'FAKE'):
                 raise CartError(error_messages['addon_only'])
 
+            if op.item.require_bundling and not op.addon_to == 'FAKE':
+                raise CartError(error_messages['bundled_only'])
+
             if op.item.max_per_order or op.item.min_per_order:
                 new_total = (
                     len([1 for p in self.positions if p.item_id == op.item.pk]) +
@@ -246,12 +251,13 @@ class CartManager:
 
     def _get_price(self, item: Item, variation: Optional[ItemVariation],
                    voucher: Optional[Voucher], custom_price: Optional[Decimal],
-                   subevent: Optional[SubEvent], cp_is_net: bool=None):
+                   subevent: Optional[SubEvent], cp_is_net: bool=None, force_custom_price=False,
+                   bundled_sum=Decimal('0.00')):
         try:
             return get_price(
                 item, variation, voucher, custom_price, subevent,
                 custom_price_is_net=cp_is_net if cp_is_net is not None else self.event.settings.display_net_prices,
-                invoice_address=self.invoice_address
+                invoice_address=self.invoice_address, force_custom_price=force_custom_price, bundled_sum=bundled_sum
             )
         except ValueError as e:
             if str(e) == 'price_too_high':
@@ -261,22 +267,52 @@ class CartManager:
 
     def extend_expired_positions(self):
         expired = self.positions.filter(expires__lte=self.now_dt).select_related(
-            'item', 'variation', 'voucher'
-        ).prefetch_related('item__quotas', 'variation__quotas')
+            'item', 'variation', 'voucher', 'addon_to', 'addon_to__item'
+        ).prefetch_related(
+            'item__quotas',
+            'variation__quotas',
+            'addons'
+        ).order_by('-is_bundled')
         err = None
+        changed_prices = {}
         for cp in expired:
-            if not cp.includes_tax:
-                price = self._get_price(cp.item, cp.variation, cp.voucher, cp.price, cp.subevent,
-                                        cp_is_net=True)
-                price = TaxedPrice(net=price.net, gross=price.net, rate=0, tax=0, name='')
+            if cp.is_bundled:
+                try:
+                    bundle = cp.addon_to.item.bundles.get(bundled_item=cp.item, bundled_variation=cp.variation)
+                    price = bundle.designated_price or 0
+                except ItemBundle.DoesNotExist:
+                    price = cp.price
+
+                changed_prices[cp.pk] = price
+
+                if not cp.includes_tax:
+                    price = self._get_price(cp.item, cp.variation, cp.voucher, price, cp.subevent,
+                                            force_custom_price=True, cp_is_net=False)
+                    price = TaxedPrice(net=price.net, gross=price.net, rate=0, tax=0, name='')
+                else:
+                    price = self._get_price(cp.item, cp.variation, cp.voucher, price, cp.subevent,
+                                            force_custom_price=True)
             else:
-                price = self._get_price(cp.item, cp.variation, cp.voucher, cp.price, cp.subevent)
+                bundled_sum = Decimal('0.00')
+                if not cp.addon_to_id:
+                    for bundledp in cp.addons.all():
+                        if bundledp.is_bundled:
+                            bundledprice = changed_prices.get(bundledp.pk, bundledp.price)
+                            bundled_sum += bundledprice
+
+                if not cp.includes_tax:
+                    price = self._get_price(cp.item, cp.variation, cp.voucher, cp.price, cp.subevent,
+                                            cp_is_net=True, bundled_sum=bundled_sum)
+                    price = TaxedPrice(net=price.net, gross=price.net, rate=0, tax=0, name='')
+                else:
+                    price = self._get_price(cp.item, cp.variation, cp.voucher, cp.price, cp.subevent,
+                                            bundled_sum=bundled_sum)
 
             quotas = list(cp.quotas)
             if not quotas:
                 self._operations.append(self.RemoveOperation(position=cp))
-                continue
                 err = error_messages['unavailable']
+                continue
 
             if not cp.voucher or (not cp.voucher.allow_ignore_quota and not cp.voucher.block_quota):
                 for quota in quotas:
@@ -341,10 +377,48 @@ class CartManager:
             else:
                 quotas = []
 
-            price = self._get_price(item, variation, voucher, i.get('price'), subevent)
+            # Fetch bundled items
+            bundled = []
+            bundled_sum = Decimal('0.00')
+            db_bundles = list(item.bundles.all())
+            self._update_items_cache([b.bundled_item_id for b in db_bundles], [b.bundled_variation_id for b in db_bundles])
+            for bundle in db_bundles:
+                if bundle.bundled_item_id not in self._items_cache or (
+                        bundle.bundled_variation_id and bundle.bundled_variation_id not in self._variations_cache
+                ):
+                    raise CartError(error_messages['not_for_sale'])
+                bitem = self._items_cache[bundle.bundled_item_id]
+                bvar = self._variations_cache[bundle.bundled_variation_id] if bundle.bundled_variation_id else None
+                bundle_quotas = list(bitem.quotas.filter(subevent=subevent)
+                                     if bvar is None else bvar.quotas.filter(subevent=subevent))
+                if not bundle_quotas:
+                    raise CartError(error_messages['unavailable'])
+                if not voucher or not voucher.allow_ignore_quota:
+                    for quota in bundle_quotas:
+                        quota_diff[quota] += bundle.count * i['count']
+                else:
+                    bundle_quotas = []
+
+                if bundle.designated_price:
+                    bprice = self._get_price(bitem, bvar, None, bundle.designated_price, subevent, force_custom_price=True,
+                                             cp_is_net=False)
+                else:
+                    bprice = TAXED_ZERO
+                bundled_sum += bundle.designated_price * bundle.count
+
+                bop = self.AddOperation(
+                    count=bundle.count, item=bitem, variation=bvar, price=bprice,
+                    voucher=None, quotas=bundle_quotas, addon_to='FAKE', subevent=subevent,
+                    includes_tax=bool(bprice.rate), bundled=[]
+                )
+                self._check_item_constraints(bop)
+                bundled.append(bop)
+
+            price = self._get_price(item, variation, voucher, i.get('price'), subevent, bundled_sum=bundled_sum)
+
             op = self.AddOperation(
                 count=i['count'], item=item, variation=variation, price=price, voucher=voucher, quotas=quotas,
-                addon_to=False, subevent=subevent, includes_tax=bool(price.rate)
+                addon_to=False, subevent=subevent, includes_tax=bool(price.rate), bundled=bundled
             )
             self._check_item_constraints(op)
             operations.append(op)
@@ -403,6 +477,7 @@ class CartManager:
             current_addons[cp] = {
                 (a.item_id, a.variation_id): a
                 for a in cp.addons.all()
+                if not a.is_bundled
             }
 
         # Create operations, perform various checks
@@ -449,7 +524,7 @@ class CartManager:
 
                 op = self.AddOperation(
                     count=1, item=item, variation=variation, price=price, voucher=None, quotas=quotas,
-                    addon_to=cp, subevent=cp.subevent, includes_tax=bool(price.rate)
+                    addon_to=cp, subevent=cp.subevent, includes_tax=bool(price.rate), bundled=[]
                 )
                 self._check_item_constraints(op)
                 operations.append(op)
@@ -609,11 +684,29 @@ class CartManager:
 
                 available_count = min(quota_available_count, voucher_available_count)
 
+                if isinstance(op, self.AddOperation):
+                    for b in op.bundled:
+                        b_quota_available_count = min(available_count * b.count, min(quotas_ok[q] for q in b.quotas))
+                        if b_quota_available_count < b.count:
+                            err = err or error_messages['unavailable']
+                            available_count = 0
+                        elif b_quota_available_count < available_count * b.count:
+                            err = err or error_messages['in_part']
+                            available_count = b_quota_available_count // b.count
+                        for q in b.quotas:
+                            quotas_ok[q] -= available_count * b.count
+                            # TODO: is this correct?
+
                 for q in op.quotas:
                     quotas_ok[q] -= available_count
                 if op.voucher:
                     vouchers_ok[op.voucher] -= available_count
 
+                if any(qa < 0 for qa in quotas_ok.values()):
+                    # Safeguard, shouldn't happen
+                    err = err or error_messages['unavailable']
+                    available_count = 0
+
                 if isinstance(op, self.AddOperation):
                     for k in range(available_count):
                         cp = CartPosition(
@@ -646,6 +739,17 @@ class CartManager:
                                 except ValidationError:
                                     pass
 
+                        if op.bundled:
+                            cp.save()  # Needs to be in the database already so we have a PK that we can reference
+                            for b in op.bundled:
+                                for j in range(b.count):
+                                    new_cart_positions.append(CartPosition(
+                                        event=self.event, item=b.item, variation=b.variation,
+                                        price=b.price.gross, expires=self._expiry, cart_id=self.cart_id,
+                                        voucher=None, addon_to=cp,
+                                        subevent=b.subevent, includes_tax=b.includes_tax, is_bundled=True
+                                    ))
+
                         new_cart_positions.append(cp)
                 elif isinstance(op, self.ExtendOperation):
                     if available_count == 1:
@@ -659,10 +763,11 @@ class CartManager:
                         raise AssertionError("ExtendOperation cannot affect more than one item")
 
         for p in new_cart_positions:
-            if p._answers:
-                p.save()
+            if getattr(p, '_answers', None):
+                if not p.pk:  # We stored some to the database already before
+                    p.save()
                 _save_answers(p, {}, p._answers)
-        CartPosition.objects.bulk_create([p for p in new_cart_positions if not p._answers])
+        CartPosition.objects.bulk_create([p for p in new_cart_positions if not getattr(p, '_answers', None) and not p.pk])
         return err
 
     def commit(self):
@@ -747,7 +852,7 @@ def add_items_to_cart(self, event: int, items: List[dict], cart_id: str=None, lo
     """
     Adds a list of items to a user's cart.
     :param event: The event ID in question
-    :param items: A list of dicts with the keys item, variation, number, custom_price, voucher
+    :param items: A list of dicts with the keys item, variation, count, custom_price, voucher
     :param cart_id: Session ID of a guest
     :raises CartError: On any error that occured
     """

src/pretix/base/services/orders.py

@@ -26,6 +26,7 @@ from pretix.base.models import (
     OrderPosition, Quota, User, Voucher,
 )
 from pretix.base.models.event import SubEvent
+from pretix.base.models.items import ItemBundle
 from pretix.base.models.orders import (
     CachedCombinedTicket, CachedTicket, InvoiceAddress, OrderFee, OrderRefund,
     generate_position_secret, generate_secret,
@@ -400,10 +401,27 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
     _check_date(event, now_dt)
 
     products_seen = Counter()
-    for i, cp in enumerate(positions):
+    changed_prices = {}
+    deleted_positions = set()
+
+    def delete(cp):
+        # Delete a cart position, including parents and children, if applicable
+        if cp.is_bundled:
+            delete(cp.addon_to)
+        else:
+            for p in cp.addons.all():
+                deleted_positions.add(p.pk)
+                p.delete()
+            deleted_positions.add(cp.pk)
+            cp.delete()
+
+    for i, cp in enumerate(sorted(positions, key=lambda s: -int(s.is_bundled))):
+        if cp.pk in deleted_positions:
+            continue
+
         if not cp.item.is_available() or (cp.variation and not cp.variation.active):
             err = err or error_messages['unavailable']
-            cp.delete()
+            delete(cp)
             continue
         quotas = list(cp.quotas)
 
@@ -412,7 +430,7 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
             err = error_messages['max_items_per_product']
             errargs = {'max': cp.item.max_per_order,
                        'product': cp.item.name}
-            cp.delete()  # Sorry!
+            delete(cp)
             break
 
         if cp.voucher:
@@ -422,27 +440,27 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
             v_avail = cp.voucher.max_usages - cp.voucher.redeemed - redeemed_in_carts.count()
             if v_avail < 1:
                 err = err or error_messages['voucher_redeemed']
-                cp.delete()  # Sorry!
+                delete(cp)
                 continue
 
         if cp.subevent and cp.subevent.presale_start and now_dt < cp.subevent.presale_start:
             err = err or error_messages['some_subevent_not_started']
-            cp.delete()
+            delete(cp)
             break
 
         if cp.subevent and cp.subevent.presale_has_ended:
             err = err or error_messages['some_subevent_ended']
-            cp.delete()
+            delete(cp)
             break
 
         if cp.item.require_voucher and cp.voucher is None:
-            cp.delete()
+            delete(cp)
             err = err or error_messages['voucher_required']
             break
 
         if cp.item.hide_without_voucher and (cp.voucher is None or cp.voucher.item is None
                                              or cp.voucher.item.pk != cp.item.pk):
-            cp.delete()
+            delete(cp)
             err = error_messages['voucher_required']
             break
 
@@ -450,18 +468,34 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
             # Other checks are not necessary
             continue
 
-        price = get_price(cp.item, cp.variation, cp.voucher, cp.price, cp.subevent, custom_price_is_net=False,
-                          addon_to=cp.addon_to, invoice_address=address)
+        if cp.is_bundled:
+            try:
+                bundle = cp.addon_to.item.bundles.get(bundled_item=cp.item, bundled_variation=cp.variation)
+                bprice = bundle.designated_price or 0
+            except ItemBundle.DoesNotExist:
+                bprice = cp.price
+            price = get_price(cp.item, cp.variation, cp.voucher, bprice, cp.subevent, custom_price_is_net=False,
+                              invoice_address=address, force_custom_price=True)
+            changed_prices[cp.pk] = bprice
+        else:
+            bundled_sum = 0
+            if not cp.addon_to_id:
+                for bundledp in cp.addons.all():
+                    if bundledp.is_bundled:
+                        bundled_sum += changed_prices.get(bundledp.pk, bundledp.price)
+
+            price = get_price(cp.item, cp.variation, cp.voucher, cp.price, cp.subevent, custom_price_is_net=False,
+                              addon_to=cp.addon_to, invoice_address=address, bundled_sum=bundled_sum)
 
         if price is False or len(quotas) == 0:
             err = err or error_messages['unavailable']
-            cp.delete()
+            delete(cp)
             continue
 
         if cp.voucher:
             if cp.voucher.valid_until and cp.voucher.valid_until < now_dt:
                 err = err or error_messages['voucher_expired']
-                cp.delete()
+                delete(cp)
                 continue
 
         if price.gross != cp.price and not (cp.item.free_price and cp.price > price.gross):
@@ -494,7 +528,8 @@ def _check_positions(event: Event, now_dt: datetime, positions: List[CartPositio
                 minutes=event.settings.get('reservation_time', as_type=int))
             cp.save()
         else:
-            cp.delete()  # Sorry!
+            # Sorry, can't let you keep that!
+            delete(cp)
     if err:
         raise OrderError(err, errargs)
 
@@ -599,7 +634,7 @@ def _perform_order(event: str, payment_provider: str, position_ids: List[str],
 
     with event.lock() as now_dt:
         positions = list(CartPosition.objects.filter(
-            id__in=position_ids).select_related('item', 'variation', 'subevent'))
+            id__in=position_ids).select_related('item', 'variation', 'subevent', 'addon_to').prefetch_related('addons'))
         if len(positions) == 0:
             raise OrderError(error_messages['empty'])
         if len(position_ids) != len(positions):

src/pretix/base/services/pricing.py

@@ -11,7 +11,8 @@ from pretix.base.models.tax import TAXED_ZERO, TaxedPrice, TaxRule
 def get_price(item: Item, variation: ItemVariation = None,
               voucher: Voucher = None, custom_price: Decimal = None,
               subevent: SubEvent = None, custom_price_is_net: bool = False,
-              addon_to: AbstractPosition = None, invoice_address: InvoiceAddress = None) -> TaxedPrice:
+              addon_to: AbstractPosition = None, invoice_address: InvoiceAddress = None,
+              force_custom_price: bool = False, bundled_sum: Decimal = Decimal('0.00')) -> TaxedPrice:
     if addon_to:
         try:
             iao = addon_to.item.addons.get(addon_category_id=item.category_id)
@@ -44,6 +45,11 @@ def get_price(item: Item, variation: ItemVariation = None,
         )
     price = tax_rule.tax(price)
 
+    if force_custom_price and custom_price is not None and custom_price != "":
+        if custom_price_is_net:
+            price = tax_rule.tax(custom_price, base_price_is='net')
+        else:
+            price = tax_rule.tax(custom_price, base_price_is='gross')
     if item.free_price and custom_price is not None and custom_price != "":
         if not isinstance(custom_price, Decimal):
             custom_price = Decimal(str(custom_price).replace(",", "."))
@@ -54,6 +60,11 @@ def get_price(item: Item, variation: ItemVariation = None,
         else:
             price = tax_rule.tax(max(custom_price, price.gross), base_price_is='gross')
 
+    if bundled_sum:
+        price = price - TaxedPrice(net=bundled_sum, gross=bundled_sum, rate=0, tax=0, name='')
+        if price.gross < Decimal('0.00'):
+            return TAXED_ZERO
+
     if invoice_address and not tax_rule.tax_applicable(invoice_address):
         price.tax = Decimal('0.00')
         price.rate = Decimal('0.00')