Connect giftcards with customer accounts (#5126)

Connect giftcards with customer accounts, show giftcards during checkout and in account , show giftcard list in backend customer view

src/pretix/base/models/customers.py

@@ -19,6 +19,8 @@
 # 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 decimal import Decimal
+
 import pycountry
 from django.conf import settings
 from django.contrib.auth.hashers import (
@@ -27,7 +29,11 @@ from django.contrib.auth.hashers import (
 from django.core.validators import RegexValidator, URLValidator
 from django.db import models
 from django.db.models import F, Q
+from django.db.models.aggregates import Sum
+from django.db.models.expressions import OuterRef, Subquery
+from django.db.models.functions.comparison import Coalesce
 from django.utils.crypto import get_random_string, salted_hmac
+from django.utils.timezone import now
 from django.utils.translation import gettext_lazy as _, pgettext_lazy
 from django_scopes import ScopedManager, scopes_disabled
 from i18nfield.fields import I18nCharField
@@ -36,6 +42,7 @@ from phonenumber_field.modelfields import PhoneNumberField
 from pretix.base.banlist import banned
 from pretix.base.models.base import LoggedModel
 from pretix.base.models.fields import MultiStringField
+from pretix.base.models.giftcards import GiftCardTransaction
 from pretix.base.models.organizer import Organizer
 from pretix.base.settings import PERSON_NAME_SCHEMES
 from pretix.helpers.countries import FastCountryField
@@ -288,6 +295,19 @@ class Customer(LoggedModel):
             organizer=self.organizer,
         )
 
+    def usable_gift_cards(self, used_cards=[]):
+        s = GiftCardTransaction.objects.filter(
+            card=OuterRef('pk')
+        ).order_by().values('card').annotate(s=Sum('value')).values('s')
+        qs = self.customer_gift_cards.annotate(
+            cached_value=Coalesce(Subquery(s), Decimal('0.00')),
+        )
+        ne_qs = qs.filter(
+            Q(expires__isnull=True) | Q(expires__gte=now()),
+        )
+        ex_qs = ne_qs.exclude(id__in=used_cards)
+        return ex_qs.filter(cached_value__gt=0)
+
 
 class AttendeeProfile(models.Model):
     customer = models.ForeignKey(