Add support for reserved seating (#1228)

* Initial work on seating

* Add seat guids

* Add product_list_top

* CartAdd: Ignore item when a seat is passed

* Cart display

* product_list_top → render_seating_plan

* Render seating plan in voucher redemption

* Fix failing tests

* Add tests for extending cart positions with seats

* Add subevent_forms to docs

* Update schema, migrations

* Dealing with expired orders

* steps to order change

* Change order positions

* Allow to add seats

* tests for ocm

* Fix things after rebase

* Seating plans API

* Add more tests for cart behaviour

* Widget support

* Adjust widget tests

* Re-enable CSP

* Update schema

* Api: position.seat

* Add guid to word list

* API: (sub)event.seating_plan

* Vali fixes

* Fix api

* Fix reference in test

* Fix test for real

src/pretix/base/models/seating.py

@@ -0,0 +1,111 @@
+import json
+from collections import namedtuple
+
+import jsonschema
+from django.contrib.staticfiles import finders
+from django.core.exceptions import ValidationError
+from django.db import models
+from django.utils.deconstruct import deconstructible
+from django.utils.timezone import now
+from django.utils.translation import ugettext_lazy as _
+
+from pretix.base.models import Event, Item, LoggedModel, Organizer, SubEvent
+
+
+@deconstructible
+class SeatingPlanLayoutValidator:
+    def __call__(self, value):
+        if not isinstance(value, dict):
+            try:
+                val = json.loads(value)
+            except ValueError:
+                raise ValidationError(_('Your layout file is not a valid JSON file.'))
+        else:
+            val = value
+        with open(finders.find('seating/seating-plan.schema.json'), 'r') as f:
+            schema = json.loads(f.read())
+        try:
+            jsonschema.validate(val, schema)
+        except jsonschema.ValidationError as e:
+            raise ValidationError(_('Your layout file is not a valid seating plan. Error message: {}').format(str(e)))
+
+
+class SeatingPlan(LoggedModel):
+    """
+    Represents an abstract seating plan, without relation to any event.
+    """
+    name = models.CharField(max_length=190, verbose_name=_('Name'))
+    organizer = models.ForeignKey(Organizer, related_name='seating_plans', on_delete=models.CASCADE)
+    layout = models.TextField(validators=[SeatingPlanLayoutValidator()])
+
+    Category = namedtuple('Categrory', 'name')
+    RawSeat = namedtuple('Seat', 'name guid number row category')
+
+    def __str__(self):
+        return self.name
+
+    @property
+    def layout_data(self):
+        return json.loads(self.layout)
+
+    @layout_data.setter
+    def layout_data(self, v):
+        self.layout = json.dumps(v)
+
+    def get_categories(self):
+        return [
+            self.Category(name=c['name'])
+            for c in self.layout_data['categories']
+        ]
+
+    def iter_all_seats(self):
+        for z in self.layout_data['zones']:
+            for r in z['rows']:
+                for s in r['seats']:
+                    yield self.RawSeat(
+                        number=s['seat_number'],
+                        guid=s['seat_guid'],
+                        name='{} {}'.format(r['row_number'], s['seat_number']),  # TODO: Zone? Variable scheme?
+                        row=r['row_number'],
+                        category=s['category']
+                    )
+
+
+class SeatCategoryMapping(models.Model):
+    """
+    Input seating plans have abstract "categories", such as "Balcony seat", etc. This model maps them to actual
+    pretix product on a per-(sub)event level.
+    """
+    event = models.ForeignKey(Event, related_name='seat_category_mappings', on_delete=models.CASCADE)
+    subevent = models.ForeignKey(SubEvent, null=True, blank=True, related_name='seat_category_mappings', on_delete=models.CASCADE)
+    layout_category = models.CharField(max_length=190)
+    product = models.ForeignKey(Item, related_name='seat_category_mappings', on_delete=models.CASCADE)
+
+
+class Seat(models.Model):
+    """
+    This model is used to represent every single specific seat within an (sub)event that can be selected. It's mainly
+    used for internal bookkeeping and not to be modified by users directly.
+    """
+    event = models.ForeignKey(Event, related_name='seats', on_delete=models.CASCADE)
+    subevent = models.ForeignKey(SubEvent, null=True, blank=True, related_name='seats', on_delete=models.CASCADE)
+    name = models.CharField(max_length=190)
+    seat_guid = models.CharField(max_length=190, db_index=True)
+    product = models.ForeignKey('Item', null=True, blank=True, related_name='seats', on_delete=models.CASCADE)
+    blocked = models.BooleanField(default=False)
+
+    def __str__(self):
+        return self.name
+
+    def is_available(self, ignore_cart=None, ignore_orderpos=None):
+        from .orders import Order
+
+        if self.blocked:
+            return False
+        opqs = self.orderposition_set.filter(order__status__in=[Order.STATUS_PENDING, Order.STATUS_PAID])
+        cpqs = self.cartposition_set.filter(expires__gte=now())
+        if ignore_cart:
+            cpqs = cpqs.exclude(pk=ignore_cart.pk)
+        if ignore_orderpos:
+            opqs = opqs.exclude(pk=ignore_orderpos.pk)
+        return not opqs.exists() and not cpqs.exists()