#
# 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/>.
#

# This file is based on an earlier version of pretix which was released under the Apache License 2.0. The full text of
# the Apache License 2.0 can be obtained at <http://www.apache.org/licenses/LICENSE-2.0>.
#
# This file may have since been changed and any changes are released under the terms of AGPLv3 as described above. A
# full history of changes and contributors is available at <https://github.com/pretix/pretix>.
#
# This file contains Apache-licensed contributions copyrighted by: Daniel, Flavia Bastos, Heok Hong Low, Jakob Schnell,
# Sanket Dasgupta, Tobias Kunze
#
# Unless required by applicable law or agreed to in writing, software distributed under the Apache License 2.0 is
# distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
# License for the specific language governing permissions and limitations under the License.

import json
import logging
import sys
from collections import Counter, defaultdict, namedtuple
from datetime import datetime, time, timedelta
from decimal import Decimal
from typing import List, Optional

from celery.exceptions import MaxRetriesExceededError
from django.conf import settings
from django.core.cache import cache
from django.core.exceptions import ValidationError
from django.db import transaction
from django.db.models import (
    Count, Exists, F, IntegerField, Max, Min, OuterRef, Q, Sum, Value,
)
from django.db.models.functions import Coalesce, Greatest
from django.db.transaction import get_connection
from django.dispatch import receiver
from django.utils.functional import cached_property
from django.utils.timezone import make_aware, now
from django.utils.translation import gettext as _
from django_scopes import scopes_disabled

from pretix.api.models import OAuthApplication
from pretix.base.channels import get_all_sales_channels
from pretix.base.email import get_email_context
from pretix.base.i18n import (
    LazyLocaleException, get_language_without_region, language,
)
from pretix.base.models import (
    CartPosition, Device, Event, GiftCard, Item, ItemVariation, Membership,
    Order, OrderPayment, OrderPosition, Quota, Seat, SeatCategoryMapping, User,
    Voucher,
)
from pretix.base.models.event import SubEvent
from pretix.base.models.orders import (
    InvoiceAddress, OrderFee, OrderRefund, generate_secret,
)
from pretix.base.models.organizer import TeamAPIToken
from pretix.base.models.tax import TAXED_ZERO, TaxedPrice, TaxRule
from pretix.base.payment import GiftCardPayment, PaymentException
from pretix.base.reldate import RelativeDateWrapper
from pretix.base.secrets import assign_ticket_secret
from pretix.base.services import tickets
from pretix.base.services.invoices import (
    generate_cancellation, generate_invoice, invoice_qualified,
)
from pretix.base.services.locking import LockTimeoutException, NoLockManager
from pretix.base.services.mail import SendMailException
from pretix.base.services.memberships import (
    create_membership, validate_memberships_in_order,
)
from pretix.base.services.pricing import (
    apply_discounts, get_listed_price, get_price,
)
from pretix.base.services.quotas import QuotaAvailability
from pretix.base.services.tasks import ProfiledEventTask, ProfiledTask
from pretix.base.signals import (
    allow_ticket_download, order_approved, order_canceled, order_changed,
    order_denied, order_expired, order_fee_calculation, order_paid,
    order_placed, order_split, periodic_task, validate_order,
)
from pretix.celery_app import app
from pretix.helpers.models import modelcopy
from pretix.helpers.periodic import minimum_interval

error_messages = {
    'unavailable': _('Some of the products you selected were no longer available. '
                     'Please see below for details.'),
    'in_part': _('Some of the products you selected were no longer available in '
                 'the quantity you selected. Please see below for details.'),
    'price_changed': _('The price of some of the items in your cart has changed in the '
                       'meantime. Please see below for details.'),
    'internal': _("An internal error occurred, please try again."),
    'empty': _("Your cart is empty."),
    'max_items_per_product': _("You cannot select more than %(max)s items of the product %(product)s. We removed the "
                               "surplus items from your cart."),
    'busy': _('We were not able to process your request completely as the '
              'server was too busy. Please try again.'),
    'not_started': _('The booking period for this event has not yet started.'),
    'ended': _('The booking period has ended.'),
    'voucher_min_usages': _('The voucher code "%(voucher)s" can only be used if you select at least %(number)s '
                            'matching products.'),
    'voucher_invalid': _('The voucher code used for one of the items in your cart is not known in our database.'),
    'voucher_redeemed': _('The voucher code used for one of the items in your cart has already been used the maximum '
                          'number of times allowed. We removed this item from your cart.'),
    'voucher_budget_used': _('The voucher code used for one of the items in your cart has already been too often. We '
                             'adjusted the price of the item in your cart.'),
    'voucher_expired': _('The voucher code used for one of the items in your cart is expired. We removed this item '
                         'from your cart.'),
    'voucher_invalid_item': _('The voucher code used for one of the items in your cart is not valid for this item. We '
                              'removed this item from your cart.'),
    'voucher_required': _('You need a valid voucher code to order one of the products.'),
    'some_subevent_not_started': _('The booking period for one of the events in your cart has not yet started. The '
                                   'affected positions have been removed from your cart.'),
    'some_subevent_ended': _('The booking period for one of the events in your cart has ended. The affected '
                             'positions have been removed from your cart.'),
    'seat_invalid': _('One of the seats in your order was invalid, we removed the position from your cart.'),
    'seat_unavailable': _('One of the seats in your order has been taken in the meantime, we removed the position from your cart.'),
    'country_blocked': _('One of the selected products is not available in the selected country.'),
    'not_for_sale': _('You selected a product which is not available for sale.'),
    'addon_invalid_base': _('You can not select an add-on for the selected product.'),
    'addon_duplicate_item': _('You can not select two variations of the same add-on product.'),
    'addon_max_count': _('You can select at most %(max)s add-ons from the category %(cat)s for the product %(base)s.'),
    'addon_min_count': _('You need to select at least %(min)s add-ons from the category %(cat)s for the '
                         'product %(base)s.'),
    'addon_no_multi': _('You can select every add-ons from the category %(cat)s for the product %(base)s at most once.'),
}

logger = logging.getLogger(__name__)


def mark_order_paid(*args, **kwargs):
    raise NotImplementedError("This method is no longer supported since pretix 1.17.")


def reactivate_order(order: Order, force: bool=False, user: User=None, auth=None):
    """
    Reactivates a canceled order. If ``force`` is not set to ``True``, this will fail if there is not
    enough quota.
    """
    if order.status != Order.STATUS_CANCELED:
        raise OrderError('The order was not canceled.')

    with order.event.lock() as now_dt:
        is_available = order._is_still_available(now_dt, count_waitinglist=False, check_voucher_usage=True,
                                                 check_memberships=True, force=force)
        if is_available is True:
            if order.payment_refund_sum >= order.total:
                order.status = Order.STATUS_PAID
            else:
                order.status = Order.STATUS_PENDING
            order.cancellation_date = None
            order.set_expires(now(),
                              order.event.subevents.filter(id__in=[p.subevent_id for p in order.positions.all()]))
            with transaction.atomic():
                order.save(update_fields=['expires', 'status', 'cancellation_date'])
                order.log_action(
                    'pretix.event.order.reactivated',
                    user=user,
                    auth=auth,
                    data={
                        'expires': order.expires,
                    }
                )
                for position in order.positions.all():
                    if position.voucher:
                        Voucher.objects.filter(pk=position.voucher.pk).update(redeemed=Greatest(0, F('redeemed') + 1))

                    for gc in position.issued_gift_cards.all():
                        gc = GiftCard.objects.select_for_update().get(pk=gc.pk)
                        gc.transactions.create(value=position.price, order=order)
                        break

                    for m in position.granted_memberships.all():
                        m.canceled = False
                        m.save()
                order.create_transactions()
        else:
            raise OrderError(is_available)

    order_approved.send(order.event, order=order)
    if order.status == Order.STATUS_PAID:
        order_paid.send(order.event, order=order)

    num_invoices = order.invoices.filter(is_cancellation=False).count()
    if num_invoices > 0 and order.invoices.filter(is_cancellation=True).count() >= num_invoices and invoice_qualified(order):
        generate_invoice(order)


def extend_order(order: Order, new_date: datetime, force: bool=False, user: User=None, auth=None):
    """
    Extends the deadline of an order. If the order is already expired, the quota will be checked to
    see if this is actually still possible. If ``force`` is set to ``True``, the result of this check
    will be ignored.
    """
    if new_date < now():
        raise OrderError(_('The new expiry date needs to be in the future.'))

    @transaction.atomic
    def change(was_expired=True):
        order.expires = new_date
        if was_expired:
            order.status = Order.STATUS_PENDING
        order.save(update_fields=['expires'] + (['status'] if was_expired else []))
        order.log_action(
            'pretix.event.order.expirychanged',
            user=user,
            auth=auth,
            data={
                'expires': order.expires,
                'state_change': was_expired
            }
        )

        if was_expired:
            num_invoices = order.invoices.filter(is_cancellation=False).count()
            if num_invoices > 0 and order.invoices.filter(is_cancellation=True).count() >= num_invoices and invoice_qualified(order):
                generate_invoice(order)
            order.create_transactions()

    if order.status == Order.STATUS_PENDING:
        change(was_expired=False)
    else:
        with order.event.lock() as now_dt:
            is_available = order._is_still_available(now_dt, count_waitinglist=False, force=force)
            if is_available is True:
                change(was_expired=True)
            else:
                raise OrderError(is_available)


@transaction.atomic
def mark_order_refunded(order, user=None, auth=None, api_token=None):
    oautha = auth.pk if isinstance(auth, OAuthApplication) else None
    device = auth.pk if isinstance(auth, Device) else None
    api_token = (api_token.pk if api_token else None) or (auth if isinstance(auth, TeamAPIToken) else None)
    return _cancel_order(
        order.pk, user.pk if user else None, send_mail=False, api_token=api_token, device=device, oauth_application=oautha
    )


def mark_order_expired(order, user=None, auth=None):
    """
    Mark this order as expired. This sets the payment status and returns the order object.
    :param order: The order to change
    :param user: The user that performed the change
    """
    with transaction.atomic():
        if isinstance(order, int):
            order = Order.objects.get(pk=order)
        if isinstance(user, int):
            user = User.objects.get(pk=user)
        with order.event.lock():
            order.status = Order.STATUS_EXPIRED
            order.save(update_fields=['status'])

        order.log_action('pretix.event.order.expired', user=user, auth=auth)
        i = order.invoices.filter(is_cancellation=False).last()
        if i and not i.refered.exists():
            generate_cancellation(i)
        order.create_transactions()

    order_expired.send(order.event, order=order)
    return order


def approve_order(order, user=None, send_mail: bool=True, auth=None, force=False):
    """
    Mark this order as approved
    :param order: The order to change
    :param user: The user that performed the change
    """
    with transaction.atomic():
        if not order.require_approval or not order.status == Order.STATUS_PENDING:
            raise OrderError(_('This order is not pending approval.'))

        order.require_approval = False
        order.set_expires(now(), order.event.subevents.filter(id__in=[p.subevent_id for p in order.positions.all()]))
        order.save(update_fields=['require_approval', 'expires'])
        order.create_transactions()

        order.log_action('pretix.event.order.approved', user=user, auth=auth)
        if order.total == Decimal('0.00'):
            p = order.payments.create(
                state=OrderPayment.PAYMENT_STATE_CREATED,
                provider='free',
                amount=0,
                fee=None
            )
            try:
                p.confirm(send_mail=False, count_waitinglist=False, user=user, auth=auth, ignore_date=True, force=force)
            except Quota.QuotaExceededException:
                raise OrderError(error_messages['unavailable'])

    order_approved.send(order.event, order=order)

    invoice = order.invoices.last()  # Might be generated by plugin already
    if order.event.settings.get('invoice_generate') == 'True' and invoice_qualified(order):
        if not invoice:
            invoice = generate_invoice(
                order,
                trigger_pdf=not order.event.settings.invoice_email_attachment or not order.email
            )
            # send_mail will trigger PDF generation later

    if send_mail:
        with language(order.locale, order.event.settings.region):
            if order.total == Decimal('0.00'):
                email_template = order.event.settings.mail_text_order_approved_free
                email_subject = order.event.settings.mail_subject_order_approved_free
            else:
                email_template = order.event.settings.mail_text_order_approved
                email_subject = order.event.settings.mail_subject_order_approved

            email_context = get_email_context(event=order.event, order=order)
            try:
                order.send_mail(
                    email_subject, email_template, email_context,
                    'pretix.event.order.email.order_approved', user,
                    attach_tickets=True,
                    invoices=[invoice] if invoice and order.event.settings.invoice_email_attachment else []
                )
            except SendMailException:
                logger.exception('Order approved email could not be sent')

    return order.pk


def deny_order(order, comment='', user=None, send_mail: bool=True, auth=None):
    """
    Mark this order as canceled
    :param order: The order to change
    :param user: The user that performed the change
    """
    with transaction.atomic():
        if not order.require_approval or not order.status == Order.STATUS_PENDING:
            raise OrderError(_('This order is not pending approval.'))

        with order.event.lock():
            order.status = Order.STATUS_CANCELED
            order.save(update_fields=['status'])

        order.log_action('pretix.event.order.denied', user=user, auth=auth, data={
            'comment': comment
        })
        i = order.invoices.filter(is_cancellation=False).last()
        if i:
            generate_cancellation(i)

        for position in order.positions.all():
            if position.voucher:
                Voucher.objects.filter(pk=position.voucher.pk).update(redeemed=Greatest(0, F('redeemed') - 1))
        order.create_transactions()

    order_denied.send(order.event, order=order)

    if send_mail:
        email_template = order.event.settings.mail_text_order_denied
        email_subject = order.event.settings.mail_subject_order_denied
        email_context = get_email_context(event=order.event, order=order, comment=comment)
        with language(order.locale, order.event.settings.region):
            try:
                order.send_mail(
                    email_subject, email_template, email_context,
                    'pretix.event.order.email.order_denied', user
                )
            except SendMailException:
                logger.exception('Order denied email could not be sent')

    return order.pk


def _cancel_order(order, user=None, send_mail: bool=True, api_token=None, device=None, oauth_application=None,
                  cancellation_fee=None, keep_fees=None, cancel_invoice=True, comment=None):
    """
    Mark this order as canceled
    :param order: The order to change
    :param user: The user that performed the change
    """
    # If new actions are added to this function, make sure to add the reverse operation to reactivate_order()
    with transaction.atomic():
        if isinstance(order, int):
            order = Order.objects.select_for_update().get(pk=order)
        if isinstance(user, int):
            user = User.objects.get(pk=user)
        if isinstance(api_token, int):
            api_token = TeamAPIToken.objects.get(pk=api_token)
        if isinstance(device, int):
            device = Device.objects.get(pk=device)
        if isinstance(oauth_application, int):
            oauth_application = OAuthApplication.objects.get(pk=oauth_application)
        if isinstance(cancellation_fee, str):
            cancellation_fee = Decimal(cancellation_fee)

        if not order.cancel_allowed():
            raise OrderError(_('You cannot cancel this order.'))
        invoices = []
        if cancel_invoice:
            i = order.invoices.filter(is_cancellation=False).last()
            if i and not i.refered.exists():
                invoices.append(generate_cancellation(i))

        for position in order.positions.all():
            for gc in position.issued_gift_cards.all():
                gc = GiftCard.objects.select_for_update().get(pk=gc.pk)
                if gc.value < position.price:
                    raise OrderError(
                        _('This order can not be canceled since the gift card {card} purchased in '
                          'this order has already been redeemed.').format(
                            card=gc.secret
                        )
                    )
                else:
                    gc.transactions.create(value=-position.price, order=order)

            for m in position.granted_memberships.all():
                m.canceled = True
                m.save()

        if cancellation_fee:
            with order.event.lock():
                for position in order.positions.all():
                    if position.voucher:
                        Voucher.objects.filter(pk=position.voucher.pk).update(redeemed=Greatest(0, F('redeemed') - 1))
                    position.canceled = True
                    assign_ticket_secret(
                        event=order.event, position=position, force_invalidate_if_revokation_list_used=True, force_invalidate=False, save=False
                    )
                    position.save(update_fields=['canceled', 'secret'])
                new_fee = cancellation_fee
                for fee in order.fees.all():
                    if keep_fees and fee in keep_fees:
                        new_fee -= fee.value
                    else:
                        fee.canceled = True
                        fee.save(update_fields=['canceled'])

                if new_fee:
                    f = OrderFee(
                        fee_type=OrderFee.FEE_TYPE_CANCELLATION,
                        value=new_fee,
                        tax_rule=order.event.settings.tax_rate_default,
                        order=order,
                    )
                    f._calculate_tax()
                    f.save()

                if cancellation_fee > order.total:
                    raise OrderError(_('The cancellation fee cannot be higher than the total amount of this order.'))
                elif order.payment_refund_sum < cancellation_fee:
                    order.status = Order.STATUS_PENDING
                    order.set_expires()
                else:
                    order.status = Order.STATUS_PAID
                order.total = cancellation_fee
                order.cancellation_date = now()
                order.save(update_fields=['status', 'cancellation_date', 'total'])

            if cancel_invoice and i:
                invoices.append(generate_invoice(order))
        else:
            with order.event.lock():
                order.status = Order.STATUS_CANCELED
                order.cancellation_date = now()
                order.save(update_fields=['status', 'cancellation_date'])

            for position in order.positions.all():
                assign_ticket_secret(
                    event=order.event, position=position, force_invalidate_if_revokation_list_used=True, force_invalidate=False, save=True
                )
                if position.voucher:
                    Voucher.objects.filter(pk=position.voucher.pk).update(redeemed=Greatest(0, F('redeemed') - 1))

        order.log_action('pretix.event.order.canceled', user=user, auth=api_token or oauth_application or device,
                         data={'cancellation_fee': cancellation_fee, 'comment': comment})
        order.cancellation_requests.all().delete()

        order.create_transactions()

        if send_mail:
            with language(order.locale, order.event.settings.region):
                email_template = order.event.settings.mail_text_order_canceled
                email_subject = order.event.settings.mail_subject_order_canceled
                email_context = get_email_context(event=order.event, order=order, comment=comment or "")
                try:
                    order.send_mail(
                        email_subject, email_template, email_context,
                        'pretix.event.order.email.order_canceled', user,
                        invoices=invoices if order.event.settings.invoice_email_attachment else []
                    )
                except SendMailException:
                    logger.exception('Order canceled email could not be sent')

    for p in order.payments.filter(state__in=(OrderPayment.PAYMENT_STATE_CREATED, OrderPayment.PAYMENT_STATE_PENDING)):
        try:
            with transaction.atomic():
                p.payment_provider.cancel_payment(p)
                order.log_action(
                    'pretix.event.order.payment.canceled',
                    {
                        'local_id': p.local_id,
                        'provider': p.provider,
                    },
                    user=user,
                    auth=api_token or oauth_application or device
                )
        except PaymentException as e:
            order.log_action(
                'pretix.event.order.payment.canceled.failed',
                {
                    'local_id': p.local_id,
                    'provider': p.provider,
                    'error': str(e)
                },
                user=user,
                auth=api_token or oauth_application or device
            )

    order_canceled.send(order.event, order=order)
    return order.pk


class OrderError(LazyLocaleException):
    def __init__(self, *args):
        msg = args[0]
        msgargs = args[1] if len(args) > 1 else None
        self.args = args
        if msgargs:
            msg = _(msg) % msgargs
        else:
            msg = _(msg)
        super().__init__(msg)


def _check_date(event: Event, now_dt: datetime):
    if event.presale_start and now_dt < event.presale_start:
        raise OrderError(error_messages['not_started'])
    if event.presale_has_ended:
        raise OrderError(error_messages['ended'])

    if not event.has_subevents:
        tlv = event.settings.get('payment_term_last', as_type=RelativeDateWrapper)
        if tlv:
            term_last = make_aware(datetime.combine(
                tlv.datetime(event).date(),
                time(hour=23, minute=59, second=59)
            ), event.timezone)
            if term_last < now_dt:
                raise OrderError(error_messages['ended'])


def _check_positions(event: Event, now_dt: datetime, positions: List[CartPosition], address: InvoiceAddress=None,
                     sales_channel='web', customer=None):
    err = None
    errargs = None
    _check_date(event, now_dt)

    products_seen = Counter()
    q_avail = Counter()
    v_avail = Counter()
    v_usages = Counter()
    v_budget = {}
    deleted_positions = set()
    seats_seen = 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()

    sorted_positions = sorted(positions, key=lambda s: -int(s.is_bundled))

    # Check availability
    for i, cp in enumerate(sorted_positions):
        if cp.pk in deleted_positions:
            continue

        if not cp.item.is_available() or (cp.variation and not cp.variation.is_available()):
            err = err or error_messages['unavailable']
            delete(cp)
            continue
        quotas = list(cp.quotas)

        products_seen[cp.item] += 1
        if cp.item.max_per_order and products_seen[cp.item] > cp.item.max_per_order:
            err = error_messages['max_items_per_product']
            errargs = {'max': cp.item.max_per_order,
                       'product': cp.item.name}
            delete(cp)
            break

        if cp.voucher:
            v_usages[cp.voucher] += 1
            if cp.voucher not in v_avail:
                redeemed_in_carts = CartPosition.objects.filter(
                    Q(voucher=cp.voucher) & Q(event=event) & Q(expires__gte=now_dt)
                ).exclude(cart_id=cp.cart_id)
                v_avail[cp.voucher] = cp.voucher.max_usages - cp.voucher.redeemed - redeemed_in_carts.count()
            v_avail[cp.voucher] -= 1
            if v_avail[cp.voucher] < 0:
                err = err or error_messages['voucher_redeemed']
                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']
            delete(cp)
            break

        if cp.subevent:
            tlv = event.settings.get('payment_term_last', as_type=RelativeDateWrapper)
            if tlv:
                term_last = make_aware(datetime.combine(
                    tlv.datetime(cp.subevent).date(),
                    time(hour=23, minute=59, second=59)
                ), event.timezone)
                if term_last < now_dt:
                    err = err or error_messages['some_subevent_ended']
                    delete(cp)
                    break

        if cp.subevent and cp.subevent.presale_has_ended:
            err = err or error_messages['some_subevent_ended']
            delete(cp)
            break

        if (cp.requires_seat and not cp.seat) or (cp.seat and not cp.requires_seat) or (cp.seat and cp.seat.product != cp.item) or cp.seat in seats_seen:
            err = err or error_messages['seat_invalid']
            delete(cp)
            break
        if cp.seat:
            seats_seen.add(cp.seat)

        if cp.item.require_voucher and cp.voucher is None and not cp.is_bundled:
            delete(cp)
            err = err or error_messages['voucher_required']
            break

        if (cp.item.hide_without_voucher or (cp.variation and cp.variation.hide_without_voucher)) and (
                cp.voucher is None or not cp.voucher.show_hidden_items or not cp.voucher.applies_to(cp.item, cp.variation)
        ) and not cp.is_bundled:
            delete(cp)
            err = error_messages['voucher_required']
            break

        if cp.seat:
            # Unlike quotas (which we blindly trust as long as the position is not expired), we check seats every
            # time, since we absolutely can not overbook a seat.
            if not cp.seat.is_available(ignore_cart=cp, ignore_voucher_id=cp.voucher_id, sales_channel=sales_channel):
                err = err or error_messages['seat_unavailable']
                delete(cp)
                continue

        if cp.expires >= now_dt and not cp.voucher:
            # Other checks are not necessary
            continue

        if len(quotas) == 0:
            err = err or error_messages['unavailable']
            delete(cp)
            continue

        if cp.subevent and cp.item.pk in cp.subevent.item_overrides and not cp.subevent.item_overrides[cp.item.pk].is_available(now_dt):
            err = err or error_messages['unavailable']
            delete(cp)
            continue

        if cp.subevent and cp.variation and cp.variation.pk in cp.subevent.var_overrides and \
                not cp.subevent.var_overrides[cp.variation.pk].is_available(now_dt):
            err = err or error_messages['unavailable']
            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']
                delete(cp)
                continue

        quota_ok = True

        ignore_all_quotas = cp.expires >= now_dt or (
            cp.voucher and (
                cp.voucher.allow_ignore_quota or (cp.voucher.block_quota and cp.voucher.quota is None)
            )
        )

        if not ignore_all_quotas:
            for quota in quotas:
                if cp.voucher and cp.voucher.block_quota and cp.voucher.quota_id == quota.pk:
                    continue
                if quota not in q_avail:
                    avail = quota.availability(now_dt)
                    q_avail[quota] = avail[1] if avail[1] is not None else sys.maxsize
                q_avail[quota] -= 1
                if q_avail[quota] < 0:
                    err = err or error_messages['unavailable']
                    quota_ok = False
                    break

        if not quota_ok:
            # Sorry, can't let you keep that!
            delete(cp)

    for voucher, cnt in v_usages.items():
        if 0 < cnt < voucher.min_usages_remaining:
            raise OrderError(error_messages['voucher_min_usages'], {
                'voucher': voucher.code,
                'number': voucher.min_usages_remaining,
            })

    # Check prices
    sorted_positions = [cp for cp in sorted_positions if cp.pk and cp.pk not in deleted_positions]
    old_total = sum(cp.price for cp in sorted_positions)
    for i, cp in enumerate(sorted_positions):
        if cp.listed_price is None:
            # migration from pre-discount cart positions
            cp.update_listed_price_and_voucher(max_discount=None)
            cp.migrate_free_price_if_necessary()

        # deal with max discount
        max_discount = None
        if cp.voucher and cp.voucher.budget is not None:
            if cp.voucher not in v_budget:
                v_budget[cp.voucher] = cp.voucher.budget - cp.voucher.budget_used()
            max_discount = max(v_budget[cp.voucher], 0)

        if cp.expires < now_dt or cp.listed_price is None:
            # Guarantee on listed price is expired
            cp.update_listed_price_and_voucher(max_discount=max_discount)
        elif cp.voucher:
            cp.update_listed_price_and_voucher(max_discount=max_discount, voucher_only=True)

        if max_discount is not None:
            v_budget[cp.voucher] = v_budget[cp.voucher] - (cp.listed_price - cp.price_after_voucher)

        try:
            cp.update_line_price(address, [b for b in sorted_positions if b.addon_to_id == cp.pk and b.is_bundled and b.pk and b.pk not in deleted_positions])
        except TaxRule.SaleNotAllowed:
            err = err or error_messages['country_blocked']
            delete(cp)
            continue

    sorted_positions = [cp for cp in sorted_positions if cp.pk and cp.pk not in deleted_positions]
    discount_results = apply_discounts(
        event,
        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 sorted_positions
        ]
    )
    for cp, (new_price, discount) in zip(sorted_positions, discount_results):
        if cp.price != new_price or cp.discount_id != (discount.pk if discount else None):
            cp.price = new_price
            cp.discount = discount
            cp.save(update_fields=['price', 'discount'])

    new_total = sum(cp.price for cp in sorted_positions)
    if old_total != new_total:
        err = err or error_messages['price_changed']

    # Store updated positions
    for cp in sorted_positions:
        cp.expires = now_dt + timedelta(
            minutes=event.settings.get('reservation_time', as_type=int))
        cp.save()

    if err:
        raise OrderError(err, errargs)


def _get_fees(positions: List[CartPosition], payment_requests: List[dict], address: InvoiceAddress,
              meta_info: dict, event: Event, require_approval=False):
    fees = []
    total = sum([c.price for c in positions])

    gift_cards = []  # for backwards compatibility
    for p in payment_requests:
        if p['provider'] == 'giftcard':
            gift_cards.append(GiftCard.objects.get(pk=p['info_data']['gift_card']))

    for recv, resp in order_fee_calculation.send(sender=event, invoice_address=address, total=total, payment_requests=payment_requests,
                                                 meta_info=meta_info, positions=positions, gift_cards=gift_cards):
        if resp:
            fees += resp
    total += sum(f.value for f in fees)

    total_remaining = total
    for p in payment_requests:
        # This algorithm of treating min/max values and fees needs to stay in sync between the following
        # places in the code base:
        # - pretix.base.services.cart.get_fees
        # - pretix.base.services.orders._get_fees
        # - pretix.presale.views.CartMixin.current_selected_payments
        if p.get('min_value') and total_remaining < Decimal(p['min_value']):
            p['payment_amount'] = Decimal('0.00')
            continue

        to_pay = total_remaining
        if p.get('max_value') and to_pay > Decimal(p['max_value']):
            to_pay = min(to_pay, Decimal(p['max_value']))

        payment_fee = p['pprov'].calculate_fee(to_pay)
        total_remaining += payment_fee
        to_pay += payment_fee

        if p.get('max_value') and to_pay > Decimal(p['max_value']):
            to_pay = min(to_pay, Decimal(p['max_value']))

        total_remaining -= to_pay

        p['payment_amount'] = to_pay
        if payment_fee:
            pf = OrderFee(fee_type=OrderFee.FEE_TYPE_PAYMENT, value=payment_fee,
                          internal_type=p['pprov'].identifier)
            fees.append(pf)
            p['fee'] = pf

    if total_remaining != Decimal('0.00') and not require_approval:
        raise OrderError(_("The selected payment methods do not cover the total balance."))

    return fees


def _create_order(event: Event, email: str, positions: List[CartPosition], now_dt: datetime,
                  payment_requests: List[dict], locale: str=None, address: InvoiceAddress=None,
                  meta_info: dict=None, sales_channel: str='web', shown_total=None,
                  customer=None):
    payments = []
    sales_channel = get_all_sales_channels()[sales_channel]

    with transaction.atomic():

        try:
            validate_memberships_in_order(customer, positions, event, lock=True, testmode=event.testmode)
        except ValidationError as e:
            raise OrderError(e.message)

        require_approval = any(p.requires_approval(invoice_address=address) for p in positions)
        fees = _get_fees(positions, payment_requests, address, meta_info, event, require_approval=require_approval)
        total = pending_sum = sum([c.price for c in positions]) + sum([c.value for c in fees])

        order = Order(
            status=Order.STATUS_PENDING,
            event=event,
            email=email,
            phone=(meta_info or {}).get('contact_form_data', {}).get('phone'),
            datetime=now_dt,
            locale=get_language_without_region(locale),
            total=total,
            testmode=True if sales_channel.testmode_supported and event.testmode else False,
            meta_info=json.dumps(meta_info or {}),
            require_approval=require_approval,
            sales_channel=sales_channel.identifier,
            customer=customer,
        )
        if customer:
            order.email_known_to_work = customer.is_verified
        order.set_expires(now_dt, event.subevents.filter(id__in=[p.subevent_id for p in positions]))
        order.save()

        if address:
            if address.order is not None:
                address.pk = None
            address.order = order
            address.save()

            order.save()

        for fee in fees:
            fee.order = order
            fee._calculate_tax()
            if fee.tax_rule and not fee.tax_rule.pk:
                fee.tax_rule = None  # TODO: deprecate
            fee.save()

        # Safety check: Is the amount we're now going to charge the same amount the user has been shown when they
        # pressed "Confirm purchase"? If not, we should better warn the user and show the confirmation page again.
        # We used to have a *known* case where this happened is if a gift card is used in two concurrent sessions,
        # but this is now a payment error instead. So currently this code branch is usually only triggered by bugs
        # in other places (e.g. tax calculation).
        if shown_total is not None:
            if Decimal(shown_total) != pending_sum:
                raise OrderError(
                    _('While trying to place your order, we noticed that the order total has changed. Either one of '
                      'the prices changed just now, or a gift card you used has been used in the meantime. Please '
                      'check the prices below and try again.')
                )

        if payment_requests and not order.require_approval:
            for p in payment_requests:
                if not p.get('multi_use_supported') or p['payment_amount'] > Decimal('0.00'):
                    payments.append(order.payments.create(
                        state=OrderPayment.PAYMENT_STATE_CREATED,
                        provider=p['provider'],
                        amount=p['payment_amount'],
                        fee=p.get('fee'),
                        info=json.dumps(p['info_data']),
                        process_initiated=False,
                    ))

        orderpositions = OrderPosition.transform_cart_positions(positions, order)
        order.create_transactions(positions=orderpositions, fees=fees, is_new=True)
        order.log_action('pretix.event.order.placed')
        if order.require_approval:
            order.log_action('pretix.event.order.placed.require_approval')
        if meta_info:
            for msg in meta_info.get('confirm_messages', []):
                order.log_action('pretix.event.order.consent', data={'msg': msg})

    order_placed.send(event, order=order)
    return order, payments


def _order_placed_email(event: Event, order: Order, email_template, subject_template,
                        log_entry: str, invoice, payments: List[OrderPayment], is_free=False):
    email_context = get_email_context(event=event, order=order, payments=payments)
    try:
        order.send_mail(
            subject_template, email_template, email_context,
            log_entry,
            invoices=[invoice] if invoice and event.settings.invoice_email_attachment else [],
            attach_tickets=True,
            attach_ical=event.settings.mail_attach_ical and (not event.settings.mail_attach_ical_paid_only or is_free),
            attach_other_files=[a for a in [
                event.settings.get('mail_attachment_new_order', as_type=str, default='')[len('file://'):]
            ] if a],
        )
    except SendMailException:
        logger.exception('Order received email could not be sent')


def _order_placed_email_attendee(event: Event, order: Order, position: OrderPosition, email_template, subject_template,
                                 log_entry: str, is_free=False):
    email_context = get_email_context(event=event, order=order, position=position)

    try:
        position.send_mail(
            subject_template, email_template, email_context,
            log_entry,
            invoices=[],
            attach_tickets=True,
            attach_ical=event.settings.mail_attach_ical and (not event.settings.mail_attach_ical_paid_only or is_free),
            attach_other_files=[a for a in [
                event.settings.get('mail_attachment_new_order', as_type=str, default='')[len('file://'):]
            ] if a],
        )
    except SendMailException:
        logger.exception('Order received email could not be sent to attendee')


def _perform_order(event: Event, payment_requests: List[dict], position_ids: List[str],
                   email: str, locale: str, address: int, meta_info: dict=None, sales_channel: str='web',
                   shown_total=None, customer=None):
    for p in payment_requests:
        p['pprov'] = event.get_payment_providers(cached=True)[p['provider']]
        if not p['pprov']:
            raise OrderError(error_messages['internal'])

    if customer:
        customer = event.organizer.customers.get(pk=customer)

    if email == settings.PRETIX_EMAIL_NONE_VALUE:
        email = None

    addr = None
    if address is not None:
        try:
            with scopes_disabled():
                addr = InvoiceAddress.objects.get(pk=address)
        except InvoiceAddress.DoesNotExist:
            pass

    requires_seat = Exists(
        SeatCategoryMapping.objects.filter(
            Q(product=OuterRef('item'))
            & (Q(subevent=OuterRef('subevent')) if event.has_subevents else Q(subevent__isnull=True))
        )
    )
    if not event.settings.seating_choice:
        requires_seat = Value(0, output_field=IntegerField())
    positions = CartPosition.objects.annotate(
        requires_seat=requires_seat
    ).filter(
        id__in=position_ids, event=event
    )

    validate_order.send(
        event,
        payment_provider=payment_requests[0]['provider'] if payment_requests else None,  # only for backwards compatibility
        payments=payment_requests,
        email=email,
        positions=positions,
        locale=locale,
        invoice_address=addr,
        meta_info=meta_info,
        customer=customer,
    )

    lockfn = NoLockManager
    locked = False
    if positions.filter(Q(voucher__isnull=False) | Q(expires__lt=now() + timedelta(minutes=2)) | Q(seat__isnull=False)).exists():
        # Performance optimization: If no voucher is used and no cart position is dangerously close to its expiry date,
        # creating this order shouldn't be prone to any race conditions and we don't need to lock the event.
        locked = True
        lockfn = event.lock

    warnings = []
    any_payment_failed = False

    with lockfn() as now_dt:
        positions = list(
            positions.select_related('item', 'variation', 'subevent', 'seat', 'addon_to').prefetch_related('addons')
        )
        positions.sort(key=lambda k: position_ids.index(k.pk))
        if len(positions) == 0:
            raise OrderError(error_messages['empty'])
        if len(position_ids) != len(positions):
            raise OrderError(error_messages['internal'])
        _check_positions(event, now_dt, positions, address=addr, sales_channel=sales_channel, customer=customer)
        order, payment_objs = _create_order(event, email, positions, now_dt, payment_requests,
                                            locale=locale, address=addr, meta_info=meta_info, sales_channel=sales_channel,
                                            shown_total=shown_total, customer=customer)
        try:
            for p in payment_objs:
                if p.provider == 'free':
                    p.confirm(send_mail=False, lock=not locked, generate_invoice=False)
        except Quota.QuotaExceededException:
            pass

    # We give special treatment to GiftCardPayment here because our invoice renderer expects gift cards to already be
    # processed, and because we historically treat gift card orders like free orders with regards to email texts.
    # It would be great to give external gift card plugins the same special treatment, but it feels to risky for now, as
    # (a) there would be no email at all if the plugin fails in a weird way and (b) we'd be able to run into
    # contradictions when a plugin set both execute_payment_needs_user=False as well as requires_invoice_immediately=True
    for p in payment_objs:
        if isinstance(p.payment_provider, GiftCardPayment):
            try:
                p.process_initiated = True
                p.save(update_fields=['process_initiated'])
                p.payment_provider.execute_payment(None, p, is_early_special_case=True)
            except PaymentException as e:
                warnings.append(str(e))
                any_payment_failed = True
            except Exception:
                logger.exception('Error during payment attempt')
            else:
                order.refresh_from_db()

    pending_sum = order.pending_sum
    free_order_flow = (
        payment_objs and
        (
            any(p['provider'] == 'free' for p in payment_requests) or
            all(p['provider'] == 'giftcard' for p in payment_requests)
        ) and
        pending_sum == Decimal('0.00') and
        not order.require_approval
    )

    invoice = order.invoices.last()  # Might be generated by plugin already
    if not invoice and invoice_qualified(order):
        invoice_required = (
            event.settings.get('invoice_generate') == 'True' or (
                event.settings.get('invoice_generate') == 'paid' and (
                    any(p['pprov'].requires_invoice_immediately for p in payment_requests) or
                    pending_sum <= Decimal('0.00')
                )
            )
        )
        if invoice_required:
            invoice = generate_invoice(
                order,
                trigger_pdf=not event.settings.invoice_email_attachment or not order.email
            )
            # send_mail will trigger PDF generation later

    if order.email:
        if order.require_approval:
            email_template = event.settings.mail_text_order_placed_require_approval
            subject_template = event.settings.mail_subject_order_placed_require_approval
            log_entry = 'pretix.event.order.email.order_placed_require_approval'

            email_attendees = False
        elif free_order_flow:
            email_template = event.settings.mail_text_order_free
            subject_template = event.settings.mail_subject_order_free
            log_entry = 'pretix.event.order.email.order_free'

            email_attendees = event.settings.mail_send_order_free_attendee
            email_attendees_template = event.settings.mail_text_order_free_attendee
            subject_attendees_template = event.settings.mail_subject_order_free_attendee
        else:
            email_template = event.settings.mail_text_order_placed
            subject_template = event.settings.mail_subject_order_placed
            log_entry = 'pretix.event.order.email.order_placed'

            email_attendees = event.settings.mail_send_order_placed_attendee
            email_attendees_template = event.settings.mail_text_order_placed_attendee
            subject_attendees_template = event.settings.mail_subject_order_placed_attendee

        if sales_channel in event.settings.mail_sales_channel_placed_paid:
            _order_placed_email(event, order, email_template, subject_template, log_entry, invoice, payment_objs,
                                is_free=free_order_flow)
            if email_attendees:
                for p in order.positions.all():
                    if p.addon_to_id is None and p.attendee_email and p.attendee_email != order.email:
                        _order_placed_email_attendee(event, order, p, email_attendees_template, subject_attendees_template, log_entry,
                                                     is_free=free_order_flow)

    if not any_payment_failed:
        for p in payment_objs:
            if not p.payment_provider.execute_payment_needs_user and not p.process_initiated:
                try:
                    p.process_initiated = True
                    p.save(update_fields=['process_initiated'])
                    resp = p.payment_provider.execute_payment(None, p)
                    if isinstance(resp, str):
                        logger.warning('Payment provider returned URL from execute_payment even though execute_payment_needs_user is not set')
                except PaymentException as e:
                    warnings.append(str(e))
                    any_payment_failed = True
                except Exception:
                    logger.exception('Error during payment attempt')

    if any_payment_failed:
        # Cancel all other payments because their amount might be wrong now.
        for p in payment_objs:
            if p.state == OrderPayment.PAYMENT_STATE_CREATED:
                p.state = OrderPayment.PAYMENT_STATE_CANCELED
                p.save(update_fields=['state'])

    return {
        'order_id': order.id,
        'warnings': warnings,
    }


@receiver(signal=periodic_task)
@scopes_disabled()
def expire_orders(sender, **kwargs):
    event_id = None
    expire = None

    qs = Order.objects.filter(
        expires__lt=now(),
        status=Order.STATUS_PENDING,
        require_approval=False
    ).exclude(
        Exists(
            OrderFee.objects.filter(order_id=OuterRef('pk'), fee_type=OrderFee.FEE_TYPE_CANCELLATION)
        )
    ).select_related('event').order_by('event_id')
    for o in qs:
        if o.event_id != event_id:
            expire = o.event.settings.get('payment_term_expire_automatically', as_type=bool)
            event_id = o.event_id
        if expire:
            mark_order_expired(o)


@receiver(signal=periodic_task)
@scopes_disabled()
@minimum_interval(minutes_after_success=60)
def send_expiry_warnings(sender, **kwargs):
    today = now().replace(hour=0, minute=0, second=0)
    days = None
    settings = None
    event_id = None

    for o in Order.objects.filter(
        expires__gte=today, expiry_reminder_sent=False, status=Order.STATUS_PENDING,
        datetime__lte=now() - timedelta(hours=2), require_approval=False
    ).only('pk', 'event_id', 'expires').order_by('event_id'):
        if event_id != o.event_id:
            settings = o.event.settings
            days = cache.get_or_set('{}:{}:setting_mail_days_order_expire_warning'.format('event', o.event_id),
                                    default=lambda: settings.get('mail_days_order_expire_warning', as_type=int),
                                    timeout=3600)
            event_id = o.event_id

        if days and (o.expires - today).days <= days:
            with transaction.atomic():
                o = Order.objects.select_related('event').select_for_update().get(pk=o.pk)
                if o.status != Order.STATUS_PENDING or o.expiry_reminder_sent:
                    # Race condition
                    continue

                with language(o.locale, settings.region):
                    o.expiry_reminder_sent = True
                    o.save(update_fields=['expiry_reminder_sent'])
                    email_template = settings.mail_text_order_expire_warning
                    email_context = get_email_context(event=o.event, order=o)
                    if settings.payment_term_expire_automatically:
                        email_subject = settings.mail_subject_order_expire_warning
                    else:
                        email_subject = settings.mail_subject_order_pending_warning

                    try:
                        o.send_mail(
                            email_subject, email_template, email_context,
                            'pretix.event.order.email.expire_warning_sent'
                        )
                    except SendMailException:
                        logger.exception('Reminder email could not be sent')


@receiver(signal=periodic_task)
@scopes_disabled()
def send_download_reminders(sender, **kwargs):
    today = now().replace(hour=0, minute=0, second=0, microsecond=0)
    qs = Order.objects.annotate(
        first_date=Coalesce(
            Min('all_positions__subevent__date_from'),
            F('event__date_from')
        )
    ).filter(
        download_reminder_sent=False,
        datetime__lte=now() - timedelta(hours=2),
        first_date__gte=today,
    ).only('pk', 'event_id', 'sales_channel').order_by('event_id')
    event_id = None
    days = None
    event = None

    for o in qs:
        if o.event_id != event_id:
            days = o.event.settings.get('mail_days_download_reminder', as_type=int)
            event = o.event
            event_id = o.event_id

        if days is None:
            continue

        if o.sales_channel not in event.settings.mail_sales_channel_download_reminder:
            continue

        reminder_date = (o.first_date - timedelta(days=days)).replace(hour=0, minute=0, second=0, microsecond=0)
        if now() < reminder_date or o.datetime > reminder_date:
            continue

        with transaction.atomic():
            o = Order.objects.select_for_update().get(pk=o.pk)
            if o.download_reminder_sent:
                # Race condition
                continue
            if not all([r for rr, r in allow_ticket_download.send(event, order=o)]):
                continue

            if not o.ticket_download_available:
                continue
            positions = o.positions.select_related('item')

            if o.status != Order.STATUS_PAID:
                if o.status != Order.STATUS_PENDING or o.require_approval or not \
                        o.event.settings.ticket_download_pending:
                    continue
            send = False
            for p in positions:
                if p.generate_ticket:
                    send = True
                    break
            if not send:
                continue

            with language(o.locale, o.event.settings.region):
                o.download_reminder_sent = True
                o.save(update_fields=['download_reminder_sent'])
                email_template = event.settings.mail_text_download_reminder
                email_subject = event.settings.mail_subject_download_reminder
                email_context = get_email_context(event=event, order=o)
                try:
                    o.send_mail(
                        email_subject, email_template, email_context,
                        'pretix.event.order.email.download_reminder_sent',
                        attach_tickets=True
                    )
                except SendMailException:
                    logger.exception('Reminder email could not be sent')

                if event.settings.mail_send_download_reminder_attendee:
                    for p in o.positions.all():
                        if not p.generate_ticket:
                            continue

                        if p.subevent_id:
                            reminder_date = (p.subevent.date_from - timedelta(days=days)).replace(
                                hour=0, minute=0, second=0, microsecond=0
                            )
                            if now() < reminder_date:
                                continue
                        if p.addon_to_id is None and p.attendee_email and p.attendee_email != o.email:
                            email_template = event.settings.mail_text_download_reminder_attendee
                            email_subject = event.settings.mail_subject_download_reminder_attendee
                            email_context = get_email_context(event=event, order=o, position=p)
                            try:
                                o.send_mail(
                                    email_subject, email_template, email_context,
                                    'pretix.event.order.email.download_reminder_sent',
                                    attach_tickets=True, position=p
                                )
                            except SendMailException:
                                logger.exception('Reminder email could not be sent to attendee')


def notify_user_changed_order(order, user=None, auth=None, invoices=[]):
    with language(order.locale, order.event.settings.region):
        email_template = order.event.settings.mail_text_order_changed
        email_context = get_email_context(event=order.event, order=order)
        email_subject = order.event.settings.mail_subject_order_changed
        try:
            order.send_mail(
                email_subject, email_template, email_context,
                'pretix.event.order.email.order_changed', user, auth=auth, invoices=invoices, attach_tickets=True,
            )
        except SendMailException:
            logger.exception('Order changed email could not be sent')


class OrderChangeManager:
    error_messages = {
        'product_without_variation': _('You need to select a variation of the product.'),
        'quota': _('The quota {name} does not have enough capacity left to perform the operation.'),
        'quota_missing': _('There is no quota defined that allows this operation.'),
        'product_invalid': _('The selected product is not active or has no price set.'),
        'complete_cancel': _('This operation would leave the order empty. Please cancel the order itself instead.'),
        'paid_to_free_exceeded': _('This operation would make the order free and therefore immediately paid, however '
                                   'no quota is available.'),
        'addon_to_required': _('This is an add-on product, please select the base position it should be added to.'),
        'addon_invalid': _('The selected base position does not allow you to add this product as an add-on.'),
        'subevent_required': _('You need to choose a subevent for the new position.'),
        'seat_unavailable': _('The selected seat "{seat}" is not available.'),
        'seat_subevent_mismatch': _('You selected seat "{seat}" for a date that does not match the selected ticket date. Please choose a seat again.'),
        'seat_required': _('The selected product requires you to select a seat.'),
        'seat_forbidden': _('The selected product does not allow to select a seat.'),
        'tax_rule_country_blocked': _('The selected country is blocked by your tax rule.'),
        'gift_card_change': _('You cannot change the price of a position that has been used to issue a gift card.'),
    }
    ItemOperation = namedtuple('ItemOperation', ('position', 'item', 'variation'))
    SubeventOperation = namedtuple('SubeventOperation', ('position', 'subevent'))
    SeatOperation = namedtuple('SubeventOperation', ('position', 'seat'))
    PriceOperation = namedtuple('PriceOperation', ('position', 'price', 'price_diff'))
    TaxRuleOperation = namedtuple('TaxRuleOperation', ('position', 'tax_rule'))
    MembershipOperation = namedtuple('MembershipOperation', ('position', 'membership'))
    CancelOperation = namedtuple('CancelOperation', ('position', 'price_diff'))
    AddOperation = namedtuple('AddOperation', ('item', 'variation', 'price', 'addon_to', 'subevent', 'seat', 'membership'))
    SplitOperation = namedtuple('SplitOperation', ('position',))
    FeeValueOperation = namedtuple('FeeValueOperation', ('fee', 'value', 'price_diff'))
    AddFeeOperation = namedtuple('AddFeeOperation', ('fee', 'price_diff'))
    CancelFeeOperation = namedtuple('CancelFeeOperation', ('fee', 'price_diff'))
    RegenerateSecretOperation = namedtuple('RegenerateSecretOperation', ('position',))

    def __init__(self, order: Order, user=None, auth=None, notify=True, reissue_invoice=True):
        self.order = order
        self.user = user
        self.auth = auth
        self.event = order.event
        self.split_order = None
        self.reissue_invoice = reissue_invoice
        self._committed = False
        self._totaldiff = 0
        self._quotadiff = Counter()
        self._seatdiff = Counter()
        self._operations = []
        self.notify = notify
        self._invoice_dirty = False
        self._invoices = []

    def change_item(self, position: OrderPosition, item: Item, variation: Optional[ItemVariation]):
        if (not variation and item.has_variations) or (variation and variation.item_id != item.pk):
            raise OrderError(self.error_messages['product_without_variation'])

        new_quotas = (variation.quotas.filter(subevent=position.subevent)
                      if variation else item.quotas.filter(subevent=position.subevent))
        if not new_quotas:
            raise OrderError(self.error_messages['quota_missing'])

        self._quotadiff.update(new_quotas)
        self._quotadiff.subtract(position.quotas)
        self._operations.append(self.ItemOperation(position, item, variation))

    def change_seat(self, position: OrderPosition, seat: Seat):
        if isinstance(seat, str):
            subev = None
            if self.event.has_subevents:
                subev = position.subevent
                for p in self._operations:
                    if isinstance(p, self.SubeventOperation) and p.position == position:
                        subev = p.subevent
            try:
                seat = Seat.objects.get(
                    event=self.event,
                    subevent=subev,
                    seat_guid=seat
                )
            except Seat.DoesNotExist:
                raise OrderError(error_messages['seat_invalid'])
        if position.seat:
            self._seatdiff.subtract([position.seat])
        if seat:
            self._seatdiff.update([seat])
        self._operations.append(self.SeatOperation(position, seat))

    def change_membership(self, position: OrderPosition, membership: Membership):
        self._operations.append(self.MembershipOperation(position, membership))

    def change_subevent(self, position: OrderPosition, subevent: SubEvent):
        try:
            price = get_price(position.item, position.variation, voucher=position.voucher, subevent=subevent,
                              invoice_address=self._invoice_address)
        except TaxRule.SaleNotAllowed:
            raise OrderError(self.error_messages['tax_rule_country_blocked'])

        if price is None:  # NOQA
            raise OrderError(self.error_messages['product_invalid'])

        new_quotas = (position.variation.quotas.filter(subevent=subevent)
                      if position.variation else position.item.quotas.filter(subevent=subevent))
        if not new_quotas:
            raise OrderError(self.error_messages['quota_missing'])

        self._quotadiff.update(new_quotas)
        self._quotadiff.subtract(position.quotas)
        self._operations.append(self.SubeventOperation(position, subevent))
        self._invoice_dirty = True

    def change_item_and_subevent(self, position: OrderPosition, item: Item, variation: Optional[ItemVariation],
                                 subevent: SubEvent):
        if (not variation and item.has_variations) or (variation and variation.item_id != item.pk):
            raise OrderError(self.error_messages['product_without_variation'])

        try:
            price = get_price(item, variation, voucher=position.voucher, subevent=subevent,
                              invoice_address=self._invoice_address)
        except TaxRule.SaleNotAllowed:
            raise OrderError(self.error_messages['tax_rule_country_blocked'])

        if price is None:  # NOQA
            raise OrderError(self.error_messages['product_invalid'])

        new_quotas = (variation.quotas.filter(subevent=subevent)
                      if variation else item.quotas.filter(subevent=subevent))
        if not new_quotas:
            raise OrderError(self.error_messages['quota_missing'])

        self._quotadiff.update(new_quotas)
        self._quotadiff.subtract(position.quotas)
        self._operations.append(self.ItemOperation(position, item, variation))
        self._operations.append(self.SubeventOperation(position, subevent))
        self._invoice_dirty = True

    def regenerate_secret(self, position: OrderPosition):
        self._operations.append(self.RegenerateSecretOperation(position))

    def change_price(self, position: OrderPosition, price: Decimal):
        tax_rule = self._current_tax_rules().get(position.pk, position.tax_rule) or TaxRule.zero()
        price = tax_rule.tax(price, base_price_is='gross')

        if position.issued_gift_cards.exists():
            raise OrderError(self.error_messages['gift_card_change'])

        self._totaldiff += price.gross - position.price

        if self.order.event.settings.invoice_include_free or price.gross != Decimal('0.00') or position.price != Decimal('0.00'):
            self._invoice_dirty = True

        self._operations.append(self.PriceOperation(position, price, price.gross - position.price))

    def change_tax_rule(self, position_or_fee, tax_rule: TaxRule):
        self._operations.append(self.TaxRuleOperation(position_or_fee, tax_rule))
        self._invoice_dirty = True

    def _current_tax_rules(self):
        tax_rules = {}
        for p in self._operations:
            if isinstance(p, self.TaxRuleOperation):
                tax_rules[p.position.pk] = p.tax_rule
            elif isinstance(p, self.ItemOperation):
                tax_rules[p.position.pk] = p.item.tax_rule
        return tax_rules

    def recalculate_taxes(self, keep='net'):
        positions = self.order.positions.select_related('item', 'item__tax_rule')
        ia = self._invoice_address
        tax_rules = self._current_tax_rules()

        for pos in positions:
            tax_rule = tax_rules.get(pos.pk, pos.tax_rule)
            if not tax_rule:
                continue
            if not pos.price:
                continue

            try:
                new_rate = tax_rule.tax_rate_for(ia)
            except TaxRule.SaleNotAllowed:
                raise OrderError(error_messages['tax_rule_country_blocked'])
            # We use override_tax_rate to make sure .tax() doesn't get clever and re-adjusts the pricing itself
            if new_rate != pos.tax_rate:
                if keep == 'net':
                    new_tax = tax_rule.tax(pos.price - pos.tax_value, base_price_is='net', currency=self.event.currency,
                                           override_tax_rate=new_rate)
                else:
                    new_tax = tax_rule.tax(pos.price, base_price_is='gross', currency=self.event.currency,
                                           override_tax_rate=new_rate)
                self._totaldiff += new_tax.gross - pos.price
                self._operations.append(self.PriceOperation(pos, new_tax, new_tax.gross - pos.price))

    def cancel_fee(self, fee: OrderFee):
        self._totaldiff -= fee.value
        self._operations.append(self.CancelFeeOperation(fee, -fee.value))
        self._invoice_dirty = True

    def add_fee(self, fee: OrderFee):
        self._totaldiff += fee.value
        self._invoice_dirty = True
        self._operations.append(self.AddFeeOperation(fee, fee.value))

    def change_fee(self, fee: OrderFee, value: Decimal):
        value = (fee.tax_rule or TaxRule.zero()).tax(value, base_price_is='gross')
        self._totaldiff += value.gross - fee.value
        self._invoice_dirty = True
        self._operations.append(self.FeeValueOperation(fee, value, value.gross - fee.value))

    def cancel(self, position: OrderPosition):
        self._totaldiff -= position.price
        self._quotadiff.subtract(position.quotas)
        self._operations.append(self.CancelOperation(position, -position.price))
        if position.seat:
            self._seatdiff.subtract([position.seat])

        if self.order.event.settings.invoice_include_free or position.price != Decimal('0.00'):
            self._invoice_dirty = True

    def add_position(self, item: Item, variation: ItemVariation, price: Decimal, addon_to: OrderPosition = None,
                     subevent: SubEvent = None, seat: Seat = None, membership: Membership = None):
        if isinstance(seat, str):
            if not seat:
                seat = None
            else:
                try:
                    seat = Seat.objects.get(
                        event=self.event,
                        subevent=subevent,
                        seat_guid=seat
                    )
                except Seat.DoesNotExist:
                    raise OrderError(error_messages['seat_invalid'])

        try:
            if price is None:
                price = get_price(item, variation, subevent=subevent, invoice_address=self._invoice_address)
            elif not isinstance(price, TaxedPrice):
                price = item.tax(price, base_price_is='gross', invoice_address=self._invoice_address)
        except TaxRule.SaleNotAllowed:
            raise OrderError(self.error_messages['tax_rule_country_blocked'])

        if price is None:
            raise OrderError(self.error_messages['product_invalid'])
        if item.variations.exists() and not variation:
            raise OrderError(self.error_messages['product_without_variation'])
        if not addon_to and item.category and item.category.is_addon:
            raise OrderError(self.error_messages['addon_to_required'])
        if addon_to:
            if not item.category or item.category_id not in addon_to.item.addons.values_list('addon_category', flat=True):
                raise OrderError(self.error_messages['addon_invalid'])
        if self.order.event.has_subevents and not subevent:
            raise OrderError(self.error_messages['subevent_required'])

        seated = item.seat_category_mappings.filter(subevent=subevent).exists()
        if seated and not seat and self.event.settings.seating_choice:
            raise OrderError(self.error_messages['seat_required'])
        elif not seated and seat:
            raise OrderError(self.error_messages['seat_forbidden'])
        if seat and subevent and seat.subevent_id != subevent.pk:
            raise OrderError(self.error_messages['seat_subevent_mismatch'].format(seat=seat.name))

        new_quotas = (variation.quotas.filter(subevent=subevent)
                      if variation else item.quotas.filter(subevent=subevent))
        if not new_quotas:
            raise OrderError(self.error_messages['quota_missing'])

        if self.order.event.settings.invoice_include_free or price.gross != Decimal('0.00'):
            self._invoice_dirty = True

        self._totaldiff += price.gross
        self._quotadiff.update(new_quotas)
        if seat:
            self._seatdiff.update([seat])
        self._operations.append(self.AddOperation(item, variation, price, addon_to, subevent, seat, membership))

    def split(self, position: OrderPosition):
        if self.order.event.settings.invoice_include_free or position.price != Decimal('0.00'):
            self._invoice_dirty = True

        self._operations.append(self.SplitOperation(position))
        for a in position.addons.all():
            self._operations.append(self.SplitOperation(a))

    def set_addons(self, addons):
        if self._operations:
            raise ValueError("Setting addons should be the first/only operation")

        # Prepare various containers to hold data later
        current_addons = defaultdict(lambda: defaultdict(list))  # OrderPos -> currently attached add-ons
        input_addons = defaultdict(Counter)  # OrderPos -> final desired set of add-ons
        selected_addons = defaultdict(Counter)  # OrderPos, ItemAddOn -> final desired set of add-ons
        opcache = {}  # OrderPos.pk -> OrderPos
        quota_diff = Counter()  # Quota -> Number of usages
        available_categories = defaultdict(set)  # OrderPos -> Category IDs to choose from
        price_included = defaultdict(dict)  # OrderPos -> CategoryID -> bool(price is included)
        toplevel_op = self.order.positions.filter(
            addon_to__isnull=True
        ).prefetch_related(
            'addons', 'item__addons', 'item__addons__addon_category'
        ).select_related('item', 'variation')

        _items_cache = {
            i.pk: i
            for i in self.event.items.select_related('category').prefetch_related(
                'addons', 'bundles', 'addons__addon_category', 'quotas'
            ).annotate(
                has_variations=Count('variations'),
            ).filter(
                id__in=[a['item'] for a in addons]
            ).order_by()
        }
        _variations_cache = {
            v.pk: v
            for v in ItemVariation.objects.filter(item__event=self.event).prefetch_related(
                'quotas'
            ).select_related('item', 'item__event').filter(
                id__in=[a['variation'] for a in addons if a.get('variation')]
            ).order_by()
        }

        # Prefill some of the cache containers
        for op in toplevel_op:
            if op.canceled:
                continue
            available_categories[op.pk] = {iao.addon_category_id for iao in op.item.addons.all()}
            price_included[op.pk] = {iao.addon_category_id: iao.price_included for iao in op.item.addons.all()}
            opcache[op.pk] = op
            for a in op.addons.all():
                if a.canceled:
                    continue

                if not a.is_bundled:
                    current_addons[op][a.item_id, a.variation_id].append(a)

        # Create operations, perform various checks
        for a in addons:
            # Check whether the specified items are part of what we just fetched from the database
            # If they are not, the user supplied item IDs which either do not exist or belong to
            # a different event
            if a['item'] not in _items_cache or (a['variation'] and a['variation'] not in _variations_cache):
                raise OrderError(error_messages['not_for_sale'])

            # Only attach addons to things that are actually in this user's cart
            if a['addon_to'] not in opcache:
                raise OrderError(error_messages['addon_invalid_base'])

            op = opcache[a['addon_to']]
            item = _items_cache[a['item']]
            subevent = op.subevent  # for now, we might lift this requirement later
            variation = _variations_cache[a['variation']] if a['variation'] is not None else None

            if item.category_id not in available_categories[op.pk]:
                raise OrderError(error_messages['addon_invalid_base'])

            # Fetch all quotas. If there are no quotas, this item is not allowed to be sold.
            quotas = list(item.quotas.filter(subevent=subevent)
                          if variation is None else variation.quotas.filter(subevent=subevent))
            if not quotas:
                raise OrderError(error_messages['unavailable'])

            if (a['item'], a['variation']) in input_addons[op.id]:
                raise OrderError(error_messages['addon_duplicate_item'])

            if item.require_voucher or item.hide_without_voucher or (variation and variation.hide_without_voucher):
                raise OrderError(error_messages['voucher_required'])

            if not item.is_available() or (variation and not variation.is_available()):
                raise OrderError(error_messages['unavailable'])

            if self.order.sales_channel not in item.sales_channels or (
                    variation and self.order.sales_channel not in variation.sales_channels):
                raise OrderError(error_messages['unavailable'])

            if subevent and item.pk in subevent.item_overrides and not subevent.item_overrides[item.pk].is_available():
                raise OrderError(error_messages['not_for_sale'])

            if subevent and variation and variation.pk in subevent.var_overrides and \
                    not subevent.var_overrides[variation.pk].is_available():
                raise OrderError(error_messages['not_for_sale'])

            if item.has_variations and not variation:
                raise OrderError(error_messages['not_for_sale'])

            if variation and variation.item_id != item.pk:
                raise OrderError(error_messages['not_for_sale'])

            if subevent and subevent.presale_start and now() < subevent.presale_start:
                raise OrderError(error_messages['not_started'])

            if (subevent and subevent.presale_has_ended) or self.event.presale_has_ended:
                raise OrderError(error_messages['ended'])

            if item.require_bundling:
                raise OrderError(error_messages['unavailable'])

            input_addons[op.id][a['item'], a['variation']] = a.get('count', 1)
            selected_addons[op.id, item.category_id][a['item'], a['variation']] = a.get('count', 1)

            if price_included[op.pk].get(item.category_id):
                price = TAXED_ZERO
            else:
                price = get_price(
                    item, variation, voucher=None, custom_price=a.get('price'), subevent=op.subevent,
                    custom_price_is_net=self.event.settings.display_net_prices,
                    invoice_address=self._invoice_address,
                )

            if a.get('count', 1) > len(current_addons[op][a['item'], a['variation']]):
                # This add-on is new, add it to the cart
                for quota in quotas:
                    quota_diff[quota] += a.get('count', 1) - len(current_addons[op][a['item'], a['variation']])

                for i in range(a.get('count', 1) - len(current_addons[op][a['item'], a['variation']])):
                    self.add_position(
                        item=item, variation=variation, price=price,
                        addon_to=op, subevent=op.subevent, seat=None,
                    )

        # Check constraints on the add-on combinations
        for op in toplevel_op:
            item = op.item
            for iao in item.addons.all():
                selected = selected_addons[op.id, iao.addon_category_id]
                n_per_i = Counter()
                for (i, v), c in selected.items():
                    n_per_i[i] += c
                if sum(selected.values()) > iao.max_count:
                    # TODO: Proper i18n
                    # TODO: Proper pluralization
                    raise OrderError(
                        error_messages['addon_max_count'],
                        {
                            'base': str(item.name),
                            'max': iao.max_count,
                            'cat': str(iao.addon_category.name),
                        }
                    )
                elif sum(selected.values()) < iao.min_count:
                    # TODO: Proper i18n
                    # TODO: Proper pluralization
                    raise OrderError(
                        error_messages['addon_min_count'],
                        {
                            'base': str(item.name),
                            'min': iao.min_count,
                            'cat': str(iao.addon_category.name),
                        }
                    )
                elif any(v > 1 for v in n_per_i.values()) and not iao.multi_allowed:
                    raise OrderError(
                        error_messages['addon_no_multi'],
                        {
                            'base': str(item.name),
                            'cat': str(iao.addon_category.name),
                        }
                    )

        # Detect removed add-ons and create RemoveOperations
        for cp, al in list(current_addons.items()):
            for k, v in al.items():
                input_num = input_addons[cp.id].get(k, 0)
                current_num = len(current_addons[cp].get(k, []))
                if input_num < current_num:
                    for a in current_addons[cp][k][:current_num - input_num]:
                        if a.canceled:
                            continue
                        self.cancel(a)

    def _check_seats(self):
        for seat, diff in self._seatdiff.items():
            if diff <= 0:
                continue
            if not seat.is_available(sales_channel=self.order.sales_channel, ignore_distancing=True) or diff > 1:
                raise OrderError(self.error_messages['seat_unavailable'].format(seat=seat.name))

        if self.event.has_subevents:
            state = {}
            for p in self.order.positions.all():
                state[p] = {'seat': p.seat, 'subevent': p.subevent}
            for op in self._operations:
                if isinstance(op, self.SeatOperation):
                    state[op.position]['seat'] = op.seat
                elif isinstance(op, self.SubeventOperation):
                    state[op.position]['subevent'] = op.subevent
            for v in state.values():
                if v['seat'] and v['seat'].subevent_id != v['subevent'].pk:
                    raise OrderError(self.error_messages['seat_subevent_mismatch'].format(seat=v['seat'].name))

    def _check_quotas(self):
        qa = QuotaAvailability()
        qa.queue(*[k for k, v in self._quotadiff.items() if v > 0])
        qa.compute()
        for quota, diff in self._quotadiff.items():
            if diff <= 0:
                continue
            avail = qa.results[quota]
            if avail[0] != Quota.AVAILABILITY_OK or (avail[1] is not None and avail[1] < diff):
                raise OrderError(self.error_messages['quota'].format(name=quota.name))

    def _check_paid_price_change(self):
        if self.order.status == Order.STATUS_PAID and self._totaldiff > 0:
            if self.order.pending_sum > Decimal('0.00'):
                self.order.status = Order.STATUS_PENDING
                self.order.set_expires(
                    now(),
                    self.order.event.subevents.filter(id__in=self.order.positions.values_list('subevent_id', flat=True))
                )
                self.order.save()
        elif self.order.status in (Order.STATUS_PENDING, Order.STATUS_EXPIRED) and self._totaldiff < 0:
            if self.order.pending_sum <= Decimal('0.00') and not self.order.require_approval:
                self.order.status = Order.STATUS_PAID
                self.order.save()
            elif self.open_payment:
                try:
                    self.open_payment.payment_provider.cancel_payment(self.open_payment)
                    self.order.log_action(
                        'pretix.event.order.payment.canceled',
                        {
                            'local_id': self.open_payment.local_id,
                            'provider': self.open_payment.provider,
                        },
                        user=self.user,
                        auth=self.auth
                    )
                except PaymentException as e:
                    self.order.log_action(
                        'pretix.event.order.payment.canceled.failed',
                        {
                            'local_id': self.open_payment.local_id,
                            'provider': self.open_payment.provider,
                            'error': str(e)
                        },
                        user=self.user,
                        auth=self.auth
                    )
        elif self.order.status in (Order.STATUS_PENDING, Order.STATUS_EXPIRED) and self._totaldiff > 0:
            if self.open_payment:
                try:
                    self.open_payment.payment_provider.cancel_payment(self.open_payment)
                    self.order.log_action('pretix.event.order.payment.canceled', {
                        'local_id': self.open_payment.local_id,
                        'provider': self.open_payment.provider,
                    }, user=self.user, auth=self.auth)
                except PaymentException as e:
                    self.order.log_action(
                        'pretix.event.order.payment.canceled.failed',
                        {
                            'local_id': self.open_payment.local_id,
                            'provider': self.open_payment.provider,
                            'error': str(e)
                        },
                        user=self.user,
                        auth=self.auth,
                    )

    def _check_paid_to_free(self):
        if self.order.total == 0 and (self._totaldiff < 0 or (self.split_order and self.split_order.total > 0)) and not self.order.require_approval:
            if not self.order.fees.exists() and not self.order.positions.exists():
                # The order is completely empty now, so we cancel it.
                self.order.status = Order.STATUS_CANCELED
                self.order.save(update_fields=['status'])
                order_canceled.send(self.order.event, order=self.order)
            elif self.order.status != Order.STATUS_CANCELED:
                # if the order becomes free, mark it paid using the 'free' provider
                # this could happen if positions have been made cheaper or removed (_totaldiff < 0)
                # or positions got split off to a new order (split_order with positive total)
                p = self.order.payments.create(
                    state=OrderPayment.PAYMENT_STATE_CREATED,
                    provider='free',
                    amount=0,
                    fee=None
                )
                try:
                    p.confirm(send_mail=False, count_waitinglist=False, user=self.user, auth=self.auth)
                except Quota.QuotaExceededException:
                    raise OrderError(self.error_messages['paid_to_free_exceeded'])

        if self.split_order and self.split_order.total == 0 and not self.split_order.require_approval:
            p = self.split_order.payments.create(
                state=OrderPayment.PAYMENT_STATE_CREATED,
                provider='free',
                amount=0,
                fee=None
            )
            try:
                p.confirm(send_mail=False, count_waitinglist=False, user=self.user, auth=self.auth)
            except Quota.QuotaExceededException:
                raise OrderError(self.error_messages['paid_to_free_exceeded'])

    def _perform_operations(self):
        nextposid = self.order.all_positions.aggregate(m=Max('positionid'))['m'] + 1
        split_positions = []

        for op in self._operations:
            if isinstance(op, self.ItemOperation):
                self.order.log_action('pretix.event.order.changed.item', user=self.user, auth=self.auth, data={
                    'position': op.position.pk,
                    'positionid': op.position.positionid,
                    'old_item': op.position.item.pk,
                    'old_variation': op.position.variation.pk if op.position.variation else None,
                    'new_item': op.item.pk,
                    'new_variation': op.variation.pk if op.variation else None,
                    'old_price': op.position.price,
                    'addon_to': op.position.addon_to_id,
                    'new_price': op.position.price
                })
                op.position.item = op.item
                op.position.variation = op.variation
                op.position._calculate_tax()

                if op.position.voucher_budget_use is not None and op.position.voucher and not op.position.addon_to_id:
                    listed_price = get_listed_price(op.position.item, op.position.variation, op.position.subevent)
                    if not op.position.item.tax_rule or op.position.item.tax_rule.price_includes_tax:
                        price_after_voucher = max(op.position.price, op.position.voucher.calculate_price(listed_price))
                    else:
                        price_after_voucher = max(op.position.price - op.position.tax_value, op.position.voucher.calculate_price(listed_price))
                    op.position.voucher_budget_use = max(listed_price - price_after_voucher, Decimal('0.00'))
                assign_ticket_secret(
                    event=self.event, position=op.position, force_invalidate=False, save=False
                )
                op.position.save()
            elif isinstance(op, self.MembershipOperation):
                self.order.log_action('pretix.event.order.changed.membership', user=self.user, auth=self.auth, data={
                    'position': op.position.pk,
                    'positionid': op.position.positionid,
                    'old_membership_id': op.position.used_membership_id,
                    'new_membership_id': op.membership.pk if op.membership else None,
                })
                op.position.used_membership = op.membership
                op.position.save()
            elif isinstance(op, self.SeatOperation):
                self.order.log_action('pretix.event.order.changed.seat', user=self.user, auth=self.auth, data={
                    'position': op.position.pk,
                    'positionid': op.position.positionid,
                    'old_seat': op.position.seat.name if op.position.seat else "-",
                    'new_seat': op.seat.name if op.seat else "-",
                    'old_seat_id': op.position.seat.pk if op.position.seat else None,
                    'new_seat_id': op.seat.pk if op.seat else None,
                })
                op.position.seat = op.seat
                assign_ticket_secret(
                    event=self.event, position=op.position, force_invalidate=False, save=False
                )
                op.position.save()
            elif isinstance(op, self.SubeventOperation):
                self.order.log_action('pretix.event.order.changed.subevent', user=self.user, auth=self.auth, data={
                    'position': op.position.pk,
                    'positionid': op.position.positionid,
                    'old_subevent': op.position.subevent.pk,
                    'new_subevent': op.subevent.pk,
                    'old_price': op.position.price,
                    'new_price': op.position.price
                })
                op.position.subevent = op.subevent
                assign_ticket_secret(
                    event=self.event, position=op.position, force_invalidate=False, save=False
                )
                if op.position.voucher_budget_use is not None and op.position.voucher and not op.position.addon_to_id:
                    listed_price = get_listed_price(op.position.item, op.position.variation, op.position.subevent)
                    if not op.position.item.tax_rule or op.position.item.tax_rule.price_includes_tax:
                        price_after_voucher = max(op.position.price, op.position.voucher.calculate_price(listed_price))
                    else:
                        price_after_voucher = max(op.position.price - op.position.tax_value, op.position.voucher.calculate_price(listed_price))
                    op.position.voucher_budget_use = max(listed_price - price_after_voucher, Decimal('0.00'))
                op.position.save()
            elif isinstance(op, self.AddFeeOperation):
                self.order.log_action('pretix.event.order.changed.addfee', user=self.user, auth=self.auth, data={
                    'fee': op.fee.pk,
                })
                op.fee.order = self.order
                op.fee._calculate_tax()
                op.fee.save()
            elif isinstance(op, self.FeeValueOperation):
                self.order.log_action('pretix.event.order.changed.feevalue', user=self.user, auth=self.auth, data={
                    'fee': op.fee.pk,
                    'old_price': op.fee.value,
                    'new_price': op.value.gross
                })
                op.fee.value = op.value.gross
                op.fee._calculate_tax()
                op.fee.save()
            elif isinstance(op, self.PriceOperation):
                self.order.log_action('pretix.event.order.changed.price', user=self.user, auth=self.auth, data={
                    'position': op.position.pk,
                    'positionid': op.position.positionid,
                    'old_price': op.position.price,
                    'addon_to': op.position.addon_to_id,
                    'new_price': op.price.gross
                })
                op.position.price = op.price.gross
                op.position.tax_rate = op.price.rate
                op.position.tax_value = op.price.tax
                op.position.save()
            elif isinstance(op, self.TaxRuleOperation):
                if isinstance(op.position, OrderPosition):
                    self.order.log_action('pretix.event.order.changed.tax_rule', user=self.user, auth=self.auth, data={
                        'position': op.position.pk,
                        'positionid': op.position.positionid,
                        'addon_to': op.position.addon_to_id,
                        'old_taxrule': op.position.tax_rule.pk if op.position.tax_rule else None,
                        'new_taxrule': op.tax_rule.pk
                    })
                elif isinstance(op.position, OrderFee):
                    self.order.log_action('pretix.event.order.changed.tax_rule', user=self.user, auth=self.auth, data={
                        'fee': op.position.pk,
                        'fee_type': op.position.fee_type,
                        'old_taxrule': op.position.tax_rule.pk if op.position.tax_rule else None,
                        'new_taxrule': op.tax_rule.pk
                    })
                op.position._calculate_tax(op.tax_rule)
                op.position.save()
            elif isinstance(op, self.CancelFeeOperation):
                self.order.log_action('pretix.event.order.changed.cancelfee', user=self.user, auth=self.auth, data={
                    'fee': op.fee.pk,
                    'fee_type': op.fee.fee_type,
                    'old_price': op.fee.value,
                })
                op.fee.canceled = True
                op.fee.save(update_fields=['canceled'])
            elif isinstance(op, self.CancelOperation):
                for gc in op.position.issued_gift_cards.all():
                    gc = GiftCard.objects.select_for_update().get(pk=gc.pk)
                    if gc.value < op.position.price:
                        raise OrderError(_(
                            'A position can not be canceled since the gift card {card} purchased in this order has '
                            'already been redeemed.').format(
                            card=gc.secret
                        ))
                    else:
                        gc.transactions.create(value=-op.position.price, order=self.order)

                for m in op.position.granted_memberships.with_usages().all():
                    m.canceled = True
                    m.save()

                for opa in op.position.addons.all():
                    for gc in opa.issued_gift_cards.all():
                        gc = GiftCard.objects.select_for_update().get(pk=gc.pk)
                        if gc.value < opa.position.price:
                            raise OrderError(_(
                                'A position can not be canceled since the gift card {card} purchased in this order has '
                                'already been redeemed.').format(
                                card=gc.secret
                            ))
                        else:
                            gc.transactions.create(value=-opa.position.price, order=self.order)

                    for m in opa.granted_memberships.with_usages().all():
                        m.canceled = True
                        m.save()

                    self.order.log_action('pretix.event.order.changed.cancel', user=self.user, auth=self.auth, data={
                        'position': opa.pk,
                        'positionid': opa.positionid,
                        'old_item': opa.item.pk,
                        'old_variation': opa.variation.pk if opa.variation else None,
                        'addon_to': opa.addon_to_id,
                        'old_price': opa.price,
                    })
                    opa.canceled = True
                    if opa.voucher:
                        Voucher.objects.filter(pk=opa.voucher.pk).update(redeemed=Greatest(0, F('redeemed') - 1))
                    assign_ticket_secret(
                        event=self.event, position=op.position, force_invalidate_if_revokation_list_used=True, force_invalidate=False, save=False
                    )
                    opa.save(update_fields=['canceled', 'secret'])
                self.order.log_action('pretix.event.order.changed.cancel', user=self.user, auth=self.auth, data={
                    'position': op.position.pk,
                    'positionid': op.position.positionid,
                    'old_item': op.position.item.pk,
                    'old_variation': op.position.variation.pk if op.position.variation else None,
                    'old_price': op.position.price,
                    'addon_to': None,
                })
                op.position.canceled = True
                if op.position.voucher:
                    Voucher.objects.filter(pk=op.position.voucher.pk).update(redeemed=Greatest(0, F('redeemed') - 1))
                assign_ticket_secret(
                    event=self.event, position=op.position, force_invalidate_if_revokation_list_used=True, force_invalidate=False, save=False
                )
                op.position.save(update_fields=['canceled', 'secret'])
            elif isinstance(op, self.AddOperation):
                pos = OrderPosition.objects.create(
                    item=op.item, variation=op.variation, addon_to=op.addon_to,
                    price=op.price.gross, order=self.order, tax_rate=op.price.rate,
                    tax_value=op.price.tax, tax_rule=op.item.tax_rule,
                    positionid=nextposid, subevent=op.subevent, seat=op.seat,
                    used_membership=op.membership,
                )
                nextposid += 1
                self.order.log_action('pretix.event.order.changed.add', user=self.user, auth=self.auth, data={
                    'position': pos.pk,
                    'item': op.item.pk,
                    'variation': op.variation.pk if op.variation else None,
                    'addon_to': op.addon_to.pk if op.addon_to else None,
                    'price': op.price.gross,
                    'positionid': pos.positionid,
                    'membership': pos.used_membership_id,
                    'subevent': op.subevent.pk if op.subevent else None,
                    'seat': op.seat.pk if op.seat else None,
                })
            elif isinstance(op, self.SplitOperation):
                split_positions.append(op.position)
            elif isinstance(op, self.RegenerateSecretOperation):
                assign_ticket_secret(
                    event=self.event, position=op.position, force_invalidate=True, save=True
                )
                tickets.invalidate_cache.apply_async(kwargs={'event': self.event.pk,
                                                             'order': self.order.pk})
                self.order.log_action('pretix.event.order.changed.secret', user=self.user, auth=self.auth, data={
                    'position': op.position.pk,
                    'positionid': op.position.positionid,
                })

        if split_positions:
            self.split_order = self._create_split_order(split_positions)

    def _create_split_order(self, split_positions):
        split_order = Order.objects.get(pk=self.order.pk)
        split_order.pk = None
        split_order.code = None
        split_order.datetime = now()
        split_order.secret = generate_secret()
        split_order.require_approval = self.order.require_approval and any(p.requires_approval(invoice_address=self._invoice_address) for p in split_positions)
        split_order.save()
        split_order.log_action('pretix.event.order.changed.split_from', user=self.user, auth=self.auth, data={
            'original_order': self.order.code
        })

        for op in split_positions:
            self.order.log_action('pretix.event.order.changed.split', user=self.user, auth=self.auth, data={
                'position': op.pk,
                'positionid': op.positionid,
                'old_item': op.item.pk,
                'old_variation': op.variation.pk if op.variation else None,
                'old_price': op.price,
                'new_order': split_order.code,
            })
            op.order = split_order
            assign_ticket_secret(
                self.event, position=op, force_invalidate=True,
            )
            op.save()

        try:
            ia = modelcopy(self.order.invoice_address)
            ia.pk = None
            ia.order = split_order
            ia.save()
        except InvoiceAddress.DoesNotExist:
            pass

        split_order.total = sum([p.price for p in split_positions if not p.canceled])

        for fee in self.order.fees.exclude(fee_type=OrderFee.FEE_TYPE_PAYMENT):
            new_fee = modelcopy(fee)
            new_fee.pk = None
            new_fee.order = split_order
            split_order.total += new_fee.value
            new_fee.save()

        if split_order.total != Decimal('0.00') and self.order.status != Order.STATUS_PAID:
            pp = self._get_payment_provider()
            if pp:
                payment_fee = pp.calculate_fee(split_order.total)
            else:
                payment_fee = Decimal('0.00')
            fee = split_order.fees.get_or_create(fee_type=OrderFee.FEE_TYPE_PAYMENT, defaults={'value': 0})[0]
            fee.value = payment_fee
            fee._calculate_tax()
            if payment_fee != 0:
                fee.save()
            elif fee.pk:
                fee.delete()
            split_order.total += fee.value

        remaining_total = sum([p.price for p in self.order.positions.all()]) + sum([f.value for f in self.order.fees.all()])
        offset_amount = min(max(0, self.completed_payment_sum - remaining_total), split_order.total)
        if offset_amount >= split_order.total:
            split_order.status = Order.STATUS_PAID
        else:
            split_order.status = Order.STATUS_PENDING
        split_order.save()

        if offset_amount > Decimal('0.00'):
            split_order.payments.create(
                state=OrderPayment.PAYMENT_STATE_CONFIRMED,
                amount=offset_amount,
                payment_date=now(),
                provider='offsetting',
                info=json.dumps({'orders': [self.order.code]})
            )
            self.order.refunds.create(
                state=OrderRefund.REFUND_STATE_DONE,
                amount=offset_amount,
                execution_date=now(),
                provider='offsetting',
                info=json.dumps({'orders': [split_order.code]})
            )

        if split_order.total != Decimal('0.00') and self.order.invoices.filter(is_cancellation=False).last():
            generate_invoice(split_order)

        order_split.send(sender=self.order.event, original=self.order, split_order=split_order)
        return split_order

    @cached_property
    def open_payment(self):
        lp = self.order.payments.last()
        if lp and lp.state not in (OrderPayment.PAYMENT_STATE_CONFIRMED,
                                   OrderPayment.PAYMENT_STATE_REFUNDED):
            return lp

    @cached_property
    def completed_payment_sum(self):
        payment_sum = self.order.payments.filter(
            state__in=(OrderPayment.PAYMENT_STATE_CONFIRMED, OrderPayment.PAYMENT_STATE_REFUNDED)
        ).aggregate(s=Sum('amount'))['s'] or Decimal('0.00')
        refund_sum = self.order.refunds.filter(
            state__in=(OrderRefund.REFUND_STATE_DONE, OrderRefund.REFUND_STATE_TRANSIT, OrderRefund.REFUND_STATE_DONE)
        ).aggregate(s=Sum('amount'))['s'] or Decimal('0.00')
        return payment_sum - refund_sum

    def _recalculate_total_and_payment_fee(self):
        total = sum([p.price for p in self.order.positions.all()]) + sum([f.value for f in self.order.fees.all()])
        payment_fee = Decimal('0.00')
        if self.open_payment:
            current_fee = Decimal('0.00')
            fee = None
            if self.open_payment.fee:
                fee = self.open_payment.fee
                if any(isinstance(op, (self.FeeValueOperation, self.CancelFeeOperation)) for op in self._operations):
                    fee.refresh_from_db()
                if not self.open_payment.fee.canceled:
                    current_fee = self.open_payment.fee.value
            total -= current_fee

            if fee and any([isinstance(op, self.FeeValueOperation) and op.fee == fee for op in self._operations]):
                # Do not automatically modify a fee that is being manually modified right now
                payment_fee = fee.value
            elif fee and any([isinstance(op, self.CancelFeeOperation) and op.fee == fee for op in self._operations]):
                # Do not automatically modify a fee that is being manually removed right now
                payment_fee = Decimal('0.00')
            elif self.order.pending_sum - current_fee != 0:
                prov = self.open_payment.payment_provider
                if prov:
                    payment_fee = prov.calculate_fee(total - self.completed_payment_sum)

            if payment_fee:
                fee = fee or OrderFee(fee_type=OrderFee.FEE_TYPE_PAYMENT, order=self.order)
                fee.value = payment_fee
                fee._calculate_tax()
                fee.save()
                if not self.open_payment.fee:
                    self.open_payment.fee = fee
                    self.open_payment.save(update_fields=['fee'])
            elif fee and not fee.canceled:
                fee.delete()

        self.order.total = total + payment_fee
        self.order.save()

    def _payment_fee_diff(self):
        total = self.order.total + self._totaldiff
        if self.open_payment:
            current_fee = Decimal('0.00')
            if self.open_payment and self.open_payment.fee:
                current_fee = self.open_payment.fee.value
            total -= current_fee

            # Do not change payment fees of paid orders
            payment_fee = Decimal('0.00')
            if self.order.pending_sum - current_fee != 0:
                prov = self.open_payment.payment_provider
                if prov:
                    payment_fee = prov.calculate_fee(total - self.completed_payment_sum)

                self._totaldiff += payment_fee - current_fee

    def _reissue_invoice(self):
        i = self.order.invoices.filter(is_cancellation=False).last()
        if self.reissue_invoice and self._invoice_dirty:
            if i and not i.refered.exists():
                self._invoices.append(generate_cancellation(i))
            if invoice_qualified(self.order) and \
                (i or
                 self.event.settings.invoice_generate == 'True' or (
                     self.open_payment is not None and self.event.settings.invoice_generate == 'paid' and
                     self.open_payment.payment_provider.requires_invoice_immediately)):
                self._invoices.append(generate_invoice(self.order))

    def _check_complete_cancel(self):
        current = self.order.positions.count()
        cancels = len([o for o in self._operations if isinstance(o, (self.CancelOperation, self.SplitOperation))])
        adds = len([o for o in self._operations if isinstance(o, self.AddOperation)])
        if current > 0 and current - cancels + adds < 1:
            raise OrderError(self.error_messages['complete_cancel'])

    @property
    def _invoice_address(self):
        try:
            return self.order.invoice_address
        except InvoiceAddress.DoesNotExist:
            return None

    def _check_and_lock_memberships(self):
        # To avoid duplicating all the logic around memberships, we simulate an application of all relevant
        # operations in a non-existing cart and then pass that to our cart checker.
        fake_cart = []
        positions_to_fake_cart = {}

        for p in self.order.positions.all():
            cp = CartPosition(
                item=p.item,
                variation=p.variation,
                attendee_name_parts=p.attendee_name_parts,
                used_membership=p.used_membership,
                subevent=p.subevent,
                seat=p.seat,
            )
            fake_cart.append(cp)
            positions_to_fake_cart[p] = cp

        for op in self._operations:
            if isinstance(op, self.ItemOperation):
                positions_to_fake_cart[op.position].item = op.item
                positions_to_fake_cart[op.position].variation = op.variation
            elif isinstance(op, self.SubeventOperation):
                positions_to_fake_cart[op.position].subevent = op.subevent
            elif isinstance(op, self.SeatOperation):
                positions_to_fake_cart[op.position].seat = op.seat
            elif isinstance(op, self.MembershipOperation):
                positions_to_fake_cart[op.position].used_membership = op.membership
            elif isinstance(op, self.CancelOperation):
                fake_cart.remove(positions_to_fake_cart[op.position])
            elif isinstance(op, self.AddOperation):
                cp = CartPosition(
                    item=op.item,
                    variation=op.variation,
                    used_membership=op.membership,
                    subevent=op.subevent,
                    seat=op.seat,
                )
                fake_cart.append(cp)
        try:
            validate_memberships_in_order(self.order.customer, fake_cart, self.event, lock=True, ignored_order=self.order, testmode=self.order.testmode)
        except ValidationError as e:
            raise OrderError(e.message)

    def commit(self, check_quotas=True):
        if self._committed:
            # an order change can only be committed once
            raise OrderError(error_messages['internal'])
        self._committed = True

        if not self._operations:
            # Do nothing
            return

        # Clear prefetched objects cache of order. We're going to modify the positions and fees and we have no guarantee
        # that every operation tuple points to a position/fee instance that has been fetched from the same object cache,
        # so it's dangerous to keep the cache around.
        self.order._prefetched_objects_cache = {}

        # finally, incorporate difference in payment fees
        self._payment_fee_diff()

        with transaction.atomic():
            with self.order.event.lock():
                if self.order.status in (Order.STATUS_PENDING, Order.STATUS_PAID):
                    if check_quotas:
                        self._check_quotas()
                    self._check_seats()
                self._check_complete_cancel()
                self._check_and_lock_memberships()
                try:
                    self._perform_operations()
                except TaxRule.SaleNotAllowed:
                    raise OrderError(self.error_messages['tax_rule_country_blocked'])
            self._recalculate_total_and_payment_fee()
            self._check_paid_price_change()
            self._check_paid_to_free()
            if self.order.status in (Order.STATUS_PENDING, Order.STATUS_PAID):
                self._reissue_invoice()
            self._clear_tickets_cache()
            self.order.touch()
            self.order.create_transactions()
            if self.split_order:
                self.split_order.create_transactions()

        if self.notify:
            notify_user_changed_order(
                self.order, self.user, self.auth,
                self._invoices if self.event.settings.invoice_email_attachment else []
            )
            if self.split_order:
                notify_user_changed_order(
                    self.split_order, self.user, self.auth,
                    list(self.split_order.invoices.all()) if self.event.settings.invoice_email_attachment else []
                )

        order_changed.send(self.order.event, order=self.order)

    def _clear_tickets_cache(self):
        tickets.invalidate_cache.apply_async(kwargs={'event': self.event.pk,
                                                     'order': self.order.pk})
        if self.split_order:
            tickets.invalidate_cache.apply_async(kwargs={'event': self.event.pk,
                                                         'order': self.split_order.pk})

    def _get_payment_provider(self):
        lp = self.order.payments.last()
        if not lp:
            return None
        pprov = lp.payment_provider
        if not pprov:
            return None
        return pprov


@app.task(base=ProfiledEventTask, bind=True, max_retries=5, default_retry_delay=1, throws=(OrderError,))
def perform_order(self, event: Event, payments: List[dict], positions: List[str],
                  email: str=None, locale: str=None, address: int=None, meta_info: dict=None,
                  sales_channel: str='web', shown_total=None, customer=None):
    with language(locale):
        try:
            try:
                return _perform_order(event, payments, positions, email, locale, address, meta_info,
                                      sales_channel, shown_total, customer)
            except LockTimeoutException:
                self.retry()
        except (MaxRetriesExceededError, LockTimeoutException):
            raise OrderError(str(error_messages['busy']))


_unset = object()


def _try_auto_refund(order, auto_refund=True, manual_refund=False, allow_partial=False,
                     source=OrderRefund.REFUND_SOURCE_BUYER,
                     refund_as_giftcard=False, giftcard_expires=_unset, giftcard_conditions=None, comment=None):
    notify_admin = False
    error = False
    if isinstance(order, int):
        order = Order.objects.get(pk=order)
    refund_amount = order.pending_sum * -1
    if refund_amount <= Decimal('0.00'):
        return

    can_auto_refund_sum = 0

    if refund_as_giftcard:
        can_auto_refund_sum = refund_amount
        with transaction.atomic():
            giftcard = order.event.organizer.issued_gift_cards.create(
                expires=order.event.organizer.default_gift_card_expiry if giftcard_expires is _unset else giftcard_expires,
                conditions=giftcard_conditions,
                currency=order.event.currency,
                testmode=order.testmode
            )
            giftcard.log_action('pretix.giftcards.created', data={})
            r = order.refunds.create(
                order=order,
                payment=None,
                source=source,
                comment=comment,
                state=OrderRefund.REFUND_STATE_CREATED,
                execution_date=now(),
                amount=can_auto_refund_sum,
                provider='giftcard',
                info=json.dumps({
                    'gift_card': giftcard.pk
                })
            )
            try:
                r.payment_provider.execute_refund(r)
            except PaymentException as e:
                with transaction.atomic():
                    r.state = OrderRefund.REFUND_STATE_FAILED
                    r.save()
                    order.log_action('pretix.event.order.refund.failed', {
                        'local_id': r.local_id,
                        'provider': r.provider,
                        'error': str(e)
                    })
                error = True
                notify_admin = True
            else:
                if r.state != OrderRefund.REFUND_STATE_DONE:
                    notify_admin = True

    elif auto_refund:
        proposals = order.propose_auto_refunds(refund_amount)
        can_auto_refund_sum = sum(proposals.values())
        if (allow_partial and can_auto_refund_sum) or can_auto_refund_sum == refund_amount:
            for p, value in proposals.items():
                with transaction.atomic():
                    r = order.refunds.create(
                        payment=p,
                        source=source,
                        state=OrderRefund.REFUND_STATE_CREATED,
                        amount=value,
                        comment=comment,
                        provider=p.provider
                    )
                    order.log_action('pretix.event.order.refund.created', {
                        'local_id': r.local_id,
                        'provider': r.provider,
                    })

                try:
                    r.payment_provider.execute_refund(r)
                except PaymentException as e:
                    with transaction.atomic():
                        r.state = OrderRefund.REFUND_STATE_FAILED
                        r.save()
                        order.log_action('pretix.event.order.refund.failed', {
                            'local_id': r.local_id,
                            'provider': r.provider,
                            'error': str(e)
                        })
                    error = True
                    notify_admin = True
                else:
                    if r.state not in (OrderRefund.REFUND_STATE_TRANSIT, OrderRefund.REFUND_STATE_DONE):
                        notify_admin = True

    if refund_amount - can_auto_refund_sum > Decimal('0.00'):
        if manual_refund:
            with transaction.atomic():
                r = order.refunds.create(
                    source=source,
                    comment=comment,
                    state=OrderRefund.REFUND_STATE_CREATED,
                    amount=refund_amount - can_auto_refund_sum,
                    provider='manual'
                )
                order.log_action('pretix.event.order.refund.created', {
                    'local_id': r.local_id,
                    'provider': r.provider,
                })
        else:
            notify_admin = True

    if notify_admin:
        order.log_action('pretix.event.order.refund.requested')
    if error:
        raise OrderError(
            _(
                'There was an error while trying to send the money back to you. Please contact the event organizer '
                'for further information.')
        )


@app.task(base=ProfiledTask, bind=True, max_retries=5, default_retry_delay=1, throws=(OrderError,))
@scopes_disabled()
def cancel_order(self, order: int, user: int=None, send_mail: bool=True, api_token=None, oauth_application=None,
                 device=None, cancellation_fee=None, try_auto_refund=False, refund_as_giftcard=False,
                 email_comment=None, refund_comment=None, cancel_invoice=True):
    try:
        try:
            ret = _cancel_order(order, user, send_mail, api_token, device, oauth_application,
                                cancellation_fee, cancel_invoice=cancel_invoice, comment=email_comment)
            if try_auto_refund:
                _try_auto_refund(order, refund_as_giftcard=refund_as_giftcard,
                                 comment=refund_comment)
            return ret
        except LockTimeoutException:
            self.retry()
    except (MaxRetriesExceededError, LockTimeoutException):
        raise OrderError(error_messages['busy'])


def change_payment_provider(order: Order, payment_provider, amount=None, new_payment=None, create_log=True,
                            recreate_invoices=True):
    if not get_connection().in_atomic_block:
        raise Exception('change_payment_provider should only be called in atomic transaction!')

    oldtotal = order.total
    e = OrderPayment.objects.filter(fee=OuterRef('pk'), state__in=(OrderPayment.PAYMENT_STATE_CONFIRMED,
                                                                   OrderPayment.PAYMENT_STATE_REFUNDED))
    open_fees = list(
        order.fees.annotate(has_p=Exists(e)).filter(
            Q(fee_type=OrderFee.FEE_TYPE_PAYMENT) & ~Q(has_p=True)
        )
    )
    if open_fees:
        fee = open_fees[0]
        if len(open_fees) > 1:
            for f in open_fees[1:]:
                f.delete()
    else:
        fee = OrderFee(fee_type=OrderFee.FEE_TYPE_PAYMENT, value=Decimal('0.00'), order=order)
    old_fee = fee.value

    new_fee = payment_provider.calculate_fee(
        order.pending_sum - old_fee if amount is None else amount
    )
    if new_fee:
        fee.value = new_fee
        fee.internal_type = payment_provider.identifier
        fee._calculate_tax()
        fee.save()
    else:
        if fee.pk:
            fee.delete()
        fee = None

    open_payment = None
    if new_payment:
        lp = order.payments.select_for_update().exclude(pk=new_payment.pk).last()
    else:
        lp = order.payments.select_for_update().last()

    if lp and lp.state in (OrderPayment.PAYMENT_STATE_PENDING, OrderPayment.PAYMENT_STATE_CREATED):
        open_payment = lp

    if open_payment:
        try:
            open_payment.payment_provider.cancel_payment(open_payment)
            order.log_action('pretix.event.order.payment.canceled', {
                'local_id': open_payment.local_id,
                'provider': open_payment.provider,
            })
        except PaymentException as e:
            order.log_action(
                'pretix.event.order.payment.canceled.failed',
                {
                    'local_id': open_payment.local_id,
                    'provider': open_payment.provider,
                    'error': str(e)
                },
            )

    order.total = (order.positions.aggregate(sum=Sum('price'))['sum'] or 0) + (order.fees.aggregate(sum=Sum('value'))['sum'] or 0)
    order.save(update_fields=['total'])

    if not new_payment:
        new_payment = order.payments.create(
            state=OrderPayment.PAYMENT_STATE_CREATED,
            provider=payment_provider.identifier,
            amount=order.pending_sum,
            fee=fee
        )
    if create_log and new_payment:
        order.log_action(
            'pretix.event.order.payment.changed' if open_payment else 'pretix.event.order.payment.started',
            {
                'fee': new_fee,
                'old_fee': old_fee,
                'provider': payment_provider.identifier,
                'payment': new_payment.pk,
                'local_id': new_payment.local_id,
            }
        )

    if recreate_invoices:
        i = order.invoices.filter(is_cancellation=False).last()
        if i and order.total != oldtotal and not i.canceled:
            generate_cancellation(i)
            generate_invoice(order)

    order.create_transactions()
    return old_fee, new_fee, fee, new_payment


@receiver(order_paid, dispatch_uid="pretixbase_order_paid_giftcards")
@receiver(order_changed, dispatch_uid="pretixbase_order_changed_giftcards")
@transaction.atomic()
def signal_listener_issue_giftcards(sender: Event, order: Order, **kwargs):
    if order.status != Order.STATUS_PAID:
        return
    any_giftcards = False
    for p in order.positions.all():
        if p.item.issue_giftcard:
            issued = Decimal('0.00')
            for gc in p.issued_gift_cards.all():
                issued += gc.transactions.first().value
            if p.price - issued > 0:
                gc = sender.organizer.issued_gift_cards.create(
                    currency=sender.currency, issued_in=p, testmode=order.testmode,
                    expires=sender.organizer.default_gift_card_expiry,
                )
                gc.transactions.create(value=p.price - issued, order=order)
                any_giftcards = True
                p.secret = gc.secret
                p.save(update_fields=['secret'])

    if any_giftcards:
        tickets.invalidate_cache.apply_async(kwargs={'event': sender.pk, 'order': order.pk})


@receiver(order_paid, dispatch_uid="pretixbase_order_paid_memberships")
@receiver(order_changed, dispatch_uid="pretixbase_order_changed_memberships")
@transaction.atomic()
def signal_listener_issue_memberships(sender: Event, order: Order, **kwargs):
    if order.status != Order.STATUS_PAID or not order.customer:
        return
    for p in order.positions.all():
        if p.item.grant_membership_type_id:
            create_membership(order.customer, p)