import contextlib

from django.db import transaction
from django.db.models import F, Q
from django.utils.timezone import now
from django_filters.rest_framework import (
    BooleanFilter, DjangoFilterBackend, FilterSet,
)
from django_scopes import scopes_disabled
from rest_framework import status, viewsets
from rest_framework.decorators import action
from rest_framework.exceptions import PermissionDenied
from rest_framework.filters import OrderingFilter
from rest_framework.response import Response

from pretix.api.serializers.voucher import VoucherSerializer
from pretix.base.models import Voucher

with scopes_disabled():
    class VoucherFilter(FilterSet):
        active = BooleanFilter(method='filter_active')

        class Meta:
            model = Voucher
            fields = ['code', 'max_usages', 'redeemed', 'block_quota', 'allow_ignore_quota',
                      'price_mode', 'value', 'item', 'variation', 'quota', 'tag', 'subevent']

        def filter_active(self, queryset, name, value):
            if value:
                return queryset.filter(Q(redeemed__lt=F('max_usages')) &
                                       (Q(valid_until__isnull=True) | Q(valid_until__gt=now())))
            else:
                return queryset.filter(Q(redeemed__gte=F('max_usages')) |
                                       (Q(valid_until__isnull=False) & Q(valid_until__lte=now())))


class VoucherViewSet(viewsets.ModelViewSet):
    serializer_class = VoucherSerializer
    queryset = Voucher.objects.none()
    filter_backends = (DjangoFilterBackend, OrderingFilter)
    ordering = ('id',)
    ordering_fields = ('id', 'code', 'max_usages', 'valid_until', 'value')
    filterset_class = VoucherFilter
    permission = 'can_view_vouchers'
    write_permission = 'can_change_vouchers'

    def get_queryset(self):
        return self.request.event.vouchers.all()

    def _predict_quota_check(self, data, instance):
        # This method predicts if Voucher.clean_quota_needs_checking
        # *migh* later require a quota check. It is only approximate
        # and returns True a little too often. The point is to avoid
        # locks when we know we won't need them.
        if 'allow_ignore_quota' in data and data.get('allow_ignore_quota'):
            return False
        if instance and 'allow_ignore_quota' not in data and instance.allow_ignore_quota:
            return False

        if 'block_quota' in data and not data.get('block_quota'):
            return False
        if instance and 'block_quota' not in data and not instance.block_quota:
            return False

        return True

    def create(self, request, *args, **kwargs):
        if self._predict_quota_check(request.data, None):
            lockfn = request.event.lock
        else:
            lockfn = contextlib.suppress  # noop context manager
        with lockfn():
            return super().create(request, *args, **kwargs)

    def perform_create(self, serializer):
        serializer.save(event=self.request.event)
        serializer.instance.log_action(
            'pretix.voucher.added',
            user=self.request.user,
            auth=self.request.auth,
            data=self.request.data
        )

    def get_serializer_context(self):
        ctx = super().get_serializer_context()
        ctx['event'] = self.request.event
        return ctx

    def update(self, request, *args, **kwargs):
        if self._predict_quota_check(request.data, self.get_object()):
            lockfn = request.event.lock
        else:
            lockfn = contextlib.suppress  # noop context manager
        with lockfn():
            return super().update(request, *args, **kwargs)

    def perform_update(self, serializer):
        serializer.save(event=self.request.event)
        serializer.instance.log_action(
            'pretix.voucher.changed',
            user=self.request.user,
            auth=self.request.auth,
            data=self.request.data
        )

    def perform_destroy(self, instance):
        if not instance.allow_delete():
            raise PermissionDenied('This voucher can not be deleted as it has already been used.')

        instance.log_action(
            'pretix.voucher.deleted',
            user=self.request.user,
            auth=self.request.auth,
        )
        with transaction.atomic():
            instance.cartposition_set.filter(addon_to__isnull=False).delete()
            instance.cartposition_set.all().delete()
            super().perform_destroy(instance)

    @action(detail=False, methods=['POST'])
    def batch_create(self, request, *args, **kwargs):
        if any(self._predict_quota_check(d, None) for d in request.data):
            lockfn = request.event.lock
        else:
            lockfn = contextlib.suppress  # noop context manager
        with lockfn():
            serializer = self.get_serializer(data=request.data, many=True)
            serializer.is_valid(raise_exception=True)
            with transaction.atomic():
                serializer.save(event=self.request.event)
                for i, v in enumerate(serializer.instance):
                    v.log_action(
                        'pretix.voucher.added',
                        user=self.request.user,
                        auth=self.request.auth,
                        data=self.request.data[i]
                    )
        headers = self.get_success_headers(serializer.data)
        return Response(serializer.data, status=status.HTTP_201_CREATED, headers=headers)