import django_filters
from taggit.models import Tag


class NumericInFilter(django_filters.BaseInFilter, django_filters.NumberFilter):
    """
    Filters for a set of numeric values. Example: id__in=100,200,300
    """
    pass


class NullableCharFieldFilter(django_filters.CharFilter):
    """
    Allow matching on null field values by passing a special string used to signify NULL.
    """
    null_value = 'NULL'

    def filter(self, qs, value):
        if value != self.null_value:
            return super().filter(qs, value)
        qs = self.get_method(qs)(**{'{}__isnull'.format(self.name): True})
        return qs.distinct() if self.distinct else qs


class TagFilter(django_filters.ModelMultipleChoiceFilter):
    """
    Match on one or more assigned tags. If multiple tags are specified (e.g. ?tag=foo&tag=bar), the queryset is filtered
    to objects matching all tags.
    """
    def __init__(self, *args, **kwargs):

        kwargs.setdefault('field_name', 'tags__slug')
        kwargs.setdefault('to_field_name', 'slug')
        kwargs.setdefault('conjoined', True)
        kwargs.setdefault('queryset', Tag.objects.all())

        super().__init__(*args, **kwargs)
