class EmailDuplicatesFilter(SimpleListFilter):
    """
    Return user duplicates by email
    """
    title = _("Duplicates")
    parameter_name = 'duplicate_field'

    def lookups(self, request, model_admin):
        return (
            ('email', _('Email')),
        )

    def queryset(self, request, queryset):
        if self.value() == 'email':
            dups = (
                queryset
                .annotate(lower_email=Lower('email'))
                .values('lower_email')
                .annotate(count=Count('lower_email'))
                .values('lower_email', 'count')
                .filter(count__gt=1)
                .order_by('lower_email', 'count')
            )

            return (
                queryset
                .annotate(lower_email=Lower('email'))
                .filter(lower_email__in=[item['lower_email'] for item in dups])
                .order_by('lower_email')
            )