''' PROCEED WITH CAUTION: this permanently deletes book data '''
from django.core.management.base import BaseCommand
from django.db.models import Count, Q
from bookwyrm import models


def remove_editions():
    ''' combine duplicate editions and update related models '''
    # not in use
    filters = {'%s__isnull' % r.name: True \
        for r in models.Edition._meta.related_objects}
    # no cover, no identifying fields
    filters['cover'] = ''
    null_fields = {'%s__isnull' % f: True for f in \
        ['isbn_10', 'isbn_13', 'oclc_number']}

    editions = models.Edition.objects.filter(
        Q(languages=[]) | Q(languages__contains=['English']),
        **filters, **null_fields
    ).annotate(Count('parent_work__editions')).filter(
        # mustn't be the only edition for the work
        parent_work__editions__count__gt=1
    )
    print(editions.count())
    editions.delete()


class Command(BaseCommand):
    ''' dedplucate allllll the book data models '''
    help = 'merges duplicate book data'
    # pylint: disable=no-self-use,unused-argument
    def handle(self, *args, **options):
        ''' run deudplications '''
        remove_editions()