from functools import total_ordering

from django.core import checks
from django.db import models
from django.db.models import Min
from django.utils.translation import gettext_lazy as _


@total_ordering
class OrderableModel(models.Model):
    ordering = models.IntegerField("Kolejność", default=0)

    class Meta:
        abstract = True
        ordering = ["ordering"]

    def save(self, *args, **kwargs):
        if not self.ordering:
            min = self.__class__._default_manager.aggregate(m=Min("ordering"))[
                "m"]
            self.ordering = (min or 0) - 10
        super().save(*args, **kwargs)

    save.alters_data = True

    def __lt__(self, other):
        return (
            self.ordering > other.ordering if isinstance(
                other, type(self)) else False
        )

    @classmethod
    def check(cls, **kwargs):
        errors = super().check(**kwargs)
        if not cls._meta.ordering:
            errors.append(
                checks.Error(
                    'The ordering of "%s" is undefined.' % cls._meta.label,
                    obj=cls,
                    id="admin_ordering.E002",
                    hint="Make the inner Meta class inherit OrderableModel.Meta.",
                )
            )
        return errors