from django.core.exceptions import ValidationError
from django.db import models
from django.utils.translation import gettext_lazy as _

from .program import Program


__all__ = (
    "Rerun",
    "RerunQuerySet",
)


class RerunQuerySet(models.QuerySet):
    """Queryset for Rerun (sub)classes."""

    def station(self, station=None, id=None):
        return (
            self.filter(program__station=station)
            if id is None
            else self.filter(program__station__id=id)
        )

    def program(self, program=None, id=None):
        return (
            self.filter(program=program)
            if id is None
            else self.filter(program__id=id)
        )

    def rerun(self):
        return self.filter(initial__isnull=False)

    def initial(self):
        return self.filter(initial__isnull=True)


class Rerun(models.Model):
    """Abstract model offering rerun facilities.

    Assume `start` is a datetime field or attribute implemented by
    subclass.
    """

    program = models.ForeignKey(
        Program,
        models.CASCADE,
        db_index=True,
        verbose_name=_("related program"),
    )
    initial = models.ForeignKey(
        "self",
        models.SET_NULL,
        related_name="rerun_set",
        verbose_name=_("rerun of"),
        limit_choices_to={"initial__isnull": True},
        blank=True,
        null=True,
        db_index=True,
    )

    objects = RerunQuerySet.as_manager()

    class Meta:
        abstract = True

    @property
    def is_initial(self):
        return self.initial is None

    @property
    def is_rerun(self):
        return self.initial is not None

    def get_initial(self):
        """Return the initial schedule (self or initial)"""
        return self if self.initial is None else self.initial.get_initial()

    def clean(self):
        super().clean()
        if (
            hasattr(self, "start")
            and self.initial is not None
            and self.initial.start >= self.start
        ):
            raise ValidationError(
                {"initial": _("rerun must happen after original")}
            )

    def save_rerun(self):
        self.program = self.initial.program

    def save_initial(self):
        pass

    def save(self, *args, **kwargs):
        if self.initial is not None:
            self.initial = self.initial.get_initial()
        if self.initial == self:
            self.initial = None

        if self.is_rerun:
            self.save_rerun()
        else:
            self.save_initial()
        super().save(*args, **kwargs)