from typing import TypeVar
from django.db.models import Avg, OuterRef, IntegerField, Value, Subquery
from django.db.models.functions import Coalesce
from django.db import models


T = TypeVar('T')

class PublicationQuerySet(models.QuerySet[T]):
    def with_score(self):
        qs = self
        qs = qs.annotate(average_score=Coalesce(Avg("ratings__score"), 0.0))
        return qs
    
    def only_publish(self):
        from .models import Publication
        qs = self
        return qs.filter(status=Publication.StatusVarioations.PUBLIC.value)
    
    def with_user_score(self, user):
        from .models import Rating

        user_rating = Rating.objects.filter(
            publication=OuterRef("pk"),
            user=user
        ).values("score")[:1]

        return self.annotate(
            current_user_score=Coalesce(
                Subquery(user_rating, output_field=IntegerField()),
                Value(0)
            )
        )


class PublicationManager(models.Manager[T]):
    def get_queryset(self):
        return PublicationQuerySet[T](self.model, using=self._db).with_score()
    
    def with_related(self):
        return self.get_queryset().select_related('user', 'category')
    
    def with_user_score(self, user):
        return self.get_queryset().with_user_score(user)
    
    def only_publish(self):
        return self.get_queryset().only_publish()