from django.db import models
from django.db.models import F
from django.db.models.expressions import Window
from django.db.models.functions import Lower, Rank, RowNumber


class Version(models.Model):
    name = models.CharField(max_length=50, unique=True)
    created_at = models.DateTimeField(auto_now_add=True)

    def __str__(self) -> str:
        return self.name


class ScoreQuerySet(models.QuerySet):
    def best_per_username(self) -> "ScoreQuerySet":
        """Keep only each user's highest score, matching usernames case-insensitively.

        Lower scores are excluded from the result but remain in the database.
        """
        best_ids = (
            self.alias(
                _row=Window(
                    expression=RowNumber(),
                    partition_by=Lower("username"),
                    order_by=[F("points").desc(), F("created_at").asc()],
                )
            )
            .filter(_row=1)
            .values_list("pk", flat=True)
        )
        return self.filter(pk__in=best_ids)

    def with_rank(self) -> "ScoreQuerySet":
        return self.annotate(
            rank=Window(
                expression=Rank(),
                order_by=F("points").desc(),
            )
        )


class ScoreManager(models.Manager.from_queryset(ScoreQuerySet)):
    def get_queryset(self) -> ScoreQuerySet:
        return super().get_queryset().select_related("version")


class Score(models.Model):
    username = models.CharField(max_length=100)
    points = models.IntegerField()
    version = models.ForeignKey(Version, on_delete=models.PROTECT, related_name="scores")
    created_at = models.DateTimeField(auto_now_add=True)

    objects = ScoreManager()

    class Meta:
        ordering = ["-points"]

    def __str__(self) -> str:
        return f"{self.username}: {self.points}"