from django.db import models
from django.contrib.contenttypes.fields import GenericForeignKey
from django.contrib.contenttypes.models import ContentType
from django.utils.text import slugify

class SlugHistory(models.Model):
    """
    Model for tracking slug changes across all models that use slugs.
    Uses generic relations to work with any model.
    """
    content_type = models.ForeignKey(ContentType, on_delete=models.CASCADE)
    object_id = models.CharField(max_length=50)  # Using CharField to work with our custom IDs
    content_object = GenericForeignKey('content_type', 'object_id')
    
    old_slug = models.SlugField(max_length=200)
    created_at = models.DateTimeField(auto_now_add=True)

    class Meta:
        indexes = [
            models.Index(fields=['content_type', 'object_id']),
            models.Index(fields=['old_slug']),
        ]
        verbose_name_plural = 'Slug histories'
        ordering = ['-created_at']

    def __str__(self):
        return f"Old slug '{self.old_slug}' for {self.content_object}"

class SluggedModel(models.Model):
    """
    Abstract base model that provides slug functionality with history tracking.
    """
    name = models.CharField(max_length=200)
    slug = models.SlugField(max_length=200, unique=True)

    class Meta:
        abstract = True

    def save(self, *args, **kwargs):
        # Get the current instance from DB if it exists
        if self.pk:
            try:
                old_instance = self.__class__.objects.get(pk=self.pk)
                # If slug has changed, save the old one to history
                if old_instance.slug != self.slug:
                    SlugHistory.objects.create(
                        content_type=ContentType.objects.get_for_model(self),
                        object_id=getattr(self, self.get_id_field_name()),
                        old_slug=old_instance.slug
                    )
            except self.__class__.DoesNotExist:
                pass

        # Generate slug if not set
        if not self.slug:
            self.slug = slugify(self.name)

        super().save(*args, **kwargs)

    def get_id_field_name(self):
        """
        Returns the name of the read-only ID field for this model.
        Should be overridden by subclasses.
        """
        raise NotImplementedError(
            "Subclasses of SluggedModel must implement get_id_field_name()"
        )

    @classmethod
    def get_by_slug(cls, slug):
        """
        Get an object by its current or historical slug.
        Returns (object, is_old_slug) tuple.
        """
        try:
            # Try to get by current slug first
            return cls.objects.get(slug=slug), False
        except cls.DoesNotExist:
            # Try to find in slug history
            history = SlugHistory.objects.filter(
                content_type=ContentType.objects.get_for_model(cls),
                old_slug=slug
            ).order_by('-created_at').first()
            
            if history:
                return cls.objects.get(
                    **{cls.get_id_field_name(): history.object_id}
                ), True
            
            raise cls.DoesNotExist(
                f"{cls.__name__} with slug '{slug}' does not exist"
            )