from django.conf import settings
from django.db import models

from apps.core.models import TimeStampedModel


class AuditLog(TimeStampedModel):
    """Append-oriented activity record. Updates and deletes are blocked in admin."""

    user = models.ForeignKey(
        settings.AUTH_USER_MODEL,
        null=True,
        blank=True,
        on_delete=models.SET_NULL,
        related_name="audit_logs",
    )
    action = models.CharField(max_length=80)
    module = models.CharField(max_length=40)
    object_type = models.CharField(max_length=80, blank=True)
    object_id = models.CharField(max_length=64, blank=True)
    object_repr = models.CharField(max_length=180, blank=True)
    previous_value = models.JSONField(null=True, blank=True)
    new_value = models.JSONField(null=True, blank=True)
    ip_address = models.GenericIPAddressField(null=True, blank=True)
    user_agent = models.CharField(max_length=255, blank=True)
    session_key = models.CharField(max_length=64, blank=True)

    class Meta:
        ordering = ["-created_at"]
        indexes = [
            models.Index(fields=["module", "action"]),
            models.Index(fields=["object_type", "object_id"]),
        ]

    def __str__(self):
        return f"{self.created_at:%Y-%m-%d %H:%M} · {self.action}"

    def save(self, *args, **kwargs):
        if self.pk:
            raise ValueError("Audit records cannot be modified.")
        super().save(*args, **kwargs)

    def delete(self, *args, **kwargs):
        raise ValueError("Audit records cannot be deleted.")