"""Signal handlers for the submissions app.

The cleanup story (plan.md §7.6): when a `Submission` row is deleted --
manually, via `cleanup_stale`, or for any other reason -- the uploaded
`.stl` file must also be unlinked from `MEDIA_ROOT`. Django's `FileField`
does NOT do this automatically (the behaviour was removed in 1.3, ages
ago), so we wire a `post_delete` signal to take care of it.
"""

from __future__ import annotations

from django.db.models.signals import post_delete
from django.dispatch import receiver

from .models import Submission


@receiver(post_delete, sender=Submission)
def unlink_stl_file_on_delete(sender, instance: Submission, **kwargs) -> None:
    """Remove the on-disk `.stl` after a Submission row is deleted.

    `FileField.delete(save=False)` is idempotent: it just calls
    `Storage.delete(name)`, and `FileSystemStorage.delete` catches
    `FileNotFoundError`. Safe to call on rows that never had a file
    (e.g. URL-source submissions) -- the `if instance.stl_file` truthiness
    check handles that.
    """
    if instance.stl_file:
        instance.stl_file.delete(save=False)