J621/backend/apps/library/similarity.py

"""Ephemeral similarity checks.

A file lands in the media temp folder only long enough to answer "is this
already in the library, and what does it look like on e621?". Nothing is
indexed: files are deleted on startup, after the TTL, on request through the
API, and by `manage.py cleanup_similarity` (for cron).
"""

import logging
from datetime import timedelta
from pathlib import Path

from django.conf import settings
from django.utils import timezone
from rest_framework import mixins, status, viewsets
from rest_framework.decorators import action
from rest_framework.parsers import FormParser, JSONParser, MultiPartParser
from rest_framework.permissions import AllowAny, IsAuthenticated
from rest_framework.response import Response

from . import services
from .models import MediaItem, SimilarityCheck
from .serializers import SimilarityCheckSerializer
from .signing_urls import load_payload
from .tools import item_brief
from .uploads import find_library_matches

logger = logging.getLogger(__name__)

TTL_MINUTES = int(getattr(settings, "SIMILARITY_TTL_MINUTES", 30))


def purge_similarity_files():
    """Delete every stored temp file without touching the database.

    Safe to call during app startup (``AppConfig.ready``) — database rows are
    removed lazily by ``purge_expired`` and the cleanup command.
    """
    root = Path(settings.MEDIA_ROOT) / "similarity"
    if not root.exists():
        return 0
    deleted = 0
    for path in sorted(root.rglob("*")):
        if not path.is_file():
            continue
        try:
            path.unlink()
            deleted += 1
        except OSError as exc:  # noqa: PERF203 - keep going past locked files
            logger.warning("Could not delete %s: %s", path, exc)
    for path in sorted(root.rglob("*"), reverse=True):
        if path.is_dir():
            try:
                path.rmdir()
            except OSError:
                pass
    return deleted


def purge_similarity_checks(older_than=None):
    """Delete checks (rows and files). ``older_than=None`` wipes them all."""
    queryset = SimilarityCheck.objects.all()
    if older_than is not None:
        queryset = queryset.filter(created_at__lt=older_than)
    deleted = 0
    for check in queryset.iterator():
        if check.file:
            check.file.delete(save=False)
        check.delete()
        deleted += 1
    return deleted


def purge_expired():
    """Remove checks past the TTL; called lazily before creating new ones."""
    return purge_similarity_checks(timezone.now() - timedelta(minutes=TTL_MINUTES))


class SimilarityCheckViewSet(
    mixins.ListModelMixin,
    mixins.RetrieveModelMixin,
    mixins.DestroyModelMixin,
    viewsets.GenericViewSet,
):
    """Check an upload against the library — exact MD5 plus visual matches."""

    serializer_class = SimilarityCheckSerializer
    permission_classes = [IsAuthenticated]
    parser_classes = [MultiPartParser, FormParser, JSONParser]
    http_method_names = ["get", "post", "delete", "head", "options"]

    def get_queryset(self):
        queryset = SimilarityCheck.objects.all()
        user = self.request.user
        if not user.is_app_staff:
            queryset = queryset.filter(user=user)
        return queryset

    def create(self, request):
        upload = request.FILES.get("file")
        if upload is None:
            return Response(
                {"detail": "A file is required."}, status=status.HTTP_400_BAD_REQUEST
            )
        extension = Path(upload.name).suffix.lower()
        if extension not in services.ALLOWED_EXTENSIONS:
            return Response(
                {"detail": f"Unsupported file type: {extension or 'unknown'}"},
                status=status.HTTP_400_BAD_REQUEST,
            )

        purge_expired()
        check = SimilarityCheck.objects.create(
            user=request.user,
            file=upload,
            original_filename=upload.name,
            size=upload.size,
        )
        check.md5 = services.compute_md5(check.file.path)

        exact = MediaItem.objects.filter(md5=check.md5).first()
        matches = find_library_matches(
            check.file.path, limit=12, user=request.user, request=request
        )
        if exact is not None:
            exact_j_id = f"J-{exact.id}"
            matches = [
                match for match in matches if match.get("j_id") != exact_j_id
            ]
        check.results = {
            "exact": item_brief(exact, request) if exact is not None else None,
            "matches": matches,
        }
        check.save(update_fields=["md5", "results"])
        return Response(
            self.get_serializer(check).data, status=status.HTTP_201_CREATED
        )

    @action(
        detail=True,
        methods=["get", "head"],
        permission_classes=[AllowAny],
        throttle_classes=[],
    )
    def file(self, request, pk=None):
        """Serve the temp file; accepts a signed URL like staged uploads."""
        check = None
        if request.user.is_authenticated:
            check = self.get_queryset().filter(pk=pk).first()
        else:
            signature = request.query_params.get("sig")
            payload = load_payload(signature, services.UPLOAD_FILE_SALT) if signature else None
            if payload and payload.get("check") == str(pk):
                check = SimilarityCheck.objects.filter(pk=pk).first()
        if check is None or not check.file:
            return Response(
                {"detail": "Not found."}, status=status.HTTP_404_NOT_FOUND
            )
        return services.serve_file(request, check.file.path)