Show PDF thumbnail on artifact admin change form (#1380)

website/admin/artifact_admin.py

@@ -1,8 +1,11 @@
 from django.contrib import admin
 from website.models import Artifact
 from django.contrib.admin import widgets
+from django.utils.html import format_html
 from sortedm2m_filter_horizontal_widget.forms import SortedFilteredSelectMultiple
 from website.utils.upload_validators import PDF_EXTENSIONS, RAW_FILE_EXTENSIONS
+from easy_thumbnails.files import get_thumbnailer
+import os
 import logging
 
 # This retrieves a Python logging instance (or creates it)
@@ -38,6 +41,10 @@ class Media:
     # (Django auto-applies DISTINCT for the M2M join). Subclasses may extend this.
     search_fields = ['title', 'forum_name', 'authors__first_name', 'authors__last_name']
 
+    # thumbnail_preview is a computed, read-only display (see below). It must be
+    # listed here so Django allows it in get_fieldsets() on the change form.
+    readonly_fields = ('thumbnail_preview',)
+
     fieldsets = [
         (None,                      {'fields': ['title', 'authors', 'date']}),
         ('Files',                   {'fields': ['pdf_file', 'raw_file']}),
@@ -46,6 +53,72 @@ class Media:
         ('Keyword Info',            {'fields': ['keywords']}),
     ]
 
+    # Height (px) of the change-form thumbnail preview image.
+    THUMBNAIL_PREVIEW_HEIGHT = 220
+
+    def thumbnail_preview(self, obj):
+        """
+        Read-only image preview of the artifact's auto-generated ``thumbnail``,
+        shown on the change form so editors can confirm the correct PDF is
+        attached (the form otherwise only shows the "Currently: ..." filename).
+
+        Renders an ``<img>`` (~220px tall) via easy_thumbnails — the same
+        pipeline as the changelist ``get_display_thumbnail`` in TalkAdmin /
+        PublicationAdmin. Degrades to a text placeholder when there is no
+        thumbnail yet or the source file is missing on disk (which happens on
+        the servers), rather than 500ing the whole change page.
+        """
+        placeholder = format_html(
+            '<span style="color:#666;">Save with a PDF attached to generate a thumbnail.</span>'
+        )
+        if obj is None or not obj.thumbnail:
+            return placeholder
+        try:
+            if not os.path.isfile(obj.thumbnail.path):
+                return placeholder
+            thumbnailer = get_thumbnailer(obj.thumbnail)
+            # (0, H) constrains height to H and lets width scale with the
+            # source aspect ratio (no crop — show the whole thumbnail).
+            thumbnail_url = thumbnailer.get_thumbnail(
+                {'size': (0, self.THUMBNAIL_PREVIEW_HEIGHT)}
+            ).url
+        except Exception:
+            _logger.exception(
+                "Could not render thumbnail preview for artifact=%s",
+                getattr(obj, 'pk', None),
+            )
+            return placeholder
+        return format_html(
+            '<img src="{}" alt="PDF thumbnail" '
+            'style="height:{}px; width:auto; border:1px solid #ddd;" />',
+            thumbnail_url, self.THUMBNAIL_PREVIEW_HEIGHT,
+        )
+
+    # Django auto-appends the trailing colon in the admin label.
+    thumbnail_preview.short_description = 'PDF thumbnail'
+
+    def get_fieldsets(self, request, obj=None):
+        """
+        Inject the read-only ``thumbnail_preview`` into the 'Files' fieldset on
+        the change form only. Done here (rather than in each child admin's
+        ``fieldsets``) so Publication / Talk / Poster all get the preview.
+        On the Add form there is no saved thumbnail yet, so it is omitted.
+        """
+        fieldsets = super().get_fieldsets(request, obj)
+        if obj is None:
+            return fieldsets
+        # Build new tuples/dicts rather than mutating the class-level fieldsets
+        # (ModelAdmin.get_fieldsets returns self.fieldsets by reference).
+        updated = []
+        for name, opts in fieldsets:
+            if name == 'Files':
+                fields = list(opts.get('fields', []))
+                if 'thumbnail_preview' not in fields:
+                    fields = fields + ['thumbnail_preview']
+                opts = {**opts, 'fields': fields}
+            updated.append((name, opts))
+        return updated
+
     def get_form(self, request, obj=None, **kwargs):
         """
         Seed the ``accept`` attribute on the file inputs from the same extension

website/tests/test_admin_thumbnail_preview.py

@@ -0,0 +1,127 @@
+"""
+Regression tests for the artifact thumbnail preview on the admin *change form*
+(#1380).
+
+``ArtifactAdmin.thumbnail_preview`` renders a read-only <img> of the artifact's
+auto-generated ``thumbnail`` so editors can confirm the right PDF is attached.
+``get_fieldsets`` injects it into the 'Files' fieldset on the change form (only)
+for all three artifact admins (Publication / Talk / Poster).
+
+Attaching a thumbnail: factory artifacts carry only a *stub* PDF, so
+Artifact.save()'s ImageMagick step can't generate a real thumbnail. We write a
+valid 1x1 GIF straight to storage and point the field at it (same trick as
+test_thumbnail_preview.py for the #840 card), so easy_thumbnails has a real
+source.
+"""
+
+from django.contrib.auth.models import User
+from django.core.files.base import ContentFile
+from django.core.files.storage import default_storage
+from django.urls import reverse
+
+from website.models import Poster, Publication, Talk
+from website.admin.admin_site import ml_admin_site
+from website.admin.poster_admin import PosterAdmin
+from website.admin.publication_admin import PublicationAdmin
+from website.admin.talk_admin import TalkAdmin
+from website.tests.base import DatabaseTestCase
+from website.tests.factories import PosterFactory, _GIF_1PX
+
+
+class ArtifactThumbnailPreviewTests(DatabaseTestCase):
+    def _attach_thumbnail(self, artifact):
+        """Give ``artifact`` a real (1x1 GIF) thumbnail without re-running
+        Artifact.save(): write the file via default storage at the artifact's
+        own thumbnail path, then persist the field name with an UPDATE."""
+        rel_path = artifact.get_upload_thumbnail_dir(f"admin_preview_{artifact.pk}.gif")
+        saved_name = default_storage.save(rel_path, ContentFile(_GIF_1PX))
+        type(artifact).objects.filter(pk=artifact.pk).update(thumbnail=saved_name)
+        artifact.refresh_from_db()
+        return artifact
+
+    def test_preview_renders_img_when_thumbnail_present(self):
+        poster = self._attach_thumbnail(PosterFactory(authors=[self.make_person()]))
+        admin = PosterAdmin(Poster, ml_admin_site)
+
+        html = admin.thumbnail_preview(poster)
+
+        self.assertIn("<img", html)
+        self.assertIn(default_storage.url(poster.thumbnail.name).rsplit("/", 1)[0], html)
+        self.assertIn("height:220px", html)
+
+    def test_preview_is_placeholder_when_no_thumbnail(self):
+        poster = PosterFactory(authors=[self.make_person()])  # stub PDF → no thumbnail
+        admin = PosterAdmin(Poster, ml_admin_site)
+
+        html = admin.thumbnail_preview(poster)
+
+        self.assertNotIn("<img", html)
+        self.assertIn("Save with a PDF", html)
+
+    def test_preview_degrades_when_source_file_missing(self):
+        """Thumbnail field set but the file is gone from disk (happens on the
+        servers) → placeholder, not a 500."""
+        poster = self._attach_thumbnail(PosterFactory(authors=[self.make_person()]))
+        default_storage.delete(poster.thumbnail.name)
+
+        admin = PosterAdmin(Poster, ml_admin_site)
+        html = admin.thumbnail_preview(poster)
+
+        self.assertNotIn("<img", html)
+        self.assertIn("Save with a PDF", html)
+
+    def test_preview_handles_none_obj(self):
+        admin = PosterAdmin(Poster, ml_admin_site)
+        # get_fieldsets passes the saved obj, but be defensive.
+        self.assertIn("Save with a PDF", admin.thumbnail_preview(None))
+
+    def _files_fields(self, admin, obj):
+        for name, opts in admin.get_fieldsets(request=None, obj=obj):
+            if name == "Files":
+                return list(opts.get("fields", []))
+        return []
+
+    def test_get_fieldsets_injects_preview_on_change_for_all_admins(self):
+        cases = (
+            (PublicationAdmin, Publication, self.make_publication()),
+            (TalkAdmin, Talk, self.make_talk()),
+            (PosterAdmin, Poster, PosterFactory(authors=[self.make_person()])),
+        )
+        for admin_cls, model, obj in cases:
+            admin = admin_cls(model, ml_admin_site)
+            change_fields = self._files_fields(admin, obj)
+            self.assertIn(
+                "thumbnail_preview", change_fields,
+                f"{admin_cls.__name__} change form should show the preview",
+            )
+
+    def test_get_fieldsets_omits_preview_on_add(self):
+        admin = PublicationAdmin(Publication, ml_admin_site)
+        add_fields = self._files_fields(admin, obj=None)
+        self.assertNotIn("thumbnail_preview", add_fields)
+
+    def test_change_form_get_renders_img_end_to_end(self):
+        """Full change-form GET through the admin: the readonly preview must
+        render the <img> as real (unescaped) HTML, not as escaped text."""
+        poster = self._attach_thumbnail(PosterFactory(authors=[self.make_person()]))
+        User.objects.create_superuser("admin", "admin@example.com", "pw")
+        self.client.force_login(User.objects.get(username="admin"))
+
+        url = reverse("admin:website_poster_change", args=[poster.pk])
+        resp = self.client.get(url)
+
+        self.assertEqual(resp.status_code, 200)
+        body = resp.content.decode()
+        self.assertIn('alt="PDF thumbnail"', body)
+        self.assertIn("<img", body)
+        # The tag is real markup, not escaped into visible text.
+        self.assertNotIn("&lt;img", body)
+
+    def test_get_fieldsets_does_not_mutate_class_fieldsets(self):
+        """Injecting the preview must not leak into the shared class-level
+        fieldsets (which would compound across requests)."""
+        admin = TalkAdmin(Talk, ml_admin_site)
+        admin.get_fieldsets(request=None, obj=self.make_talk())
+        for name, opts in TalkAdmin.fieldsets:
+            if name == "Files":
+                self.assertNotIn("thumbnail_preview", opts["fields"])