refactor: add dimensions to thumbnails in Image REST API

Any frontend will need the dimensions of the supplied thumbnails
to select the appropriate thumbnail in different rendering contexts.

Apart from that the thumbnail name is not that helpful, as we need
the full thumbnail URL to be able to display it.

program/serializers.py

@@ -18,7 +18,7 @@
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #
 
-from typing import List
+from typing import List, TypedDict
 
 from rest_framework import serializers
 
@@ -197,18 +197,31 @@ class HostLinkSerializer(serializers.ModelSerializer):
         fields = ("type", "url")
 
 
+class Thumbnail(TypedDict):
+    width: float
+    height: float
+    url: str
+
+
 class ImageSerializer(serializers.ModelSerializer):
     ppoi = serializers.CharField(max_length=20)  # PPOIField max_length
     thumbnails = serializers.SerializerMethodField()
 
     @staticmethod
-    def get_thumbnails(instance) -> List[str]:
+    def get_thumbnails(instance) -> List[Thumbnail]:
         """Returns thumbnails"""
         thumbnails = []
 
         if instance.image.name and THUMBNAIL_SIZES:
             for size in THUMBNAIL_SIZES:
-                thumbnails.append(instance.image.crop[size].name)
+                [width, height] = size.split("x")
+                thumbnails.append(
+                    {
+                        "width": int(width),
+                        "height": int(height),
+                        "url": instance.image.crop[size].url,
+                    }
+                )
 
         return thumbnails