Infer extension from the background image

app/models/template.py

@@ -196,10 +196,16 @@ def build_custom_url(
         with suppress(IndexError):
             for index, text in enumerate(self.text):
                 text_lines[index] = text.normalize(text_lines[index])
+        if not extension and background:
+            url = furl(background)
+            extension = url.path.segments[-1].split(".")[-1]
         if extension not in settings.ALLOWED_EXTENSIONS:
             extension = settings.DEFAULT_EXTENSION
         if style == "default":
             style = ""
+        elif style == "animated":
+            extension = "gif"
+            style = ""
         url = request.app.url_for(
             "images.detail_text",
             template_id="custom" if self.id == "_custom" else self.id,

app/tests/test_views_images.py

@@ -427,6 +427,18 @@ def it_supports_custom_backgrounds(expect, client, as_json):
                 "?background=https://www.gstatic.com/webp/gallery/3.png"
             }
 
+        def it_returns_gif_when_background_is_gif(expect, client):
+            data = {
+                "background": "https://media.giphy.com/media/ICOgUNjpvO0PC/giphy.gif",
+                "text_lines[]": ["foo", "bar"],
+            }
+            request, response = client.post("/images/custom", data=data)
+            expect(response.status) == 201
+            expect(response.json) == {
+                "url": "http://localhost:5000/images/custom/foo/bar.gif"
+                "?background=https://media.giphy.com/media/ICOgUNjpvO0PC/giphy.gif"
+            }
+
         def it_redirects_if_requested(expect, client):
             data = {
                 "background": "https://www.gstatic.com/webp/gallery/4.png",

app/views/helpers.py

@@ -46,12 +46,7 @@ async def generate_url(
     background = utils.urls.arg(payload, "", "background", "image_url")
     extension = utils.urls.arg(payload, "", "extension")
 
-    if style == "animated":
-        extension = "gif"
-        style = ""
-
     status = 201
-
     if template_id:
         template: models.Template = models.Template.objects.get_or_create(template_id)
         url = template.build_custom_url(