Improved robustness of file downloads (#225)

lib/pinchflat/metadata/metadata_file_helpers.ex

@@ -54,24 +54,36 @@ defmodule Pinchflat.Metadata.MetadataFileHelpers do
 
   @doc """
   Downloads and stores a thumbnail for a media item, returning the filepath.
-  Chooses the highest quality jpg thumbnail available.
+  Chooses the highest quality thumbnail available (preferring jpg). Returns
+  nil if no thumbnails are available.
 
-  Returns binary()
+  Returns binary() | nil
   """
   def download_and_store_thumbnail_for(database_record, metadata_map) do
-    thumbnail_url =
-      metadata_map["thumbnails"]
-      |> Enum.filter(&(&1["preference"] && String.ends_with?(&1["url"], ".jpg")))
-      |> Enum.sort(&(&1["preference"] >= &2["preference"]))
-      |> List.first()
-      |> Map.get("url")
+    thumbnails =
+      (metadata_map["thumbnails"] || [])
+      # Give it a low preference if the `preference` key doesn't exist
+      |> Enum.map(&Map.put_new(&1, "preference", -1000))
+      # Give it a low preference if image isn't a jpg
+      |> Enum.map(fn t ->
+        preference_weight = if String.ends_with?(t["url"], ".jpg"), do: t["preference"], else: t["preference"] - 1000
 
-    filepath = generate_filepath_for(database_record, Path.basename(thumbnail_url))
-    thumbnail_blob = fetch_thumbnail_from_url(thumbnail_url)
+        Map.put(t, "preference", preference_weight)
+      end)
 
-    :ok = FilesystemUtils.write_p!(filepath, thumbnail_blob)
+    case Enum.sort_by(thumbnails, & &1["preference"], :desc) do
+      [thumbnail_map | _] ->
+        thumbnail_url = thumbnail_map["url"]
+        filepath = generate_filepath_for(database_record, Path.basename(thumbnail_url))
+        thumbnail_blob = fetch_thumbnail_from_url(thumbnail_url)
 
-    filepath
+        :ok = FilesystemUtils.write_p!(filepath, thumbnail_blob)
+
+        filepath
+
+      _ ->
+        nil
+    end
   end
 
   @doc """