Support arbitrary resizing in cover controller

lib/music_library/records/cover.ex

@@ -1,8 +1,8 @@
 defmodule MusicLibrary.Records.Cover do
   @size 600
 
-  def resize(cover_data) do
-    {:ok, thumb} = Vix.Vips.Operation.thumbnail_buffer(cover_data, @size)
+  def resize(cover_data, size \\ @size) do
+    {:ok, thumb} = Vix.Vips.Operation.thumbnail_buffer(cover_data, size)
     Vix.Vips.Image.write_to_buffer(thumb, ".jpg")
   end
 

lib/music_library_web/controllers/cover_controller.ex

@@ -2,6 +2,36 @@ defmodule MusicLibraryWeb.CoverController do
   use MusicLibraryWeb, :controller
 
   alias MusicLibrary.Records
+  alias MusicLibrary.Records.Cover
+
+  def show(conn, %{"record_id" => record_id, "size" => size}) do
+    case Records.get_cover(record_id) do
+      nil ->
+        conn
+        |> put_status(:not_found)
+        |> text("Not found")
+
+      %{cover_data: cover_data} ->
+        {:ok, thumb_data} = Cover.resize(cover_data, String.to_integer(size))
+        hash = :crypto.hash(:sha256, thumb_data) |> Base.encode16()
+
+        case get_req_header(conn, "if-none-match") do
+          [^hash] ->
+            conn
+            # 24 hours
+            |> put_resp_header("cache-control", "public, max-age=86400")
+            |> send_resp(304, "")
+
+          _ ->
+            conn
+            |> put_resp_content_type("image/jpeg", "utf-8")
+            # 24 hours
+            |> put_resp_header("cache-control", "public, max-age=86400")
+            |> put_resp_header("etag", hash)
+            |> send_resp(200, thumb_data)
+        end
+    end
+  end
 
   def show(conn, %{"record_id" => record_id}) do
     case Records.get_cover(record_id) do