content type priority

config/initializers/marcel.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+priority = %w[application/pdf image/jpeg image/png]
+
+indexes = Marcel::MAGIC.each_with_index.with_object({}) do |((type, _), i), acc|
+  acc[type] = i if priority.include?(type)
+
+  break acc if acc.size == priority.size
+end
+
+pdf_index, jpg_index, png_index = indexes.values_at(*priority)
+
+Marcel::MAGIC[0], Marcel::MAGIC[pdf_index] = Marcel::MAGIC[pdf_index], Marcel::MAGIC[0]
+Marcel::MAGIC[1], Marcel::MAGIC[jpg_index] = Marcel::MAGIC[jpg_index], Marcel::MAGIC[1]
+Marcel::MAGIC[2], Marcel::MAGIC[png_index] = Marcel::MAGIC[png_index], Marcel::MAGIC[2]