Detect extension for preview card (#2679)

* Detect extension for preview card

* next

app/models/concerns/attachmentable.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+module Attachmentable
+  extend ActiveSupport::Concern
+
+  included do
+    before_post_process :set_file_extensions
+  end
+
+  private
+
+  def set_file_extensions
+    self.class.attachment_definitions.each_key do |attachment_name|
+      attachment = send(attachment_name)
+      next if attachment.blank?
+      extension = Paperclip::Interpolations.content_type_extension(attachment, :original)
+      basename  = Paperclip::Interpolations.basename(attachment, :original)
+      attachment.instance_write :file_name, [basename, extension].delete_if(&:empty?).join('.')
+    end
+  end
+end