Only download files when they don't exist yet

app/models/filedrop_file.rb

@@ -17,7 +17,11 @@ class FiledropFile < ApplicationRecord
   end
 
   def download(url)
-    # TBD: only download if orig_created is newer than actual file change time
+    if File.exist?(local_path)
+      local_sha1 = Digest::SHA1.file(local_path).hexdigest
+      return if local_sha1 == checksum
+    end
+
     response = HTTParty.get(url)
     if response.success?
       File.open(local_path, 'wb') do |file|