Allows skipping files during the transformation

[jni-]

Use case :

I want all media files to be handles through arc, but images need to
have 3 versions (:original, :thumb, :viewable) and videos simply need to
have :original and :thumb (since :viewable is just a low-res image that
acts as a place holder). Maybe I'm creating problems for myself by
handling videos and pictures all in one, but I feel like this could be a
nice addition.

Still quite new to the elixir world, so I may not have used a proper
technique to do the test. It doesn't feel quite right.

[MartinElvar]

@stavro Just a friendly ping, this is greatly need. :)

[pedep]

Am i correct in my understanding of this PRs intention, that you wish to add conditionals to the transforms, allowing you to have the same functionality as :noaction, but without the file being persisted to storage?

Like this?

def transform(_, {file, scope}) do
  if is_image(file) do
    {:convert, [...]}
  else
    :skip
  end
end

If the intention is to skip uploading certain versions, what is the intended behavior when a skipped version is requested MyDef.url({file, scope}, :skipped)?

[jni-]

@pedep Yes this was exactly my intention.

In my case I treated the case in the logic (if it's a video, it doesn't attempt to use that intermediate format). I can see how this could be problematic however.

On one hand I believe that if your logic dictates skipping this format, then it must equally dictates not to display this format. In this case the :skip is fine.

Alternatively, this could be changed to {:fallback, :other_format} which would make MyDef.url() consistent across all formats, it's just that MyDef.url(_, :skipped) and MyDef.url(_, :other_format) would return the same image.

What do you think? Should we keep it at :skip, or go for :fallback?

[pedep]

I think both are useful, but since the :skip option was intended to be handled by application logic, i think :fallback provides the same functionality (ability to just ignore the output of MyDef.url() in the case of a skipped version via application logic) along with providing the ability to define fallbacks / aliases

[jni-]

Yeah your comment made me realize that :skip was a specific case of :fallback or :alias. I'm in the middle of grading exams right now so what little remains of my 24h I try to sleep, but I'll give this a shot later this week. Thanks for the idea!

[pedep]

No problem 😄

[stavro]

Fixed via de0bcc2. Thank you!