Carrierwave processing facts

1. Class-level process definitions are only applied to the original file
2. Versions are generated based on the processed original file
3. Callbacks (before/after) are applied to original file and each version by itself
4. Under the hood, a version is an instance of the uploader class that has no versions
5. Version uploader and original uploader can be distinguished by checking #version_name: version uploaders return the version name, whereas the original uploader instance returns nil
6. Version instances do not have a reference to their parent uploader

class DemoUploader < CarrierWave::Uploader::Base

  process :resize # 1

  before :cache, :do_something # 3

  version :thumb do # 2
    process :crop
  end

  private

  def do_something(file)
    case version_name # 5
    # ...
  end

end