module ActiveStorage::Blob::Representable

def representation(transformations)

See ActiveStorage::Blob#preview and ActiveStorage::Blob#variant for more information.

ActiveStorage::Blob#representable? to determine whether a blob is representable.
Raises ActiveStorage::UnrepresentableError if the receiving blob is neither variable nor previewable. Call

blob.representation(resize: "100x100").processed.service_url

Returns an ActiveStorage::Preview for a previewable blob or an ActiveStorage::Variant for a variable image blob. 
def representation(transformations)
  case
  when previewable?
    preview transformations
  when variable?
    variant transformations
  else
    raise ActiveStorage::UnrepresentableError
  end
end