class Rails::MailersController

def find_preview
  candidates = []
  params[:path].to_s.scan(%r{/|$}){ candidates << $` }
  preview = candidates.detect{ |candidate| ActionMailer::Preview.exists?(candidate) }
  if preview
    @preview = ActionMailer::Preview.find(preview)
  else
    raise AbstractController::ActionNotFound, "Mailer preview '#{params[:path]}' not found"
  end
end