simple "monkey patch" way how to generate simple_form form with class representing model name ('document_name') and action ('new') ... I'm sure there is better practice to do this but this is fine for my requirement app/helpers/custom_simple_form_helper.rb

custom_simple_form_helper.rb

module CustomSimpleFormHelper
  def simple_form_for(object, *args, &block)
    options = args.extract_options!

    action_classes = [object.class.model_name.underscore , (object.persisted? ? 'edit' : 'new')]

    options[:html]={} unless options[:html]

    if options[:html].empty?
      options[:html][:class] = action_classes
    else
      if options[:html][:class].is_a? String
        options[:html][:class] += " #{action_classes.join(' ')}"
      elsif options[:html][:class].is_a? Array
        options[:html][:class] += action_classes
      else
        options[:html][:class] = action_classes
      end
    end

    super(object, *(args << options), &block)
  end
end