bs_cols.rb

SimpleForm::FormBuilder.class_eval do

  def input_with_bs_cols(attribute_name, options = {}, &block)
    bs_cols_classes = parse_bs_cols_option(options)

    if bs_cols_classes
      wrapper_html_options = (options[:wrapper_html] || {})
        .merge_html_attributes(class: bs_cols_classes.join(' '))

      options[:wrapper_html] = wrapper_html_options
    end

    input_without_bs_cols(attribute_name, options, &block)
  end

  alias_method_chain :input, :bs_cols

  def parse_bs_cols_option(options)
    if layout = options[:bs_cols]
      sizes = %w(xs sm md lg)
      values = layout.split('-')

      values.zip(sizes).map do |(value, size)|
        "col-#{size}-#{value}"
      end
    end
  end

end