class SimpleForm::Inputs::GroupedCollectionSelectInput

def collection
  @collection ||= grouped_collection.first.try(:send, group_method) || []
end

def group_label_method
  label = options.delete(:group_label_method)
  unless label
    common_method_for = detect_common_display_methods(detect_collection_classes(grouped_collection))
    label = common_method_for[:label]
  end
  label
end

def group_method
  @group_method ||= options.delete(:group_method)
end

def grouped_collection
  @grouped_collection ||= begin
    grouped_collection = options.delete(:collection)
    grouped_collection.respond_to?(:call) ? grouped_collection.call : grouped_collection.to_a
  end
end

def input
  label_method, value_method = detect_collection_methods
  @builder.grouped_collection_select(attribute_name, grouped_collection,
                group_method, group_label_method, value_method, label_method,
                input_options, input_html_options)
end