class ActiveAdmin::HasManyBuilder

nested decorators.
to build a has_many block. Nested has_many blocks are handled by
Decorates a FormBuilder with the additional attributes and methods

def allow_destroy?(form_object) 

def allow_destroy?(form_object)
  !! case destroy_option
     when Symbol, String
       form_object.public_send destroy_option
     when Proc
       destroy_option.call form_object
     else
       destroy_option
     end
end

def assoc_klass 

def assoc_klass
  @assoc_klass ||= __getobj__.object.class.reflect_on_association(assoc).klass
end

def content_has_many(&block) 

def content_has_many(&block)
  form_block = proc do |form_builder|
    render_has_many_form(form_builder, options[:parent], &block)
  end
  template.assigns[:has_many_block] = true
  contents = without_wrapper { inputs(options, &form_block) }
  contents ||= "".html_safe
  js = new_record ? js_for_has_many(options[:class], &form_block) : ''
  contents << js
end

def default_heading 

def default_heading
  assoc_klass.model_name.
    human(count: ::ActiveAdmin::Helpers::I18n::PLURAL_MANY_COUNT)
end

def extract_custom_settings!(options)

remove options that should not render as attributes 
def extract_custom_settings!(options)
  @heading = options.key?(:heading) ? options.delete(:heading) : default_heading
  @sortable_column = options.delete(:sortable)
  @sortable_start  = options.delete(:sortable_start) || 0
  @new_record = options.key?(:new_record) ? options.delete(:new_record) : true
  @destroy_option = options.delete(:allow_destroy)
  options
end

def has_many_actions(form_builder, contents) 

def has_many_actions(form_builder, contents)
  if form_builder.object.new_record?
    contents << template.content_tag(:li) do
      template.link_to I18n.t('active_admin.has_many_remove'), "#", class: 'button has_many_remove'
    end
  elsif allow_destroy?(form_builder.object)
    form_builder.input(:_destroy, as: :boolean,
                        wrapper_html: { class: 'has_many_delete' },
                        label: I18n.t('active_admin.has_many_delete'))
  end
  if sortable_column
    form_builder.input sortable_column, as: :hidden
    contents << template.content_tag(:li, class: 'handle') do
      I18n.t('active_admin.move')
    end
  end
  contents
end

def initialize(has_many_form, assoc, options) 

def initialize(has_many_form, assoc, options)
  super has_many_form
  @assoc = assoc
  @options = extract_custom_settings!(options.dup)
  @options.reverse_merge!(for: assoc)
  @options[:class] = [options[:class], "inputs has_many_fields"].compact.join(' ')
  if sortable_column
    @options[:for] = [assoc, sorted_children(sortable_column)]
  end
end

def js_for_has_many(class_string, &form_block)

Capture the ADD JS 
def js_for_has_many(class_string, &form_block)
  assoc_name       = assoc_klass.model_name
  placeholder      = "NEW_#{assoc_name.to_s.underscore.upcase.gsub(/\//, '_')}_RECORD"
  opts = {
    for: [assoc, assoc_klass.new],
    class: class_string,
    for_options: { child_index: placeholder }
  }
  html = template.capture { __getobj__.send(:inputs_for_nested_attributes, opts, &form_block) }
  text = new_record.is_a?(String) ? new_record : I18n.t('active_admin.has_many_new', model: assoc_name.human)
  template.link_to text, '#', class: "button has_many_add", data: {
    html: CGI.escapeHTML(html).html_safe, placeholder: placeholder
  }
end

def render(&block) 

def render(&block)
  html = "".html_safe
  html << template.content_tag(:h3) { heading } if heading.present?
  html << template.capture { content_has_many(&block) }
  html = wrap_div_or_li(html)
  template.concat(html) if template.output_buffer
  html
end

def render_has_many_form(form_builder, parent, &block)

Renders the Formtastic inputs then appends ActiveAdmin delete and sort actions. 
def render_has_many_form(form_builder, parent, &block)
  index = parent && form_builder.send(:parent_child_index, parent)
  template.concat template.capture { yield(form_builder, index) }
  template.concat has_many_actions(form_builder, "".html_safe)
end

def sorted_children(column) 

def sorted_children(column)
  __getobj__.object.public_send(assoc).sort_by do |o|
    attribute = o.public_send column
    [attribute.nil? ? Float::INFINITY : attribute, o.id || Float::INFINITY]
  end
end

def without_wrapper 

def without_wrapper
  is_being_wrapped = already_in_an_inputs_block
  self.already_in_an_inputs_block = false
  html = yield
  self.already_in_an_inputs_block = is_being_wrapped
  html
end

def wrap_div_or_li(html) 

def wrap_div_or_li(html)
  template.content_tag(already_in_an_inputs_block ? :li : :div,
                       html,
                       class: "has_many_container #{assoc}",
                       'data-sortable' => sortable_column,
                       'data-sortable-start' => sortable_start)
end