RubyFeatures.define 'dynamic_fields_for' do

  dependency 'activerecord_devkit/association_soft_build'

  apply_to 'ActionView::Helpers::FormBuilder' do

    applied do
      alias_method_chain :fields_for, :dynamic_fields
      alias_method_chain :fields_for_nested_model, :dynamic_fields
    end

    instance_methods do
      def fields_for_with_dynamic_fields(association, record_object = nil, options = {}, &block)
        #Inherit the native parameters adjustment
        options, record_object = record_object, nil if record_object.is_a?(Hash) && record_object.extractable_options?

        return fields_for_without_dynamic_fields(association, record_object, options, &block) unless options.delete(:dynamic)

        new_object = @object.association(association).soft_build

        options[:child_index] = 'dynamic_fields_index'
        remove_template = fields_for_without_dynamic_fields(association, new_object, options) do |f|
          f.hidden_field(:id, value: 'dynamic_fields_object_id') +
          f.hidden_field(:_destroy, value: true)
        end

        options[:dynamic_fields_id] = dynamic_fields_id(association)
        add_template = fields_for_without_dynamic_fields(association, new_object, options, &block)

        options.delete(:child_index)
        collection_output = fields_for_without_dynamic_fields(association, record_object, options, &block)

        cover_by_anchors(
          {
            begin: options[:dynamic_fields_id],
            'add-template' => CGI.escapeHTML(add_template),
            'remove-template' => CGI.escapeHTML(remove_template)
          },
          collection_output,
          {end: options[:dynamic_fields_id]}
        )
      end

      def add_fields_link(association, label, options = {})
        @template.link_to(label, '#', dynamic_fields_data_options(add: dynamic_fields_id(association)).deep_merge(options))
      end

      def remove_fields_link(label, options = {})
        anchor_options = {}.tap do |mem|
          if @options.has_key?(:dynamic_fields_id)
            mem[:remove] = @options[:dynamic_fields_id]
            mem['remove-id'] = @object.id if @object.try(:persisted?)
          end
        end

        @template.link_to(label, '#', dynamic_fields_data_options(anchor_options).deep_merge(options))
      end

      def fields_for_nested_model_with_dynamic_fields(name, object, fields_options, block)
        cover_by_anchors_if(
          fields_options.has_key?(:dynamic_fields_id),
          {'item-begin' => fields_options[:dynamic_fields_id]},
          fields_for_nested_model_without_dynamic_fields(name, object, fields_options, block)
        )
      end

      private

      def dynamic_fields_id(association)
        "#{self.object_id}-#{association}"
      end

      def dynamic_fields_data_options(anchor_options)
        return nil if anchor_options.nil?

        anchor_options.inject({data: {}}) do |mem, (key, value)|
          mem[:data][:"dynamic-fields-#{key}"] = value.html_safe? ? value : value.html_safe
          mem
        end
      end

      def cover_by_anchors(begin_anchor_options, content, end_anchor_options = nil)
        anchor(begin_anchor_options) + content + anchor(end_anchor_options)
      end

      def cover_by_anchors_if(condition, begin_anchor_options, content, end_anchor_options = nil)
        condition ?
          cover_by_anchors(begin_anchor_options, content, end_anchor_options) :
          content
      end

      def anchor(anchor_options)
        return ''.html_safe if anchor_options.nil?

        @template.content_tag(:script, nil, dynamic_fields_data_options(anchor_options))
      end
    end
  end
end.apply