WIP extending govuk form builder so radio inputs support checked defaults

gistfile1.txt

Rails.application.config.action_view.default_form_builder = GOVUKDesignSystemFormBuilder::FormBuilder

# Don't use XHR when submitting forms
Rails.application.config.action_view.form_with_generates_remote_forms = false

# Use activerecord.attributes.model.attribute_name for label scope
module GOVUKDesignSystemFormBuilder
  module Builder
    def govuk_collection_radio_buttons(attribute_name, collection, value_method, text_method, hint_method = nil, hint_text: nil, legend: {}, inline: false, small: false, bold_labels: false, checked: false, classes: nil, &block)
      Elements::Radios::Collection.new(
        self,
        object_name,
        attribute_name,
        collection,
        value_method: value_method,
        text_method: text_method,
        hint_method: hint_method,
        hint_text: hint_text,
        legend: legend,
        inline: inline,
        small: small,
        bold_labels: bold_labels,
        classes: classes,
        checked: checked,
        &block
      ).html
    end
  end

  class Base
    private def localised_text(context)
      key = localisation_key(context)

      return nil unless I18n.exists?(key)

      translation = I18n.translate(key)
      translation = translation.fetch(:html).html_safe if translation.is_a?(Hash) && translation.key?(:html)
      translation
    end

    private def localisation_key(context)
      return nil unless @object_name.present? && @attribute_name.present?

      if context == "label"
        ["activerecord", "attributes", @object_name, @attribute_name].join(".")
      else
        ["helpers", context, @object_name, @attribute_name].join(".")
      end
    end

    def has_errors?
      @builder.object.errors.any? &&
        @builder.object.errors.messages.dig(
          translated_attribute_name(attribute_name: @attribute_name)
        ).present?
    end

    # In order to support associations where the model association is
    # eg. `provider` but the form attribute needs to be `provider_id`.
    # The form field must be wrapped in errors and be linkable from the summary.
    #
    # 1. We cannot change the form field to `provider` since the value will
    # not read from an object with a value already set.
    #
    # 2. We cannot change the model association to be `provider_id` as calling
    # `transaction.provider_id` rather than the resource  `transaction.provider`
    # would be unconventional and also require a hack.
    #
    # 3. We cannot overwride the @attribute_name on create since that will have
    # the same affect as point 1.
    private def translated_attribute_name(attribute_name:)
      translations = @builder.object.class.try("::FORM_FIELD_TRANSLATIONS") || {}

      if translations[attribute_name].present?
        translations[attribute_name]
      else
        attribute_name
      end
    end
  end
end

module GOVUKDesignSystemFormBuilder
  module Elements
    class Select < GOVUKDesignSystemFormBuilder::Base
      def error_element
        @error_element ||= Elements::ErrorMessage.new(
          @builder,
          @object_name,
          translated_attribute_name(attribute_name: @attribute_name)
        )
      end

      def field_id(link_errors: false)
        if link_errors && has_errors?
          build_id(
            "field-error",
            include_value: false,
            attribute_name: translated_attribute_name(attribute_name: @attribute_name)
          )
        else
          build_id("field")
        end
      end
    end

    module Radios
      def initialize(builder, object_name, attribute_name, collection, value_method:, text_method:, hint_method:, hint_text:, legend:, inline:, small:, bold_labels:, checked: false, classes:, &block)
        super(builder, object_name, attribute_name, &block)

        @collection    = collection
        @value_method  = value_method
        @text_method   = text_method
        @hint_method   = hint_method
        @inline        = inline
        @small         = small
        @legend        = legend
        @hint_text     = hint_text
        @classes       = classes
        @bold_labels   = hint_method.present? || bold_labels
        @checked       = checked
      end

      class CollectionRadioButton < GOVUKDesignSystemFormBuilder::Base
        def initialize(builder, object_name, attribute_name, item, value_method:, text_method:, hint_method:, link_errors: false, bold_labels:, checked: false)
          super(builder, object_name, attribute_name)

          @item        = item
          @value       = retrieve(item, value_method)
          @label_text  = retrieve(item, text_method)
          @hint_text   = retrieve(item, hint_method)
          @link_errors = link_errors
          @bold_labels = bold_labels
          @checked     = checked
        end

        def retrieve(item, method)
          case method
          when Symbol, String
            item.send(method)
          when Proc
            method.call(item)
          end
        end

        def html
          content_tag('div', class: 'govuk-radios__item') do
            safe_join(
              [
                @builder.radio_button(
                  @attribute_name,
                  @value,
                  id: field_id(link_errors: @link_errors),
                  aria: { describedby: hint_id },
                  class: %w(govuk-radios__input),
                  checked: @checked,
                ),
                label_element.html,
                hint_element.html
              ]
            )
          end
        end
        def field_id(link_errors: false)
          if link_errors && has_errors?
            build_id(
              "field-error",
              include_value: false,
              attribute_name: translated_attribute_name(attribute_name: @attribute_name)
            )
          else
            build_id("field")
          end
        end
      end
    end
  end
end