module GOVUKDesignSystemFormBuilder
  module PrefixableArray
    refine Array do
      def prefix(text, delimiter: '-')
        map { |item| text + delimiter + item }
      end
    end
  end

  class Base
    delegate :capture, :content_tag, :safe_join, :tag, :raw, :link_to, to: :@builder
    delegate :config, to: GOVUKDesignSystemFormBuilder

    def initialize(builder, object_name, attribute_name, &block)
      @builder        = builder
      @object_name    = object_name
      @attribute_name = attribute_name
      @block_content  = capture { block.call } if block_given?
    end

    # objects that implement #to_s can be passed directly into #safe_join
    def to_s
      html || ''
    end

  private

    def brand(override = nil)
      override || config.brand
    end

    # returns the id value used for the input
    #
    # @note field_id is overridden so that the error summary can link to the
    #   correct element.
    #
    #   It's straightforward for inputs with a single element (like a textarea
    #   or text input) but the GOV.UK Design System requires that the error
    #   summary link to the first checkbox or radio in a list, so additional
    #   logic is requred
    #
    # @return [String] the element's +id+
    # @see https://design-system.service.gov.uk/components/error-summary/#linking-from-the-error-summary-to-each-answer
    #   GOV.UK linking to elements from the error summary
    def field_id(link_errors: false)
      if link_errors && has_errors?
        build_id('field-error', include_value: false)
      else
        build_id('field')
      end
    end

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

    def described_by(*ids)
      ids.flatten.compact.join(' ').presence
    end

    # Builds the values used for HTML id attributes throughout the builder
    #
    # @param id_type [String] a description of the id's type, eg +hint+, +error+
    # @param delimiter [String] the characters used to 'split' the output
    # @param replace [String] the targets to be replaced by the delimiter
    # @param attribute_name [String] overrides the object's +@attribute_name+
    # @param include_value [Boolean] controls whether or not the value will form part
    #   of the final id
    #
    # @return [String] the id composed of object, attribute, value and type
    #
    # @example
    #   build_id('hint') #=> "person-name-hint"
    def build_id(id_type, delimiter = '-', replace = '_', attribute_name: nil, include_value: true)
      attribute = attribute_name || @attribute_name
      value     = include_value && @value || nil
      [
        @object_name,
        attribute,
        value,
        id_type
      ]
        .compact
        .join(delimiter)
        .parameterize
        .tr(replace, delimiter)
    end
  end
end