rails--rails/actionpack/lib/action_controller/metal/helpers.rb

module ActionController
  # The Rails framework provides a large number of helpers for working with +assets+, +dates+, +forms+,
  # +numbers+ and model objects, to name a few. These helpers are available to all templates
  # by default.
  #
  # In addition to using the standard template helpers provided in the Rails framework, creating custom helpers to
  # extract complicated logic or reusable functionality is strongly encouraged. By default, the controller will
  # include a helper whose name matches that of the controller, e.g., <tt>MyController</tt> will automatically
  # include <tt>MyHelper</tt>.
  #
  # Additional helpers can be specified using the +helper+ class method in <tt>ActionController::Base</tt> or any
  # controller which inherits from it.
  #
  # ==== Examples
  # The +to_s+ method from the Time class can be wrapped in a helper method to display a custom message if
  # the Time object is blank:
  #
  #   module FormattedTimeHelper
  #     def format_time(time, format=:long, blank_message="&nbsp;")
  #       time.blank? ? blank_message : time.to_s(format)
  #     end
  #   end
  #
  # FormattedTimeHelper can now be included in a controller, using the +helper+ class method:
  #
  #   class EventsController < ActionController::Base
  #     helper FormattedTimeHelper
  #     def index
  #       @events = Event.find(:all)
  #     end
  #   end
  #
  # Then, in any view rendered by <tt>EventController</tt>, the <tt>format_time</tt> method can be called:
  #
  #   <% @events.each do |event| -%>
  #     <p>
  #       <% format_time(event.time, :short, "N/A") %> | <%= event.name %>
  #     </p>
  #   <% end -%>
  #
  # Finally, assuming we have two event instances, one which has a time and one which does not,
  # the output might look like this:
  #
  #   23 Aug 11:30 | Carolina Railhawks Soccer Match
  #   N/A | Carolina Railhaws Training Workshop
  #
  module Helpers
    extend ActiveSupport::Concern

    include AbstractController::Helpers

    included do
      # Set the default directory for helpers
      extlib_inheritable_accessor(:helpers_dir) do
        defined?(Rails.root) ? "#{Rails.root}/app/helpers" : "app/helpers"
      end
    end

    module ClassMethods
      def inherited(klass)
        klass.class_eval { default_helper_module! unless name.blank? }
        super
      end

      # Declares helper accessors for controller attributes. For example, the
      # following adds new +name+ and <tt>name=</tt> instance methods to a
      # controller and makes them available to the view:
      #   helper_attr :name
      #   attr_accessor :name
      #
      # ==== Parameters
      # *attrs<Array[String, Symbol]>:: Names of attributes to be converted
      #   into helpers.
      def helper_attr(*attrs)
        attrs.flatten.each { |attr| helper_method(attr, "#{attr}=") }
      end

      # Provides a proxy to access helpers methods from outside the view.
      def helpers
        @helper_proxy ||= ActionView::Base.new.extend(_helpers)
      end

    private
      # Overwrite _modules_for_helpers to accept :all as argument, which loads
      # all helpers in helpers_dir.
      #
      # ==== Parameters
      # args<Array[String, Symbol, Module, all]>:: A list of helpers
      #
      # ==== Returns
      # Array[Module]:: A normalized list of modules for the list of
      #   helpers provided.
      def _modules_for_helpers(args)
        args += all_application_helpers if args.delete(:all)
        super(args)
      end

      def default_helper_module!
        module_name = name.sub(/Controller$/, '')
        module_path = module_name.underscore
        helper module_path
      rescue MissingSourceFile => e
        raise e unless e.is_missing? "helpers/#{module_path}_helper"
      rescue NameError => e
        raise e unless e.missing_name? "#{module_name}Helper"
      end

      # Extract helper names from files in app/helpers/**/*.rb
      def all_application_helpers
        extract = /^#{Regexp.quote(helpers_dir)}\/?(.*)_helper.rb$/
        Dir["#{helpers_dir}/**/*_helper.rb"].map { |file| file.sub extract, '\1' }
      end
    end
  end
end