root/plugins/atom_feed_helper/lib/atom_feed_helper.rb

# Adds easy defaults to writing Atom feeds with the Builder template engine (this does not work on ERb or any other
# template languages).
module AtomFeedHelper
  # Full usage example:
  #
  #   config/routes.rb:
  #     ActionController::Routing::Routes.draw do |map|
  #       map.resources :posts
  #       map.root :controller => "posts"
  #     end
  #
  #   app/controllers/posts_controller.rb:
  #     class PostsController < ApplicationController::Base
  #       # GET /posts.html
  #       # GET /posts.atom
  #       def index
  #         @posts = Post.find(:all)
  #         
  #         respond_to do |format|
  #           format.html
  #           format.atom
  #         end
  #       end
  #     end
  #
  #   app/views/posts/index.atom.builder:
  #     atom_feed(:tag_uri => "2008") do |feed|
  #       feed.title("My great blog!")
  #       feed.updated((@posts.first.created_at))
  #     
  #       for post in @posts
  #         feed.entry(post) do |entry|
  #           entry.title(post.title)
  #           entry.content(post.body, :type => 'html')
  #     
  #           entry.author do |author|
  #             author.name("DHH")
  #           end
  #         end
  #       end
  #     end
  #
  # The options are for atom_feed are:
  #
  # * <tt>:schema_date</tt>: Required. The date at which the tag scheme for the feed was first used. A good default is the year you created the feed. See http://feedvalidator.org/docs/error/InvalidTAG.html for more information.
  # * <tt>:language</tt>: Defaults to "en-US".
  # * <tt>:root_url</tt>: The HTML alternative that this feed is doubling for. Defaults to / on the current host.
  # * <tt>:url</tt>: The URL for this feed. Defaults to the current URL.
  #
  # atom_feed yields a AtomFeedBuilder instance.
  def atom_feed(options = {}, &block)
    if options[:schema_date].blank?
      logger.warn("You must provide the :schema_date option to atom_feed for your feed to be valid. A good default is the year you first created this feed.") unless logger.nil?
    else
      options[:schema_date] = options[:schema_date].strftime("%Y-%m-%d") if options[:schema_date].respond_to?(:strftime)
    end
    
    xml = options[:xml] || eval("xml", block.binding)
    xml.instruct!

    xml.feed "xml:lang" => options[:language] || "en-US", "xmlns" => 'http://www.w3.org/2005/Atom' do
      xml.id("tag:#{request.host},#{options[:schema_date]}:#{request.request_uri.split(".")[0]}")      
      xml.link(:rel => 'alternate', :type => 'text/html', :href => options[:root_url] || (request.protocol + request.host_with_port))
      xml.link(:rel => 'self', :type => 'application/atom+xml', :href => options[:url] || request.url)
      
      yield AtomFeedBuilder.new(xml, self, options)
    end
  end


  class AtomFeedBuilder
    def initialize(xml, view, feed_options = {})
      @xml, @view, @feed_options = xml, view, feed_options
    end
    
    # Accepts a Date or Time object and inserts it in the proper format. If nil is passed, current time in UTC is used.
    def updated(date_or_time = nil)
      @xml.updated((date_or_time || Time.now.utc).xmlschema)
    end

    # Creates an entry tag for a specific record and prefills the id using class and id.
    #
    # Options:
    #
    # * <tt>:updated</tt>: Time of update. Defaults to the created_at attribute on the record if one such exists.
    # * <tt>:published</tt>: Time first published. Defaults to the updated_at attribute on the record if one such exists.
    # * <tt>:url</tt>: The URL for this entry. Defaults to the polymorphic_url for the record.
    def entry(record, options = {})
      @xml.entry do 
        @xml.id("tag:#{@view.request.host},#{@feed_options[:schema_date]}:#{record.class}/#{record.id}")

        if options[:published] || (record.respond_to?(:created_at) && record.created_at)
          @xml.published((options[:published] || record.created_at).xmlschema)
        end

        if options[:updated] || (record.respond_to?(:updated_at) && record.updated_at)
          @xml.updated((options[:updated] || record.updated_at).xmlschema)
        end

        @xml.link(:rel => 'alternate', :type => 'text/html', :href => options[:url] || @view.polymorphic_url(record))

        yield @xml
      end
    end

    private
      def method_missing(method, *arguments, &block)
        @xml.__send__(method, *arguments, &block)
      end
  end
end