require 'set'

module ActionView
  # = Action View Atom Feed Helpers
  module Helpers
    module AtomFeedHelper
      # Adds easy defaults to writing Atom feeds with the Builder template engine (this does not work on ERB or any other
      # template languages).
      #
      # Full usage example:
      #
      #   config/routes.rb:
      #     Rails.application.routes.draw do
      #       resources :posts
      #       root to: "posts#index"
      #     end
      #
      #   app/controllers/posts_controller.rb:
      #     class PostsController < ApplicationController
      #       # GET /posts.html
      #       # GET /posts.atom
      #       def index
      #         @posts = Post.all
      #
      #         respond_to do |format|
      #           format.html
      #           format.atom
      #         end
      #       end
      #     end
      #
      #   app/views/posts/index.atom.builder:
      #     atom_feed do |feed|
      #       feed.title("My great blog!")
      #       feed.updated(@posts[0].created_at) if @posts.length > 0
      #
      #       @posts.each do |post|
      #         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 for atom_feed are:
      #
      # * <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.
      # * <tt>:id</tt>: The id for this feed. Defaults to "tag:localhost,2005:/posts", in this case.
      # * <tt>:schema_date</tt>: 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. If not specified,
      #   2005 is used (as an "I don't care" value).
      # * <tt>:instruct</tt>: Hash of XML processing instructions in the form {target => {attribute => value, }} or {target => [{attribute => value, }, ]}
      #
      # Other namespaces can be added to the root element:
      #
      #   app/views/posts/index.atom.builder:
      #     atom_feed({'xmlns:app' => 'http://www.w3.org/2007/app',
      #         'xmlns:openSearch' => 'http://a9.com/-/spec/opensearch/1.1/'}) do |feed|
      #       feed.title("My great blog!")
      #       feed.updated((@posts.first.created_at))
      #       feed.tag!('openSearch:totalResults', 10)
      #
      #       @posts.each do |post|
      #         feed.entry(post) do |entry|
      #           entry.title(post.title)
      #           entry.content(post.body, type: 'html')
      #           entry.tag!('app:edited', Time.now)
      #
      #           entry.author do |author|
      #             author.name("DHH")
      #           end
      #         end
      #       end
      #     end
      #
      # The Atom spec defines five elements (content rights title subtitle
      # summary) which may directly contain xhtml content if type: 'xhtml'
      # is specified as an attribute. If so, this helper will take care of
      # the enclosing div and xhtml namespace declaration. Example usage:
      #
      #    entry.summary type: 'xhtml' do |xhtml|
      #      xhtml.p pluralize(order.line_items.count, "line item")
      #      xhtml.p "Shipped to #{order.address}"
      #      xhtml.p "Paid by #{order.pay_type}"
      #    end
      #
      #
      # <tt>atom_feed</tt> yields an +AtomFeedBuilder+ instance. Nested elements yield
      # an +AtomBuilder+ instance.
      def atom_feed(options = {}, &block)
        if options[:schema_date]
          options[:schema_date] = options[:schema_date].strftime("%Y-%m-%d") if options[:schema_date].respond_to?(:strftime)
        else
          options[:schema_date] = "2005" # The Atom spec copyright date
        end

        xml = options.delete(:xml) || eval("xml", block.binding)
        xml.instruct!
        if options[:instruct]
          options[:instruct].each do |target,attrs|
            if attrs.respond_to?(:keys)
              xml.instruct!(target, attrs)
            elsif attrs.respond_to?(:each)
              attrs.each { |attr_group| xml.instruct!(target, attr_group) }
            end
          end
        end

        feed_opts = {"xml:lang" => options[:language] || "en-US", "xmlns" => 'http://www.w3.org/2005/Atom'}
        feed_opts.merge!(options).reject!{|k,v| !k.to_s.match(/^xml/)}

        xml.feed(feed_opts) do
          xml.id(options[:id] || "tag:#{request.host},#{options[:schema_date]}:#{request.fullpath.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 AtomBuilder #:nodoc:
        XHTML_TAG_NAMES = %w(content rights title subtitle summary).to_set

        def initialize(xml)
          @xml = xml
        end

        private
          # Delegate to xml builder, first wrapping the element in an xhtml
          # namespaced div element if the method and arguments indicate
          # that an xhtml_block? is desired.
          def method_missing(method, *arguments, &block)
            if xhtml_block?(method, arguments)
              @xml.__send__(method, *arguments) do
                @xml.div(:xmlns => 'http://www.w3.org/1999/xhtml') do |xhtml|
                  block.call(xhtml)
                end
              end
            else
              @xml.__send__(method, *arguments, &block)
            end
          end

          # True if the method name matches one of the five elements defined
          # in the Atom spec as potentially containing XHTML content and
          # if type: 'xhtml' is, in fact, specified.
          def xhtml_block?(method, arguments)
            if XHTML_TAG_NAMES.include?(method.to_s)
              last = arguments.last
              last.is_a?(Hash) && last[:type].to_s == 'xhtml'
            end
          end
      end

      class AtomFeedBuilder < AtomBuilder #:nodoc:
        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>:published</tt>: Time first published. Defaults to the created_at attribute on the record if one such exists.
        # * <tt>:updated</tt>: Time of update. Defaults to the updated_at attribute on the record if one such exists.
        # * <tt>:url</tt>: The URL for this entry or false or nil for not having a link tag. Defaults to the polymorphic_url for the record.
        # * <tt>:id</tt>: The ID for this entry. Defaults to "tag:#{@view.request.host},#{@feed_options[:schema_date]}:#{record.class}/#{record.id}"
        # * <tt>:type</tt>: The TYPE for this entry. Defaults to "text/html".
        def entry(record, options = {})
          @xml.entry do
            @xml.id(options[: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

            type = options.fetch(:type, 'text/html')

            url = options.fetch(:url) { @view.polymorphic_url(record) }
            @xml.link(:rel => 'alternate', :type => type, :href => url) if url

            yield AtomBuilder.new(@xml)
          end
        end
      end

    end
  end
end