module Nanoc::Helpers

  # Nanoc::Helpers::XMLSitemap contains functionality for building XML
  # sitemaps that will be crawled by search engines. See the Sitemaps protocol
  # web site, http://www.sitemaps.org, for details.
  module XMLSitemap

    # Returns the XML sitemap as a string.
    #
    # The following attributes can optionally be set on pages to change the
    # behaviour of the sitemap:
    #
    # * 'changefreq', containing the estimated change frequency as defined by
    #   the Sitemaps protocol.
    #
    # * 'priority', containing the page's priority, ranging from 0.0 to 1.0,
    #   as defined by the Sitemaps protocol.
    #
    # The sitemap will also include dates on which the pages were updated.
    # These are generated automatically; the way this happens depends on the
    # used data source (the filesystem data source checks the file mtimes, for
    # instance).
    #
    # The sitemap page will need to have the following attributes:
    #
    # * 'base_url', containing the URL to the site, without trailing slash.
    #   For example, if the site is at "http://example.com/", the base_url
    #   would be "http://example.com". It is probably a good idea to define
    #   this in the page defaults, i.e. the 'meta.yaml' file (at least if the
    #   filesystem data source is being used, which is probably the case).
    def xml_sitemap
      require 'builder'

      # Create builder
      buffer = ''
      xml = Builder::XmlMarkup.new(:target => buffer, :indent => 2)

      # Build sitemap
      xml.instruct!
      xml.urlset(:xmlns => 'http://www.google.com/schemas/sitemap/0.84') do
        # Add page
        @pages.reject { |p| p.is_hidden }.each do |page|
          xml.url do
            xml.loc         @page.base_url + page.path
            xml.lastmod     page.mtime.to_iso8601_date unless page.mtime.nil?
            xml.changefreq  page.changefreq unless page.changefreq.nil?
            xml.priority    page.priority unless page.priority.nil?
          end
        end
      end

      # Return sitemap
      buffer
    end

  end

end