ActiveRecord::Base.class_eval do
  include ActionView::Helpers::TagHelper, ActionView::Helpers::TextHelper, WhiteListHelper
  def self.format_attribute(attr_name)
    class << self; include ActionView::Helpers::TagHelper, ActionView::Helpers::TextHelper, WhiteListHelper; end
    define_method(:body)       { read_attribute attr_name }
    define_method(:body_html)  { read_attribute "#{attr_name}_html" }
    define_method(:body_html=) { |value| write_attribute "#{attr_name}_html", value }
    before_save :format_content
  end

  def dom_id
    [self.class.name.downcase.pluralize.dasherize, id] * '-'
  end

  protected
    def format_content
      body.strip! if body.respond_to?(:strip!)
      self.body_html = body.blank? ? '' : body_html_with_formatting
    end

    # 2013-09-04 (ADH): See "body_html_with_formatting" for ddetails.
    #
    FOOTNOTE_NAME_REGEXP = Regexp.new('^fnr?\d+$')  # E.g. "fn30" or "fnr30"
    FOOTNOTE_HREF_REGEXP = Regexp.new('^#fnr?\d+$') # E.g. "#fn30" or "#fnr30"

    def body_html_with_formatting

      # 2013-09-04 (ADH):
      #
      # On the assumption we are called within a new Post or an edited Post,
      # generate a reasonably-likely-to-be-unique ID. We can't use the model
      # ID as in the "new" case it hasn't been saved yet so doesn't have one.
      #
      # We'll use this to patch up Textile footnote references. There's no
      # way to ask Textile to add a suffix to the IDs and names it generates,
      # so instead postprocess the output since we're being called for all
      # generated HTML nodes by the white list engine anyway (see
      # WhiteListHelper stuff in "config/environment.rb" for details). If we
      # don't do this, multiple posts on a page can contain the same foonote
      # IDs/names resulting in invalid HTML and useless HTML anchors.
      #
      # Since the ID is only used for that specific case, we're not *too*
      # worried if it turns out to be non-unique, but given it's based on
      # the time of day down to the microsecond and the post's user ID, it
      # is *extremely* unlikely that a real user would be able to generate
      # two posts with the same ID suffix for footnotes!
      #
      now       = Time.now
      fn_id_sfx = "#{now.to_i}#{now.usec}#{self.user_id || 0}"

      # Generate the body by auto-linking, running through RedCloth and then
      # passing it to the white list engine which in turn calls back for all
      # of the HTML nodes.
      #
      body_html = auto_link body { |text| truncate(text, 50) }
      white_list(RedCloth.new(body_html).to_html) do | node, bad |
        if WhiteListHelper.bad_tags.include?(bad)
          node.to_s.gsub(/</, '&lt;')
        else
          node.class == HTML::Tag && node.attributes && case(bad)
            when "sup", "p"
              if (node.attributes['class'] == 'footnote')
                match = FOOTNOTE_NAME_REGEXP.match(node.attributes['id'] || '')
                node.attributes['id'] << fn_id_sfx if (match)
              end
            when "a"
              match = FOOTNOTE_HREF_REGEXP.match(node.attributes['href'] || '')
              node.attributes['href'] << fn_id_sfx if (match)
          end

          node.to_s
        end
      end
    end
end