# Auto shorten url with shorturl gem.
  # FIXME: There're 2 bugs in ShortURL by Vincent Foley.
  # [#8376] tinyurls redirect to URLs with encoded chars, causing 404.
  # http://rubyforge.org/tracker/index.php?func=detail&aid=8376&group_id=732&atid=2893
  # [#15415] Invalid RubyURL
  # http://rubyforge.org/tracker/index.php?func=detail&aid=15415&group_id=732&atid=2893
  def auto_short_urls(text, service = :tinyurl)
    text.gsub(Helper::AUTO_LINK_RE) do
      all, a, b, c, d = $&, $1, $2, $3, $4
      if a =~ /<a\s/i # don't replace URL's that are already linked
        all
      else
        long_url  = b + c
        short_url = WWW::ShortURL.shorten(long_url, service)
        %(#{a}<a href="#{short_url}">#{short_url}</a>#{d})
      end
    end
  end