class Asciidoctor::Block

def htmlify(string)
  unless string.nil?
    html = string.dup
    # Convert reference links to "link:" asciidoc for later HTMLification.
    # This ensures that eg. "<<some reference>>" is turned into a link but
    # "`<<<<<` and `>>>>>` are conflict markers" is not.  This is much
    # easier before the HTML is escaped and <> are turned into entities.
    html.gsub!( /(^|[^<])<<([^<>,]+)(,([^>]*))?>>/ ) { "#{$1}link:##{$2}[" + ($4.nil? ? document.references[$2] : $4).to_s + "]" }
    # Do the same with URLs
    html.gsub!( /(^|[^(`|link:)])(https?:\/\/[^\[ ]+)(\[+[^\]]*\]+)?/ ) do
      pre = $1
      url = $2
      link = ( $3 || $2 ).gsub( /(^\[|\]$)/,'' )
      link = url if link.empty?
      "#{pre}link:#{url}[#{link}]"
    end
    html.gsub!(Asciidoctor::REGEXP[:biblio], '<a name="\1">[\1]</a>')
    html.gsub!(Asciidoctor::REGEXP[:ruler], "<hr>\n")
    html.gsub!(/``([^`']*)''/m, '&ldquo;\1&rdquo;')
    html.gsub!(/(?:\s|^)`([^`']*)'/m, '&lsquo;\1&rsquo;')
    # TODO: This text thus quoted is supposed to be rendered as an
    # "inline literal passthrough", meaning that it is rendered
    # in a monospace font, but also doesn't go through any further
    # text substitution, except for special character substitution.
    # So we need to technically pull this text out, sha it and store
    # a marker and replace it after the other gsub!s are done in here.
    # See:  http://www.methods.co.nz/asciidoc/userguide.html#X80
    html.gsub!(/`([^`]+)`/m) { "<tt>#{$1.gsub( '*', '{asterisk}' ).gsub( '\'', '{apostrophe}' )}</tt>" }
    html.gsub!(/([\s\W])#(.+?)#([\s\W])/, '\1\2\3')
    # "Unconstrained" quotes
    html.gsub!(/\_\_([^\_]+)\_\_/m, '<em>\1</em>')
    html.gsub!(/\*\*([^\*]+)\*\*/m, '<strong>\1</strong>')
    html.gsub!(/\+\+([^\+]+)\+\+/m, '<tt>\1</tt>')
    html.gsub!(/\^\^([^\^]+)\^\^/m, '<sup>\1</sup>')
    html.gsub!(/\~\~([^\~]+)\~\~/m, '<sub>\1</sub>')
    # "Constrained" quotes, which must be bounded by white space or
    # common punctuation characters
    html.gsub!(/(^|\s|\W)\*([^\*]+)\*(\s|\W|$)/m, '\1<strong>\2</strong>\3')
    html.gsub!(/(^|\s|\W)'(.+?)'(\s|\W|$)/m, '\1<em>\2</em>\3')
    # restore escaped single quotes after processing emphasis
    html.gsub!(/(\w)\\'(\w)/, '\1\'\2')
    html.gsub!(/(^|\s|\W)_([^_]+)_(\s|\W|$)/m, '\1<em>\2</em>\3')
    html.gsub!(/(^|\s|\W)\+([^\+]+)\+(\s|\W|$)/m, '\1<tt>\2</tt>\3')
    html.gsub!(/(^|\s|\W)\^([^\^]+)\^(\s|\W|$)/m, '\1<sup>\2</sup>\3')
    html.gsub!(/(^|\s|\W)\~([^\~]+)\~(\s|\W|$)/m, '\1<sub>\2</sub>\3')
    html.gsub!(/\\([\{\}\-])/, '\1')
    html.gsub!(/linkgit:([^\]]+)\[(\d+)\]/, '<a href="\1.html">\1(\2)</a>')
    html.gsub!(/link:([^\[]+)(\[+[^\]]*\]+)/ ) { "<a href=\"#{$1}\">#{$2.gsub( /(^\[|\]$)/,'' )}</a>" }
    html.gsub!(Asciidoctor::REGEXP[:line_break], '\1<br/>')
    html
  end
end