module RDoc::Text

def to_html text
  if Object.const_defined? :Encoding then
    html = ''.encode text.encoding
    encoded = RDoc::Text::TO_HTML_CHARACTERS[text.encoding]
  else
    html = ''
    encoded = {
      :close_dquote => '”',
      :close_squote => '’',
      :copyright    => '©',
      :ellipsis     => '…',
      :em_dash      => '—',
      :en_dash      => '–',
      :open_dquote  => '“',
      :open_squote  => '‘',
      :trademark    => '®',
    }
  end
  s = StringScanner.new text
  insquotes = false
  indquotes = false
  after_word = nil
  until s.eos? do
    case
    when s.scan(/<(tt|code)>.*?<\/\1>/) then # skip contents of tt
      html << s.matched.gsub('\\\\', '\\')
    when s.scan(/<(tt|code)>.*?/) then
      warn "mismatched <#{s[1]}> tag" # TODO signal file/line
      html << s.matched
    when s.scan(/<[^>]+\/?s*>/) then # skip HTML tags
      html << s.matched
    when s.scan(/\\(\S)/) then # unhandled suppressed crossref
      html << s[1]
      after_word = nil
    when s.scan(/\.\.\.(\.?)/) then
      html << s[1] << encoded[:ellipsis]
      after_word = nil
    when s.scan(/\(c\)/) then
      html << encoded[:copyright]
      after_word = nil
    when s.scan(/\(r\)/) then
      html << encoded[:trademark]
      after_word = nil
    when s.scan(/---/) then
      html << encoded[:em_dash]
      after_word = nil
    when s.scan(/--/) then
      html << encoded[:en_dash]
      after_word = nil
    when s.scan(/&quot;|"/) then
      html << encoded[indquotes ? :close_dquote : :open_dquote]
      indquotes = !indquotes
      after_word = nil
    when s.scan(/``/) then # backtick double quote
      html << encoded[:open_dquote]
      after_word = nil
    when s.scan(/''/) then # tick double quote
      html << encoded[:close_dquote]
      after_word = nil
    when s.scan(/'/) then # single quote
      if insquotes
        html << encoded[:close_squote]
        insquotes = false
      elsif after_word
        # Mary's dog, my parents' house: do not start paired quotes
        html << encoded[:close_squote]
      else
        html << encoded[:open_squote]
        insquotes = true
      end
      after_word = nil
    else # advance to the next potentially significant character
      match = s.scan(/.+?(?=[<\\.("'`&-])/) #"
      if match then
        html << match
        after_word = match =~ /\w$/
      else
        html << s.rest
        break
      end
    end
  end
  html
end