wpautop ported to Ruby (including an incidental "fix" for an obscure bug in the PHP version - which will be lost to the world because no one will ever look at this gist lol)

wpautop.rb

def autop(px, br = true)
  pre_tags = []
  return '' if px.strip == ""
  px = px + "\n"
  if px =~ /<pre/
    px_parts = px.split "</pre>"
    last_px = px_parts.pop
    px = ""
    i = 0
    px_parts.each do |px_part|
      start = px_part.index("<pre")

      #malformed html?
      if !start
        px += px_part
      else
        name = "<pre wp-pre-tag-#{i}></pre>"
        pre_tags[name] = px_part[start..-1] + "</pre>"
        px += px_part[0..start] + name
        i += 1
      end
    end
    px += last_px
  end
  px = px.gsub(/<br \/>\s*<br \/>/, "\n\n")
  # Space things out a little
  allblocks = "(?:table|thead|tfoot|caption|col|colgroup|tbody|tr|td|th|div|dl|dd|dt|ul|ol|li|pre|select|option|form|map|area|blockquote|address|math|style|p|h[1-6]|hr|fieldset|noscript|samp|legend|section|article|aside|hgroup|header|footer|nav|figure|figcaption|details|menu|summary)"
  px = px.gsub(/(<#{allblocks}[^>]*>)/, "\n" + '\1')
  px = px.gsub(/(<\/#{allblocks}>)/, '\1' + "\n\n")
  px = px.gsub(/\r\n|\r/, "\n")
  if px.index("<object")
    px = px.gsub(/\s*<param([^>]*)>\s*/, "<param" + '\1' + ">")
    px = px.gsub(/\s*<\/embed>\s*/, "</embed>")
  end
  px = px.gsub(/\n\n+/, "\n\n")
  pxs = px.split(/\n\s*\n/).reject { |a| a.empty? }
  px = ""
  pxs.each do |t|
    px += "<p>" + t.gsub(/\A\n+/, "").gsub(/\n+\Z/, "") + "</p>\n"
  end
  px = px.gsub(/<p>\s*<\/p>/, "")
  px = px.gsub(/<p>([^<]+)<\/(div|address|form)>/, "<p>" + '\1' + "</p></" + '\2' + ">")
  px = px.gsub(/<p>\s*(<\/?#{allblocks}[^>]*>)\s*<\/p>/, '\1')
  px = px.gsub(/<p>(<li.+?)<\/p>/, '\1')
  px = px.gsub(/<p><blockquote([^>]*)>/, "<blockquote" + '\1' + "><p>")
  px = px.gsub(/<\/blockquote><\/p>/, "</p></blockquote>")
  px = px.gsub(/<p>\s*(<\/?#{allblocks}[^>]*>)/, '\1')
  px = px.gsub(/(<\/?#{allblocks}[^>]*>)\s*<\/p>/, '\1')
  if br
    px.scan(/<(script|style).*?<\/\\1>/) { |s| px = px.gsub(s, "\n<WPPreserveNewline />") }
    px = px.gsub(/(?<!<br \/>)\s*\n/, "<br />\n")
    px = px.gsub(/<WPPreserveNewline \/>/, "\n")
  end
  px = px.gsub(/(<\/?#{allblocks}[^>]*>)\s*<br \/>/, '\1')
  px = px.gsub(/<br \/>(\s*<\/?(?:p|li|div|dl|dd|dt|th|pre|td|ul|ol)[^>]*>)/, '\1')
  px = px.gsub(/\n<\/p>\Z/, "</p>")
  unless pre_tags.empty?
    pre_tags.each { |k, v| px = px.gsub(/#{k}/, v) }
  end
  px
end