module Pidgin2Adium
  # Balances tags of string using a modified stack. Returns a balanced
  # string, but also affects the text passed into it!
  # Use text = balance_tags(text).

  # From Wordpress's formatting.php; rewritten in Ruby by Gabe
  # Berke-Williams, 2009.
  # Author:: Leonard Lin <leonard@acm.org>
  # License:: GPL v2.0
  # Copyright:: November 4, 2001
  def Pidgin2Adium.balance_tags( text )
    tagstack = []
    stacksize = 0
    tagqueue = ''
    newtext = ''
    single_tags = %w{br hr img input meta} # Known single-entity/self-closing tags
    #nestable_tags = %w{blockquote div span} # Tags that can be immediately nested within themselves
    nestable_tags = %w{blockquote div span font} # Tags that can be immediately nested within themselves
    # 1: tagname, with possible leading "/"
    # 2: attributes
    tag_regex = /<(\/?\w*)\s*([^>]*)>/

    # WP bug fix for comments - in case you REALLY meant to type '< !--'
    text.gsub!('< !--', '<    !--')

    # WP bug fix for LOVE <3 (and other situations with '<' before a number)
    text.gsub!(/<([0-9]{1})/, '&lt;\1')

    while ( pos = (text =~ tag_regex) )
      newtext << tagqueue
      tag = $1.downcase
      attributes = $2
      matchlen = $~[0].size

      # clear the shifter
      tagqueue = ''
      # Pop or Push
      if (tag[0,1] == "/") # End Tag
        tag.slice!(0,1)
        # if too many closing tags
        if(stacksize <= 0)
          tag = ''
          #or close to be safe: tag = '/' << tag
        elsif (tagstack[stacksize - 1] == tag) # found closing tag
          # if stacktop value == tag close value then pop
          tag = '</' << tag << '>' # Close Tag
          # Pop
          tagstack.pop
          stacksize -= 1
        else # closing tag not at top, search for it
          (stacksize-1).downto(0) do |j|
            if (tagstack[j] == tag)
              # add tag to tagqueue
              ss = stacksize - 1
              ss.downto(j) do |k|
                tagqueue << '</' << tagstack.pop << '>'
                stacksize -= 1
              end
              break
            end
          end
          tag = ''
        end
      else
        # Begin Tag

        # Tag Cleaning
        if( (attributes[-1,1] == '/') || (tag == '') )
          # If: self-closing or '', don't do anything.
        elsif ( single_tags.include?(tag) )
          # ElseIf: it's a known single-entity tag but it doesn't close itself, do so
          attributes << '/'
        else
          # Push the tag onto the stack
          # If the top of the stack is the same as the tag we want to push, close previous tag
          if ((stacksize > 0) &&
              ! nestable_tags.include?(tag) &&
              (tagstack[stacksize - 1] == tag))
            tagqueue = '</' << tagstack.pop << '>'
            stacksize -= 1
          end
          tagstack.push(tag)
          stacksize += 1
        end

        # Attributes
        if(attributes != '')
          attributes = ' ' << attributes
        end
        tag = '<' << tag << attributes << '>'
        #If already queuing a close tag, then put this tag on, too
        if (tagqueue)
          tagqueue << tag
          tag = ''
        end
      end
      newtext << text[0,pos] << tag
      text = text[pos+matchlen, text.length - (pos+matchlen)]
    end

    # Clear Tag Queue
    newtext << tagqueue

    # Add Remaining text
    newtext << text

    # Empty Stack
    tagstack.reverse_each do |t|
      newtext << '</' << t << '>' # Add remaining tags to close
    end

    # WP fix for the bug with HTML comments
    newtext.gsub!("< !--", "<!--")
    newtext.gsub!("<    !--", "< !--")

    return newtext
  end
end