/Markdown.class.php

<?php

# A php class for parsing Markdown markup in comments, without authorizing
# html tags. This is an adaptation of PHP Markdown by Michel Fortin.
#
# PHP Markdown for comments
# Adaptation of PHP Markdown by Pierre Monchalin
# <http://github.com/piero-la-lune/PHP-Markdown-for-comments>
#
# PHP Markdown
# Copyright (c) 2004-2012 Michel Fortin
# <http://michelf.com/projects/php-markdown/>
#
# Original Markdown
# Copyright (c) 2004-2006 John Gruber  
# <http://daringfireball.net/projects/markdown/>
#
#
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program. If not, see <http://www.gnu.org/licenses/>.

class Markdown {

	# Regex to match balanced [brackets].
	# Needed to insert a maximum bracked depth while converting to PHP.
	protected $nested_brackets_depth = 6;
	protected $nested_brackets_re;

	protected $nested_url_parenthesis_depth = 4;
	protected $nested_url_parenthesis_re;

	# Table of hash values for escaped characters:
	protected $escape_chars = '\`*_{}[]()>#+-.!';
	protected $escape_chars_re;

	# Predefined urls and titles for reference links and images.
	protected $predef_urls = array();
	protected $predef_titles = array();

	protected $tab_width = 4;

	protected $document_gamut = array(
		'stripLinkDefinitions',
		'runBlockGamut'
	);

	# These are all the transformations that form block-level tags like
	# paragraphs, headers, and list items.
	protected $block_gamut = array(
		'doHeaders',
		'doHorizontalRules',
		'doLists',
		'doCodeBlocks',
		'doBlockQuotes'
	);

	# These are all the transformations that occur *within* block-level tags
	# like paragraphs, headers, and list items.
	protected $span_gamut = array(
		# Process character escapes, code spans, and inline HTML in one shot.
		'parseSpan',

		# Process anchor and image tags. Images must come first, because 
		# ![foo][f] looks like an anchor.
		'doImages',
		'doAnchors',

		# Make links out of things like `<http://example.com/>`
		# Must come after doAnchors, because you can use < and > delimiters in
		# inline links like [this](<url>).
		'doAutoLinks',
		'encodeAmpsAndAngles',

		'doItalicsAndBold',
		'doHardBreaks'
	);


	public function __construct() {
		$this->prepareItalicsAndBold();

		$this->nested_brackets_re = 
			str_repeat('(?>[^\[\]]+|\[', $this->nested_brackets_depth).
			str_repeat('\])*', $this->nested_brackets_depth);

		$this->nested_url_parenthesis_re = 
			str_repeat('(?>[^()\s]+|\(', $this->nested_url_parenthesis_depth).
			str_repeat('(?>\)))*', $this->nested_url_parenthesis_depth);

		$this->escape_chars_re = '['.preg_quote($this->escape_chars).']';
	}

#
# Main function. Performs some preprocessing on the input text and pass it
# through the document gamut.
#
	public function transform($text) {
		$this->setup();

		# Remove UTF-8 BOM and marker character in input, if present.
		$text = preg_replace('{^\xEF\xBB\xBF|\x1A}', '', $text);

		# Standardize line endings: DOS to Unix and Mac to Unix
		$text = preg_replace('{\r\n?}', "\n", $text);

		# Make sure $text ends with a couple of newlines:
		$text .= "\n\n";

		# Convert all tabs to spaces.
		$text = $this->detab($text);

		# Strip any lines consisting only of spaces and tabs.
		# This makes subsequent regexen easier to write, because we can match
		# consecutive blank lines with /\n+/ instead of something contorted
		# like /[ ]*\n+/ .
		$text = preg_replace('/^[ ]+$/m', '', $text);

		# Run document gamut methods.
		foreach ($this->document_gamut as $method) {
			$text = $this->$method($text);
		}

		$this->teardown();

		return $text . "\n";
	}

#
# Prepare regular expressions for searching emphasis tokens in any context.
#
	private $em_relist = array(
		''  => '(?:(?<!\*)\*(?!\*)|(?<!_)_(?!_))(?=\S|$)(?![\.,:;]\s)',
		'*' => '(?<=\S|^)(?<!\*)\*(?!\*)',
		'_' => '(?<=\S|^)(?<!_)_(?!_)',
	);
	private $strong_relist = array(
		''   => '(?:(?<!\*)\*\*(?!\*)|(?<!_)__(?!_))(?=\S|$)(?![\.,:;]\s)',
		'**' => '(?<=\S|^)(?<!\*)\*\*(?!\*)',
		'__' => '(?<=\S|^)(?<!_)__(?!_)',
	);
	private $em_strong_relist = array(
		''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<!_)___(?!_))(?=\S|$)(?![\.,:;]\s)',
		'***' => '(?<=\S|^)(?<!\*)\*\*\*(?!\*)',
		'___' => '(?<=\S|^)(?<!_)___(?!_)',
	);
	private $em_strong_prepared_relist;

	protected function prepareItalicsAndBold() {
		foreach ($this->em_relist as $em => $em_re) {
			foreach ($this->strong_relist as $strong => $strong_re) {
				# Construct list of allowed token expressions.
				$token_relist = array();
				if (isset($this->em_strong_relist["$em$strong"])) {
					$token_relist[] = $this->em_strong_relist["$em$strong"];
				}
				$token_relist[] = $em_re;
				$token_relist[] = $strong_re;

				# Construct master expression from list.
				$token_re = '{('. implode('|', $token_relist) .')}';
				$this->em_strong_prepared_relist["$em$strong"] = $token_re;
			}
		}
	}

#
# Called before the transformation process starts to setup parser states.
#
	# Internal hashes used during transformation.
	private $urls = array();
	private $titles = array();
	private $html_hashes = array();

	# Status flag to avoid invalid nesting.
	private $in_anchor = false;

	protected function setup() {
		# Clear global hashes.
		$this->urls = $this->predef_urls;
		$this->titles = $this->predef_titles;
		$this->html_hashes = array();

		$in_anchor = false;
	}

#
# Called after the transformation process to clear any variable which may be
# taking up memory unnecessarly.
#
	protected function teardown() {
		$this->urls = array();
		$this->titles = array();
		$this->html_hashes = array();
	}

#
# Remove one level of line-leading tabs or spaces
#
	protected function outdent($text) {
		return preg_replace('/^(\t|[ ]{1,'.$this->tab_width.'})/m', '', $text);
	}

#
# Replace tabs with the appropriate amount of space.
#
	protected function detab($text) {
		# For each line we separate the line in blocks delemited by tab
		# characters. Then we reconstruct every line by adding the appropriate
		# number of space between each blocks.

		$text = preg_replace_callback('/^.*\t.*$/m',
			array(&$this, '_detab_callback'), $text);

		return $text;
	}
	protected function _detab_callback($matches) {
		$line = $matches[0];

		# Split in blocks.
		$blocks = explode("\t", $line);
		# Add each blocks to the line.
		$line = $blocks[0];
		unset($blocks[0]); # Do not add first block twice.
		foreach ($blocks as $block) {
			# Calculate amount of space, insert spaces, insert block.
			$amount = $this->tab_width - 
				mb_strlen($line, 'UTF-8') % $this->tab_width;
			$line .= str_repeat(" ", $amount) . $block;
		}
		return $line;
	}

#
# Strips link definitions from text, stores the URLs and titles in hash
# references.
#
	protected function stripLinkDefinitions($text) {

		$less_than_tab = $this->tab_width - 1;

		# Link defs are in the form: ^[id]: url "optional title"
		$text = preg_replace_callback('{
							^[ ]{0,'.$less_than_tab.'}\[(.+)\][ ]?:	# id = $1
							  [ ]*
							  \n?				# maybe *one* newline
							  [ ]*
							(?:
							  <(.+?)>			# url = $2
							|
							  (\S+?)			# url = $3
							)
							  [ ]*
							  \n?				# maybe one newline
							  [ ]*
							(?:
								(?<=\s)			# lookbehind for whitespace
								["(]
								(.*?)			# title = $4
								[")]
								[ ]*
							)?	# title is optional
							(?:\n+|\Z)
			}xm',
			array(&$this, '_stripLinkDefinitions_callback'),
			$text);
		return $text;
	}
	protected function _stripLinkDefinitions_callback($matches) {
		$link_id = strtolower($matches[1]);
		$url = $matches[2] == '' ? $matches[3] : $matches[2];
		$this->urls[$link_id] = $url;
		$this->titles[$link_id] =& $matches[4];
		return ''; # String that will replace the block
	}

#
# Run block gamut tranformations, without hashing HTML blocks.
#
	protected function runBlockGamut($text) {

		foreach ($this->block_gamut as $method) {
			$text = $this->$method($text);
		}

		# Finally form paragraph and restore hashed blocks.
		$text = $this->formParagraphs($text);

		return $text;
	}

#
# Run span gamut tranformations.
#
	protected function runSpanGamut($text) {
		foreach ($this->span_gamut as $method) {
			$text = $this->$method($text);
		}
		return $text;
	}

#
# Params:
#	$text - string to process with html <p> tags
#
	protected function formParagraphs($text) {
		# Strip leading and trailing lines:
		$text = preg_replace('/\A\n+|\n+\z/', '', $text);

		$grafs = preg_split('/\n{2,}/', $text, -1, PREG_SPLIT_NO_EMPTY);

		#
		# Wrap <p> tags and unhashify HTML blocks
		#
		foreach ($grafs as $key => $value) {
			if (!preg_match('/^B\x1A[0-9]+B$/', $value)) {
				# Is a paragraph.
				$value = $this->runSpanGamut($value);
				$value = preg_replace('/^([ ]*)/', "<p>", $value);
				$value .= "</p>";
				$grafs[$key] = $this->unhash($value);
			}
			else {
				# Is a block.
				# Modify elements of @grafs in-place...
				$graf = $value;
				$block = $this->html_hashes[$graf];
				$graf = $block;
				$grafs[$key] = $graf;
			}
		}

		return implode("\n\n", $grafs);
	}

#
# Process headers
# Note : this function was adapted, not allowing levels 1 and 2 for titles.
#
	protected function doHeaders($text) {
		# Setext-style headers:
		#	  Header 1
		#	  ========
		#  
		#	  Header 2
		#	  --------
		#
		$text = preg_replace_callback('{ ^(.+?)[ ]*\n(=+|-+)[ ]*\n+ }mx',
			array(&$this, '_doHeaders_callback_setext'), $text);

		# atx-style headers:
		#	# Header 1
		#	## Header 2
		#	## Header 2 with closing hashes ##
		#	...
		#	#### Header 4
		#
		$text = preg_replace_callback('{
				^(\#{1,4})	# $1 = string of #\'s
				[ ]*
				(.+?)		# $2 = Header text
				[ ]*
				\#*			# optional closing #\'s (not counted)
				\n+
			}xm',
			array(&$this, '_doHeaders_callback_atx'), $text);

		return $text;
	}
	protected function _doHeaders_callback_setext($matches) {
		# Terrible hack to check we haven't found an empty list item.
		if ($matches[2] == '-' && preg_match('{^-(?: |$)}', $matches[1]))
			return $matches[0];

		$level = $matches[2]{0} == '=' ? 3 : 4;
		$block = "<h$level>".$this->runSpanGamut($matches[1])."</h$level>";
		return "\n" . $this->hashBlock($block) . "\n\n";
	}
	protected function _doHeaders_callback_atx($matches) {
		$level = strlen($matches[1])+2;
		$block = "<h$level>".$this->runSpanGamut($matches[2])."</h$level>";
		return "\n" . $this->hashBlock($block) . "\n\n";
	}

#
# Process horizontal rules
#
	protected function doHorizontalRules($text) {
		return preg_replace(
			'{
				^[ ]{0,3}	# Leading space
				([-*_])		# $1: First marker
				(?>			# Repeated marker group
					[ ]{0,2}	# Zero, one, or two spaces.
					\1			# Marker character
				){2,}		# Group repeated at least twice
				[ ]*		# Tailing spaces
				$			# End of line.
			}mx',
			"\n".$this->hashBlock("<hr />")."\n", 
			$text);
	}

#
# Form HTML ordered (numbered) and unordered (bulleted) lists.
#
	protected function doLists($text) {
		$less_than_tab = $this->tab_width - 1;

		# Re-usable patterns to match list item bullets and number markers:
		$marker_ul_re  = '[*+-]';
		$marker_ol_re  = '\d+[\.]';
		$marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";

		$markers_relist = array(
			$marker_ul_re => $marker_ol_re,
			$marker_ol_re => $marker_ul_re,
			);

		foreach ($markers_relist as $marker_re => $other_marker_re) {
			# Re-usable pattern to match any entirel ul or ol list:
			$whole_list_re = '
				(								# $1 = whole list
				  (								# $2
					([ ]{0,'.$less_than_tab.'})	# $3 = number of spaces
					('.$marker_re.')			# $4 = first list item marker
					[ ]+
				  )
				  (?s:.+?)
				  (								# $5
					  \z
					|
					  \n{2,}
					  (?=\S)
					  (?!						# Negative lookahead for another list item marker
						[ ]*
						'.$marker_re.'[ ]+
					  )
					|
					  (?=						# Lookahead for another kind of list
					    \n
						\3						# Must have the same indentation
						'.$other_marker_re.'[ ]+
					  )
				  )
				)
			'; // mx

			# We use a different prefix before nested lists than top-level lists.
			# See extended comment in _ProcessListItems().

			if ($this->list_level) {
				$text = preg_replace_callback('{
						^
						'.$whole_list_re.'
					}mx',
					array(&$this, '_doLists_callback'), $text);
			}
			else {
				$text = preg_replace_callback('{
						(?:(?<=\n)\n|\A\n?) # Must eat the newline
						'.$whole_list_re.'
					}mx',
					array(&$this, '_doLists_callback'), $text);
			}
		}

		return $text;
	}
	protected function _doLists_callback($matches) {
		# Re-usable patterns to match list item bullets and number markers:
		$marker_ul_re  = '[*+-]';
		$marker_ol_re  = '\d+[\.]';
		$marker_any_re = "(?:$marker_ul_re|$marker_ol_re)";

		$list = $matches[1];
		$list_type = preg_match("/$marker_ul_re/", $matches[4]) ? "ul" : "ol";

		$marker_any_re = ( $list_type == "ul" ? $marker_ul_re : $marker_ol_re );

		$list .= "\n";
		$result = $this->processListItems($list, $marker_any_re);

		$result = $this->hashBlock("<$list_type>\n" . $result . "</$list_type>");
		return "\n". $result ."\n\n";
	}

#
#	Process the contents of a single ordered or unordered list, splitting it
#	into individual list items.
#
	# The $this->list_level global keeps track of when we're inside a list.
	# Each time we enter a list, we increment it; when we leave a list,
	# we decrement. If it's zero, we're not in a list anymore.
	#
	# We do this because when we're not inside a list, we want to treat
	# something like this:
	#
	#		I recommend upgrading to version
	#		8. Oops, now this line is treated
	#		as a sub-list.
	#
	# As a single paragraph, despite the fact that the second line starts
	# with a digit-period-space sequence.
	#
	# Whereas when we're inside a list (or sub-list), that line will be
	# treated as the start of a sub-list. What a kludge, huh? This is
	# an aspect of Markdown's syntax that's hard to parse perfectly
	# without resorting to mind-reading. Perhaps the solution is to
	# change the syntax rules such that sub-lists must start with a
	# starting cardinal number; e.g. "1." or "a.".
	private $list_level = 0;

	protected function processListItems($list_str, $marker_any_re) {
		$this->list_level++;

		# trim trailing blank lines:
		$list_str = preg_replace("/\n{2,}\\z/", "\n", $list_str);

		$list_str = preg_replace_callback('{
			(\n)?							# leading line = $1
			(^[ ]*)							# leading whitespace = $2
			('.$marker_any_re.'				# list marker and space = $3
				(?:[ ]+|(?=\n))	# space only required if item is not empty
			)
			((?s:.*?))						# list item text   = $4
			(?:(\n+(?=\n))|\n)				# tailing blank line = $5
			(?= \n* (\z | \2 ('.$marker_any_re.') (?:[ ]+|(?=\n))))
			}xm',
			array(&$this, '_processListItems_callback'), $list_str);

		$this->list_level--;
		return $list_str;
	}
	protected function _processListItems_callback($matches) {
		$item = $matches[4];
		$leading_line =& $matches[1];
		$leading_space =& $matches[2];
		$marker_space = $matches[3];
		$tailing_blank_line =& $matches[5];

		if ($leading_line || $tailing_blank_line || 
			preg_match('/\n{2,}/', $item))
		{
			# Replace marker with the appropriate whitespace indentation
			$item = $leading_space . str_repeat(' ', strlen($marker_space)) . $item;
			$item = $this->runBlockGamut($this->outdent($item)."\n");
		}
		else {
			# Recursion for sub-lists:
			$item = $this->doLists($this->outdent($item));
			$item = preg_replace('/\n+$/', '', $item);
			$item = $this->runSpanGamut($item);
		}

		return "<li>" . $item . "</li>\n";
	}

#
#	Process Markdown `<pre><code>` blocks.
#
	protected function doCodeBlocks($text) {
		$text = preg_replace_callback('{
				(?:\n\n|\A\n?)
				(	            # $1 = the code block -- one or more lines, starting with a space/tab
				  (?>
					[ ]{'.$this->tab_width.'}  # Lines must start with a tab or a tab-width of spaces
					.*\n+
				  )+
				)
				((?=^[ ]{0,'.$this->tab_width.'}\S)|\Z)	# Lookahead for non-space at line-start, or end of doc
			}xm',
			array(&$this, '_doCodeBlocks_callback'), $text);

		return $text;
	}
	protected function _doCodeBlocks_callback($matches) {
		$codeblock = $matches[1];

		$codeblock = $this->outdent($codeblock);
		$codeblock = htmlspecialchars($codeblock, ENT_NOQUOTES);

		# trim leading newlines and trailing newlines
		$codeblock = preg_replace('/\A\n+|\n+\z/', '', $codeblock);

		$codeblock = "<pre><code>$codeblock\n</code></pre>";
		return "\n\n".$this->hashBlock($codeblock)."\n\n";
	}

#
# Process blockquotes.
#
	protected function doBlockQuotes($text) {
		$text = preg_replace_callback('/
			  (								# Wrap whole match in $1
				(?>
				  ^[ ]*>[ ]?			# ">" at the start of a line
					.+\n					# rest of the first line
				  (.+\n)*					# subsequent consecutive lines
				  \n*						# blanks
				)+
			  )
			/xm',
			array(&$this, '_doBlockQuotes_callback'), $text);

		return $text;
	}
	protected function _doBlockQuotes_callback($matches) {
		$bq = $matches[1];
		# trim one level of quoting - trim whitespace-only lines
		$bq = preg_replace('/^[ ]*>[ ]?|^[ ]+$/m', '', $bq);
		$bq = $this->runBlockGamut($bq);		# recurse

		$bq = preg_replace('/^/m', "  ", $bq);
		# These leading spaces cause problem with <pre> content, 
		# so we need to fix that:
		$bq = preg_replace_callback('{(\s*<pre>.+?</pre>)}sx', 
			array(&$this, '_doBlockQuotes_callback2'), $bq);

		return "\n". $this->hashBlock("<blockquote>\n$bq\n</blockquote>")."\n\n";
	}
	protected function _doBlockQuotes_callback2($matches) {
		$pre = $matches[1];
		$pre = preg_replace('/^  /m', '', $pre);
		return $pre;
	}

#
# Take the string $str and parse it into tokens, hashing embeded HTML, escaped
# characters and handling code spans.
#
	protected function parseSpan($str) {
		$output = '';

		$span_re = '{
				(
					\\\\'.$this->escape_chars_re.'
				|
					(?<![`\\\\])
					`+						# code span marker
				)
				}xs';

		while (1) {
			#
			# Each loop iteration seach for either the next tag, the next 
			# openning code span marker, or the next escaped character. 
			# Each token is then passed to handleSpanToken.
			#
			$parts = preg_split($span_re, $str, 2, PREG_SPLIT_DELIM_CAPTURE);

			# Create token from text preceding tag.
			if ($parts[0] != "") {
				$output .= $parts[0];
			}

			# Check if we reach the end.
			if (isset($parts[1])) {
				$output .= $this->handleSpanToken($parts[1], $parts[2]);
				$str = $parts[2];
			}
			else {
				break;
			}
		}

		return $output;
	}

#
# Handle $token provided by parseSpan by determining its nature and returning
# the corresponding value that should replace it.
#
	protected function handleSpanToken($token, &$str) {
		switch ($token{0}) {
			case "\\":
				return $this->hashPart("&#". ord($token{1}). ";");
			case "`":
				# Search for end marker in remaining text.
				if (preg_match('/^(.*?[^`])'.preg_quote($token).'(?!`)(.*)$/sm', 
					$str, $matches))
				{
					$str = $matches[2];
					$codespan = $this->makeCodeSpan($matches[1]);
					return $this->hashPart($codespan);
				}
				return $token; // return as text since no ending marker found.
			default:
				return $this->hashPart($token);
		}
	}

#
# Create a code span markup for $code.
#
	protected function makeCodeSpan($code) {
		$code = htmlspecialchars(trim($code), ENT_NOQUOTES);
		return $this->hashPart("<code>$code</code>");
	}

#
# Turn Markdown image shortcuts into <img> tags.
#
	protected function doImages($text) {
		#
		# First, handle reference-style labeled images: ![alt text][id]
		#
		$text = preg_replace_callback('{
			(				# wrap whole match in $1
			  !\[
				('.$this->nested_brackets_re.')		# alt text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]

			)
			}xs', 
			array(&$this, '_doImages_reference_callback'), $text);

		#
		# Next, handle inline images:  ![alt text](url "optional title")
		# Don't forget: encode * and _
		#
		$text = preg_replace_callback('{
			(				# wrap whole match in $1
			  !\[
				('.$this->nested_brackets_re.')		# alt text = $2
			  \]
			  \s?			# One optional whitespace character
			  \(			# literal paren
				[ \n]*
				(?:
					<(\S*)>	# src url = $3
				|
					('.$this->nested_url_parenthesis_re.')	# src url = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# title = $7
				  \6		# matching quote
				  [ \n]*
				)?			# title is optional
			  \)
			)
			}xs',
			array(&$this, '_doImages_inline_callback'), $text);

		return $text;
	}
	protected function _doImages_reference_callback($matches) {
		$whole_match = $matches[1];
		$alt_text    = $matches[2];
		$link_id     = strtolower($matches[3]);

		if ($link_id == "") {
			$link_id = strtolower($alt_text); # for shortcut links like ![this][].
		}

		$alt_text = $this->encodeAttribute($alt_text);
		if (isset($this->urls[$link_id])) {
			$url = $this->encodeAttribute($this->urls[$link_id]);
			$result = "<img src=\"$url\" alt=\"$alt_text\"";
			if (isset($this->titles[$link_id])) {
				$title = $this->titles[$link_id];
				$title = $this->encodeAttribute($title);
				$result .=  " title=\"$title\"";
			}
			$result .= ' />';
			$result = $this->hashPart($result);
		}
		else {
			# If there's no such link ID, leave intact:
			$result = $whole_match;
		}

		return $result;
	}
	protected function _doImages_inline_callback($matches) {
		$whole_match	= $matches[1];
		$alt_text		= $matches[2];
		$url			= $matches[3] == '' ? $matches[4] : $matches[3];
		$title			=& $matches[7];

		$alt_text = $this->encodeAttribute($alt_text);
		$url = $this->encodeAttribute($url);
		$result = "<img src=\"$url\" alt=\"$alt_text\"";
		if (isset($title)) {
			$title = $this->encodeAttribute($title);
			$result .=  " title=\"$title\""; # $title already quoted
		}
		$result .= ' />';

		return $this->hashPart($result);
	}

#
# Turn Markdown link shortcuts into XHTML <a> tags.
#
	protected function doAnchors($text) {
		if ($this->in_anchor) return $text;
		$this->in_anchor = true;

		#
		# First, handle reference-style links: [link text] [id]
		#
		$text = preg_replace_callback('{
			(					# wrap whole match in $1
			  \[
				('.$this->nested_brackets_re.')	# link text = $2
			  \]

			  [ ]?				# one optional space
			  (?:\n[ ]*)?		# one optional newline followed by spaces

			  \[
				(.*?)		# id = $3
			  \]
			)
			}xs',
			array(&$this, '_doAnchors_reference_callback'), $text);

		#
		# Next, inline-style links: [link text](url "optional title")
		#
		$text = preg_replace_callback('{
			(				# wrap whole match in $1
			  \[
				('.$this->nested_brackets_re.')	# link text = $2
			  \]
			  \(			# literal paren
				[ \n]*
				(?:
					<(.+?)>	# href = $3
				|
					('.$this->nested_url_parenthesis_re.')	# href = $4
				)
				[ \n]*
				(			# $5
				  ([\'"])	# quote char = $6
				  (.*?)		# Title = $7
				  \6		# matching quote
				  [ \n]*	# ignore any spaces/tabs between closing quote and )
				)?			# title is optional
			  \)
			)
			}xs',
			array(&$this, '_doAnchors_inline_callback'), $text);

		#
		# Last, handle reference-style shortcuts: [link text]
		# These must come last in case you've also got [link text][1]
		# or [link text](/foo)
		#
		$text = preg_replace_callback('{
			(					# wrap whole match in $1
			  \[
				([^\[\]]+)		# link text = $2; can\'t contain [ or ]
			  \]
			)
			}xs',
			array(&$this, '_doAnchors_reference_callback'), $text);

		$this->in_anchor = false;
		return $text;
	}
	protected function _doAnchors_reference_callback($matches) {
		$whole_match =  $matches[1];
		$link_text   =  $matches[2];
		$link_id     =& $matches[3];

		if ($link_id == "") {
			# for shortcut links like [this][] or [this].
			$link_id = $link_text;
		}

		# lower-case and turn embedded newlines into spaces
		$link_id = strtolower($link_id);
		$link_id = preg_replace('{[ ]?\n}', ' ', $link_id);

		if (isset($this->urls[$link_id])) {
			$url = $this->urls[$link_id];
			$url = $this->encodeAttribute($url);

			$result = "<a href=\"$url\"";
			if ( isset( $this->titles[$link_id] ) ) {
				$title = $this->titles[$link_id];
				$title = $this->encodeAttribute($title);
				$result .=  " title=\"$title\"";
			}

			$link_text = $this->runSpanGamut($link_text);
			$result .= ">$link_text</a>";
			$result = $this->hashPart($result);
		}
		else {
			$result = $whole_match;
		}
		return $result;
	}
	protected function _doAnchors_inline_callback($matches) {
		$whole_match	=  $matches[1];
		$link_text		=  $this->runSpanGamut($matches[2]);
		$url			=  $matches[3] == '' ? $matches[4] : $matches[3];
		$title			=& $matches[7];

		$url = $this->encodeAttribute($url);

		$result = "<a href=\"$url\"";
		if (isset($title)) {
			$title = $this->encodeAttribute($title);
			$result .=  " title=\"$title\"";
		}

		$link_text = $this->runSpanGamut($link_text);
		$result .= ">$link_text</a>";

		return $this->hashPart($result);
	}

#
# Process <email> or <url>
#
	protected function doAutoLinks($text) {
		$text = preg_replace_callback('{<((https?|ftp|dict):[^\'">\s]+)>}i', 
			array(&$this, '_doAutoLinks_url_callback'), $text);

		# Email addresses: <address@domain.foo>
		$text = preg_replace_callback('{
			<
			(?:mailto:)?
			(
				(?:
					[-!#$%&\'*+/=?^_`.{|}~\w\x80-\xFF]+
				|
					".*?"
				)
				\@
				(?:
					[-a-z0-9\x80-\xFF]+(\.[-a-z0-9\x80-\xFF]+)*\.[a-z]+
				|
					\[[\d.a-fA-F:]+\]	# IPv4 & IPv6
				)
			)
			>
			}xi',
			array(&$this, '_doAutoLinks_email_callback'), $text);

		return $text;
	}
	protected function _doAutoLinks_url_callback($matches) {
		$url = $this->encodeAttribute($matches[1]);
		$link = "<a href=\"$url\">$url</a>";
		return $this->hashPart($link);
	}
	protected function _doAutoLinks_email_callback($matches) {
		$address = $matches[1];
		$link = $this->encodeEmailAddress($address);
		return $this->hashPart($link);
	}

#
#	Input: an email address, e.g. "foo@example.com"
#
#	Output: the email address as a mailto link, with each character
#		of the address encoded as either a decimal or hex entity, in
#		the hopes of foiling most address harvesting spam bots. E.g.:
#
#	  <p><a href="&#109;&#x61;&#105;&#x6c;&#116;&#x6f;&#58;&#x66;o&#111;
#        &#x40;&#101;&#x78;&#97;&#x6d;&#112;&#x6c;&#101;&#46;&#x63;&#111;
#        &#x6d;">&#x66;o&#111;&#x40;&#101;&#x78;&#97;&#x6d;&#112;&#x6c;
#        &#101;&#46;&#x63;&#111;&#x6d;</a></p>
#
#	Based by a filter by Matthew Wickline, posted to BBEdit-Talk.
#   With some optimizations by Milian Wolff.
#
	protected function encodeEmailAddress($addr) {
		$addr = "mailto:" . $addr;
		$chars = preg_split('/(?<!^)(?!$)/', $addr);
		$seed = (int)abs(crc32($addr) / strlen($addr)); # Deterministic seed.

		foreach ($chars as $key => $char) {
			$ord = ord($char);
			# Ignore non-ascii chars.
			if ($ord < 128) {
				$r = ($seed * (1 + $key)) % 100; # Pseudo-random function.
				# roughly 10% raw, 45% hex, 45% dec
				# '@' *must* be encoded. I insist.
				if ($r > 90 && $char != '@') /* do nothing */;
				else if ($r < 45) $chars[$key] = '&#x'.dechex($ord).';';
				else              $chars[$key] = '&#'.$ord.';';
			}
		}

		$addr = implode('', $chars);
		$text = implode('', array_slice($chars, 7)); # text without `mailto:`
		$addr = "<a href=\"$addr\">$text</a>";

		return $addr;
	}

#
# Process italic and bold
#
	protected function doItalicsAndBold($text) {
		$token_stack = array('');
		$text_stack = array('');
		$em = '';
		$strong = '';
		$tree_char_em = false;

		while (1) {
			#
			# Get prepared regular expression for seraching emphasis tokens
			# in current context.
			#
			$token_re = $this->em_strong_prepared_relist["$em$strong"];

			#
			# Each loop iteration search for the next emphasis token. 
			# Each token is then passed to handleSpanToken.
			#
			$parts = preg_split($token_re, $text, 2, PREG_SPLIT_DELIM_CAPTURE);
			$text_stack[0] .= $parts[0];
			$token =& $parts[1];
			$text =& $parts[2];

			if (empty($token)) {
				# Reached end of text span: empty stack without emitting.
				# any more emphasis.
				while ($token_stack[0]) {
					$text_stack[1] .= array_shift($token_stack);
					$text_stack[0] .= array_shift($text_stack);
				}
				break;
			}

			$token_len = strlen($token);
			if ($tree_char_em) {
				# Reached closing marker while inside a three-char emphasis.
				if ($token_len == 3) {
					# Three-char closing marker, close em and strong.
					array_shift($token_stack);
					$span = array_shift($text_stack);
					$span = $this->runSpanGamut($span);
					$span = "<strong><em>$span</em></strong>";
					$text_stack[0] .= $this->hashPart($span);
					$em = '';
					$strong = '';
				} else {
					# Other closing marker: close one em or strong and
					# change current token state to match the other
					$token_stack[0] = str_repeat($token{0}, 3-$token_len);
					$tag = $token_len == 2 ? "strong" : "em";
					$span = $text_stack[0];
					$span = $this->runSpanGamut($span);
					$span = "<$tag>$span</$tag>";
					$text_stack[0] = $this->hashPart($span);
					$$tag = ''; # $$tag stands for $em or $strong
				}
				$tree_char_em = false;
			} else if ($token_len == 3) {
				if ($em) {
					# Reached closing marker for both em and strong.
					# Closing strong marker:
					for ($i = 0; $i < 2; ++$i) {
						$shifted_token = array_shift($token_stack);
						$tag = strlen($shifted_token) == 2 ? "strong" : "em";
						$span = array_shift($text_stack);
						$span = $this->runSpanGamut($span);
						$span = "<$tag>$span</$tag>";
						$text_stack[0] .= $this->hashPart($span);
						$$tag = ''; # $$tag stands for $em or $strong
					}
				} else {
					# Reached opening three-char emphasis marker. Push on token 
					# stack; will be handled by the special condition above.
					$em = $token{0};
					$strong = "$em$em";
					array_unshift($token_stack, $token);
					array_unshift($text_stack, '');
					$tree_char_em = true;
				}
			} else if ($token_len == 2) {
				if ($strong) {
					# Unwind any dangling emphasis marker:
					if (strlen($token_stack[0]) == 1) {
						$text_stack[1] .= array_shift($token_stack);
						$text_stack[0] .= array_shift($text_stack);
					}
					# Closing strong marker:
					array_shift($token_stack);
					$span = array_shift($text_stack);
					$span = $this->runSpanGamut($span);
					$span = "<strong>$span</strong>";
					$text_stack[0] .= $this->hashPart($span);
					$strong = '';
				} else {
					array_unshift($token_stack, $token);
					array_unshift($text_stack, '');
					$strong = $token;
				}
			} else {
				# Here $token_len == 1
				if ($em) {
					if (strlen($token_stack[0]) == 1) {
						# Closing emphasis marker:
						array_shift($token_stack);
						$span = array_shift($text_stack);
						$span = $this->runSpanGamut($span);
						$span = "<em>$span</em>";
						$text_stack[0] .= $this->hashPart($span);
						$em = '';
					} else {
						$text_stack[0] .= $token;
					}
				} else {
					array_unshift($token_stack, $token);
					array_unshift($text_stack, '');
					$em = $token;
				}
			}
		}
		return $text_stack[0];
	}

#
# Process hard breaks
#
	protected function doHardBreaks($text) {
		return preg_replace_callback('/ {2,}\n/', 
			array(&$this, '_doHardBreaks_callback'), $text);
	}
	protected function _doHardBreaks_callback($matches) {
		return $this->hashPart("<br />\n");
	}

#
# Called whenever a tag must be hashed when a function insert an atomic 
# element in the text stream. Passing $text to through this function gives
# a unique text-token which will be reverted back when calling unhash.
#
# The $boundary argument specify what character should be used to surround
# the token. By convension, "B" is used for block elements that needs not
# to be wrapped into paragraph tags at the end, ":" is used for elements
# that are word separators and "X" is used in the general case.
#
	protected function hashPart($text, $boundary = 'X') {
		# Swap back any tag hash found in $text so we do not have to `unhash`
		# multiple times at the end.
		$text = $this->unhash($text);

		# Then hash the block.
		static $i = 0;
		$key = "$boundary\x1A" . ++$i . $boundary;
		$this->html_hashes[$key] = $text;
		return $key; # String that will replace the tag.
	}

#
# Shortcut function for hashPart with block-level boundaries.
#
	protected function hashBlock($text) {
		return $this->hashPart($text, 'B');
	}

#
# Swap back in all the tags hashed by _HashHTMLBlocks.
# Is this function still usefull, considering _HashHTMLBlocks was removed (no 
# html tags authorized in comments)?
#
	protected function unhash($text) {
		return preg_replace_callback('/(.)\x1A[0-9]+\1/', 
			array(&$this, '_unhash_callback'), $text);
	}
	protected function _unhash_callback($matches) {
		return $this->html_hashes[$matches[0]];
	}

#
# Encode text for a double-quoted HTML attribute. This function is *not*
# suitable for attributes enclosed in single quotes.
#
	protected function encodeAttribute($text) {
		$text = $this->encodeAmpsAndAngles($text);
		$text = str_replace('"', '&quot;', $text);
		return $text;
	}

#
# Smart processing for ampersands and angle brackets that need to be encoded.
# Valid character entities are left alone unless the no-entities mode is set.
#
	protected function encodeAmpsAndAngles($text) {
		# Ampersand-encoding based entirely on Nat Irons's Amputator
		# MT plugin: <http://bumppo.net/projects/amputator/>
		$text = preg_replace('/&(?!#?[xX]?(?:[0-9a-fA-F]+|\w+);)/', 
							'&amp;', $text);;
		# Encode remaining <'s
		$text = str_replace('<', '&lt;', $text);

		return $text;
	}
}

?>