Markdown.php

<?php defined('SYSPATH') or die('No direct script access.');
/**
* A text-to-HTML conversion tool for web writers for Kohana 3.
*
* Based off the php created by Michel Fortin under the gpl lisense. For more
* information, please refer to:
* <http://michelf.com/projects/php-markdown/>
*
* Original Markdown concept by John Gruber. Please refer to:
* <http://daringfireball.net/projects/markdown/>
*
* Markdown is a text-to-HTML filter; it translates an easy-to-read /
* easy-to-write structured text format into HTML. Markdown's text format
* is most similar to that of plain text email, and supports features such
* as headers, *emphasis*, code blocks, blockquotes, and links.
*
* Markdown's syntax is designed not as a generic markup language, but
* specifically to serve as a front-end to (X)HTML. You can use span-level
* HTML tags anywhere in a Markdown document, and you can use block level
* HTML tags (like <div> and <table> as well).
*
* For more information about Markdown's syntax, see:
* <http://daringfireball.net/projects/markdown/>
*
* @Gary Stidston-Broadbent <kohana_api@stroppytux.net>
* @package Markdown
* @copyright (c) 2010 Unmagnify team
* @license http://www.gnu.org/licenses/old-licenses/gpl-2.0.txt
* @version $id$
* @link http://www.stroppytux.net/projects/kohana-markdown/
* @since Available since Release 1.0
*/

class Kohana_Markdown
{
	/* Paramaters used for singleton */
	public static $instances = array();
	public static $default = 'default';
	protected $_config;

	/* Regex to use in the Validation class */
	public static $validate = '/[[:punct:][:space:]]{0,}/';

	/* Regex to match balanced [brackets] used to insert max bracked depth */
	protected $nested_url_parenthesis_depth = 4;
	protected $nested_url_parenthesis_re;
	protected $nested_brackets_depth = 6;
	protected $nested_brackets_re;

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

	/* Change to ">" for HTML output. */
	protected $suffix = ' />';
	protected $tab_width = 4;

	/* Change to `true` to disallow markup or entities. */
	protected $no_entities = false;
	protected $no_markup = false;

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

	/* Internal hashes used during transformation. */
	protected $urls = array();
	protected $titles = array();
	protected $html_hashes = array();

	/* Status flag to avoid invalid nesting. */
	protected $in_anchor = false;
	protected $list_level = 0;

	/* Strip link definitions, store in hashes. */
	protected $document_gamut = array(
		"strip_link_definitions"=> 20,
		"run_basic_block_gamut"	=> 30,
		);

	/* Transformations to form block-level tags. eg. p, h1,h2,h3, ol,ul. */
	protected $block_gamut = array(
		"do_headers"			=> 10,
		"do_horizontal_rules"	=> 20,
		"do_lists"				=> 40,
		"do_code_blocks"		=> 50,
		"do_block_quotes"		=> 60,
		);

	/* Transformations that occur *within* block-level tags */
	protected $span_gamut = array(
		/* Process char escapes, code spans, and inline HTML in one shot. */
		"parseSpan"				=> -30,

		/* Process anchor and image tags. Images must come first, because
		 * ![foo][f] looks like an anchor.
		 */
		"do_images"				=> 10,
		"do_anchors"			=> 20,

		/* Make links out of things like `<http://example.com/>`. Must come
		 * after do_anchors, because you can use < and > delimiters in inline
		 * links like [this](<url>).
		 */
		"doAutoLinks"			=> 30,
		"encode_amps_and_angles"	=> 40,

		"do_italics_and_bold"	=> 50,
		"do_hard_breaks"		=> 60,
		);

	protected $em_relist = array(
		''  => '(?:(?<!\*)\*(?!\*)|(?<!_)_(?!_))(?=\S|$)(?![.,:;]\s)',
		'*' => '(?<=\S|^)(?<!\*)\*(?!\*)',
		'_' => '(?<=\S|^)(?<!_)_(?!_)',
		);
	protected $strong_relist = array(
		''   => '(?:(?<!\*)\*\*(?!\*)|(?<!_)__(?!_))(?=\S|$)(?![.,:;]\s)',
		'**' => '(?<=\S|^)(?<!\*)\*\*(?!\*)',
		'__' => '(?<=\S|^)(?<!_)__(?!_)',
		);
	protected $em_strong_relist = array(
		''    => '(?:(?<!\*)\*\*\*(?!\*)|(?<!_)___(?!_))(?=\S|$)(?![.,:;]\s)',
		'***' => '(?<=\S|^)(?<!\*)\*\*\*(?!\*)',
		'___' => '(?<=\S|^)(?<!_)___(?!_)',
		);
	protected $em_strong_prepared_relist;

	/* String length function for detab. `init_detab` will create a function to 
	 * hanlde UTF-8 if the default function does not exist.
	 */
	protected $utf8_strlen = 'mb_strlen';

	/**
	 * Constructs the markdown parser. This method cannot be invoked externally.
	 * The markdown parser must be instantiated using `Markdown::instance()`.
	 *
	 * @param   array    config 
	 * @throws  Kohana_Markdown_Exception
	 */
	protected function __construct(array $config)
	{
		/* Load our configuration options */
		$this->_config = $config;
		$this->suffix = ($this->_config['tab_width'] == 'html') ? '>' : ' />';
		$this->tab_width = $this->_config['tab_width'];
		$this->no_entities = $this->_config['no_entities'];
		$this->no_markup = $this->_config['no_markup'];

		$this->init_detab();
		$this->prepare_italics_and_bold();

		$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).']';

		# Sort document, block, and span gamut in ascendent priority order.
		asort($this->document_gamut);
		asort($this->block_gamut);
		asort($this->span_gamut);
	}

	/**
	 * Creates a singleton of a Kohana Markdown parser. If no parser is supplied
	 * the __default__ markdown parser is used.
	 *
	 *     // Create an instance of the default parser
	 *     $default_parser = Markdown::instance();
	 *
	 *     // Create an instance of a parser
	 *     $foo_parser = Markdown::instance('foo');
	 *
	 *     // Access an instantiated parser directly
	 *     $foo_parser = Markdown::$instances['default'];
	 *
	 * @param   string   the name of the markdown parser to use [Optional]
	 * @return  Markdown
	 * @throws  Kohana_Markdown_Exception
	 */
	public static function instance($parser = NULL)
	{
		/* If there is no parser supplied, use the default parser */
		if ($parser === NULL) {
			$parser = Markdown::$default;
		}

		/* Return the current parser if its already initiated */
		if (isset(Markdown::$instances[$parser])) {
			return Markdown::$instances[$parser];
		}

		$config = Kohana::$config->load('markdown');
		if (!$config->offsetExists($parser)) {
			throw new Kohana_Markdown_Exception('Failed to load Kohana Markdown parser: :parser', array(':parser' => $parser));
		}
		$config = $config->get($parser);

		/* Create a new markdown instance */
		Markdown::$instances[$parser] = new Markdown($config);

		/* Return the instance */
		return Markdown::$instances[$parser];
	}

	/**
	 * Overload the __clone() method to prevent cloning
	 *
	 * @return  void
	 * @throws  Kohana_Markdown_Exception
	 */
	public function __clone()
	{
		throw new Kohana_Markdown_Exception('Cloning of Kohana_Markdown objects is forbidden');
	}

	/**
	 * Called before the transformation process starts to setup parser states.
	 *
	 * @return  void
	 */
	protected function before()
	{
		/* Clear out the 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.
	 *
	 * @return  void
	 */
	protected function after()
	{
		$this->urls = array();
		$this->titles = array();
		$this->html_hashes = array();
	}

	/**
	 * Main function. Performs some preprocessing on the input text and pass it
	 * through the document gamut.
	 *
	 * @param   string	The markdown content to be transformed into (x)html.
	 * @return  string	The transformed (x)html.
	 */
	public function transform($text)
	{
		/* Initialise the storage arrays */
		$this->before();

		/* 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);

		/* Turn block-level HTML blocks into hash entries */
		$text = $this->hash_HTML_blocks($text);

		/* Strip any lines consisting only of spaces and tabs. This makes any
		 * 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 => $priority) {
			$text = $this->$method($text);
		}

		/* Cleanup memory */
		$this->after();

		/* Return the new (x)html content */
		return $text . "\n";
	}

	/**
	 * Strips link definitions from text, stores the URLs and titles in hash
	 * references.
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   The resulting hash references for link definitions.
	 */
	protected function strip_link_definitions($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, '_strip_link_definitions_callback'), $text);
		return $text;
	}

	protected function _strip_link_definitions_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 */
	}

	/**
	 * Hashify HTML blocks:
	 * We only want to do this for block-level HTML tags, such as headers,
	 * lists, and tables. That's because we still want to wrap <p>s around
	 * "paragraphs" that are wrapped in non-block-level tags, such as anchors,
	 * phrase emphasis, and spans. The list of tags we're looking for is
	 * hard-coded:
	 *
	 * *  List "a" is made of tags which can be both inline or block-level.
	 *    These will be treated block-level when the start tag is alone on 
	 *    its line, otherwise they're not matched here and will be taken as 
	 *    inline later.
	 * *  List "b" is made of tags which are always block-level;
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   The resulting hash references for link definitions.
	 */
	protected function hash_HTML_blocks($text)
	{
		if ($this->no_markup)  return $text;

		$less_than_tab = $this->tab_width - 1;

		$block_tags_a_re = 'ins|del';
		$block_tags_b_re = 'p|div|h[1-6]|blockquote|pre|table|dl|ol|ul|address|'.
						   'script|noscript|form|fieldset|iframe|math';

		/* Regular expression for the content of a block tag. */
		$nested_tags_level = 4;
		$attr = '
			(?>				# optional tag attributes
			  \s			# starts with whitespace
			  (?>
				[^>"/]+		# text outside quotes
			  |
				/+(?!>)		# slash not followed by ">"
			  |
				"[^"]*"		# text inside double quotes (tolerate ">")
			  |
				\'[^\']*\'	# text inside single quotes (tolerate ">")
			  )*
			)?	
			';
		$content =
			str_repeat('
				(?>
				  [^<]+			# content without tag
				|
				  <\2			# nested opening tag
					'.$attr.'	# attributes
					(?>
					  />
					|
					  >', $nested_tags_level).	# end of opening tag
					  '.*?'.					# last level nested tag content
			str_repeat('
					  </\2\s*>	# closing nested tag
					)
				  |				
					<(?!/\2\s*>	# other tags with a different name
				  )
				)*',
				$nested_tags_level);
		$content2 = str_replace('\2', '\3', $content);

		/* First, look for nested blocks, e.g.:
		 * 	<div>
		 * 		<div>
		 * 		tags for inner block must be indented.
		 * 		</div>
		 * 	</div>
		 *
		 * The outermost tags must start at the left margin for this to match, and
		 * the inner nested divs must be indented.
		 * We need to do this before the next, more liberal match, because the next
		 * match will start at the first `<div>` and stop at the first `</div>`.
		 */
		$text = preg_replace_callback('{(?>
			(?>
				(?<=\n\n)		# Starting after a blank line
				|				# or
				\A\n?			# the beginning of the doc
			)
			(						# save in $1

			  # Match from `\n<tag>` to `</tag>\n`, handling nested tags 
			  # in between.
					
						[ ]{0,'.$less_than_tab.'}
						<('.$block_tags_b_re.')# start tag = $2
						'.$attr.'>			# attributes followed by > and \n
						'.$content.'		# content, support nesting
						</\2>				# the matching end tag
						[ ]*				# trailing spaces/tabs
						(?=\n+|\Z)	# followed by a newline or end of document

			| # Special version for tags of group a.

						[ ]{0,'.$less_than_tab.'}
						<('.$block_tags_a_re.')# start tag = $3
						'.$attr.'>[ ]*\n	# attributes followed by >
						'.$content2.'		# content, support nesting
						</\3>				# the matching end tag
						[ ]*				# trailing spaces/tabs
						(?=\n+|\Z)	# followed by a newline or end of document
					
			| # Special case just for <hr />. It was easier to make a special 
			  # case than to make the other regex more complicated.
			
						[ ]{0,'.$less_than_tab.'}
						<(hr)				# start tag = $2
						'.$attr.'			# attributes
						/?>					# the matching end tag
						[ ]*
						(?=\n{2,}|\Z)		# followed by a blank line or end of document
			
			| # Special case for standalone HTML comments:
			
					[ ]{0,'.$less_than_tab.'}
					(?s:
						<!-- .*? -->
					)
					[ ]*
					(?=\n{2,}|\Z)		# followed by a blank line or end of document
			
			| # PHP and ASP-style processor instructions (<? and <%)
			
					[ ]{0,'.$less_than_tab.'}
					(?s:
						<([?%])			# $2
						.*?
						\2>
					)
					[ ]*
					(?=\n{2,}|\Z)		# followed by a blank line or end of document
					
			)
			)}Sxmi',
			array(&$this, '_hash_HTML_blocks_callback'),
			$text);

		return $text;
	}

	protected function _hash_HTML_blocks_callback($matches)
	{
		$text = $matches[1];
		$key  = $this->hash_block($text);
		return "\n\n$key\n\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 $boundary argument specify what character should be used to surround
	 * the token. By convension, "B" is used for block elements that needs not
	 * to be wrapped into paragraph tags at the end, ":" is used for elements
	 * that are word separators and "X" is used in the general case.
	 *
	 * @param   string   The markdown getting transformed.
	 * @param   string   The boundry to use to surround a token.
	 * @return  string   String that will replace the tag.
	 */
	protected function hash_part($text, $boundary = 'X')
	{
		/* Swap back any tag hash found in $text so we dont 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;
	}

	/**
	 * Shortcut function for hash_part with block-level boundaries.
	 * @param   string   The markdown getting transformed.
	 * @return  string   String that will replace the tag.
	 */
	protected function hash_block($text)
	{
		return $this->hash_part($text, 'B');
	}

	/**
	 * Run block gamut tranformations.
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   String that will replace the tag.
	 */
	protected function run_block_gamut($text)
	{
		/* We need to escape raw HTML in Markdown source before doing anything 
		 * else. This need to be done for each block, and not only at the 
		 * begining in the Markdown function since hashed blocks can be part of
		 * list items and could have been indented. Indented blocks would have 
		 * been seen as a code block in a previous pass of hash_HTML_blocks.
		 */
		$text = $this->hash_HTML_blocks($text);
		
		return $this->run_basic_block_gamut($text);
	}

	/**
	 * Run block gamut tranformations, without hashing HTML blocks. This is 
	 * useful when HTML blocks are known to be already hashed, like in the first
	 * whole-document pass.
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   String that will replace the tag.
	 */
	protected function run_basic_block_gamut($text)
	{
		foreach ($this->block_gamut as $method => $priority) {
			$text = $this->$method($text);
		}
		
		# Finally form paragraph and restore hashed blocks.
		$text = $this->form_paragraphs($text);

		return $text;
	}

	/**
	 * Add horizontal rules to the output.
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   String that will replace the tag.
	 */
	protected function do_horizontal_rules($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".$this->hash_block("<hr$this->suffix")."\n", 
			$text);
	}

	/**
	 * Run span gamut tranformations.
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   String that will replace the tag.
	 */
	protected function run_span_gamut($text)
	{
		foreach ($this->span_gamut as $method => $priority) {
			$text = $this->$method($text);
		}

		return $text;
	}

	/**
	 * Do hard breaks:
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   String that will replace the tag.
	 */
	protected function do_hard_breaks($text)
	{
		return preg_replace_callback('/ {2,}\n/', 
			array(&$this, '_do_hard_breaks_callback'), $text);
	}

	protected function _do_hard_breaks_callback($matches)
	{
		return $this->hash_part("<br$this->suffix\n");
	}

	/**
	 * Turn Markdown link shortcuts into (x)html <a> tags.
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   String that will replace the tag.
	 */
	function do_anchors($text)
	{
		if ($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, '_do_anchors_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, '_do_anchors_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, '_do_anchors_reference_callback'), $text);

		$this->in_anchor = false;
		return $text;
	}

	protected function _do_anchors_reference_callback($matches)
	{
		$whole_match =  $matches[1];
		$link_text   =  $matches[2];
		$link_id     =& $matches[3];

		/* for shortcut links like [this][] or [this]. */
		if ($link_id == "") {
			$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 = $this->encode_attribute($url);

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

			$link_text = $this->run_span_gamut($link_text);
			$result .= ">$link_text</a>";
			$result = $this->hash_part($result);
		} else {
			$result = $whole_match;
		}
		return $result;
	}

	protected function _do_anchors_inline_callback($matches)
	{
		$whole_match	=  $matches[1];
		$link_text		=  $this->run_span_gamut($matches[2]);
		$url			=  $matches[3] == '' ? $matches[4] : $matches[3];
		$title			=& $matches[7];

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

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

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

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

	/**
	 * Turn Markdown image shortcuts into <img> tags.
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   String that will replace the tag.
	 */
	protected function do_images($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, '_do_images_reference_callback'), $text);

		/* Next, handle inline images: ![alt text](url "optional title"). */
		$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, '_do_images_inline_callback'), $text);

		return $text;
	}

	protected function _do_images_reference_callback($matches)
	{
		$whole_match = $matches[1];
		$alt_text    = $matches[2];
		$link_id     = strtolower($matches[3]);

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

		$alt_text = $this->encode_attribute($alt_text);
		if (isset($this->urls[$link_id])) {
			$url = $this->encode_attribute($this->urls[$link_id]);
			$result = "<img src=\"$url\" alt=\"$alt_text\"";
			if (isset($this->titles[$link_id])) {
				$title = $this->titles[$link_id];
				$title = $this->encode_attribute($title);
				$result .=  " title=\"$title\"";
			}
			$result .= $this->suffix;
			$result = $this->hash_part($result);

		/* If there's no such link ID, leave intact: */
		} else {
			$result = $whole_match;
		}

		return $result;
	}

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

		$alt_text = $this->encode_attribute($alt_text);
		$url = $this->encode_attribute($url);
		$result = "<img src=\"$url\" alt=\"$alt_text\"";

		/* $title already quoted */
		if (isset($title)) {
			$title = $this->encode_attribute($title);
			$result .=  " title=\"$title\"";
		}
		$result .= $this->suffix;

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

	/**
	 * Turn Markdown headers into (x)html h[1-6] tags.
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   String that will replace the tag.
	 */
	protected function do_headers($text)
	{
		/* Setext-style headers:
		 *		Header 1
		 *		========
		 *
		 *		Header 2
		 *		--------
		 */
		$text = preg_replace_callback('{ ^(.+?)[ ]*\n(=+|-+)[ ]*\n+ }mx',
			array(&$this, '_do_headers_callback_setext'), $text);

		/* atx-style headers:
		 *		# Header 1
		 *		## Header 2
		 *	## Header 2 with closing hashes ##
		 *	...
		 *	###### Header 6
		 */
		$text = preg_replace_callback('{
				^(\#{1,6})	# $1 = string of #\'s
				[ ]*
				(.+?)		# $2 = Header text
				[ ]*
				\#*			# optional closing #\'s (not counted)
				\n+
			}xm',
			array(&$this, '_do_headers_callback_atx'), $text);

		return $text;
	}

	protected function _do_headers_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} == '=' ? 1 : 2;
		$block = "<h$level>".$this->run_span_gamut($matches[1])."</h$level>";
		return "\n" . $this->hash_block($block) . "\n\n";
	}

	protected function _do_headers_callback_atx($matches)
	{
		$level = strlen($matches[1]);
		$block = "<h$level>".$this->run_span_gamut($matches[2])."</h$level>";
		return "\n" . $this->hash_block($block) . "\n\n";
	}

	/**
	 * Form HTML ordered (numbered) and unordered (bulleted) lists.
	 *
	 * @param   string   The markdown getting transformed.
	 * @return  string   String that will replace the tag.
	 */
	protected function do_lists($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.'[ ]+
					  )
				  )
				)
			';

			/* We use different prefix before nested lists than top-level lists.
			 * See extended comment in _process_list_items().
			 */
			if ($this->list_level) {
				$text = preg_replace_callback('{
						^
						'.$whole_list_re.'
					}mx',
					array(&$this, '_do_lists_callback'), $text);
			} else {
				$text = preg_replace_callback('{
						(?:(?<=\n)\n|\A\n?) # Must eat the newline
						'.$whole_list_re.'
					}mx',
					array(&$this, '_do_lists_callback'), $text);
			}
		}

		return $text;
	}

	protected function _do_lists_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 = $this->process_list_items($list, $marker_any_re);
		
		$result = $this->hash_block("<$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.
	 */
	protected function process_list_items($list_str, $marker_any_re)
	{
		/*
		 * 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.".
		 */
		$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, '_process_list_items_callback'), $list_str);

		$this->list_level--;
		return $list_str;
	}

	protected function _process_list_items_callback($matches)
	{
		$item = $matches[4];
		$leading_line =& $matches[1];
		$leading_space =& $matches[2];
		$marker_space = $matches[3];
		$tailing_blank_line =& $matches[5];

		/* Replace marker with the appropriate whitespace indentation */
		if ($leading_line || $tailing_blank_line || 
			preg_match('/\n{2,}/', $item))
		{
			$item = $leading_space . str_repeat(' ', strlen($marker_space)) . $item;
			$item = $this->run_block_gamut($this->outdent($item)."\n");

		/* Recursion for sub-lists: */
		} else {
			$item = $this->do_lists($this->outdent($item));
			$item = preg_replace('/\n+$/', '', $item);
			$item = $this->run_span_gamut($item);
		}

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

	/**
	 * Process Markdown `<pre><code>` blocks.
	 */
	protected function do_code_blocks($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, '_do_code_blocks_callback'), $text);

		return $text;
	}

	protected function _do_code_blocks_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".$this->hash_block($codeblock)."\n\n";
	}

	/**
	 * Create a code span markup for $code. Called from handleSpanToken.
	 */
	protected function make_code_span($code)
	{
		$code = htmlspecialchars(trim($code), ENT_NOQUOTES);
		return $this->hash_part("<code>$code</code>");
	}

	/**
	 * Prepare regular expressions for searching emphasis tokens in any
	 * context.
	 */
	protected function prepare_italics_and_bold()
	{
		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;
			}
		}
	}

	protected function do_italics_and_bold($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 next emphasis token. Each token
				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 = $this->run_span_gamut($span);
					$span = "<strong><em>$span</em></strong>";
					$text_stack[0] .= $this->hash_part($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 = $this->run_span_gamut($span);
					$span = "<$tag>$span</$tag>";
					$text_stack[0] = $this->hash_part($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 = $this->run_span_gamut($span);
						$span = "<$tag>$span</$tag>";
						$text_stack[0] .= $this->hash_part($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 = $this->run_span_gamut($span);
					$span = "<strong>$span</strong>";
					$text_stack[0] .= $this->hash_part($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 = $this->run_span_gamut($span);
						$span = "<em>$span</em>";
						$text_stack[0] .= $this->hash_part($span);
						$em = '';
					} else {
						$text_stack[0] .= $token;
					}
				} else {
					array_unshift($token_stack, $token);
					array_unshift($text_stack, '');
					$em = $token;
				}
			}
		}
		return $text_stack[0];
	}

	protected function do_block_quotes($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, '_do_block_quotes_callback'), $text);

		return $text;
	}

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

		$bq = preg_replace('/^/m', "  ", $bq);
		/* Leading spaces cause problem with <pre> content, so fix that: */
		$bq = preg_replace_callback('{(\s*<pre>.+?</pre>)}sx', 
			array(&$this, '_do_block_quotes_callback2'), $bq);

		return "\n". $this->hash_block("<blockquote>\n$bq\n</blockquote>")."\n\n";
	}

	protected function _do_block_quotes_callback2($matches)
	{
		$pre = $matches[1];
		$pre = preg_replace('/^  /m', '', $pre);
		return $pre;
	}

	/**
	 *	Params:
	 *		$text - string to process with html <p> tags
	 */
	protected function form_paragraphs($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 = $this->run_span_gamut($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);
	}

	/**
	 * Encode text for a double-quoted HTML attribute. This function
	 * is *not* suitable for attributes enclosed in single quotes.
	 */
	protected function encode_attribute($text)
	{
		$text = $this->encode_amps_and_angles($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 encode_amps_and_angles($text)
	{
		if ($this->no_entities) {
			$text = str_replace('&', '&amp;', $text);
		} else {
			/* 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;
	}

	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 = $this->encode_attribute($matches[1]);
		$link = "<a href=\"$url\">$url</a>";
		return $this->hash_part($link);
	}

	protected function _doAutoLinks_email_callback($matches)
	{
		$address = $matches[1];
		$link = $this->encodeEmailAddress($address);
		return $this->hash_part($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;
	}

	/**
	 * 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
			'.( $this->no_markup ? '' : '
				|
					<!--    .*?     -->		# comment
				|
					<\?.*?\?> | <%.*?%>		# processing instruction
				|
					<[/!$]?[-a-zA-Z0-9:_]+	# regular tags
					(?>
						\s
						(?>[^"\'>]+|"[^"]*"|\'[^\']*\')*
					)?
					>
			').'
				)
				}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 $this->hash_part("&#". ord($token{1}). ";");
			case "`":
				# Search for end marker in remaining text.
				if (preg_match('/^(.*?[^`])'.preg_quote($token).'(?!`)(.*)$/sm', 
					$str, $matches))
				{
					$str = $matches[2];
					$codespan = $this->make_code_span($matches[1]);
					return $this->hash_part($codespan);
				}
				return $token; // return as text since no ending marker found.
			default:
				return $this->hash_part($token);
		}
	}

	/**
	 * 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];
		$strlen = $this->utf8_strlen; # strlen function for UTF-8.

		# 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 - 
				$strlen($line, 'UTF-8') % $this->tab_width;
			$line .= str_repeat(" ", $amount) . $block;
		}
		return $line;
	}

	/**
	 * Check for the availability of the function in the `utf8_strlen` property
	 * (initially `mb_strlen`). If the function is not available, create a 
	 * function that will loosely count the number of UTF-8 characters with a
	 * regular expression.
	 */
	protected function init_detab()
	{
		if (function_exists($this->utf8_strlen)) return;
		$this->utf8_strlen = create_function('$text', 'return preg_match_all(
			"/[\\\\x00-\\\\xBF]|[\\\\xC0-\\\\xFF][\\\\x80-\\\\xBF]*/", 
			$text, $m);');
	}

	/**
	 * Swap back in all the tags hashed by _Hash_HTML_blocks.
	 */
	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]];
	}
}
?>