<?php
/**
 * A simple parser that allows you to map BBCode-like "shortcodes" to an arbitrary callback.
 *
 * See the documentation at docs/reference/shortcodes.md .
 *
 * @package framework
 * @subpackage misc
 */
class ShortcodeParser {
	
	public function img_shortcode($attrs) {
		return "<img src='".$attrs['src']."'>";
	}
	
	private static $instances = array();
	
	private static $active_instance = 'default';
	
	// --------------------------------------------------------------------------------------------------------------
	
	protected $shortcodes = array();
	
	// --------------------------------------------------------------------------------------------------------------
	
	/**
	 * Get the {@link ShortcodeParser} instance that is attached to a particular identifier.
	 *
	 * @param string $identifier Defaults to "default".
	 * @return ShortcodeParser
	 */
	public static function get($identifier = 'default') {
		if(!array_key_exists($identifier, self::$instances)) {
			self::$instances[$identifier] = new ShortcodeParser();
		}
		
		return self::$instances[$identifier];
	}
	
	/**
	 * Get the currently active/default {@link ShortcodeParser} instance.
	 *
	 * @return ShortcodeParser
	 */
	public static function get_active() {
		return self::get(self::$active_instance);
	}
	
	/**
	 * Set the identifier to use for the current active/default {@link ShortcodeParser} instance.
	 *
	 * @param string $identifier
	 */
	public static function set_active($identifier) {
		self::$active_instance = (string) $identifier;
	}
	
	// --------------------------------------------------------------------------------------------------------------
	
	/**
	 * Register a shortcode, and attach it to a PHP callback.
	 *
	 * The callback for a shortcode will have the following arguments passed to it:
	 *   - Any parameters attached to the shortcode as an associative array (keys are lower-case).
	 *   - Any content enclosed within the shortcode (if it is an enclosing shortcode). Note that any content within
	 *     this will not have been parsed, and can optionally be fed back into the parser.
	 *   - The {@link ShortcodeParser} instance used to parse the content.
	 *   - The shortcode tag name that was matched within the parsed content.
	 *
	 * @param string $shortcode The shortcode tag to map to the callback - normally in lowercase_underscore format.
	 * @param callback $callback The callback to replace the shortcode with.
	 */
	public function register($shortcode, $callback) {
		if(is_callable($callback)) $this->shortcodes[$shortcode] = $callback;
	}
	
	/**
	 * Check if a shortcode has been registered.
	 *
	 * @param string $shortcode
	 * @return bool
	 */
	public function registered($shortcode) {
		return array_key_exists($shortcode, $this->shortcodes);
	}
	
	/**
	 * Remove a specific registered shortcode.
	 *
	 * @param string $shortcode
	 */
	public function unregister($shortcode) {
		if($this->registered($shortcode)) unset($this->shortcodes[$shortcode]);
	}
	
	/**
	 * Remove all registered shortcodes.
	 */
	public function clear() {
		$this->shortcodes = array();
	}
	
	public function callShortcode($tag, $attributes, $content) {
		if (!isset($this->shortcodes[$tag])) return false;
		return call_user_func($this->shortcodes[$tag], $attributes, $content, $this, $tag);
	}
	
	// --------------------------------------------------------------------------------------------------------------
	
	protected function removeNode($node) {
		$node->parentNode->removeChild($node);
	}
	
	protected function insertAfter($new, $after) {
		$parent = $after->parentNode; $next = $after->nextSibling;
		
		if ($next) {
			$parent->insertBefore($new, $next);
		}
		else {
			$parent->appendChild($new);
		}
	}
	
	protected function insertListAfter($new, $after) {
		$doc = $after->ownerDocument; $parent = $after->parentNode; $next = $after->nextSibling;

		for ($i = 0; $i < $new->length; $i++) {
			$imported = $doc->importNode($new->item($i), true);

			if ($next) {
				$parent->insertBefore($imported, $next);	
			} 
			else {
				$parent->appendChild($imported);
			}
		}
	}

	private static $marker_class = '--ss-shortcode-marker';

	private static $block_level_elements = array(
		'address', 'article', 'aside', 'audio', 'blockquote', 'canvas', 'dd', 'div', 'dl', 'fieldset', 'figcaption',
		'figure', 'footer', 'form', 'h1', 'h2', 'h3', 'h4', 'h5', 'h6', 'header', 'hgroup', 'ol', 'output', 'p',
		'pre', 'section', 'table', 'ul'
	);

	private static $tagrx = '/
		<(?<element>(?:"[^"]*"[\'"]*|\'[^\']*\'[\'"]*|[^\'">])+)>    |   # HTML Tag - skip attribute scoped tags
		\[   (?<escaped>\[.*?\]) \]                                  |   # Escaped block
		\[   (?<open>\w+) (?<attrs>.*?) (?<selfclosed>\/?) \]        |   # Opening tag
		\[\/ (?<close>\w+) \]                                            # Closing tag
/x';

	private static $attrrx = '/
		([^\s\/\'"=,]+)       # Name  
		\s* = \s*
		(?:
			(?:\'([^\']+)\') | # Value surrounded by \'
			(?:"([^"]+)")    | # Value surrounded by "
			(\w+)              # Bare value
		)
/x';


	const WARN = 'warn';
	const STRIP = 'strip';
	const LEAVE = 'leave';
	const ERROR = 'error';

	public static $error_behavior = self::LEAVE;


	/**
	 * Look through a string that contains shortcode tags and pull out the locations and details
	 * of those tags
	 * 
	 * Doesn't support nested shortcode tags
	 * 
	 * @param string $content
	 * @return array - The list of tags found. When using an open/close pair, only one item will be in the array,
	 * with "content" set to the text between the tags
	 */
	protected function extractTags(&$content) {
		$tags = array();
		$escapes = array();

		if(preg_match_all(self::$tagrx, $content, $matches, PREG_SET_ORDER | PREG_OFFSET_CAPTURE)) {
			foreach($matches as $match) {
				// Record escaped tags
				if (!empty($match['escaped'][0])) {
					$escapes[] = array(
						's' => $match[0][1],
						'e' => $match[0][1] + strlen($match[0][0]),
						'content' => $match['escaped']
					);
				}
				
				// Ignore any elements
				if (empty($match['open'][0]) && empty($match['close'][0])) continue;
				
				// Pull the attributes out into a key/value hash
				$attrs = array();
				
				if (!empty($match['attrs'][0])) {
					preg_match_all(self::$attrrx, $match['attrs'][0], $attrmatches, PREG_SET_ORDER);

					foreach ($attrmatches as $attr) {
						list($whole, $name, $value) = array_values(array_filter($attr));
						$attrs[$name] = $value;
					}
				}
				
				// And store the indexes, tag details, etc
				$tags[] = array(
					'text' => $match[0][0],
					's' => $match[0][1],
					'e' => $match[0][1] + strlen($match[0][0]),
					'open' =>  @$match['open'][0],
					'close' => @$match['close'][0],
					'attrs' => $attrs,
					'content' => ''
				);
			}
		}

		$i = count($tags);
		while($i--) {
			if($tags[$i]['close']) {
				// If the tag just before this one isn't the related opening tag, throw an error
				$err = null;
				
				if ($i == 0) {
					$err = 'Close tag "'.$tags[$i]['close'].'" is the first found tag, so has no related open tag';
				}
				else if (!$tags[$i-1]['open']) {
					$err = 'Close tag "'.$tags[$i]['close'].'" preceded by another close tag "'.$tags[$i-1]['close'].'"';
				}
				else if ($tags[$i]['close'] != $tags[$i-1]['open']) {
					$err = 'Close tag "'.$tags[$i]['close'].'" doesn\'t match preceding open tag "'.$tags[$i-1]['open'].'"';
				}

				if($err) {
					if(self::$error_behavior == self::ERROR) user_error($err, E_USER_ERRROR);	
				} 
				else {
					// Otherwise, grab content between tags, save in opening tag & delete the closing one
					$tags[$i-1]['text'] = substr($content, $tags[$i-1]['s'], $tags[$i]['e'] - $tags[$i-1]['s']);
					$tags[$i-1]['content'] = substr($content, $tags[$i-1]['e'], $tags[$i]['s'] - $tags[$i-1]['e']);
					$tags[$i-1]['e'] = $tags[$i]['e'];
					unset($tags[$i]);
				}
			}
		}
		
		$i = count($escapes);
		while($i--) {
			$escape = $escapes[$i];
			$content = substr_replace($content, $escape['content'], $escape['s'], $escape['e'] - $escape['s']);
		}

		return array_values($tags);
	}

	/**
	 * Replaces the shortcode tags extracted by extractTags with HTML element "markers", so that
	 * we can parse the resulting string as HTML and easily mutate the shortcodes in the DOM
	 *
	 * @param string $content - The HTML string with [tag] style shortcodes embedded
	 * @param array $tags - The tags extracted by extractTags
	 * @return string - The HTML string with [tag] style shortcodes replaced by markers
	 */
	protected function replaceTagsWithText($content, $tags, $generator) {
		// The string with tags replaced with markers
		$str = '';
		// The start index of the next tag, remembered as we step backwards through the list
		$li = null;

		$i = count($tags);
		while($i--) {
			if ($li === null) $tail = substr($content, $tags[$i]['e']);
			else $tail = substr($content, $tags[$i]['e'], $li - $tags[$i]['e']);

			$str = $generator($i, $tags[$i]). $tail . $str;
			$li = $tags[$i]['s'];
		}

		return substr($content, 0, $tags[0]['s']) . $str;
	}

	/**
	 * Replace the shortcodes in attribute values with the calculated content
	 *
	 * We don't use markers with attributes because there's no point, it's easier to do all the matching
	 * in-DOM after the XML parse
	 *
	 * @param DOMDocument $doc
	 */
	protected function replaceAttributeTagsWithContent($doc) {
		$xp = new DOMXPath($doc);
		$attributes = $xp->query('//@*[contains(.,"[")][contains(.,"]")]');
		$parser = $this;

		for($i = 0; $i < $attributes->length; $i++) {
			$node = $attributes->item($i);
			$tags = $this->extractTags($node->nodeValue);

			if($tags) {
				$node->nodeValue = $this->replaceTagsWithText($node->nodeValue, $tags, function($idx, $tag) use ($parser){
					return $parser->callShortcode($tag['open'], $tag['attrs'], $tag['content']);
				});
			}
		}
	}

	/**
	 * Replace the element-scoped tags with markers
	 *
	 * @param string $content
	 */
	protected function replaceElementTagsWithMarkers($content) {
		$tags = $this->extractTags($content);
		
		if($tags) {
			$markerClass = self::$marker_class;
			
			$content = $this->replaceTagsWithText($content, $tags, function($idx, $tag) use ($markerClass) {
				return '<img class="'.$markerClass.'" data-tagid="'.$idx.'" />';
			});
		}
		
		return array($content, $tags);
	}

	protected function findParentsForMarkers($nodes) {
		$parents = array();
		
		foreach($nodes as $node) {
			$parent = $node;

			do {
				$parent = $parent->parentNode;
			}
			while($parent instanceof DOMElement && !in_array(strtolower($parent->tagName), self::$block_level_elements));

			$node->setAttribute('data-parentid', count($parents));
			$parents[] = $parent;
		}
		
		return $parents;
	}
	
	const BEFORE = 'before';
	const AFTER = 'after';
	const SPLIT = 'split';
	const INLINE = 'inline';
	
	/**
	 * Given a node with represents a shortcode marker and a location string, mutates the DOM to put the
	 * marker in the compliant location
	 * 
	 * For shortcodes inserted BEFORE, that location is just before the block container that
	 * the marker is in
	 * 
	 * For shortcodes inserted AFTER, that location is just after the block container that
	 * the marker is in
	 * 
	 * For shortcodes inserted SPLIT, that location is where the marker is, but the DOM
	 * is split around it up to the block container the marker is in - for instance,
	 * 
	 *   <p>A<span>B<marker />C</span>D</p>
	 * 
	 * becomes 
	 * 
	 *   <p>A<span>B</span></p><marker /><p><span>C</span>D</p>
	 * 
	 * For shortcodes inserted INLINE, no modification is needed (but in that case the shortcode handler needs to
	 * generate only inline blocks)
	 *
	 * @param DOMElement $node
	 * @param int $location - ShortcodeParser::BEFORE, ShortcodeParser::SPLIT or ShortcodeParser::INLINE
	 */
	protected function moveMarkerToCompliantHome($node, $parent, $location) {
		// Move before block parent
		if($location == self::BEFORE) {
			$parent->parentNode->insertBefore($node, $parent);
		}
		// Move after block parent
		else if($location == self::AFTER) {
			$this->insertAfter($node, $parent);
		}
		// Split parent at node
		else if($location == self::SPLIT) {
			$at = $node; $splitee = $node->parentNode;

			while($splitee !== $parent->parentNode) {
				$spliter = $splitee->cloneNode(false);

				$this->insertAfter($spliter, $splitee);

				while($at->nextSibling) {
					$spliter->appendChild($at->nextSibling);
				}

				$at = $splitee; $splitee = $splitee->parentNode;
			}

			$this->insertAfter($node, $parent);
		}
		// Do nothing
		else if($location == self::INLINE) {
			if(in_array(strtolower($node->tagName), self::$block_level_elements)) {
				user_error(
					'Requested to insert block tag '.$node->tagName.' inline - probably this will break HTML compliance', 
					E_USER_WARNING
				);
			}
			// NOP
		}
		else {
			user_error('Unknown value for $location argument '.$location, E_USER_ERROR);
		}
	}
 
	/**
	 * Given a node with represents a shortcode marker and some informationabout the shortcode, call the 
	 * shortcode handler & replace the marker with the actual content
	 * 
	 * @param DOMElement $node
	 * @param array $tag
	 */
	protected function replaceMarkerWithContent($node, $tag) {
		$content = false;
		if($tag['open']) $content = $this->callShortcode($tag['open'], $tag['attrs'], $tag['content']);

		if ($content === false) {
			if(self::$error_behavior == self::ERROR) {
				user_error('Unknown shortcode tag '.$tag['open'], E_USER_ERRROR);
			}
			if (self::$error_behavior == self::WARN) {
				$content = '<strong class="warning">'.$tag['text'].'</strong>';
			}
			else if (self::$error_behavior == self::LEAVE) {
				$content = $tag['text'];
			}
			else {
 				// self::$error_behavior == self::STRIP - NOP
			}
		}
		
		if ($content) {
			$parsed = HTML5_Parser::parseFragment($content, 'div');
			$this->insertListAfter($parsed, $node);
		}
		
		$this->removeNode($node);
	}

	protected function loadHTML($html) {
		require_once(THIRDPARTY_PATH.'/html5lib/HTML5/Parser.php');

		// Convert any errors to exceptions
		set_error_handler(
			function($no, $str){
				throw new Exception("HTML Parse Error: ".$str);
			},
			error_reporting()
		);
		
		// Use HTML5lib to parse the HTML fragment
		try {
			$bases = HTML5_Parser::parseFragment(trim($html), 'div');
		}
		catch (Exception $e) {
			$bases = null;
		}
		
		// Disable our error handler (restoring to previous value)
		restore_error_handler();
		
		return $bases;
	}
	
	/**
	 * Parse a string, and replace any registered shortcodes within it with the result of the mapped callback.
	 *
	 * @param string $content
	 * @return string
	 */
	public function parse($content) {
		// If no shortcodes defined, don't try and parse any
		if(!$this->shortcodes) return $content;

		// If no content, don't try and parse it
		if (!trim($content)) return $content;

		// First we operate in text mode, replacing any shortcodes with marker elements so that later we can
		// use a proper DOM
		list($content, $tags) = $this->replaceElementTagsWithMarkers($content);

		// Now parse the result into a DOM
		$bases = $this->loadHTML($content);
		
		// If we couldn't parse the HTML, error out
		if (!$bases || !$bases->length) {
			if(self::$error_behavior == self::ERROR) {
				user_error('Couldn\'t decode HTML when processing short codes', E_USER_ERRROR);
			}
			else {
				return $content;
			}
		}

		$res = '';
		$container = $bases->item(0)->parentNode;
		$doc = $container->ownerDocument;

		$xp = new DOMXPath($doc);

		// First, replace any shortcodes that are in attributes
		$this->replaceAttributeTagsWithContent($doc);

		// Find all the element scoped shortcode markers
		$shortcodes = $xp->query('//img[@class="'.self::$marker_class.'"]');

		// Find the parents. Do this before DOM modification, since SPLIT might cause parents to move otherwise
		$parents = $this->findParentsForMarkers($shortcodes);
		
		foreach($shortcodes as $shortcode) {
			$tag = $tags[$shortcode->getAttribute('data-tagid')];
			$parent = $parents[$shortcode->getAttribute('data-parentid')];
			
			$class = null;
			if(!empty($tag['attrs']['location'])) $class = $tag['attrs']['location']; 
			else if(!empty($tag['attrs']['class'])) $class = $tag['attrs']['class'];
			
			$location = self::INLINE;
			if($class == 'left' || $class == 'right') $location = self::BEFORE;
			if($class == 'center' || $class == 'leftALone') $location = self::SPLIT;

			if(!$parent) {
				if($location !== self::INLINE) {
					user_error("Parent block for shortcode couldn't be found, but location wasn't INLINE", E_USER_ERROR);
				}
			}
			else {
				$this->moveMarkerToCompliantHome($shortcode, $parent, $location);
			}

			$this->replaceMarkerWithContent($shortcode, $tag);
		}
		
		foreach($container->childNodes as $child) $res .= $doc->saveHTML($child);

		return $res;
	}
	
	
}