<?php
/**
 * A simple parser that allows you to map BBCode-like "shortcodes" to an arbitrary callback.
 * It is a simple regex based parser that allows you to replace simple bbcode-like tags
 * within a HTMLText or HTMLVarchar field when rendered into a template. The API is inspired by and very similar to the
 * [Wordpress implementation](http://codex.wordpress.org/Shortcode_API) of shortcodes.
 * 
 * @see http://doc.silverstripe.org/framework/en/reference/shortcodes
 * @package framework
 * @subpackage misc
 */
class ShortcodeParser extends Object {
	
	public function img_shortcode($attrs) {
		return "<img src='".$attrs['src']."'>";
	}
	
	protected static $instances = array();
	
	protected 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] = static::create();
		}
		
		return self::$instances[$identifier];
	}
	
	/**
	 * Get the currently active/default {@link ShortcodeParser} instance.
	 *
	 * @return ShortcodeParser
	 */
	public static function get_active() {
		return static::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.
	 *   - An associative array of extra information about the shortcode being parsed.
	 *
	 * @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();
	}
	
	/**
	 * Call a shortcode and return its replacement text
	 * Returns false if the shortcode isn't registered
	 */
	public function callShortcode($tag, $attributes, $content, $extra = array()) {
		if (!$tag || !isset($this->shortcodes[$tag])) return false;
		return call_user_func($this->shortcodes[$tag], $attributes, $content, $this, $tag, $extra);
	}
	
	/**
	 * Return the text to insert in place of a shoprtcode.
	 * Behaviour in the case of missing shortcodes depends on the setting of ShortcodeParser::$error_behavior.
	 * @param $tag A map containing the the following keys:
	 *  - 'open': The name of the tag
	 *  - 'attrs': Attributes of the tag
	 *  - 'content': Content of the tag
	 * @param $extra Extra-meta data
	 * @param $isHTMLAllowed A boolean indicating whether it's okay to insert HTML tags into the result
	 */
	function getShortcodeReplacementText($tag, $extra = array(), $isHTMLAllowed = true) {
		$content = $this->callShortcode($tag['open'], $tag['attrs'], $tag['content'], $extra);

		// Missing tag
		if ($content === false) {
			if(ShortcodeParser::$error_behavior == ShortcodeParser::ERROR) {
				user_error('Unknown shortcode tag '.$tag['open'], E_USER_ERRROR);
			}
			else if (self::$error_behavior == self::WARN && $isHTMLAllowed) {
				$content = '<strong class="warning">'.$tag['text'].'</strong>';
			}
			else if(ShortcodeParser::$error_behavior == ShortcodeParser::STRIP) {
				return '';
			}
			else {
				return $tag['text'];
			}
		}

		return $content;
	}

	// --------------------------------------------------------------------------------------------------------------
	
	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);
			}
		}
	}

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

	protected 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'
	);
	
	protected static $attrrx = '
		([^\s\/\'"=,]+)       # Name  
		\s* = \s*
		(?:
			(?:\'([^\']+)\') | # Value surrounded by \'
			(?:"([^"]+)")    | # Value surrounded by "
			([^\s,\]]+)          # Bare value
		)
';
	
	protected static function attrrx() {
		return '/'.self::$attrrx.'/xS';
	}

	protected static $tagrx = '
		# HTML Tag
		<(?<element>(?:"[^"]*"[\'"]*|\'[^\']*\'[\'"]*|[^\'">])+)>
		 
		| # Opening tag
		(?<oesc>\[?) 
		\[ 
			(?<open>\w+) 
			[\s,]*
			(?<attrs> (?: %s [\s,]*)* ) 
		\/?\] 
		(?<cesc1>\]?)
		 
		| # Closing tag
		\[\/ 
			(?<close>\w+) 
		\] 
		(?<cesc2>\]?)  
';

	protected static function tagrx() {
		return '/'.sprintf(self::$tagrx, self::$attrrx).'/xS';
	}

	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();
		
		// Step 1: perform basic regex scan of individual tags
		if(preg_match_all(static::tagrx(), $content, $matches, PREG_SET_ORDER | PREG_OFFSET_CAPTURE)) {
			foreach($matches as $match) {
				// Ignore any elements
				if (empty($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(static::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' =>  isset($match['open'][0]) ? $match['open'][0] : null,
					'close' => isset($match['close'][0]) ? $match['close'][0] : null,
					'attrs' => $attrs,
					'content' => '',
					'escaped' => !empty($match['oesc'][0]) || !empty($match['cesc1'][0]) || !empty($match['cesc2'][0])
				);
			}
		}

		// Step 2: cluster open/close tag pairs into single entries
		$i = count($tags);
		while($i--) {
			if(!empty($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($err, E_USER_ERRROR);	
				} 
				else {
					if ($tags[$i]['escaped']) {
						if (!$tags[$i-1]['escaped']) {
							$tags[$i]['e'] -= 1;
							$tags[$i]['escaped'] = false;
						}
					}
					else {
						if ($tags[$i-1]['escaped']) {
							$tags[$i-1]['s'] += 1;
							$tags[$i-1]['escaped'] = false;
						}
					}
					
					// 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]);
				}
			}
		}

		// Step 3: remove any tags that don't have handlers registered
		// Only do this if self::$error_behavior == self::LEAVE
		// This is optional but speeds things up.
		if(self::$error_behavior == self::LEAVE) {
			foreach($tags as $i => $tag) {
				if(empty($this->shortcodes[$tag['open']])) {
					unset($tags[$i]);
				}
			}
		}

		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']);

			if ($tags[$i]['escaped']) {
				$str = substr($content, $tags[$i]['s']+1, $tags[$i]['e'] - $tags[$i]['s'] - 2) . $tail . $str;
			}
			else {
				$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 $doc
	 */
	protected function replaceAttributeTagsWithContent($htmlvalue) {
		$attributes = $htmlvalue->query('//@*[contains(.,"[")][contains(.,"]")]');
		$parser = $this;

		for($i = 0; $i < $attributes->length; $i++) {
			$node = $attributes->item($i);
			$tags = $this->extractTags($node->nodeValue);
			$extra = array('node' => $node, 'element' => $node->ownerElement);

			if($tags) {
				$node->nodeValue = $this->replaceTagsWithText($node->nodeValue, $tags,
					function($idx, $tag) use ($parser, $extra) {
						return $parser->getShortcodeReplacementText($tag, $extra, false);
					}
				);
			}
		}
	}
	
	/**
	 * 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) {
		if (isset($parent->parentNode))
			$parent->parentNode->insertBefore($node, $parent);
		} else if($location == self::AFTER) {
			// Move after block parent
			$this->insertAfter($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 information about 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 = $this->getShortcodeReplacementText($tag);
		
		if ($content) {
			$parsed = Injector::inst()->create('HTMLValue', $content);
			$body = $parsed->getBody();
			if ($body) $this->insertListAfter($body->childNodes, $node);
		}
		
		$this->removeNode($node);
	}

	/**
	 * 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);

		$htmlvalue = Injector::inst()->create('HTMLValue', $content);

		// Now parse the result into a DOM
		if (!$htmlvalue->isValid()){
			if(self::$error_behavior == self::ERROR) {
				user_error('Couldn\'t decode HTML when processing short codes', E_USER_ERRROR);
			}
			else {
				return $content;
			}
		}

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

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

		$content = $htmlvalue->getContent();

		// Clean up any marker classes left over, for example, those injected into <script> tags
		$parser = $this;
		$content = preg_replace_callback(
			// Not a general-case parser; assumes that the HTML generated in replaceElementTagsWithMarkers()
			// hasn't been heavily modified
			'/<img[^>]+class="'.preg_quote(self::$marker_class).'"[^>]+data-tagid="([^"]+)"[^>]+>/i',
			function ($matches) use ($tags, $parser) {
				$tag = $tags[$matches[1]];
				return $parser->getShortcodeReplacementText($tag);
			},
			$content
		);

		return $content;
	}
}