<?php

/**
 * This class provides functions for converting CSS styles into inline style attributes in your HTML code
 *
 * For more information, please see the README.md file.
 *
 * @author Cameron Brooks
 * @author Jaime Prado
 * @author Roman Ožana <ozana@omdesign.cz>
 */

namespace MPHB\Libraries\Emogrifier;

class Emogrifier {

	/**
	 * @var string
	 */
	const ENCODING = 'UTF-8';

	/**
	 * @var integer
	 */
	const CACHE_KEY_CSS = 0;

	/**
	 * @var integer
	 */
	const CACHE_KEY_SELECTOR = 1;

	/**
	 * @var integer
	 */
	const CACHE_KEY_XPATH = 2;

	/**
	 * @var integer
	 */
	const CACHE_KEY_CSS_DECLARATION_BLOCK = 3;

	/**
	 * for calculating nth-of-type and nth-child selectors.
	 *
	 * @var integer
	 */
	const INDEX = 0;

	/**
	 * for calculating nth-of-type and nth-child selectors.
	 *
	 * @var integer
	 */
	const MULTIPLIER = 1;

	/**
	 * @var string
	 */
	const ID_ATTRIBUTE_MATCHER = '/(\\w+)?\\#([\\w\\-]+)/';

	/**
	 * @var string
	 */
	const CLASS_ATTRIBUTE_MATCHER = '/(\\w+|[\\*\\]])?((\\.[\\w\\-]+)+)/';

	/**
	 * @var string
	 */
	private $html = '';

	/**
	 * @var string
	 */
	private $css = '';

	/**
	 * @var array<string>
	 */
	private $unprocessableHtmlTags = array( 'wbr' );

	/**
	 * @var array<array>
	 */
	private $caches = array(
		self::CACHE_KEY_CSS                   => array(),
		self::CACHE_KEY_SELECTOR              => array(),
		self::CACHE_KEY_XPATH                 => array(),
		self::CACHE_KEY_CSS_DECLARATION_BLOCK => array(),
	);

	/**
	 * the visited nodes with the XPath paths as array keys.
	 *
	 * @var array<\DOMNode>
	 */
	private $visitedNodes = array();

	/**
	 * the styles to apply to the nodes with the XPath paths as array keys for the outer array and the attribute names/values.
	 * as key/value pairs for the inner array.
	 *
	 * @var array<array><string>
	 */
	private $styleAttributesForNodes = array();

	/**
	 * This attribute applies to the case where you want to preserve your original text encoding.
	 *
	 * By default, emogrifier translates your text into HTML entities for two reasons:
	 *
	 * 1. Because of client incompatibilities, it is better practice to send out HTML entities rather than unicode over email.
	 *
	 * 2. It translates any illegal XML characters that DOMDocument cannot work with.
	 *
	 * If you would like to preserve your original encoding, set this attribute to TRUE.
	 *
	 * @var boolean
	 */
	public $preserveEncoding = false;
	public static $_media    = '';

	/**
	 * The constructor.
	 *
	 * @param string $html the HTML to emogrify, must be UTF-8-encoded
	 * @param string $css the CSS to merge, must be UTF-8-encoded
	 */
	public function __construct( $html = '', $css = '' ) {
		$this->setHtml( $html );
		$this->setCss( $css );
	}

	/**
	 * The destructor.
	 */
	public function __destruct() {
		$this->purgeVisitedNodes();
	}

	/**
	 * Sets the HTML to emogrify.
	 *
	 * @param string $html the HTML to emogrify, must be UTF-8-encoded
	 */
	public function setHtml( $html = '' ) {
		$this->html = $html;
	}

	/**
	 * Sets the CSS to merge with the HTML.
	 *
	 * @param string $css the CSS to merge, must be UTF-8-encoded
	 */
	public function setCss( $css = '' ) {
		$this->css = $css;
	}

	/**
	 * Clears all caches.
	 */
	private function clearAllCaches() {
		$this->clearCache( self::CACHE_KEY_CSS );
		$this->clearCache( self::CACHE_KEY_SELECTOR );
		$this->clearCache( self::CACHE_KEY_XPATH );
		$this->clearCache( self::CACHE_KEY_CSS_DECLARATION_BLOCK );
	}

	/**
	 * Clears a single cache by key.
	 *
	 * @param integer $key the cache key, must be CACHE_KEY_CSS, CACHE_KEY_SELECTOR, CACHE_KEY_XPATH or CACHE_KEY_CSS_DECLARATION_BLOCK
	 *
	 * @throws InvalidArgumentException
	 */
	private function clearCache( $key ) {
		$allowedCacheKeys = array(
			self::CACHE_KEY_CSS,
			self::CACHE_KEY_SELECTOR,
			self::CACHE_KEY_XPATH,
			self::CACHE_KEY_CSS_DECLARATION_BLOCK,
		);
		if ( ! in_array( $key, $allowedCacheKeys, true ) ) {
			throw new \InvalidArgumentException( 'Invalid cache key: ' . $key, 1391822035 );
		}

		$this->caches[ $key ] = array();
	}

	/**
	 * Purges the visited nodes.
	 */
	private function purgeVisitedNodes() {
		$this->visitedNodes            = array();
		$this->styleAttributesForNodes = array();
	}

	/**
	 * Marks a tag for removal.
	 *
	 * There are some HTML tags that DOMDocument cannot process, and it will throw an error if it encounters them.
	 * In particular, DOMDocument will complain if you try to use HTML5 tags in an XHTML document.
	 *
	 * Note: The tags will not be removed if they have any content.
	 *
	 * @param string $tagName the tag name, e.g., "p"
	 */
	public function addUnprocessableHtmlTag( $tagName ) {
		$this->unprocessableHtmlTags[] = $tagName;
	}

	/**
	 * Drops a tag from the removal list.
	 *
	 * @param string $tagName the tag name, e.g., "p"
	 */
	public function removeUnprocessableHtmlTag( $tagName ) {
		$key = array_search( $tagName, $this->unprocessableHtmlTags, true );
		if ( $key !== false ) {
			unset( $this->unprocessableHtmlTags[ $key ] );
		}
	}

	/**
	 * Applies the CSS you submit to the HTML you submit.
	 *
	 * This method places the CSS inline.
	 *
	 * @return string
	 *
	 * @throws BadMethodCallException
	 */
	public function emogrify() {
		if ( $this->html === '' ) {
			throw new \BadMethodCallException( 'Please set some HTML first before calling emogrify.', 1390393096 );
		}

		$xmlDocument = $this->createXmlDocument();
		$xpath       = new \DOMXPath( $xmlDocument );
		$this->clearAllCaches();

		// before be begin processing the CSS file, parse the document and normalize all existing CSS attributes (changes 'DISPLAY: none' to 'display: none');
		// we wouldn't have to do this if DOMXPath supported XPath 2.0.
		// also store a reference of nodes with existing inline styles so we don't overwrite them
		$this->purgeVisitedNodes();

		$nodesWithStyleAttributes = $xpath->query( '//*[@style]' );
		if ( $nodesWithStyleAttributes !== false ) {
			/**
			 * @var $nodeWithStyleAttribute DOMNode
			 */
			foreach ( $nodesWithStyleAttributes as $node ) {
				$normalizedOriginalStyle = preg_replace_callback(
					'/[A-z\\-]+(?=\\:)/S',
					array(
						$this,
						'strtolower',
					),
					$node->getAttribute( 'style' )
				);

				// in order to not overwrite existing style attributes in the HTML, we have to save the original HTML styles
				$nodePath = $node->getNodePath();
				if ( ! isset( $this->styleAttributesForNodes[ $nodePath ] ) ) {
					$this->styleAttributesForNodes[ $nodePath ] = $this->parseCssDeclarationBlock( $normalizedOriginalStyle );
					$this->visitedNodes[ $nodePath ]            = $node;
				}

				$node->setAttribute( 'style', $normalizedOriginalStyle );
			}
		}

		// grab any existing style blocks from the html and append them to the existing CSS
		// (these blocks should be appended so as to have precedence over conflicting styles in the existing CSS)
		$allCss = $this->css;

		$allCss .= $this->getCssFromAllStyleNodes( $xpath );

		$cssParts     = $this->splitCssAndMediaQuery( $allCss );
		self::$_media = ''; // reset

		$cssKey = md5( $cssParts['css'] );
		if ( ! isset( $this->caches[ self::CACHE_KEY_CSS ][ $cssKey ] ) ) {
			// process the CSS file for selectors and definitions
			preg_match_all( '/(?:^|[\\s^{}]*)([^{]+){([^}]*)}/mis', $cssParts['css'], $matches, PREG_SET_ORDER );

			$allSelectors = array();
			foreach ( $matches as $key => $selectorString ) {
				// if there is a blank definition, skip
				if ( ! strlen( trim( $selectorString[2] ) ) ) {
					continue;
				}

				// else split by commas and duplicate attributes so we can sort by selector precedence
				$selectors = explode( ',', $selectorString[1] );
				foreach ( $selectors as $selector ) {
					// don't process pseudo-elements and behavioral (dynamic) pseudo-classes; ONLY allow structural pseudo-classes
					if ( strpos( $selector, ':' ) !== false && ! preg_match( '/:\\S+\\-(child|type)\\(/i', $selector ) ) {
						continue;
					}

					$allSelectors[] = array(
						'selector'   => trim( $selector ),
						'attributes' => trim( $selectorString[2] ),
						// keep track of where it appears in the file, since order is important
						'line'       => $key,
					);
				}
			}

			// now sort the selectors by precedence
			usort( $allSelectors, array( $this, 'sortBySelectorPrecedence' ) );

			$this->caches[ self::CACHE_KEY_CSS ][ $cssKey ] = $allSelectors;
		}

		foreach ( $this->caches[ self::CACHE_KEY_CSS ][ $cssKey ] as $value ) {
			// query the body for the xpath selector
			$nodesMatchingCssSelectors = $xpath->query( $this->translateCssToXpath( $value['selector'] ) );

			/**
			 * @var $node \DOMNode
			 */
			foreach ( $nodesMatchingCssSelectors as $node ) {
				// if it has a style attribute, get it, process it, and append (overwrite) new stuff
				if ( $node->hasAttribute( 'style' ) ) {
					// break it up into an associative array
					$oldStyleDeclarations = $this->parseCssDeclarationBlock( $node->getAttribute( 'style' ) );
				} else {
					$oldStyleDeclarations = array();
				}
				$newStyleDeclarations = $this->parseCssDeclarationBlock( $value['attributes'] );
				$node->setAttribute( 'style', $this->generateStyleStringFromDeclarationsArrays( $oldStyleDeclarations, $newStyleDeclarations ) );
			}
		}

		// now iterate through the nodes that contained inline styles in the original HTML
		foreach ( $this->styleAttributesForNodes as $nodePath => $styleAttributesForNode ) {
			$node                   = $this->visitedNodes[ $nodePath ];
			$currentStyleAttributes = $this->parseCssDeclarationBlock( $node->getAttribute( 'style' ) );
			$node->setAttribute( 'style', $this->generateStyleStringFromDeclarationsArrays( $currentStyleAttributes, $styleAttributesForNode ) );
		}

		// This removes styles from your email that contain display:none.
		// We need to look for display:none, but we need to do a case-insensitive search. Since DOMDocument only supports XPath 1.0,
		// lower-case() isn't available to us. We've thus far only set attributes to lowercase, not attribute values. Consequently, we need
		// to translate() the letters that would be in 'NONE' ("NOE") to lowercase.
		$nodesWithStyleDisplayNone = $xpath->query( '//*[contains(translate(translate(@style," ",""),"NOE","noe"),"display:none")]' );
		// The checks on parentNode and is_callable below ensure that if we've deleted the parent node,
		// we don't try to call removeChild on a nonexistent child node
		if ( $nodesWithStyleDisplayNone->length > 0 ) {
			/**
			 * @var $node \DOMNode
			 */
			foreach ( $nodesWithStyleDisplayNone as $node ) {
				if ( $node->parentNode && is_callable( array( $node->parentNode, 'removeChild' ) ) ) {
					$node->parentNode->removeChild( $node );
				}
			}
		}

		$this->copyCssWithMediaToStyleNode( $cssParts, $xmlDocument );

		if ( $this->preserveEncoding ) {
			if ( function_exists( 'mb_convert_encoding' ) ) {
				return mb_convert_encoding( $xmlDocument->saveHTML(), self::ENCODING, 'HTML-ENTITIES' );
			} else {
				return htmlspecialchars_decode( utf8_encode( html_entity_decode( $xmlDocument->saveHTML(), ENT_COMPAT, self::ENCODING ) ) );
			}
		} else {
			return $xmlDocument->saveHTML();
		}
	}

	public function strtolower( array $m ) {
		return strtolower( $m[0] );
	}

	/**
	 * This method merges old or existing name/value array with new name/value array.
	 * and then generates a string of the combined style suitable for placing inline.
	 * This becomes the single point for CSS string generation allowing for consistent.
	 * CSS output no matter where the CSS originally came from.
	 *
	 * @param array $oldStyles
	 * @param array $newStyles
	 * @return string
	 */
	private function generateStyleStringFromDeclarationsArrays( array $oldStyles, array $newStyles ) {
		$combinedStyles = array_merge( $oldStyles, $newStyles );
		$style          = '';
		foreach ( $combinedStyles as $attributeName => $attributeValue ) {
			$style .= ( strtolower( trim( $attributeName ) ) . ': ' . trim( $attributeValue ) . '; ' );
		}
		return trim( $style );
	}

	/**
	 * Copies the media part from CSS array parts to $xmlDocument.
	 *
	 * @param array        $cssParts
	 * @param \DOMDocument $xmlDocument
	 */
	public function copyCssWithMediaToStyleNode( array $cssParts, \DOMDocument $xmlDocument ) {
		if ( isset( $cssParts['media'] ) && $cssParts['media'] !== '' ) {
			$this->addStyleElementToDocument( $xmlDocument, $cssParts['media'] );
		}
	}

	/**
	 * Returns CSS content.
	 *
	 * @param \DOMXPath $xpath
	 * @return string
	 */
	private function getCssFromAllStyleNodes( \DOMXPath $xpath ) {
		$styleNodes = $xpath->query( '//style' );

		if ( $styleNodes === false ) {
			return '';
		}

		$css = '';
		/**
		 * @var $styleNode \DOMNode
		 */
		foreach ( $styleNodes as $styleNode ) {
			$css .= "\n\n" . $styleNode->nodeValue;
			$styleNode->parentNode->removeChild( $styleNode );
		}

		return $css;
	}

	/**
	 * Adds a style element with $css to $document.
	 *
	 * @param \DOMDocument $document
	 * @param string       $css
	 */
	private function addStyleElementToDocument( \DOMDocument $document, $css ) {
		$styleElement          = $document->createElement( 'style', $css );
		$styleAttribute        = $document->createAttribute( 'type' );
		$styleAttribute->value = 'text/css';
		$styleElement->appendChild( $styleAttribute );

		$head = $this->getOrCreateHeadElement( $document );
		$head->appendChild( $styleElement );
	}

	/**
	 * Returns the existing or creates a new head element in $document.
	 *
	 * @param \DOMDocument $document
	 * @return \DOMNode the head element
	 */
	private function getOrCreateHeadElement( \DOMDocument $document ) {
		$head = $document->getElementsByTagName( 'head' )->item( 0 );

		if ( $head === null ) {
			$head = $document->createElement( 'head' );
			$html = $document->getElementsByTagName( 'html' )->item( 0 );
			$html->insertBefore( $head, $document->getElementsByTagName( 'body' )->item( 0 ) );
		}

		return $head;
	}

	/**
	 * Splits input CSS code to an array where:
	 *
	 * - key "css" will be contains clean CSS code.
	 * - key "media" will be contains all valuable media queries.
	 *
	 * Example:
	 *
	 * The CSS code.
	 *
	 *   "@import "file.css"; h1 { color:red; } @media { h1 {}} @media tv { h1 {}}"
	 *
	 * will be parsed into the following array:
	 *
	 *   "css" => "h1 { color:red; }"
	 *   "media" => "@media { h1 {}}"
	 *
	 * @param string $css
	 * @return array
	 */
	private function splitCssAndMediaQuery( $css ) {
		$css = preg_replace_callback(
			'#@media\\s+(?:only\\s)?(?:[\\s{\(]|screen|all)\\s?[^{]+{.*}\\s*}\\s*#misU',
			array(
				$this,
				'_media_concat',
			),
			$css
		);

		// filter the CSS
		$search = array(
			// get rid of css comment code
			'/\\/\\*.*\\*\\//sU',
			// strip out any import directives
			'/^\\s*@import\\s[^;]+;/misU',
			// strip remains media enclosures
			'/^\\s*@media\\s[^{]+{(.*)}\\s*}\\s/misU',
		);

		$replace = array(
			'',
			'',
			'',
		);

		// clean CSS before output
		$css = preg_replace( $search, $replace, $css );

		return array(
			'css'   => $css,
			'media' => self::$_media,
		);
	}

	private function _media_concat( $matches ) {
		self::$_media .= $matches[0];
	}

	/**
	 * Creates a DOMDocument instance with the current HTML.
	 *
	 * @return DOMDocument
	 */
	private function createXmlDocument() {
		$xmlDocument                      = new \DOMDocument();
		$xmlDocument->encoding            = self::ENCODING;
		$xmlDocument->strictErrorChecking = false;
		$xmlDocument->formatOutput        = true;
		$libXmlState                      = libxml_use_internal_errors( true );
		$xmlDocument->loadHTML( $this->getUnifiedHtml() );
		libxml_clear_errors();
		libxml_use_internal_errors( $libXmlState );
		$xmlDocument->normalizeDocument();

		return $xmlDocument;
	}

	/**
	 * Returns the HTML with the non-ASCII characters converts into HTML entities and the unprocessable HTML tags removed.
	 *
	 * @return string the unified HTML
	 *
	 * @throws \BadMethodCallException
	 */
	private function getUnifiedHtml() {
		if ( ! empty( $this->unprocessableHtmlTags ) ) {
			$unprocessableHtmlTags        = implode( '|', $this->unprocessableHtmlTags );
			$bodyWithoutUnprocessableTags = preg_replace( '/<\\/?(' . $unprocessableHtmlTags . ')[^>]*>/i', '', $this->html );
		} else {
			$bodyWithoutUnprocessableTags = $this->html;
		}

		if ( function_exists( 'mb_convert_encoding' ) ) {
			return mb_convert_encoding( $bodyWithoutUnprocessableTags, 'HTML-ENTITIES', self::ENCODING );
		} else {
			return htmlspecialchars_decode( utf8_decode( htmlentities( $bodyWithoutUnprocessableTags, ENT_COMPAT, self::ENCODING, false ) ) );
		}
	}

	/**
	 * @param array $a
	 * @param array $b
	 *
	 * @return integer
	 */
	private function sortBySelectorPrecedence( array $a, array $b ) {
		$precedenceA = $this->getCssSelectorPrecedence( $a['selector'] );
		$precedenceB = $this->getCssSelectorPrecedence( $b['selector'] );

		// We want these sorted in ascending order so selectors with lesser precedence get processed first and
		// selectors with greater precedence get sorted last.
		// The parenthesis around the -1 are necessary to avoid a PHP_CodeSniffer warning about missing spaces around
		// arithmetic operators.
		// @see http://forge.typo3.org/issues/55605
		$precedenceForEquals    = ( $a['line'] < $b['line'] ? ( -1 ) : 1 );
		$precedenceForNotEquals = ( $precedenceA < $precedenceB ? ( -1 ) : 1 );
		return ( $precedenceA === $precedenceB ) ? $precedenceForEquals : $precedenceForNotEquals;
	}

	/**
	 * @param string $selector
	 *
	 * @return integer
	 */
	private function getCssSelectorPrecedence( $selector ) {
		$selectorKey = md5( $selector );
		if ( ! isset( $this->caches[ self::CACHE_KEY_SELECTOR ][ $selectorKey ] ) ) {
			$precedence = 0;
			$value      = 100;
			// ids: worth 100, classes: worth 10, elements: worth 1
			$search = array( '\\#', '\\.', '' );

			foreach ( $search as $s ) {
				if ( trim( $selector == '' ) ) {
					break;
				}
				$number      = 0;
				$selector    = preg_replace( '/' . $s . '\\w+/', '', $selector, -1, $number );
				$precedence += ( $value * $number );
				$value      /= 10;
			}
			$this->caches[ self::CACHE_KEY_SELECTOR ][ $selectorKey ] = $precedence;
		}

		return $this->caches[ self::CACHE_KEY_SELECTOR ][ $selectorKey ];
	}

	/**
	 * Right now, we support all CSS 1 selectors and most CSS2/3 selectors.
	 *
	 * @see http://plasmasturm.org/log/444/
	 *
	 * @param string $paramCssSelector
	 *
	 * @return string
	 */
	private function translateCssToXpath( $paramCssSelector ) {
		$cssSelector = ' ' . $paramCssSelector . ' ';
		$cssSelector = preg_replace_callback( '/\s+\w+\s+/', array( $this, 'strtolower' ), $cssSelector );
		$cssSelector = trim( $cssSelector );
		$xpathKey    = md5( $cssSelector );
		if ( ! isset( $this->caches[ self::CACHE_KEY_XPATH ][ $xpathKey ] ) ) {
			// returns an Xpath selector
			$search  = array(
				// Matches any element that is a child of parent.
				'/\\s+>\\s+/',
				// Matches any element that is an adjacent sibling.
				'/\\s+\\+\\s+/',
				// Matches any element that is a descendant of an parent element element.
				'/\\s+/',
				// first-child pseudo-selector
				'/([^\\/]+):first-child/i',
				// last-child pseudo-selector
				'/([^\\/]+):last-child/i',
				// Matches attribute only selector
				'/^\\[(\\w+)\\]/',
				// Matches element with attribute
				'/(\\w)\\[(\\w+)\\]/',
				// Matches element with EXACT attribute
				'/(\\w)\\[(\\w+)\\=[\'"]?(\\w+)[\'"]?\\]/',
			);
			$replace = array(
				'/',
				'/following-sibling::*[1]/self::',
				'//',
				'*[1]/self::\\1',
				'*[last()]/self::\\1',
				'*[@\\1]',
				'\\1[@\\2]',
				'\\1[@\\2="\\3"]',
			);

			$cssSelector = '//' . preg_replace( $search, $replace, $cssSelector );

			$cssSelector = preg_replace_callback(
				self::ID_ATTRIBUTE_MATCHER,
				array(
					$this,
					'matchIdAttributes',
				),
				$cssSelector
			);
			$cssSelector = preg_replace_callback(
				self::CLASS_ATTRIBUTE_MATCHER,
				array(
					$this,
					'matchClassAttributes',
				),
				$cssSelector
			);

			// Advanced selectors are going to require a bit more advanced emogrification.
			// When we required PHP 5.3, we could do this with closures.
			$cssSelector = preg_replace_callback(
				'/([^\\/]+):nth-child\\(\s*(odd|even|[+\-]?\\d|[+\\-]?\\d?n(\\s*[+\\-]\\s*\\d)?)\\s*\\)/i',
				array(
					$this,
					'translateNthChild',
				),
				$cssSelector
			);
			$cssSelector = preg_replace_callback(
				'/([^\\/]+):nth-of-type\\(\s*(odd|even|[+\-]?\\d|[+\\-]?\\d?n(\\s*[+\\-]\\s*\\d)?)\\s*\\)/i',
				array(
					$this,
					'translateNthOfType',
				),
				$cssSelector
			);

			$this->caches[ self::CACHE_KEY_SELECTOR ][ $xpathKey ] = $cssSelector;
		}
		return $this->caches[ self::CACHE_KEY_SELECTOR ][ $xpathKey ];
	}

	/**
	 * @param array $match
	 *
	 * @return string
	 */
	private function matchIdAttributes( array $match ) {
		return ( strlen( $match[1] ) ? $match[1] : '*' ) . '[@id="' . $match[2] . '"]';
	}

	/**
	 * @param array $match
	 *
	 * @return string
	 */
	private function matchClassAttributes( array $match ) {
		return ( strlen( $match[1] ) ? $match[1] : '*' ) . '[contains(concat(" ",@class," "),concat(" ","' .
			implode(
				'"," "))][contains(concat(" ",@class," "),concat(" ","',
				explode( '.', substr( $match[2], 1 ) )
			) . '"," "))]';
	}

	/**
	 * @param array $match
	 *
	 * @return string
	 */
	private function translateNthChild( array $match ) {
		$result = $this->parseNth( $match );

		if ( isset( $result[ self::MULTIPLIER ] ) ) {
			if ( $result[ self::MULTIPLIER ] < 0 ) {
				$result[ self::MULTIPLIER ] = abs( $result[ self::MULTIPLIER ] );
				return sprintf( '*[(last() - position()) mod %u = %u]/self::%s', $result[ self::MULTIPLIER ], $result[ self::INDEX ], $match[1] );
			} else {
				return sprintf( '*[position() mod %u = %u]/self::%s', $result[ self::MULTIPLIER ], $result[ self::INDEX ], $match[1] );
			}
		} else {
			return sprintf( '*[%u]/self::%s', $result[ self::INDEX ], $match[1] );
		}
	}

	/**
	 * @param array $match
	 *
	 * @return string
	 */
	private function translateNthOfType( array $match ) {
		$result = $this->parseNth( $match );

		if ( isset( $result[ self::MULTIPLIER ] ) ) {
			if ( $result[ self::MULTIPLIER ] < 0 ) {
				$result[ self::MULTIPLIER ] = abs( $result[ self::MULTIPLIER ] );
				return sprintf( '%s[(last() - position()) mod %u = %u]', $match[1], $result[ self::MULTIPLIER ], $result[ self::INDEX ] );
			} else {
				return sprintf( '%s[position() mod %u = %u]', $match[1], $result[ self::MULTIPLIER ], $result[ self::INDEX ] );
			}
		} else {
			return sprintf( '%s[%u]', $match[1], $result[ self::INDEX ] );
		}
	}

	/**
	 * @param array $match
	 *
	 * @return array
	 */
	private function parseNth( array $match ) {
		if ( in_array( strtolower( $match[2] ), array( 'even', 'odd' ) ) ) {
			$index = strtolower( $match[2] ) == 'even' ? 0 : 1;
			return array(
				self::MULTIPLIER => 2,
				self::INDEX      => $index,
			);
		} elseif ( stripos( $match[2], 'n' ) === false ) {
			// if there is a multiplier
			$index = intval( str_replace( ' ', '', $match[2] ) );
			return array( self::INDEX => $index );
		} else {
			if ( isset( $match[3] ) ) {
				$multipleTerm = str_replace( $match[3], '', $match[2] );
				$index        = intval( str_replace( ' ', '', $match[3] ) );
			} else {
				$multipleTerm = $match[2];
				$index        = 0;
			}

			$multiplier = str_ireplace( 'n', '', $multipleTerm );

			if ( ! strlen( $multiplier ) ) {
				$multiplier = 1;
			} elseif ( $multiplier == 0 ) {
				return array( self::INDEX => $index );
			} else {
				$multiplier = intval( $multiplier );
			}

			while ( $index < 0 ) {
				$index += abs( $multiplier );
			}

			return array(
				self::MULTIPLIER => $multiplier,
				self::INDEX      => $index,
			);
		}
	}

	/**
	 * Parses a CSS declaration block into property name/value pairs.
	 *
	 * Example:
	 *
	 * The declaration block.
	 *
	 *   "color: #000; font-weight: bold;".
	 *
	 * will be parsed into the following array:
	 *
	 *   "color" => "#000"
	 *   "font-weight" => "bold"
	 *
	 * @param string $cssDeclarationBlock the CSS declaration block without the curly braces, may be empty
	 *
	 * @return array the CSS declarations with the property names as array keys and the property values as array values
	 */
	private function parseCssDeclarationBlock( $cssDeclarationBlock ) {
		if ( isset( $this->caches[ self::CACHE_KEY_CSS_DECLARATION_BLOCK ][ $cssDeclarationBlock ] ) ) {
			return $this->caches[ self::CACHE_KEY_CSS_DECLARATION_BLOCK ][ $cssDeclarationBlock ];
		}

		$properties   = array();
		$declarations = explode( ';', $cssDeclarationBlock );
		foreach ( $declarations as $declaration ) {
			$matches = array();
			if ( ! preg_match( '/ *([A-Za-z\\-]+) *: *([^;]+) */', $declaration, $matches ) ) {
				continue;
			}
			$propertyName                = strtolower( $matches[1] );
			$propertyValue               = $matches[2];
			$properties[ $propertyName ] = $propertyValue;
		}
		$this->caches[ self::CACHE_KEY_CSS_DECLARATION_BLOCK ][ $cssDeclarationBlock ] = $properties;

		return $properties;
	}

}
