<?php

namespace Pelago\Emogrifier;

use Pelago\Emogrifier\HtmlProcessor\AbstractHtmlProcessor;
use Symfony\Component\CssSelector\CssSelectorConverter;
use Symfony\Component\CssSelector\Exception\SyntaxErrorException;

/**
 * This class provides functions for converting CSS styles into inline style attributes in your HTML code.
 *
 * For Emogrifier 3.0.0, this will be the successor to the \Pelago\Emogrifier class (which then will be deprecated).
 *
 * For more information, please see the README.md file.
 *
 * @internal This class currently is a new technology preview, and its API is still in flux. Don't use it in production.
 *
 * @author Cameron Brooks
 * @author Jaime Prado
 * @author Oliver Klee <github@oliverklee.de>
 * @author Roman Ožana <ozana@omdesign.cz>
 * @author Sander Kruger <s.kruger@invessel.com>
 * @author Zoli Szabó <zoli.szabo+github@gmail.com>
 */
#[\AllowDynamicProperties]
class CssInliner extends AbstractHtmlProcessor {
	/**
	 * @var int
	 */
	const CACHE_KEY_CSS = 0;

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

	/**
	 * @var int
	 */
	const CACHE_KEY_CSS_DECLARATIONS_BLOCK = 2;

	/**
	 * @var int
	 */
	const CACHE_KEY_COMBINED_STYLES = 3;

	/**
	 * Regular expression component matching a static pseudo class in a selector, without the preceding ":",
	 * for which the applicable elements can be determined (by converting the selector to an XPath expression).
	 * (Contains alternation without a group and is intended to be placed within a capturing, non-capturing or lookahead
	 * group, as appropriate for the usage context.)
	 *
	 * @var string
	 */
	const PSEUDO_CLASS_MATCHER = '\\S+\\-(?:child|type\\()|not\\([[:ascii:]]*\\)';

	/**
	 * @var bool[]
	 */
	private $excludedSelectors = array();

	/**
	 * @var string[]
	 */
	private $unprocessableHtmlTags = array();

	/**
	 * @var bool[]
	 */
	private $allowedMediaTypes = array(
		'all'    => true,
		'screen' => true,
		'print'  => true,
	);

	/**
	 * @var mixed[]
	 */
	private $caches = array(
		self::CACHE_KEY_CSS                    => array(),
		self::CACHE_KEY_SELECTOR               => array(),
		self::CACHE_KEY_CSS_DECLARATIONS_BLOCK => array(),
		self::CACHE_KEY_COMBINED_STYLES        => array(),
	);

	/**
	 * @var CssSelectorConverter
	 */
	private $cssSelectorConverter = null;

	/**
	 * the visited nodes with the XPath paths as array keys
	 *
	 * @var \DOMElement[]
	 */
	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 string[][]
	 */
	private $styleAttributesForNodes = array();

	/**
	 * Determines whether the "style" attributes of tags in the the HTML passed to this class should be preserved.
	 * If set to false, the value of the style attributes will be discarded.
	 *
	 * @var bool
	 */
	private $isInlineStyleAttributesParsingEnabled = true;

	/**
	 * Determines whether the <style> blocks in the HTML passed to this class should be parsed.
	 *
	 * If set to true, the <style> blocks will be removed from the HTML and their contents will be applied to the HTML
	 * via inline styles.
	 *
	 * If set to false, the <style> blocks will be left as they are in the HTML.
	 *
	 * @var bool
	 */
	private $isStyleBlocksParsingEnabled = true;

	/**
	 * Determines whether elements with the `display: none` property are
	 * removed from the DOM.
	 *
	 * @var bool
	 */
	private $shouldRemoveInvisibleNodes = true;

	/**
	 * For calculating selector precedence order.
	 * Keys are a regular expression part to match before a CSS name.
	 * Values are a multiplier factor per match to weight specificity.
	 *
	 * @var int[]
	 */
	private $selectorPrecedenceMatchers = array(
		// IDs: worth 10000
		'\\#'                           => 10000,
		// classes, attributes, pseudo-classes (not pseudo-elements) except `:not`: worth 100
		'(?:\\.|\\[|(?<!:):(?!not\\())' => 100,
		// elements (not attribute values or `:not`), pseudo-elements: worth 1
		'(?:(?<![="\':\\w\\-])|::)'     => 1,
	);

	/**
	 * Emogrifier will throw Exceptions when it encounters an error instead of silently ignoring them.
	 *
	 * @var bool
	 */
	private $debug = false;

	/**
	 * @return CssSelectorConverter
	 */
	private function getCssSelectorConverter() {
		if ( $this->cssSelectorConverter === null ) {
			$this->cssSelectorConverter = new CssSelectorConverter();
		}

		return $this->cssSelectorConverter;
	}

	/**
	 * Returns the HEAD element.
	 *
	 * This method assumes that there always is a HEAD element.
	 *
	 * @return \DOMElement
	 */
	private function getHeadElement() {
		return $this->domDocument->getElementsByTagName( 'head' )->item( 0 );
	}

	/**
	 * Inlines the given CSS into the existing HTML.
	 *
	 * @param string $css the CSS to inline, must be UTF-8-encoded
	 *
	 * @return CssInliner fluent interface
	 *
	 * @throws SyntaxErrorException
	 */
	public function inlineCss( $css ) {
		$this->clearAllCaches();
		$this->purgeVisitedNodes();

		$xPath = new \DOMXPath( $this->domDocument );
		$this->removeUnprocessableTags();
		$this->normalizeStyleAttributesOfAllNodes( $xPath );

		$combinedCss = $css;
		// 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)
		if ( $this->isStyleBlocksParsingEnabled ) {
			$combinedCss .= $this->getCssFromAllStyleNodes( $xPath );
		}

		$excludedNodes        = $this->getNodesToExclude( $xPath );
		$cssRules             = $this->parseCssRules( $combinedCss );
		$cssSelectorConverter = $this->getCssSelectorConverter();
		foreach ( $cssRules['inlineable'] as $cssRule ) {
			try {
				$nodesMatchingCssSelectors = $xPath->query( $cssSelectorConverter->toXPath( $cssRule['selector'] ) );
			} catch ( SyntaxErrorException $e ) {
				if ( $this->debug ) {
					throw $e;
				}
				continue;
			}

			/** @var \DOMElement $node */
			foreach ( $nodesMatchingCssSelectors as $node ) {
				if ( \in_array( $node, $excludedNodes, true ) ) {
					continue;
				}
				$this->copyInlineableCssToStyleAttribute( $node, $cssRule );
			}
		}

		if ( $this->isInlineStyleAttributesParsingEnabled ) {
			$this->fillStyleAttributesWithMergedStyles();
		}
		$this->postProcess( $xPath );

		$this->removeImportantAnnotationFromAllInlineStyles( $xPath );

		$this->copyUninlineableCssToStyleNode( $xPath, $cssRules['uninlineable'] );

		return $this;
	}

	/**
	 * Applies some optional post-processing to the HTML in the DOM document.
	 *
	 * @param \DOMXPath $xPath
	 *
	 * @return void
	 */
	private function postProcess( \DOMXPath $xPath ) {
		if ( $this->shouldRemoveInvisibleNodes ) {
			$this->removeInvisibleNodes( $xPath );
		}
	}

	/**
	 * Searches for all nodes with a style attribute and removes the "!important" annotations out of
	 * the inline style declarations, eventually by rearranging declarations.
	 *
	 * @param \DOMXPath $xPath
	 *
	 * @return void
	 */
	private function removeImportantAnnotationFromAllInlineStyles( \DOMXPath $xPath ) {
		foreach ( $this->getAllNodesWithStyleAttribute( $xPath ) as $node ) {
			$this->removeImportantAnnotationFromNodeInlineStyle( $node );
		}
	}

	/**
	 * Removes the "!important" annotations out of the inline style declarations,
	 * eventually by rearranging declarations.
	 * Rearranging needed when !important shorthand properties are followed by some of their
	 * not !important expanded-version properties.
	 * For example "font: 12px serif !important; font-size: 13px;" must be reordered
	 * to "font-size: 13px; font: 12px serif;" in order to remain correct.
	 *
	 * @param \DOMElement $node
	 *
	 * @return void
	 */
	private function removeImportantAnnotationFromNodeInlineStyle( \DOMElement $node ) {
		$inlineStyleDeclarations    = $this->parseCssDeclarationsBlock( $node->getAttribute( 'style' ) );
		$regularStyleDeclarations   = array();
		$importantStyleDeclarations = array();
		foreach ( $inlineStyleDeclarations as $property => $value ) {
			if ( $this->attributeValueIsImportant( $value ) ) {
				$importantStyleDeclarations[ $property ] = \trim( \str_replace( '!important', '', $value ) );
			} else {
				$regularStyleDeclarations[ $property ] = $value;
			}
		}
		$inlineStyleDeclarationsInNewOrder = \array_merge( $regularStyleDeclarations, $importantStyleDeclarations );
		$node->setAttribute( 'style', $this->generateStyleStringFromSingleDeclarationsArray( $inlineStyleDeclarationsInNewOrder ) );
	}

	/**
	 * Returns a list with all DOM nodes that have a style attribute.
	 *
	 * @param \DOMXPath $xPath
	 *
	 * @return \DOMNodeList
	 */
	private function getAllNodesWithStyleAttribute( \DOMXPath $xPath ) {
		return $xPath->query( '//*[@style]' );
	}

	/**
	 * Extracts and parses the individual rules from a CSS string.
	 *
	 * @param string $css a string of raw CSS code
	 *
	 * @return string[][][] A 2-entry array with the key "inlineable" containing rules which can be inlined as `style`
	 *         attributes and the key "uninlineable" containing rules which cannot.  Each value is an array of string
	 *         sub-arrays with the keys
	 *         "media" (the media query string, e.g. "@media screen and (max-width: 480px)",
	 *         or an empty string if not from a `@media` rule),
	 *         "selector" (the CSS selector, e.g., "*" or "header h1"),
	 *         "hasUnmatchablePseudo" (true if that selector contains psuedo-elements or dynamic pseudo-classes
	 *         such that the declarations cannot be applied inline),
	 *         "declarationsBlock" (the semicolon-separated CSS declarations for that selector,
	 *         e.g., "color: red; height: 4px;"),
	 *         and "line" (the line number e.g. 42)
	 */
	private function parseCssRules( $css ) {
		$cssKey = \md5( $css );
		if ( ! isset( $this->caches[ static::CACHE_KEY_CSS ][ $cssKey ] ) ) {
			$matches = $this->getCssRuleMatches( $css );

			$cssRules = array(
				'inlineable'   => array(),
				'uninlineable' => array(),
			);
			/** @var string[][] $matches */
			/** @var string[] $cssRule */
			foreach ( $matches as $key => $cssRule ) {
				$cssDeclaration = \trim( $cssRule['declarations'] );
				if ( $cssDeclaration === '' ) {
					continue;
				}

				$selectors = \explode( ',', $cssRule['selectors'] );
				foreach ( $selectors as $selector ) {
					// don't process pseudo-elements and behavioral (dynamic) pseudo-classes;
					// only allow structural pseudo-classes
					$hasPseudoElement          = \strpos( $selector, '::' ) !== false;
					$hasUnsupportedPseudoClass = (bool) \preg_match( '/:(?!' . static::PSEUDO_CLASS_MATCHER . ')[\\w\\-]/i', $selector );
					$hasUnmatchablePseudo      = $hasPseudoElement || $hasUnsupportedPseudoClass;

					$parsedCssRule           = array(
						'media'                => $cssRule['media'],
						'selector'             => \trim( $selector ),
						'hasUnmatchablePseudo' => $hasUnmatchablePseudo,
						'declarationsBlock'    => $cssDeclaration,
						// keep track of where it appears in the file, since order is important
						'line'                 => $key,
					);
					$ruleType                = ( $cssRule['media'] === '' && ! $hasUnmatchablePseudo ) ? 'inlineable' : 'uninlineable';
					$cssRules[ $ruleType ][] = $parsedCssRule;
				}
			}

			\usort( $cssRules['inlineable'], array( $this, 'sortBySelectorPrecedence' ) );

			$this->caches[ static::CACHE_KEY_CSS ][ $cssKey ] = $cssRules;
		}

		return $this->caches[ static::CACHE_KEY_CSS ][ $cssKey ];
	}

	/**
	 * Parses a string of CSS into the media query, selectors and declarations for each ruleset in order.
	 *
	 * @param string $css
	 *
	 * @return string[][] Array of string sub-arrays with the keys
	 *         "media" (the media query string, e.g. "@media screen and (max-width: 480px)",
	 *         or an empty string if not from an `@media` rule),
	 *         "selectors" (the CSS selector(s), e.g., "*" or "h1, h2"),
	 *         "declarations" (the semicolon-separated CSS declarations for that/those selector(s),
	 *         e.g., "color: red; height: 4px;"),
	 */
	private function getCssRuleMatches( $css ) {
		$ruleMatches = array();

		$splitCss = $this->splitCssAndMediaQuery( $css );
		foreach ( $splitCss as $cssPart ) {
			// process each part for selectors and definitions
			\preg_match_all( '/(?:^|[\\s^{}]*)([^{]+){([^}]*)}/mi', $cssPart['css'], $matches, PREG_SET_ORDER );

			/** @var string[][] $matches */
			foreach ( $matches as $cssRule ) {
				$ruleMatches[] = array(
					'media'        => $cssPart['media'],
					'selectors'    => $cssRule[1],
					'declarations' => $cssRule[2],
				);
			}
		}

		return $ruleMatches;
	}

	/**
	 * Disables the parsing of inline styles.
	 *
	 * @return void
	 */
	public function disableInlineStyleAttributesParsing() {
		$this->isInlineStyleAttributesParsingEnabled = false;
	}

	/**
	 * Disables the parsing of <style> blocks.
	 *
	 * @return void
	 */
	public function disableStyleBlocksParsing() {
		$this->isStyleBlocksParsingEnabled = false;
	}

	/**
	 * Disables the removal of elements with `display: none` properties.
	 *
	 * @return void
	 *
	 * @deprecated will be removed in Emogrifier 3.0
	 */
	public function disableInvisibleNodeRemoval() {
		$this->shouldRemoveInvisibleNodes = false;
	}

	/**
	 * Clears all caches.
	 *
	 * @return void
	 */
	private function clearAllCaches() {
		$this->caches = array(
			static::CACHE_KEY_CSS                    => array(),
			static::CACHE_KEY_SELECTOR               => array(),
			static::CACHE_KEY_CSS_DECLARATIONS_BLOCK => array(),
			static::CACHE_KEY_COMBINED_STYLES        => array(),
		);
	}

	/**
	 * Purges the visited nodes.
	 *
	 * @return void
	 */
	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"
	 *
	 * @return void
	 */
	public function addUnprocessableHtmlTag( $tagName ) {
		$this->unprocessableHtmlTags[] = $tagName;
	}

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

	/**
	 * Marks a media query type to keep.
	 *
	 * @param string $mediaName the media type name, e.g., "braille"
	 *
	 * @return void
	 */
	public function addAllowedMediaType( $mediaName ) {
		$this->allowedMediaTypes[ $mediaName ] = true;
	}

	/**
	 * Drops a media query type from the allowed list.
	 *
	 * @param string $mediaName the tag name, e.g., "braille"
	 *
	 * @return void
	 */
	public function removeAllowedMediaType( $mediaName ) {
		if ( isset( $this->allowedMediaTypes[ $mediaName ] ) ) {
			unset( $this->allowedMediaTypes[ $mediaName ] );
		}
	}

	/**
	 * Adds a selector to exclude nodes from emogrification.
	 *
	 * Any nodes that match the selector will not have their style altered.
	 *
	 * @param string $selector the selector to exclude, e.g., ".editor"
	 *
	 * @return void
	 */
	public function addExcludedSelector( $selector ) {
		$this->excludedSelectors[ $selector ] = true;
	}

	/**
	 * No longer excludes the nodes matching this selector from emogrification.
	 *
	 * @param string $selector the selector to no longer exclude, e.g., ".editor"
	 *
	 * @return void
	 */
	public function removeExcludedSelector( $selector ) {
		if ( isset( $this->excludedSelectors[ $selector ] ) ) {
			unset( $this->excludedSelectors[ $selector ] );
		}
	}

	/**
	 * 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.
	 *
	 * @param \DOMXPath $xPath
	 *
	 * @return void
	 */
	private function removeInvisibleNodes( \DOMXPath $xPath ) {
		$nodesWithStyleDisplayNone = $xPath->query( '//*[contains(translate(translate(@style," ",""),"NOE","noe"),"display:none")]' );
		if ( $nodesWithStyleDisplayNone->length === 0 ) {
			return;
		}

		// 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
		/** @var \DOMNode $node */
		foreach ( $nodesWithStyleDisplayNone as $node ) {
			if ( $node->parentNode && \is_callable( array( $node->parentNode, 'removeChild' ) ) ) {
				$node->parentNode->removeChild( $node );
			}
		}
	}

	/**
	 * Parses the document and normalizes all existing CSS attributes.
	 * This changes 'DISPLAY: none' to 'display: none'.
	 * We wouldn't have to do this if DOMXPath supported XPath 2.0.
	 * Also stores a reference of nodes with existing inline styles so we don't overwrite them.
	 *
	 * @param \DOMXPath $xPath
	 *
	 * @return void
	 */
	private function normalizeStyleAttributesOfAllNodes( \DOMXPath $xPath ) {
		/** @var \DOMElement $node */
		foreach ( $this->getAllNodesWithStyleAttribute( $xPath ) as $node ) {
			if ( $this->isInlineStyleAttributesParsingEnabled ) {
				$this->normalizeStyleAttributes( $node );
			}
			// Remove style attribute in every case, so we can add them back (if inline style attributes
			// parsing is enabled) to the end of the style list, thus keeping the right priority of CSS rules;
			// else original inline style rules may remain at the beginning of the final inline style definition
			// of a node, which may give not the desired results
			$node->removeAttribute( 'style' );
		}
	}

	/**
	 * Normalizes the value of the "style" attribute and saves it.
	 *
	 * @param \DOMElement $node
	 *
	 * @return void
	 */
	private function normalizeStyleAttributes( \DOMElement $node ) {
		$normalizedOriginalStyle = \preg_replace_callback(
			'/[A-z\\-]+(?=\\:)/S',
			function ( array $m ) {
				return \strtolower( $m[0] );
			},
			$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->parseCssDeclarationsBlock( $normalizedOriginalStyle );
			$this->visitedNodes[ $nodePath ]            = $node;
		}

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

	/**
	 * Merges styles from styles attributes and style nodes and applies them to the attribute nodes
	 *
	 * @return void
	 */
	private function fillStyleAttributesWithMergedStyles() {
		foreach ( $this->styleAttributesForNodes as $nodePath => $styleAttributesForNode ) {
			$node                   = $this->visitedNodes[ $nodePath ];
			$currentStyleAttributes = $this->parseCssDeclarationsBlock( $node->getAttribute( 'style' ) );
			$node->setAttribute( 'style', $this->generateStyleStringFromDeclarationsArrays( $currentStyleAttributes, $styleAttributesForNode ) );
		}
	}

	/**
	 * 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 string[] $oldStyles
	 * @param string[] $newStyles
	 *
	 * @return string
	 */
	private function generateStyleStringFromDeclarationsArrays( array $oldStyles, array $newStyles ) {
		$cacheKey = \serialize( array( $oldStyles, $newStyles ) );
		if ( isset( $this->caches[ static::CACHE_KEY_COMBINED_STYLES ][ $cacheKey ] ) ) {
			return $this->caches[ static::CACHE_KEY_COMBINED_STYLES ][ $cacheKey ];
		}

		// Unset the overridden styles to preserve order, important if shorthand and individual properties are mixed
		foreach ( $oldStyles as $attributeName => $attributeValue ) {
			if ( ! isset( $newStyles[ $attributeName ] ) ) {
				continue;
			}

			$newAttributeValue = $newStyles[ $attributeName ];
			if ( $this->attributeValueIsImportant( $attributeValue ) && ! $this->attributeValueIsImportant( $newAttributeValue ) ) {
				unset( $newStyles[ $attributeName ] );
			} else {
				unset( $oldStyles[ $attributeName ] );
			}
		}

		$combinedStyles = \array_merge( $oldStyles, $newStyles );

		$style = '';
		foreach ( $combinedStyles as $attributeName => $attributeValue ) {
			$style .= \strtolower( \trim( $attributeName ) ) . ': ' . \trim( $attributeValue ) . '; ';
		}
		$trimmedStyle = \rtrim( $style );

		$this->caches[ static::CACHE_KEY_COMBINED_STYLES ][ $cacheKey ] = $trimmedStyle;

		return $trimmedStyle;
	}

	/**
	 * Generates a CSS style string suitable to be used inline from the $styleDeclarations property => value array.
	 *
	 * @param string[] $styleDeclarations
	 *
	 * @return string
	 */
	private function generateStyleStringFromSingleDeclarationsArray( array $styleDeclarations ) {
		return $this->generateStyleStringFromDeclarationsArrays( array(), $styleDeclarations );
	}

	/**
	 * Checks whether $attributeValue is marked as !important.
	 *
	 * @param string $attributeValue
	 *
	 * @return bool
	 */
	private function attributeValueIsImportant( $attributeValue ) {
		return \strtolower( \substr( \trim( $attributeValue ), - 10 ) ) === '!important';
	}

	/**
	 * Applies $cssRules to $this->domDocument, limited to the rules that actually apply to the document.
	 *
	 * @param \DOMXPath  $xPath
	 * @param string[][] $cssRules The "uninlineable" array of CSS rules returned by `parseCssRules`
	 *
	 * @return void
	 */
	private function copyUninlineableCssToStyleNode( \DOMXPath $xPath, array $cssRules ) {
		$cssRulesRelevantForDocument = \array_filter(
			$cssRules,
			function ( array $cssRule ) use ( $xPath ) {
				$selector = $cssRule['selector'];
				if ( $cssRule['hasUnmatchablePseudo'] ) {
					$selector = $this->removeUnmatchablePseudoComponents( $selector );
				}

				return $this->existsMatchForCssSelector( $xPath, $selector );
			}
		);

		if ( $cssRulesRelevantForDocument === array() ) {
			// avoid adding empty style element (or including unneeded class dependency)
			return;
		}

		$cssConcatenator = new CssConcatenator();
		foreach ( $cssRulesRelevantForDocument as $cssRule ) {
			$cssConcatenator->append( array( $cssRule['selector'] ), $cssRule['declarationsBlock'], $cssRule['media'] );
		}

		$this->addStyleElementToDocument( $cssConcatenator->getCss() );
	}

	/**
	 * Removes pseudo-elements and dynamic pseudo-classes from a CSS selector, replacing them with "*" if necessary.
	 *
	 * @param string $selector
	 *
	 * @return string Selector which will match the relevant DOM elements if the pseudo-classes are assumed to apply,
	 *                or in the case of pseudo-elements will match their originating element.
	 */
	private function removeUnmatchablePseudoComponents( $selector ) {
		$pseudoComponentMatcher = ':(?!' . static::PSEUDO_CLASS_MATCHER . '):?+[\\w\\-]++(?:\\([^\\)]*+\\))?+';

		return \preg_replace( array( '/(\\s|^)' . $pseudoComponentMatcher . '/i', '/' . $pseudoComponentMatcher . '/i' ), array( '$1*', '' ), $selector );
	}

	/**
	 * Copies $cssRule into the style attribute of $node.
	 *
	 * Note: This method does not check whether $cssRule matches $node.
	 *
	 * @param \DOMElement $node
	 * @param string[][]  $cssRule
	 *
	 * @return void
	 */
	private function copyInlineableCssToStyleAttribute( \DOMElement $node, array $cssRule ) {
		// 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->parseCssDeclarationsBlock( $node->getAttribute( 'style' ) );
		} else {
			$oldStyleDeclarations = array();
		}
		$newStyleDeclarations = $this->parseCssDeclarationsBlock( $cssRule['declarationsBlock'] );
		$node->setAttribute( 'style', $this->generateStyleStringFromDeclarationsArrays( $oldStyleDeclarations, $newStyleDeclarations ) );
	}

	/**
	 * Checks whether there is at least one matching element for $cssSelector.
	 * When not in debug mode, it returns true also for invalid selectors (because they may be valid,
	 * just not implemented/recognized yet by Emogrifier).
	 *
	 * @param \DOMXPath $xPath
	 * @param string    $cssSelector
	 *
	 * @return bool
	 *
	 * @throws SyntaxErrorException
	 */
	private function existsMatchForCssSelector( \DOMXPath $xPath, $cssSelector ) {
		try {
			$nodesMatchingSelector = $xPath->query( $this->getCssSelectorConverter()->toXPath( $cssSelector ) );
		} catch ( SyntaxErrorException $e ) {
			if ( $this->debug ) {
				throw $e;
			}

			return true;
		}

		return $nodesMatchingSelector !== false && $nodesMatchingSelector->length !== 0;
	}

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

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

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

		return $css;
	}

	/**
	 * Adds a style element with $css to $this->domDocument.
	 *
	 * This method is protected to allow overriding.
	 *
	 * @see https://github.com/MyIntervals/emogrifier/issues/103
	 *
	 * @param string $css
	 *
	 * @return void
	 */
	protected function addStyleElementToDocument( $css ) {
		$styleElement          = $this->domDocument->createElement( 'style', $css );
		$styleAttribute        = $this->domDocument->createAttribute( 'type' );
		$styleAttribute->value = 'text/css';
		$styleElement->appendChild( $styleAttribute );

		$headElement = $this->getHeadElement();
		$headElement->appendChild( $styleElement );
	}

	/**
	 * Splits input CSS code into an array of parts for different media querues, in order.
	 * Each part is an array where:
	 *
	 * - key "css" will contain clean CSS code (for @media rules this will be the group rule body within "{...}")
	 * - key "media" will contain "@media " followed by the media query list, for all allowed media queries,
	 *   or an empty string for CSS not within a media query
	 *
	 * Example:
	 *
	 * The CSS code
	 *
	 *   "@import "file.css"; h1 { color:red; } @media { h1 {}} @media tv { h1 {}}"
	 *
	 * will be parsed into the following array:
	 *
	 *   0 => [
	 *     "css" => "h1 { color:red; }",
	 *     "media" => ""
	 *   ],
	 *   1 => [
	 *     "css" => " h1 {}",
	 *     "media" => "@media "
	 *   ]
	 *
	 * @param string $css
	 *
	 * @return string[][]
	 */
	private function splitCssAndMediaQuery( $css ) {
		$cssWithoutComments = \preg_replace( '/\\/\\*.*\\*\\//sU', '', $css );

		$mediaTypesExpression = '';
		if ( ! empty( $this->allowedMediaTypes ) ) {
			$mediaTypesExpression = '|' . \implode( '|', \array_keys( $this->allowedMediaTypes ) );
		}

		$mediaRuleBodyMatcher = '[^{]*+{(?:[^{}]*+{.*})?\\s*+}\\s*+';

		$cssSplitForAllowedMediaTypes = \preg_split( '#(@media\\s++(?:only\\s++)?+(?:(?=[{\\(])' . $mediaTypesExpression . ')' . $mediaRuleBodyMatcher . ')#misU', $cssWithoutComments, - 1, PREG_SPLIT_DELIM_CAPTURE );

		// filter the CSS outside/between allowed @media rules
		$cssCleaningMatchers = array(
			'import/charset directives'  => '/\\s*+@(?:import|charset)\\s[^;]++;/i',
			'remaining media enclosures' => '/\\s*+@media\\s' . $mediaRuleBodyMatcher . '/isU',
		);

		$splitCss = array();
		foreach ( $cssSplitForAllowedMediaTypes as $index => $cssPart ) {
			$isMediaRule = $index % 2 !== 0;
			if ( $isMediaRule ) {
				\preg_match( '/^([^{]*+){(.*)}[^}]*+$/s', $cssPart, $matches );
				$splitCss[] = array(
					'css'   => $matches[2],
					'media' => $matches[1],
				);
			} else {
				$cleanedCss = \trim( \preg_replace( $cssCleaningMatchers, '', $cssPart ) );
				if ( $cleanedCss !== '' ) {
					$splitCss[] = array(
						'css'   => $cleanedCss,
						'media' => '',
					);
				}
			}
		}

		return $splitCss;
	}

	/**
	 * Removes empty unprocessable tags from the DOM document.
	 *
	 * @return void
	 */
	private function removeUnprocessableTags() {
		foreach ( $this->unprocessableHtmlTags as $tagName ) {
			// Deleting nodes from a 'live' NodeList invalidates iteration on it, so a copy must be made to iterate.
			$nodes = array();
			foreach ( $this->domDocument->getElementsByTagName( $tagName ) as $node ) {
				$nodes[] = $node;
			}
			/** @var \DOMNode $node */
			foreach ( $nodes as $node ) {
				$hasContent = $node->hasChildNodes() || $node->hasChildNodes();
				if ( ! $hasContent ) {
					$node->parentNode->removeChild( $node );
				}
			}
		}
	}

	/**
	 * @param string[] $a
	 * @param string[] $b
	 *
	 * @return int
	 */
	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.
		$precedenceForEquals    = ( $a['line'] < $b['line'] ? - 1 : 1 );
		$precedenceForNotEquals = ( $precedenceA < $precedenceB ? - 1 : 1 );

		return ( $precedenceA === $precedenceB ) ? $precedenceForEquals : $precedenceForNotEquals;
	}

	/**
	 * @param string $selector
	 *
	 * @return int
	 */
	private function getCssSelectorPrecedence( $selector ) {
		$selectorKey = \md5( $selector );
		if ( ! isset( $this->caches[ static::CACHE_KEY_SELECTOR ][ $selectorKey ] ) ) {
			$precedence = 0;
			foreach ( $this->selectorPrecedenceMatchers as $matcher => $value ) {
				if ( \trim( $selector ) === '' ) {
					break;
				}
				$number      = 0;
				$selector    = \preg_replace( '/' . $matcher . '\\w+/', '', $selector, - 1, $number );
				$precedence += ( $value * $number );
			}
			$this->caches[ static::CACHE_KEY_SELECTOR ][ $selectorKey ] = $precedence;
		}

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

	/**
	 * 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 $cssDeclarationsBlock the CSS declarations block without the curly braces, may be empty
	 *
	 * @return string[]
	 *         the CSS declarations with the property names as array keys and the property values as array values
	 */
	private function parseCssDeclarationsBlock( $cssDeclarationsBlock ) {
		if ( isset( $this->caches[ static::CACHE_KEY_CSS_DECLARATIONS_BLOCK ][ $cssDeclarationsBlock ] ) ) {
			return $this->caches[ static::CACHE_KEY_CSS_DECLARATIONS_BLOCK ][ $cssDeclarationsBlock ];
		}

		$properties   = array();
		$declarations = \preg_split( '/;(?!base64|charset)/', $cssDeclarationsBlock );

		foreach ( $declarations as $declaration ) {
			$matches = array();
			if ( ! \preg_match( '/^([A-Za-z\\-]+)\\s*:\\s*(.+)$/s', \trim( $declaration ), $matches ) ) {
				continue;
			}

			$propertyName                = \strtolower( $matches[1] );
			$propertyValue               = $matches[2];
			$properties[ $propertyName ] = $propertyValue;
		}
		$this->caches[ static::CACHE_KEY_CSS_DECLARATIONS_BLOCK ][ $cssDeclarationsBlock ] = $properties;

		return $properties;
	}

	/**
	 * Find the nodes that are not to be emogrified.
	 *
	 * @param \DOMXPath $xPath
	 *
	 * @return \DOMElement[]
	 *
	 * @throws SyntaxErrorException
	 */
	private function getNodesToExclude( \DOMXPath $xPath ) {
		$excludedNodes = array();
		foreach ( \array_keys( $this->excludedSelectors ) as $selectorToExclude ) {
			try {
				$matchingNodes = $xPath->query( $this->getCssSelectorConverter()->toXPath( $selectorToExclude ) );
			} catch ( SyntaxErrorException $e ) {
				if ( $this->debug ) {
					throw $e;
				}
				continue;
			}
			foreach ( $matchingNodes as $node ) {
				$excludedNodes[] = $node;
			}
		}

		return $excludedNodes;
	}

	/**
	 * Sets the debug mode.
	 *
	 * @param bool $debug set to true to enable debug mode
	 *
	 * @return void
	 */
	public function setDebug( $debug ) {
		$this->debug = $debug;
	}
}
