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Pelago\Emogrifier

CssInliner{} WC 1.0

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.

Хуков нет.

Возвращает

Null. Ничего.

Использование

$CssInliner = new CssInliner();
// use class methods

Методы

  1. addAllowedMediaType($mediaName)
  2. addExcludedSelector($selector)
  3. addStyleElementToDocument($css)
  4. attributeValueIsImportant($attributeValue)
  5. clearAllCaches()
  6. copyInlinableCssToStyleAttribute(\DOMElement $node, array $cssRule)
  7. copyUninlinableCssToStyleNode($cssImportRules)
  8. determineMatchingUninlinableCssRules(array $cssRules)
  9. disableInlineStyleAttributesParsing()
  10. disableStyleBlocksParsing()
  11. existsMatchForCssSelector($cssSelector)
  12. existsMatchForSelectorInCssRule(array $cssRule)
  13. extractImportAndCharsetRules($css)
  14. fillStyleAttributesWithMergedStyles()
  15. generateStyleStringFromDeclarationsArrays(array $oldStyles, array $newStyles)
  16. generateStyleStringFromSingleDeclarationsArray(array $styleDeclarations)
  17. getAllNodesWithStyleAttribute()
  18. getCssFromAllStyleNodes()
  19. getCssRuleMatches($css)
  20. getCssSelectorConverter()
  21. getCssSelectorPrecedence($selector)
  22. getHeadElement()
  23. getMatchingUninlinableSelectors()
  24. getNodesToExclude()
  25. inlineCss($css = '')
  26. normalizeStyleAttributes(\DOMElement $node)
  27. normalizeStyleAttributesOfAllNodes()
  28. parseCssDeclarationsBlock($cssDeclarationsBlock)
  29. parseCssRules($css)
  30. purgeVisitedNodes()
  31. removeAllowedMediaType($mediaName)
  32. removeCssComments($css)
  33. removeExcludedSelector($selector)
  34. removeImportantAnnotationFromAllInlineStyles()
  35. removeImportantAnnotationFromNodeInlineStyle(\DOMElement $node)
  36. removeUnmatchablePseudoComponents($selector)
  37. replaceUnmatchableNotComponent(array $matches)
  38. setDebug($debug)
  39. sortBySelectorPrecedence(array $a, array $b)
  40. splitCssAndMediaQuery($css)

Код CssInliner{} WC 4.6.1

<?php
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
        = 'empty|(?:first|last|nth(?:-last)?+|only)-child|(?:first|last|nth(?:-last)?+)-of-type|not\\([[:ascii:]]*\\)';

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

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

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

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

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

    /**
     * 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 = [];

    /**
     * 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;

    /**
     * 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 = [
        // 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,
    ];

    /**
     * array of data describing CSS rules which apply to the document but cannot be inlined, in the format returned by
     * `parseCssRules`
     *
     * @var string[][]
     */
    private $matchingUninlinableCssRules = null;

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

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

        $this->normalizeStyleAttributesOfAllNodes();

        $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();
        }

        $cssWithoutComments = $this->removeCssComments($combinedCss);
        list($cssWithoutCommentsCharsetOrImport, $cssImportRules)
            = $this->extractImportAndCharsetRules($cssWithoutComments);

        $excludedNodes = $this->getNodesToExclude();
        $cssRules = $this->parseCssRules($cssWithoutCommentsCharsetOrImport);
        $cssSelectorConverter = $this->getCssSelectorConverter();
        foreach ($cssRules['inlinable'] as $cssRule) {
            try {
                $nodesMatchingCssSelectors = $this->xPath->query($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;
                }
                $this->copyInlinableCssToStyleAttribute($node, $cssRule);
            }
        }

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

        $this->removeImportantAnnotationFromAllInlineStyles();

        $this->determineMatchingUninlinableCssRules($cssRules['uninlinable']);
        $this->copyUninlinableCssToStyleNode($cssImportRules);

        return $this;
    }

    /**
     * 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;
    }

    /**
     * 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]);
        }
    }

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

    /**
     * Gets the array of selectors present in the CSS provided to `inlineCss()` for which the declarations could not be
     * applied as inline styles, but which may affect elements in the HTML.  The relevant CSS will have been placed in a
     * `<style>` element.  The selectors may include those used within `@media` rules or those involving dynamic
     * pseudo-classes (such as `:hover`) or pseudo-elements (such as `::after`).
     *
     * @return string[]
     *
     * @throws \BadMethodCallException if `inlineCss` has not been called first
     */
    public function getMatchingUninlinableSelectors()
    {
        if ($this->matchingUninlinableCssRules === null) {
            throw new \BadMethodCallException('inlineCss must be called first', 1568385221);
        }

        return \array_column($this->matchingUninlinableCssRules, 'selector');
    }

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

    /**
     * Purges the visited nodes.
     *
     * @return void
     */
    private function purgeVisitedNodes()
    {
        $this->visitedNodes = [];
        $this->styleAttributesForNodes = [];
    }

    /**
     * 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.
     *
     * @return void
     */
    private function normalizeStyleAttributesOfAllNodes()
    {
        /** @var \DOMElement $node */
        foreach ($this->getAllNodesWithStyleAttribute() 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');
        }
    }

    /**
     * Returns a list with all DOM nodes that have a style attribute.
     *
     * @return \DOMNodeList
     */
    private function getAllNodesWithStyleAttribute()
    {
        return $this->xPath->query('//*[@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-zA-Z][\\w\\-]*+(?=:)/S',
            static 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);
    }

    /**
     * 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($this->caches[self::CACHE_KEY_CSS_DECLARATIONS_BLOCK][$cssDeclarationsBlock])) {
            return $this->caches[self::CACHE_KEY_CSS_DECLARATIONS_BLOCK][$cssDeclarationsBlock];
        }

        $properties = [];
        foreach (\preg_split('/;(?!base64|charset)/', $cssDeclarationsBlock) as $declaration) {
            $matches = [];
            if (!\preg_match('/^([A-Za-z\\-]+)\\s*:\\s*(.+)$/s', \trim($declaration), $matches)) {
                continue;
            }

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

        return $properties;
    }

    /**
     * Returns CSS content.
     *
     * @return string
     */
    private function getCssFromAllStyleNodes()
    {
        $styleNodes = $this->xPath->query('//style');
        if ($styleNodes === false) {
            return '';
        }

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

        return $css;
    }

    /**
     * Removes comments from the supplied CSS.
     *
     * @param string $css
     *
     * @return string CSS with the comments removed
     */
    private function removeCssComments($css)
    {
        return \preg_replace('%/\\*[^*]*+(?:\\*(?!/)[^*]*+)*+\\*/%', '', $css);
    }

    /**
     * Extracts `@import` and `@charset` rules from the supplied CSS.  These rules must not be preceded by any other
     * rules, or they will be ignored.  (From the CSS 2.1 specification: "CSS 2.1 user agents must ignore any '@import'
     * rule that occurs inside a block or after any non-ignored statement other than an @charset or an @import rule."
     * Note also that `@charset` is case sensitive whereas `@import` is not.)
     *
     * @param string $css CSS with comments removed
     *
     * @return string[] The first element is the CSS with the valid `@import` and `@charset` rules removed.  The second
     * element contains a concatenation of the valid `@import` rules, each followed by whatever whitespace followed it
     * in the original CSS (so that either unminified or minified formatting is preserved); if there were no `@import`
     * rules, it will be an empty string.  The (valid) `@charset` rules are discarded.
     */
    private function extractImportAndCharsetRules($css)
    {
        $possiblyModifiedCss = $css;
        $importRules = '';

        while (
            \preg_match(
                '/^\\s*+(@((?i)import(?-i)|charset)\\s[^;]++;\\s*+)/',
                $possiblyModifiedCss,
                $matches
            )
        ) {
            list($fullMatch, $atRuleAndFollowingWhitespace, $atRuleName) = $matches;

            if (\strtolower($atRuleName) === 'import') {
                $importRules .= $atRuleAndFollowingWhitespace;
            }

            $possiblyModifiedCss = \substr($possiblyModifiedCss, \strlen($fullMatch));
        }

        return [$possiblyModifiedCss, $importRules];
    }

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

        return $excludedNodes;
    }

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

        return $this->cssSelectorConverter;
    }

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

        $matches = $this->getCssRuleMatches($css);

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

            foreach (\explode(',', $cssRule['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(
                    '/:(?!' . self::PSEUDO_CLASS_MATCHER . ')[\\w\\-]/i',
                    $selector
                );
                $hasUnmatchablePseudo = $hasPseudoElement || $hasUnsupportedPseudoClass;

                $parsedCssRule = [
                    '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) ? 'inlinable' : 'uninlinable';
                $cssRules[$ruleType][] = $parsedCssRule;
            }
        }

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

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

        return $cssRules;
    }

    /**
     * @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($this->caches[self::CACHE_KEY_SELECTOR][$selectorKey])) {
            return $this->caches[self::CACHE_KEY_SELECTOR][$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);
        }
        $this->caches[self::CACHE_KEY_SELECTOR][$selectorKey] = $precedence;

        return $precedence;
    }

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

        $ruleMatches = [];
        foreach ($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[] = [
                    'media' => $cssPart['media'],
                    'selectors' => $cssRule[1],
                    'declarations' => $cssRule[2],
                ];
            }
        }

        return $ruleMatches;
    }

    /**
     * Splits input CSS code into an array of parts for different media queries, 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)
    {
        $mediaTypesExpression = '';
        if (!empty($this->allowedMediaTypes)) {
            $mediaTypesExpression = '|' . \implode('|', \array_keys($this->allowedMediaTypes));
        }

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

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

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

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

    /**
     * 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 copyInlinableCssToStyleAttribute(\DOMElement $node, array $cssRule)
    {
        $newStyleDeclarations = $this->parseCssDeclarationsBlock($cssRule['declarationsBlock']);
        if ($newStyleDeclarations === []) {
            return;
        }

        // 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 = [];
        }
        $node->setAttribute(
            'style',
            $this->generateStyleStringFromDeclarationsArrays($oldStyleDeclarations, $newStyleDeclarations)
        );
    }

    /**
     * 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)
    {
        $cacheKey = \serialize([$oldStyles, $newStyles]);
        if (isset($this->caches[self::CACHE_KEY_COMBINED_STYLES][$cacheKey])) {
            return $this->caches[self::CACHE_KEY_COMBINED_STYLES][$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);

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

        return $trimmedStyle;
    }

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

    /**
     * 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
                )
            );
        }
    }

    /**
     * Searches for all nodes with a style attribute and removes the "!important" annotations out of
     * the inline style declarations, eventually by rearranging declarations.
     *
     * @return void
     */
    private function removeImportantAnnotationFromAllInlineStyles()
    {
        foreach ($this->getAllNodesWithStyleAttribute() 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 = [];
        $importantStyleDeclarations = [];
        foreach ($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)
        );
    }

    /**
     * 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([], $styleDeclarations);
    }

    /**
     * Determines which of `$cssRules` actually apply to `$this->domDocument`, and sets them in
     * `$this->matchingUninlinableCssRules`.
     *
     * @param string[][] $cssRules the "uninlinable" array of CSS rules returned by `parseCssRules`
     *
     * @return void
     */
    private function determineMatchingUninlinableCssRules(array $cssRules)
    {
        $this->matchingUninlinableCssRules = \array_filter($cssRules, [$this, 'existsMatchForSelectorInCssRule']);
    }

    /**
     * Checks whether there is at least one matching element for the CSS selector contained in the `selector` element
     * of the provided CSS rule.
     *
     * Any dynamic pseudo-classes will be assumed to apply. If the selector matches a pseudo-element,
     * it will test for a match with its originating element.
     *
     * @param string[] $cssRule
     *
     * @return bool
     *
     * @throws SyntaxErrorException
     */
    private function existsMatchForSelectorInCssRule(array $cssRule)
    {
        $selector = $cssRule['selector'];
        if ($cssRule['hasUnmatchablePseudo']) {
            $selector = $this->removeUnmatchablePseudoComponents($selector);
        }
        return $this->existsMatchForCssSelector($selector);
    }

    /**
     * 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 string $cssSelector
     *
     * @return bool
     *
     * @throws SyntaxErrorException
     */
    private function existsMatchForCssSelector($cssSelector)
    {
        try {
            $nodesMatchingSelector = $this->xPath->query($this->getCssSelectorConverter()->toXPath($cssSelector));
        } catch (SyntaxErrorException $e) {
            if ($this->debug) {
                throw $e;
            }
            return true;
        }

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

    /**
     * Removes pseudo-elements and dynamic pseudo-classes from a CSS selector, replacing them with "*" if necessary.
     * If such a pseudo-component is within the argument of `:not`, the entire `:not` component is removed or replaced.
     *
     * @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)
    {
        // The regex allows nested brackets via `(?2)`.
        // A space is temporarily prepended because the callback can't determine if the match was at the very start.
        $selectorWithoutNots = \ltrim(\preg_replace_callback(
            '/(\\s?+):not(\\([^()]*+(?:(?2)[^()]*+)*+\\))/i',
            [$this, 'replaceUnmatchableNotComponent'],
            ' ' . $selector
        ));

        $pseudoComponentMatcher = ':(?!' . self::PSEUDO_CLASS_MATCHER . '):?+[\\w\\-]++(?:\\([^\\)]*+\\))?+';
        return \preg_replace(
            ['/(\\s|^)' . $pseudoComponentMatcher . '/i', '/' . $pseudoComponentMatcher . '/i'],
            ['$1*', ''],
            $selectorWithoutNots
        );
    }

    /**
     * Helps `removeUnmatchablePseudoComponents()` replace or remove a selector `:not(...)` component if its argument
     * contains pseudo-elements or dynamic pseudo-classes.
     *
     * @param string[] $matches array of elements matched by the regular expression
     *
     * @return string the full match if there were no unmatchable pseudo components within; otherwise, any preceding
     *         whitespace followed by "*", or an empty string if there was no preceding whitespace
     */
    private function replaceUnmatchableNotComponent(array $matches)
    {
        list($notComponentWithAnyPrecedingWhitespace, $anyPrecedingWhitespace, $notArgumentInBrackets) = $matches;

        $hasUnmatchablePseudo = \preg_match(
            '/:(?!' . self::PSEUDO_CLASS_MATCHER . ')[\\w\\-:]/i',
            $notArgumentInBrackets
        );

        if ($hasUnmatchablePseudo) {
            return $anyPrecedingWhitespace !== '' ? $anyPrecedingWhitespace . '*' : '';
        }
        return $notComponentWithAnyPrecedingWhitespace;
    }

    /**
     * Applies `$this->matchingUninlinableCssRules` to `$this->domDocument` by placing them as CSS in a `<style>`
     * element.
     *
     * @param string $cssImportRules This may contain any `@import` rules that should precede the CSS placed in the
     *        `<style>` element.  If there are no unlinlinable CSS rules to copy there, a `<style>` element will be
     *        created containing just `$cssImportRules`.  `$cssImportRules` may be an empty string; if it is, and there
     *        are no unlinlinable CSS rules, an empty `<style>` element will not be created.
     *
     * @return void
     */
    private function copyUninlinableCssToStyleNode($cssImportRules)
    {
        $css = $cssImportRules;

        // avoid including unneeded class dependency if there are no rules
        if ($this->matchingUninlinableCssRules !== []) {
            $cssConcatenator = new CssConcatenator();
            foreach ($this->matchingUninlinableCssRules as $cssRule) {
                $cssConcatenator->append([$cssRule['selector']], $cssRule['declarationsBlock'], $cssRule['media']);
            }
            $css .= $cssConcatenator->getCss();
        }

        // avoid adding empty style element
        if ($css !== '') {
            $this->addStyleElementToDocument($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);
    }

    /**
     * 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);
    }
}