# weforms/1.5.4/includes/library/Emogrifier.php

weForms – Easy Drag &amp; Drop Contact Form Builder For WordPress, version 1.5.4. 1,533 lines.

- Page: https://pluginprobe.com/plugins/weforms/1.5.4/code/includes/library/Emogrifier.php
- Raw: https://pluginprobe.com/plugins/weforms/1.5.4/raw/includes/library/Emogrifier.php
- Modified: 2020-10-20T13:26:26+00:00

Line numbers below start at 1. Link to a line or a range by appending a fragment to the
page URL, for example `https://pluginprobe.com/plugins/weforms/1.5.4/code/includes/library/Emogrifier.php#L10-L20`.

```php
<?php

use BadMethodCallException;
use InvalidArgumentException;

/**
 * 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.
 *
 * @version 1.2.0
 *
 * @author Cameron Brooks
 * @author Jaime Prado
 * @author Oliver Klee <typo3-coding@oliverklee.de>
 * @author Roman Ožana <ozana@omdesign.cz>
 * @author Sander Kruger <s.kruger@invessel.com>
 */
class Emogrifier {
    /**
     * @var int
     */
    const CACHE_KEY_CSS = 0;

    /**
     * @var int
     */
    const CACHE_KEY_SELECTOR = 1;

    /**
     * @var int
     */
    const CACHE_KEY_XPATH = 2;

    /**
     * @var int
     */
    const CACHE_KEY_CSS_DECLARATIONS_BLOCK = 3;

    /**
     * @var int
     */
    const CACHE_KEY_COMBINED_STYLES = 4;

    /**
     * for calculating nth-of-type and nth-child selectors
     *
     * @var int
     */
    const INDEX = 0;

    /**
     * for calculating nth-of-type and nth-child selectors
     *
     * @var int
     */
    const MULTIPLIER = 1;

    /**
     * @var string
     */
    const ID_ATTRIBUTE_MATCHER = '/(\\w+)?\\#([\\w\\-]+)/';

    /**
     * @var string
     */
    const CLASS_ATTRIBUTE_MATCHER = '/(\\w+|[\\*\\]])?((\\.[\\w\\-]+)+)/';

    /**
     * @var string
     */
    const CONTENT_TYPE_META_TAG = '<meta http-equiv="Content-Type" content="text/html; charset=utf-8">';

    /**
     * @var string
     */
    const DEFAULT_DOCUMENT_TYPE = '<!DOCTYPE html>';

    /**
     * @var string
     */
    private $html = '';

    /**
     * @var string
     */
    private $css = '';

    /**
     * @var bool[]
     */
    private $excludedSelectors = [];

    /**
     * @var string[]
     */
    private $unprocessableHtmlTags = ['wbr'];

    /**
     * @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_XPATH                  => [],
        self::CACHE_KEY_CSS_DECLARATIONS_BLOCK => [],
        self::CACHE_KEY_COMBINED_STYLES        => [],
    ];

    /**
     * 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;

    /**
     * Determines whether elements with the `display: none` property are
     * removed from the DOM.
     *
     * @var bool
     */
    private $shouldKeepInvisibleNodes = true;

    /**
     * @var string[]
     */
    private $xPathRules = [
        // child
        '/\\s*>\\s*/'                              => '/',
        // adjacent sibling
        '/\\s+\\+\\s+/'                            => '/following-sibling::*[1]/self::',
        // descendant
        '/\\s+(?=.*[^\\]]{1}$)/'                   => '//',
        // :first-child
        '/([^\\/]+):first-child/i'                 => '*[1]/self::\\1',
        // :last-child
        '/([^\\/]+):last-child/i'                  => '*[last()]/self::\\1',
        // attribute only
        '/^\\[(\\w+|\\w+\\=[\'"]?\\w+[\'"]?)\\]/'  => '*[@\\1]',
        // attribute
        '/(\\w)\\[(\\w+)\\]/'                      => '\\1[@\\2]',
        // exact attribute
        '/(\\w)\\[(\\w+)\\=[\'"]?([\\w\\s]+)[\'"]?\\]/' => '\\1[@\\2="\\3"]',
        // element attribute~=
        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\~\\=[\\s]*[\'"]?([\\w-_\\/]+)[\'"]?\\]/' => '\\1[contains(concat(" ", @\\2, " "), concat(" ", "\\3", " "))]',
        // element attribute^=
        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\^\\=[\\s]*[\'"]?([\\w-_\\/]+)[\'"]?\\]/' => '\\1[starts-with(@\\2, "\\3")]',
        // element attribute*=
        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\*\\=[\\s]*[\'"]?([\\w-_\\s\\/:;]+)[\'"]?\\]/' => '\\1[contains(@\\2, "\\3")]',
        // element attribute$=
        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\$\\=[\\s]*[\'"]?([\\w-_\\s\\/]+)[\'"]?\\]/' => '\\1[substring(@\\2, string-length(@\\2) - string-length("\\3") + 1) = "\\3"]',
        // element attribute|=
        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\|\\=[\\s]*[\'"]?([\\w-_\\s\\/]+)[\'"]?\\]/' => '\\1[@\\2="\\3" or starts-with(@\\2, concat("\\3", "-"))]',
    ];

    /**
     * Determines whether CSS styles that have an equivalent HTML attribute
     * should be mapped and attached to those elements.
     *
     * @var bool
     */
    private $shouldMapCssToHtml = false;

    /**
     * This multi-level array contains simple mappings of CSS properties to
     * HTML attributes. If a mapping only applies to certain HTML nodes or
     * only for certain values, the mapping is an object with a whitelist
     * of nodes and values.
     *
     * @var mixed[][]
     */
    private $cssToHtmlMap = [
        'background-color' => [
            'attribute' => 'bgcolor',
        ],
        'text-align' => [
            'attribute' => 'align',
            'nodes'     => ['p', 'div', 'td'],
            'values'    => ['left', 'right', 'center', 'justify'],
        ],
        'float' => [
            'attribute' => 'align',
            'nodes'     => ['table', 'img'],
            'values'    => ['left', 'right'],
        ],
        'border-spacing' => [
            'attribute' => 'cellspacing',
            'nodes'     => ['table'],
        ],
    ];

    /**
     * Emogrifier will throw Exceptions when it encounters an error instead of silently ignoring them.
     *
     * @var bool
     */
    private $debug = false;

    /**
     * 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
     *
     * @return void
     */
    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
     *
     * @return void
     */
    public function setCss( $css ) {
        $this->css = $css;
    }

    /**
     * Applies $this->css to $this->html and returns the HTML with the CSS
     * applied.
     *
     * 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();
        $this->process( $xmlDocument );

        return $xmlDocument->saveHTML();
    }

    /**
     * Applies $this->css to $this->html and returns only the HTML content
     * within the <body> tag.
     *
     * This method places the CSS inline.
     *
     * @return string
     *
     * @throws BadMethodCallException
     */
    public function emogrifyBodyContent() {
        if ( $this->html === '' ) {
            throw new BadMethodCallException( 'Please set some HTML first before calling emogrify.', 1390393096 );
        }

        $xmlDocument = $this->createXmlDocument();
        $this->process( $xmlDocument );

        $innerDocument = new \DOMDocument();

        foreach ( $xmlDocument->documentElement->getElementsByTagName( 'body' )->item( 0 )->childNodes as $childNode ) {
            $innerDocument->appendChild( $innerDocument->importNode( $childNode, true ) );
        }

        return html_entity_decode( $innerDocument->saveHTML() );
    }

    /**
     * Applies $this->css to $xmlDocument.
     *
     * This method places the CSS inline.
     *
     * @param \DOMDocument $xmlDocument
     *
     * @return void
     *
     * @throws InvalidArgumentException
     */
    protected function process( DOMDocument $xmlDocument ) {
        $xPath = new \DOMXPath( $xmlDocument );
        $this->clearAllCaches();

        // Before be begin processing the CSS file, parse the document and normalize 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 store a reference of nodes with existing inline styles so we don't overwrite them.
        $this->purgeVisitedNodes();

        set_error_handler( [$this, 'handleXpathError'], E_WARNING );

        $nodesWithStyleAttributes = $xPath->query( '//*[@style]' );

        if ( $nodesWithStyleAttributes !== false ) {
            /** @var \DOMElement $node */
            foreach ( $nodesWithStyleAttributes as $node ) {
                if ( $this->isInlineStyleAttributesParsingEnabled ) {
                    $this->normalizeStyleAttributes( $node );
                } else {
                    $node->removeAttribute( 'style' );
                }
            }
        }

        // 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;

        if ( $this->isStyleBlocksParsingEnabled ) {
            $allCss .= $this->getCssFromAllStyleNodes( $xPath );
        }

        $cssParts      = $this->splitCssAndMediaQuery( $allCss );
        $excludedNodes = $this->getNodesToExclude( $xPath );
        $cssRules      = $this->parseCssRules( $cssParts['css'] );

        foreach ( $cssRules as $cssRule ) {
            // query the body for the xpath selector
            $nodesMatchingCssSelectors = $xPath->query( $this->translateCssToXpath( $cssRule['selector'] ) );
            // ignore invalid selectors
            if ( $nodesMatchingCssSelectors === false ) {
                continue;
            }

            /** @var \DOMElement $node */
            foreach ( $nodesMatchingCssSelectors as $node ) {
                if ( in_array( $node, $excludedNodes, true ) ) {
                    continue;
                }

                // 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 = [];
                }
                $newStyleDeclarations = $this->parseCssDeclarationsBlock( $cssRule['declarationsBlock'] );

                if ( $this->shouldMapCssToHtml ) {
                    $this->mapCssToHtmlAttributes( $newStyleDeclarations, $node );
                }
                $node->setAttribute( 
                    'style',
                    $this->generateStyleStringFromDeclarationsArrays( $oldStyleDeclarations, $newStyleDeclarations )
                  );
            }
        }

        restore_error_handler();

        if ( $this->isInlineStyleAttributesParsingEnabled ) {
            $this->fillStyleAttributesWithMergedStyles();
        }

        if ( $this->shouldKeepInvisibleNodes ) {
            $this->removeInvisibleNodes( $xPath );
        }

        $this->copyCssWithMediaToStyleNode( $xmlDocument, $xPath, $cssParts['media'] );
    }

    /**
     * Applies $styles to $node.
     *
     * This method maps CSS styles to HTML attributes and adds those to the
     * node.
     *
     * @param string[] $styles the new CSS styles taken from the global styles to be applied to this node
     * @param \DOMNode $node   node to apply styles to
     *
     * @return void
     */
    private function mapCssToHtmlAttributes( array $styles, DOMNode $node ) {
        foreach ( $styles as $property => $value ) {
            // Strip !important indicator
            $value = trim( str_replace( '!important', '', $value ) );
            $this->mapCssToHtmlAttribute( $property, $value, $node );
        }
    }

    /**
     * Tries to apply the CSS style to $node as an attribute.
     *
     * This method maps a CSS rule to HTML attributes and adds those to the node.
     *
     * @param string   $property the name of the CSS property to map
     * @param string   $value    the value of the style rule to map
     * @param \DOMNode $node     node to apply styles to
     *
     * @return void
     */
    private function mapCssToHtmlAttribute( $property, $value, DOMNode $node ) {
        if ( !$this->mapSimpleCssProperty( $property, $value, $node ) ) {
            $this->mapComplexCssProperty( $property, $value, $node );
        }
    }

    /**
     * Looks up the CSS property in the mapping table and maps it if it matches the conditions.
     *
     * @param string   $property the name of the CSS property to map
     * @param string   $value    the value of the style rule to map
     * @param \DOMNode $node     node to apply styles to
     *
     * @return bool true if the property cab be mapped using the simple mapping table
     */
    private function mapSimpleCssProperty( $property, $value, DOMNode $node ) {
        if ( !isset( $this->cssToHtmlMap[$property] ) ) {
            return false;
        }

        $mapping     = $this->cssToHtmlMap[$property];
        $nodesMatch  = !isset( $mapping['nodes'] ) || in_array( $node->nodeName, $mapping['nodes'], true );
        $valuesMatch = !isset( $mapping['values'] ) || in_array( $value, $mapping['values'], true );

        if ( !$nodesMatch || !$valuesMatch ) {
            return false;
        }

        $node->setAttribute( $mapping['attribute'], $value );

        return true;
    }

    /**
     * Maps CSS properties that need special transformation to an HTML attribute.
     *
     * @param string   $property the name of the CSS property to map
     * @param string   $value    the value of the style rule to map
     * @param \DOMNode $node     node to apply styles to
     *
     * @return void
     */
    private function mapComplexCssProperty( $property, $value, DOMNode $node ) {
        $nodeName       = $node->nodeName;
        $isTable        = $nodeName === 'table';
        $isImage        = $nodeName === 'img';
        $isTableOrImage = $isTable || $isImage;

        switch ( $property ) {
            case 'background':
                // Parse out the color, if any
                $styles = explode( ' ', $value );
                $first  = $styles[0];

                if ( !is_numeric( substr( $first, 0, 1 ) ) && substr( $first, 0, 3 ) !== 'url' ) {
                    // This is not a position or image, assume it's a color
                    $node->setAttribute( 'bgcolor', $first );
                }
                break;

            case 'width':
                // intentional fall-through
            case 'height':
                // Only parse values in px and %, but not values like "auto".
                if ( preg_match( '/^\d+(px|%)$/', $value ) ) {
                    // Remove 'px'. This regex only conserves numbers and %
                    $number = preg_replace( '/[^0-9.%]/', '', $value );
                    $node->setAttribute( $property, $number );
                }
                break;

            case 'margin':
                if ( $isTableOrImage ) {
                    $margins = $this->parseCssShorthandValue( $value );

                    if ( $margins['left'] === 'auto' && $margins['right'] === 'auto' ) {
                        $node->setAttribute( 'align', 'center' );
                    }
                }
                break;

            case 'border':
                if ( $isTableOrImage ) {
                    if ( $value === 'none' || $value === '0' ) {
                        $node->setAttribute( 'border', '0' );
                    }
                }
                break;
            default:
        }
    }

    /**
     * Parses a shorthand CSS value and splits it into individual values
     *
     * @param string $value a string of CSS value with 1, 2, 3 or 4 sizes
     *                      For example: padding: 0 auto;
     *                      '0 auto' is split into top: 0, left: auto, bottom: 0,
     *                      right: auto
     *
     * @return string[] an array of values for top, right, bottom and left (using these as associative array keys)
     */
    private function parseCssShorthandValue( $value ) {
        $values = preg_split( '/\\s+/', $value );

        $css           = [];
        $css['top']    = $values[0];
        $css['right']  = ( count( $values ) > 1 ) ? $values[1] : $css['top'];
        $css['bottom'] = ( count( $values ) > 2 ) ? $values[2] : $css['top'];
        $css['left']   = ( count( $values ) > 3 ) ? $values[3] : $css['right'];

        return $css;
    }

    /**
     * Extracts and parses the individual rules from a CSS string.
     *
     * @param string $css a string of raw CSS code
     *
     * @return string[][] an array of string sub-arrays with the keys
     *                    "selector" (the CSS selector(s), e.g., "*" or "h1"),
     *                    "declarationsBLock" (the semicolon-separated CSS declarations for that selector(s),
     *                    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] ) ) {
            // process the CSS file for selectors and definitions
            preg_match_all( '/(?:^|[\\s^{}]*)([^{]+){([^}]*)}/mis', $css, $matches, PREG_SET_ORDER );

            $cssRules = [];
            /** @var string[] $cssRule */
            foreach ( $matches as $key => $cssRule ) {
                $cssDeclaration = trim( $cssRule[2] );

                if ( $cssDeclaration === '' ) {
                    continue;
                }

                $selectors = explode( ',', $cssRule[1] );

                foreach ( $selectors as $selector ) {
                    // don't process pseudo-elements and behavioral (dynamic) pseudo-classes;
                    // only allow structural pseudo-classes
                    $hasPseudoElement        = strpos( $selector, '::' ) !== false;
                    $hasAnyPseudoClass       = (bool) preg_match( '/:[a-zA-Z]/', $selector );
                    $hasSupportedPseudoClass = (bool) preg_match( '/:\\S+\\-(child|type\\()/i', $selector );

                    if ( $hasPseudoElement || ( $hasAnyPseudoClass && !$hasSupportedPseudoClass ) ) {
                        continue;
                    }

                    $cssRules[] = [
                        'selector'          => trim( $selector ),
                        'declarationsBlock' => $cssDeclaration,
                        // keep track of where it appears in the file, since order is important
                        'line' => $key,
                    ];
                }
            }

            usort( $cssRules, [$this, 'sortBySelectorPrecedence'] );

            $this->caches[self::CACHE_KEY_CSS][$cssKey] = $cssRules;
        }

        return $this->caches[self::CACHE_KEY_CSS][$cssKey];
    }

    /**
     * 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
     */
    public function disableInvisibleNodeRemoval() {
        $this->shouldKeepInvisibleNodes = false;
    }

    /**
     * Enables the attachment/override of HTML attributes for which a
     * corresponding CSS property has been set.
     *
     * @return void
     */
    public function enableCssToHtmlMapping() {
        $this->shouldMapCssToHtml = true;
    }

    /**
     * Clears all caches.
     *
     * @return void
     */
    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_DECLARATIONS_BLOCK );
        $this->clearCache( self::CACHE_KEY_COMBINED_STYLES );
    }

    /**
     * Clears a single cache by key.
     *
     * @param int $key the cache key, must be CACHE_KEY_CSS, CACHE_KEY_SELECTOR, CACHE_KEY_XPATH
     *                 or CACHE_KEY_CSS_DECLARATION_BLOCK
     *
     * @return void
     *
     * @throws InvalidArgumentException
     */
    private function clearCache( $key ) {
        $allowedCacheKeys = [
            self::CACHE_KEY_CSS,
            self::CACHE_KEY_SELECTOR,
            self::CACHE_KEY_XPATH,
            self::CACHE_KEY_CSS_DECLARATIONS_BLOCK,
            self::CACHE_KEY_COMBINED_STYLES,
        ];

        if ( !in_array( $key, $allowedCacheKeys, true ) ) {
            throw new InvalidArgumentException( 'Invalid cache key: ' . $key, 1391822035 );
        }

        $this->caches[$key] = [];
    }

    /**
     * Purges the visited nodes.
     *
     * @return void
     */
    private function purgeVisitedNodes() {
        $this->visitedNodes            = [];
        $this->styleAttributesForNodes = [];
    }

    /**
     * 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 ( $node->parentNode && is_callable( [$node->parentNode, 'removeChild'] ) ) {
                $node->parentNode->removeChild( $node );
            }
        }
    }

    /**
     * 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 ) {
        $combinedStyles = array_merge( $oldStyles, $newStyles );
        $cacheKey       = serialize( $combinedStyles );

        if ( isset( $this->caches[self::CACHE_KEY_COMBINED_STYLES][$cacheKey] ) ) {
            return $this->caches[self::CACHE_KEY_COMBINED_STYLES][$cacheKey];
        }

        foreach ( $oldStyles as $attributeName => $attributeValue ) {
            if ( !isset( $newStyles[$attributeName] ) ) {
                continue;
            }

            $newAttributeValue = $newStyles[$attributeName];

            if ( $this->attributeValueIsImportant( $attributeValue )
                && !$this->attributeValueIsImportant( $newAttributeValue )
              ) {
                $combinedStyles[$attributeName] = $attributeValue;
            }
        }

        $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';
    }

    /**
     * Applies $css to $xmlDocument, limited to the media queries that actually apply to the document.
     *
     * @param \DOMDocument $xmlDocument the document to match against
     * @param \DOMXPath    $xPath
     * @param string       $css         a string of CSS
     *
     * @return void
     */
    private function copyCssWithMediaToStyleNode( DOMDocument $xmlDocument, DOMXPath $xPath, $css ) {
        if ( $css === '' ) {
            return;
        }

        $mediaQueriesRelevantForDocument = [];

        foreach ( $this->extractMediaQueriesFromCss( $css ) as $mediaQuery ) {
            foreach ( $this->parseCssRules( $mediaQuery['css'] ) as $selector ) {
                if ( $this->existsMatchForCssSelector( $xPath, $selector['selector'] ) ) {
                    $mediaQueriesRelevantForDocument[] = $mediaQuery['query'];
                    break;
                }
            }
        }

        $this->addStyleElementToDocument( $xmlDocument, implode( $mediaQueriesRelevantForDocument ) );
    }

    /**
     * Extracts the media queries from $css while skipping empty media queries.
     *
     * @param string $css
     *
     * @return string[][] numeric array with string sub-arrays with the keys "css" and "query"
     */
    private function extractMediaQueriesFromCss( $css ) {
        preg_match_all( '/@media\\b[^{]*({((?:[^{}]+|(?1))*)})/', $css, $rawMediaQueries, PREG_SET_ORDER );
        $parsedQueries = [];

        foreach ( $rawMediaQueries as $mediaQuery ) {
            if ( $mediaQuery[2] !== '' ) {
                $parsedQueries[] = [
                    'css'   => $mediaQuery[2],
                    'query' => $mediaQuery[0],
                ];
            }
        }

        return $parsedQueries;
    }

    /**
     * Checks whether there is at least one matching element for $cssSelector.
     *
     * @param \DOMXPath $xPath
     * @param string    $cssSelector
     *
     * @return bool
     */
    private function existsMatchForCssSelector( DOMXPath $xPath, $cssSelector ) {
        $nodesMatchingSelector = $xPath->query( $this->translateCssToXpath( $cssSelector ) );

        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 $document.
     *
     * This method is protected to allow overriding.
     *
     * @see https://github.com/jjriv/emogrifier/issues/103
     *
     * @param \DOMDocument $document
     * @param string       $css
     *
     * @return void
     */
    protected 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 string[]
     */
    private function splitCssAndMediaQuery( $css ) {
        $cssWithoutComments = preg_replace( '/\\/\\*.*\\*\\//sU', '', $css );

        $mediaTypesExpression = '';

        if ( !empty( $this->allowedMediaTypes ) ) {
            $mediaTypesExpression = '|' . implode( '|', array_keys( $this->allowedMediaTypes ) );
        }

        $media                   = '';
        $cssForAllowedMediaTypes = preg_replace_callback( 
            '#@media\\s+(?:only\\s)?(?:[\\s{\\(]' . $mediaTypesExpression . ')\\s?[^{]+{.*}\\s*}\\s*#misU',
            function ( $matches ) use ( &$media ) {
                $media .= $matches[0];
            },
            $cssWithoutComments
          );

        // filter the CSS
        $search = [
            'import directives'          => '/^\\s*@import\\s[^;]+;/misU',
            'remaining media enclosures' => '/^\\s*@media\\s[^{]+{(.*)}\\s*}\\s/misU',
        ];

        $cleanedCss = preg_replace( $search, '', $cssForAllowedMediaTypes );

        return ['css' => $cleanedCss, 'media' => $media];
    }

    /**
     * Creates a DOMDocument instance with the current HTML.
     *
     * @return \DOMDocument
     */
    private function createXmlDocument() {
        $xmlDocument                      = new \DOMDocument();
        $xmlDocument->encoding            = 'UTF-8';
        $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 unprocessable HTML tags removed and
     * with added document type and Content-Type meta tag if needed.
     *
     * @return string the unified HTML
     *
     * @throws BadMethodCallException
     */
    private function getUnifiedHtml() {
        $htmlWithoutUnprocessableTags = $this->removeUnprocessableTags( $this->html );
        $htmlWithDocumentType         = $this->ensureDocumentType( $htmlWithoutUnprocessableTags );

        return $this->addContentTypeMetaTag( $htmlWithDocumentType );
    }

    /**
     * Removes the unprocessable tags from $html (if this feature is enabled).
     *
     * @param string $html
     *
     * @return string the reworked HTML with the unprocessable tags removed
     */
    private function removeUnprocessableTags( $html ) {
        if ( empty( $this->unprocessableHtmlTags ) ) {
            return $html;
        }

        $unprocessableHtmlTags = implode( '|', $this->unprocessableHtmlTags );

        return preg_replace( 
            '/<\\/?(' . $unprocessableHtmlTags . ')[^>]*>/i',
            '',
            $html
          );
    }

    /**
     * Makes sure that the passed HTML has a document type.
     *
     * @param string $html
     *
     * @return string HTML with document type
     */
    private function ensureDocumentType( $html ) {
        $hasDocumentType = stripos( $html, '<!DOCTYPE' ) !== false;

        if ( $hasDocumentType ) {
            return $html;
        }

        return self::DEFAULT_DOCUMENT_TYPE . $html;
    }

    /**
     * Adds a Content-Type meta tag for the charset.
     *
     * @param string $html
     *
     * @return string the HTML with the meta tag added
     */
    private function addContentTypeMetaTag( $html ) {
        $hasContentTypeMetaTag = stristr( $html, 'Content-Type' ) !== false;

        if ( $hasContentTypeMetaTag ) {
            return $html;
        }

        // We are trying to insert the meta tag to the right spot in the DOM.
        // If we just prepended it to the HTML, we would lose attributes set to the HTML tag.
        $hasHeadTag = stripos( $html, '<head' ) !== false;
        $hasHtmlTag = stripos( $html, '<html' ) !== false;

        if ( $hasHeadTag ) {
            $reworkedHtml = preg_replace( '/<head(.*?)>/i', '<head$1>' . self::CONTENT_TYPE_META_TAG, $html );
        } elseif ( $hasHtmlTag ) {
            $reworkedHtml = preg_replace( 
                '/<html(.*?)>/i',
                '<html$1><head>' . self::CONTENT_TYPE_META_TAG . '</head>',
                $html
              );
        } else {
            $reworkedHtml = self::CONTENT_TYPE_META_TAG . $html;
        }

        return $reworkedHtml;
    }

    /**
     * @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] ) ) {
            $precedence = 0;
            $value      = 100;
            // ids: worth 100, classes: worth 10, elements: worth 1
            $search = ['\\#', '\\.', ''];

            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];
    }

    /**
     * Maps a CSS selector to an XPath query string.
     *
     * @see http://plasmasturm.org/log/444/
     *
     * @param string $cssSelector a CSS selector
     *
     * @return string the corresponding XPath selector
     */
    private function translateCssToXpath( $cssSelector ) {
        $paddedSelector          = ' ' . $cssSelector . ' ';
        $lowercasePaddedSelector = preg_replace_callback( 
            '/\\s+\\w+\\s+/',
            function ( array $matches ) {
                return strtolower( $matches[0] );
            },
            $paddedSelector
          );
        $trimmedLowercaseSelector = trim( $lowercasePaddedSelector );
        $xPathKey                 = md5( $trimmedLowercaseSelector );

        if ( !isset( $this->caches[self::CACHE_KEY_XPATH][$xPathKey] ) ) {
            $roughXpath = '//' . preg_replace( 
                array_keys( $this->xPathRules ),
                $this->xPathRules,
                $trimmedLowercaseSelector
              );
            $xPathWithIdAttributeMatchers = preg_replace_callback( 
                self::ID_ATTRIBUTE_MATCHER,
                [$this, 'matchIdAttributes'],
                $roughXpath
              );
            $xPathWithIdAttributeAndClassMatchers = preg_replace_callback( 
                self::CLASS_ATTRIBUTE_MATCHER,
                [$this, 'matchClassAttributes'],
                $xPathWithIdAttributeMatchers
              );

            // Advanced selectors are going to require a bit more advanced emogrification.
            // When we required PHP 5.3, we could do this with closures.
            $xPathWithIdAttributeAndClassMatchers = preg_replace_callback( 
                '/([^\\/]+):nth-child\\(\\s*(odd|even|[+\\-]?\\d|[+\\-]?\\d?n(\\s*[+\\-]\\s*\\d)?)\\s*\\)/i',
                [$this, 'translateNthChild'],
                $xPathWithIdAttributeAndClassMatchers
              );
            $finalXpath = preg_replace_callback( 
                '/([^\\/]+):nth-of-type\\(\s*(odd|even|[+\\-]?\\d|[+\\-]?\\d?n(\\s*[+\\-]\\s*\\d)?)\\s*\\)/i',
                [$this, 'translateNthOfType'],
                $xPathWithIdAttributeAndClassMatchers
              );

            $this->caches[self::CACHE_KEY_SELECTOR][$xPathKey] = $finalXpath;
        }

        return $this->caches[self::CACHE_KEY_SELECTOR][$xPathKey];
    }

    /**
     * @param string[] $match
     *
     * @return string
     */
    private function matchIdAttributes( array $match ) {
        return ( $match[1] !== '' ? $match[1] : '*' ) . '[@id="' . $match[2] . '"]';
    }

    /**
     * @param string[] $match
     *
     * @return string
     */
    private function matchClassAttributes( array $match ) {
        return ( $match[1] !== '' ? $match[1] : '*' ) . '[contains(concat(" ",@class," "),concat(" ","' .
            implode( 
                '"," "))][contains(concat(" ",@class," "),concat(" ","',
                explode( '.', substr( $match[2], 1 ) )
              ) . '"," "))]';
    }

    /**
     * @param string[] $match
     *
     * @return string
     */
    private function translateNthChild( array $match ) {
        $parseResult = $this->parseNth( $match );

        if ( isset( $parseResult[self::MULTIPLIER] ) ) {
            if ( $parseResult[self::MULTIPLIER] < 0 ) {
                $parseResult[self::MULTIPLIER] = abs( $parseResult[self::MULTIPLIER] );
                $xPathExpression               = sprintf( 
                    '*[(last() - position()) mod %u = %u]/self::%s',
                    $parseResult[self::MULTIPLIER],
                    $parseResult[self::INDEX],
                    $match[1]
                  );
            } else {
                $xPathExpression = sprintf( 
                    '*[position() mod %u = %u]/self::%s',
                    $parseResult[self::MULTIPLIER],
                    $parseResult[self::INDEX],
                    $match[1]
                  );
            }
        } else {
            $xPathExpression = sprintf( '*[%u]/self::%s', $parseResult[self::INDEX], $match[1] );
        }

        return $xPathExpression;
    }

    /**
     * @param string[] $match
     *
     * @return string
     */
    private function translateNthOfType( array $match ) {
        $parseResult = $this->parseNth( $match );

        if ( isset( $parseResult[self::MULTIPLIER] ) ) {
            if ( $parseResult[self::MULTIPLIER] < 0 ) {
                $parseResult[self::MULTIPLIER] = abs( $parseResult[self::MULTIPLIER] );
                $xPathExpression               = sprintf( 
                    '%s[(last() - position()) mod %u = %u]',
                    $match[1],
                    $parseResult[self::MULTIPLIER],
                    $parseResult[self::INDEX]
                  );
            } else {
                $xPathExpression = sprintf( 
                    '%s[position() mod %u = %u]',
                    $match[1],
                    $parseResult[self::MULTIPLIER],
                    $parseResult[self::INDEX]
                  );
            }
        } else {
            $xPathExpression = sprintf( '%s[%u]', $match[1], $parseResult[self::INDEX] );
        }

        return $xPathExpression;
    }

    /**
     * @param string[] $match
     *
     * @return int[]
     */
    private function parseNth( array $match ) {
        if ( in_array( strtolower( $match[2] ), ['even', 'odd'], true ) ) {
            // we have "even" or "odd"
            $index = strtolower( $match[2] ) === 'even' ? 0 : 1;

            return [self::MULTIPLIER => 2, self::INDEX => $index];
        }

        if ( stripos( $match[2], 'n' ) === false ) {
            // if there is a multiplier
            $index = (int) str_replace( ' ', '', $match[2] );

            return [self::INDEX => $index];
        }

        if ( isset( $match[3] ) ) {
            $multipleTerm = str_replace( $match[3], '', $match[2] );
            $index        = (int) str_replace( ' ', '', $match[3] );
        } else {
            $multipleTerm = $match[2];
            $index        = 0;
        }

        $multiplier = str_ireplace( 'n', '', $multipleTerm );

        if ( $multiplier === '' ) {
            $multiplier = 1;
        } elseif ( $multiplier === '0' ) {
            return [self::INDEX => $index];
        } else {
            $multiplier = (int) $multiplier;
        }

        while ( $index < 0 ) {
            $index += abs( $multiplier );
        }

        return [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 $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   = [];
        $declarations = preg_split( '/;(?!base64|charset)/', $cssDeclarationsBlock );

        foreach ( $declarations as $declaration ) {
            $matches = [];

            if ( !preg_match( '/^([A-Za-z\\-]+)\\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;
    }

    /**
     * Find the nodes that are not to be emogrified.
     *
     * @param \DOMXPath $xPath
     *
     * @return \DOMElement[]
     */
    private function getNodesToExclude( DOMXPath $xPath ) {
        $excludedNodes = [];

        foreach ( array_keys( $this->excludedSelectors ) as $selectorToExclude ) {
            foreach ( $xPath->query( $this->translateCssToXpath( $selectorToExclude ) ) as $node ) {
                $excludedNodes[] = $node;
            }
        }

        return $excludedNodes;
    }

    /**
     * Handles invalid xPath expression warnings, generated by process() method,
     * during querying \DOMDocument and trigger \InvalidArgumentException
     * with invalid selector.
     *
     * @param int    $type
     * @param string $message
     * @param string $file
     * @param int    $line
     *
     * @return bool always false
     *
     * @throws InvalidArgumentException
     */
    public function handleXpathError( $type, $message, $file, $line, array $context ) {
        if ( $this->debug && $type === E_WARNING && isset( $context['cssRule']['selector'] ) ) {
            throw new InvalidArgumentException( sprintf( '%s in selector >> %s << in %s on line %s', $message, $context['cssRule']['selector'], $file, $line ) );
        }

        // the normal error handling continues when handler return false
        return false;
    }

    /**
     * Sets the debug mode.
     *
     * @param bool $debug set to true to enable debug mode
     *
     * @return void
     */
    public function setDebug( $debug ) {
        $this->debug = $debug;
    }
}

```
