<?php
/**
 * This class provides functions for converting CSS styles into inline style attributes in your HTML code.
 *
 * For more information, please see the README.md file.
 *
 * @version WC-2.0.0
 *
 * @author Cameron Brooks
 * @author Jaime Prado
 * @author Oliver Klee <github@oliverklee.de>
 * @author Roman Ožana <ozana@omdesign.cz>
 * @author Sander Kruger <s.kruger@invessel.com>
 * @author Zoli Szabó <zoli.szabo+github@gmail.com>
 */
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 $xPathRules = [
        // attribute presence
        '/^\\[(\\w+|\\w+\\=[\'"]?\\w+[\'"]?)\\]/' => '*[@\\1]',
        // type and attribute exact value
        '/(\\w)\\[(\\w+)\\=[\'"]?([\\w\\s]+)[\'"]?\\]/' => '\\1[@\\2="\\3"]',
        // type and attribute value with ~ (one word within a whitespace-separated list of words)
        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\~\\=[\\s]*[\'"]?([\\w\\-_\\/]+)[\'"]?\\]/'
        => '\\1[contains(concat(" ", @\\2, " "), concat(" ", "\\3", " "))]',
        // type and attribute value with | (either exact value match or prefix followed by a hyphen)
        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\|\\=[\\s]*[\'"]?([\\w\\-_\\s\\/]+)[\'"]?\\]/'
        => '\\1[@\\2="\\3" or starts-with(@\\2, concat("\\3", "-"))]',
        // type and attribute value with ^ (prefix match)
        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\^\\=[\\s]*[\'"]?([\\w\\-_\\/]+)[\'"]?\\]/' => '\\1[starts-with(@\\2, "\\3")]',
        // type and attribute value with * (substring match)
        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\*\\=[\\s]*[\'"]?([\\w\\-_\\s\\/:;]+)[\'"]?\\]/' => '\\1[contains(@\\2, "\\3")]',
        // adjacent sibling
        '/\\s+\\+\\s+/' => '/following-sibling::*[1]/self::',
        // child
        '/\\s*>\\s*/' => '/',
        // descendant
        '/\\s+(?=.*[^\\]]{1}$)/' => '//',
        // type and :first-child
        '/([^\\/]+):first-child/i' => '*[1]/self::\\1',
        // type and :last-child
        '/([^\\/]+):last-child/i' => '*[last()]/self::\\1',

        // The following matcher will break things if it is placed before the adjacent matcher.
        // So one of the matchers matches either too much or not enough.
        // type and attribute value with $ (suffix match)
        '/([\\w\\*]+)\\[(\\w+)[\\s]*\\$\\=[\\s]*[\'"]?([\\w\\-_\\s\\/]+)[\'"]?\\]/'
        => '\\1[substring(@\\2, string-length(@\\2) - string-length("\\3") + 1) = "\\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()
    {
        return $this->createAndProcessXmlDocument()->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()
    {
        $xmlDocument = $this->createAndProcessXmlDocument();
        $bodyNodeHtml = $xmlDocument->saveHTML($this->getBodyElement($xmlDocument));

        return str_replace(['<body>', '</body>'], '', $bodyNodeHtml);
    }

    /**
     * Creates an XML document from $this->html and emogrifies ist.
     *
     * @return \DOMDocument
     *
     * @throws \BadMethodCallException
     */
    private function createAndProcessXmlDocument()
    {
        if ($this->html === '') {
            throw new \BadMethodCallException('Please set some HTML first.', 1390393096);
        }

        $xmlDocument = $this->createRawXmlDocument();
        $this->ensureExistenceOfBodyElement($xmlDocument);
        $this->process($xmlDocument);

        return $xmlDocument;
    }

    /**
     * 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();
        $this->purgeVisitedNodes();
        set_error_handler([$this, 'handleXpathQueryWarnings'], E_WARNING);

        $this->normalizeStyleAttributesOfAllNodes($xPath);

        // 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) {
            // There's no real way to test "PHP Warning" output generated by the following XPath query unless PHPUnit
            // converts it to an exception. Unfortunately, this would only apply to tests and not work for production
            // executions, which can still flood logs/output unnecessarily. Instead, Emogrifier's error handler should
            // always throw an exception and it must be caught here and only rethrown if in debug mode.
            try {
                // \DOMXPath::query will always return a DOMNodeList or an exception when errors are caught.
                $nodesMatchingCssSelectors = $xPath->query($this->translateCssToXpath($cssRule['selector']));
            } catch (\InvalidArgumentException $e) {
                if ($this->debug) {
                    throw $e;
                }
                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']);
                $node->setAttribute(
                    'style',
                    $this->generateStyleStringFromDeclarationsArrays($oldStyleDeclarations, $newStyleDeclarations)
                );
            }
        }

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

        if ($this->shouldMapCssToHtml) {
            $this->mapAllInlineStylesToHtmlAttributes($xPath);
        }

        if ($this->shouldKeepInvisibleNodes) {
            $this->removeInvisibleNodes($xPath);
        }

        $this->removeImportantAnnotationFromAllInlineStyles($xPath);

        $this->copyCssWithMediaToStyleNode($xmlDocument, $xPath, $cssParts['media']);

        restore_error_handler();
    }

    /**
     * Searches for all nodes with a style attribute, transforms the CSS found
     * to HTML attributes and adds those attributes to each node.
     *
     * @param \DOMXPath $xPath
     *
     * @return void
     */
    private function mapAllInlineStylesToHtmlAttributes(\DOMXPath $xPath)
    {
        /** @var \DOMElement $node */
        foreach ($this->getAllNodesWithStyleAttribute($xPath) as $node) {
            $inlineStyleDeclarations = $this->parseCssDeclarationsBlock($node->getAttribute('style'));
            $this->mapCssToHtmlAttributes($inlineStyleDeclarations, $node);
        }
    }

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

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

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

    /**
     * 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 \DOMElement $node node to apply styles to
     *
     * @return void
     */
    private function mapCssToHtmlAttributes(array $styles, \DOMElement $node)
    {
        foreach ($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 \DOMElement $node node to apply styles to
     *
     * @return void
     */
    private function mapCssToHtmlAttribute($property, $value, \DOMElement $node)
    {
        if (!$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 \DOMElement $node node to apply styles to
     *
     * @return bool true if the property cab be mapped using the simple mapping table
     */
    private function mapSimpleCssProperty($property, $value, \DOMElement $node)
    {
        if (!isset($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 \DOMElement $node node to apply styles to
     *
     * @return void
     */
    private function mapComplexCssProperty($property, $value, \DOMElement $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 = $styles[0];
                if (!is_numeric($first[0]) && strpos($first, 'url') !== 0) {
                    // 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^{}]*)([^{]+){([^}]*)}/mi', $css, $matches, PREG_SET_ORDER);

            $cssRules = [];
            /** @var string[][] $matches */
            /** @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\\()|not\\([[:ascii:]]*\\))/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);
            }
        }
    }

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

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

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

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

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

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

    /**
     * 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);
    }

    /**
     * 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 = [];

        /** @var string[][] $rawMediaQueries */
        foreach ($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.
     * When not in debug mode, it returns true also for invalid selectors (because they may be valid,
     * just not implemented/recognized yet by Emogrifier).
     *
     * @param \DOMXPath $xPath
     * @param string $cssSelector
     *
     * @return bool
     *
     * @throws \InvalidArgumentException
     */
    private function existsMatchForCssSelector(\DOMXPath $xPath, $cssSelector)
    {
        try {
            $nodesMatchingSelector = $xPath->query($this->translateCssToXpath($cssSelector));
        } catch (\InvalidArgumentException $e) {
            if ($this->debug) {
                throw $e;
            }
            return true;
        }

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

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

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

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

        return $css;
    }

    /**
     * Adds a style element with $css to $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);

        $bodyElement = $this->getBodyElement($document);
        $bodyElement->appendChild($styleElement);
    }

    /**
     * Checks that $document has a BODY element and adds it if it is missing.
     *
     * @param \DOMDocument $document
     */
    private function ensureExistenceOfBodyElement(\DOMDocument $document)
    {
        if ($document->getElementsByTagName('body')->item(0) !== null) {
            return;
        }

        $htmlElement = $document->getElementsByTagName('html')->item(0);

        $htmlElement->appendChild($document->createElement('body'));
    }

    /**
     * Returns the BODY element.
     *
     * This method assumes that there always is a BODY element.
     *
     * @param \DOMDocument $document
     *
     * @return \DOMElement
     *
     * @throws \BadMethodCallException
     */
    private function getBodyElement(\DOMDocument $document)
    {
        $bodyElement = $document->getElementsByTagName('body')->item(0);
        if ($bodyElement === null) {
            throw new \BadMethodCallException(
                'getBodyElement method may only be called after ensureExistenceOfBodyElement has been called.',
                1508173775427
            );
        }

        return $bodyElement;
    }

    /**
     * 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{\\(]\\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 createRawXmlDocument()
    {
        $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)
    {
        $hasContentTypeMetaTag = stripos($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])) {
            return $this->caches[self::CACHE_KEY_SELECTOR][$xPathKey];
        }

        $hasNotSelector = (bool)preg_match(
            '/^([^:]+):not\\(\\s*([[:ascii:]]+)\\s*\\)$/',
            $trimmedLowercaseSelector,
            $matches
        );
        if (!$hasNotSelector) {
            $xPath = '//' . $this->translateCssToXpathPass($trimmedLowercaseSelector);
        } else {
            /** @var string[] $matches */
            $partBeforeNot = $matches[1];
            $notContents = $matches[2];
            $xPath = '//' . $this->translateCssToXpathPass($partBeforeNot) .
                '[not(' . $this->translateCssToXpathPassInline($notContents) . ')]';
        }
        $this->caches[self::CACHE_KEY_SELECTOR][$xPathKey] = $xPath;

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

    /**
     * Flexibly translates the CSS selector $trimmedLowercaseSelector to an xPath selector.
     *
     * @param string $trimmedLowercaseSelector
     *
     * @return string
     */
    private function translateCssToXpathPass($trimmedLowercaseSelector)
    {
        return $this->translateCssToXpathPassWithMatchClassAttributesCallback(
            $trimmedLowercaseSelector,
            [$this, 'matchClassAttributes']
        );
    }

    /**
     * Flexibly translates the CSS selector $trimmedLowercaseSelector to an xPath selector for inline usage.
     *
     * @param string $trimmedLowercaseSelector
     *
     * @return string
     */
    private function translateCssToXpathPassInline($trimmedLowercaseSelector)
    {
        return $this->translateCssToXpathPassWithMatchClassAttributesCallback(
            $trimmedLowercaseSelector,
            [$this, 'matchClassAttributesInline']
        );
    }

    /**
     * Flexibly translates the CSS selector $trimmedLowercaseSelector to an xPath selector while using
     * $matchClassAttributesCallback as to match the class attributes.
     *
     * @param string $trimmedLowercaseSelector
     * @param callable $matchClassAttributesCallback
     *
     * @return string
     */
    private function translateCssToXpathPassWithMatchClassAttributesCallback(
        $trimmedLowercaseSelector,
        callable $matchClassAttributesCallback
    ) {
        $roughXpath = preg_replace(array_keys($this->xPathRules), $this->xPathRules, $trimmedLowercaseSelector);
        $xPathWithIdAttributeMatchers = preg_replace_callback(
            self::ID_ATTRIBUTE_MATCHER,
            [$this, 'matchIdAttributes'],
            $roughXpath
        );
        $xPathWithIdAttributeAndClassMatchers = preg_replace_callback(
            self::CLASS_ATTRIBUTE_MATCHER,
            $matchClassAttributesCallback,
            $xPathWithIdAttributeMatchers
        );

        // Advanced selectors are going to require a bit more advanced emogrification.
        $xPathWithIdAttributeAndClassMatchers = preg_replace_callback(
            '/([^\\/]+):nth-child\\(\\s*(odd|even|[+\\-]?\\d|[+\\-]?\\d?n(\\s*[+\\-]\\s*\\d)?)\\s*\\)/i',
            [$this, 'translateNthChild'],
            $xPathWithIdAttributeAndClassMatchers
        );
        $finalXpath = preg_replace_callback(
            '/([^\\/]+):nth-of-type\\(\s*(odd|even|[+\\-]?\\d|[+\\-]?\\d?n(\\s*[+\\-]\\s*\\d)?)\\s*\\)/i',
            [$this, 'translateNthOfType'],
            $xPathWithIdAttributeAndClassMatchers
        );

        return $finalXpath;
    }

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

    /**
     * @param string[] $match
     *
     * @return string xPath class attribute query wrapped in element selector
     */
    private function matchClassAttributes(array $match)
    {
        return ($match[1] !== '' ? $match[1] : '*') . '[' . $this->matchClassAttributesInline($match) . ']';
    }

    /**
     * @param string[] $match
     *
     * @return string xPath class attribute query
     */
    private function matchClassAttributesInline(array $match)
    {
        return 'contains(concat(" ",@class," "),concat(" ","' .
            implode(
                '"," "))][contains(concat(" ",@class," "),concat(" ","',
                explode('.', substr($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]);
                $xPathExpression = sprintf(
                    '*[(last() - position()) mod %1%u = %2$u]/self::%3$s',
                    $parseResult[self::MULTIPLIER],
                    $parseResult[self::INDEX],
                    $match[1]
                );
            } else {
                $xPathExpression = sprintf(
                    '*[position() mod %1$u = %2$u]/self::%3$s',
                    $parseResult[self::MULTIPLIER],
                    $parseResult[self::INDEX],
                    $match[1]
                );
            }
        } else {
            $xPathExpression = sprintf('*[%1$u]/self::%2$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]);
                $xPathExpression = sprintf(
                    '%1$s[(last() - position()) mod %2$u = %3$u]',
                    $match[1],
                    $parseResult[self::MULTIPLIER],
                    $parseResult[self::INDEX]
                );
            } else {
                $xPathExpression = sprintf(
                    '%1$s[position() mod %2$u = %3$u]',
                    $match[1],
                    $parseResult[self::MULTIPLIER],
                    $parseResult[self::INDEX]
                );
            }
        } else {
            $xPathExpression = sprintf('%1$s[%2$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[]
     *
     * @throws \InvalidArgumentException
     */
    private function getNodesToExclude(\DOMXPath $xPath)
    {
        $excludedNodes = [];
        foreach (array_keys($this->excludedSelectors) as $selectorToExclude) {
            try {
                $matchingNodes = $xPath->query($this->translateCssToXpath($selectorToExclude));
            } catch (\InvalidArgumentException $e) {
                if ($this->debug) {
                    throw $e;
                }
                continue;
            }
            foreach ($matchingNodes as $node) {
                $excludedNodes[] = $node;
            }
        }

        return $excludedNodes;
    }

    /**
     * Handles invalid xPath expression warnings, generated during the process() method,
     * during querying \DOMDocument and trigger \InvalidArgumentException with invalid selector
     * or \RuntimeException, depending on the source of the warning.
     *
     * @param int $type
     * @param string $message
     * @param string $file
     * @param int $line
     * @param array $context
     *
     * @return bool always false
     *
     * @throws \InvalidArgumentException
     * @throws \RuntimeException
     */
    public function handleXpathQueryWarnings( // @codingStandardsIgnoreLine
        $type,
        $message,
        $file,
        $line,
        array $context
    ) {
        $selector = '';
        if (isset($context['cssRule']['selector'])) {
            // warnings generated by invalid/unrecognized selectors in method process()
            $selector = $context['cssRule']['selector'];
        } elseif (isset($context['selectorToExclude'])) {
            // warnings generated by invalid/unrecognized selectors in method getNodesToExclude()
            $selector = $context['selectorToExclude'];
        } elseif (isset($context['cssSelector'])) {
            // warnings generated by invalid/unrecognized selectors in method existsMatchForCssSelector()
            $selector = $context['cssSelector'];
        }

        if ($selector !== '') {
            throw new \InvalidArgumentException(
                sprintf('%1$s in selector >> %2$s << in %3$s on line %4$u', $message, $selector, $file, $line),
                1509279985
            );
        }

        // Catches eventual warnings generated by method getAllNodesWithStyleAttribute()
        if (isset($context['xPath'])) {
            throw new \RuntimeException(
                sprintf('%1$s in %2$s on line %3$u', $message, $file, $line),
                1509280067
            );
        }

        // 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;
    }
}
