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Edit File: CSS.php

<?php

/**
 * CSS Minifier.
 *
 * Please report bugs on https://github.com/matthiasmullie/minify/issues
 *
 * @author Matthias Mullie <minify@mullie.eu>
 * @copyright Copyright (c) 2012, Matthias Mullie. All rights reserved
 * @license MIT License
 */

namespace MatthiasMullie\Minify;

use MatthiasMullie\Minify\Exceptions\FileImportException;
use MatthiasMullie\Minify\Exceptions\PatternMatchException;
use MatthiasMullie\PathConverter\Converter;
use MatthiasMullie\PathConverter\ConverterInterface;

/**
 * CSS minifier.
 *
 * Please report bugs on https://github.com/matthiasmullie/minify/issues
 *
 * @author Matthias Mullie <minify@mullie.eu>
 * @author Tijs Verkoyen <minify@verkoyen.eu>
 * @copyright Copyright (c) 2012, Matthias Mullie. All rights reserved
 * @license MIT License
 */
class CSS extends Minify
{
    /**
     * @var int maximum inport size in kB
     */
    protected $maxImportSize = 5;

/**
     * @var string[] valid import extensions
     */
    protected $importExtensions = array(
        'gif' => 'data:image/gif',
        'png' => 'data:image/png',
        'jpe' => 'data:image/jpeg',
        'jpg' => 'data:image/jpeg',
        'jpeg' => 'data:image/jpeg',
        'svg' => 'data:image/svg+xml',
        'woff' => 'data:application/x-font-woff',
        'woff2' => 'data:application/x-font-woff2',
        'avif' => 'data:image/avif',
        'apng' => 'data:image/apng',
        'webp' => 'data:image/webp',
        'tif' => 'image/tiff',
        'tiff' => 'image/tiff',
        'xbm' => 'image/x-xbitmap',
    );

/**
     * Set the maximum size if files to be imported.
     *
     * Files larger than this size (in kB) will not be imported into the CSS.
     * Importing files into the CSS as data-uri will save you some connections,
     * but we should only import relatively small decorative images so that our
     * CSS file doesn't get too bulky.
     *
     * @param int $size Size in kB
     */
    public function setMaxImportSize($size)
    {
        $this->maxImportSize = $size;
    }

/**
     * Set the type of extensions to be imported into the CSS (to save network
     * connections).
     * Keys of the array should be the file extensions & respective values
     * should be the data type.
     *
     * @param string[] $extensions Array of file extensions
     */
    public function setImportExtensions(array $extensions)
    {
        $this->importExtensions = $extensions;
    }

/**
     * Move any import statements to the top.
     *
     * @param string $content Nearly finished CSS content
     *
     * @return string
     */
    protected function moveImportsToTop($content)
    {
        if (preg_match_all('/(;?)(@import (?<url>url$)?(?P<quotes>["\']?).+?(?P=quotes)(?(url)$));?/', $content, $matches)) {
            // remove from content
            foreach ($matches[0] as $import) {
                $content = str_replace($import, '', $content);
            }

// add to top
            $content = implode(';', $matches[2]) . ';' . trim($content, ';');
        }

return $content;
    }

/**
     * Combine CSS from import statements.
     *
     * \@import's will be loaded and their content merged into the original file,
     * to save HTTP requests.
     *
     * @param string $source The file to combine imports for
     * @param string $content The CSS content to combine imports for
     * @param string[] $parents Parent paths, for circular reference checks
     *
     * @return string
     *
     * @throws FileImportException
     */
    protected function combineImports($source, $content, $parents)
    {
        $importRegexes = array(
            // @import url(xxx)
            '/
            # import statement
            @import

# whitespace
            \s+

# open url()
                url\(

# (optional) open path enclosure
                    (?P<quotes>["\']?)

# fetch path
                        (?P<path>.+?)

# (optional) close path enclosure
                    (?P=quotes)

# close url()
                \)

# (optional) trailing whitespace
                \s*

# (optional) media statement(s)
                (?P<media>[^;]*)

# (optional) trailing whitespace
                \s*

# (optional) closing semi-colon
            ;?

/ix',

// @import 'xxx'
            '/

# import statement
            @import

# whitespace
            \s+

# open path enclosure
                (?P<quotes>["\'])

# fetch path
                    (?P<path>.+?)

# close path enclosure
                (?P=quotes)

# (optional) trailing whitespace
                \s*

# (optional) media statement(s)
                (?P<media>[^;]*)

# (optional) trailing whitespace
                \s*

# (optional) closing semi-colon
            ;?

/ix',
        );

// find all relative imports in css
        $matches = array();
        foreach ($importRegexes as $importRegex) {
            if (preg_match_all($importRegex, $content, $regexMatches, PREG_SET_ORDER)) {
                $matches = array_merge($matches, $regexMatches);
            }
        }

$search = array();
        $replace = array();

// loop the matches
        foreach ($matches as $match) {
            // get the path for the file that will be imported
            $importPath = dirname($source) . '/' . $match['path'];

// only replace the import with the content if we can grab the
            // content of the file
            if (!$this->canImportByPath($match['path']) || !$this->canImportFile($importPath)) {
                continue;
            }

// check if current file was not imported previously in the same
            // import chain.
            if (in_array($importPath, $parents)) {
                throw new FileImportException('Failed to import file "' . $importPath . '": circular reference detected.');
            }

// grab referenced file & minify it (which may include importing
            // yet other @import statements recursively)
            $minifier = new self($importPath);
            $minifier->setMaxImportSize($this->maxImportSize);
            $minifier->setImportExtensions($this->importExtensions);
            $importContent = $minifier->execute($source, $parents);

// check if this is only valid for certain media
            if (!empty($match['media'])) {
                $importContent = '@media ' . $match['media'] . '{' . $importContent . '}';
            }

// add to replacement array
            $search[] = $match[0];
            $replace[] = $importContent;
        }

// replace the import statements
        return str_replace($search, $replace, $content);
    }

/**
     * Import files into the CSS, base64-ized.
     *
     * @url(image.jpg) images will be loaded and their content merged into the
     * original file, to save HTTP requests.
     *
     * @param string $source The file to import files for
     * @param string $content The CSS content to import files for
     *
     * @return string
     */
    protected function importFiles($source, $content)
    {
        $regex = '/url$(["\']?)(.+?)\\1$/i';
        if ($this->importExtensions && preg_match_all($regex, $content, $matches, PREG_SET_ORDER)) {
            $search = array();
            $replace = array();

// loop the matches
            foreach ($matches as $match) {
                $extension = substr(strrchr($match[2], '.'), 1);
                if ($extension && !array_key_exists($extension, $this->importExtensions)) {
                    continue;
                }

// get the path for the file that will be imported
                $path = $match[2];
                $path = dirname($source) . '/' . $path;

// only replace the import with the content if we're able to get
                // the content of the file, and it's relatively small
                if ($this->canImportFile($path) && $this->canImportBySize($path)) {
                    // grab content && base64-ize
                    $importContent = $this->load($path);
                    $importContent = base64_encode($importContent);

// build replacement
                    $search[] = $match[0];
                    $replace[] = 'url(' . $this->importExtensions[$extension] . ';base64,' . $importContent . ')';
                }
            }

// replace the import statements
            $content = str_replace($search, $replace, $content);
        }

return $content;
    }

/**
     * Minify the data.
     * Perform CSS optimizations.
     *
     * @param string[optional] $path    Path to write the data to
     * @param string[] $parents Parent paths, for circular reference checks
     *
     * @return string The minified data
     *
     * @throws PatternMatchException
     */
    public function execute($path = null, $parents = array())
    {
        $content = '';

// loop CSS data (raw data and files)
        foreach ($this->data as $source => $css) {
            /*
             * Let's first take out strings & comments, since we can't just
             * remove whitespace anywhere. If whitespace occurs inside a string,
             * we should leave it alone. E.g.:
             * p { content: "a   test" }
             */
            $this->extractStrings();
            $this->stripComments();
            $this->extractMath();
            $this->extractCustomProperties();
            $css = $this->replace($css);

$css = $this->stripWhitespace($css);
            $css = $this->convertLegacyColors($css);
            $css = $this->cleanupModernColors($css);
            $css = $this->shortenHEXColors($css);
            $css = $this->shortenZeroes($css);
            $css = $this->shortenFontWeights($css);
            $css = $this->stripEmptyTags($css);

// restore the string we've extracted earlier
            $css = $this->restoreExtractedData($css);

$source = is_int($source) ? '' : $source;
            $parents = $source ? array_merge($parents, array($source)) : $parents;
            $css = $this->combineImports($source, $css, $parents);
            $css = $this->importFiles($source, $css);

/*
             * If we'll save to a new path, we'll have to fix the relative paths
             * to be relative no longer to the source file, but to the new path.
             * If we don't write to a file, fall back to same path so no
             * conversion happens (because we still want it to go through most
             * of the move code, which also addresses url() & @import syntax...)
             */
            $converter = $this->getPathConverter($source, $path ?: $source);
            $css = $this->move($converter, $css);

// combine css
            $content .= $css;
        }

$content = $this->moveImportsToTop($content);

return $content;
    }

/**
     * Moving a css file should update all relative urls.
     * Relative references (e.g. ../images/image.gif) in a certain css file,
     * will have to be updated when a file is being saved at another location
     * (e.g. ../../images/image.gif, if the new CSS file is 1 folder deeper).
     *
     * @param ConverterInterface $converter Relative path converter
     * @param string $content The CSS content to update relative urls for
     *
     * @return string
     */
    protected function move(ConverterInterface $converter, $content)
    {
        /*
         * Relative path references will usually be enclosed by url(). @import
         * is an exception, where url() is not necessary around the path (but is
         * allowed).
         * This *could* be 1 regular expression, where both regular expressions
         * in this array are on different sides of a |. But we're using named
         * patterns in both regexes, the same name on both regexes. This is only
         * possible with a (?J) modifier, but that only works after a fairly
         * recent PCRE version. That's why I'm doing 2 separate regular
         * expressions & combining the matches after executing of both.
         */
        $relativeRegexes = array(
            // url(xxx)
            '/
            # open url()
            url\(

\s*

# open path enclosure
                (?P<quotes>["\'])?

# fetch path
                    (?P<path>.+?)

# close path enclosure
                (?(quotes)(?P=quotes))

\s*

# close url()
            \)

/ix',

// @import "xxx"
            '/
            # import statement
            @import

# whitespace
            \s+

# we don\'t have to check for @import url(), because the
                # condition above will already catch these

# open path enclosure
                (?P<quotes>["\'])

# fetch path
                    (?P<path>.+?)

# close path enclosure
                (?P=quotes)

/ix',
        );

// find all relative urls in css
        $matches = array();
        foreach ($relativeRegexes as $relativeRegex) {
            if (preg_match_all($relativeRegex, $content, $regexMatches, PREG_SET_ORDER)) {
                $matches = array_merge($matches, $regexMatches);
            }
        }

$search = array();
        $replace = array();

// loop all urls
        foreach ($matches as $match) {
            // determine if it's a url() or an @import match
            $type = (strpos($match[0], '@import') === 0 ? 'import' : 'url');

$url = $match['path'];
            if ($this->canImportByPath($url)) {
                // attempting to interpret GET-params makes no sense, so let's discard them for awhile
                $params = strrchr($url, '?');
                $url = $params ? substr($url, 0, -strlen($params)) : $url;

// fix relative url
                $url = $converter->convert($url);

// now that the path has been converted, re-apply GET-params
                $url .= $params;
            }

/*
             * Urls with control characters above 0x7e should be quoted.
             * According to Mozilla's parser, whitespace is only allowed at the
             * end of unquoted urls.
             * Urls with `)` (as could happen with data: uris) should also be
             * quoted to avoid being confused for the url() closing parentheses.
             * And urls with a # have also been reported to cause issues.
             * Urls with quotes inside should also remain escaped.
             *
             * @see https://developer.mozilla.org/nl/docs/Web/CSS/url#The_url()_functional_notation
             * @see https://hg.mozilla.org/mozilla-central/rev/14abca4e7378
             * @see https://github.com/matthiasmullie/minify/issues/193
             */
            $url = trim($url);
            if (preg_match('/[\s\)\'"#\x{7f}-\x{9f}]/u', $url)) {
                $url = $match['quotes'] . $url . $match['quotes'];
            }

// build replacement
            $search[] = $match[0];
            if ($type === 'url') {
                $replace[] = 'url(' . $url . ')';
            } elseif ($type === 'import') {
                $replace[] = '@import "' . $url . '"';
            }
        }

// replace urls
        return str_replace($search, $replace, $content);
    }

/**
     * Shorthand HEX color codes.
     * #FF0000FF -> #f00 -> red
     * #FF00FF00 -> transparent.
     *
     * @param string $content The CSS content to shorten the HEX color codes for
     *
     * @return string
     */
    protected function shortenHexColors($content)
    {
        // shorten repeating patterns within HEX ..
        $content = preg_replace('/(?<=[: ])#([0-9a-f])\\1([0-9a-f])\\2([0-9a-f])\\3(?:([0-9a-f])\\4)?(?=[; }])/i', '#$1$2$3$4', $content);

// remove alpha channel if it's pointless ..
        $content = preg_replace('/(?<=[: ])#([0-9a-f]{6})ff(?=[; }])/i', '#$1', $content);
        $content = preg_replace('/(?<=[: ])#([0-9a-f]{3})f(?=[; }])/i', '#$1', $content);

// replace `transparent` with shortcut ..
        $content = preg_replace('/(?<=[: ])#[0-9a-f]{6}00(?=[; }])/i', '#fff0', $content);

$colors = array(
            // make these more readable
            '#00f' => 'blue',
            '#dc143c' => 'crimson',
            '#0ff' => 'cyan',
            '#8b0000' => 'darkred',
            '#696969' => 'dimgray',
            '#ff69b4' => 'hotpink',
            '#0f0' => 'lime',
            '#fdf5e6' => 'oldlace',
            '#87ceeb' => 'skyblue',
            '#d8bfd8' => 'thistle',
            // we can shorten some even more by replacing them with their color name
            '#f0ffff' => 'azure',
            '#f5f5dc' => 'beige',
            '#ffe4c4' => 'bisque',
            '#a52a2a' => 'brown',
            '#ff7f50' => 'coral',
            '#ffd700' => 'gold',
            '#808080' => 'gray',
            '#008000' => 'green',
            '#4b0082' => 'indigo',
            '#fffff0' => 'ivory',
            '#f0e68c' => 'khaki',
            '#faf0e6' => 'linen',
            '#800000' => 'maroon',
            '#000080' => 'navy',
            '#808000' => 'olive',
            '#ffa500' => 'orange',
            '#da70d6' => 'orchid',
            '#cd853f' => 'peru',
            '#ffc0cb' => 'pink',
            '#dda0dd' => 'plum',
            '#800080' => 'purple',
            '#f00' => 'red',
            '#fa8072' => 'salmon',
            '#a0522d' => 'sienna',
            '#c0c0c0' => 'silver',
            '#fffafa' => 'snow',
            '#d2b48c' => 'tan',
            '#008080' => 'teal',
            '#ff6347' => 'tomato',
            '#ee82ee' => 'violet',
            '#f5deb3' => 'wheat',
            // or the other way around
            'black' => '#000',
            'fuchsia' => '#f0f',
            'magenta' => '#f0f',
            'white' => '#fff',
            'yellow' => '#ff0',
            // and also `transparent`
            'transparent' => '#fff0',
        );

return preg_replace_callback(
            '/(?<=[: ])(' . implode('|', array_keys($colors)) . ')(?=[; }])/i',
            function ($match) use ($colors) {
                return $colors[strtolower($match[0])];
            },
            $content
        );
    }

/**
     * Convert RGB|HSL color codes.
     * rgb(255,0,0,.5) -> rgb(255 0 0 / .5).
     * rgb(255,0,0) -> #f00.
     *
     * @param string $content The CSS content to shorten the RGB color codes for
     *
     * @return string
     */
    protected function convertLegacyColors($content)
    {
        /*
          https://drafts.csswg.org/css-color/#color-syntax-legacy
          https://developer.mozilla.org/en-US/docs/Web/CSS/color_value/rgb
          https://developer.mozilla.org/en-US/docs/Web/CSS/color_value/hsl
        */

// convert legacy color syntax
        $content = preg_replace('/(rgb)a?$\s*([0-9]{1,3}%?)\s*,\s*([0-9]{1,3}%?)\s*,\s*([0-9]{1,3}%?)\s*,\s*([0,1]?(?:\.[0-9]*)?)\s*$/i', '$1($2 $3 $4 / $5)', $content);
        $content = preg_replace('/(rgb)a?$\s*([0-9]{1,3}%?)\s*,\s*([0-9]{1,3}%?)\s*,\s*([0-9]{1,3}%?)\s*$/i', '$1($2 $3 $4)', $content);
        $content = preg_replace('/(hsl)a?$\s*([0-9]+(?:deg|grad|rad|turn)?)\s*,\s*([0-9]{1,3}%)\s*,\s*([0-9]{1,3}%)\s*,\s*([0,1]?(?:\.[0-9]*)?)\s*$/i', '$1($2 $3 $4 / $5)', $content);
        $content = preg_replace('/(hsl)a?$\s*([0-9]+(?:deg|grad|rad|turn)?)\s*,\s*([0-9]{1,3}%)\s*,\s*([0-9]{1,3}%)\s*$/i', '$1($2 $3 $4)', $content);

// convert `rgb` to `hex`
        $dec = '([01]?[0-9]?[0-9]|2[0-4][0-9]|25[0-5])';

return preg_replace_callback(
            "/rgb$$dec $dec $dec$/i",
            function ($match) {
                return sprintf('#%02x%02x%02x', $match[1], $match[2], $match[3]);
            },
            $content
        );
    }

/**
     * Cleanup RGB|HSL|HWB|LCH|LAB
     * rgb(255 0 0 / 1) -> rgb(255 0 0).
     * rgb(255 0 0 / 0) -> transparent.
     *
     * @param string $content The CSS content to cleanup HSL|HWB|LCH|LAB
     *
     * @return string
     */
    protected function cleanupModernColors($content)
    {
        /*
          https://drafts.csswg.org/css-color/#color-syntax-modern
          https://developer.mozilla.org/en-US/docs/Web/CSS/color_value/hwb
          https://developer.mozilla.org/en-US/docs/Web/CSS/color_value/lch
          https://developer.mozilla.org/en-US/docs/Web/CSS/color_value/lab
          https://developer.mozilla.org/en-US/docs/Web/CSS/color_value/oklch
          https://developer.mozilla.org/en-US/docs/Web/CSS/color_value/oklab
        */
        $tag = '(rgb|hsl|hwb|(?:(?:ok)?(?:lch|lab)))';

// remove alpha channel if it's pointless ..
        $content = preg_replace('/' . $tag . '$\s*([^\s)]+)\s+([^\s)]+)\s+([^\s)]+)\s+\/\s+1(?:(?:\.\d?)*|00%)?\s*$/i', '$1($2 $3 $4)', $content);

// replace `transparent` with shortcut ..
        $content = preg_replace('/' . $tag . '$\s*[^\s)]+\s+[^\s)]+\s+[^\s)]+\s+\/\s+0(?:[\.0%]*)?\s*$/i', '#fff0', $content);

return $content;
    }

/**
     * Shorten CSS font weights.
     *
     * @param string $content The CSS content to shorten the font weights for
     *
     * @return string
     */
    protected function shortenFontWeights($content)
    {
        $weights = array(
            'normal' => 400,
            'bold' => 700,
        );

$callback = function ($match) use ($weights) {
            return $match[1] . $weights[$match[2]];
        };

return preg_replace_callback('/(font-weight\s*:\s*)(' . implode('|', array_keys($weights)) . ')(?=[;}])/', $callback, $content);
    }

/**
     * Shorthand 0 values to plain 0, instead of e.g. -0em.
     *
     * @param string $content The CSS content to shorten the zero values for
     *
     * @return string
     */
    protected function shortenZeroes($content)
    {
        // we don't want to strip units in `calc()` expressions:
        // `5px - 0px` is valid, but `5px - 0` is not
        // `10px * 0` is valid (equates to 0), and so is `10 * 0px`, but
        // `10 * 0` is invalid
        // we've extracted calcs earlier, so we don't need to worry about this

// reusable bits of code throughout these regexes:
        // before & after are used to make sure we don't match lose unintended
        // 0-like values (e.g. in #000, or in http://url/1.0)
        // units can be stripped from 0 values, or used to recognize non 0
        // values (where wa may be able to strip a .0 suffix)
        $before = '(?<=[:(, ])';
        $after = '(?=[ ,);}])';
        $units = '(em|ex|%|px|cm|mm|in|pt|pc|ch|rem|vh|vw|vmin|vmax|vm)';

// strip units after zeroes (0px -> 0)
        // NOTE: it should be safe to remove all units for a 0 value, but in
        // practice, Webkit (especially Safari) seems to stumble over at least
        // 0%, potentially other units as well. Only stripping 'px' for now.
        // @see https://github.com/matthiasmullie/minify/issues/60
        $content = preg_replace('/' . $before . '(-?0*(\.0+)?)(?<=0)px' . $after . '/', '\\1', $content);

// strip 0-digits (.0 -> 0)
        $content = preg_replace('/' . $before . '\.0+' . $units . '?' . $after . '/', '0\\1', $content);
        // strip trailing 0: 50.10 -> 50.1, 50.10px -> 50.1px
        $content = preg_replace('/' . $before . '(-?[0-9]+\.[0-9]+)0+' . $units . '?' . $after . '/', '\\1\\2', $content);
        // strip trailing 0: 50.00 -> 50, 50.00px -> 50px
        $content = preg_replace('/' . $before . '(-?[0-9]+)\.0+' . $units . '?' . $after . '/', '\\1\\2', $content);
        // strip leading 0: 0.1 -> .1, 01.1 -> 1.1
        $content = preg_replace('/' . $before . '(-?)0+([0-9]*\.[0-9]+)' . $units . '?' . $after . '/', '\\1\\2\\3', $content);

// strip negative zeroes (-0 -> 0) & truncate zeroes (00 -> 0)
        $content = preg_replace('/' . $before . '-?0+' . $units . '?' . $after . '/', '0\\1', $content);

// IE doesn't seem to understand a unitless flex-basis value (correct -
        // it goes against the spec), so let's add it in again (make it `%`,
        // which is only 1 char: 0%, 0px, 0 anything, it's all just the same)
        // @see https://developer.mozilla.org/nl/docs/Web/CSS/flex
        $content = preg_replace('/flex:([0-9]+\s[0-9]+\s)0([;\}])/', 'flex:${1}0%${2}', $content);
        $content = preg_replace('/flex-basis:0([;\}])/', 'flex-basis:0%${1}', $content);

return $content;
    }

/**
     * Strip empty tags from source code.
     *
     * @param string $content
     *
     * @return string
     */
    protected function stripEmptyTags($content)
    {
        $content = preg_replace('/(?<=^)[^\{\};]+\{\s*\}/', '', $content);
        $content = preg_replace('/(?<=(\}|;))[^\{\};]+\{\s*\}/', '', $content);

return $content;
    }

/**
     * Strip comments from source code.
     */
    protected function stripComments()
    {
        $this->stripMultilineComments();
    }

/**
     * Strip whitespace.
     *
     * @param string $content The CSS content to strip the whitespace for
     *
     * @return string
     *
     * @throws PatternMatchException
     */
    protected function stripWhitespace($content)
    {
        // remove leading & trailing whitespace
        $content = $this->pregReplace('/^\s*/m', '', $content);
        $content = $this->pregReplace('/\s*$/m', '', $content);

// replace newlines with a single space
        $content = $this->pregReplace('/\s+/', ' ', $content);

// remove whitespace around meta characters
        // inspired by stackoverflow.com/questions/15195750/minify-compress-css-with-regex
        $content = $this->pregReplace('/\s*([\*$~^|]?+=|[{};,>~]|!important\b)\s*/', '$1', $content);
        $content = $this->pregReplace('/([\[(:>\+])\s+/', '$1', $content);
        $content = $this->pregReplace('/\s+([\]\)>\+])/', '$1', $content);
        $content = $this->pregReplace('/\s+(:)(?![^\}]*\{)/', '$1', $content);

// whitespace around + and - can only be stripped inside some pseudo-
        // classes, like `:nth-child(3+2n)`
        // not in things like `calc(3px + 2px)`, shorthands like `3px -2px`, or
        // selectors like `div.weird- p`
        $pseudos = array('nth-child', 'nth-last-child', 'nth-last-of-type', 'nth-of-type');
        $content = $this->pregReplace('/:(' . implode('|', $pseudos) . ')$\s*([+-]?)\s*(.+?)\s*([+-]?)\s*(.*?)\s*$/', ':$1($2$3$4$5)', $content);

// remove semicolon/whitespace followed by closing bracket
        $content = str_replace(';}', '}', $content);

return trim($content);
    }

/**
     * Perform a preg_replace and check for errors.
     *
     * @param string $pattern Pattern
     * @param string $replacement Replacement
     * @param string $subject String to process
     *
     * @return string
     *
     * @throws PatternMatchException
     */
    protected function pregReplace($pattern, $replacement, $subject)
    {
        $result = preg_replace($pattern, $replacement, $subject);
        if ($result === null) {
            throw PatternMatchException::fromLastError("Failed to replace with pattern '$pattern'");
        }

return $result;
    }

/**
     * Replace all occurrences of functions that may contain math, where
     * whitespace around operators needs to be preserved (e.g. calc, clamp).
     */
    protected function extractMath()
    {
        $functions = array('calc', 'clamp', 'min', 'max');
        $pattern = '/\b(' . implode('|', $functions) . ')(\(.+?)(?=$|;|})/m';

// PHP only supports $this inside anonymous functions since 5.4
        $minifier = $this;
        $callback = function ($match) use ($minifier, $pattern, &$callback) {
            $function = $match[1];
            $length = strlen($match[2]);
            $expr = '';
            $opened = 0;

// the regular expression for extracting math has 1 significant problem:
            // it can't determine the correct closing parenthesis...
            // instead, it'll match a larger portion of code to where it's certain that
            // the calc() musts have ended, and we'll figure out which is the correct
            // closing parenthesis here, by counting how many have opened
            for ($i = 0; $i < $length; ++$i) {
                $char = $match[2][$i];
                $expr .= $char;
                if ($char === '(') {
                    ++$opened;
                } elseif ($char === ')' && --$opened === 0) {
                    break;
                }
            }

// now that we've figured out where the calc() starts and ends, extract it
            $count = count($minifier->extracted);
            $placeholder = 'math(' . $count . ')';
            $minifier->extracted[$placeholder] = $function . '(' . trim(substr($expr, 1, -1)) . ')';

// and since we've captured more code than required, we may have some leftover
            // calc() in here too - go recursive on the remaining but of code to go figure
            // that out and extract what is needed
            $rest = $minifier->str_replace_first($function . $expr, '', $match[0]);
            $rest = preg_replace_callback($pattern, $callback, $rest);

return $placeholder . $rest;
        };

$this->registerPattern($pattern, $callback);
    }

/**
     * Replace custom properties, whose values may be used in scenarios where
     * we wouldn't want them to be minified (e.g. inside calc).
     */
    protected function extractCustomProperties()
    {
        // PHP only supports $this inside anonymous functions since 5.4
        $minifier = $this;
        $this->registerPattern(
            '/(?<=^|[;}{])\s*(--[^:;{}"\'\s]+)\s*:([^;{}]+)/m',
            function ($match) use ($minifier) {
                $placeholder = '--custom-' . count($minifier->extracted) . ':0';
                $minifier->extracted[$placeholder] = $match[1] . ':' . trim($match[2]);

return $placeholder;
            }
        );
    }

/**
     * Check if file is small enough to be imported.
     *
     * @param string $path The path to the file
     *
     * @return bool
     */
    protected function canImportBySize($path)
    {
        return ($size = @filesize($path)) && $size <= $this->maxImportSize * 1024;
    }

/**
     * Check if file a file can be imported, going by the path.
     *
     * @param string $path
     *
     * @return bool
     */
    protected function canImportByPath($path)
    {
        return preg_match('/^(data:|https?:|\\/)/', $path) === 0;
    }

/**
     * Return a converter to update relative paths to be relative to the new
     * destination.
     *
     * @param string $source
     * @param string $target
     *
     * @return ConverterInterface
     */
    protected function getPathConverter($source, $target)
    {
        return new Converter($source, $target);
    }
}