/lib/csslib.php

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<?php
// This file is part of Moodle - http://moodle.org/
//
// Moodle is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Moodle is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.

/**
 * This file contains CSS related class, and function for the CSS optimiser
 *
 * Please see the {@link css_optimiser} class for greater detail.
 *
 * @package core
 * @subpackage cssoptimiser
 * @copyright 2012 Sam Hemelryk
 * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */

defined('MOODLE_INTERNAL') || die();

/**
 * Stores CSS in a file at the given path.
 *
 * This function either succeeds or throws an exception.
 *
 * @param theme_config $theme The theme that the CSS belongs to.
 * @param string $csspath The path to store the CSS at.
 * @param array $cssfiles The CSS files to store.
 * @param bool $chunk If set to true these files will be chunked to ensure
 *      that no one file contains more than 4095 selectors.
 * @param string $chunkurl If the CSS is be chunked then we need to know the URL
 *      to use for the chunked files.
 */
function css_store_css(theme_config $theme, $csspath, array $cssfiles, $chunk = false, $chunkurl = null) {
    global $CFG;

    $css = '';
    foreach ($cssfiles as $file) {
        $css .= file_get_contents($file)."\n";
    }

    // Check if both the CSS optimiser is enabled and the theme supports it.
    if (!empty($CFG->enablecssoptimiser) && $theme->supportscssoptimisation) {
        // This is an experimental feature introduced in Moodle 2.3
        // The CSS optimiser organises the CSS in order to reduce the overall number
        // of rules and styles being sent to the client. It does this by collating
        // the CSS before it is cached removing excess styles and rules and stripping
        // out any extraneous content such as comments and empty rules.
        $optimiser = new css_optimiser;
        $css = $theme->post_process($css);
        $css = $optimiser->process($css);

        // If cssoptimisestats is set then stats from the optimisation are collected
        // and output at the beginning of the CSS.
        if (!empty($CFG->cssoptimiserstats)) {
            $css = $optimiser->output_stats_css().$css;
        }
    } else {
        // This is the default behaviour.
        // The cssoptimise setting was introduced in Moodle 2.3 and will hopefully
        // in the future be changed from an experimental setting to the default.
        // The css_minify_css will method will use the Minify library remove
        // comments, additional whitespace and other minor measures to reduce the
        // the overall CSS being sent.
        // However it has the distinct disadvantage of having to minify the CSS
        // before running the post process functions. Potentially things may break
        // here if theme designers try to push things with CSS post processing.
        $css = $theme->post_process($css);
        $css = core_minify::css($css);
    }

    clearstatcache();
    if (!file_exists(dirname($csspath))) {
        @mkdir(dirname($csspath), $CFG->directorypermissions, true);
    }

    // Prevent serving of incomplete file from concurrent request,
    // the rename() should be more atomic than fwrite().
    ignore_user_abort(true);

    // First up write out the single file for all those using decent browsers.
    css_write_file($csspath, $css);

    if ($chunk) {
        // If we need to chunk the CSS for browsers that are sub-par.
        $css = css_chunk_by_selector_count($css, $chunkurl);
        $files = count($css);
        $count = 1;
        foreach ($css as $content) {
            if ($count === $files) {
                // If there is more than one file and this IS the last file.
                $filename = preg_replace('#\.css$#', '.0.css', $csspath);
            } else {
                // If there is more than one file and this is not the last file.
                $filename = preg_replace('#\.css$#', '.'.$count.'.css', $csspath);
            }
            $count++;
            css_write_file($filename, $content);
        }
    }

    ignore_user_abort(false);
    if (connection_aborted()) {
        die;
    }
}

/**
 * Writes a CSS file.
 *
 * @param string $filename
 * @param string $content
 */
function css_write_file($filename, $content) {
    global $CFG;
    if ($fp = fopen($filename.'.tmp', 'xb')) {
        fwrite($fp, $content);
        fclose($fp);
        rename($filename.'.tmp', $filename);
        @chmod($filename, $CFG->filepermissions);
        @unlink($filename.'.tmp'); // Just in case anything fails.
    }
}

/**
 * Takes CSS and chunks it if the number of selectors within it exceeds $maxselectors.
 *
 * The chunking will not split a group of selectors, or a media query. That means that
 * if n > $maxselectors and there are n selectors grouped together,
 * they will not be chunked and you could end up with more selectors than desired.
 * The same applies for a media query that has more than n selectors.
 *
 * Also, as we do not split group of selectors or media queries, the chunking might
 * not be as optimal as it could be, having files with less selectors than it could
 * potentially contain.
 *
 * String functions used here are not compliant with unicode characters. But that is
 * not an issue as the syntax of CSS is using ASCII codes. Even if we have unicode
 * characters in comments, or in the property 'content: ""', it will behave correcly.
 *
 * Please note that this strips out the comments if chunking happens.
 *
 * @param string $css The CSS to chunk.
 * @param string $importurl The URL to use for import statements.
 * @param int $maxselectors The number of selectors to limit a chunk to.
 * @param int $buffer Not used any more.
 * @return array An array of CSS chunks.
 */
function css_chunk_by_selector_count($css, $importurl, $maxselectors = 4095, $buffer = 50) {

    // Check if we need to chunk this CSS file.
    $count = substr_count($css, ',') + substr_count($css, '{');
    if ($count < $maxselectors) {
        // The number of selectors is less then the max - we're fine.
        return array($css);
    }

    $chunks = array();                  // The final chunks.
    $offsets = array();                 // The indexes to chunk at.
    $offset = 0;                        // The current offset.
    $selectorcount = 0;                 // The number of selectors since the last split.
    $lastvalidoffset = 0;               // The last valid index to split at.
    $lastvalidoffsetselectorcount = 0;  // The number of selectors used at the time were could split.
    $inrule = 0;                        // The number of rules we are in, should not be greater than 1.
    $inmedia = false;                   // Whether or not we are in a media query.
    $mediacoming = false;               // Whether or not we are expeting a media query.
    $currentoffseterror = null;         // Not null when we have recorded an error for the current split.
    $offseterrors = array();            // The offsets where we found errors.

    // Remove the comments. Because it's easier, safer and probably a lot of other good reasons.
    $css = preg_replace('#/\*(.*?)\*/#s', '', $css);
    $strlen = strlen($css);

    // Walk through the CSS content character by character.
    for ($i = 1; $i <= $strlen; $i++) {
        $char = $css[$i - 1];
        $offset = $i;

        // Is that a media query that I see coming towards us?
        if ($char === '@') {
            if (!$inmedia && substr($css, $offset, 5) === 'media') {
                $mediacoming = true;
            }
        }

        // So we are entering a rule or a media query...
        if ($char === '{') {
            if ($mediacoming) {
                $inmedia = true;
                $mediacoming = false;
            } else {
                $inrule++;
                $selectorcount++;
            }
        }

        // Let's count the number of selectors, but only if we are not in a rule, or in
        // the definition of a media query, as they can contain commas too.
        if (!$mediacoming && !$inrule && $char === ',') {
            $selectorcount++;
        }

        // We reached the end of something.
        if ($char === '}') {
            // Oh, we are in a media query.
            if ($inmedia) {
                if (!$inrule) {
                    // This is the end of the media query.
                    $inmedia = false;
                } else {
                    // We were in a rule, in the media query.
                    $inrule--;
                }
            } else {
                $inrule--;
                // Handle stupid broken CSS where there are too many } brackets,
                // as this can cause it to break (with chunking) where it would
                // coincidentally have worked otherwise.
                if ($inrule < 0) {
                    $inrule = 0;
                }
            }

            // We are not in a media query, and there is no pending rule, it is safe to split here.
            if (!$inmedia && !$inrule) {
                $lastvalidoffset = $offset;
                $lastvalidoffsetselectorcount = $selectorcount;
            }
        }

        // Alright, this is splitting time...
        if ($selectorcount > $maxselectors) {
            if (!$lastvalidoffset) {
                // We must have reached more selectors into one set than we were allowed. That means that either
                // the chunk size value is too small, or that we have a gigantic group of selectors, or that a media
                // query contains more selectors than the chunk size. We have to ignore this because we do not
                // support split inside a group of selectors or media query.
                if ($currentoffseterror === null) {
                    $currentoffseterror = $offset;
                    $offseterrors[] = $currentoffseterror;
                }
            } else {
                // We identify the offset to split at and reset the number of selectors found from there.
                $offsets[] = $lastvalidoffset;
                $selectorcount = $selectorcount - $lastvalidoffsetselectorcount;
                $lastvalidoffset = 0;
                $currentoffseterror = null;
            }
        }
    }

    // Report offset errors.
    if (!empty($offseterrors)) {
        debugging('Could not find a safe place to split at offset(s): ' . implode(', ', $offseterrors) . '. Those were ignored.',
            DEBUG_DEVELOPER);
    }

    // Now that we have got the offets, we can chunk the CSS.
    $offsetcount = count($offsets);
    foreach ($offsets as $key => $index) {
        $start = 0;
        if ($key > 0) {
            $start = $offsets[$key - 1];
        }
        // From somewhere up to the offset.
        $chunks[] = substr($css, $start, $index - $start);
    }
    // Add the last chunk (if there is one), from the last offset to the end of the string.
    if (end($offsets) != $strlen) {
        $chunks[] = substr($css, end($offsets));
    }

    // The array $chunks now contains CSS split into perfect sized chunks.
    // Import statements can only appear at the very top of a CSS file.
    // Imported sheets are applied in the the order they are imported and
    // are followed by the contents of the CSS.
    // This is terrible for performance.
    // It means we must put the import statements at the top of the last chunk
    // to ensure that things are always applied in the correct order.
    // This way the chunked files are included in the order they were chunked
    // followed by the contents of the final chunk in the actual sheet.
    $importcss = '';
    $slashargs = strpos($importurl, '.php?') === false;
    $parts = count($chunks);
    for ($i = 1; $i < $parts; $i++) {
        if ($slashargs) {
            $importcss .= "@import url({$importurl}/chunk{$i});\n";
        } else {
            $importcss .= "@import url({$importurl}&chunk={$i});\n";
        }
    }
    $importcss .= end($chunks);
    $chunks[key($chunks)] = $importcss;

    return $chunks;
}

/**
 * Sends a cached CSS file
 *
 * This function sends the cached CSS file. Remember it is generated on the first
 * request, then optimised/minified, and finally cached for serving.
 *
 * @param string $csspath The path to the CSS file we want to serve.
 * @param string $etag The revision to make sure we utilise any caches.
 */
function css_send_cached_css($csspath, $etag) {
    // 60 days only - the revision may get incremented quite often.
    $lifetime = 60*60*24*60;

    header('Etag: "'.$etag.'"');
    header('Content-Disposition: inline; filename="styles.php"');
    header('Last-Modified: '. gmdate('D, d M Y H:i:s', filemtime($csspath)) .' GMT');
    header('Expires: '. gmdate('D, d M Y H:i:s', time() + $lifetime) .' GMT');
    header('Pragma: ');
    header('Cache-Control: public, max-age='.$lifetime);
    header('Accept-Ranges: none');
    header('Content-Type: text/css; charset=utf-8');
    if (!min_enable_zlib_compression()) {
        header('Content-Length: '.filesize($csspath));
    }

    readfile($csspath);
    die;
}

/**
 * Sends CSS directly without caching it.
 *
 * This function takes a raw CSS string, optimises it if required, and then
 * serves it.
 * Turning both themedesignermode and CSS optimiser on at the same time is awful
 * for performance because of the optimiser running here. However it was done so
 * that theme designers could utilise the optimised output during development to
 * help them optimise their CSS... not that they should write lazy CSS.
 *
 * @param string $css
 */
function css_send_uncached_css($css) {
    header('Content-Disposition: inline; filename="styles_debug.php"');
    header('Last-Modified: '. gmdate('D, d M Y H:i:s', time()) .' GMT');
    header('Expires: '. gmdate('D, d M Y H:i:s', time() + THEME_DESIGNER_CACHE_LIFETIME) .' GMT');
    header('Pragma: ');
    header('Accept-Ranges: none');
    header('Content-Type: text/css; charset=utf-8');

    if (is_array($css)) {
        $css = implode("\n\n", $css);
    }
    echo $css;
    die;
}

/**
 * Send file not modified headers
 *
 * @param int $lastmodified
 * @param string $etag
 */
function css_send_unmodified($lastmodified, $etag) {
    // 60 days only - the revision may get incremented quite often.
    $lifetime = 60*60*24*60;
    header('HTTP/1.1 304 Not Modified');
    header('Expires: '. gmdate('D, d M Y H:i:s', time() + $lifetime) .' GMT');
    header('Cache-Control: public, max-age='.$lifetime);
    header('Content-Type: text/css; charset=utf-8');
    header('Etag: "'.$etag.'"');
    if ($lastmodified) {
        header('Last-Modified: '. gmdate('D, d M Y H:i:s', $lastmodified) .' GMT');
    }
    die;
}

/**
 * Sends a 404 message about CSS not being found.
 */
function css_send_css_not_found() {
    header('HTTP/1.0 404 not found');
    die('CSS was not found, sorry.');
}

/**
 * Determines if the given value is a valid CSS colour.
 *
 * A CSS colour can be one of the following:
 *    - Hex colour:  #AA66BB
 *    - RGB colour:  rgb(0-255, 0-255, 0-255)
 *    - RGBA colour: rgba(0-255, 0-255, 0-255, 0-1)
 *    - HSL colour:  hsl(0-360, 0-100%, 0-100%)
 *    - HSLA colour: hsla(0-360, 0-100%, 0-100%, 0-1)
 *
 * Or a recognised browser colour mapping {@link css_optimiser::$htmlcolours}
 *
 * @param string $value The colour value to check
 * @return bool
 */
function css_is_colour($value) {
    $value = trim($value);

    $hex  = '/^#([a-fA-F0-9]{1,3}|[a-fA-F0-9]{6})$/';
    $rgb  = '#^rgb\s*\(\s*(\d{1,3})\s*,\s*(\d{1,3})\s*,\s*(\d{1,3})\s*\)$#i';
    $rgba = '#^rgba\s*\(\s*(\d{1,3})\s*,\s*(\d{1,3})\s*,\s*(\d{1,3})\s*,\s*(\d{1}(\.\d+)?)\s*\)$#i';
    $hsl  = '#^hsl\s*\(\s*(\d{1,3})\s*,\s*(\d{1,3})\%\s*,\s*(\d{1,3})\%\s*\)$#i';
    $hsla = '#^hsla\s*\(\s*(\d{1,3})\s*,\s*(\d{1,3})\%\s*,\s*(\d{1,3})\%\s*,\s*(\d{1}(\.\d+)?)\s*\)$#i';

    if (in_array(strtolower($value), array('inherit'))) {
        return true;
    } else if (preg_match($hex, $value)) {
        return true;
    } else if (in_array(strtolower($value), array_keys(css_optimiser::$htmlcolours))) {
        return true;
    } else if (preg_match($rgb, $value, $m) && $m[1] < 256 && $m[2] < 256 && $m[3] < 256) {
        // It is an RGB colour.
        return true;
    } else if (preg_match($rgba, $value, $m) && $m[1] < 256 && $m[2] < 256 && $m[3] < 256) {
        // It is an RGBA colour.
        return true;
    } else if (preg_match($hsl, $value, $m) && $m[1] <= 360 && $m[2] <= 100 && $m[3] <= 100) {
        // It is an HSL colour.
        return true;
    } else if (preg_match($hsla, $value, $m) && $m[1] <= 360 && $m[2] <= 100 && $m[3] <= 100) {
        // It is an HSLA colour.
        return true;
    }
    // Doesn't look like a colour.
    return false;
}

/**
 * Returns true is the passed value looks like a CSS width.
 * In order to pass this test the value must be purely numerical or end with a
 * valid CSS unit term.
 *
 * @param string|int $value
 * @return boolean
 */
function css_is_width($value) {
    $value = trim($value);
    if (in_array(strtolower($value), array('auto', 'inherit'))) {
        return true;
    }
    if ((string)$value === '0' || preg_match('#^(\-\s*)?(\d*\.)?(\d+)\s*(em|px|pt|\%|in|cm|mm|ex|pc)$#i', $value)) {
        return true;
    }
    return false;
}

/**
 * A simple sorting function to sort two array values on the number of items they contain
 *
 * @param array $a
 * @param array $b
 * @return int
 */
function css_sort_by_count(array $a, array $b) {
    $a = count($a);
    $b = count($b);
    if ($a == $b) {
        return 0;
    }
    return ($a > $b) ? -1 : 1;
}

/**
 * A basic CSS optimiser that strips out unwanted things and then processes CSS organising and cleaning styles.
 *
 * This CSS optimiser works by reading through a CSS string one character at a
 * time and building an object structure of the CSS.
 * As part of that processing styles are expanded out as much as they can be to
 * ensure we collect all mappings, at the end of the processing those styles are
 * then combined into an optimised form to keep them as short as possible.
 *
 * @package core
 * @subpackage cssoptimiser
 * @copyright 2012 Sam Hemelryk
 * @license http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
 */
class css_optimiser {

    /**
     * Used when the processor is about to start processing.
     * Processing states. Used internally.
     */
    const PROCESSING_START = 0;

    /**
     * Used when the processor is currently processing a selector.
     * Processing states. Used internally.
     */
    const PROCESSING_SELECTORS = 0;

    /**
     * Used when the processor is currently processing a style.
     * Processing states. Used internally.
     */
    const PROCESSING_STYLES = 1;

    /**
     * Used when the processor is currently processing a comment.
     * Processing states. Used internally.
     */
    const PROCESSING_COMMENT = 2;

    /**
     * Used when the processor is currently processing an @ rule.
     * Processing states. Used internally.
     */
    const PROCESSING_ATRULE = 3;

    /**
     * The raw string length before optimisation.
     * Stats variables set during and after processing
     * @var int
     */
    protected $rawstrlen = 0;

    /**
     * The number of comments that were removed during optimisation.
     * Stats variables set during and after processing
     * @var int
     */
    protected $commentsincss = 0;

    /**
     * The number of rules in the CSS before optimisation.
     * Stats variables set during and after processing
     * @var int
     */
    protected $rawrules = 0;

    /**
     * The number of selectors using in CSS rules before optimisation.
     * Stats variables set during and after processing
     * @var int
     */
    protected $rawselectors = 0;

    /**
     * The string length after optimisation.
     * Stats variables set during and after processing
     * @var int
     */
    protected $optimisedstrlen = 0;

    /**
     * The number of rules after optimisation.
     * Stats variables set during and after processing
     * @var int
     */
    protected $optimisedrules = 0;

    /**
     * The number of selectors used in rules after optimisation.
     * Stats variables set during and after processing
     * @var int
     */
    protected $optimisedselectors = 0;

    /**
     * The start time of the optimisation.
     * Stats variables set during and after processing
     * @var int
     */
    protected $timestart = 0;

    /**
     * The end time of the optimisation.
     * Stats variables set during and after processing
     * @var int
     */
    protected $timecomplete = 0;

    /**
     * Will be set to any errors that may have occured during processing.
     * This is updated only at the end of processing NOT during.
     *
     * @var array
     */
    protected $errors = array();

    /**
     * Processes incoming CSS optimising it and then returning it.
     *
     * @param string $css The raw CSS to optimise
     * @return string The optimised CSS
     */
    public function process($css) {
        // Easiest win there is.
        $css = trim($css);

        $this->reset_stats();
        $this->timestart = microtime(true);
        $this->rawstrlen = strlen($css);

        // Don't try to process files with no content... it just doesn't make sense.
        // But we should produce an error for them, an empty CSS file will lead to a
        // useless request for those running theme designer mode.
        if ($this->rawstrlen === 0) {
            $this->errors[] = 'Skipping file as it has no content.';
            return '';
        }

        // First up we need to remove all line breaks - this allows us to instantly
        // reduce our processing requirements and as we will process everything
        // into a new structure there's really nothing lost.
        $css = preg_replace('#\r?\n#', ' ', $css);

        // Next remove the comments... no need to them in an optimised world and
        // knowing they're all gone allows us to REALLY make our processing simpler.
        $css = preg_replace('#/\*(.*?)\*/#m', '', $css, -1, $this->commentsincss);

        $medias = array(
            'all' => new css_media()
        );
        $imports = array();
        $charset = false;
        // Keyframes are used for CSS animation they will be processed right at the very end.
        $keyframes = array();

        $currentprocess = self::PROCESSING_START;
        $currentrule = css_rule::init();
        $currentselector = css_selector::init();
        $inquotes = false;      // ' or "
        $inbraces = false;      // {
        $inbrackets = false;    // [
        $inparenthesis = false; // (
        /* @var css_media $currentmedia */
        $currentmedia = $medias['all'];
        $currentatrule = null;
        $suspectatrule = false;

        $buffer = '';
        $char = null;

        // Next we are going to iterate over every single character in $css.
        // This is why we removed line breaks and comments!
        for ($i = 0; $i < $this->rawstrlen; $i++) {
            $lastchar = $char;
            $char = substr($css, $i, 1);
            if ($char == '@' && $buffer == '') {
                $suspectatrule = true;
            }
            switch ($currentprocess) {
                // Start processing an @ rule e.g. @media, @page, @keyframes.
                case self::PROCESSING_ATRULE:
                    switch ($char) {
                        case ';':
                            if (!$inbraces) {
                                $buffer .= $char;
                                if ($currentatrule == 'import') {
                                    $imports[] = $buffer;
                                    $currentprocess = self::PROCESSING_SELECTORS;
                                } else if ($currentatrule == 'charset') {
                                    $charset = $buffer;
                                    $currentprocess = self::PROCESSING_SELECTORS;
                                }
                            }
                            if ($currentatrule !== 'media') {
                                $buffer = '';
                                $currentatrule = false;
                            }
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                        case '{':
                            $regexmediabasic = '#\s*@media\s*([a-zA-Z0-9]+(\s*,\s*[a-zA-Z0-9]+)*)\s*{#';
                            $regexadvmedia = '#\s*@media\s*([^{]+)#';
                            $regexkeyframes = '#@((\-moz\-|\-webkit\-|\-ms\-|\-o\-)?keyframes)\s*([^\s]+)#';

                            if ($currentatrule == 'media' && preg_match($regexmediabasic, $buffer, $matches)) {
                                // Basic media declaration.
                                $mediatypes = str_replace(' ', '', $matches[1]);
                                if (!array_key_exists($mediatypes, $medias)) {
                                    $medias[$mediatypes] = new css_media($mediatypes);
                                }
                                $currentmedia = $medias[$mediatypes];
                                $currentprocess = self::PROCESSING_SELECTORS;
                                $buffer = '';
                            } else if ($currentatrule == 'media' && preg_match($regexadvmedia, $buffer, $matches)) {
                                // Advanced media query declaration http://www.w3.org/TR/css3-mediaqueries/.
                                $mediatypes = $matches[1];
                                $hash = md5($mediatypes);
                                $medias[$hash] = new css_media($mediatypes);
                                $currentmedia = $medias[$hash];
                                $currentprocess = self::PROCESSING_SELECTORS;
                                $buffer = '';
                            } else if ($currentatrule == 'keyframes' && preg_match($regexkeyframes, $buffer, $matches)) {
                                // Keyframes declaration, we treat it exactly like a @media declaration except we don't allow
                                // them to be overridden to ensure we don't mess anything up. (means we keep everything in order).
                                $keyframefor = $matches[1];
                                $keyframename = $matches[3];
                                $keyframe = new css_keyframe($keyframefor, $keyframename);
                                $keyframes[] = $keyframe;
                                $currentmedia = $keyframe;
                                $currentprocess = self::PROCESSING_SELECTORS;
                                $buffer = '';
                            }
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                    }
                    break;
                // Start processing selectors.
                case self::PROCESSING_START:
                case self::PROCESSING_SELECTORS:
                    $regexatrule = '#@(media|import|charset|(\-moz\-|\-webkit\-|\-ms\-|\-o\-)?(keyframes))\s*#';
                    switch ($char) {
                        case '[':
                            $inbrackets ++;
                            $buffer .= $char;
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                        case ']':
                            $inbrackets --;
                            $buffer .= $char;
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                        case ' ':
                            if ($inbrackets) {
                                // Continue 1: The switch processing chars
                                // Continue 2: The switch processing the state
                                // Continue 3: The for loop.
                                continue 3;
                            }
                            if (!empty($buffer)) {
                                // Check for known @ rules.
                                if ($suspectatrule && preg_match($regexatrule, $buffer, $matches)) {
                                    $currentatrule = (!empty($matches[3]))?$matches[3]:$matches[1];
                                    $currentprocess = self::PROCESSING_ATRULE;
                                    $buffer .= $char;
                                } else {
                                    $currentselector->add($buffer);
                                    $buffer = '';
                                }
                            }
                            $suspectatrule = false;
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                        case '{':
                            if ($inbrackets) {
                                // Continue 1: The switch processing chars
                                // Continue 2: The switch processing the state
                                // Continue 3: The for loop.
                                continue 3;
                            }
                            // Check for known @ rules.
                            if ($suspectatrule && preg_match($regexatrule, $buffer, $matches)) {
                                // Ahh we've been in an @rule, lets rewind one and have the @rule case process this.
                                $currentatrule = (!empty($matches[3]))?$matches[3]:$matches[1];
                                $currentprocess = self::PROCESSING_ATRULE;
                                $i--;
                                $suspectatrule = false;
                                // Continue 1: The switch processing chars
                                // Continue 2: The switch processing the state
                                // Continue 3: The for loop.
                                continue 3;
                            }
                            if ($buffer !== '') {
                                $currentselector->add($buffer);
                            }
                            $currentrule->add_selector($currentselector);
                            $currentselector = css_selector::init();
                            $currentprocess = self::PROCESSING_STYLES;

                            $buffer = '';
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                        case '}':
                            if ($inbrackets) {
                                // Continue 1: The switch processing chars
                                // Continue 2: The switch processing the state
                                // Continue 3: The for loop.
                                continue 3;
                            }
                            if ($currentatrule == 'media') {
                                $currentmedia = $medias['all'];
                                $currentatrule = false;
                                $buffer = '';
                            } else if (strpos($currentatrule, 'keyframes') !== false) {
                                $currentmedia = $medias['all'];
                                $currentatrule = false;
                                $buffer = '';
                            }
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                        case ',':
                            if ($inbrackets) {
                                // Continue 1: The switch processing chars
                                // Continue 2: The switch processing the state
                                // Continue 3: The for loop.
                                continue 3;
                            }
                            $currentselector->add($buffer);
                            $currentrule->add_selector($currentselector);
                            $currentselector = css_selector::init();
                            $buffer = '';
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                    }
                    break;
                // Start processing styles.
                case self::PROCESSING_STYLES:
                    if ($char == '"' || $char == "'") {
                        if ($inquotes === false) {
                            $inquotes = $char;
                        }
                        if ($inquotes === $char && $lastchar !== '\\') {
                            $inquotes = false;
                        }
                    }
                    if ($inquotes) {
                        $buffer .= $char;
                        continue 2;
                    }
                    switch ($char) {
                        case ';':
                            if ($inparenthesis) {
                                $buffer .= $char;
                                // Continue 1: The switch processing chars
                                // Continue 2: The switch processing the state
                                // Continue 3: The for loop.
                                continue 3;
                            }
                            $currentrule->add_style($buffer);
                            $buffer = '';
                            $inquotes = false;
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                        case '}':
                            $currentrule->add_style($buffer);
                            $this->rawselectors += $currentrule->get_selector_count();

                            $currentmedia->add_rule($currentrule);

                            $currentrule = css_rule::init();
                            $currentprocess = self::PROCESSING_SELECTORS;
                            $this->rawrules++;
                            $buffer = '';
                            $inquotes = false;
                            $inparenthesis = false;
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                        case '(':
                            $inparenthesis = true;
                            $buffer .= $char;
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                        case ')':
                            $inparenthesis = false;
                            $buffer .= $char;
                            // Continue 1: The switch processing chars
                            // Continue 2: The switch processing the state
                            // Continue 3: The for loop.
                            continue 3;
                    }
                    break;
            }
            $buffer .= $char;
        }

        foreach ($medias as $media) {
            $this->optimise($media);
        }
        $css = $this->produce_css($charset, $imports, $medias, $keyframes);

        $this->timecomplete = microtime(true);
        return trim($css);
    }

    /**
     * Produces CSS for the given charset, imports, media, and keyframes
     * @param string $charset
     * @param array $imports
     * @param css_media[] $medias
     * @param css_keyframe[] $keyframes
     * @return string
     */
    protected function produce_css($charset, array $imports, array $medias, array $keyframes) {
        $css = '';
        if (!empty($charset)) {
            $imports[] = $charset;
        }
        if (!empty($imports)) {
            $css .= implode("\n", $imports);
            $css .= "\n\n";
        }

        $cssreset = array();
        $cssstandard = array();
        $csskeyframes = array();

        // Process each media declaration individually.
        foreach ($medias as $media) {
            // If this declaration applies to all media types.
            if (in_array('all', $media->get_types())) {
                // Collect all rules that represet reset rules and remove them from the media object at the same time.
                // We do this because we prioritise reset rules to the top of a CSS output. This ensures that they
                // can't end up out of order because of optimisation.
                $resetrules = $media->get_reset_rules(true);
                if (!empty($resetrules)) {
                    $cssreset[] = css_writer::media('all', $resetrules);
                }
            }
            // Get the standard cSS.
            $cssstandard[] = $media->out();
        }

        // Finally if there are any keyframe declarations process them now.
        if (count($keyframes) > 0) {
            foreach ($keyframes as $keyframe) {
                $this->optimisedrules += $keyframe->count_rules();
                $this->optimisedselectors +=  $keyframe->count_selectors();
                if ($keyframe->has_errors()) {
                    $this->errors += $keyframe->get_errors();
                }
                $csskeyframes[] = $keyframe->out();
            }
        }

        // Join it all together.
        $css .= join('', $cssreset);
        $css .= join('', $cssstandard);
        $css .= join('', $csskeyframes);

        // Record the strlenght of the now optimised CSS.
        $this->optimisedstrlen = strlen($css);

        // Return the now produced CSS.
        return $css;
    }

    /**
     * Optimises the CSS rules within a rule collection of one form or another
     *
     * @param css_rule_collection $media
     * @return void This function acts in reference
     */
    protected function optimise(css_rule_collection $media) {
        $media->organise_rules_by_selectors();
        $this->optimisedrules += $media->count_rules();
        $this->optimisedselectors +=  $media->count_selectors();
        if ($media->has_errors()) {
            $this->errors += $media->get_errors();
        }
    }

    /**
     * Returns an array of stats from the last processing run
     * @return string
     */
    public function get_stats() {
        $stats = array(
            'timestart'             => $this->timestart,
            'timecomplete'          => $this->timecomplete,
            'timetaken'             => round($this->timecomplete - $this->timestart, 4),
            'commentsincss'         => $this->commentsincss,
            'rawstrlen'             => $this->rawstrlen,
            'rawselectors'          => $this->rawselectors,
            'rawrules'              => $this->rawrules,
            'optimisedstrlen'       => $this->optimisedstrlen,
            'optimisedrules'        => $this->optimisedrules,
            'optimisedselectors'    => $this->optimisedselectors,
            'improvementstrlen'     => '-',
            'improvementrules'     => '-',
            'improvementselectors'     => '-',
        );
        // Avoid division by 0 errors by checking we have valid raw values.
        if ($this->rawstrlen > 0) {
            $stats['improvementstrlen'] = round(100 - ($this->optimisedstrlen / $this->rawstrlen) * 100, 1).'%';
        }
        if ($this->rawrules > 0) {
            $stats['improvementrules'] = round(100 - ($this->optimisedrules / $this->rawrules) * 100, 1).'%';
        }
        if ($this->rawselectors > 0) {
            $stats['improvementselectors'] = round(100 - ($this->optimisedselectors / $this->rawselectors) * 100, 1).'%';
        }
        return $stats;
    }

    /**
     * Returns true if any errors have occured during processing
     *
     * @return bool
     */
    public function has_errors() {
        return !empty($this->errors);
    }

    /**
     * Returns an array of errors that have occured
     *
     * @param bool $clear If set to true the errors will be cleared after being returned.
     * @return array
     */
    public function get_errors($clear = false) {
        $errors = $this->errors;
        if ($clear) {
            // Reset the error array.
            $this->errors = array();
        }
        return $errors;
    }

    /**
     * Returns any errors as a string that can be included in CSS.
     *
     * @return string
     */
    public function output_errors_css() {
        $computedcss  = "/****************************************\n";
        $computedcss .= " *--- Errors found during processing ----\n";
        foreach ($this->errors as $error) {
            $computedcss .= preg_replace('#^#m', '* ', $error);
        }
        $computedcss .= " ****************************************/\n\n";
        return $computedcss;
    }

    /**
     * Returns a string to display stats about the last generation within CSS output
     *
     * @return string
     */
    public function output_stats_css() {

        $computedcss  = "/****************************************\n";
        $computedcss .= " *------- CSS Optimisation stats --------\n";

        if ($this->rawstrlen === 0) {
            $computedcss .= " File not processed as it has no content /\n\n";
            $computedcss .= " ****************************************/\n\n";
            return $computedcss;
        } else if ($this->rawrules === 0) {
            $computedcss .= " File contained no rules to be processed /\n\n";
            $computedcss .= " ****************************************/\n\n";
            return $computedcss;
        }

        $stats = $this->get_stats();

        $computedcss .= " *  ".date('r')."\n";
        $computedcss .= " *  {$stats['commentsincss']}  \t comments removed\n";
        $computedcss .= " *  Optimisation took {$stats['timetaken']} seconds\n";
        $computedcss .= " *--------------- before ----------------\n";
        $computedcss .= " *  {$stats['rawstrlen']}  \t chars read in\n";
        $computedcss .= " *  {$stats['rawrules']}  \t rules read in\n";
        $computedcss .= " *  {$stats['rawselectors']}  \t total selectors\n";
        $computedcss .= " *---------------- after ----------------\n";
        $computedcss .= " *  {$stats['optimisedstrlen']}  \t chars once optimized\n";
        $computedcss .= " *  {$stats['optimisedrules']}  \t optimized rules\n";
        $computedcss .= " *  {$stats['optimisedselectors']}  \t total selectors once optimized\n";
        $computedcss .= " *---------------- stats ----------------\n";
        $computedcss .= " *  {$stats['improvementstrlen']}  \t reduction in chars\n";
        $computedcss .= " *  {$stats['improvementrules']}  \t reduction in rules\n";
        $computedcss .= " *  {$stats['improvementselectors']}  \t reduction in selectors\n";
        $computedcss .= " ****************************************/\n\n";

        return $computedcss;
    }

    /**
     * Resets the stats ready for another fresh processing
     */
    public function reset_stats() {
        $this->commentsincss = 0;
        $this->optimisedrules = 0;
        $this->optimisedselectors = 0;
        $this->optimisedstrlen = 0;
        $this->rawrules = 0;
        $this->rawselectors = 0;
        $this->rawstrlen = 0;
        $this->timecomplete = 0;
        $this->timestart = 0;
    }

    /**
     * An array of the common HTML colours that are supported by most browsers.
     *
     * This reference table is used to allow us to unify colours, and will aid
     * us in identifying buggy CSS using unsupported colours.
     *
     * @var string[]
     */
    public static $htmlcolours = array(
        'aliceblue' => '#F0F8FF',
        'antiquewhite' => '#FAEBD7',
        'aqua' => '#00FFFF',
        'aquamarine' => '#7FFFD4',
        'azure' => '#F0FFFF',
        'beige' => '#F5F5DC',
        'bisque' => '#FFE4C4',
        'black' => '#000000',
        'blanchedalmond' => '#FFEBCD',
        'blue' => '#0000FF',
        'blueviolet' => '#8A2BE2',
        'brown' => '#A52A2A',
        'burlywood' => '#DEB887',
        'cadetblue' => '#5F9EA0',
        'chartreuse' => '#7FFF00',
        'chocolate' => '#D2691E',
        'coral' => '#FF7F50',
        'cornflowerblue' => '#6495ED',
        'cornsilk' => '#FFF8DC',
        'crimson' => '#DC143C',
        'cyan' => '#00FFFF',
        'darkblue' => '#00008B',
        'darkcyan' => '#008B8B',
        'darkgoldenrod' => '#B8860B',
        'darkgray' => '#A9A9A9',
        'darkgrey' => '#A9A9A9',
        'darkgreen' => '#006400',
        'darkKhaki' => '#BDB76B',
        'darkmagenta' => '#8B008B',
        'darkolivegreen' => '#556B2F',
        'arkorange' => '#FF8C00',
        'darkorchid' => '#9932CC',
        'darkred' => '#8B0000',
        'darksalmon' => '#E9967A',
        'darkseagreen' => '#8FBC8F',
        'darkslateblue' => '#483D8B',
        'darkslategray' => '#2F4F4F',
        'darkslategrey' => '#2F4F4F',
        'darkturquoise' => '#00CED1',
        'darkviolet' => '#9400D3',
        'deeppink' => '#FF1493',
        'deepskyblue' => '#00BFFF',
        'dimgray' => '#696969',
        'dimgrey' => '#696969',
        'dodgerblue' => '#1E90FF',
        'firebrick' => '#B22222',
        'floralwhite' => '#FFFAF0',
        'forestgreen' => '#228B22',
        'fuchsia' => '#FF00FF',
        'gainsboro' => '#DCDCDC',
        'ghostwhite' => '#F8F8FF',
        'gold' => '#FFD700',
        'goldenrod' => '#DAA520',
        'gray' => '#808080',
        'grey' => '#808080',
        'green' => '#008000',
        'greenyellow' => '#ADFF2F',
        'honeydew' => '#F0FFF0',
        'hotpink' => '#FF69B4',
        'indianred ' => '#CD5C5C',
        'indigo ' => '#4B0082',
        'ivory' => '#FFFFF0',
        'khaki' => '#F0E68C',
        'lavender' => '#E6E6FA',
        'lavenderblush' => '#FFF0F5',
        'lawngreen' => '#7CFC00',
        'lemonchiffon' => '#FFFACD',
        'lightblue' => '#ADD8E6',
        'lightcoral' => '#F08080',
        'lightcyan' => '#E0FFFF',
        'lightgoldenrodyellow' => '#FAFAD2',
        'lightgray' => '#D3D3D3',
        'lightgrey' => '#D3D3D3',
        'lightgreen' => '#90EE90',
        'lightpink' => '#FFB6C1',
        'lightsalmon' => '#FFA07A',
        'lightseagreen' => '#20B2AA',
        'lightskyblue' => '#87CEFA',
        'lightslategray' => '#778899',
        'lightslategrey' => '#778899',
        'lightsteelblue' => '#B0C4DE',
        'lightyellow' => '#FFFFE0',
        'lime' => '#00FF00',
        'limegreen' => '#32CD32',
        'linen' => '#FAF0E6',
        'magenta' => '#FF00FF',
        'maroon' => '#800000',
        'mediumaquamarine' => '#66CDAA',
        'mediumblue' => '#0000CD',
        'mediumorchid' => '#BA55D3',
        'mediumpurple' => '#9370D8',
        'mediumseagreen' => '#3CB371',
        'mediumslateblue' => '#7B68EE',
        'mediumspringgreen' => '#00FA9A',
        'mediumturquoise' => '#48D1CC',
        'mediumvioletred' => '#C71585',
        'midnightblue' => '#191970',
        'mintcream' => '#F5FFFA',
        'mistyrose' => '#FFE4E1',
        'moccasin' => '#FFE4B5',
        'navajowhite' => '#FFDEAD',
        'navy' => '#000080',
        'oldlace' => '#FDF5E6',
        'olive' => '#808000',
        'olivedrab' => '#6B8E23',
        'orange' => '#FFA500',
        'orangered' => '#FF4500',
        'orchid' => '#DA70D6',
        'palegoldenrod' => '#EEE8AA',
        'palegreen' => '#98FB98',
        'paleturquoise' => '#AFEEEE',
        'palevioletred' => '#D87093',
        'papayawhip' => '#FFEFD5',
        'peachpuff' => '#FFDAB9',
        'peru' => '#CD853F',
        'pink' => '#FFC0CB',
        'plum' => '#DDA0DD',
        'powderblue' => '#B0E0E6',
        'purple' => '#800080',
        'red' => '#FF0000',
        'rosybrown' => '#BC8F8F',
        'royalblue' => '#4169E1',
        'saddlebrown' => '#8B4513',
        'salmon' => '#FA8072',
        'sandybrown' => '#F4A460',
        'seagreen' => '#2…

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