Css Minification on the Fly

minify.php

<?php

require_once('../includes/utils.php');

/**
 * minify
 * 
 * Class that handles the minification of all required CSS files
 */
class minify
{
    public $css = '';
    public $changed = false;
    public $fileLastModified;

    private $RequestedFiles = array();

    /**
     * __constructor()
     * 
     * Builds the minified string
     *
     * @param array $GET
     */
    function __construct($GET)
    {
        foreach($GET as $key => $val) {
            if(util::strContains($key, 'css_')) {
                $fileName = urldecode($val);

                $this->RequestedFiles[] = $fileName;

                if(!empty($_SESSION['lastRequestedCSS']) && !in_array($fileName, $_SESSION['lastRequestedCSS'])) {
                    $this->changed = true;
                }
            }
        }

        $_SESSION['lastRequestedCSS'] = $this->RequestedFiles;

        foreach($GET as $key => $val) {
            if(util::strContains($key, 'css_')) {
                $fileName = urldecode($val) . '.css';

                $fileModified = filemtime($fileName);
                if(empty($this->lastModified) || $fileModified > $this->lastModified) {
                    $this->lastModified = $fileModified;
                }

                $strFileContents = file_get_contents($fileName);

                if($strFileContents) {
                    $this->css .= $this->doMinify($strFileContents) . "\r\n";
                }
            }
        }
    }

    /**
     * doMinify()
     * 
     * Perform the minification on the passed in string
     * 
     * @param string $strFile
     * 
     * @return string
     */
    private function doMinify($strFile)
    {
        /* Strips Comments */
        $strFile = preg_replace('!/\*.*?\*/!s','', $strFile);
        $strFile = preg_replace('/\n\s*\n/',"\n", $strFile);

        /* Minifies */
        $strFile = preg_replace('/[\n\r \t]/',' ', $strFile);
        $strFile = preg_replace('/ +/',' ', $strFile);
        $strFile = preg_replace('/ ?([,:;{}]) ?/','$1',$strFile);

        /* Kill Trailing Semicolon */
        $strFile = preg_replace('/;}/','}',$strFile);

        /* Return Minified CSS */
        return $strFile;
    }
}

session_start();

$minifier = new minify($_GET);

header("Last-Modified: " . gmdate("D, d M Y H:i:s", $minifier->lastModified) . " GMT");

if (isset($_SERVER['HTTP_IF_MODIFIED_SINCE']) && strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) >= $minifier->lastModified) { 
    header("HTTP/1.1 304 Not Modified");
    exit;
}

header('Content-type: text/css');
echo $minifier->css;