mogu file cache

<?php

$config = array(
    'work_dir'=>'D:SoftEasyPHP-12.1wwwhtmlcache',
    'default_timeout'=>600,
);

class mogu_file_cache{

    public $work_dir;
    public $default_timeout;

    function __construct(){
        global $config;
        if(is_writeable($config['work_dir'])){
            $this->work_dir = $config['work_dir'];
            $this->default_timeout = $config['default_timeout'];
        }else{
            return false;
        }
    }

    function exists($key){
        return $this->get($key);
    }

    /*
    *
    */
    function set($key, $value, $time = 0){
        if($time == 0){
            $time = $this->default_timeout;
        }
        $key = md5($key);
        $cache_dir = $this->work_dir.'/'.substr($key, 0, 3).'/'.substr($key, 3, 3);
        if(!file_exists($cache_dir)){
            mkdir($cache_dir, 0755, true);
        }
        $result = array(
            'value'=>$value,
            'time'=>time() + $time
        );
        return file_put_contents($cache_dir.'/'.$key, serialize($result));
    }

    function get($key){
        $key = md5($key);
        $cache_dir = $this->work_dir.'/'.substr($key, 0, 3).'/'.substr($key, 3, 3);
        $cache_file = $cache_dir.'/'.$key;
        if(file_exists($cache_file)){
            $result = unserialize(file_get_contents($cache_file));
            if( $result['time'] > time() ){
                return $result['value'];
            }else{
                unlink($cache_file);
                return false;
            }
        }else{
            return false;
        }
    }

    function replace($key, $value, $time = 0){
        return $this->set($key, $value, $time);
    }

    function del($key){
        $key = md5($key);
        $cache_dir = $this->work_dir.'/'.substr($key, 0, 3).'/'.substr($key, 3, 3);
        unlink($cache_dir.'/'.$key);
    }

    function clear(){
        
    }

}

$cache = new mogu_file_cache();

$cache->set('user%&^&*^%', 'mogu');

$result = $cache->get('user%&^&*^%');

var_dump($result);