<?php
class fileCacheHandler
{
    private static $_instance = null;
    private static $cacheDir = "/dev/shm/cache_file/";
    public static function getInstance()
    {
        if (!static::$_instance) {
            static::$_instance = new static;
        }
        if(!is_dir(static::$cacheDir)){
            mkdir(static::$cacheDir,0777);
        }
        return static::$_instance;
    }

    public function set($k, $v)
    {
        $cacheFile = static::$cacheDir.$k;
        return file_put_contents($cacheFile, $v);
    }

    public function get($k)
    {
        $cacheFile = static::$cacheDir.$k;
        clearstatcache(true, $cacheFile);
        $mtime = filemtime($cacheFile);
        if (time() > intval($mtime)) {
            return false;
        }
        return file_get_contents($cacheFile);
    }

    public function expire($k, $expiresAfter = 300)
    {
        $cacheFile    = static::$cacheDir.$k;
        return touch($cacheFile, time() + $expiresAfter);
    }

    public function clearCache()
    {
        $res = true;
        $files = array_diff(scandir(static::$cacheDir), array('.','..'));
        foreach ($files as $file) {
            $f   = sprintf('%s/%s', static::$cacheDir, $file);
            $res = $res && (is_file($f) ? unlink($f) : false);
        }
        return $res;
    }
}