<?php
/**
 * Caching
 *
 * $Id$
 *
 * @author gERD Schaufelberger <gerd@php-tools.net>
 * @license PHP License
 * @package WB
 * @subpackage base
 */

/**
 * Caching
 *
 * Very simple to use caching interface.
 *
 * @version 0.3.1
 * @package WB
 * @subpackage base
 */
class WBCache extends WBStdClass
{
    /**
     * used driver
     * @var WBCache_Driver
     */
    static protected $driver;

    /**
     * cache index
     * @var array
     */
    static protected $index;

    /**
     * constructor
     *
     * Avoid creating object
     */
    private function __construct()
    {
    }

    /**
     * fetch cache data
     *
     * Load cached data with id. In case cache-id does not exists, null is returned.
     * Also expire-information will be evaluated.
     *
     * Expire values:
     *  - filemtime
     *    Makes cache invalid of cached data is older than file's modification time.
     *  - use
     *    The use counter tells how often cache data may be loaded from cache. Beyond that
     *    count, cached data will be flushed
     *  - ttl
     *    The ttl is a number of seconds the cache may be valid.
     *
     * @see set()
     * @param string $id
     * @param string $minDate timestamp - cache must be younger than give minDate
     * @return mixed return whatever was cached or null
     */
    static function get($id, $minDate = null)
    {
        if (!WBParam::get('wb/cache/use', true)) {
            return null;
        }

        self::startDriver();

        $id =   md5($id);
        if (!isset(self::$index[$id])) {
            return null;
        }

        $expire =   self::$index[$id];

        // minimum timestamp
        if (!empty($minDate)) {
            $minDate    =   strtotime($minDate);
            if ($minDate > $expire['cached']) {
                unset(self::$index[$id]);
                self::$driver->flush($id);
                return null;
            }
        }

        // filemtime
        if (isset($expire['filemtime'])) {
            if (filemtime($expire['filemtime']) > $expire['cached']) {
                unset(self::$index[$id]);
                self::$driver->flush($id);
                return null;
            }
        }

        // evaluate time to live
        if (isset($expire['ttl'])) {
            if (($expire['ttl'] + $expire['cached'] ) < time()) {
                unset(self::$index[$id]);
                self::$driver->flush($id);
                return null;
            }
        }

        // max count of uses
        if (isset($expire['use']) && $expire['use'] < $expire['used']) {
            unset(self::$index[$id]);
            self::$driver->flush($id);
            return null;
        }

        ++self::$index[$id]['used'];
        return self::$driver->get($id);
    }

    /**
     * store data in cache
     *
     * Use id to store in cache. See get() for a list of expire parameter
     *
     * @see get()
     * @param string $id
     * @param mixed $data whatever you want to cache
     * @param array $expire parameter to tell
     * @return bool true on success
     */
    static function set($id, $data, $expire = array())
    {
        if (!WBParam::get('wb/cache/use', true)) {
            return true;
        }

        self::startDriver();
        $id =   md5($id);

        if (!is_array($expire)) {
            $expire =   array();
        }

        $expire['used']     =   0;
        $expire['cached']   =   time();
        self::$index[$id]   =   $expire;

        return self::$driver->set($id, $data);
    }

    /**
     * Fluh cache data
     *
     * Use any cache id
     *
     * @param string $id
     */
    static public function flush($id)
    {
        if (!WBParam::get('wb/cache/use', true)) {
            return;
        }
        self::startDriver();

        $id =   md5($id);
        if (!isset(self::$index[$id])) {
            return;
        }

        unset(self::$index[$id]);
        self::$driver->flush($id);
    }

   /**
    * Start driver on demand
    *
    * Start cache driver and load index
    */
    static protected function startDriver()
    {
        if (self::$driver) {
            return true;
        }

        $driver =   WBParam::get('wb/cache/driver', 'file');
        $driver =   ucfirst(strtolower($driver));

        self::$driver   =   WBClass::create('WBCache_Driver_' . $driver);
        self::$index    =&  self::$driver->getIndex();
        return true;
    }
}