<?php
/**
* This library 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 2 of the License, or
* (at your option) any later version.
*
* This library 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 this software; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
* 
* © Copyright 2005 Richard Heyes
*/

/**
* Caching Libraries for PHP5
* 
* Handles data and output caching. Defaults to /dev/shm
* (shared memory). All methods are static.
* 
* Eg: (output caching)
* 
* if (!OutputCache::Start('group', 'unique id', 600)) {
* 
*   // ... Output
* 
*   OutputCache::End();
* }
* 
* Eg: (data caching)
* 
* if (!$data = DataCache::Get('group', 'unique id')) {
* 
*   $data = time();
* 
*   DataCache::Put('group', 'unique id', 10, $data);
* }
* 
* echo $data;
*/
    class Cache
    {
        /**
        * Whether caching is enabled
        * @var bool
        */
        public static $enabled = true;

        /**
        * Place to store the cache files
        * @var string
        */
        protected static $store = '/dev/shm/';
        
        /**
        * Prefix to use on cache files
        * @var string
        */
        protected static $prefix = 'cache_';

        /**
        * Stores data
        * 
        * @param string $group Group to store data under
        * @param string $id    Unique ID of this data
        * @param int    $ttl   How long to cache for (in seconds)
        */
        protected static function write($group, $id, $ttl, $data)
        {
            $filename = self::getFilename($group, $id);
            
            if (self::$enabled && $fp = fopen($filename, 'xb')) {
            
                if (flock($fp, LOCK_EX)) {
                    fwrite($fp, $data);
                }
                fclose($fp);
                
                // Set filemtime
                touch($filename, time() + $ttl);
            }
        }
        
        /**
        * Reads data
        * 
        * @param string $group Group to store data under
        * @param string $id    Unique ID of this data
        */
        protected static function read($group, $id)
        {
            $filename = self::getFilename($group, $id);
            
            return file_get_contents($filename);
        }
        
        /**
        * Determines if an entry is cached
        * 
        * @param string $group Group to store data under
        * @param string $id    Unique ID of this data
        */
        protected static function isCached($group, $id)
        {
            $filename = self::getFilename($group, $id);

            if (self::$enabled && file_exists($filename) && filemtime($filename) > time()) {
                return true;
            }

            @unlink($filename);

            return false;
        }
        
        /**
        * Builds a filename/path from group, id and
        * store.
        * 
        * @param string $group Group to store data under
        * @param string $id    Unique ID of this data
        */
        protected static function getFilename($group, $id)
        {
            $id = md5($id);

            return self::$store . self::$prefix . "{$group}_{$id}";
        }
        
        /**
        * Sets the filename prefix to use
        * 
        * @param string $prefix Filename Prefix to use
        */
        public static function setPrefix($prefix)
        {
            self::$prefix = $prefix;
        }

        /**
        * Sets the store for cache files. Defaults to
        * /dev/shm. Must have trailing slash.
        * 
        * @param string $store The dir to store the cache data in
        */
        public static function setStore($store)
        {
            self::$store = $store;
        }
    }
    
    /**
    * Output Cache extension of base caching class
    */
    class OutputCache extends Cache
    {
        /**
        * Group of currently being recorded data
        * @var string
        */
        private static $group;
        
        /**
        * ID of currently being recorded data
        * @var string
        */
        private static $id;
        
        /**
        * Ttl of currently being recorded data
        * @var int
        */
        private static $ttl;

        /**
        * Starts caching off. Returns true if cached, and dumps
        * the output. False if not cached and start output buffering.
        * 
        * @param  string $group Group to store data under
        * @param  string $id    Unique ID of this data
        * @param  int    $ttl   How long to cache for (in seconds)
        * @return bool          True if cached, false if not
        */
        public static function Start($group, $id, $ttl)
        {
            if (self::isCached($group, $id)) {
                echo self::read($group, $id);
                return true;
            
            } else {
                
                ob_start();
                
                self::$group = $group;
                self::$id    = $id;
                self::$ttl   = $ttl;
                
                return false;
            }
        }
        
        /**
        * Ends caching. Writes data to disk.
        */
        public static function End()
        {
            $data = ob_get_contents();
            ob_end_flush();
            
            self::write(self::$group, self::$id, self::$ttl, $data);
        }
    }
    
    /**
    * Data cache extension of base caching class
    */
    class DataCache extends Cache
    {
    
        /**
        * Retrieves data from the cache
        * 
        * @param  string $group Group this data belongs to
        * @param  string $id    Unique ID of the data
        * @return mixed         Either the resulting data, or null
        */
        public static function Get($group, $id)
        {
            if (self::isCached($group, $id)) {
                return unserialize(self::read($group, $id));
            }
            
            return null;
        }
        
        /**
        * Stores data in the cache
        * 
        * @param string $group Group this data belongs to
        * @param string $id    Unique ID of the data
        * @param int    $ttl   How long to cache for (in seconds)
        * @param mixed  $data  The data to store
        */
        public static function Put($group, $id, $ttl, $data)
        {
            self::write($group, $id, $ttl, serialize($data));
        }
    }
?>