<?php
/**
 * The Strangecode Codebase - a general application development framework for PHP
 * For details visit the project site: <http://trac.strangecode.com/codebase/>
 * Copyright 2001-2010 Strangecode, LLC
 * 
 * This file is part of The Strangecode Codebase.
 *
 * The Strangecode Codebase 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 3 of the License, or (at your option)
 * any later version.
 * 
 * The Strangecode Codebase 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
 * The Strangecode Codebase. If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * Cache.inc.php
 *
 * Provides an API for storing a limited amount of data
 * intended to have a short lifetime in a user's session.
 *
 * @author  Quinn Comendant <quinn@strangecode.com>
 * @version 2.1
 * @since   2001
 */
 
// Flags.
define('CACHE_ALLOW_OVERSIZED', 1);

class Cache {

    // Namespace of this instance of Prefs.
    var $_ns;

    // Configuration parameters for this object.
    var $_params = array(
        
        // If false nothing will be cached or retrieved. Useful for testing realtime data requests.
        'enabled' => true,

        // The maximum size in bytes of any one variable.
        'item_size_limit' => 4194304, // 4 MB
        
        // The maximum size in bytes before the cache will begin flushing out old items.
        'stack_size_limit' => 4194304, // 4 MB
        
        // The minimum items to keep in the cache regardless of item or cache size.
        'min_items' => 5,
    );
    
    /*
    * Constructor
    *
    * @access   public
    * @param    string  $namespace  This object will store data under this realm.
    * @author   Quinn Comendant <quinn@strangecode.com>
    * @version  1.0
    * @since    05 Jun 2006 23:14:21
    */
    function Cache($namespace='')
    {
        $app =& App::getInstance();
        
        $this->_ns = $namespace;

        if (true !== $app->getParam('enable_session')) {
            $app->logMsg('Cache disabled, enable_session is false.', LOG_DEBUG, __FILE__, __LINE__);
            $this->setParam(array('enabled' => false));
        }
        
        if (!isset($_SESSION['_cache'][$this->_ns])) {
            $this->clear();
        }
    }

    /**
     * This method enforces the singleton pattern for this class.
     *
     * @return  object  Reference to the global Cache object.
     * @access  public
     * @static
     */
    function &getInstance($namespace='')
    {
        static $instances = array();

        if (!array_key_exists($namespace, $instances)) {
            $instances[$namespace] = new Cache($namespace);
        }

        return $instances[$namespace];
    }

    /**
     * Set (or overwrite existing) parameters by passing an array of new parameters.
     *
     * @access public
     * @param  array    $params     Array of parameters (key => val pairs).
     */
    function setParam($params)
    {
		$app =& App::getInstance();

        if (isset($params) && is_array($params)) {
            // Merge new parameters with old overriding only those passed.
            $this->_params = array_merge($this->_params, $params);
        } else {
            $app->logMsg(sprintf('Parameters are not an array: %s', $params), LOG_ERR, __FILE__, __LINE__);
        }
    }

    /**
     * Return the value of a parameter, if it exists.
     *
     * @access public
     * @param string $param        Which parameter to return.
     * @return mixed               Configured parameter value.
     */
    function getParam($param)
    {
		$app =& App::getInstance();
    
        if (isset($this->_params[$param])) {
            return $this->_params[$param];
        } else {
            $app->logMsg(sprintf('Parameter is not set: %s', $param), LOG_DEBUG, __FILE__, __LINE__);
            return null;
        }
    }

    /**
     * Stores a new variable in the session cache. The $key should not be numeric
     * because the array_shift function will reset the key to the next largest 
     * int key. Weird behavior I can't understand. For example $cache["123"] will become $cache[0]
     *
     * @param str   $key        An identifier for the cached object.
     * @param mixed $var        The var to store in the session cache.
     * @param bool  $flags      If we have something really big that we
     *                          still want to cache, setting this to
     *                          CACHE_ALLOW_OVERSIZED allows this.
     * @return bool             True on success, false otherwise.
     */
    function set($key, $var, $flags=0)
    {
		$app =& App::getInstance();

        if (true !== $this->getParam('enabled')) {
            $app->logMsg(sprintf('Cache disabled, not saving data.', null), LOG_DEBUG, __FILE__, __LINE__);
            return false;
        }

        $var = serialize($var);
        $var_len = mb_strlen($var);

        if ($var_len >= $this->getParam('item_size_limit')) {
            $app->logMsg(sprintf('Serialized variable (%s bytes) more than item_size_limit (%s bytes).', $var_len, $this->getParam('item_size_limit')), LOG_NOTICE, __FILE__, __LINE__);
            return false;
        }

        if ($flags & CACHE_ALLOW_OVERSIZED == 0 && $var_len >= $this->getParam('stack_size_limit')) {
            $app->logMsg(sprintf('Serialized variable (%s bytes) more than stack_size_limit (%s bytes).', $var_len, $this->getParam('stack_size_limit')), LOG_NOTICE, __FILE__, __LINE__);
            return false;
        }        

        // Remove any value already stored under this key.
        unset($_SESSION['_cache'][$this->_ns][$key]);

        // Continue to prune the cache if its size is greater than stack_size_limit, but keep at least min_items.
        while (mb_strlen(serialize($_SESSION['_cache'][$this->_ns])) + $var_len >= $this->getParam('stack_size_limit') && sizeof($_SESSION['_cache'][$this->_ns]) >= $this->getParam('min_items')) {
            array_shift($_SESSION['_cache'][$this->_ns]);
        }

        // Save this value under the specified key.
        $_SESSION['_cache'][$this->_ns][$key] =& $var;

        if ($var_len >= 1024000) {
            $app->logMsg(sprintf('Successfully cached oversized variable (%s bytes).', $var_len), LOG_DEBUG, __FILE__, __LINE__);
        }

        return true;
    }

    /**
     * Retrieves an object from the session cache and returns it unserialized.
     * It also moves it to the top of the stack, which makes it such that the
     * cache flushing mechanism of putCache deletes the oldest referenced items
     * first.
     *
     * @param string $key  The key for the datum to retrieve.
     * @return mixed          The requested datum, or false on failure.
     */
    function get($key)
    {
        $app =& App::getInstance();

        if (true !== $this->getParam('enabled')) {
            $app->logMsg(sprintf('Cache disabled, not getting data.', null), LOG_DEBUG, __FILE__, __LINE__);
            return false;
        }

        if (array_key_exists($key, $_SESSION['_cache'][$this->_ns])) {
            $app->logMsg(sprintf('Retreiving %s from cache.', $key), LOG_DEBUG, __FILE__, __LINE__);
            // Move the accessed cached datum to the top of the stack. Maybe somebody knows a better way to do this?
            $tmp =& $_SESSION['_cache'][$this->_ns][$key];
            unset($_SESSION['_cache'][$this->_ns][$key]);
            $_SESSION['_cache'][$this->_ns][$key] =& $tmp;
            // Return the unserialized datum.
            return unserialize($_SESSION['_cache'][$this->_ns][$key]);
        } else {
            $app->logMsg(sprintf('Missing %s from cache.', $key), LOG_DEBUG, __FILE__, __LINE__);
            return false;
        }
    }

    /**
     * Tells you if the object is cached.
     *
     * @param string $key  The key of the object to check.
     * @return bool         True if a value exists for the given key.
     */
    function exists($key)
    {
        if (true !== $this->getParam('enabled')) {
            return false;
        }

        return array_key_exists($key, $_SESSION['_cache'][$this->_ns]);
    }

    /**
     * Removes a cached object.
     *
     * @param string $key  The key of the object to check.
     * @return bool         True if the value existed before being unset.
     */
    function delete($key)
    {
        if (array_key_exists($key, $_SESSION['_cache'][$this->_ns])) {
            unset($_SESSION['_cache'][$this->_ns][$key]);
            return true;
        } else {
            return false;
        }
    }
    
    /*
    * Delete all existing items from the cache.
    *
    * @access   public
    * @author   Quinn Comendant <quinn@strangecode.com>
    * @version  1.0
    * @since    05 Jun 2006 23:51:34
    */
    function clear()
    {
        $_SESSION['_cache'][$this->_ns] = array();
    }

// END Cache
}

?>