<?php
/**
 * The Strangecode Codebase - a general application development framework for PHP
 * For details visit the project site: <http://trac.strangecode.com/codebase/>
 * Copyright 2001-2012 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.
 *
 * Disable cache per-request by adding '_disable_cache=1' to a GET or POST parameter.
 *
 * @author  Quinn Comendant <quinn@strangecode.com>
 * @version 2.1
 * @since   2001
 */

class Cache
{

    // A place to keep object instances for the singleton pattern.
    protected static $instances = array();

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

    // Configuration parameters for this object.
    protected $_params = array(

        // Type of cache. Currently only 'session' is supported.
        'type' => 'session',

        // 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,

        // How long in seconds before items in the cache are considered expired.
        // When the cache expires, Cache->get() returns null.
        'expires' => 900,
    );

    /*
    * Constructor. This is publicly accessible for compatibility with older implementations,
    * but the preferred method of instantiation is by use of the singleton pattern:
    *   $cache =& Cache::getInstance('namespace');
    *   $cache->setParam(array('enabled' => true));
    *
    * @access   public
    * @param    string  $namespace  This object will store data under this realm.
    * @author   Quinn Comendant <quinn@strangecode.com>
    * @version  1.0
    * @since    05 Jun 2006 23:14:21
    */
    public function __construct($namespace='')
    {
        $app =& App::getInstance();

        $this->_ns = $namespace;

        if (true !== $app->getParam('enable_session')) {
            // Force disable the cache because there is no session to save to.
            $app->logMsg('Cache disabled, enable_session != true.', LOG_DEBUG, __FILE__, __LINE__);
            $this->setParam(array('enabled' => false));
        } else if (!isset($_SESSION['_cache'][$this->_ns])) {
            // Otherwise, clear to initialize the session variable.
            $this->clear();
        }
    }

    /**
     * This method enforces the singleton pattern for this class.
     *
     * @return  object  Reference to the global Cache object.
     * @access  public
     * @static
     */
    public static function &getInstance($namespace='')
    {
        if (!array_key_exists($namespace, self::$instances)) {
            self::$instances[$namespace] = new self($namespace);
        }
        return self::$instances[$namespace];
    }

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

        if (array_key_exists($param, $this->_params)) {
            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 data to store in the session cache.
     * @param bool  $allow_oversized    If we have something really big that we still want to cache, setting this to true allows this.
     * @return bool                     True on success, false otherwise.
     */
    public function set($key, $var, $allow_oversized=false)
    {
        $app =& App::getInstance();

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

        if (is_numeric($key)) {
            $app->logMsg(sprintf('Cache::set key value should not be numeric (%s given)', $key), LOG_WARNING, __FILE__, __LINE__);
        }

        $var = serialize($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 ($allow_oversized && $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] = array(
            'var' => $var,
            'time' => time(),
        );

        $app->logMsg(sprintf('Set cache item “%s”', $key), LOG_DEBUG, __FILE__, __LINE__);

        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 $key  The key for the datum to retrieve.
     * @return mixed          The requested datum, or false on failure.
     */
    public function get($key)
    {
        $app =& App::getInstance();

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

        if (isset($_SESSION['_cache'][$this->_ns]) && array_key_exists($key, $_SESSION['_cache'][$this->_ns])) {
            if (isset($_SESSION['_cache'][$this->_ns][$key]['time']) && $_SESSION['_cache'][$this->_ns][$key]['time'] > (time() - $this->getParam('expires'))) {
                $app->logMsg(sprintf('Retrieving %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]['var']);
            } else {
                // Cached item has expired.
                $app->logMsg(sprintf('Cached %s expired %s ago', $key, humanTime(time() - $_SESSION['_cache'][$this->_ns][$key]['time'])), LOG_DEBUG, __FILE__, __LINE__);
                return null;
            }
        } else {
            $app->logMsg(sprintf('Missing %s from cache.', $key), LOG_DEBUG, __FILE__, __LINE__);
            return false;
        }
    }

    /**
     * Tells you if the object is cached.
     *
     * @param string $key  The key of the object to check.
     * @return bool         True if a value exists for the given key.
     */
    public function exists($key)
    {
        $app =& App::getInstance();

        if (true !== $this->getParam('enabled') || getFormData('_disable_cache')) {
            $app->logMsg(sprintf('Cache disabled on exist assertion.', null), LOG_DEBUG, __FILE__, __LINE__);
            return false;
        }

        if (isset($_SESSION['_cache'][$this->_ns])
        && array_key_exists($key, $_SESSION['_cache'][$this->_ns])
        && isset($_SESSION['_cache'][$this->_ns][$key]['time'])
        && $_SESSION['_cache'][$this->_ns][$key]['time'] > (time() - $this->getParam('expires'))) {
            $app->logMsg(sprintf('Cache item “%s” exists', $key), LOG_DEBUG, __FILE__, __LINE__);
            return true;
        } else {
            $app->logMsg(sprintf('Cache item “%s” missing or expired', $key), LOG_DEBUG, __FILE__, __LINE__);
            return false;
        }
    }

    /**
     * Removes a cached object.
     *
     * @param string $key  The key of the object to check.
     * @return bool         True if the value existed before being unset.
     */
    public function delete($key)
    {
        $app =& App::getInstance();

        if (true !== $this->getParam('enabled') || getFormData('_disable_cache')) {
            $app->logMsg(sprintf('Cache disabled, skipping delete of %s', $key), LOG_DEBUG, __FILE__, __LINE__);
            return false;
        }

        if (isset($_SESSION['_cache'][$this->_ns]) && array_key_exists($key, $_SESSION['_cache'][$this->_ns])) {
            $app->logMsg(sprintf('Deleting cache item “%s”', $key), LOG_DEBUG, __FILE__, __LINE__);
            unset($_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
    */
    public function clear()
    {
        $app =& App::getInstance();

        $_SESSION['_cache'][$this->_ns] = array();
        $app->logMsg(sprintf('Cleared %s cache', $this->_ns), LOG_DEBUG, __FILE__, __LINE__);
    }

// END Cache
}