<?php

/**
 * Abstract class representing Definition cache managers that implements
 * useful common methods and is a factory.
 * @todo Create a separate maintenance file advanced users can use to
 *       cache their custom HTMLDefinition, which can be loaded
 *       via a configuration directive
 * @todo Implement memcached
 */
abstract class HTMLPurifier_DefinitionCache
{

    public $type;

    /**
     * @param $name Type of definition objects this instance of the
     *      cache will handle.
     */
    public function __construct($type) {
        $this->type = $type;
    }

    /**
     * Generates a unique identifier for a particular configuration
     * @param Instance of HTMLPurifier_Config
     */
    public function generateKey($config) {
        return $config->version . ',' . // possibly replace with function calls
               $config->getBatchSerial($this->type) . ',' .
               $config->get($this->type . '.DefinitionRev');
    }

    /**
     * Tests whether or not a key is old with respect to the configuration's
     * version and revision number.
     * @param $key Key to test
     * @param $config Instance of HTMLPurifier_Config to test against
     */
    public function isOld($key, $config) {
        if (substr_count($key, ',') < 2) return true;
        list($version, $hash, $revision) = explode(',', $key, 3);
        $compare = version_compare($version, $config->version);
        // version mismatch, is always old
        if ($compare != 0) return true;
        // versions match, ids match, check revision number
        if (
            $hash == $config->getBatchSerial($this->type) &&
            $revision < $config->get($this->type . '.DefinitionRev')
        ) return true;
        return false;
    }

    /**
     * Checks if a definition's type jives with the cache's type
     * @note Throws an error on failure
     * @param $def Definition object to check
     * @return Boolean true if good, false if not
     */
    public function checkDefType($def) {
        if ($def->type !== $this->type) {
            trigger_error("Cannot use definition of type {$def->type} in cache for {$this->type}");
            return false;
        }
        return true;
    }

    /**
     * Adds a definition object to the cache
     */
    abstract public function add($def, $config);

    /**
     * Unconditionally saves a definition object to the cache
     */
    abstract public function set($def, $config);

    /**
     * Replace an object in the cache
     */
    abstract public function replace($def, $config);

    /**
     * Retrieves a definition object from the cache
     */
    abstract public function get($config);

    /**
     * Removes a definition object to the cache
     */
    abstract public function remove($config);

    /**
     * Clears all objects from cache
     */
    abstract public function flush($config);

    /**
     * Clears all expired (older version or revision) objects from cache
     * @note Be carefuly implementing this method as flush. Flush must
     *       not interfere with other Definition types, and cleanup()
     *       should not be repeatedly called by userland code.
     */
    abstract public function cleanup($config);

}

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