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<?php

/**

 * @file

 * Plugins to handle cache-indirection.

 *

 * Simple plugin management to allow clients to more tightly control where

 * object caches are stored.

 *

 * CTools provides an object cache mechanism, and it also provides a number

 * of subsystems that are designed to plug into larger systems. When doing

 * caching on multi-step forms (in particular during AJAX operations) these

 * subsystems often need to operate their own cache. In reality, its best

 * for everyone if they are able to piggyback off of the larger cache.

 *

 * This system allows this by registering plugins to control where caches

 * are actually stored. For the most part, the subsystems could care less

 * where the data is fetched from and stored to. All it needs to know is

 * that it can 'get', 'set' and 'clear' caches. Additionally, some caches

 * might need extra operations such as 'lock' and 'finalize', and other

 * operations may be needed based upon the specific uses for the cache

 * plugins.

 *

 * To utilize cache plugins, there are two pieces of data. First, there is

 * the mechanism, which is simply the name of the plugin to use. CTools

 * provides a 'simple' mechanism which goes straight through to the object

 * cache. The second piece of data is the 'key' which is a unique identifier

 * that can be used to find the data needed. Keys can be generated any number

 * of ways, and the plugin must be agnostic about the key itself.

 *

 * That said, the 'mechanism' can be specified as pluginame::data and that

 * data can be used to derive additional data. For example, it is often

 * desirable to NOT store any cached data until original data (i.e, user

 * input) has been received. The data can be used to derive this original

 * data so that when a 'get' is called, if the cache is missed it can create

 * the data needed. This can help prevent unwanted cache entries from

 * building up just by visiting edit UIs without actually modifying anything.

 *

 * Modules wishing to implement cache indirection mechanisms need to implement

 * a plugin of type 'cache' for the module 'ctools' and provide the .inc file.

 * It should provide callbacks for 'cache set', 'cache get', and 'cache clear'.

 * It can provide callbacks for 'break' and 'finalize' if these are relevant

 * to the caching mechanism (i.e, for use with locking caches such as the page

 * manager cache). Other operations may be utilized but at this time are not part

 * of CTools.

 */

/**

 * Fetch data from an indirect cache.

 *

 * @param string $mechanism

 *   A string containing the plugin name, and an optional data element to

 *   send to the plugin separated by two colons.

 *

 * @param string $key

 *   The key used to identify the cache.

 *

 * @return mixed

 *   The cached data. This can be any format as the plugin does not necessarily

 *   have knowledge of what is being cached.

 */

function ctools_cache_get($mechanism, $key) {

  return ctools_cache_operation($mechanism, $key, 'get');

}

/**

 * Store data in an indirect cache.

 *

 * @param string $mechanism

 *   A string containing the plugin name, and an optional data element to

 *   send to the plugin separated by two colons.

 *

 * @param string $key

 *   The key used to identify the cache.

 *

 * @param mixed $object

 *   The data to cache. This can be any format as the plugin does not

 *   necessarily have knowledge of what is being cached.

 */

function ctools_cache_set($mechanism, $key, $object) {

  return ctools_cache_operation($mechanism, $key, 'set', $object);

}

/**

 * Clear data from an indirect cache.

 *

 * @param string $mechanism

 *   A string containing the plugin name, and an optional data element to

 *   send to the plugin separated by two colons.

 *

 * @param string $key

 *   The key used to identify the cache.

 */

function ctools_cache_clear($mechanism, $key) {

  return ctools_cache_operation($mechanism, $key, 'clear');

}

/**

 * Perform a secondary operation on an indirect cache.

 *

 * Additional operations, beyond get, set and clear may be items

 * such as 'break' and 'finalize', which are needed to support cache

 * locking. Other operations may be added by users of the indirect

 * caching functions as needed.

 *

 * @param string $mechanism

 *   A string containing the plugin name, and an optional data element to

 *   send to the plugin separated by two colons.

 *

 * @param string $key

 *   The key used to identify the cache.

 *

 * @param string $op

 *   The operation to call, such as 'break' or 'finalize'.

 *

 * @param mixed $object

 *   The cache data being operated on, in case it is necessary. This is

 *   optional so no references should be used.

 *

 * @return mixed

 *   The operation may or may not return a value.

 */

function ctools_cache_operation($mechanism, $key, $op, $object = NULL) {

  list($plugin, $data) = ctools_cache_find_plugin($mechanism);

  if (empty($plugin)) {

    return;

  }

  $function = ctools_plugin_get_function($plugin, "cache $op");

  if (empty($function)) {

    return;

  }

  return $function($data, $key, $object, $op);

}

/**

 * Take a mechanism and return a plugin and data.

 *

 * @param string $mechanism

 *   A string containing the plugin name, and an optional data element to

 *   send to the plugin separated by two colons.

 *

 * @return array

 *   An array, the first element will be the plugin and the second element

 *   will be the data. If the plugin could not be found, the $plugin will

 *   be NULL.

 */

function ctools_cache_find_plugin($mechanism) {

  if (strpos($mechanism, '::') !== FALSE) {

    // Use explode(2) to ensure that the data can contain double

    // colons, just in case.

    list($name, $data) = explode('::', $mechanism, 2);

  }

  else {

    $name = $mechanism;

    $data = '';

  }

  if (empty($name)) {

    return array(NULL, $data);

  }

  ctools_include('plugins');

  $plugin = ctools_get_plugins('ctools', 'cache', $name);

  return array($plugin, $data);

}