drupal-civicrm/sites/all/modules/civicrm/CRM/Contact/BAO/GroupContactCache.php

<?php
/*
 +--------------------------------------------------------------------+
 | CiviCRM version 4.7                                                |
 +--------------------------------------------------------------------+
 | Copyright CiviCRM LLC (c) 2004-2017                                |
 +--------------------------------------------------------------------+
 | This file is a part of CiviCRM.                                    |
 |                                                                    |
 | CiviCRM is free software; you can copy, modify, and distribute it  |
 | under the terms of the GNU Affero General Public License           |
 | Version 3, 19 November 2007 and the CiviCRM Licensing Exception.   |
 |                                                                    |
 | CiviCRM 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 Affero General Public License for more details.        |
 |                                                                    |
 | You should have received a copy of the GNU Affero General Public   |
 | License and the CiviCRM Licensing Exception along                  |
 | with this program; if not, contact CiviCRM LLC                     |
 | at info[AT]civicrm[DOT]org. If you have questions about the        |
 | GNU Affero General Public License or the licensing of CiviCRM,     |
 | see the CiviCRM license FAQ at http://civicrm.org/licensing        |
 +--------------------------------------------------------------------+
 */

/**
 *
 * @package CRM
 * @copyright CiviCRM LLC (c) 2004-2017
 */
class CRM_Contact_BAO_GroupContactCache extends CRM_Contact_DAO_GroupContactCache {

  static $_alreadyLoaded = array();

  /**
   * Get a list of caching modes.
   *
   * @return array
   */
  public static function getModes() {
    return array(
      // Flush expired caches in response to user actions.
      'opportunistic' => ts('Opportunistic Flush'),

      // Flush expired caches via background cron jobs.
      'deterministic' => ts('Cron Flush'),
    );
  }

  /**
   * Check to see if we have cache entries for this group.
   *
   * If not, regenerate, else return.
   *
   * @param array $groupIDs
   *   Of group that we are checking against.
   *
   * @return bool
   *   TRUE if we did not regenerate, FALSE if we did
   */
  public static function check($groupIDs) {
    if (empty($groupIDs)) {
      return TRUE;
    }

    return self::loadAll($groupIDs);
  }

  /**
   * Formulate the query to see which groups needs to be refreshed.
   *
   * The calculation is based on their cache date and the smartGroupCacheTimeOut
   *
   * @param string $groupIDClause
   *   The clause which limits which groups we need to evaluate.
   * @param bool $includeHiddenGroups
   *   Hidden groups are excluded by default.
   *
   * @return string
   *   the sql query which lists the groups that need to be refreshed
   */
  public static function groupRefreshedClause($groupIDClause = NULL, $includeHiddenGroups = FALSE) {
    $smartGroupCacheTimeoutDateTime = self::getCacheInvalidDateTime();

    $query = "
SELECT  g.id
FROM    civicrm_group g
WHERE   ( g.saved_search_id IS NOT NULL OR g.children IS NOT NULL )
AND     g.is_active = 1
AND (
  g.cache_date IS NULL
  OR cache_date <= $smartGroupCacheTimeoutDateTime
  OR NOW() >= g.refresh_date
)";

    if (!$includeHiddenGroups) {
      $query .= "AND (g.is_hidden = 0 OR g.is_hidden IS NULL)";
    }

    if (!empty($groupIDClause)) {
      $query .= " AND ( $groupIDClause ) ";
    }

    return $query;
  }

  /**
   * Check to see if a group has been refreshed recently.
   *
   * This is primarily used in a locking scenario when some other process might have refreshed things underneath
   * this process
   *
   * @param int $groupID
   *   The group ID.
   * @param bool $includeHiddenGroups
   *   Hidden groups are excluded by default.
   *
   * @return string
   *   the sql query which lists the groups that need to be refreshed
   */
  public static function shouldGroupBeRefreshed($groupID, $includeHiddenGroups = FALSE) {
    $query = self::groupRefreshedClause("g.id = %1", $includeHiddenGroups);
    $params = array(1 => array($groupID, 'Integer'));

    // if the query returns the group ID, it means the group is a valid candidate for refreshing
    return CRM_Core_DAO::singleValueQuery($query, $params);
  }

  /**
   * Check to see if we have cache entries for this group.
   *
   * if not, regenerate, else return
   *
   * @param int|array $groupIDs groupIDs of group that we are checking against
   *                           if empty, all groups are checked
   * @param int $limit
   *   Limits the number of groups we evaluate.
   *
   * @return bool
   *   TRUE if we did not regenerate, FALSE if we did
   */
  public static function loadAll($groupIDs = NULL, $limit = 0) {
    // ensure that all the smart groups are loaded
    // this function is expensive and should be sparingly used if groupIDs is empty
    if (empty($groupIDs)) {
      $groupIDClause = NULL;
      $groupIDs = array();
    }
    else {
      if (!is_array($groupIDs)) {
        $groupIDs = array($groupIDs);
      }

      // note escapeString is a must here and we can't send the imploded value as second argument to
      // the executeQuery(), since that would put single quote around the string and such a string
      // of comma separated integers would not work.
      $groupIDString = CRM_Core_DAO::escapeString(implode(', ', $groupIDs));

      $groupIDClause = "g.id IN ({$groupIDString})";
    }

    $query = self::groupRefreshedClause($groupIDClause);

    $limitClause = $orderClause = NULL;
    if ($limit > 0) {
      $limitClause = " LIMIT 0, $limit";
      $orderClause = " ORDER BY g.cache_date, g.refresh_date";
    }
    // We ignore hidden groups and disabled groups
    $query .= "
        $orderClause
        $limitClause
";

    $dao = CRM_Core_DAO::executeQuery($query);
    $processGroupIDs = array();
    $refreshGroupIDs = $groupIDs;
    while ($dao->fetch()) {
      $processGroupIDs[] = $dao->id;

      // remove this id from refreshGroupIDs
      foreach ($refreshGroupIDs as $idx => $gid) {
        if ($gid == $dao->id) {
          unset($refreshGroupIDs[$idx]);
          break;
        }
      }
    }

    if (!empty($refreshGroupIDs)) {
      $refreshGroupIDString = CRM_Core_DAO::escapeString(implode(', ', $refreshGroupIDs));
      $time = self::getRefreshDateTime();
      $query = "
UPDATE civicrm_group g
SET    g.refresh_date = $time
WHERE  g.id IN ( {$refreshGroupIDString} )
AND    g.refresh_date IS NULL
";
      CRM_Core_DAO::executeQuery($query);
    }

    if (empty($processGroupIDs)) {
      return TRUE;
    }
    else {
      self::add($processGroupIDs);
      return FALSE;
    }
  }

  /**
   * Build the smart group cache for given groups.
   *
   * @param array $groupIDs
   */
  public static function add($groupIDs) {
    $groupIDs = (array) $groupIDs;

    foreach ($groupIDs as $groupID) {
      // first delete the current cache
      self::clearGroupContactCache($groupID);
      $params = array(array('group', 'IN', array($groupID), 0, 0));
      // the below call updates the cache table as a byproduct of the query
      CRM_Contact_BAO_Query::apiQuery($params, array('contact_id'), NULL, NULL, 0, 0, FALSE);
    }
  }

  /**
   * Store values into the group contact cache.
   *
   * @todo review use of INSERT IGNORE. This function appears to be slower that inserting
   * with a left join. Also, 200 at once seems too little.
   *
   * @param array $groupID
   * @param array $values
   */
  public static function store($groupID, &$values) {
    $processed = FALSE;

    // sort the values so we put group IDs in front and hence optimize
    // mysql storage (or so we think) CRM-9493
    sort($values);

    // to avoid long strings, lets do BULK_INSERT_COUNT values at a time
    while (!empty($values)) {
      $processed = TRUE;
      $input = array_splice($values, 0, CRM_Core_DAO::BULK_INSERT_COUNT);
      $str = implode(',', $input);
      $sql = "INSERT IGNORE INTO civicrm_group_contact_cache (group_id,contact_id) VALUES $str;";
      CRM_Core_DAO::executeQuery($sql);
    }
    self::updateCacheTime($groupID, $processed);
  }

  /**
   * Change the cache_date.
   *
   * @param array $groupID
   * @param bool $processed
   *   Whether the cache data was recently modified.
   */
  public static function updateCacheTime($groupID, $processed) {
    // only update cache entry if we had any values
    if ($processed) {
      // also update the group with cache date information
      $now = date('YmdHis');
      $refresh = 'null';
    }
    else {
      $now = 'null';
      $refresh = 'null';
    }

    $groupIDs = implode(',', $groupID);
    $sql = "
UPDATE civicrm_group
SET    cache_date = $now, refresh_date = $refresh
WHERE  id IN ( $groupIDs )
";
    CRM_Core_DAO::executeQuery($sql);
  }

  /**
   * @deprecated function - the best function to call is
   * CRM_Contact_BAO_Contact::updateContactCache at the moment, or api job.group_cache_flush
   * to really force a flush.
   *
   * Remove this function altogether by mid 2018.
   *
   * However, if updating code outside core to use this (or any BAO function) it is recommended that
   * you add an api call to lock in into our contract. Currently there is not really a supported
   * method for non core functions.
   */
  public static function remove() {
    Civi::log()
      ->warning('Deprecated code. This function should not be called without groupIDs. Extensions can use the api job.group_cache_flush for a hard flush or add an api option for soft flush', array('civi.tag' => 'deprecated'));
    CRM_Contact_BAO_GroupContactCache::opportunisticCacheFlush();
  }

  /**
   * Function to clear group contact cache and reset the corresponding
   *  group's cache and refresh date
   *
   * @param int $groupID
   *
   */
  public static function clearGroupContactCache($groupID) {
    $transaction = new CRM_Core_Transaction();
    $query = "
    DELETE  g
      FROM  civicrm_group_contact_cache g
      WHERE  g.group_id = %1 ";

    $update = "
  UPDATE civicrm_group g
    SET    cache_date = null, refresh_date = null
    WHERE  id = %1 ";

    $params = array(
      1 => array($groupID, 'Integer'),
    );

    CRM_Core_DAO::executeQuery($query, $params);
    // also update the cache_date for these groups
    CRM_Core_DAO::executeQuery($update, $params);
    unset(self::$_alreadyLoaded[$groupID]);

    $transaction->commit();
  }

  /**
   * Refresh the smart group cache tables.
   *
   * This involves clearing out any aged entries (based on the site timeout setting) and resetting the time outs.
   *
   * This function should be called via the opportunistic or deterministic cache refresh function to make the intent
   * clear.
   */
  protected static function flushCaches() {
    try {
      $lock = self::getLockForRefresh();
    }
    catch (CRM_Core_Exception $e) {
      // Someone else is kindly doing the refresh for us right now.
      return;
    }
    $params = array(1 => array(self::getCacheInvalidDateTime(), 'String'));
    // @todo this is consistent with previous behaviour but as the first query could take several seconds the second
    // could become inaccurate. It seems to make more sense to fetch them first & delete from an array (which would
    // also reduce joins). If we do this we should also consider how best to iterate the groups. If we do them one at
    // a time we could call a hook, allowing people to manage the frequency on their groups, or possibly custom searches
    // might do that too. However, for 2000 groups that's 2000 iterations. If we do all once we potentially create a
    // slow query. It's worth noting the speed issue generally relates to the size of the group but if one slow group
    // is in a query with 500 fast ones all 500 get locked. One approach might be to calculate group size or the
    // number of groups & then process all at once or many query runs depending on what is found. Of course those
    // preliminary queries would need speed testing.
    CRM_Core_DAO::executeQuery(
      "
        DELETE gc
        FROM civicrm_group_contact_cache gc
        INNER JOIN civicrm_group g ON g.id = gc.group_id
        WHERE g.cache_date <= %1
      ",
      $params
    );

    // Clear these out without resetting them because we are not building caches here, only clearing them,
    // so the state is 'as if they had never been built'.
    CRM_Core_DAO::executeQuery(
      "
        UPDATE civicrm_group g
        SET    cache_date = NULL,
        refresh_date = NULL
        WHERE  g.cache_date <= %1
      ",
      $params
    );
    $lock->release();
  }

  /**
   * Check if the refresh is already initiated.
   *
   * We have 2 imperfect methods for this:
   *   1) a static variable in the function. This works fine within a request
   *   2) a mysql lock. This works fine as long as CiviMail is not running, or if mysql is version 5.7+
   *
   * Where these 2 locks fail we get 2 processes running at the same time, but we have at least minimised that.
   *
   * @return \Civi\Core\Lock\LockInterface
   * @throws \CRM_Core_Exception
   */
  protected static function getLockForRefresh() {
    if (!isset(Civi::$statics[__CLASS__]['is_refresh_init'])) {
      Civi::$statics[__CLASS__] = array('is_refresh_init' => FALSE);
    }

    if (Civi::$statics[__CLASS__]['is_refresh_init']) {
      throw new CRM_Core_Exception('A refresh has already run in this process');
    }
    $lock = Civi::lockManager()->acquire('data.core.group.refresh');
    if ($lock->isAcquired()) {
      Civi::$statics[__CLASS__]['is_refresh_init'] = TRUE;
      return $lock;
    }
    throw new CRM_Core_Exception('Mysql lock unavailable');
  }

  /**
   * Do an opportunistic cache refresh if the site is configured for these.
   *
   * Sites that do not run the smart group clearing cron job should refresh the
   * caches on demand. The user session will be forced to wait so it is less
   * ideal.
   */
  public static function opportunisticCacheFlush() {
    if (Civi::settings()->get('smart_group_cache_refresh_mode') == 'opportunistic') {
      self::flushCaches();
    }
  }

  /**
   * Do a forced cache refresh.
   *
   * This function is appropriate to be called by system jobs & non-user sessions.
   */
  public static function deterministicCacheFlush() {
    if (self::smartGroupCacheTimeout() == 0) {
      CRM_Core_DAO::executeQuery("TRUNCATE civicrm_group_contact_cache");
      CRM_Core_DAO::executeQuery("
        UPDATE civicrm_group g
        SET cache_date = null, refresh_date = null");
    }
    else {
      self::flushCaches();
    }
  }

  /**
   * Remove one or more contacts from the smart group cache.
   *
   * @param int|array $cid
   * @param int $groupId
   *
   * @return bool
   *   TRUE if successful.
   */
  public static function removeContact($cid, $groupId = NULL) {
    $cids = array();
    // sanitize input
    foreach ((array) $cid as $c) {
      $cids[] = CRM_Utils_Type::escape($c, 'Integer');
    }
    if ($cids) {
      $condition = count($cids) == 1 ? "= {$cids[0]}" : "IN (" . implode(',', $cids) . ")";
      if ($groupId) {
        $condition .= " AND group_id = " . CRM_Utils_Type::escape($groupId, 'Integer');
      }
      $sql = "DELETE FROM civicrm_group_contact_cache WHERE contact_id $condition";
      CRM_Core_DAO::executeQuery($sql);
      return TRUE;
    }
    return FALSE;
  }

  /**
   * Load the smart group cache for a saved search.
   *
   * @param object $group
   *   The smart group that needs to be loaded.
   * @param bool $force
   *   Should we force a search through.
   */
  public static function load(&$group, $force = FALSE) {
    $groupID = $group->id;
    $savedSearchID = $group->saved_search_id;
    if (array_key_exists($groupID, self::$_alreadyLoaded) && !$force) {
      return;
    }

    // grab a lock so other processes don't compete and do the same query
    $lock = Civi::lockManager()->acquire("data.core.group.{$groupID}");
    if (!$lock->isAcquired()) {
      // this can cause inconsistent results since we don't know if the other process
      // will fill up the cache before our calling routine needs it.
      // however this routine does not return the status either, so basically
      // its a "lets return and hope for the best"
      return;
    }

    self::$_alreadyLoaded[$groupID] = 1;

    // we now have the lock, but some other process could have actually done the work
    // before we got here, so before we do any work, lets ensure that work needs to be
    // done
    // we allow hidden groups here since we dont know if the caller wants to evaluate an
    // hidden group
    if (!$force && !self::shouldGroupBeRefreshed($groupID, TRUE)) {
      $lock->release();
      return;
    }

    $sql = NULL;
    $idName = 'id';
    $customClass = NULL;
    if ($savedSearchID) {
      $ssParams = CRM_Contact_BAO_SavedSearch::getSearchParams($savedSearchID);

      // rectify params to what proximity search expects if there is a value for prox_distance
      // CRM-7021
      if (!empty($ssParams)) {
        CRM_Contact_BAO_ProximityQuery::fixInputParams($ssParams);
      }

      $returnProperties = array();
      if (CRM_Core_DAO::getFieldValue('CRM_Contact_DAO_SavedSearch', $savedSearchID, 'mapping_id')) {
        $fv = CRM_Contact_BAO_SavedSearch::getFormValues($savedSearchID);
        $returnProperties = CRM_Core_BAO_Mapping::returnProperties($fv);
      }

      if (isset($ssParams['customSearchID'])) {
        // if custom search

        // we split it up and store custom class
        // so temp tables are not destroyed if they are used
        // hence customClass is defined above at top of function
        $customClass = CRM_Contact_BAO_SearchCustom::customClass($ssParams['customSearchID'], $savedSearchID);
        $searchSQL = $customClass->contactIDs();
        $searchSQL = str_replace('ORDER BY contact_a.id ASC', '', $searchSQL);
        if (!strstr($searchSQL, 'WHERE')) {
          $searchSQL .= " WHERE ( 1 ) ";
        }
        $idName = 'contact_id';
      }
      else {
        $formValues = CRM_Contact_BAO_SavedSearch::getFormValues($savedSearchID);
        // CRM-17075 using the formValues in this way imposes extra logic and complexity.
        // we have the where_clause and where tables stored in the saved_search table
        // and should use these rather than re-processing the form criteria (which over-works
        // the link between the form layer & the query layer too).
        // It's hard to think of when you would want to use anything other than return
        // properties = array('contact_id' => 1) here as the point would appear to be to
        // generate the list of contact ids in the group.
        // @todo review this to use values in saved_search table (preferably for 4.8).
        $query
          = new CRM_Contact_BAO_Query(
            $ssParams, $returnProperties, NULL,
            FALSE, FALSE, 1,
            TRUE, TRUE,
            FALSE,
            CRM_Utils_Array::value('display_relationship_type', $formValues),
            CRM_Utils_Array::value('operator', $formValues, 'AND')
          );
        $query->_useDistinct = FALSE;
        $query->_useGroupBy = FALSE;
        $searchSQL
          = $query->searchQuery(
            0, 0, NULL,
            FALSE, FALSE,
            FALSE, TRUE,
            TRUE,
            NULL, NULL, NULL,
            TRUE
          );
      }
      $groupID = CRM_Utils_Type::escape($groupID, 'Integer');
      $sql = $searchSQL . " AND contact_a.id NOT IN (
                              SELECT contact_id FROM civicrm_group_contact
                              WHERE civicrm_group_contact.status = 'Removed'
                              AND   civicrm_group_contact.group_id = $groupID ) ";
    }

    if ($sql) {
      $sql = preg_replace("/^\s*SELECT/", "SELECT $groupID as group_id, ", $sql);
    }

    // lets also store the records that are explicitly added to the group
    // this allows us to skip the group contact LEFT JOIN
    $sqlB = "
SELECT $groupID as group_id, contact_id as $idName
FROM   civicrm_group_contact
WHERE  civicrm_group_contact.status = 'Added'
  AND  civicrm_group_contact.group_id = $groupID ";

    self::clearGroupContactCache($groupID);

    $processed = FALSE;
    $tempTable = 'civicrm_temp_group_contact_cache' . rand(0, 2000);
    foreach (array($sql, $sqlB) as $selectSql) {
      if (!$selectSql) {
        continue;
      }
      $insertSql = "CREATE TEMPORARY TABLE $tempTable ($selectSql);";
      $processed = TRUE;
      CRM_Core_DAO::executeQuery($insertSql);
      CRM_Core_DAO::executeQuery(
        "INSERT IGNORE INTO civicrm_group_contact_cache (contact_id, group_id)
        SELECT DISTINCT $idName, group_id FROM $tempTable
      ");
      CRM_Core_DAO::executeQuery(" DROP TEMPORARY TABLE $tempTable");
    }

    self::updateCacheTime(array($groupID), $processed);

    if ($group->children) {

      //Store a list of contacts who are removed from the parent group
      $sql = "
SELECT contact_id
FROM civicrm_group_contact
WHERE  civicrm_group_contact.status = 'Removed'
AND  civicrm_group_contact.group_id = $groupID ";
      $dao = CRM_Core_DAO::executeQuery($sql);
      $removed_contacts = array();
      while ($dao->fetch()) {
        $removed_contacts[] = $dao->contact_id;
      }

      $childrenIDs = explode(',', $group->children);
      foreach ($childrenIDs as $childID) {
        $contactIDs = CRM_Contact_BAO_Group::getMember($childID, FALSE);
        //Unset each contact that is removed from the parent group
        foreach ($removed_contacts as $removed_contact) {
          unset($contactIDs[$removed_contact]);
        }
        $values = array();
        foreach ($contactIDs as $contactID => $dontCare) {
          $values[] = "({$groupID},{$contactID})";
        }

        self::store(array($groupID), $values);
      }
    }

    $lock->release();
  }

  /**
   * Retrieve the smart group cache timeout in minutes.
   *
   * This checks if a timeout has been configured. If one has then smart groups should not
   * be refreshed more frequently than the time out. If a group was recently refreshed it should not
   * refresh again within that period.
   *
   * @return int
   */
  public static function smartGroupCacheTimeout() {
    $config = CRM_Core_Config::singleton();

    if (
      isset($config->smartGroupCacheTimeout) &&
      is_numeric($config->smartGroupCacheTimeout)
    ) {
      return $config->smartGroupCacheTimeout;
    }

    // Default to 5 minutes.
    return 5;
  }

  /**
   * Get all the smart groups that this contact belongs to.
   *
   * Note that this could potentially be a super slow function since
   * it ensure that all contact groups are loaded in the cache
   *
   * @param int $contactID
   * @param bool $showHidden
   *   Hidden groups are shown only if this flag is set.
   *
   * @return array
   *   an array of groups that this contact belongs to
   */
  public static function contactGroup($contactID, $showHidden = FALSE) {
    if (empty($contactID)) {
      return NULL;
    }

    if (is_array($contactID)) {
      $contactIDs = $contactID;
    }
    else {
      $contactIDs = array($contactID);
    }

    self::loadAll();

    $hiddenClause = '';
    if (!$showHidden) {
      $hiddenClause = ' AND (g.is_hidden = 0 OR g.is_hidden IS NULL) ';
    }

    $contactIDString = CRM_Core_DAO::escapeString(implode(', ', $contactIDs));
    $sql = "
SELECT     gc.group_id, gc.contact_id, g.title, g.children, g.description
FROM       civicrm_group_contact_cache gc
INNER JOIN civicrm_group g ON g.id = gc.group_id
WHERE      gc.contact_id IN ($contactIDString)
           $hiddenClause
ORDER BY   gc.contact_id, g.children
";

    $dao = CRM_Core_DAO::executeQuery($sql);
    $contactGroup = array();
    $prevContactID = NULL;
    while ($dao->fetch()) {
      if (
        $prevContactID &&
        $prevContactID != $dao->contact_id
      ) {
        $contactGroup[$prevContactID]['groupTitle'] = implode(', ', $contactGroup[$prevContactID]['groupTitle']);
      }
      $prevContactID = $dao->contact_id;
      if (!array_key_exists($dao->contact_id, $contactGroup)) {
        $contactGroup[$dao->contact_id]
          = array('group' => array(), 'groupTitle' => array());
      }

      $contactGroup[$dao->contact_id]['group'][]
        = array(
          'id' => $dao->group_id,
          'title' => $dao->title,
          'description' => $dao->description,
          'children' => $dao->children,
        );
      $contactGroup[$dao->contact_id]['groupTitle'][] = $dao->title;
    }

    if ($prevContactID) {
      $contactGroup[$prevContactID]['groupTitle'] = implode(', ', $contactGroup[$prevContactID]['groupTitle']);
    }

    if ((!empty($contactGroup[$contactID]) && is_numeric($contactID))) {
      return $contactGroup[$contactID];
    }
    else {
      return $contactGroup;
    }
  }

  /**
   * Get the datetime from which the cache should be considered invalid.
   *
   * Ie if the smartgroup cache timeout is 5 minutes ago then the cache is invalid if it was
   * refreshed 6 minutes ago, but not if it was refreshed 4 minutes ago.
   *
   * @return string
   */
  public static function getCacheInvalidDateTime() {
    return date('YmdHis', strtotime("-" . self::smartGroupCacheTimeout() . " Minutes"));
  }

  /**
   * Get the date when the cache should be refreshed from.
   *
   * Ie. now + the offset & we will delete anything prior to then.
   *
   * @return string
   */
  public static function getRefreshDateTime() {
    return date('YmdHis', strtotime("+ " . self::smartGroupCacheTimeout() . " Minutes"));
  }

}