Static file caching for expensive perch queries

layouts-adminlogin.php

<?php
// layout to prepend to restricted pages
$Users = new PerchUsers;
$CurrentUser = $Users->get_current_user();

if (!(is_object($CurrentUser) && $CurrentUser->logged_in())) {
    // user is not logged in to Perch
    exit('Please log in first.');
}

// Note:
// if ($CurrentUser->userMasterAdmin()){
//     // user is the *primary* admin
// }

layouts-helpers.php

<?php
// layout to include where needed

// helper function for caching
function sanitizeStringForFilename($string){
  // sanitize string for filename http://stackoverflow.com/a/2021729/160968
  $r = mb_ereg_replace("([^\w\s\d\-_~,;\[\]\(\).])", '', $string);
  $r = mb_ereg_replace("([\.]{2,})", '', $r);
  return $r;
}

/*
 * Helper function to save static copy of any string
 * manually make sure that the id of the file is unique!
 * @param $content string
 * @param $id string
*/
function saveStaticCopy($content,$id){
  $id = sanitizeStringForFilename($id);
  $cacheFile = PATH_TO_CACHE_DIR_WITH_ENDING_SLASH . $id . '.txt';
  file_put_contents($cacheFile,$content);
  return false;
}


/*
 * Helper function to read static copy of any string
 * @param $id string
 * @param $maxAgeHours int
*/
function loadStaticCopy($id,$maxAgeHours){
  $id = sanitizeStringForFilename($id);
  $cacheFile = PATH_TO_CACHE_DIR_WITH_ENDING_SLASH . $id . '.txt';
  if (file_exists($cacheFile)) {
    $cacheFileModificationTime = filemtime($cacheFile);
    $now = time();
    $maxAge = $maxAgeHours * 60 * 60;
    if (($now - $cacheFileModificationTime) < $maxAge) {
      return file_get_contents($cacheFile);
    }
    // file is too old
    return false;
  }
  // file does not exist
  return false;
}

pages-pagewithexpensivecontent.php

<?php
  perch_layout('helpers');
  $cachingId = 'somedynamicallycreatedvalue';
  $cachedContent = loadStaticCopy($cachingId,24); // returns false if inexistant or older than maxAgeHours
  // output the content regularly
  if (!empty($cachedContent)){
    echo $cachedContent;
  }
  else {
    // output what we've got already
    PerchUtil::flush_output();
    // render list
    $r = perch_collection('Things', [
      // options
      },
    ], true);
    saveStaticCopy($r,$cachingId);
    echo $r;
  }

pages-supersimplecacheclearer.php

<?php

// external users can't access this page
perch_layout('adminlogin');

// clear /cache/ folder
$files = glob(PATH_TO_CACHE_DIR_WITH_ENDING_SLASH.'*'); // get all file names
foreach($files as $file){ // iterate files
  if(is_file($file)){
    unlink($file); // delete file
  }
}
  die('ok! Cache cleared.');