<?php
////
// Author: Sean Colombo
// Date: 20080321
//
// Used to cache the results of various expensive operations.
//
// To create the map used here, send the mySQL query: 
//    "CREATE TABLE pageCache (keyName VARCHAR(255), pageData TEXT, updatedAt TIMESTAMP, PRIMARY KEY(keyName));"
//
// NOTE: If array-data needs to be cached and is not a string yet, use the serialize_nested/deserialize_nested functions
// in utils.php.  They will turn arbitrary depth, non-associative arrays into serialized strings and back into arrays.  An example
// of this use can be found in the randTumbs() function in tools.php.
////

////
// Class for caching chunks of info (that can optionally expire).
// The cached data itself does not have an inherent expiration date, but it does record when it
// was cached so that at runtime any calling code can decide how old of a cache it wants to allow.
////
class Cache{
	private $db;

	function Cache(){
		profiler_beginSection(__METHOD__);
		$this->db = dil_connect(); // remembers the database
		profiler_endSection(__METHOD__);
	}

	////
	// Fetches data if it is cached (regardless of when it was cached) and null if it isn't cached.
	// Use fetchExpire() for expiring caches.
	////
	function fetch($key){
		profiler_beginSection(__METHOD__);
		$retVal = null;
		$oldestAllowed = date("Y-m-d H:i:s", $oldestAllowed); // convert the time to a format mySQL will understand
		$queryString = "SELECT pageData FROM pageCache WHERE keyName='$key'";
		if($result = mysql_query($queryString,$this->db)){
			if(($numRows = mysql_num_rows($result)) && ($numRows > 0)){
				$retVal = mysql_result($result, 0, "pageData");
			}
		}
		profiler_endSection(__METHOD__);
		return $retVal;
	} // end fetch()

	////
	// Fetches data if it is cached and up to date.  The validAfter var is the time which the cache would have had
	// to be made more recently than in order to not be expired.  An easy way to generate this value is with strtotime.
	// Eg: strtotime('-2 hour'); // only uses the cache if it is 2 hours old or less.
	//
	// If the value is not cached or is expired, the value returned will be null.
	////
	function fetchExpire($key, $validAfter){
		profiler_beginSection(__METHOD__);
		$retVal = null;
		$validAfter = date("Y-m-d H:i:s", $validAfter); // convert the time to a format mySQL will understand
		$queryString = "SELECT pageData FROM pageCache WHERE keyName='$key' AND updatedAt >= '$validAfter'";
		if($result = mysql_query($queryString,$this->db)){
			if(($numRows = mysql_num_rows($result)) && ($numRows > 0)){
				$retVal = mysql_result($result, 0, "pageData");
			}
		}
		profiler_endSection(__METHOD__);
		return $retVal;
	} // end fetchExpire()
	
	////
	// Stores a value in the cache (it will be automatically timestamped).
	////
	function cacheValue($key, $source){
		profiler_beginSection(__METHOD__);
		$source = str_replace("'", "\'", $source); // to prevent query errors
		$queryString = "REPLACE INTO pageCache (keyName, pageData) VALUES ('$key', '$source')";
		$retVal = mysql_query($queryString, $this->db);
		profiler_endSection(__METHOD__);
		return $retVal;
	} // end cacheValue()

} // end class Cache

?>