Determines the file modification date and whether or not to append a query string to the file path

assetQueryString.php

function assetQueryString ($filePath, $maxAge = 7) {
	$today = intval(strtotime(date("Y-m-d")) / 86400);
	$fileDate = intval(strtotime(date("Y-m-d", filemtime($_SERVER['DOCUMENT_ROOT'].$filePath))) / 86400);
	$days = $today - $fileDate;

	if ($days <= $maxAge) {
		$filePath .= "?".$fileDate;
	}
	echo $filePath;
}

// more info: http://mattbrundage.com/2011/08/12/stale-cache-mitigation-with-query-string-automation/
//
// sample usage:
// <link rel="stylesheet" href="<?php assetQueryString("/templates/style/main.css"); ?>">