อยากถามเกี่ยวกับการใช้ preg_replace แปลงค่าเป็นปีพ.ศ.

<?php
/**
 * @author vee
 * @copyright http://www.okvee.net
 * 
 * thaidate
 * convert php timestamp to thai date
 * 
 */

/**
 * thaidate
 * @param string $format
 * @param int $timestamp
 * @param boolean $be 
 */
function thaidate($format = '', $timestamp = '', $be = true) {
	if ( $timestamp == null ) {$timestamp = time();}
	// month values
	$en_month_long = array("January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December");
	$en_month_short = array("Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec");
	$th_month_long = array("มกราคม", "กุมภาพันธ์", "มีนาคม", "เมษายน", "พฤษภาคม", "มิถุนายน", "กรกฎาคม", "สิงหาคม", "กันยายน", "ตุลาคม", "พฤศจิกายน", "ธันวาคม");
	$th_month_short = array("ม.ค.", "ก.พ.", "มี.ค.", "เม.ย.", "พ.ค.", "มิ.ย.", "ก.ค.", "ส.ค.", "ก.ย.", "ต.ค.", "พ.ย.", "ธ.ค.");
	// day values
	$en_day_long = array("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday");
	$en_day_short = array("Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat");
	$th_day_long = array("อาทิตย์", "จันทร์", "อังคาร", "พุธ", "พฤหัสบดี", "ศุกร์", "เสาร์");
	$th_day_short = array("อา.", "จ.", "อ.", "พ.", "พฤ.", "ศ.", "ส.");
	// replace eng to thai from long to short
	$thaidate = date($format, $timestamp);
	if ( mb_strpos($format, "F") !== false ) {
		$thaidate = str_replace($en_month_long, $th_month_long, $thaidate);
	} else {
		$thaidate = str_replace($en_month_short, $th_month_short, $thaidate);
	}
	$thaidate = str_replace($en_day_long, $th_day_long, $thaidate);
	$thaidate = str_replace($en_day_short, $th_day_short, $thaidate);
	// convert year to buddha era (rg. 2554, 2555, 2556)?
	if ( $be == true ) {
		if ( mb_strpos($format, "o") !== false || mb_strpos($format, "Y") !== false ) {
			// ทำไงดี??
		} elseif ( mb_strpos($format, "y") !== false) {
			// ทำไงดี??
		}
	}
	return $thaidate;
}// thaidate

?>

require("thaidate.php");
echo "thai date " . thaidate("j l F Y H:i:s") . "<br />\n";