<?php
$tz_input = $_GET['tz'] ?? 'UTC';
$timezone = in_array($tz_input, timezone_identifiers_list())
? new DateTimeZone($tz_input)
: new DateTimeZone('UTC');

$nowOtc  = new DateTimeImmutable('now', $timezone);
$year = (int) $nowOtc->format('Y');

$hour = $nowOtc->format('H');
$min  = $nowOtc->format('i');
$sec  = $nowOtc->format('s');

$new_year = new DateTimeImmutable("{$year}-03-20", $timezone);
if ($nowOtc < $new_year) {
$year--;
$new_year = new DateTimeImmutable("{$year}-03-20", $timezone);
}

$final_year = $year - 2000;
$final_day  = (int) $new_year->diff($nowOtc)->days + 1;

$zero_year      = str_pad((string) $final_year, 3, '0', STR_PAD_LEFT);
$zero_final_day = str_pad((string) $final_day,  3, '0', STR_PAD_LEFT);

// print date
$o_date = ($hour . ":" . $min . ":" . $sec . " " . $final_day . " " . $zero_year);

// file date
$o_file_date  = $zero_year;
$o_file_date .= $zero_final_day;
$o_file_date .= $hour;
$o_file_date .= $min;
$o_file_date .= $sec;
?>