<?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;
?>