<?php
    $tvInput = $_GET['tz'] ?? 'UTC';
    $timeZone = in_array($tvInput, timeZone_identifiers_list())
        ? new DatetimeZone($tvInput)
        : 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');

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

    $finalYear = $year - 2000;
    $finalDay  = (int) $newYear->diff($nowOtc)->days + 1;

    $zeroYear      = str_pad((string) $finalYear, 3, '0', STR_PAD_LEFT);
    $zeroFinalDay = str_pad((string) $finalDay,  3, '0', STR_PAD_LEFT);

    // print date
    $otcDate = ($hour . ":" . $min . ":" . $sec . " " . $finalDay . " " . $zeroYear);

    // file date
    $otcFileDate  = $zeroYear;
    $otcFileDate .= $zeroFinalDay;
    $otcFileDate .= $hour;
    $otcFileDate .= $min;
    $otcFileDate .= $sec;
?>