XLSXWriter::convert_date_time PHP Метод

    public static function convert_date_time($date_input)
    {
        $days = 0;
        # Number of days since epoch
        $seconds = 0;
        # Time expressed as fraction of 24h hours in seconds
        $year = $month = $day = 0;
        $hour = $min = $sec = 0;
        $date_time = $date_input;
        if (preg_match("/(\\d{4})\\-(\\d{2})\\-(\\d{2})/", $date_time, $matches)) {
            list($junk, $year, $month, $day) = $matches;
        }
        if (preg_match("/(\\d{2}):(\\d{2}):(\\d{2})/", $date_time, $matches)) {
            list($junk, $hour, $min, $sec) = $matches;
            $seconds = ($hour * 60 * 60 + $min * 60 + $sec) / (24 * 60 * 60);
        }
        //using 1900 as epoch, not 1904, ignoring 1904 special case
        # Special cases for Excel.
        if ("{$year}-{$month}-{$day}" == '1899-12-31') {
            return $seconds;
        }
        # Excel 1900 epoch
        if ("{$year}-{$month}-{$day}" == '1900-01-00') {
            return $seconds;
        }
        # Excel 1900 epoch
        if ("{$year}-{$month}-{$day}" == '1900-02-29') {
            return 60 + $seconds;
        }
        # Excel false leapday
        # We calculate the date by calculating the number of days since the epoch
        # and adjust for the number of leap days. We calculate the number of leap
        # days by normalising the year in relation to the epoch. Thus the year 2000
        # becomes 100 for 4 and 100 year leapdays and 400 for 400 year leapdays.
        $epoch = 1900;
        $offset = 0;
        $norm = 300;
        $range = $year - $epoch;
        # Set month days and check for leap year.
        $leap = $year % 400 == 0 || $year % 4 == 0 && $year % 100 ? 1 : 0;
        $mdays = array(31, $leap ? 29 : 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31);
        # Some boundary checks
        if ($year < $epoch || $year > 9999) {
            return 0;
        }
        if ($month < 1 || $month > 12) {
            return 0;
        }
        if ($day < 1 || $day > $mdays[$month - 1]) {
            return 0;
        }
        # Accumulate the number of days since the epoch.
        $days = $day;
        # Add days for current month
        $days += array_sum(array_slice($mdays, 0, $month - 1));
        # Add days for past months
        $days += $range * 365;
        # Add days for past years
        $days += intval($range / 4);
        # Add leapdays
        $days -= intval(($range + $offset) / 100);
        # Subtract 100 year leapdays
        $days += intval(($range + $offset + $norm) / 400);
        # Add 400 year leapdays
        $days -= $leap;
        # Already counted above
        # Adjust for Excel erroneously treating 1900 as a leap year.
        if ($days > 59) {
            $days++;
        }
        return $days + $seconds;
    }