Find Week Number for Current Date Within Total Week Count Bounds in PHP

I have an 18 week schedule and a start date:

Total Weeks = 18

Start Date = 9/1/20

I want to know which week number (NOT PHP W but actual number between 1 and 18) at any time. So I would pass into a function: Current Date, Start Date and Total Weeks and it would output what current week number it is 1 to 18

I had a what seems like a very convoluted way of doing this but it’s not accurately giving me the week number.

function get_current_week($current_datetime, $start_date, $total_weeks) {

        $date = date('Y-m-d', strtotime($current_datetime));
        $day_of_week = date('N', strtotime($current_datetime)); 
        $today = new DateTime($date);

        $begin = new DateTime($start_date);
        $i = 0; // first week number
        $end_date = clone $begin;
        $end_date->modify($gl_total_weeks . ' weeks');
        $interval = new DateInterval('P1W');
        $range = new DatePeriod($begin, $interval, $end_date);
        $dates = array();
        $found = false;
        foreach($range as $date) {
            if($date >= $today && !$found) {
                $found = true;
                $current_week = ($day_of_week >= 2 ? $i : $i -1);
            }
            $dates['Week ' . $i] = $date->format('Y-m-d');
            $i++;
        }

        if (!$current_week) {
            $current_week = 1;
        }
        return $current_week;
    }   

Thanks for help.

Answer

Without a Dateinterval it becomes easier. Only the difference in days from the start to the current date is required. The rest is some math. The start date is set internally to the Monday of the week. The end date is not controlled. The counting of the weeks continues cyclically.

function getWeekNumber($current_datetime, $start_date, $total_weeks) {
  $curDate = date_create($current_datetime);
  $start = date_create($start_date)
    ->modify('+1 day')
    ->modify('last Monday')
  ;
  $totalDays = $total_weeks * 7;
  $dayDiff = $start->diff($curDate)->days;
  return (int)(($dayDiff%$totalDays)/7+1);
}

Note: The counting of the weeks starts with 1. For counting from 0 only the +1 in the return line has to be removed.