get week numbers between dates

calendar.php

<?php

$min_date = '2015-12-01';
$max_date = '2017-01-03';

$firstWeek = date('W', strtotime($min_date));
$lastWeek = date('W', strtotime($max_date));

$startTime = strtotime($min_date);
$endTime = strtotime($max_date);

$weeks = array();

$diff = strtotime($max_date, 0) - strtotime($min_date, 0);
$sum = ceil($diff / 604800);
while ($startTime < $endTime) {
    $diff_days = (($endTime - $startTime) / 86400);
    $diff_weeks = $diff_days / 7;

    $weeks[] = date('W', $startTime);
    $startTime += strtotime('+1 week', 0);

    if (count($weeks) == $sum && $diff_days != 0) {
        $last_inserted_week = $weeks[count($weeks) - 1];
        $max_date_week = date('W', strtotime($max_date));

        if ($last_inserted_week != $max_date_week)
            $weeks[] = $max_date_week;
    }

}
$variable = $weeks; echo '<pre>'; print_r($variable); echo '</pre>';