Getting date start & end for every week (Mon - Sun) by given month

example.php

<?php

$weeks = get_week_dates('2021-01');

var_dump($weeks);

// Output:
// array(5) {
//   [0]=>
//   array(2) {
//     ["start"]=>
//     string(10) "2021-01-01"
//     ["end"]=>
//     string(10) "2021-01-03"
//   }
//   [1]=>
//   array(2) {
//     ["start"]=>
//     string(10) "2021-01-04"
//     ["end"]=>
//     string(10) "2021-01-10"
//   }
//   [2]=>
//   array(2) {
//     ["start"]=>
//     string(10) "2021-01-11"
//     ["end"]=>
//     string(10) "2021-01-17"
//   }
//   [3]=>
//   array(2) {
//     ["start"]=>
//     string(10) "2021-01-18"
//     ["end"]=>
//     string(10) "2021-01-24"
//   }
//   [4]=>
//   array(2) {
//     ["start"]=>
//     string(10) "2021-01-25"
//     ["end"]=>
//     string(10) "2021-01-31"
//   }
// }

week_dates.php

<?php

/**
 * @author Nur Muhammad<blog.nurmuhammad@gmail.com>
 *
 * @param $month The month to process, format: Y-m (e.g. 2021-01) 
 * @return array
 */
function get_week_dates($month)
{
  $start = new DateTime($month.'-01');
  $end = new DateTime();
  $end->setDate($start->format('Y'), $start->format('m'), $start->format('t'));

  $interval = DateInterval::createFromDateString('1 day');
  $period = new DatePeriod($start, $interval, $end);

  $weeks = array();
  $week_key = 0;
  $first = true;
  foreach ($period as $dt) {    
    if ($first) {
      $weeks[$week_key]['start'] = $dt->format('Y-m-d');
      $first = false;
    }

    if ($dt->format('D') == 'Sun' || $dt->format('d') == $end->format('d')) {
      $weeks[$week_key]['end'] = $dt->format('Y-m-d');
      $week_key++;
      $first = true;
    }
  }
  return $weeks;
}