<?php
/**
 * This function gets a calendar from the selected month of the selected year.
 * It's calculating the week number from the first and the last day of the month,
 * starting with the first day of the first week number of the current month
 * and ends with the last day of the last week number of the current month.
 *
 * @author Joel Bladt<joel@bladt.de>
 * @param int $month
 * @param null|int $year
 * @return array
 */
function getCalendarOfMonth(int $month, int $year = null): array {
  $dt = new \DateTime();

  $year  = (int) (is_null($year)) ? $dt->format('Y') : $year;
  $last  = (int) $dt->setDate($year, $month + 1, 0)->format('W');
  $first = (int) $dt->setDate($year, $month, 1)->format('W');

  $first = ($first > $last) ? 0 : $first;

  for (; $first <= $last; $first++) {
    $dt->setISODate($year, $first);

    for ($i = 0; $i < 7; $i++) {
      if ($i > 0) {
        $dt->modify('+1 day');
      }

      $result[] = $dt->format('d.m.Y');
    }
  }

  return $result;
}