Задачка сортировка массива

sect_sort.php

<?php

function sect_sort($array, $start, $length = null) 
{
  $ar_start = [];
  $ar_sort = [];
  $ar_end = [];
  
  $sort_index = 0;
    
  foreach($array as $i => $element) 
  {
    if ($i < $start) {
      $ar_start[] = $element;
    } elseif (is_null($length) || (is_int($length) && $sort_index < $length)) {
      $ar_sort[] = $element;
      $sort_index++;
    } else {
      $ar_end[] = $element;
    }
  }
  
  sort($ar_sort);
  
  return array_merge($ar_start, $ar_sort, $ar_end);
}

task.txt

https://www.codewars.com/kata/58ef87dc4db9b24c6c000092/train/php

In this kata you are given an array to sort but you're expected to start sorting from a specific position of the array (in ascending order) and optionally you're given the number of items to sort.

Examples:
sect_sort([1, 2, 5, 7, 4, 6, 3, 9, 8], 2) //=> [1, 2, 3, 4, 5, 6, 7, 8, 9]
sect_sort([9, 7, 4, 2, 5, 3, 1, 8, 6], 2, 5) //=> [9, 7, 1, 2, 3, 4, 5, 8, 6]

Documentation:
sect_sort($array, $start, $length);

array - array to sort
start - position to begin sorting
length - number of items to sort (optional)

if the length argument is not passed or is zero, you sort all items to the right of the start position in the array