Audiogram - problem 1 .php

<?php
# Problem 1:

# Functions:

function previousPosition(int $current, int $shift, int $length) {
    return ($amount = $current - $shift) < 0 ? $length + $amount : $amount;
}

function rotatePrevious(array $list, int $shift, $startFrom, $replaceWith, $startRoot) {
    $currIndex = $startFrom;
    $prevIndex = previousPosition($currIndex, $shift, count($list));
    $prevElement = $list[$prevIndex];

    $list[$prevIndex] = $replaceWith;
    if ($prevIndex == $startRoot)
        return $list;
    return rotatePrevious($list, $shift, $prevIndex, $prevElement, $startRoot);
}

function rotateList(array $list, int $shift) {
    $shift = $shift % count($list);
    $i = count($list);
    while ($i > count($list) - $shift && $i != $shift) {
        $i--;
        $list = rotatePrevious($list, $shift, $i, $list[$i], $i);
    }
    return $list;
}

# Function Usage:
while (true) {
    echo 'Insert a list of strings: ';
    $stringList = fgets(fopen("php://stdin", "r"));
    $list = json_decode($stringList);

    echo 'Insert the amount of shift (k): ';
    $k = fgets(fopen('php://stdin', 'r'));

    echo json_encode(rotateList($list, (int)$k)), PHP_EOL;
}