Prevent an link becoming double encoded in PHP

Question

I have the following URL in a MySQL database for a PHP application - part of our system allows a user to edit their previous post with these links and save - however as the url gets encoded again when a user edits this is then breaks the url as displayed below.

Is there an easy way or existing PHP function to determine if the string already has been encoded and to alter the string to remove the unwanted characters so it remains in the expected output below.

Expected output url: https://r5uy4lmtdqka6a1rzyexlusfl-902rjcrzfe6k93co7a644-tom.s3.eu-west-2.amazonaws.com/Carbon%20Monoxide/Summer%20CO%20Campaign/CO%20Summer%202022/CO%20Summer%20you%20can%20smell%20the%20BBQ%20-%20600x600.jpg

Actual output url: https://r5uy4lmtdqka6a1rzyexlusfl-902rjcrzfe6k93co7a644-tom.s3.eu-west-2.amazonaws.com/Carbon%2520Monoxide/Summer%2520CO%2520Campaign/CO%2520Summer%25202022/CO%2520Summer%2520you%2520can%2520smell%2520the%2520BBQ%2520-%2520600x600.jpg

Answer 1

As suggested in comments, double decode, then encode (only the query string part).

<?php
$str = "https://r5uy4lmtdqka6a1rzyexlusfl-902rjcrzfe6k93co7a644-tom.s3.eu-west-2.amazonaws.com/Carbon%2520Monoxide/Summer%2520CO%2520Campaign/CO%2520Summer%25202022/CO%2520Summer%2520you%2520can%2520smell%2520the%2520BBQ%2520-%2520600x600.jpg";
$str = "https://r5uy4lmtdqka6a1rzyexlusfl-902rjcrzfe6k93co7a644-tom.s3.eu-west-2.amazonaws.com/Carbon%20Monoxide/Summer%20CO%20Campaign/CO%20Summer%202022/CO%20Summer%20you%20can%20smell%20the%20BBQ%20-%20600x600.jpg";

function fix_url($str)
{
    $arr = explode('/', $str, 4);
    $qs = $arr[3]; // add if at all check?

    while (true) {
        $decoded = urldecode($qs);
        if ($decoded == $qs) {
            break;
        }
        $qs = $decoded;
    }
    $encoded = urlencode($decoded);
    $result = $arr[0] . '//' . $arr[2] . $encoded;
    return $result;
}

echo fix_url($str);