How to write recursive combination and arrangement function in PHP?

php numbers are recursively combined and arranged:
$a="123,45,6789,...";//There is no limit to the number of digits in each segment. If it is a 4-segment number, the resulting combination will be 4 digits, and so on.
Need to get the combined array:
6,4,1
6,4,2
6,4,3
6,5,1
6,5,2
6,5,3
7,4,1
7 ,4,2
7,4,3
7,5,1
7,5,2
7,5,3
8,4,1
8,4,2
8,4,3
8,5 ,1
...
Looking for php recursive function

Reply content:

php numbers are recursively combined and arranged:
$a="123,45,6789,...";//There is no limit to the number of digits in each segment. If it is a 4-segment number, the resulting combination will be 4 digits, and so on.
Need to get the combined array:
6,4,1
6,4,2
6,4,3
6,5,1
6,5,2
6,5,3
7,4,1
7 ,4,2
7,4,3
7,5,1
7,5,2
7,5,3
8,4,1
8,4,2
8,4,3
8,5 ,1
...
Looking for php recursive function

<code>function recursion($groups, $echo = '')
{
    $current = array_pop($groups);
    $end = empty($groups);

    $echo .= $echo ? ',' : '';

    foreach (str_split($current) as $item) {
        $rEcho = $echo . $item;

        if ($end) {
            echo $rEcho . "\n";
        } else {
            recursion($groups, $rEcho);
        }
    }
}

recursion(explode(',', '123,45,6789'));</code>