Parses query string

parser.php

<?php

$str = "/v1/combinedObjects:(id,user_id,value,title,person:(id,name,activities_count,owner_id:(name),activities_count),organization:(id,name))";

print_r(queryParser($str));

function queryParser($query){
    
    // split tokens
    $tokens = preg_split('/,|(?=:\\(|\\))|(?<=:\\(|\\))/', $query, -1, PREG_SPLIT_NO_EMPTY);
    array_shift($tokens);

    // current level elements
    $node = array();

    // parents for recursion
    $path = array();

    // placeholder for closed node 
    $last = false;

    // current key name
    $key = false;

    foreach($tokens as $i => $token){
        switch($token){

            // go one level deeper, save current level to $path and open a new one
            case ":(":
                $path[] = array($key, $node);
                $node = array();
                break;

            // close current level, go up one step and store current list to parent level
            case ")":
                $last = $node;
                list($key, $node) = array_pop($path);
                
                if(!count($node) && !$key){
                    $node = $last;
                }else{
                    $node[] = array("key" => $key, "fields" => $last);    
                }
                break;

            // if next element is :( then this is a key, otherwise append to current level
            default:
                if($tokens[$i + 1] == ":("){
                    $key = $token;    
                }else{
                    $node[] = $token;    
                }
                break;
        }
    }

    return $node;
}

print_r

Array
(
    [0] => id
    [1] => user_id
    [2] => value
    [3] => title
    [4] => Array
        (
            [key] => person
            [fields] => Array
                (
                    [0] => id
                    [1] => name
                    [2] => activities_count
                    [3] => Array
                        (
                            [key] => owner_id
                            [fields] => Array
                                (
                                    [0] => name
                                )

                        )

                    [4] => activities_count
                )

        )

    [5] => Array
        (
            [key] => organization
            [fields] => Array
                (
                    [0] => id
                    [1] => name
                )

        )

)