PathStringToTree.php

<?php

/**
 *  Convert Path String to Tree
 *  see https://www.gnu.org/software/bash/manual/html_node/Brace-Expansion.html
 *
 */

function convertPathsStringToTree(string $dataPathsString): array
{
    $tree = [];
    $stack = [&$tree];
    $exitStackFrames = [0];
    $dataPathsString = str_replace(' ', '',$dataPathsString);
    $tokens = preg_split('~(/|[,{}])~', $dataPathsString, -1, PREG_SPLIT_DELIM_CAPTURE | PREG_SPLIT_NO_EMPTY);

    if ($errors = validatePathsTokens($tokens)) {
        throw new Exception('Invalid data paths format: '. implode(', ', $errors));
    }

    foreach ($tokens as $token) {
        $current = &$stack[array_key_last($stack)];
        switch ($token) {
            case '/':
                $current['children'] = [];
                $stack[] = &$current['children'];
                break;
            case '{':
                $exitStackFrames[] = array_key_last($stack);
                break;
            case '}':
                array_pop($exitStackFrames);
                break;
            case ',':
                $exitStackFrame = $exitStackFrames[array_key_last($exitStackFrames)];
                $stack = array_slice($stack, 0, $exitStackFrame + 1, true);
                break;
            default:
                $current[$token] = ['propertyName' => $token];
                $stack[] = &$current[$token];
                break;
        }
    }

    return $tree;
}

function validatePathsTokens(array $tokens): array
{
    $errors = [];
    foreach ($tokens as $token) {
        $tokenType = in_array($token, ['/', '{','}',',']) ? $token : 'propertyName';
        if (isset($prevTokenType)) {
            if ($tokenType !== ',' && $prevTokenType === '}') {
                $errors[] = 'A closing brace } must be followed by a comma or be at the end.';
            }

            if ($tokenType === ',' && $prevTokenType !== '/' && $prevTokenType !== '}') {
                $errors[] = 'Syntax Error: A comma is allowed only after an element or a closing brace }';
            }

            if ($tokenType === '/' && $prevTokenType !== 'propertyName') {
                $errors[] = 'Syntax Error: The / operator must be preceded by an element.';
            }

            if ($tokenType === '{' && $prevTokenType !== '/') {
                $errors[] = 'Syntax Error: An opening brace { must be preceded by /.';
            }
        } elseif ($tokenType !== 'propertyName') {
            $errors[] = 'Syntax Error: The first element in the data paths string must be a propertyName.';
        }
        $prevTokenType = $tokenType;
    }

    return $errors;
}