Validator.php

<?php
/**
 * Copyright © Magento, Inc. All rights reserved.
 * See COPYING.txt for license details.
 */

namespace Magento\Theme\Model\Design\Config;

use \Magento\Framework\Exception\LocalizedException;
use \Magento\Theme\Api\Data\DesignConfigInterface;
use \Magento\Theme\Api\Data\DesignConfigDataInterface;
use \Magento\Framework\Mail\TemplateInterfaceFactory as TemplateFactory;
use \Magento\Framework\Filter\Template;
use \Magento\Framework\Filter\Template\Tokenizer\Parameter as ParameterTokenizer;

/**
 * Design configuration validator
 */
class Validator
{
    /**
     * @var string[]
     */
    private $fields = [];

    /**
     * @var TemplateFactory
     */
    private $templateFactory;

    /**
     * Initialize dependencies.
     *
     * @param TemplateFactory $templateFactory
     * @param string[] $fields
     */
    public function __construct(TemplateFactory $templateFactory, $fields = [])
    {
        $this->templateFactory = $templateFactory;
        $this->fields = $fields;
    }

    /**
     * Validate if design configuration has recursive references
     *
     * @param DesignConfigInterface $designConfig
     *
     * @throws LocalizedException
     * @return void
     */
    public function validate(DesignConfigInterface $designConfig)
    {
        /** @var DesignConfigDataInterface[] $designConfigData */
        $designConfigData = $designConfig->getExtensionAttributes()->getDesignConfigData();
        $elements = [];
        foreach ($designConfigData as $designElement) {
            if (!in_array($designElement->getFieldConfig()['field'], $this->fields)) {
                continue;
            }
            /* Save mapping between field names and config paths */
            $elements[$designElement->getFieldConfig()['field']] = [
                'config_path' => $designElement->getPath(),
                'value' => $designElement->getValue()
            ];
        }

        foreach ($elements as $name => $data) {
            $templateId = $data['value'];
            $text = $this->getTemplateText($templateId, $designConfig);
            // Check if template body has a reference to the same config path
            if (preg_match_all(Template::CONSTRUCTION_TEMPLATE_PATTERN, $text, $constructions, PREG_SET_ORDER)) {
                foreach ($constructions as $construction) {
                    $configPath = isset($construction[2]) ? $construction[2] : '';
                    $params = $this->getParameters($configPath);
                    if (isset($params['config_path']) && $params['config_path'] == $data['config_path']) {
                        throw new LocalizedException(
                            __(
                                'The "%templateName" template contains an incorrect configuration, with a reference '
                                . 'to itself. Remove or change the reference, then try again.',
                                ["templateName" => $name]
                            )
                        );
                    }
                }
            }
        }
    }

    /**
     * Returns store identifier if is store scope
     *
     * @param DesignConfigInterface $designConfig
     * @return string|bool
     */
    private function getScopeId(DesignConfigInterface $designConfig)
    {
        if ($designConfig->getScope() == 'stores') {
            return $designConfig->getScopeId();
        }
        return false;
    }
    /**
     * Load template text in configured scope
     *
     * @param integer|string $templateId
     * @param DesignConfigInterface $designConfig
     * @return string
     */
    private function getTemplateText($templateId, DesignConfigInterface $designConfig)
    {
        // Load template object by configured template id
        $template = $this->templateFactory->create();
        $template->emulateDesign($this->getScopeId($designConfig));
        if (is_numeric($templateId)) {
            $template->load($templateId);
        } else {
            $template->setForcedArea($templateId);
            $template->loadDefault($templateId);
        }
        $text = $template->getTemplateText();
        $template->revertDesign();
        return $text;
    }

    /**
     * Return associative array of parameters.
     *
     * @param string $value raw parameters
     * @return array
     */
    private function getParameters($value)
    {
        $tokenizer = new ParameterTokenizer();
        $tokenizer->setString($value);
        $params = $tokenizer->tokenize();
        return $params;
    }
}