class HelpTopicDiscovery

class HelpTopicDiscovery implements DiscoveryInterface {
    use DiscoveryTrait;
    
    /**
     * Defines the key in the discovered data where the file path is stored.
     */
    const FILE_KEY = '_discovered_file_path';
    
    /**
     * An array of directories to scan, keyed by the provider.
     *
     * The value can either be a string or an array of strings. The string values
     * should be the path of a directory to scan.
     *
     * @var array
     */
    protected $directories = [];
    
    /**
     * Constructs a HelpTopicDiscovery object.
     *
     * @param array $directories
     *   An array of directories to scan, keyed by the provider. The value can
     *   either be a string or an array of strings. The string values should be
     *   the path of a directory to scan.
     */
    public function __construct(array $directories) {
        $this->directories = $directories;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getDefinitions() {
        $plugins = $this->findAll();
        // Flatten definitions into what's expected from plugins.
        $definitions = [];
        foreach ($plugins as $list) {
            foreach ($list as $id => $definition) {
                $definitions[$id] = $definition;
            }
        }
        return $definitions;
    }
    
    /**
     * Returns an array of discoverable items.
     *
     * @return array
     *   An array of discovered data keyed by provider.
     *
     * @throws \Drupal\Component\Discovery\DiscoveryException
     *   Exception thrown if there is a problem during discovery.
     */
    public function findAll() {
        $all = [];
        $files = $this->findFiles();
        $file_cache = FileCacheFactory::get('help_topic_discovery:help_topics');
        // Try to load from the file cache first.
        foreach ($file_cache->getMultiple(array_keys($files)) as $file => $data) {
            $all[$files[$file]][$data['id']] = $data;
            unset($files[$file]);
        }
        // If there are files left that were not returned from the cache, load and
        // parse them now. This list was flipped above and is keyed by filename.
        if ($files) {
            foreach ($files as $file => $provider) {
                $plugin_id = substr(basename($file), 0, -10);
                // The plugin ID begins with provider.
                list($file_name_provider, ) = explode('.', $plugin_id, 2);
                // Only the Help Topics module can provide help for other extensions.
                // @todo https://www.drupal.org/project/drupal/issues/3072312 Remove
                //   help_topics special case once Help Topics is stable and core
                //   modules can provide their own help topics.
                if ($provider !== 'help_topics' && $provider !== $file_name_provider) {
                    throw new DiscoveryException("{$file} file name should begin with '{$provider}'");
                }
                $data = [
                    // The plugin ID is derived from the filename. The extension
                    // '.html.twig' is removed.
'id' => $plugin_id,
                    'provider' => $file_name_provider,
                    'class' => HelpTopicTwig::class,
                    static::FILE_KEY => $file,
                ];
                // Get the rest of the plugin definition from front matter contained in
                // the help topic Twig file.
                try {
                    $front_matter = FrontMatter::load(file_get_contents($file), Yaml::class)->getData();
                } catch (InvalidDataTypeException $e) {
                    throw new DiscoveryException(sprintf('Malformed YAML in help topic "%s": %s.', $file, $e->getMessage()));
                }
                foreach ($front_matter as $key => $value) {
                    switch ($key) {
                        case 'related':
                            if (!is_array($value)) {
                                throw new DiscoveryException("{$file} contains invalid value for 'related' key, the value must be an array of strings");
                            }
                            $data[$key] = $value;
                            break;
                        case 'top_level':
                            if (!is_bool($value)) {
                                throw new DiscoveryException("{$file} contains invalid value for 'top_level' key, the value must be a Boolean");
                            }
                            $data[$key] = $value;
                            break;
                        case 'label':
                            $data[$key] = new TranslatableMarkup($value);
                            break;
                        default:
                            throw new DiscoveryException("{$file} contains invalid key='{$key}'");
                    }
                }
                if (!isset($data['label'])) {
                    throw new DiscoveryException("{$file} does not contain the required key with name='label'");
                }
                $all[$provider][$data['id']] = $data;
                $file_cache->set($file, $data);
            }
        }
        return $all;
    }
    
    /**
     * Returns an array of providers keyed by file path.
     *
     * @return array
     *   An array of providers keyed by file path.
     */
    protected function findFiles() {
        $file_list = [];
        foreach ($this->directories as $provider => $directories) {
            $directories = (array) $directories;
            foreach ($directories as $directory) {
                if (is_dir($directory)) {
                    
                    /** @var \SplFileInfo $fileInfo */
                    $iterator = new RegexDirectoryIterator($directory, '/\\.html\\.twig$/i');
                    foreach ($iterator as $fileInfo) {
                        $file_list[$fileInfo->getPathname()] = $provider;
                    }
                }
            }
        }
        return $file_list;
    }

}