class ExtensionDiscovery

class ExtensionDiscovery {
    
    /**
     * Origin directory weight: Core.
     */
    const ORIGIN_CORE = 0;
    
    /**
     * Origin directory weight: Installation profile.
     */
    const ORIGIN_PROFILE = 1;
    
    /**
     * Origin directory weight: sites/all.
     */
    const ORIGIN_SITES_ALL = 2;
    
    /**
     * Origin directory weight: Site-wide directory.
     */
    const ORIGIN_ROOT = 3;
    
    /**
     * Origin directory weight: Parent site directory of a test site environment.
     */
    const ORIGIN_PARENT_SITE = 4;
    
    /**
     * Origin directory weight: Site-specific directory.
     */
    const ORIGIN_SITE = 5;
    
    /**
     * Regular expression to match PHP function names.
     *
     * @see http://php.net/manual/functions.user-defined.php
     */
    const PHP_FUNCTION_PATTERN = '/^[a-zA-Z_\\x7f-\\xff][a-zA-Z0-9_\\x7f-\\xff]*$/';
    
    /**
     * Previously discovered files keyed by origin directory and extension type.
     *
     * @var array
     */
    protected static $files = [];
    
    /**
     * List of installation profile directories to additionally scan.
     *
     * @var array
     */
    protected $profileDirectories;
    
    /**
     * The app root for the current operation.
     *
     * @var string
     */
    protected $root;
    
    /**
     * The file cache object.
     *
     * @var \Drupal\Component\FileCache\FileCacheInterface
     */
    protected $fileCache;
    
    /**
     * The site path.
     *
     * @var string
     */
    protected $sitePath;
    
    /**
     * Constructs a new ExtensionDiscovery object.
     *
     * @param string $root
     *   The app root.
     * @param bool $use_file_cache
     *   Whether file cache should be used.
     * @param string[] $profile_directories
     *   The available profile directories
     * @param string $site_path
     *   The path to the site.
     */
    public function __construct(string $root, $use_file_cache = TRUE, array $profile_directories = NULL, string $site_path = NULL) {
        $this->root = $root;
        $this->fileCache = $use_file_cache ? FileCacheFactory::get('extension_discovery') : NULL;
        $this->profileDirectories = $profile_directories;
        $this->sitePath = $site_path;
    }
    
    /**
     * Discovers available extensions of a given type.
     *
     * Finds all extensions (modules, themes, etc) that exist on the site. It
     * searches in several locations. For instance, to discover all available
     * modules:
     * @code
     * $listing = new ExtensionDiscovery(\Drupal::root());
     * $modules = $listing->scan('module');
     * @endcode
     *
     * The following directories will be searched (in the order stated):
     * - the core directory; i.e., /core
     * - the installation profile directory; e.g., /core/profiles/standard
     * - the legacy site-wide directory; i.e., /sites/all
     * - the site-wide directory; i.e., /
     * - the site-specific directory; e.g., /sites/example.com
     *
     * To also find test modules, add
     * @code
     * $settings['extension_discovery_scan_tests'] = TRUE;
     * @endcode
     * to your settings.php.
     *
     * The information is returned in an associative array, keyed by the extension
     * name (without .info.yml extension). Extensions found later in the search
     * will take precedence over extensions found earlier - unless they are not
     * compatible with the current version of Drupal core.
     *
     * @param string $type
     *   The extension type to search for. One of 'profile', 'module', 'theme', or
     *   'theme_engine'.
     * @param bool $include_tests
     *   (optional) Whether to explicitly include or exclude test extensions. By
     *   default, test extensions are only discovered when in a test environment.
     *
     * @return \Drupal\Core\Extension\Extension[]
     *   An associative array of Extension objects, keyed by extension name.
     */
    public function scan($type, $include_tests = NULL) {
        // Determine the installation profile directories to scan for extensions,
        // unless explicit profile directories have been set. Exclude profiles as we
        // cannot have profiles within profiles.
        if (!isset($this->profileDirectories) && $type != 'profile') {
            $this->setProfileDirectoriesFromSettings();
        }
        // Search the core directory.
        $searchdirs[static::ORIGIN_CORE] = 'core';
        // Search the legacy sites/all directory.
        $searchdirs[static::ORIGIN_SITES_ALL] = 'sites/all';
        // Search for contributed and custom extensions in top-level directories.
        // The scan uses a list of extension types to limit recursion to the
        // expected extension type specific directory names only.
        $searchdirs[static::ORIGIN_ROOT] = '';
        // Simpletest uses the regular built-in multi-site functionality of Drupal
        // for running web tests. As a consequence, extensions of the parent site
        // located in a different site-specific directory are not discovered in a
        // test site environment, because the site directories are not the same.
        // Therefore, add the site directory of the parent site to the search paths,
        // so that contained extensions are still discovered.
        // @see \Drupal\Core\Test\FunctionalTestSetupTrait::prepareSettings().
        if ($parent_site = Settings::get('test_parent_site')) {
            $searchdirs[static::ORIGIN_PARENT_SITE] = $parent_site;
        }
        // Find the site-specific directory to search. Since we are using this
        // method to discover extensions including profiles, we might be doing this
        // at install time. Therefore Kernel service is not always available, but is
        // preferred.
        if (\Drupal::hasService('kernel')) {
            $searchdirs[static::ORIGIN_SITE] = \Drupal::getContainer()->getParameter('site.path');
        }
        else {
            $searchdirs[static::ORIGIN_SITE] = $this->sitePath ?: DrupalKernel::findSitePath(Request::createFromGlobals());
        }
        // Unless an explicit value has been passed, manually check whether we are
        // in a test environment, in which case test extensions must be included.
        // Test extensions can also be included for debugging purposes by setting a
        // variable in settings.php.
        if (!isset($include_tests)) {
            $include_tests = Settings::get('extension_discovery_scan_tests') || drupal_valid_test_ua();
        }
        $files = [];
        foreach ($searchdirs as $dir) {
            // Discover all extensions in the directory, unless we did already.
            if (!isset(static::$files[$this->root][$dir][$include_tests])) {
                static::$files[$this->root][$dir][$include_tests] = $this->scanDirectory($dir, $include_tests);
            }
            // Only return extensions of the requested type.
            if (isset(static::$files[$this->root][$dir][$include_tests][$type])) {
                $files += static::$files[$this->root][$dir][$include_tests][$type];
            }
        }
        // If applicable, filter out extensions that do not belong to the current
        // installation profiles.
        $files = $this->filterByProfileDirectories($files);
        // Sort the discovered extensions by their originating directories.
        $origin_weights = array_flip($searchdirs);
        $files = $this->sort($files, $origin_weights);
        // Process and return the list of extensions keyed by extension name.
        return $this->process($files);
    }
    
    /**
     * Sets installation profile directories based on current site settings.
     *
     * @return $this
     */
    public function setProfileDirectoriesFromSettings() {
        $this->profileDirectories = [];
        if ($profile = \Drupal::installProfile()) {
            $this->profileDirectories[] = \Drupal::service('extension.list.profile')->getPath($profile);
        }
        return $this;
    }
    
    /**
     * Gets the installation profile directories to be scanned.
     *
     * @return array
     *   A list of installation profile directory paths relative to the system
     *   root directory.
     */
    public function getProfileDirectories() {
        return $this->profileDirectories;
    }
    
    /**
     * Sets explicit profile directories to scan.
     *
     * @param array $paths
     *   A list of installation profile directory paths relative to the system
     *   root directory (without trailing slash) to search for extensions.
     *
     * @return $this
     */
    public function setProfileDirectories(array $paths = NULL) {
        $this->profileDirectories = $paths;
        return $this;
    }
    
    /**
     * Filters out extensions not belonging to the scanned installation profiles.
     *
     * @param \Drupal\Core\Extension\Extension[] $all_files
     *   The list of all extensions.
     *
     * @return \Drupal\Core\Extension\Extension[]
     *   The filtered list of extensions.
     */
    protected function filterByProfileDirectories(array $all_files) {
        if (empty($this->profileDirectories)) {
            return $all_files;
        }
        $all_files = array_filter($all_files, function ($file) {
            if (strpos($file->subpath, 'profiles') !== 0) {
                // This extension doesn't belong to a profile, ignore it.
                return TRUE;
            }
            foreach ($this->profileDirectories as $profile_path) {
                if (strpos($file->getPath(), $profile_path) === 0) {
                    // Parent profile found.
                    return TRUE;
                }
            }
            return FALSE;
        });
        return $all_files;
    }
    
    /**
     * Sorts the discovered extensions.
     *
     * @param \Drupal\Core\Extension\Extension[] $all_files
     *   The list of all extensions.
     * @param array $weights
     *   An array of weights, keyed by originating directory.
     *
     * @return \Drupal\Core\Extension\Extension[]
     *   The sorted list of extensions.
     */
    protected function sort(array $all_files, array $weights) {
        $origins = [];
        $profiles = [];
        foreach ($all_files as $key => $file) {
            // If the extension does not belong to a profile, just apply the weight
            // of the originating directory.
            if (strpos($file->subpath, 'profiles') !== 0) {
                $origins[$key] = $weights[$file->origin];
                $profiles[$key] = NULL;
            }
            elseif (empty($this->profileDirectories)) {
                $origins[$key] = static::ORIGIN_PROFILE;
                $profiles[$key] = NULL;
            }
            else {
                // Apply the weight of the originating profile directory.
                foreach ($this->profileDirectories as $weight => $profile_path) {
                    if (strpos($file->getPath(), $profile_path) === 0) {
                        $origins[$key] = static::ORIGIN_PROFILE;
                        $profiles[$key] = $weight;
                        continue 2;
                    }
                }
            }
        }
        // Now sort the extensions by origin and installation profile(s).
        // The result of this multisort can be depicted like the following matrix,
        // whereas the first integer is the weight of the originating directory and
        // the second is the weight of the originating installation profile:
        // 0   core/modules/node/node.module
        // 1 0 profiles/parent_profile/modules/parent_module/parent_module.module
        // 1 1 core/profiles/testing/modules/compatible_test/compatible_test.module
        // 2   sites/all/modules/common/common.module
        // 3   modules/devel/devel.module
        // 4   sites/default/modules/custom/custom.module
        array_multisort($origins, SORT_ASC, $profiles, SORT_ASC, $all_files);
        return $all_files;
    }
    
    /**
     * Processes the filtered and sorted list of extensions.
     *
     * Extensions discovered in later search paths override earlier, unless they
     * are not compatible with the current version of Drupal core.
     *
     * @param \Drupal\Core\Extension\Extension[] $all_files
     *   The sorted list of all extensions that were found.
     *
     * @return \Drupal\Core\Extension\Extension[]
     *   The filtered list of extensions, keyed by extension name.
     */
    protected function process(array $all_files) {
        $files = [];
        // Duplicate files found in later search directories take precedence over
        // earlier ones; they replace the extension in the existing $files array.
        foreach ($all_files as $file) {
            $files[$file->getName()] = $file;
        }
        return $files;
    }
    
    /**
     * Recursively scans a base directory for the extensions it contains.
     *
     * @param string $dir
     *   A relative base directory path to scan, without trailing slash.
     * @param bool $include_tests
     *   Whether to include test extensions. If FALSE, all 'tests' directories are
     *   excluded in the search.
     *
     * @return array
     *   An associative array whose keys are extension type names and whose values
     *   are associative arrays of \Drupal\Core\Extension\Extension objects, keyed
     *   by absolute path name.
     *
     * @see \Drupal\Core\Extension\Discovery\RecursiveExtensionFilterIterator
     */
    protected function scanDirectory($dir, $include_tests) {
        $files = [];
        // In order to scan top-level directories, absolute directory paths have to
        // be used (which also improves performance, since any configured PHP
        // include_paths will not be consulted). Retain the relative originating
        // directory being scanned, so relative paths can be reconstructed below
        // (all paths are expected to be relative to $this->root).
        $dir_prefix = $dir == '' ? '' : "{$dir}/";
        $absolute_dir = $dir == '' ? $this->root : $this->root . "/{$dir}";
        if (!is_dir($absolute_dir)) {
            return $files;
        }
        // Use Unix paths regardless of platform, skip dot directories, follow
        // symlinks (to allow extensions to be linked from elsewhere), and return
        // the RecursiveDirectoryIterator instance to have access to getSubPath(),
        // since SplFileInfo does not support relative paths.
        $flags = \FilesystemIterator::UNIX_PATHS;
        $flags |= \FilesystemIterator::SKIP_DOTS;
        $flags |= \FilesystemIterator::FOLLOW_SYMLINKS;
        $flags |= \FilesystemIterator::CURRENT_AS_SELF;
        $directory_iterator = new \RecursiveDirectoryIterator($absolute_dir, $flags);
        // Allow directories specified in settings.php to be ignored. You can use
        // this to not check for files in common special-purpose directories. For
        // example, node_modules and bower_components. Ignoring irrelevant
        // directories is a performance boost.
        $ignore_directories = Settings::get('file_scan_ignore_directories', []);
        // Filter the recursive scan to discover extensions only.
        // Important: Without a RecursiveFilterIterator, RecursiveDirectoryIterator
        // would recurse into the entire filesystem directory tree without any kind
        // of limitations.
        $filter = new RecursiveExtensionFilterIterator($directory_iterator, $ignore_directories);
        $filter->acceptTests($include_tests);
        // The actual recursive filesystem scan is only invoked by instantiating the
        // RecursiveIteratorIterator.
        $iterator = new \RecursiveIteratorIterator($filter, \RecursiveIteratorIterator::LEAVES_ONLY, \RecursiveIteratorIterator::CATCH_GET_CHILD);
        foreach ($iterator as $key => $fileinfo) {
            // All extension names in Drupal have to be valid PHP function names due
            // to the module hook architecture.
            if (!preg_match(static::PHP_FUNCTION_PATTERN, $fileinfo->getBasename('.info.yml'))) {
                continue;
            }
            $extension_arguments = $this->fileCache ? $this->fileCache
                ->get($fileinfo->getPathName()) : FALSE;
            // Ensure $extension_arguments is an array. Previously, the Extension
            // object was cached and now needs to be replaced with the array.
            if (empty($extension_arguments) || !is_array($extension_arguments)) {
                // Determine extension type from info file.
                $type = FALSE;
                $file = $fileinfo->openFile('r');
                while (!$type && !$file->eof()) {
                    preg_match('@^type:\\s*(\'|")?(\\w+)\\1?\\s*(?:\\#.*)?$@', $file->fgets(), $matches);
                    if (isset($matches[2])) {
                        $type = $matches[2];
                    }
                }
                if (empty($type)) {
                    continue;
                }
                $name = $fileinfo->getBasename('.info.yml');
                $pathname = $dir_prefix . $fileinfo->getSubPathname();
                // Determine whether the extension has a main extension file.
                // For theme engines, the file extension is .engine.
                if ($type == 'theme_engine') {
                    $filename = $name . '.engine';
                }
                else {
                    $filename = $name . '.' . $type;
                }
                if (!file_exists($this->root . '/' . dirname($pathname) . '/' . $filename)) {
                    $filename = NULL;
                }
                $extension_arguments = [
                    'type' => $type,
                    'pathname' => $pathname,
                    'filename' => $filename,
                    'subpath' => $fileinfo->getSubPath(),
                ];
                if ($this->fileCache) {
                    $this->fileCache
                        ->set($fileinfo->getPathName(), $extension_arguments);
                }
            }
            $extension = new Extension($this->root, $extension_arguments['type'], $extension_arguments['pathname'], $extension_arguments['filename']);
            // Track the originating directory for sorting purposes.
            $extension->subpath = $extension_arguments['subpath'];
            $extension->origin = $dir;
            $files[$extension_arguments['type']][$key] = $extension;
        }
        return $files;
    }

}