class UpdateRegistry

class UpdateRegistry {
    
    /**
     * The used update name.
     *
     * @var string
     */
    protected $updateType = 'post_update';
    
    /**
     * The app root.
     *
     * @var string
     */
    protected $root;
    
    /**
     * The filename of the log file.
     *
     * @var string
     */
    protected $logFilename;
    
    /**
     * @var string[]
     */
    protected $enabledModules;
    
    /**
     * The key value storage.
     *
     * @var \Drupal\Core\KeyValueStore\KeyValueStoreInterface
     */
    protected $keyValue;
    
    /**
     * Should we respect update functions in tests.
     *
     * @var bool|null
     */
    protected $includeTests = NULL;
    
    /**
     * The site path.
     *
     * @var string
     */
    protected $sitePath;
    
    /**
     * Constructs a new UpdateRegistry.
     *
     * @param string $root
     *   The app root.
     * @param string $site_path
     *   The site path.
     * @param string[] $enabled_modules
     *   A list of enabled modules.
     * @param \Drupal\Core\KeyValueStore\KeyValueStoreInterface $key_value
     *   The key value store.
     * @param bool|null $include_tests
     *   (optional) A flag whether to include tests in the scanning of modules.
     */
    public function __construct($root, $site_path, array $enabled_modules, KeyValueStoreInterface $key_value, $include_tests = NULL) {
        $this->root = $root;
        $this->sitePath = $site_path;
        $this->enabledModules = $enabled_modules;
        $this->keyValue = $key_value;
        $this->includeTests = $include_tests;
    }
    
    /**
     * Gets removed hook_post_update_NAME() implementations for a module.
     *
     * @return string[]
     *   A list of post-update functions that have been removed.
     */
    public function getRemovedPostUpdates($module) {
        $this->scanExtensionsAndLoadUpdateFiles();
        $function = "{$module}_removed_post_updates";
        if (function_exists($function)) {
            return $function();
        }
        return [];
    }
    
    /**
     * Gets all available update functions.
     *
     * @return callable[]
     *   A list of update functions.
     */
    protected function getAvailableUpdateFunctions() {
        $regexp = '/^(?<module>.+)_' . $this->updateType . '_(?<name>.+)$/';
        $functions = get_defined_functions();
        $updates = [];
        foreach (preg_grep('/_' . $this->updateType . '_/', $functions['user']) as $function) {
            // If this function is a module update function, add it to the list of
            // module updates.
            if (preg_match($regexp, $function, $matches)) {
                if (in_array($matches['module'], $this->enabledModules)) {
                    $function_name = $matches['module'] . '_' . $this->updateType . '_' . $matches['name'];
                    if ($this->updateType === 'post_update') {
                        $removed = array_keys($this->getRemovedPostUpdates($matches['module']));
                        if (array_search($function_name, $removed) !== FALSE) {
                            throw new RemovedPostUpdateNameException(sprintf('The following update is specified as removed in hook_removed_post_updates() but still exists in the code base: %s', $function_name));
                        }
                    }
                    $updates[] = $function_name;
                }
            }
        }
        // Ensure that the update order is deterministic.
        sort($updates);
        return $updates;
    }
    
    /**
     * Find all update functions that haven't been executed.
     *
     * @return callable[]
     *   A list of update functions.
     */
    public function getPendingUpdateFunctions() {
        // We need a) the list of active modules (we get that from the config
        // bootstrap factory) and b) the path to the modules, we use the extension
        // discovery for that.
        $this->scanExtensionsAndLoadUpdateFiles();
        // First figure out which hook_{$this->updateType}_NAME got executed
        // already.
        $existing_update_functions = $this->keyValue
            ->get('existing_updates', []);
        $available_update_functions = $this->getAvailableUpdateFunctions();
        $not_executed_update_functions = array_diff($available_update_functions, $existing_update_functions);
        return $not_executed_update_functions;
    }
    
    /**
     * Loads all update files for a given list of extension.
     *
     * @param \Drupal\Core\Extension\Extension[] $module_extensions
     *   The extensions used for loading.
     */
    protected function loadUpdateFiles(array $module_extensions) {
        // Load all the {$this->updateType}.php files.
        foreach ($this->enabledModules as $module) {
            if (isset($module_extensions[$module])) {
                $this->loadUpdateFile($module_extensions[$module]);
            }
        }
    }
    
    /**
     * Loads the {$this->updateType}.php file for a given extension.
     *
     * @param \Drupal\Core\Extension\Extension $module
     *   The extension of the module to load its file.
     */
    protected function loadUpdateFile(Extension $module) {
        $filename = $this->root . '/' . $module->getPath() . '/' . $module->getName() . ".{$this->updateType}.php";
        if (file_exists($filename)) {
            include_once $filename;
        }
    }
    
    /**
     * Returns a list of all the pending updates.
     *
     * @return array[]
     *   An associative array keyed by module name which contains all information
     *   about database updates that need to be run, and any updates that are not
     *   going to proceed due to missing requirements.
     *
     *   The subarray for each module can contain the following keys:
     *   - start: The starting update that is to be processed. If this does not
     *       exist then do not process any updates for this module as there are
     *       other requirements that need to be resolved.
     *   - pending: An array of all the pending updates for the module including
     *       the description from source code comment for each update function.
     *       This array is keyed by the update name.
     */
    public function getPendingUpdateInformation() {
        $functions = $this->getPendingUpdateFunctions();
        $ret = [];
        foreach ($functions as $function) {
            list($module, $update) = explode("_{$this->updateType}_", $function);
            // The description for an update comes from its Doxygen.
            $func = new \ReflectionFunction($function);
            $description = trim(str_replace([
                "\n",
                '*',
                '/',
            ], '', $func->getDocComment()), ' ');
            $ret[$module]['pending'][$update] = $description;
            if (!isset($ret[$module]['start'])) {
                $ret[$module]['start'] = $update;
            }
        }
        return $ret;
    }
    
    /**
     * Registers that update functions were executed.
     *
     * @param string[] $function_names
     *   The executed update functions.
     *
     * @return $this
     */
    public function registerInvokedUpdates(array $function_names) {
        $executed_updates = $this->keyValue
            ->get('existing_updates', []);
        $executed_updates = array_merge($executed_updates, $function_names);
        $this->keyValue
            ->set('existing_updates', $executed_updates);
        return $this;
    }
    
    /**
     * Returns all available updates for a given module.
     *
     * @param string $module_name
     *   The module name.
     *
     * @return callable[]
     *   A list of update functions.
     */
    public function getModuleUpdateFunctions($module_name) {
        $this->scanExtensionsAndLoadUpdateFiles();
        $all_functions = $this->getAvailableUpdateFunctions();
        return array_filter($all_functions, function ($function_name) use ($module_name) {
            list($function_module_name, ) = explode("_{$this->updateType}_", $function_name);
            return $function_module_name === $module_name;
        });
    }
    
    /**
     * Scans all module + profile extensions and load the update files.
     */
    protected function scanExtensionsAndLoadUpdateFiles() {
        // Scan the module list.
        $extension_discovery = new ExtensionDiscovery($this->root, FALSE, [], $this->sitePath);
        $module_extensions = $extension_discovery->scan('module');
        $profile_extensions = $extension_discovery->scan('profile');
        $extensions = array_merge($module_extensions, $profile_extensions);
        $this->loadUpdateFiles($extensions);
    }
    
    /**
     * Filters out already executed update functions by module.
     *
     * @param string $module
     *   The module name.
     */
    public function filterOutInvokedUpdatesByModule($module) {
        $existing_update_functions = $this->keyValue
            ->get('existing_updates', []);
        $remaining_update_functions = array_filter($existing_update_functions, function ($function_name) use ($module) {
            return strpos($function_name, "{$module}_{$this->updateType}_") !== 0;
        });
        $this->keyValue
            ->set('existing_updates', array_values($remaining_update_functions));
    }

}