class DefaultPluginManager

class DefaultPluginManager extends PluginManagerBase implements PluginManagerInterface, CachedDiscoveryInterface, CacheableDependencyInterface {
    use DiscoveryCachedTrait;
    use UseCacheBackendTrait;
    
    /**
     * The cache key.
     *
     * @var string
     */
    protected $cacheKey;
    
    /**
     * An array of cache tags to use for the cached definitions.
     *
     * @var array
     */
    protected $cacheTags = [];
    
    /**
     * Name of the alter hook if one should be invoked.
     *
     * @var string
     */
    protected $alterHook;
    
    /**
     * The subdirectory within a namespace to look for plugins.
     *
     * Set to FALSE if the plugins are in the top level of the namespace.
     *
     * @var string|bool
     */
    protected $subdir;
    
    /**
     * The module handler to invoke the alter hook.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * A set of defaults to be referenced by $this->processDefinition().
     *
     * Allows for additional processing of plugins when necessary or helpful for
     * development purposes.
     *
     * @var array
     */
    protected $defaults = [];
    
    /**
     * The name of the annotation that contains the plugin definition.
     *
     * @var string
     */
    protected $pluginDefinitionAnnotationName;
    
    /**
     * The interface each plugin should implement.
     *
     * @var string|null
     */
    protected $pluginInterface;
    
    /**
     * An object of root paths that are traversable.
     *
     * The root paths are keyed by the corresponding namespace to look for plugin
     * implementations.
     *
     * @var \Traversable
     */
    protected $namespaces;
    
    /**
     * Additional annotation namespaces.
     *
     * The annotation discovery mechanism should scan these for annotation
     * definitions.
     *
     * @var string[]
     */
    protected $additionalAnnotationNamespaces = [];
    
    /**
     * Creates the discovery object.
     *
     * @param string|bool $subdir
     *   The plugin's subdirectory, for example Plugin/views/filter.
     * @param \Traversable $namespaces
     *   An object that implements \Traversable which contains the root paths
     *   keyed by the corresponding namespace to look for plugin implementations.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     * @param string|null $plugin_interface
     *   (optional) The interface each plugin should implement.
     * @param string $plugin_definition_annotation_name
     *   (optional) The name of the annotation that contains the plugin definition.
     *   Defaults to 'Drupal\Component\Annotation\Plugin'.
     * @param string[] $additional_annotation_namespaces
     *   (optional) Additional namespaces to scan for annotation definitions.
     */
    public function __construct($subdir, \Traversable $namespaces, ModuleHandlerInterface $module_handler, $plugin_interface = NULL, $plugin_definition_annotation_name = 'Drupal\\Component\\Annotation\\Plugin', array $additional_annotation_namespaces = []) {
        $this->subdir = $subdir;
        $this->namespaces = $namespaces;
        $this->pluginDefinitionAnnotationName = $plugin_definition_annotation_name;
        $this->pluginInterface = $plugin_interface;
        $this->moduleHandler = $module_handler;
        $this->additionalAnnotationNamespaces = $additional_annotation_namespaces;
    }
    
    /**
     * Initialize the cache backend.
     *
     * Plugin definitions are cached using the provided cache backend.
     *
     * @param \Drupal\Core\Cache\CacheBackendInterface $cache_backend
     *   Cache backend instance to use.
     * @param string $cache_key
     *   Cache key prefix to use.
     * @param array $cache_tags
     *   (optional) When providing a list of cache tags, the cached plugin
     *   definitions are tagged with the provided cache tags. These cache tags can
     *   then be used to clear the corresponding cached plugin definitions. Note
     *   that this should be used with care! For clearing all cached plugin
     *   definitions of a plugin manager, call that plugin manager's
     *   clearCachedDefinitions() method. Only use cache tags when cached plugin
     *   definitions should be cleared along with other, related cache entries.
     */
    public function setCacheBackend(CacheBackendInterface $cache_backend, $cache_key, array $cache_tags = []) {
        assert(Inspector::assertAllStrings($cache_tags), 'Cache Tags must be strings.');
        $this->cacheBackend = $cache_backend;
        $this->cacheKey = $cache_key;
        $this->cacheTags = $cache_tags;
    }
    
    /**
     * Sets the alter hook name.
     *
     * @param string $alter_hook
     *   Name of the alter hook; for example, to invoke
     *   hook_mymodule_data_alter() pass in "mymodule_data".
     */
    protected function alterInfo($alter_hook) {
        $this->alterHook = $alter_hook;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getDefinitions() {
        $definitions = $this->getCachedDefinitions();
        if (!isset($definitions)) {
            $definitions = $this->findDefinitions();
            $this->setCachedDefinitions($definitions);
        }
        return $definitions;
    }
    
    /**
     * {@inheritdoc}
     */
    public function clearCachedDefinitions() {
        if ($this->cacheBackend) {
            if ($this->cacheTags) {
                // Use the cache tags to clear the cache.
                Cache::invalidateTags($this->cacheTags);
            }
            else {
                $this->cacheBackend
                    ->delete($this->cacheKey);
            }
        }
        $this->definitions = NULL;
    }
    
    /**
     * Returns the cached plugin definitions of the decorated discovery class.
     *
     * @return array|null
     *   On success this will return an array of plugin definitions. On failure
     *   this should return NULL, indicating to other methods that this has not
     *   yet been defined. Success with no values should return as an empty array
     *   and would actually be returned by the getDefinitions() method.
     */
    protected function getCachedDefinitions() {
        if (!isset($this->definitions) && ($cache = $this->cacheGet($this->cacheKey))) {
            $this->definitions = $cache->data;
        }
        return $this->definitions;
    }
    
    /**
     * Sets a cache of plugin definitions for the decorated discovery class.
     *
     * @param array $definitions
     *   List of definitions to store in cache.
     */
    protected function setCachedDefinitions($definitions) {
        $this->cacheSet($this->cacheKey, $definitions, Cache::PERMANENT, $this->cacheTags);
        $this->definitions = $definitions;
    }
    
    /**
     * {@inheritdoc}
     */
    public function useCaches($use_caches = FALSE) {
        $this->useCaches = $use_caches;
        if (!$use_caches) {
            $this->definitions = NULL;
        }
    }
    
    /**
     * Performs extra processing on plugin definitions.
     *
     * By default we add defaults for the type to the definition. If a type has
     * additional processing logic they can do that by replacing or extending the
     * method.
     */
    public function processDefinition(&$definition, $plugin_id) {
        // Only array-based definitions can have defaults merged in.
        if (is_array($definition) && !empty($this->defaults) && is_array($this->defaults)) {
            $definition = NestedArray::mergeDeep($this->defaults, $definition);
        }
        // Keep class definitions standard with no leading slash.
        if ($definition instanceof PluginDefinitionInterface) {
            assert(is_string($definition->getClass()), 'Plugin definitions must have a class');
            $definition->setClass(ltrim($definition->getClass(), '\\'));
        }
        elseif (is_array($definition) && isset($definition['class'])) {
            $definition['class'] = ltrim($definition['class'], '\\');
        }
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getDiscovery() {
        if (!$this->discovery) {
            $discovery = new AnnotatedClassDiscovery($this->subdir, $this->namespaces, $this->pluginDefinitionAnnotationName, $this->additionalAnnotationNamespaces);
            $this->discovery = new ContainerDerivativeDiscoveryDecorator($discovery);
        }
        return $this->discovery;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getFactory() {
        if (!$this->factory) {
            $this->factory = new ContainerFactory($this, $this->pluginInterface);
        }
        return $this->factory;
    }
    
    /**
     * Finds plugin definitions.
     *
     * @return array
     *   List of definitions to store in cache.
     */
    protected function findDefinitions() {
        $definitions = $this->getDiscovery()
            ->getDefinitions();
        foreach ($definitions as $plugin_id => &$definition) {
            $this->processDefinition($definition, $plugin_id);
        }
        $this->alterDefinitions($definitions);
        // If this plugin was provided by a module that does not exist, remove the
        // plugin definition.
        foreach ($definitions as $plugin_id => $plugin_definition) {
            $provider = $this->extractProviderFromDefinition($plugin_definition);
            if ($provider && !in_array($provider, [
                'core',
                'component',
            ]) && !$this->providerExists($provider)) {
                unset($definitions[$plugin_id]);
            }
        }
        return $definitions;
    }
    
    /**
     * Extracts the provider from a plugin definition.
     *
     * @param mixed $plugin_definition
     *   The plugin definition. Usually either an array or an instance of
     *   \Drupal\Component\Plugin\Definition\PluginDefinitionInterface
     *
     * @return string|null
     *   The provider string, if it exists. NULL otherwise.
     */
    protected function extractProviderFromDefinition($plugin_definition) {
        if ($plugin_definition instanceof PluginDefinitionInterface) {
            return $plugin_definition->getProvider();
        }
        // Attempt to convert the plugin definition to an array.
        if (is_object($plugin_definition)) {
            $plugin_definition = (array) $plugin_definition;
        }
        if (isset($plugin_definition['provider'])) {
            return $plugin_definition['provider'];
        }
    }
    
    /**
     * Invokes the hook to alter the definitions if the alter hook is set.
     *
     * @param $definitions
     *   The discovered plugin definitions.
     */
    protected function alterDefinitions(&$definitions) {
        if ($this->alterHook) {
            $this->moduleHandler
                ->alter($this->alterHook, $definitions);
        }
    }
    
    /**
     * Determines if the provider of a definition exists.
     *
     * @return bool
     *   TRUE if provider exists, FALSE otherwise.
     */
    protected function providerExists($provider) {
        return $this->moduleHandler
            ->moduleExists($provider);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheContexts() {
        return [];
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheTags() {
        return $this->cacheTags;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getCacheMaxAge() {
        return Cache::PERMANENT;
    }

}