class LibraryDiscoveryCollector

class LibraryDiscoveryCollector extends CacheCollector {
    
    /**
     * The library discovery parser.
     *
     * @var \Drupal\Core\Asset\LibraryDiscoveryParser
     */
    protected $discoveryParser;
    
    /**
     * The theme manager.
     *
     * @var \Drupal\Core\Theme\ThemeManagerInterface
     */
    protected $themeManager;
    
    /**
     * Constructs a CacheCollector object.
     *
     * @param \Drupal\Core\Cache\CacheBackendInterface $cache
     *   The cache backend.
     * @param \Drupal\Core\Lock\LockBackendInterface $lock
     *   The lock backend.
     * @param \Drupal\Core\Asset\LibraryDiscoveryParser $discovery_parser
     *   The library discovery parser.
     * @param \Drupal\Core\Theme\ThemeManagerInterface $theme_manager
     *   The theme manager.
     */
    public function __construct(CacheBackendInterface $cache, LockBackendInterface $lock, LibraryDiscoveryParser $discovery_parser, ThemeManagerInterface $theme_manager) {
        $this->themeManager = $theme_manager;
        parent::__construct(NULL, $cache, $lock, [
            'library_info',
        ]);
        $this->discoveryParser = $discovery_parser;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getCid() {
        if (!isset($this->cid)) {
            $this->cid = 'library_info:' . $this->themeManager
                ->getActiveTheme()
                ->getName();
        }
        return $this->cid;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function resolveCacheMiss($key) {
        $this->storage[$key] = $this->getLibraryDefinitions($key);
        $this->persist($key);
        return $this->storage[$key];
    }
    
    /**
     * Returns the library definitions for a given extension.
     *
     * This also implements libraries-overrides for entire libraries that have
     * been specified by the LibraryDiscoveryParser.
     *
     * @param string $extension
     *   The name of the extension for which library definitions will be returned.
     *
     * @return array
     *   The library definitions for $extension with overrides applied.
     *
     * @throws \Drupal\Core\Asset\Exception\InvalidLibrariesOverrideSpecificationException
     */
    protected function getLibraryDefinitions($extension) {
        $libraries = $this->discoveryParser
            ->buildByExtension($extension);
        foreach ($libraries as $name => $definition) {
            // Handle libraries that are marked for override or removal.
            // @see \Drupal\Core\Asset\LibraryDiscoveryParser::applyLibrariesOverride()
            if (isset($definition['override'])) {
                if ($definition['override'] === FALSE) {
                    // Remove the library definition if FALSE is given.
                    unset($libraries[$name]);
                }
                else {
                    // Otherwise replace with existing library definition if it exists.
                    // Throw an exception if it doesn't.
                    list($replacement_extension, $replacement_name) = explode('/', $definition['override']);
                    $replacement_definition = $this->get($replacement_extension);
                    if (isset($replacement_definition[$replacement_name])) {
                        $libraries[$name] = $replacement_definition[$replacement_name];
                    }
                    else {
                        throw new InvalidLibrariesOverrideSpecificationException(sprintf('The specified library %s does not exist.', $definition['override']));
                    }
                }
            }
            else {
                // If libraries are not overridden, then apply libraries-extend.
                $libraries[$name] = $this->applyLibrariesExtend($extension, $name, $definition);
            }
        }
        return $libraries;
    }
    
    /**
     * Applies the libraries-extend specified by the active theme.
     *
     * This extends the library definitions with the those specified by the
     * libraries-extend specifications for the active theme.
     *
     * @param string $extension
     *   The name of the extension for which library definitions will be extended.
     * @param string $library_name
     *   The name of the library whose definitions is to be extended.
     * @param $library_definition
     *   The library definition to be extended.
     *
     * @return array
     *   The library definition extended as specified by libraries-extend.
     *
     * @throws \Drupal\Core\Asset\Exception\InvalidLibrariesExtendSpecificationException
     */
    protected function applyLibrariesExtend($extension, $library_name, $library_definition) {
        $libraries_extend = $this->themeManager
            ->getActiveTheme()
            ->getLibrariesExtend();
        if (!empty($libraries_extend["{$extension}/{$library_name}"])) {
            foreach ($libraries_extend["{$extension}/{$library_name}"] as $library_extend_name) {
                if (!is_string($library_extend_name)) {
                    // Only string library names are allowed.
                    throw new InvalidLibrariesExtendSpecificationException('The libraries-extend specification for each library must be a list of strings.');
                }
                list($new_extension, $new_library_name) = explode('/', $library_extend_name, 2);
                $new_libraries = $this->get($new_extension);
                if (isset($new_libraries[$new_library_name])) {
                    $library_definition = NestedArray::mergeDeep($library_definition, $new_libraries[$new_library_name]);
                }
                else {
                    throw new InvalidLibrariesExtendSpecificationException(sprintf('The specified library "%s" does not exist.', $library_extend_name));
                }
            }
        }
        return $library_definition;
    }
    
    /**
     * {@inheritdoc}
     */
    public function reset() {
        parent::reset();
        $this->cid = NULL;
    }

}