LibraryDiscoveryParser.php

<?php

namespace Drupal\Core\Asset;

use Drupal\Component\FileCache\FileCacheFactory;
use Drupal\Component\FileCache\FileCacheInterface;
use Drupal\Component\Serialization\Exception\InvalidDataTypeException;
use Drupal\Component\Utility\NestedArray;
use Drupal\Core\Asset\Exception\IncompleteLibraryDefinitionException;
use Drupal\Core\Asset\Exception\InvalidLibrariesOverrideSpecificationException;
use Drupal\Core\Asset\Exception\InvalidLibraryFileException;
use Drupal\Core\Asset\Exception\LibraryDefinitionMissingLicenseException;
use Drupal\Core\Extension\ExtensionPathResolver;
use Drupal\Core\Extension\ModuleHandlerInterface;
use Drupal\Core\Serialization\Yaml;
use Drupal\Core\StreamWrapper\StreamWrapperManagerInterface;
use Drupal\Core\Theme\ComponentPluginManager;
use Drupal\Core\Theme\ActiveTheme;
use Drupal\Core\Theme\ThemeManagerInterface;
use Drupal\Core\Plugin\Component;

/**
 * Parses library files to get extension data.
 */
class LibraryDiscoveryParser {
    
    /**
     * The module handler.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * The theme manager.
     *
     * @var \Drupal\Core\Theme\ThemeManagerInterface
     */
    protected $themeManager;
    
    /**
     * The app root.
     *
     * @var string
     */
    protected $root;
    
    /**
     * The stream wrapper manager.
     *
     * @var \Drupal\Core\StreamWrapper\StreamWrapperManagerInterface
     */
    protected $streamWrapperManager;
    
    /**
     * The libraries directory file finder.
     *
     * @var \Drupal\Core\Asset\LibrariesDirectoryFileFinder
     */
    protected $librariesDirectoryFileFinder;
    
    /**
     * The component plugin manager.
     *
     * @var \Drupal\Core\Theme\ComponentPluginManager
     */
    protected $componentPluginManager;
    
    /**
     * The extension path resolver.
     *
     * @var \Drupal\Core\Extension\ExtensionPathResolver
     */
    protected $extensionPathResolver;
    
    /**
     * The file cache.
     *
     * @var \Drupal\Component\FileCache\FileCacheInterface
     */
    protected FileCacheInterface $fileCache;
    
    /**
     * Constructs a new LibraryDiscoveryParser instance.
     *
     * @param string $root
     *   The app root.
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     * @param \Drupal\Core\Theme\ThemeManagerInterface $theme_manager
     *   The theme manager.
     * @param \Drupal\Core\StreamWrapper\StreamWrapperManagerInterface $stream_wrapper_manager
     *   The stream wrapper manager.
     * @param \Drupal\Core\Asset\LibrariesDirectoryFileFinder $libraries_directory_file_finder
     *   The libraries directory file finder.
     * @param \Drupal\Core\Extension\ExtensionPathResolver $extension_path_resolver
     *   The extension path resolver.
     * @param \Drupal\Core\Theme\ComponentPluginManager|null $component_plugin_manager
     *   The component plugin manager.
     */
    public function __construct($root, ModuleHandlerInterface $module_handler, ThemeManagerInterface $theme_manager, StreamWrapperManagerInterface $stream_wrapper_manager, LibrariesDirectoryFileFinder $libraries_directory_file_finder, ExtensionPathResolver $extension_path_resolver, ?ComponentPluginManager $component_plugin_manager = NULL) {
        $this->root = $root;
        $this->moduleHandler = $module_handler;
        $this->themeManager = $theme_manager;
        $this->streamWrapperManager = $stream_wrapper_manager;
        $this->librariesDirectoryFileFinder = $libraries_directory_file_finder;
        $this->extensionPathResolver = $extension_path_resolver;
        $this->fileCache = FileCacheFactory::get('library_parser');
        if (!isset($component_plugin_manager)) {
            @trigger_error('Calling ' . __METHOD__ . '() without the $component_plugin_manager argument is deprecated in drupal:10.3.0 and will be required in drupal:11.0.0. See https://www.drupal.org/node/3410260', E_USER_DEPRECATED);
            $component_plugin_manager = \Drupal::service('plugin.manager.sdc');
        }
        $this->componentPluginManager = $component_plugin_manager;
    }
    
    /**
     * Parses and builds up all the libraries information of an extension.
     *
     * @param string $extension
     *   The name of the extension that registered a library.
     *
     * @return array
     *   All library definitions of the passed extension.
     *
     * @throws \Drupal\Core\Asset\Exception\IncompleteLibraryDefinitionException
     *   Thrown when a library has no js/css/setting.
     * @throws \UnexpectedValueException
     *   Thrown when a js file defines a positive weight.
     * @throws \UnknownExtensionTypeException
     *   Thrown when the extension type is unknown.
     * @throws \UnknownExtensionException
     *   Thrown when the extension is unknown.
     * @throws \InvalidLibraryFileException
     *   Thrown when the library file is invalid.
     * @throws \InvalidLibrariesOverrideSpecificationException
     *   Thrown when a definition refers to a non-existent library.
     * @throws \Drupal\Core\Asset\Exception\LibraryDefinitionMissingLicenseException
     *   Thrown when a library definition has no license information.
     * @throws \LogicException
     *   Thrown when a header key in a library definition is invalid.
     */
    public function buildByExtension($extension) {
        if ($extension === 'core') {
            $path = 'core';
            $extension_type = 'core';
        }
        else {
            if ($this->moduleHandler
                ->moduleExists($extension)) {
                $extension_type = 'module';
            }
            else {
                $extension_type = 'theme';
            }
            $path = $this->extensionPathResolver
                ->getPath($extension_type, $extension);
        }
        $libraries = $this->parseLibraryInfo($extension, $path);
        $libraries = $this->applyLibrariesOverride($libraries, $extension);
        foreach ($libraries as $id => &$library) {
            if (!isset($library['js']) && !isset($library['css']) && !isset($library['drupalSettings']) && !isset($library['dependencies'])) {
                throw new IncompleteLibraryDefinitionException(sprintf("Incomplete library definition for definition '%s' in extension '%s'", $id, $extension));
            }
            $library += [
                'dependencies' => [],
                'js' => [],
                'css' => [],
            ];
            if (isset($library['header']) && !is_bool($library['header'])) {
                throw new \LogicException(sprintf("The 'header' key in the library definition '%s' in extension '%s' is invalid: it must be a boolean.", $id, $extension));
            }
            if (isset($library['version'])) {
                // @todo Retrieve version of a non-core extension.
                if ($library['version'] === 'VERSION') {
                    $library['version'] = \Drupal::VERSION;
                }
                elseif (is_string($library['version']) && $library['version'][0] === 'v') {
                    $library['version'] = substr($library['version'], 1);
                }
            }
            // If this is a 3rd party library, the license info is required.
            if (isset($library['remote']) && !isset($library['license'])) {
                throw new LibraryDefinitionMissingLicenseException(sprintf("Missing license information in library definition for definition '%s' extension '%s': it has a remote, but no license.", $id, $extension));
            }
            // Assign Drupal's license to libraries that don't have license info.
            if (!isset($library['license'])) {
                $library['license'] = [
                    'name' => 'GPL-2.0-or-later',
                    'url' => 'https://www.drupal.org/licensing/faq',
                    'gpl-compatible' => TRUE,
                ];
            }
            foreach ([
                'js',
                'css',
            ] as $type) {
                // Prepare (flatten) the SMACSS-categorized definitions.
                // @todo After Asset(ic) changes, retain the definitions as-is and
                //   properly resolve dependencies for all (css) libraries per category,
                //   and only once prior to rendering out an HTML page.
                if ($type == 'css' && !empty($library[$type])) {
                    assert(static::validateCssLibrary($library[$type]) < 2, 'CSS files should be specified as key/value pairs, where the values are configuration options. See https://www.drupal.org/node/2274843.');
                    assert(static::validateCssLibrary($library[$type]) === 0, 'CSS must be nested under a category. See https://www.drupal.org/node/2274843.');
                    foreach ($library[$type] as $category => $files) {
                        $category_weight = 'CSS_' . strtoupper($category);
                        assert(defined($category_weight), 'Invalid CSS category: ' . $category . '. See https://www.drupal.org/node/2274843.');
                        foreach ($files as $source => $options) {
                            if (!isset($options['weight'])) {
                                $options['weight'] = 0;
                            }
                            // Apply the corresponding weight defined by CSS_* constants.
                            $options['weight'] += constant($category_weight);
                            $library[$type][$source] = $options;
                        }
                        unset($library[$type][$category]);
                    }
                }
                foreach ($library[$type] as $source => $options) {
                    unset($library[$type][$source]);
                    // Allow to omit the options hashmap in YAML declarations.
                    if (!is_array($options)) {
                        $options = [];
                    }
                    if ($type == 'js' && isset($options['weight']) && $options['weight'] > 0) {
                        throw new \UnexpectedValueException("The {$extension}/{$id} library defines a positive weight for '{$source}'. Only negative weights are allowed (but should be avoided). Instead of a positive weight, specify accurate dependencies for this library.");
                    }
                    // Unconditionally apply default groups for the defined asset files.
                    // The library system is a dependency management system. Each library
                    // properly specifies its dependencies instead of relying on a custom
                    // processing order.
                    if ($type == 'js') {
                        $options['group'] = JS_LIBRARY;
                    }
                    elseif ($type == 'css') {
                        $options['group'] = $extension_type == 'theme' ? CSS_AGGREGATE_THEME : CSS_AGGREGATE_DEFAULT;
                    }
                    // By default, all library assets are files.
                    if (!isset($options['type'])) {
                        $options['type'] = 'file';
                    }
                    if ($options['type'] == 'external') {
                        $options['data'] = $source;
                    }
                    else {
                        if ($source[0] === '/') {
                            // An absolute path maps to DRUPAL_ROOT / base_path().
                            if ($source[1] !== '/') {
                                $source = substr($source, 1);
                                // Non core provided libraries can be in multiple locations.
                                if (str_starts_with($source, 'libraries/')) {
                                    $path_to_source = $this->librariesDirectoryFileFinder
                                        ->find(substr($source, 10));
                                    if ($path_to_source) {
                                        $source = $path_to_source;
                                    }
                                }
                                $options['data'] = $source;
                            }
                            else {
                                $options['type'] = 'external';
                                $options['data'] = $source;
                            }
                        }
                        elseif ($this->streamWrapperManager
                            ->isValidUri($source)) {
                            $options['data'] = $source;
                        }
                        elseif ($this->isValidUri($source)) {
                            $options['type'] = 'external';
                            $options['data'] = $source;
                        }
                        else {
                            $options['data'] = $path . '/' . $source;
                        }
                    }
                    if (!isset($library['version'])) {
                        // @todo Get the information from the extension.
                        $options['version'] = -1;
                    }
                    else {
                        $options['version'] = $library['version'];
                    }
                    // Set the 'minified' flag on JS file assets, default to FALSE.
                    if ($type == 'js' && $options['type'] == 'file') {
                        $options['minified'] = $options['minified'] ?? FALSE;
                    }
                    $library[$type][] = $options;
                }
            }
        }
        return $libraries;
    }
    
    /**
     * Parses a given library file and allows modules and themes to alter it.
     *
     * This method sets the parsed information onto the library property.
     *
     * Library information is parsed from *.libraries.yml files; see
     * editor.libraries.yml for an example. Every library must have at least one
     * js or css entry. Each entry starts with a machine name and defines the
     * following elements:
     * - js: A list of JavaScript files to include. Each file is keyed by the file
     *   path. An item can have several attributes (like HTML
     *   attributes). For example:
     *   @code
     *   js:
     *     path/js/file.js: { attributes: { defer: true } }
     *   @endcode
     *   If the file has no special attributes, just use an empty object:
     *   @code
     *   js:
     *     path/js/file.js: {}
     *   @endcode
     *   The path of the file is relative to the module or theme directory, unless
     *   it starts with a /, in which case it is relative to the Drupal root. If
     *   the file path starts with //, it will be treated as a protocol-free,
     *   external resource (e.g., //cdn.com/library.js). Full URLs
     *   (e.g., http://cdn.com/library.js) as well as URLs that use a valid
     *   stream wrapper (e.g., public://path/to/file.js) are also supported.
     * - css: A list of categories for which the library provides CSS files. The
     *   available categories are:
     *   - base
     *   - layout
     *   - component
     *   - state
     *   - theme
     *   Each category is itself a key for a sub-list of CSS files to include:
     *   @code
     *   css:
     *     component:
     *       css/file.css: {}
     *   @endcode
     *   Just like with JavaScript files, each CSS file is the key of an object
     *   that can define specific attributes. The format of the file path is the
     *   same as for the JavaScript files.
     *   If the JavaScript or CSS file starts with /libraries/ the
     *   library.libraries_directory_file_finder service is used to find the files
     *   in the following locations:
     *   - A libraries directory in the current site directory, for example:
     *     sites/default/libraries.
     *   - The root libraries directory.
     *   - A libraries directory in the selected installation profile, for
     *     example: profiles/my_install_profile/libraries.
     * - dependencies: A list of libraries this library depends on.
     * - version: The library version. The string "VERSION" can be used to mean
     *   the current Drupal core version.
     * - header: By default, JavaScript files are included in the footer. If the
     *   script must be included in the header (along with all its dependencies),
     *   set this to true. Defaults to false.
     * - minified: If the file is already minified, set this to true to avoid
     *   minifying it again. Defaults to false.
     * - remote: If the library is a third-party script, this provides the
     *   repository URL for reference.
     * - license: If the remote property is set, the license information is
     *   required. It has 3 properties:
     *   - name: A System Package Data Exchange (SPDX) license identifier such as
     *     "GPL-2.0-or-later" (see https://spdx.org/licenses/), or if not
     *     applicable, the human-readable name of the license.
     *   - url: The URL of the license file/information for the version of the
     *     library used.
     *   - gpl-compatible: A Boolean for whether this library is GPL compatible.
     *
     * See https://www.drupal.org/node/2274843#define-library for more
     * information.
     *
     * @param string $extension
     *   The name of the extension that registered a library.
     * @param string $path
     *   The relative path to the extension.
     *
     * @return array
     *   An array of parsed library data.
     *
     * @throws \Drupal\Core\Asset\Exception\InvalidLibraryFileException
     *   Thrown when a parser exception got thrown.
     */
    protected function parseLibraryInfo($extension, $path) {
        $libraries = [];
        $library_file = $path . '/' . $extension . '.libraries.yml';
        $library_path = $this->root . '/' . $library_file;
        if (file_exists($library_path)) {
            $libraries = $this->fileCache
                ->get($library_path);
            if ($libraries === NULL) {
                try {
                    $libraries = Yaml::decode(file_get_contents($this->root . '/' . $library_file)) ?? [];
                    $this->fileCache
                        ->set($library_path, $libraries);
                } catch (InvalidDataTypeException $e) {
                    // Rethrow a more helpful exception to provide context.
                    throw new InvalidLibraryFileException(sprintf('Invalid library definition in %s: %s', $library_file, $e->getMessage()), 0, $e);
                }
            }
        }
        // Core also provides additional libraries that don't come from the YAML,
        // file nor the hook_library_info_build. They come from single-directory
        // component definitions.
        $additional_libraries = $extension === 'core' ? $this->librariesForComponents() : [];
        $libraries = array_merge($additional_libraries, $libraries);
        // Allow modules to add dynamic library definitions.
        $hook = 'library_info_build';
        if ($this->moduleHandler
            ->hasImplementations($hook, $extension)) {
            $libraries = NestedArray::mergeDeep($libraries, $this->moduleHandler
                ->invoke($extension, $hook));
        }
        // Allow modules to alter the module's registered libraries.
        $this->moduleHandler
            ->alter('library_info', $libraries, $extension);
        $this->themeManager
            ->alter('library_info', $libraries, $extension);
        return $libraries;
    }
    
    /**
     * Apply overrides to files that have moved.
     *
     * @param array $library
     *   The library definition.
     * @param string $library_name
     *   The library name.
     * @param string $extension
     *   The extension name.
     * @param array $overrides
     *   The library overrides.
     * @param Drupal\Core\Theme\ActiveTheme $active_theme
     *   The active theme.
     *
     * @return array
     *   The modified library overrides.
     */
    protected function applyLibrariesMovedOverrides(array $library, string $library_name, string $extension, array $overrides, ActiveTheme $active_theme) : array {
        if (!isset($library['moved_files'])) {
            return $overrides;
        }
        foreach ($library['moved_files'] as $old_library_name => $moved_files) {
            $deprecation_version = $moved_files['deprecation_version'];
            $removed_version = $moved_files['removed_version'];
            $deprecation_link = $moved_files['deprecation_link'];
            if (isset($overrides[$old_library_name]['css']) && isset($moved_files['css'])) {
                foreach ($overrides[$old_library_name]['css'] as $key => $files) {
                    foreach ($files as $original => $target) {
                        if (isset($moved_files['css'][$key][$original])) {
                            $new_key = array_key_first($moved_files['css'][$key][$original]);
                            $new_file = $moved_files['css'][$key][$original][$new_key];
                            $theme_name = $active_theme->getName();
                            // phpcs:ignore
                            @trigger_error("Targeting {$old_library_name} {$original} from {$theme_name} library_overrides is deprecated in {$deprecation_version} and will be removed in {$removed_version}. Target {$extension}/{$library_name} {$new_file} instead. See {$deprecation_link}", E_USER_DEPRECATED);
                            $overrides[$extension . '/' . $library_name]['css'][$new_key][$new_file] = $target;
                        }
                    }
                }
            }
            if (isset($overrides[$old_library_name]['js']) && isset($moved_files['js'])) {
                foreach ($overrides[$old_library_name]['js'] as $original => $target) {
                    if (isset($moved_files['js'][$original])) {
                        $new_file = $moved_files['js'][$original];
                        $theme_name = $active_theme->getName();
                        // phpcs:ignore
                        @trigger_error("Targeting {$old_library_name} {$original} from {$theme_name} library_overrides is deprecated in {$deprecation_version} and will be removed in {$removed_version}. Target {$extension}/{$library_name} {$new_file} instead. See {$deprecation_link}", E_USER_DEPRECATED);
                        $overrides[$extension . '/' . $library_name]['js'][$new_file] = $target;
                    }
                }
            }
        }
        return $overrides;
    }
    
    /**
     * Builds the dynamic library definitions for single-directory components.
     *
     * @return array
     *   The core library definitions for Single-Directory Components.
     */
    protected function librariesForComponents() : array {
        // Iterate over all the components to get the CSS and JS files.
        $components = $this->componentPluginManager
            ->getAllComponents();
        $libraries = array_reduce($components, static function (array $libraries, Component $component) {
            $library = $component->library;
            if (empty($library)) {
                return $libraries;
            }
            $library_name = $component->getLibraryName();
            [
                ,
                $library_id,
            ] = explode('/', $library_name);
            return array_merge($libraries, [
                $library_id => $library,
            ]);
        }, []);
        $libraries['components.all'] = [
            'dependencies' => array_map(static fn(Component $component) => $component->getLibraryName(), $components),
        ];
        return $libraries;
    }
    
    /**
     * Apply libraries overrides specified for the current active theme.
     *
     * @param array $libraries
     *   The libraries definitions.
     * @param string $extension
     *   The extension in which these libraries are defined.
     *
     * @return array
     *   The modified libraries definitions.
     */
    protected function applyLibrariesOverride($libraries, $extension) {
        $active_theme = $this->themeManager
            ->getActiveTheme();
        // ActiveTheme::getLibrariesOverride() returns libraries-overrides for the
        // current theme as well as all its base themes.
        $all_libraries_overrides = $active_theme->getLibrariesOverride();
        foreach ($all_libraries_overrides as $theme_path => $libraries_overrides) {
            foreach ($libraries as $library_name => $library) {
                $libraries_overrides = $this->applyLibrariesMovedOverrides($library, $library_name, $extension, $libraries_overrides, $active_theme);
                // Process libraries overrides.
                if (isset($libraries_overrides["{$extension}/{$library_name}"])) {
                    if (isset($library['deprecated'])) {
                        $override_message = sprintf('Theme "%s" is overriding a deprecated library.', $extension);
                        $library_deprecation = str_replace('%library_id%', "{$extension}/{$library_name}", $library['deprecated']);
                        // phpcs:ignore Drupal.Semantics.FunctionTriggerError
                        @trigger_error("{$override_message} {$library_deprecation}", E_USER_DEPRECATED);
                    }
                    // Active theme defines an override for this library.
                    $override_definition = $libraries_overrides["{$extension}/{$library_name}"];
                    if (is_string($override_definition) || $override_definition === FALSE) {
                        // A string or boolean definition implies an override (or removal)
                        // for the whole library. Use the override key to specify that this
                        // library will be overridden when it is called.
                        // @see \Drupal\Core\Asset\LibraryDiscovery::getLibraryByName()
                        if ($override_definition) {
                            $libraries[$library_name]['override'] = $override_definition;
                        }
                        else {
                            $libraries[$library_name]['override'] = FALSE;
                        }
                    }
                    elseif (is_array($override_definition)) {
                        // An array definition implies an override for an asset within this
                        // library.
                        foreach ($override_definition as $sub_key => $value) {
                            // Throw an exception if the asset is not properly specified.
                            if (!is_array($value)) {
                                throw new InvalidLibrariesOverrideSpecificationException(sprintf('Library asset %s is not correctly specified. It should be in the form "extension/library_name/sub_key/path/to/asset.js".', "{$extension}/{$library_name}/{$sub_key}"));
                            }
                            if ($sub_key === 'drupalSettings') {
                                // drupalSettings may not be overridden.
                                throw new InvalidLibrariesOverrideSpecificationException(sprintf('drupalSettings may not be overridden in libraries-override. Trying to override %s. Use hook_library_info_alter() instead.', "{$extension}/{$library_name}/{$sub_key}"));
                            }
                            elseif ($sub_key === 'css') {
                                // SMACSS category should be incorporated into the asset name.
                                foreach ($value as $category => $overrides) {
                                    $this->setOverrideValue($libraries[$library_name], [
                                        $sub_key,
                                        $category,
                                    ], $overrides, $theme_path);
                                }
                            }
                            else {
                                $this->setOverrideValue($libraries[$library_name], [
                                    $sub_key,
                                ], $value, $theme_path);
                            }
                        }
                    }
                }
            }
        }
        return $libraries;
    }
    
    /**
     * Determines if the supplied string is a valid URI.
     */
    protected function isValidUri($string) {
        return count(explode('://', $string)) === 2;
    }
    
    /**
     * Overrides the specified library asset.
     *
     * @param array $library
     *   The containing library definition.
     * @param array $sub_key
     *   An array containing the sub-keys specifying the library asset, e.g.
     *   ['js'] or ['css', 'component'].
     * @param array $overrides
     *   Specifies the overrides, this is an array where the key is the asset to
     *   be overridden while the value is overriding asset.
     * @param string $theme_path
     *   The theme or base theme.
     */
    protected function setOverrideValue(array &$library, array $sub_key, array $overrides, $theme_path) {
        foreach ($overrides as $original => $replacement) {
            // Get the attributes of the asset to be overridden. If the key does
            // not exist, then throw an exception.
            $key_exists = NULL;
            $parents = array_merge($sub_key, [
                $original,
            ]);
            // Save the attributes of the library asset to be overridden.
            $attributes = NestedArray::getValue($library, $parents, $key_exists);
            if ($key_exists) {
                // Remove asset to be overridden.
                NestedArray::unsetValue($library, $parents);
                // No need to replace if FALSE is specified, since that is a removal.
                if ($replacement) {
                    // Ensure the replacement path is relative to drupal root.
                    $replacement = $this->resolveThemeAssetPath($theme_path, $replacement);
                    $new_parents = array_merge($sub_key, [
                        $replacement,
                    ]);
                    // Replace with an override if specified.
                    NestedArray::setValue($library, $new_parents, $attributes);
                }
            }
        }
    }
    
    /**
     * Ensures that a full path is returned for an overriding theme asset.
     *
     * @param string $theme_path
     *   The theme or base theme.
     * @param string $overriding_asset
     *   The overriding library asset.
     *
     * @return string
     *   A fully resolved theme asset path relative to the Drupal directory.
     */
    protected function resolveThemeAssetPath($theme_path, $overriding_asset) {
        if ($overriding_asset[0] !== '/' && !$this->isValidUri($overriding_asset)) {
            // The destination is not an absolute path and it's not a URI (e.g.
            // public://generated_js/example.js or http://example.com/js/my_js.js), so
            // it's relative to the theme.
            return '/' . $theme_path . '/' . $overriding_asset;
        }
        return $overriding_asset;
    }
    
    /**
     * Validates CSS library structure.
     *
     * @param array $library
     *   The library definition array.
     *
     * @return int
     *   Returns based on validity:
     *     - 0 if the library definition is valid
     *     - 1 if the library definition has improper nesting
     *     - 2 if the library definition specifies files as an array
     */
    public static function validateCssLibrary($library) {
        $categories = [];
        // Verify options first and return early if invalid.
        foreach ($library as $category => $files) {
            if (!is_array($files)) {
                return 2;
            }
            $categories[] = $category;
            foreach ($files as $options) {
                if (!is_array($options)) {
                    return 1;
                }
            }
        }
        return 0;
    }

}