class PermissionHandler

class PermissionHandler implements PermissionHandlerInterface {
    use StringTranslationTrait;
    
    /**
     * The module handler.
     *
     * @var \Drupal\Core\Extension\ModuleHandlerInterface
     */
    protected $moduleHandler;
    
    /**
     * The YAML discovery class to find all .permissions.yml files.
     *
     * @var \Drupal\Core\Discovery\YamlDiscovery
     */
    protected $yamlDiscovery;
    
    /**
     * The controller resolver.
     *
     * @var \Drupal\Core\Controller\ControllerResolverInterface
     */
    protected $controllerResolver;
    
    /**
     * Constructs a new PermissionHandler.
     *
     * @param \Drupal\Core\Extension\ModuleHandlerInterface $module_handler
     *   The module handler.
     * @param \Drupal\Core\StringTranslation\TranslationInterface $string_translation
     *   The string translation.
     * @param \Drupal\Core\Controller\ControllerResolverInterface $controller_resolver
     *   The controller resolver.
     */
    public function __construct(ModuleHandlerInterface $module_handler, TranslationInterface $string_translation, ControllerResolverInterface $controller_resolver) {
        // @todo It would be nice if you could pull all module directories from the
        //   container.
        $this->moduleHandler = $module_handler;
        $this->stringTranslation = $string_translation;
        $this->controllerResolver = $controller_resolver;
    }
    
    /**
     * Gets the YAML discovery.
     *
     * @return \Drupal\Core\Discovery\YamlDiscovery
     *   The YAML discovery.
     */
    protected function getYamlDiscovery() {
        if (!isset($this->yamlDiscovery)) {
            $this->yamlDiscovery = new YamlDiscovery('permissions', $this->moduleHandler
                ->getModuleDirectories());
        }
        return $this->yamlDiscovery;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getPermissions() {
        $all_permissions = $this->buildPermissionsYaml();
        return $this->sortPermissions($all_permissions);
    }
    
    /**
     * {@inheritdoc}
     */
    public function moduleProvidesPermissions($module_name) {
        // @TODO Static cache this information, see
        // https://www.drupal.org/node/2339487
        $permissions = $this->getPermissions();
        foreach ($permissions as $permission) {
            if ($permission['provider'] == $module_name) {
                return TRUE;
            }
        }
        return FALSE;
    }
    
    /**
     * Builds all permissions provided by .permissions.yml files.
     *
     * @return array[]
     *   Each return permission is an array with the following keys:
     *   - title: The title of the permission.
     *   - description: The description of the permission, defaults to NULL.
     *   - provider: The provider of the permission.
     */
    protected function buildPermissionsYaml() {
        $all_permissions = [];
        $all_callback_permissions = [];
        foreach ($this->getYamlDiscovery()
            ->findAll() as $provider => $permissions) {
            // The top-level 'permissions_callback' is a list of methods in controller
            // syntax, see \Drupal\Core\Controller\ControllerResolver. These methods
            // should return an array of permissions in the same structure.
            if (isset($permissions['permission_callbacks'])) {
                foreach ($permissions['permission_callbacks'] as $permission_callback) {
                    $callback = $this->controllerResolver
                        ->getControllerFromDefinition($permission_callback);
                    if ($callback_permissions = call_user_func($callback)) {
                        // Add any callback permissions to the array of permissions. Any
                        // defaults can then get processed below.
                        foreach ($callback_permissions as $name => $callback_permission) {
                            if (!is_array($callback_permission)) {
                                $callback_permission = [
                                    'title' => $callback_permission,
                                ];
                            }
                            $callback_permission += [
                                'description' => NULL,
                                'provider' => $provider,
                            ];
                            $all_callback_permissions[$name] = $callback_permission;
                        }
                    }
                }
                unset($permissions['permission_callbacks']);
            }
            foreach ($permissions as &$permission) {
                if (!is_array($permission)) {
                    $permission = [
                        'title' => $permission,
                    ];
                }
                $permission['title'] = $this->t($permission['title']);
                $permission['description'] = isset($permission['description']) ? $this->t($permission['description']) : NULL;
                $permission['provider'] = !empty($permission['provider']) ? $permission['provider'] : $provider;
            }
            $all_permissions += $permissions;
        }
        return $all_permissions + $all_callback_permissions;
    }
    
    /**
     * Sorts the given permissions by provider name and title.
     *
     * @param array $all_permissions
     *   The permissions to be sorted.
     *
     * @return array[]
     *   Each return permission is an array with the following keys:
     *   - title: The title of the permission.
     *   - description: The description of the permission, defaults to NULL.
     *   - provider: The provider of the permission.
     */
    protected function sortPermissions(array $all_permissions = []) {
        // Get a list of all the modules providing permissions and sort by
        // display name.
        $modules = $this->getModuleNames();
        uasort($all_permissions, function (array $permission_a, array $permission_b) use ($modules) {
            if ($modules[$permission_a['provider']] == $modules[$permission_b['provider']]) {
                return $permission_a['title'] <=> $permission_b['title'];
            }
            else {
                return $modules[$permission_a['provider']] <=> $modules[$permission_b['provider']];
            }
        });
        return $all_permissions;
    }
    
    /**
     * Returns all module names.
     *
     * @return string[]
     *   Returns the human readable names of all modules keyed by machine name.
     */
    protected function getModuleNames() {
        $modules = [];
        foreach (array_keys($this->moduleHandler
            ->getModuleList()) as $module) {
            $modules[$module] = $this->moduleHandler
                ->getName($module);
        }
        asort($modules);
        return $modules;
    }

}