interface FileUsageInterface

interface FileUsageInterface {
    
    /**
     * Records that a module is using a file.
     *
     * Examples:
     * - A module that associates files with nodes, so $type would be
     *   'node' and $id would be the node's nid. Files for all revisions are
     *   stored within a single nid.
     * - The User module associates an image with a user, so $type would be 'user'
     *   and the $id would be the user's uid.
     *
     * @param \Drupal\file\FileInterface $file
     *   A file entity.
     * @param string $module
     *   The name of the module using the file.
     * @param string $type
     *   The type of the object that contains the referenced file.
     * @param string $id
     *   The unique ID of the object containing the referenced file.
     * @param int $count
     *   (optional) The number of references to add to the object. Defaults to 1.
     */
    public function add(FileInterface $file, $module, $type, $id, $count = 1);
    
    /**
     * Removes a record to indicate that a module is no longer using a file.
     *
     * @param \Drupal\file\FileInterface $file
     *   A file entity.
     * @param string $module
     *   The name of the module using the file.
     * @param string $type
     *   (optional) The type of the object that contains the referenced file. May
     *   be omitted if all module references to a file are being deleted. Defaults
     *   to NULL.
     * @param string $id
     *   (optional) The unique ID of the object containing the referenced file.
     *   May be omitted if all module references to a file are being deleted.
     *   Defaults to NULL.
     * @param int $count
     *   (optional) The number of references to delete from the object. Defaults
     *   to 1. Zero may be specified to delete all references to the file within a
     *   specific object.
     */
    public function delete(FileInterface $file, $module, $type = NULL, $id = NULL, $count = 1);
    
    /**
     * Determines where a file is used.
     *
     * @param \Drupal\file\FileInterface $file
     *   A file entity.
     *
     * @return array
     *   A nested array with usage data. The first level is keyed by module name,
     *   the second by object type and the third by the object id. The value of
     *   the third level contains the usage count.
     */
    public function listUsage(FileInterface $file);

}