class OrderOperation

abstract class OrderOperation {
    
    /**
     * Changes the order of a list of hook implementations.
     *
     * @param list<string> $identifiers
     *   Hook implementation identifiers, as "$class::$method", to be changed by
     *   reference.
     *   The order operation must make sure that the array remains a list, and
     *   that the values are the same as before.
     * @param array<string, string> $module_finder
     *   Lookup map to find a module name for each implementation.
     *   This may contain more entries than $identifiers.
     */
    public abstract function apply(array &$identifiers, array $module_finder) : void;
    
    /**
     * Converts the operation to a structure that can be stored in the container.
     *
     * @return array
     *   Packed operation.
     */
    public final function pack() : array {
        $is_before_or_after = match (get_class($this)) {    BeforeOrAfter::class => TRUE,
            FirstOrLast::class => FALSE,
        
        };
        return [
            $is_before_or_after,
            get_object_vars($this),
        ];
    }
    
    /**
     * Converts the stored operation to objects that can apply ordering rules.
     *
     * @param array $packed_operation
     *   Packed operation.
     *
     * @return self
     *   Unpacked operation.
     */
    public static final function unpack(array $packed_operation) : self {
        [
            $is_before_or_after,
            $args,
        ] = $packed_operation;
        $class = $is_before_or_after ? BeforeOrAfter::class : FirstOrLast::class;
        return new $class(...$args);
    }

}