Memento - Design Pattern

Hoje eu estava estudando o pattern Memento e pelo o que eu entendi ele é como um rollback (me corrijam se eu estiver errado).

Pelo o que eu estudei, criei isso, para arquivos. Gostaria de saber se apliquei o pattern corretamente.

class Memento{

 private $storage;

 public function __construct( $storage ){
 $this->storage = $storage;
 }

 public function get(){
 return $this->storage;
 }
}

class CareTaker{

 private $texts;

 public function __construct(){
 $this->texts = array();
 }

 public function add( Memento $text ){
 $this->texts[] = $text;
 }

 public function getUltimateState(){
 if( count( $this->texts ) <= 0 ){
 return null;
 }
 $ultimateState = $this->texts[ count( $this->texts ) - 1 ];
 unset( $this->texts[ count( $this->texts ) - 1 ] );
 return $ultimateState;
 }
}

class FileEditor{

 private $file;
 private $fileContent;
 private $caretaker;

 public function __construct( $file ){
 $this->file = $file;
 $fopen = fopen( $file, 'r' );
 $this->fileContent = fgets( $fopen, 1024 );
 fclose( $fopen );
 $this->caretaker = new CareTaker;
 }

 public function addContent( $content ){
 $content = file_get_contents( $this->file );
 $memento = new Memento( $content );
 $this->caretaker->add( $memento );
 $fopen = fopen( $this->file, 'a+' );
 $fwrite = fwrite( $fopen, $content );
 fclose( $fopen );
 $this->fileContent = file_get_contents( $this->file );
 }

 public function undoContent(){
 $fopen = fopen( $this->file, 'w' );
 $fwrite = fwrite( $fopen, $this->caretaker->getUltimateState()->get() );
 fclose( $fopen );
 }

 public function getContent(){
 return $this->fileContent;
 }
}

$editor = new FileEditor( 'file-txt.txt' );
$editor->addContent( 'Esse código' );
$editor->addContent( ' foi escrito' );
$editor->addContent( ' numa IDE' );
$editor->undoContent();