public Book[] BookByTitle(String title)
 {
     Library lib = new Library();
     lib.UpdateDB();
     return lib.FindBooksByName(title);
 }
 public Book[] BookByWriter(String writer)
 {
     Library lib = new Library();
     lib.UpdateDB();
     return lib.FindBooksByAuthor(writer);
 }
 public Book BookByGUID(string GUID)
 {
     Library lib = new Library();
     lib.UpdateDB();
     return lib.FindBookByGUID(GUID);
 }
 public Book[] AllBooks()
 {
     Library lib = new Library();
     lib.UpdateDB();
     return lib.Books.ToArray<Book>();
 }
 public bool AddUser(String username, String adress, String zipcode, String city, String password)
 {
     Library lib = new Library();
     lib.UpdateDB();
     return (lib.AddUserDB(username, adress, zipcode, city, password));
 }
 public bool VerifyUser(String username, String password)
 {
     Library lib = new Library();
     lib.UpdateDB();
     return lib.VerifyUser(username, password);
 }
 public string RegisterOrder(string username, Book[] books, string creditcard, ContactDetails shipping, ContactDetails invoicing)
 {
     string guid = null;
     if (Order.VerifyCreditCard(creditcard) == true)
     {
         int i = 0;
         bool verifybook = true;
         Library lib = new Library();
         lib.UpdateDB();
         while (i < books.Length && verifybook == true)
         {
             verifybook = lib.Contains(books[i++]);
         }
         if (verifybook == true)
         {
             Order toregister = new Order(shipping, invoicing, creditcard, books);
             toregister.OrderSerializer();
             toregister.OrderStorage(username);
             guid = toregister.Ordernumber;
         }
     }
     return guid;
 }