text: from src.zad3.isbn import Isbn
  
  class Book(object):
      def __init__(self, book_storage = None):
          self.book_storage = book_storage
          self.isbn = Isbn()
  
      def add_book(self, book):
          if self.isbn.is_valid(book["isbn"]):
              return self.book_storage.add(book)
          return "invalid isbn number"
  
      def delete_book(self, book_id):
          book = self.book_storage.find(book_id)
  
          if book:
              self.book_storage.delete(book)
              return True
  
          return False
  
      def get_all_books(self):
          return self.book_storage.find()
  
      def get_book_by_id(self, book_id):
          if type(book_id) is not int or book_id < 0:
              return "Book_id is incorrect"
  
          res = self.book_storage.find(book_id)
          if res:
              return res
          else:
              return "Book not found"
  
      def get_books_title(self, book_id):
          book = self.get_book_by_id(book_id)
  
          if isinstance(book, list):
              return book["title"]
          
          return book
  
      def get_books_author(self, book_id):
          book = self.get_book_by_id(book_id)
  
          return book["author"]
  