public string SaveBook(Book book)
{
bool isExisted = bookGateway.ExistISBN(book);
if (isExisted)
{
return("Already Exists");
}
else
{
if (book.ISBN.Length == 13)
{
bool isSaved = bookGateway.SaveBook(book);
if (isSaved)
{
return("Book Saved Successfully");
}
else
{
return("Failed to Save");
}
}
else
{
return("ISBN must be 13 digit");
}
}
}