private string GenerateValidISBN(string isbn, ISBNGenerator generator) { return generator(isbn); }
private string GenerateNewISBN(ISBNGenerator generator) { string nextNumber = ""; if (lastNumber != null) { double LastISBN = ParseISBNString(lastNumber); nextNumber = GenerateValidISBN((LastISBN + 1).ToString(), generator); } else { nextNumber = "000-000-001"; } lastNumber = nextNumber; return nextNumber; }