public function generate(Books $books)
{
$tmpBook = $books->duplicate();
$groupOfBooks = [];
do {
$numbers = $tmpBook->names();
$unique = array_keys(array_unique($numbers));
$groupOfBooks[] = $tmpBook->remove($unique);
} while ($tmpBook->hasBooks());
return [new BooksGroup($groupOfBooks)];
}
private function hasFiveDifferentBooks(Books $books)
{
$bookNames = $books->names();
return count(array_unique($bookNames)) == 5;
}