1class RunewordsCalculator:
 2    def __init__(self, runewords):
 3        self.runewords = runewords
 4        self.added_runes = []
 5        self.returned_runes = []
 6
 7    def __iter__(self):
 8        return self
 9
10    def __next__(self):
11        if len(self.runewords) == len(self.returned_runes):
12            raise StopIteration
13        for name, recipe in self.runewords.items():
14            if name not in self.returned_runes:
15                current_indices_in_recipe = self.__use_recipe(recipe)
16                if len(current_indices_in_recipe) == len(recipe):
17                    self.returned_runes.append(name)
18                    self.__remove_spent_runes(current_indices_in_recipe)
19                    return name
20        return None
21
22    def add_runes(self, runes):
23        self.added_runes.extend(runes)
24
25    def __use_recipe(self, wanted_recipe):
26        used_runes_indices = []
27        recipe_index = 0
28        for rune_index, rune in enumerate(self.added_runes):
29            if recipe_index < len(wanted_recipe) and rune == wanted_recipe[recipe_index]:
30                used_runes_indices.append(rune_index)
31                recipe_index +=1
32        return used_runes_indices
33
34    def __remove_spent_runes(self, used_runes):
35        for rune_index in reversed(used_runes):
36            del self.added_runes[rune_index]