TDD demo: code

class Game:
    def __init__(self):
        self.total = 0
        self.num_rolls = 0
        self.score_of_previous_frames = 0
        self.should_add_next_roll_as_bonus = False
        self.bonus_points = 0

        self.error = -1

    def put_into_error_state(self):
        self.total = self.error

    def roll(self, pins):
        self.num_rolls = self.num_rolls + 1

        if self.total == self.error:
            return
        if pins > 10:
            self.put_into_error_state()
        else:
            self.total = self.total + pins

        if self.should_add_next_roll_as_bonus and not self.total == self.error:
            self.bonus_points = self.bonus_points + pins
            self.should_add_next_roll_as_bonus = False

        is_end_of_frame = self.num_rolls % 2 == 0 # TODO: make this work with strikes
        if is_end_of_frame:
            this_frame_score = self.total - self.score_of_previous_frames
            if this_frame_score > 10:
                self.put_into_error_state()
            elif this_frame_score == 10:
                self.should_add_next_roll_as_bonus = True
            self.score_of_previous_frames = self.total

    def score(self):
        if self.num_rolls != 20:
            return self.error

        self.total = self.total + self.bonus_points
        return self.total