class TaskThread(Thread):
    def __init__(self, task, key, username, password):
        Thread.__init__(self)
        self.task = encode if task == "encode" else decode
        self.key = key
        self.username = username
        self.password = password
        self.stopped = Event()
        self.return_value = None

    def run(self):
        self.return_value = (self.task(self.key, self.username),
                             self.task(self.key, self.password))
        return self.return_value

    def join(self):
        if self.is_alive():
            self.stopped.set()
            Thread.join(self)
        return self.username, self.password


class IntervalThread(TaskThread):
    def __init__(self, period, task, key, username, password):
        super().__init__(task, key, username, password)
        self.period = period

    def run(self):
        self.username, self.password = super().run()
        while not self.stopped.is_set():
            time.sleep(self.period)
            self.username, self.password = super().run()