class StateManager:

    def __init__(self):
        self.previous = None


    def update(self, current):

        if current is None or current.get("health") is None:
            return None, None

        # 第一次收到有效数据，只记录，不触发事件
        if self.previous is None:
            self.previous = current
            return None, None
        
        old = self.previous

        self.previous = current

        return old, current