class UIContext:
    context = "all"
    prev_context = ""
    data = {
        "feed": "",
        "post_url": "",
        "search_query": "",
        "items": [],
    }

    def revert_context(self):
        self.context, self.prev_context = self.prev_context, self.context

    def change_context(self, new_context):
        if new_context not in ["all", "feed", "unread", "search"]:
            raise NotImplementedError(f"There is no UI context {new_context}.")
        self.prev_context = self.context
        self.context = new_context
        # Clear data fields so there's no lingering state from previous context
        self.data["feed"] = ""
        self.data["post_url"] = ""
        self.data["search_query"] = ""
        self.data["items"] = []