enum class State {
    OFF,
    ON
};

enum class Event {
    TOGGLE
};

#include <iostream>
#include <map>

class LightFSM {
public:
    LightFSM() : currentState(State::OFF) {}

    void handleEvent(Event e) {
        auto it = transitions.find({currentState, e});
        if (it != transitions.end()) {
            State newState = it->second;
            exitAction(currentState);
            currentState = newState;
            entryAction(currentState);
        } else {
            std::cout << "No valid transition from current state for this event.\n";
        }
    }

private:
    State currentState;

    // 状态转移表：{当前状态, 事件} -> 下一状态
    std::map<std::pair<State, Event>, State> transitions = {
        {{State::OFF, Event::TOGGLE}, State::ON},
        {{State::ON,  Event::TOGGLE}, State::OFF}
    };

    // 进入状态时的动作
    void entryAction(State s) {
        if (s == State::ON) {
            std::cout << "Light is ON.\n";
        } else if (s == State::OFF) {
            std::cout << "Light is OFF.\n";
        }
    }

    // 退出状态时的动作
    void exitAction(State s) {
        if (s == State::ON) {
            std::cout << "Turning light OFF...\n";
        }
    }
};

int main() {
    LightFSM light;
    
    light.handleEvent(Event::TOGGLE); // 输出：Turning light OFF... Light is ON.
    light.handleEvent(Event::TOGGLE); // 输出：Turning light OFF... Light is OFF.
    light.handleEvent(Event::TOGGLE); // 输出：Light is ON.

    return 0;
}