行为设计模式之状态模式

// 抽象状态类
class State {
public:
    virtual void Handle(std::string input, std::shared_ptr<State> &currentState) = 0;
};
// 具体状态A
class StateA : public State {
public:
    void Handle(std::string input, std::shared_ptr<State> &currentState) override {
        if (input == "A") {
            std::cout << "StateA: Handle input A." << std::endl;
        } else if (input == "B") {
            std::cout << "StateA: Transition to StateB." << std::endl;
            currentState = std::make_shared<StateB>();
        } else {
            std::cout << "StateA: Invalid input." << std::endl;
        }
    }
};
// 具体状态B
class StateB : public State {
public:
    void Handle(std::string input, std::shared_ptr<State> &currentState) override {
        if (input == "B") {
            std::cout << "StateB: Handle input B." << std::endl;
        } else if (input == "C") {
            std::cout << "StateB: Transition to StateC." << std::endl;
            currentState = std::make_shared<StateC>();
        } else {
            std::cout << "StateB: Invalid input." << std::endl;
        }
    }
};
// 具体状态C
class StateC : public State {
public:
    void Handle(std::string input, std::shared_ptr<State> &currentState) override {
        if (input == "C") {
            std::cout << "StateC: Handle input C." << std::endl;
        } else if (input == "A") {
            std::cout << "StateC: Transition to StateA." << std::endl;
            currentState = std::make_shared<StateA>();
        } else {
            std::cout << "StateC: Invalid input." << std::endl;
        }
    }
};
// 上下文类，维护当前状态并执行请求
class Context {
private:
    std::shared_ptr<State> currentState;
public:
    Context(std::shared_ptr<State> initialState) : currentState(initialState) {}
    void Request(std::string input) {
        currentState->Handle(input, currentState);
    }
};