command.cpp

// Command design pattern

#include <cstddef>
#include <iostream>

// device interface (receivers)
class IDevice {
  protected:
    bool is_on_ = false;
    std::size_t volume_ = 0;

  public:
    virtual void on() = 0;
    virtual void off() = 0;
    virtual void up() = 0;
    virtual void down() = 0;
    virtual ~IDevice() = default;

    bool is_on() const { return is_on_; }

    std::size_t get_volume() const { return volume_; }
};

// command interface
class ICommand {
  protected:
    IDevice& device_;

  public:
    ICommand(IDevice& device) : device_{device} {}
    virtual void execute() = 0;
    virtual void undo() = 0;
    virtual ~ICommand() = default;
};

// devices
class TV : public IDevice {
    void on() override {
        is_on_ = true;
        std::cout << "TV is ON\n";
    }

    void off() override {
        is_on_ = false;
        std::cout << "TV is OFF\n";
    }

    void up() override {
        if (volume_ < 10) {
            ++volume_;
        }
        std::cout << "Turning volume up to   " << volume_ << '\n';
    }

    void down() override {
        if (volume_ > 0) {
            --volume_;
        }
        std::cout << "Turning volume down to " << volume_ << '\n';
    }
};

// commands
class Turn_ON : public ICommand {
  public:
    using ICommand::ICommand;
    void execute() override { device_.on(); }

    void undo() override { device_.off(); }
};

class Turn_OFF : public ICommand {
  public:
    using ICommand::ICommand;
    void execute() override { device_.off(); }

    void undo() override { device_.on(); }
};

class Turn_UP : public ICommand {
  public:
    using ICommand::ICommand;
    void execute() override { device_.up(); }

    void undo() override { device_.down(); }
};

class Turn_DOWN : public ICommand {
  public:
    using ICommand::ICommand;
    void execute() override { device_.down(); }

    void undo() override { device_.up(); }
};

int main() {
    TV tv; // a concrete device

    // some commands
    Turn_ON turn_on(tv);
    Turn_OFF turn_off(tv);
    Turn_UP turn_up(tv);
    Turn_DOWN turn_down(tv);

    // execute/undo the commands
    turn_on.execute(); // execute
    turn_off.execute();
    turn_off.undo(); // undo

    turn_up.execute();
    turn_up.execute();
    turn_down.execute();
    turn_up.undo();
    turn_up.undo(); // the volume cannot be less than zero

    for (std::size_t i = 0; i < 12; ++i) {
        turn_up.execute(); // the volume cannot be greater than 10
    }

    turn_off.execute();

    std::cout << "Is the TV ON? " << std::boolalpha << tv.is_on() << '\n';
    std::cout << "Final TV volume: " << tv.get_volume() << '\n';
}