#include <thread>
#include <chrono>
#include <functional>
#include <iostream>

template<typename I>
class StatisticMonitor {
public:
  typedef std::function<I()> Watcher;

  StatisticMonitor &watch(Watcher tput) {
    this->current_value = tput;
    return *this;
  }

  StatisticMonitor &set_name(std::string name) {
    this->name = std::move(name);
    return *this;
  }

  void launch() {
    if (timer != nullptr) {
      return;
    }
    timer = new std::thread([=]() {
      while (non_terminated) {
      std::cout << name << ": " << current_value() << std::endl;
        std::this_thread::sleep_for(std::chrono::milliseconds(1000));
      }
      std::cout << name << " now terminates. " << endl;
    });
  }

  void terminate() {
    if (timer != nullptr) {
      non_terminated = false;
      timer->join();
      delete timer;
      timer = nullptr;
    }
  }

private:
  bool non_terminated = true;
  std::thread *timer = nullptr;
  std::string name;
  Watcher current_value;
};