// g++ -o main main.cpp
#include <unistd.h>
#include <dirent.h>
#include <sys/stat.h>
#include <signal.h>

#include <cstdio>
#include <cstdint>
#include <iostream>
#include <fstream>
#include <algorithm>
#include <string>
#include <cstring>
#include <chrono>
#include <thread>

static bool should_exit = false;

static void SignalHandler(int sig)
{
    if (sig == SIGINT)
    {
        std::cerr << "KeyboardInterrupt" << std::endl;
        should_exit = true;
    }
}

class Sampler
{
public:
    inline Sampler(double frequency)
        : expected_cycle_time_(static_cast<int32_t>((1.0 / frequency) * 1000000))
    {
        signal(SIGINT, SignalHandler);
    }

    template <typename Fn, typename... Args>
    inline void Run(Fn&& fx, Args&& ... args)
    {
        auto func = std::bind(std::forward<Fn>(fx), std::forward<Args>(args)...);

        start_ = std::chrono::steady_clock::now();
        while (!should_exit)
        {
            func();
            Sleep();
        }
    }

private:
    inline bool Sleep()
    {
        std::chrono::steady_clock::time_point expected_end = start_ + expected_cycle_time_;
        std::chrono::steady_clock::time_point actual_end = std::chrono::steady_clock::now();

        // detect backward jumps in time
        if (actual_end < start_)
        {
            expected_end = actual_end + expected_cycle_time_;
        }

        // calculate the time we'll sleep for
        std::chrono::duration<int32_t, std::micro> sleep_time = std::chrono::duration_cast<std::chrono::microseconds>(expected_end - actual_end);
        // make sure to reset our start time
        start_ = expected_end;

        // if we've taken too much time we won't sleep
        if (sleep_time <= std::chrono::duration<int32_t, std::micro>(0))
        {
            // if we've jumped forward in time, or the loop has taken more than
a full extra
            // cycle, reset our cycle
            if (actual_end > expected_end + expected_cycle_time_)
            {
                start_ = actual_end;
            }

            // return false to show that the desired rate was not met
            return false;
        }

        std::this_thread::sleep_for(sleep_time);
        return true;
    }

private:
    std::chrono::steady_clock::time_point start_;
    std::chrono::duration<int32_t, std::micro> expected_cycle_time_;
};

inline uint64_t NowTimestampMs()
{
    return static_cast<uint64_t>(std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::system_clock::now().time_since_epoch()).count());
}

inline bool IsNumber(std::string &s)
{
    return std::all_of(s.begin(), s.end(), [](char c){ return std::isdigit(c) != 0; });
}

inline bool IsNumber(const char *s)
{
    return std::all_of(s, s + std::strlen(s), [](char c){ return std::isdigit(c) != 0; });
}

int64_t CollectMemoryInfo()
{
    static const std::string ProcPath = "/proc";

    DIR *dir {nullptr};
    struct dirent *ptr {nullptr};
    std::string stmt_path{};
    char line_buffer[256];

    int64_t all = 0;

    if ((dir = opendir(ProcPath.c_str())) == nullptr)
    {
        std::cerr << "Failed to open " << ProcPath << std::endl;
        exit(1);
    }

    while ((ptr = readdir(dir)) != nullptr)
    {
        struct stat buff{};

        if (ptr->d_type == DT_DIR && IsNumber(ptr->d_name))
        {
            stmt_path.clear();

            stmt_path.append(ProcPath).append("/").append(ptr->d_name).append("/").append("smaps");

            if (access(stmt_path.c_str(), R_OK) == 0)
            {
                std::ifstream ifs(stmt_path);

                while (ifs.getline(line_buffer, sizeof(line_buffer)))
                {
                    if (std::sscanf(line_buffer, "Pss: %d", &pss) == 1)
                    {
                        all += pss;
                    }
                }
            }
        }
    }
    closedir(dir);

    return all;
}

int main ()
{
    Sampler sampler(50);

    sampler.Run([]{
        auto memory_usage_in_kb = CollectMemoryInfo();
        auto now_timestamp_ms = NowTimestampMs();

        std::cout << now_timestamp_ms << "," << memory_usage_in_kb << "\n";
    });

    return 0;
}