/*
  ntp_clock.h

  https://stackoverflow.com/a/17138183
*/
#pragma once

#include <chrono>

/**
 * @brief The ntp_clock class
 */
struct ntp_clock
{
    typedef std::chrono::nanoseconds           duration;     //!< nanosecond resolution
    typedef duration::rep                      rep;          //!< as per duration
    typedef duration::period                   period;       //!< as per duration
    typedef std::chrono::time_point<ntp_clock> time_point;   //!< time points in this clock
    static const bool is_steady =              false;        //!< not a steady clock

    /**
     * Use the system clock (POSIX epoch, 1/1/1970) to calculate time since the start of
     * the \cite NTPv4 NTP epoch 0, 1/1/1900.
     *
     * @return
     */
    static time_point now() noexcept
    {
        using namespace std::chrono;
        return time_point
            (
                duration_cast<duration>(system_clock::now().time_since_epoch())
                                        + seconds(2208988800)   // difference between epochs
            );
    }
};