#include <errno.h>
#include <inttypes.h>
#include <signal.h>
#include <stdio.h>
#include <time.h>

static volatile sig_atomic_t g_run = 1;
static void stop(int s){ (void)s; g_run = 0; }

static double mono(void){
    struct timespec t; clock_gettime(CLOCK_MONOTONIC, &t);
    return (double)t.tv_sec + (double)t.tv_nsec/1e9;
}

int main(void){
    signal(SIGINT, stop); signal(SIGTERM, stop);
    struct timespec base; clock_gettime(CLOCK_REALTIME, &base);
    base.tv_nsec = 0; base.tv_sec += 1;
    double t0 = mono();
    uint64_t tick = 0;

    while (g_run){
        struct timespec dl = base;
        dl.tv_sec += (time_t)tick;
        int rc = clock_nanosleep(CLOCK_REALTIME, TIMER_ABSTIME, &dl, NULL);
        if (rc != 0 && rc != EINTR) break;
        double now = mono();
        double drift = (now - t0 - (double)tick) * 1e3;
        struct timespec r; clock_gettime(CLOCK_REALTIME, &r);
        struct tm mv; localtime_r(&r.tv_sec, &mv);
        printf("[%05" PRIu64 "] t+%09.6fs drift %+7.2fms %02d:%02d:%02d\n",
               tick, now - t0, drift, mv.tm_hour, mv.tm_min, mv.tm_sec);
        fflush(stdout);
        tick++;
    }
    return 0;
}