/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2023 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/calls/calls.h"
#include "libc/calls/struct/itimerval.h"
#include "libc/calls/struct/sigaction.h"
#include "libc/calls/struct/timespec.h"
#include "libc/calls/struct/timeval.h"
#include "libc/fmt/itoa.h"
#include "libc/sysv/consts/itimer.h"
#include "libc/sysv/consts/sig.h"

#define HZ 120

struct timeval start;
struct timeval expect;
struct timeval interval = {0, 1e6 / HZ};

void OnTick(int sig) {
  char ibuf[27];
  struct timeval now = timeval_real();
  switch (timeval_cmp(now, expect)) {
    case 0:
      tinyprint(1, "100% precise\n", NULL);
      break;
    case -1:
      FormatInt64Thousands(ibuf, timeval_tomicros(timeval_sub(expect, now)));
      tinyprint(1, ibuf, " µs early\n", NULL);
      break;
    case +1:
      FormatInt64Thousands(ibuf, timeval_tomicros(timeval_sub(now, expect)));
      tinyprint(1, ibuf, " µs late\n", NULL);
      break;
    default:
      __builtin_unreachable();
  }
  expect = timeval_add(expect, interval);
}

int main(int argc, char *argv[]) {
  start = timeval_real();
  expect = timeval_add(start, interval);
  signal(SIGALRM, OnTick);
  setitimer(ITIMER_REAL, &(struct itimerval){interval, interval}, 0);
  for (;;) pause();
}