#include <sys/event.h>
#include <sys/time.h>
#include <stdio.h>
#include <sched.h>
#include <err.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h> 
#include <unistd.h>
#include <getopt.h>
#include <signal.h>
#include <stdbool.h>

static int verbose;
const struct sched_param param = {.sched_priority = 15};
static struct option longopts[] = {
	{ "period",   required_argument,      NULL, 'p' },
	{ "verbose",  no_argument      ,  &verbose,  1  },
	{ NULL,	0, NULL, 0 }
};

void fd_close(int *fd) {
	close(*fd);
	*fd = -1;
}
#define _smartfd __attribute((cleanup(fd_close)))

void file_close(FILE **fd) {
	fclose(*fd);
	*fd = NULL;
}
#define _smartfile __attribute((cleanup(file_close)))

__attribute__((noreturn))static int usage(void)
{
	fputs("kq_timer [--verbose] [--period ms]\n", stderr);
	exit (EXIT_SUCCESS);
}

__attribute__((const)) static double diff_ms(const struct timespec * restrict time1, const struct timespec * restrict time0)
{
	return (double)(time1->tv_sec - time0->tv_sec) * 1000.0
		+ (double)(time1->tv_nsec - time0->tv_nsec) / 1000000.0;
}

static void sig_handler(int sig)
{
	signal(SIGINT, SIG_DFL);
}

int main(int argc, char *argv[])
{
	struct kevent change; /* event we want to monitor */
	struct kevent event;  /* event that was triggered */
	_smartfd int kq;
	int nev; /* handlers */
	int ch; /* opt long */

	int period = 1000; /* Default to 1 sec. */
	size_t counter = 0;
	size_t total = 0;
	_smartfile FILE *fd = NULL;
	char template[64];
	int rc = EXIT_FAILURE;
	struct	timespec t0 = { 0, 0};

	while ((ch = getopt_long(argc, argv, "hvp:", longopts, NULL)) != -1) {
		switch (ch) {
			case 'v':
				verbose = 1;
				break;
			case 'p':
				period = atoi(optarg);
				break;
			case 0:
				/* long option */
				break;
			default:
				usage();
		}
	}

	argc -= optind;
	argv += optind;

	if (*argv)
		usage();

	/* create a new kernel event queue */
	if ((kq = kqueue()) == -1)
		err(EXIT_FAILURE, "kqueue() failure");

	/* initalise kevent structure */
	EV_SET(&change, 1, EVFILT_TIMER, EV_ADD | EV_ENABLE, NOTE_MSECONDS, 1, 0);

	/* Dummy file to store measurements */
	strncpy(template, "/tmp/timer.XXXXXX", sizeof template);
	if (mkstemp(template) == -1) {
		warn("mkstemp() failure");
		return EXIT_FAILURE;
	}

	fd = fopen(template, "w");
	if (fd == NULL) {
		warn("fopen() failure");
		return EXIT_FAILURE;
	}

	printf("Log file: %s\n", template);

	/* process priority */
	if (-1 == sched_setscheduler(0, SCHED_RR, &param)) {
		warn("set scheduler() failure");
	}

	signal(SIGINT, sig_handler);

	while (true) {
		nev = kevent(kq, &change, 1, &event, 1, NULL);

		if (nev < 0) {
			if (errno != EINTR)
				warn("kevent wait:");
			/* interrupted */
			break;
		}

		if (nev > 0) {

			/* measurements */
			struct	timespec t1;
			clock_gettime(CLOCK_MONOTONIC, &t1);

			if (!(t0.tv_sec == 0 && t0.tv_nsec == 0)) {
				fprintf(fd, "%06.3f\n", diff_ms(&t1, &t0));
				++total;
			}

			t0 = t1;

			if (event.flags & EV_ERROR) {
				fprintf(stderr, "EV_ERROR: %s\n", strerror((int)event.data));
				rc = EXIT_FAILURE;
				break;
			}

			/* verbose mode */
			++counter;
			if (counter == period) {
				if (verbose) {
					fputs(".", stdout);
					fflush(stdout);
				}

				counter = 0;
			}
		}
	}

	rc = EXIT_SUCCESS;

	fprintf(stdout, "\n%zu entries stored.\n", total);
	fprintf(stdout, "%zu cycles counted.\n", counter);

	return rc;
}