/*
 * nqtail [FILES...] - follow output of nq jobs, quitting when they are done
 *
 * To the extent possible under law, Leah Neukirchen <leah@vuxu.org>
 * has waived all copyright and related or neighboring rights to this work.
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

#include <sys/file.h>
#include <sys/stat.h>
#include <sys/types.h>

#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <limits.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define DELAY 250000

#ifdef __linux__
#define USE_INOTIFY
#endif

#if defined(__FreeBSD__) || defined(__APPLE__)
#define USE_KEVENT
#endif

#ifdef USE_INOTIFY
#include <sys/inotify.h>
char ibuf[8192];
#endif

#ifdef USE_KEVENT
#include <sys/event.h>
#endif

char buf[8192];

static int
islocked(int fd)
{
	if (flock(fd, LOCK_SH | LOCK_NB) == -1) {
		return (errno == EWOULDBLOCK);
	} else {
		flock(fd, LOCK_UN);
		return 0;
	}
}

static int
alphabetic(const void *a, const void *b)
{
	return strcmp(*(char **)a, *(char **)b);
}

int
main(int argc, char *argv[])
{
	int i, fd, dirfd;
	off_t off, loff;
	ssize_t rd;
	int didsth = 0, seen_nl = 0;
	int opt = 0, aflag = 0, nflag = 0, qflag = 0;
	char *path;

#ifdef USE_INOTIFY
	int ifd, wd;
#endif
#ifdef USE_KEVENT
	int kq, note;
	struct kevent kev;
#endif

	close(0);

	while ((opt = getopt(argc, argv, "+anq")) != -1) {
		switch (opt) {
		case 'a':
			aflag = 1;
			break;
		case 'n':
			nflag = 1;
			break;
		case 'q':
			qflag = 1;
			break;
		default:
			fputs("usage: nqtail [-anq] [JOBID...]\n", stderr);
			exit(1);
		}
	}

	path = getenv("NQDIR");
	if (!path)
		path = ".";

#ifdef O_DIRECTORY
	dirfd = open(path, O_RDONLY | O_DIRECTORY);
#else
	dirfd = open(path, O_RDONLY);
#endif
	if (dirfd < 0) {
		perror("open dir");
		exit(111);
	}

	if (optind == argc) {   /* behave as if $NQDIR/,* was passed. */
		DIR *dir;
		struct dirent *d;
		int len = 0;

		argc = 0;
		argv = 0;
		optind = 0;

		dir = fdopendir(dirfd);
		if (!dir) {
			perror("fdopendir");
			exit(111);
		}

		while ((d = readdir(dir))) {
			if (d->d_name[0] != ',')
				continue;
			if (argc >= len) {
				len = 2*len + 1;
				argv = realloc(argv, len * sizeof (char *));
				if (!argv)
					exit(222);
			}
			argv[argc] = strdup(d->d_name);
			if (!argv[argc])
				exit(222);
			argc++;
		}

		qsort(argv, argc, sizeof (char *), alphabetic);
	}

#ifdef USE_INOTIFY
	ifd = inotify_init();
	if (ifd < 0)
		exit(111);
#endif
#ifdef USE_KEVENT
	kq = kqueue();
	if (kq < 0)
		exit(111);
#endif

	for (i = optind; i < argc; i++) {
		loff = 0;
		seen_nl = 0;

		fd = openat(dirfd, argv[i], O_RDONLY);
		if (fd < 0)
			continue;

		/* skip not running jobs, unless -a was passed, or we did not
		 * output anything yet and are at the last argument.  */
		if (!aflag && !islocked(fd) && (didsth || i != argc - 1)) {
			close(fd);
			continue;
		}

		write(1, "==> ", 4);
		write(1, argv[i], strlen(argv[i]));
		write(1, qflag ? " " : "\n", 1);

		didsth = 1;

#ifdef USE_INOTIFY
		char fullpath[PATH_MAX];
		snprintf(fullpath, sizeof fullpath, "%s/%s", path, argv[i]);
		wd = inotify_add_watch(ifd, fullpath, IN_MODIFY | IN_CLOSE_WRITE);
		if (wd == -1) {
			perror("inotify_add_watch");
			exit(111);
		}
#endif
#ifdef USE_KEVENT
		note = NOTE_WRITE;
#ifdef __APPLE__
		note |= NOTE_FUNLOCK;
#endif
#ifdef __FreeBSD__
		note |= NOTE_CLOSE_WRITE;
#endif
		EV_SET(&kev, fd, EVFILT_VNODE, EV_ADD | EV_CLEAR, note, 0, NULL);
		if (kevent(kq, &kev, 1, NULL, 0, NULL) < 0) {
			perror("kevent");
			exit(111);
		}
#endif

		while (1) {
			off = lseek(fd, 0, SEEK_END);

			if (off < loff)
				loff = off;               /* file truncated */

			if (off == loff) {
				if (nflag && islocked(fd))
					break;

				if (flock(fd, LOCK_SH | LOCK_NB) == -1 &&
				    errno == EWOULDBLOCK) {
#if defined(USE_INOTIFY)
					/* any inotify event is good */
					read(ifd, ibuf, sizeof ibuf);
#elif defined(USE_KEVENT)
					kevent(kq, NULL, 0, &kev, 1, NULL);
#else
					/* poll for size change */
					while (off == lseek(fd, 0, SEEK_END))
						usleep(DELAY);
#endif
					continue;
				} else {
					flock(fd, LOCK_UN);
					break;
				}
			}

			if (off - loff > sizeof buf)
				off = loff + sizeof buf;

			rd = pread(fd, &buf, off - loff, loff);
			if (qflag) {
				if (!seen_nl) {
					char *s;
					if ((s = memchr(buf, '\n', rd))) {
						write(1, buf, s+1-buf);
						seen_nl = 1;
					} else {
						write(1, buf, rd);
					}
				}
			} else {
				write(1, buf, rd);
			}

			loff += rd;
		}

		if (qflag && !seen_nl)
			write(1, "\n", 1);

#ifdef USE_INOTIFY
		inotify_rm_watch(ifd, wd);
#endif
#ifdef USE_KEVENT
		EV_SET(&kev, fd, EVFILT_VNODE, EV_DELETE, 0, 0, NULL);
		kevent(kq, &kev, 1, NULL, 0, NULL);
#endif
		close(fd);
	}

#ifdef USE_INOTIFY
	close(ifd);
#endif
#ifdef USE_KEVENT
	close(kq);
#endif
	return 0;
}