/*
 * inotail.c
 * A fast implementation of tail which uses the inotify-API present in
 * recent Linux Kernels.
 *
 * Copyright (C) 2005-2006, Tobias Klauser <tklauser@distanz.ch>
 *
 * The idea was taken from turbotail.
 *
 * This program is free software; you can redistribute it and/or modify it under
 * the terms of the GNU General Public License as published by the Free Software
 * Foundation; either version 2, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
 * FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
 * details.
 *
 * You should have received a copy of the GNU General Public License along with
 * this program; if not, write to the Free Software Foundation, Inc., 51
 * Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
 */

#define _GNU_SOURCE

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <getopt.h>
#include <sys/types.h>
#include <sys/stat.h>

#include "inotify.h"
#include "inotify-syscalls.h"

#include "inotail.h"

#define PROGRAM_NAME "inotail"
#define BUFFER_SIZE 4096

/* Print header with filename before tailing the file? */
static char verbose = 0;

static const struct option long_opts[] = {
	{"bytes", required_argument, NULL, 'c'},
	{"follow", optional_argument, NULL, 'f'},
	{"lines", required_argument, NULL, 'n'},
	{"verbose", no_argument, NULL, 'v'},
	{"help", no_argument, NULL, 'h'},
	{"version", no_argument, NULL, 'V'},
	{NULL, 0, NULL, 0}
};

static void usage(const int status)
{
	fprintf(stderr, "Usage: %s [OPTION]... [FILE]...\n\n", PROGRAM_NAME);
	fprintf(stderr, "  -c N, --bytes=N    output the last N bytes\n");
	fprintf(stderr, "  -f,   --follow     output as the file grows\n");
	fprintf(stderr, "  -n N, --lines=N    output the last N lines (default: %d)\n", DEFAULT_N_LINES);
	fprintf(stderr, "  -v,   --verbose    print headers with file names\n");
	fprintf(stderr, "  -h,   --help       show this help and exit\n");
	fprintf(stderr, "  -V,   --version    show version and exit\n");

	exit(status);
}

static void setup_file(struct file_struct *f)
{
	f->fd = -1;
	f->st_size = 0;
	f->ignore = 0;
	f->i_watch = -1;
}

static char *pretty_name(char *filename)
{
	return (strncmp(filename, "-", 1) == 0) ? "standard input" : filename;
}

static void write_header(char *filename)
{
	static unsigned short first_file = 1;

	fprintf(stdout, "%s==> %s <==\n", (first_file ? "" : "\n"), pretty_name(filename));
	first_file = 0;
}

static off_t lines_to_offset(struct file_struct *f, unsigned int n_lines)
{
	char buf[BUFFER_SIZE];
	off_t offset = f->st_size;

	memset(&buf, 0, sizeof(buf));

	/* We also count the last \n */
	n_lines += 1;

	while (offset > 0 && n_lines > 0) {
		int i, rc;
		int block_size = BUFFER_SIZE; /* Size of the current block we're reading */

		if (offset < BUFFER_SIZE)
			block_size = offset;

		/* Start of current block */
		offset -= block_size;

		lseek(f->fd, offset, SEEK_SET);

		rc = read(f->fd, &buf, block_size);
		if (rc < 0) {
			fprintf(stderr, "Error: Could not read from file '%s' (%s)\n", f->name, strerror(errno));
			return -1;
		}

		for (i = block_size; i > 0; i--) {
			if (buf[i] == '\n') {
				n_lines--;

				if (n_lines == 0) {
					offset += i + 1; /* We don't want the first \n */
					break;
				}
			}
		}
	}

	return offset;
}

static int bytes_to_offset(struct file_struct *f, int n_lines)
{
	int ret = f->st_size - n_lines;

	return (ret < 0 ? 0 : ret);
}

/* We will just tail everything here */
static int tail_pipe(struct file_struct *f)
{
	if (verbose)
		write_header(f->name);
	return 0;
}

static int tail_file(struct file_struct *f, int n_lines, char mode)
{
	ssize_t rc = 0;
	off_t offset = 0;
	char buf[BUFFER_SIZE];
	struct stat finfo;

	if (strncmp(f->name, "-", 1) == 0)
		f->fd = STDIN_FILENO;
	else {
		f->fd = open(f->name, O_RDONLY);
		if (f->fd < 0) {
			fprintf(stderr, "Error: Could not open file '%s' (%s)\n", f->name, strerror(errno));
			return -1;
		}
	}

	if (fstat(f->fd, &finfo) < 0) {
		fprintf(stderr, "Error: Could not stat file '%s' (%s)\n", f->name, strerror(errno));
		close(f->fd);
		return -1;
	}

	/* We cannot seek on these */
	if (!S_ISREG(finfo.st_mode) || f->fd == STDIN_FILENO)
		return tail_pipe(f);

	f->st_size = finfo.st_size;

	if (mode == M_LINES)
		offset = lines_to_offset(f, n_lines);
	else /* Bytewise tail, n_lines is number of bytes here */
		offset = bytes_to_offset(f, n_lines);

	/* We only get negative offsets on errors */
	if (offset < 0)
		return -1;

	if (verbose)
		write_header(f->name);

	lseek(f->fd, offset, SEEK_SET);

	while ((rc = read(f->fd, &buf, BUFFER_SIZE)) > 0)
		write(STDOUT_FILENO, buf, (size_t) rc);

	if (close(f->fd) < 0)
		fprintf(stderr, "Error: Could not close file '%s' (%s)\n", f->name, strerror(errno));

	return 0;
}

static int watch_files(struct file_struct *f, int n_files)
{
	int ifd, i, n_ignored = 0;
	off_t offset;
	struct inotify_event *inev;
	char buf[sizeof(struct inotify_event) * 32];	/* Let's hope we don't get more than 32 events at a time */

	ifd = inotify_init();
	if (ifd < 0) {
		fprintf(stderr, "Error: Inotify is not supported by the kernel you're currently running.\n");
		exit(EXIT_FAILURE);
	}

	for (i = 0; i < n_files; i++) {
		if (!f[i].ignore)
			f[i].i_watch = inotify_add_watch(ifd, f[i].name,
						IN_MODIFY|IN_DELETE_SELF|IN_MOVE_SELF|IN_UNMOUNT);
		else
			n_ignored++;
	}

	memset(&buf, 0, sizeof(buf));

	while (n_ignored < n_files) {
		int len;

		len = read(ifd, buf, sizeof(buf));
		inev = (struct inotify_event *) &buf;

		while (len > 0) {
			struct file_struct *fil;

			/* Which file has produced the event? */
			for (i = 0; i < n_files; i++) {
				if (!f[i].ignore && f[i].fd >= 0 && f[i].i_watch == inev->wd) {
					fil = &f[i];
					break;
				}
			}

			/* XXX: Is it possible that no file in the list produced the event? */
			if (inev->mask & IN_MODIFY) {
				int rc;
				char fbuf[BUFFER_SIZE];
				struct stat finfo;

				fil->fd = open(fil->name, O_RDONLY);
				if (fil->fd < 0) {
					fil->ignore = 1;
					n_ignored++;
					fprintf(stderr, "Error: Could not open file '%s' (%s)\n", f->name, strerror(errno));
					continue;
				}

				if (fstat(fil->fd, &finfo) < 0) {
					fil->ignore = 1;
					n_ignored++;
					fprintf(stderr, "Error: Could not stat file '%s' (%s)\n", f->name, strerror(errno));
					close(fil->fd);
					continue;
				}

				offset = fil->st_size;
				fil->st_size = finfo.st_size;

				if (verbose)
					write_header(fil->name);

				memset(&fbuf, 0, sizeof(fbuf));

				lseek(fil->fd, offset, SEEK_SET);
				while ((rc = read(fil->fd, &fbuf, BUFFER_SIZE)) != 0)
					write(STDOUT_FILENO, fbuf, rc);

				close(fil->fd);
			} else if (inev->mask & IN_DELETE_SELF) {
				fil->ignore = 1;
				n_ignored++;
				fprintf(stderr, "File '%s' deleted.\n", fil->name);
			} else if (inev->mask & IN_MOVE_SELF) {
				fil->ignore = 1;
				n_ignored++;
				fprintf(stderr, "File '%s' moved.\n", fil->name);
				/* TODO: Try to follow file/fd */
			} else if (inev->mask & IN_UNMOUNT) {
				fil->ignore = 1;
				n_ignored++;
				fprintf(stderr, "Device containing file '%s' unmounted.\n", fil->name);
			}

			len -= sizeof(struct inotify_event) + inev->len;
			inev = (struct inotify_event *) ((char *) inev + sizeof(struct inotify_event) + inev->len);
		}
	}

	close(ifd);

	return -1;
}

int main(int argc, char **argv)
{
	int i, c, ret = 0;
	int n_files = 0;
	int n_lines = DEFAULT_N_LINES;
	char forever = 0, mode = M_LINES;
	char **filenames;
	struct file_struct *files;

	while ((c = getopt_long(argc, argv, "c:n:fvVh", long_opts, NULL)) != -1) {
		switch (c) {
		case 'c':
		case 'n':
			if (c == 'c')
				mode = M_BYTES;
			n_lines = strtoul(optarg, NULL, 0);
			if (n_lines < 0)
				n_lines = 0;
			break;
                case 'f':
			forever = 1;
			break;
		case 'v':
			verbose = 1;
			break;
		case 'V':
			fprintf(stderr, "%s %s\n", PROGRAM_NAME, VERSION);
			return 0;
		case 'h':
			usage(EXIT_SUCCESS);
		default:
			usage(EXIT_FAILURE);
		}
	}

	/* Do we have some files to read from? */
	if (optind < argc) {
		n_files = argc - optind;
		filenames = argv + optind;
	} else {
		/* It must be stdin then */
		static char *dummy_stdin = "-";
		n_files++;
		filenames = &dummy_stdin;

		/* POSIX says that -f is ignored if no file operand is
		   specified and standard input is a pipe. */
		if (forever) {
			struct stat finfo;
			if (fstat(STDIN_FILENO, &finfo) == 0
					&& (S_ISFIFO(finfo.st_mode) || S_ISSOCK(finfo.st_mode)))
				forever = 0;
		}
	}

	files = malloc(n_files * sizeof(struct file_struct));
	for (i = 0; i < n_files; i++) {
		files[i].name = filenames[i];
		setup_file(&files[i]);
		ret = tail_file(&files[i], n_lines, mode);
		if (ret < 0)
			files[i].ignore = 1;
	}

	if (forever)
		ret = watch_files(files, n_files);

	free(files);

	return ret;
}