/*
 * UNG's Not GNU
 *
 * Copyright (c) 2022, Jakob Kaivo <jkk@ung.org>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

#define _POSIX_C_SOURCE 200809L
#include <ctype.h>
#include <errno.h>
#include <fcntl.h>
#include <locale.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <time.h>
#include <unistd.h>

enum times {
	ACCESS = (1<<0),
	MODIFY = (1<<1),
};

static int touch(const char *path, struct timespec times[2], int create)
{
	if (access(path, F_OK) == 0) {
		return utimensat(AT_FDCWD, path, times, 0);
	}

	if (!create) {
		return 0;
	}

	int fd = creat(path, S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
	if (fd == -1) {
		fprintf(stderr, "touch: %s: %s\n", path, strerror(errno));
		return 1;
	}

	if (futimens(fd, times) != 0) {
		fprintf(stderr, "touch: %s: %s\n", path, strerror(errno));
		close(fd);
		return 1;
	}

	return 0;
}

static int twodigits(const char *s, int min, int max)
{
	char buf[3] = { s[0], s[1], '\0' };
	if (!(isdigit(buf[0]) && isdigit(buf[1]))) {
		fprintf(stderr, "touch: invalid time\n");
		exit(1);
	}
	int ret = atoi(buf);
	if (ret < min || ret > max) {
		fprintf(stderr, "touch: invalid time\n");
		exit(1);
	}
	return ret;
}

static struct timespec convert_time(const char *date)
{
	struct timespec ts = { 0 };
	time_t now = time(NULL);
	struct tm *tm = localtime(&now);
	tm->tm_yday = 0;
	tm->tm_wday = 0;
	int century = -1;

	char *dot = strchr(date, '.');
	if (dot) {
		if (strlen(dot + 1) != 2) {
			fprintf(stderr, "invalid time\n");
			exit(1);
		}
		tm->tm_sec = twodigits(dot + 1, 0, 60);
	} else {
		tm->tm_sec = 0;
	}

	switch (strlen(date) - (dot ? 3 : 0)) {
	case 12:	/* CC */
		century = twodigits(date, 0, 100) - 19;
		date += 2;
		/* FALLTHRU */
	case 10:	/* YY */
		if (century == -1) {
			tm->tm_year = twodigits(date, 0, 100);
			if (00 <= tm->tm_year && tm->tm_year <= 68) {
				tm->tm_year += 100;
			}
		} else {
			tm->tm_year = (century * 100) + twodigits(date, 0, 100);
		}
		date += 2;
		/* FALLTHRU */
	case 8:		/* MM */
		tm->tm_mon = twodigits(date, 1, 12) - 1;
		date += 2;
		tm->tm_mday = twodigits(date, 1, 31);
		date += 2;
		tm->tm_hour = twodigits(date, 0, 23);
		date += 2;
		tm->tm_min = twodigits(date, 0, 59);
		break;
	default:
		fprintf(stderr, "invalid time\n");
		exit(1);
	}

	/* TODO: account for TZ */
	/* TODO: time too great to represent */

	ts.tv_sec = mktime(tm);

	return ts;
}

static int getnext(const char *current, char **next, size_t ndigits, char *term, int min, int max)
{
	char buf[ndigits + 1];
	for (size_t i = 0; i < ndigits; i++) {
		if (!isdigit(current[i])) {
			return -1;
		}
		buf[i] = current[i];
	}
	buf[ndigits] = '\0';

	char *end = NULL;
	long ret = strtol(buf, &end, 10);
	if (!strchr(term, *end)) {
		fprintf(stderr, "touch: invalid date\n");
		exit(1);
	}
	if (ret < min || ret > max) {
		fprintf(stderr, "touch: invalid date\n");
		exit(1);
	}

	*next = (char*)current + ndigits + 1;
	return ret;
}

static struct timespec convert_date(char *date)
{
	struct timespec ts = { 0 };
	struct tm tm = { 0 };
	char *next = (char*)date;

	tm.tm_year = getnext(next, &next, 4, "-", 0, 10000) - 1900;
	tm.tm_mon = getnext(next, &next, 2, "-", 1, 12) - 1;
	tm.tm_mday = getnext(next, &next, 2, "T ", 1, 31);
	tm.tm_hour = getnext(next, &next, 2, ":", 0, 23);
	tm.tm_min = getnext(next, &next, 2, ":", 0, 59);
	tm.tm_sec = getnext(next, &next, 2, ".,", 0, 60);

	char *dec = strchr(date, '.') ? strchr(date, '.') : strchr(date, ',');
	if (dec) {
		*dec = '.';
		double d = strtod(dec, &next);
		ts.tv_nsec = d * 1000000000;
	}

	/* TODO: tz */
	/* TODO: time is too large */

	ts.tv_sec = mktime(&tm);

	return ts;
}

int main(int argc, char *argv[])
{
	setlocale(LC_ALL, "");
	enum times which = 0;
	int create = 1;
	enum { CURRENT, TIME, DATE, FILE } how = CURRENT;
	char *source = NULL;

	int c;
	while ((c = getopt(argc, argv, "acmr:t:d:")) != -1) {
		switch(c) {
		case 'a':
			which |= ACCESS;
			break;

		case 'c':
			create = 0;
			break;

		case 'm':
			which |= MODIFY;
			break;

		case 'd':
			if (how != CURRENT) {
				fprintf(stderr, "touch: only one of -d, -r, and -t is allowed\n");
				return 1;
			}
			how = DATE;
			source = optarg;
			break;

		case 'r':
			if (how != CURRENT) {
				fprintf(stderr, "touch: only one of -d, -r, and -t is allowed\n");
				return 1;
			}
			how = FILE;
			source = optarg;
			break;

		case 't':
			if (how != CURRENT) {
				fprintf(stderr, "touch: only one of -d, -r, and -t is allowed\n");
				return 1;
			}
			how = TIME;
			source = optarg;
			break;

		default:
			return 1;
		}
	}

	if (optind >= argc) {
		fprintf(stderr, "touch: missing operands\n");
		return 1;
	}

	struct timespec times[2] = { { 0 } };
	struct stat st;

	switch (how) {
	case CURRENT:
		times[0].tv_nsec = UTIME_NOW;
		times[1].tv_nsec = UTIME_NOW;
		break;
	case DATE:
		times[0] = times[1] = convert_date(source);
		break;
	case TIME:
		times[0] = times[1] = convert_time(source);
		break;
	case FILE:
		if (stat(source, &st) != 0) {
			fprintf(stderr, "touch: %s: %s\n", source, strerror(errno));
			return 1;
		}
		times[0] = st.st_atim;
		times[1] = st.st_mtim;
	}

	if (which == 0) {
		which = ACCESS | MODIFY;
	}

	if (!(which & ACCESS)) {
		times[0].tv_nsec = UTIME_OMIT;
	}

	if (!(which & MODIFY)) {
		times[1].tv_nsec = UTIME_OMIT;
	}

	int ret = 0;
	do {
		ret |= touch(argv[optind++], times, create);
	} while (optind < argc);
	return ret;
}