/*	$NetBSD: tm.c,v 1.7 2022/09/23 12:15:33 christos Exp $	*/

/*
 * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
 *
 * SPDX-License-Identifier: MPL-2.0 AND BSD-2-Clause
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, you can obtain one at https://mozilla.org/MPL/2.0/.
 *
 * See the COPYRIGHT file distributed with this work for additional
 * information regarding copyright ownership.
 */

/*-
 * Copyright (c) 1997, 1998 The NetBSD Foundation, Inc.
 * All rights reserved.
 *
 * This code was contributed to The NetBSD Foundation by Klaus Klein.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 * POSSIBILITY OF SUCH DAMAGE.
 */

#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#include <isc/tm.h>
#include <isc/util.h>

/*
 * Portable conversion routines for struct tm, replacing
 * timegm() and strptime(), which are not available on all
 * platforms and don't always behave the same way when they
 * are.
 */

/*
 * We do not implement alternate representations. However, we always
 * check whether a given modifier is allowed for a certain conversion.
 */
#define ALT_E 0x01
#define ALT_O 0x02
#define LEGAL_ALT(x)                          \
	{                                     \
		if ((alt_format & ~(x)) != 0) \
			return ((0));         \
	}

#ifndef TM_YEAR_BASE
#define TM_YEAR_BASE 1900
#endif /* ifndef TM_YEAR_BASE */

static const char *day[7] = { "Sunday",	  "Monday", "Tuesday", "Wednesday",
			      "Thursday", "Friday", "Saturday" };
static const char *abday[7] = {
	"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
};
static const char *mon[12] = {
	"January", "February", "March",	    "April",   "May",	   "June",
	"July",	   "August",   "September", "October", "November", "December"
};
static const char *abmon[12] = { "Jan", "Feb", "Mar", "Apr", "May", "Jun",
				 "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" };
static const char *am_pm[2] = { "AM", "PM" };

static int
conv_num(const char **buf, int *dest, int llim, int ulim) {
	int result = 0;

	/* The limit also determines the number of valid digits. */
	int rulim = ulim;

	if (!isdigit((unsigned char)**buf)) {
		return (0);
	}

	do {
		result *= 10;
		result += *(*buf)++ - '0';
		rulim /= 10;
	} while ((result * 10 <= ulim) && rulim && **buf >= '0' &&
		 **buf <= '9');

	if (result < llim || result > ulim) {
		return (0);
	}

	*dest = result;
	return (1);
}

time_t
isc_tm_timegm(struct tm *tm) {
	time_t ret;
	int i, yday = 0, leapday;
	int mdays[] = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30 };

	leapday = ((((tm->tm_year + 1900) % 4) == 0 &&
		    ((tm->tm_year + 1900) % 100) != 0) ||
		   ((tm->tm_year + 1900) % 400) == 0)
			  ? 1
			  : 0;
	mdays[1] += leapday;

	yday = tm->tm_mday - 1;
	for (i = 1; i <= tm->tm_mon; i++) {
		yday += mdays[i - 1];
	}
	ret = tm->tm_sec + (60 * tm->tm_min) + (3600 * tm->tm_hour) +
	      (86400 *
	       (yday + ((tm->tm_year - 70) * 365) + ((tm->tm_year - 69) / 4) -
		((tm->tm_year - 1) / 100) + ((tm->tm_year + 299) / 400)));
	return (ret);
}

char *
isc_tm_strptime(const char *buf, const char *fmt, struct tm *tm) {
	char c, *ret;
	const char *bp;
	size_t len = 0;
	int alt_format, i, split_year = 0;

	REQUIRE(buf != NULL);
	REQUIRE(fmt != NULL);
	REQUIRE(tm != NULL);

	memset(tm, 0, sizeof(struct tm));

	bp = buf;

	while ((c = *fmt) != '\0') {
		/* Clear `alternate' modifier prior to new conversion. */
		alt_format = 0;

		/* Eat up white-space. */
		if (isspace((unsigned char)c)) {
			while (isspace((unsigned char)*bp)) {
				bp++;
			}

			fmt++;
			continue;
		}

		if ((c = *fmt++) != '%') {
			goto literal;
		}

	again:
		switch (c = *fmt++) {
		case '%': /* "%%" is converted to "%". */
		literal:
			if (c != *bp++) {
				return (0);
			}
			break;

		/*
		 * "Alternative" modifiers. Just set the appropriate flag
		 * and start over again.
		 */
		case 'E': /* "%E?" alternative conversion modifier. */
			LEGAL_ALT(0);
			alt_format |= ALT_E;
			goto again;

		case 'O': /* "%O?" alternative conversion modifier. */
			LEGAL_ALT(0);
			alt_format |= ALT_O;
			goto again;

		/*
		 * "Complex" conversion rules, implemented through recursion.
		 */
		case 'c': /* Date and time, using the locale's format. */
			LEGAL_ALT(ALT_E);
			if (!(bp = isc_tm_strptime(bp, "%x %X", tm))) {
				return (0);
			}
			break;

		case 'D': /* The date as "%m/%d/%y". */
			LEGAL_ALT(0);
			if (!(bp = isc_tm_strptime(bp, "%m/%d/%y", tm))) {
				return (0);
			}
			break;

		case 'R': /* The time as "%H:%M". */
			LEGAL_ALT(0);
			if (!(bp = isc_tm_strptime(bp, "%H:%M", tm))) {
				return (0);
			}
			break;

		case 'r': /* The time in 12-hour clock representation. */
			LEGAL_ALT(0);
			if (!(bp = isc_tm_strptime(bp, "%I:%M:%S %p", tm))) {
				return (0);
			}
			break;

		case 'T': /* The time as "%H:%M:%S". */
			LEGAL_ALT(0);
			if (!(bp = isc_tm_strptime(bp, "%H:%M:%S", tm))) {
				return (0);
			}
			break;

		case 'X': /* The time, using the locale's format. */
			LEGAL_ALT(ALT_E);
			if (!(bp = isc_tm_strptime(bp, "%H:%M:%S", tm))) {
				return (0);
			}
			break;

		case 'x': /* The date, using the locale's format. */
			LEGAL_ALT(ALT_E);
			if (!(bp = isc_tm_strptime(bp, "%m/%d/%y", tm))) {
				return (0);
			}
			break;

		/*
		 * "Elementary" conversion rules.
		 */
		case 'A': /* The day of week, using the locale's form. */
		case 'a':
			LEGAL_ALT(0);
			for (i = 0; i < 7; i++) {
				/* Full name. */
				len = strlen(day[i]);
				if (strncasecmp(day[i], bp, len) == 0) {
					break;
				}

				/* Abbreviated name. */
				len = strlen(abday[i]);
				if (strncasecmp(abday[i], bp, len) == 0) {
					break;
				}
			}

			/* Nothing matched. */
			if (i == 7) {
				return (0);
			}

			tm->tm_wday = i;
			bp += len;
			break;

		case 'B': /* The month, using the locale's form. */
		case 'b':
		case 'h':
			LEGAL_ALT(0);
			for (i = 0; i < 12; i++) {
				/* Full name. */
				len = strlen(mon[i]);
				if (strncasecmp(mon[i], bp, len) == 0) {
					break;
				}

				/* Abbreviated name. */
				len = strlen(abmon[i]);
				if (strncasecmp(abmon[i], bp, len) == 0) {
					break;
				}
			}

			/* Nothing matched. */
			if (i == 12) {
				return (0);
			}

			tm->tm_mon = i;
			bp += len;
			break;

		case 'C': /* The century number. */
			LEGAL_ALT(ALT_E);
			if (!(conv_num(&bp, &i, 0, 99))) {
				return (0);
			}

			if (split_year) {
				tm->tm_year = (tm->tm_year % 100) + (i * 100);
			} else {
				tm->tm_year = i * 100;
				split_year = 1;
			}
			break;

		case 'd': /* The day of month. */
		case 'e':
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_mday, 1, 31))) {
				return (0);
			}
			break;

		case 'k': /* The hour (24-hour clock representation). */
			LEGAL_ALT(0);
			FALLTHROUGH;
		case 'H':
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_hour, 0, 23))) {
				return (0);
			}
			break;

		case 'l': /* The hour (12-hour clock representation). */
			LEGAL_ALT(0);
			FALLTHROUGH;
		case 'I':
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_hour, 1, 12))) {
				return (0);
			}
			if (tm->tm_hour == 12) {
				tm->tm_hour = 0;
			}
			break;

		case 'j': /* The day of year. */
			LEGAL_ALT(0);
			if (!(conv_num(&bp, &i, 1, 366))) {
				return (0);
			}
			tm->tm_yday = i - 1;
			break;

		case 'M': /* The minute. */
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_min, 0, 59))) {
				return (0);
			}
			break;

		case 'm': /* The month. */
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &i, 1, 12))) {
				return (0);
			}
			tm->tm_mon = i - 1;
			break;

		case 'p': /* The locale's equivalent of AM/PM. */
			LEGAL_ALT(0);
			/* AM? */
			if (strcasecmp(am_pm[0], bp) == 0) {
				if (tm->tm_hour > 11) {
					return (0);
				}

				bp += strlen(am_pm[0]);
				break;
			}
			/* PM? */
			else if (strcasecmp(am_pm[1], bp) == 0)
			{
				if (tm->tm_hour > 11) {
					return (0);
				}

				tm->tm_hour += 12;
				bp += strlen(am_pm[1]);
				break;
			}

			/* Nothing matched. */
			return (0);

		case 'S': /* The seconds. */
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_sec, 0, 61))) {
				return (0);
			}
			break;

		case 'U': /* The week of year, beginning on sunday. */
		case 'W': /* The week of year, beginning on monday. */
			LEGAL_ALT(ALT_O);
			/*
			 * XXX This is bogus, as we can not assume any valid
			 * information present in the tm structure at this
			 * point to calculate a real value, so just check the
			 * range for now.
			 */
			if (!(conv_num(&bp, &i, 0, 53))) {
				return (0);
			}
			break;

		case 'w': /* The day of week, beginning on sunday. */
			LEGAL_ALT(ALT_O);
			if (!(conv_num(&bp, &tm->tm_wday, 0, 6))) {
				return (0);
			}
			break;

		case 'Y': /* The year. */
			LEGAL_ALT(ALT_E);
			if (!(conv_num(&bp, &i, 0, 9999))) {
				return (0);
			}

			tm->tm_year = i - TM_YEAR_BASE;
			break;

		case 'y': /* The year within 100 years of the epoch. */
			LEGAL_ALT(ALT_E | ALT_O);
			if (!(conv_num(&bp, &i, 0, 99))) {
				return (0);
			}

			if (split_year) {
				tm->tm_year = ((tm->tm_year / 100) * 100) + i;
				break;
			}
			split_year = 1;
			if (i <= 68) {
				tm->tm_year = i + 2000 - TM_YEAR_BASE;
			} else {
				tm->tm_year = i + 1900 - TM_YEAR_BASE;
			}
			break;

		/*
		 * Miscellaneous conversions.
		 */
		case 'n': /* Any kind of white-space. */
		case 't':
			LEGAL_ALT(0);
			while (isspace((unsigned char)*bp)) {
				bp++;
			}
			break;

		default: /* Unknown/unsupported conversion. */
			return (0);
		}
	}

	/* LINTED functional specification */
	DE_CONST(bp, ret);
	return (ret);
}