/*
 * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017,
 *               2018
 *   Jonathan Schleifer <js@heap.zone>
 *
 * All rights reserved.
 *
 * This file is part of ObjFW. It may be distributed under the terms of the
 * Q Public License 1.0, which can be found in the file LICENSE.QPL included in
 * the packaging of this file.
 *
 * Alternatively, it may be distributed under the terms of the GNU General
 * Public License, either version 2 or 3, which can be found in the file
 * LICENSE.GPLv2 or LICENSE.GPLv3 respectively included in the packaging of this
 * file.
 */

#include "config.h"

#include <string.h>

#include <time.h>

#import "macros.h"

const char *
of_strptime(const char *buffer, const char *format, struct tm *tm, int16_t *tz)
{
	enum {
		SEARCH_CONVERSION_SPECIFIER,
		IN_CONVERSION_SPECIFIER
	} state = SEARCH_CONVERSION_SPECIFIER;
	size_t j, bufferLen, formatLen;

	bufferLen = strlen(buffer);
	formatLen = strlen(format);

	j = 0;
	for (size_t i = 0; i < formatLen; i++) {
		if (j >= bufferLen)
			return NULL;

		switch (state) {
		case SEARCH_CONVERSION_SPECIFIER:
			if (format[i] == '%')
				state = IN_CONVERSION_SPECIFIER;
			else if (format[i] != buffer[j++])
				return NULL;

			break;

		case IN_CONVERSION_SPECIFIER:;
			int k, maxLen, number = 0;

			switch (format[i]) {
			case 'd':
			case 'e':
			case 'H':
			case 'm':
			case 'M':
			case 'S':
			case 'y':
				maxLen = 2;
				break;
			case 'Y':
				maxLen = 4;
				break;
			case '%':
			case 'a':
			case 'b':
			case 'n':
			case 't':
			case 'z':
				maxLen = 0;
				break;
			default:
				return NULL;
			}

			if (maxLen > 0 && (buffer[j] < '0' || buffer[j] > '9'))
				return NULL;

			for (k = 0; k < maxLen && j < bufferLen &&
			    buffer[j] >= '0' && buffer[j] <= '9'; k++, j++) {
				number *= 10;
				number += buffer[j] - '0';
			}

			switch (format[i]) {
			case 'a':
				if (bufferLen < j + 3)
					return NULL;

				if (memcmp(buffer + j, "Sun", 3) == 0)
					tm->tm_wday = 0;
				else if (memcmp(buffer + j, "Mon", 3) == 0)
					tm->tm_wday = 1;
				else if (memcmp(buffer + j, "Tue", 3) == 0)
					tm->tm_wday = 2;
				else if (memcmp(buffer + j, "Wed", 3) == 0)
					tm->tm_wday = 3;
				else if (memcmp(buffer + j, "Thu", 3) == 0)
					tm->tm_wday = 4;
				else if (memcmp(buffer + j, "Fri", 3) == 0)
					tm->tm_wday = 5;
				else if (memcmp(buffer + j, "Sat", 3) == 0)
					tm->tm_wday = 6;
				else
					return NULL;

				j += 3;
				break;
			case 'b':
				if (bufferLen < j + 3)
					return NULL;

				if (memcmp(buffer + j, "Jan", 3) == 0)
					tm->tm_mon = 0;
				else if (memcmp(buffer + j, "Feb", 3) == 0)
					tm->tm_mon = 1;
				else if (memcmp(buffer + j, "Mar", 3) == 0)
					tm->tm_mon = 2;
				else if (memcmp(buffer + j, "Apr", 3) == 0)
					tm->tm_mon = 3;
				else if (memcmp(buffer + j, "May", 3) == 0)
					tm->tm_mon = 4;
				else if (memcmp(buffer + j, "Jun", 3) == 0)
					tm->tm_mon = 5;
				else if (memcmp(buffer + j, "Jul", 3) == 0)
					tm->tm_mon = 6;
				else if (memcmp(buffer + j, "Aug", 3) == 0)
					tm->tm_mon = 7;
				else if (memcmp(buffer + j, "Sep", 3) == 0)
					tm->tm_mon = 8;
				else if (memcmp(buffer + j, "Oct", 3) == 0)
					tm->tm_mon = 9;
				else if (memcmp(buffer + j, "Nov", 3) == 0)
					tm->tm_mon = 10;
				else if (memcmp(buffer + j, "Dec", 3) == 0)
					tm->tm_mon = 11;
				else
					return NULL;

				j += 3;
				break;
			case 'd':
			case 'e':
				tm->tm_mday = number;
				break;
			case 'H':
				tm->tm_hour = number;
				break;
			case 'm':
				tm->tm_mon = number - 1;
				break;
			case 'M':
				tm->tm_min = number;
				break;
			case 'S':
				tm->tm_sec = number;
				break;
			case 'y':
				if (number <= 68)
					number += 100;

				tm->tm_year = number;
				break;
			case 'Y':
				if (number < 1900)
					return NULL;

				tm->tm_year = number - 1900;
				break;
			case 'z':
				if (buffer[j] == '-' || buffer[j] == '+') {
					const char *b = buffer + j;

					if (bufferLen < j + 5)
						return NULL;

					if (tz == NULL)
						break;

					*tz = (((int16_t)b[1] - '0') * 600 +
					    ((int16_t)b[2] - '0') * 60 +
					    ((int16_t)b[3] - '0') * 10 +
					    ((int16_t)b[4] - '0')) *
					    (b[0] == '-' ? -1 : 1);

					j += 5;
				} else if (buffer[j] == 'Z') {
					if (tz != NULL)
						*tz = 0;

					j++;
				} else if (buffer[j] == 'G') {
					if (bufferLen < j + 3)
						return NULL;

					if (buffer[j + 1] != 'M' ||
					    buffer[j + 2] != 'T')
						return NULL;

					if (tz != NULL)
						*tz = 0;

					j += 3;
				} else
					return NULL;

				break;
			case '%':
				if (buffer[j++] != '%')
					return NULL;
				break;
			case 'n':
				if (buffer[j++] != '\n')
					return NULL;
				break;
			case 't':
				if (buffer[j++] != '\t')
					return NULL;
				break;
			}

			state = SEARCH_CONVERSION_SPECIFIER;

			break;
		}
	}

	return buffer + j;
}