/*
 * Copyright (C) 2021  P. J. McDermott
 *
 * This file is part of @
 *
 * @ 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 3 of the License, or
 * (at your option) any later version.
 *
 * @ 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 @.  If not, see <http://www.gnu.org/licenses/>.
 */

#define _XOPEN_SOURCE

#include <ctype.h>
#include <errno.h>
#include <limits.h>
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include "datetime.h"

static const char *DATETIME_FMTS_[] = {
#include "datetime-formats.c"
	NULL
};

static char *
datetime_concat_args(int argc, const char *argv[])
{
	int   buf_l;
	int   i;
	char *buf;
	int   buf_i;
	int   j;

	buf_l = 0;
	for (i = 0; i < argc; ++i) {
		buf_l += strlen(argv[i]) + 1;
	}

	buf = calloc(buf_l, sizeof(*buf));
	if (buf == NULL) {
		fprintf(stderr, "Failed to allocate buffer: %s\n",
				strerror(errno));
		return NULL;
	}

	buf_i = 0;
	for (i = 0; i < argc; ++i) {
		for (j = 0; argv[i][j] != '\0'; ++j) {
			buf[buf_i++] = argv[i][j];
		}
		buf[buf_i++] = ' ';
	}
	buf[--buf_i] = '\0';

	return buf;
}

int
datetime_parse(int argc, const char *argv[], struct tm *arg_tm)
{
	char      *buf;
	int        i;
	char      *end;
	time_t     arg_sec;
	time_t     now_sec;
	struct tm *now_tm;

	buf = datetime_concat_args(argc, argv);
	if (buf == NULL) {
		return -1;
	}

	arg_tm->tm_mday = INT_MIN;  /* Sentinel */
	arg_tm->tm_sec  = 0;        /* Default */

	for (i = 0; DATETIME_FMTS_[i] != NULL; ++i) {
		/* printf("%s =~ %s\n", buf, DATETIME_FMTS_[i]); */
		end = strptime(buf, DATETIME_FMTS_[i], arg_tm);
		if (end != NULL && *end == '\0') {
			goto found;
		}
	}

	free(buf);
	fprintf(stderr, "Unknown date format\n");
	return -1;

 found:
	/* TODO: Support %a-only dates and optional years */
	if (arg_tm->tm_mday == INT_MIN) {
		/* No date specified; try today. */
		now_sec = time(NULL);
		now_tm = localtime(&now_sec);
		arg_tm->tm_year = now_tm->tm_year;
		arg_tm->tm_mon  = now_tm->tm_mon;
		arg_tm->tm_mday = now_tm->tm_mday;
		arg_sec = mktime(arg_tm);
		if (arg_sec <= mktime(now_tm)) {
			/* Specified time already happened today; use tomorrow.
			 * Adding the number of seconds in a day is a shortcut
			 * that ignores leap seconds.  One better method would
			 * be to increment tm_mday % days in tm_mon, etc. */
			arg_sec += 60 * 60 * 24;
			now_tm = localtime(&arg_sec);
			arg_tm->tm_year = now_tm->tm_year;
			arg_tm->tm_mon  = now_tm->tm_mon;
			arg_tm->tm_mday = now_tm->tm_mday;
		}
	}

	free(buf);
	return 0;
}