/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2015-2021 Derick Rethans
 * Copyright (c) 2021 MongoDB
 *
 * 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.
 */

#include "timelib.h"
#include "timelib_private.h"

/* Converts Unix epoch days (days since 1970-01-01) to a date. Algorithm from:
 * http://howardhinnant.github.io/date_algorithms.html#civil_from_days */
void timelib_date_from_epoch_days(timelib_sll epoch_days, timelib_sll *y, timelib_sll *m, timelib_sll *d)
{
	timelib_sll days, era;
	timelib_ull day_of_era, year_of_era, day_of_year, month_portion;

	/* Calculate days since algorithm's epoch (0000-03-01) */
	days = epoch_days + HINNANT_EPOCH_SHIFT;

	era = (days >= 0 ? days : days - DAYS_PER_ERA + 1) / DAYS_PER_ERA;
	day_of_era = days - era * DAYS_PER_ERA;
	year_of_era = (day_of_era - day_of_era / 1460 + day_of_era / 36524 - day_of_era / 146096) / DAYS_PER_YEAR;
	*y = year_of_era + era * YEARS_PER_ERA;
	day_of_year = day_of_era - (DAYS_PER_YEAR * year_of_era + year_of_era / 4 - year_of_era / 100);
	month_portion = (5 * day_of_year + 2) / 153;
	*d = day_of_year - (153 * month_portion + 2) / 5 + 1;
	*m = month_portion + (month_portion < 10 ? 3 : -9);
	*y += (*m <= 2);
}

void timelib_unixtime2date(timelib_sll ts, timelib_sll *y, timelib_sll *m, timelib_sll *d)
{
	timelib_sll epoch_days, t;

	epoch_days = ts / SECS_PER_DAY;

	/* Adjustment for a negative time portion */
	t = ts % SECS_PER_DAY;
	epoch_days += (t < 0) ? -1 : 0;

	timelib_date_from_epoch_days(epoch_days, y, m, d);

	TIMELIB_DEBUG(printf("A: ts=%lld, year=%lld, month=%lld, day=%lld,", ts, *y, *m, *d););
}

/* Converts a Unix timestamp value into broken down time, in GMT */
void timelib_unixtime2gmt(timelib_time* tm, timelib_sll ts)
{
	timelib_sll remainder;
	timelib_sll hours, minutes, seconds;

	timelib_unixtime2date(ts, &tm->y, &tm->m, &tm->d);
	remainder = ts % SECS_PER_DAY;
	remainder += (remainder < 0) * SECS_PER_DAY;

	/* That was the date, now we do the time */
	hours = remainder / 3600;
	minutes = (remainder - hours * 3600) / 60;
	seconds = remainder % 60;
	TIMELIB_DEBUG(printf(" hour=%lld, minute=%lld, second=%lld\n", hours, minutes, seconds););

	tm->h = hours;
	tm->i = minutes;
	tm->s = seconds;
	tm->z = 0;
	tm->dst = 0;
	tm->sse = ts;
	tm->sse_uptodate = 1;
	tm->tim_uptodate = 1;
	tm->is_localtime = 0;
}

void timelib_update_from_sse(timelib_time *tm)
{
	timelib_sll sse;
	int z = tm->z;
	signed int dst = tm->dst;

	sse = tm->sse;

	switch (tm->zone_type) {
		case TIMELIB_ZONETYPE_ABBR:
		case TIMELIB_ZONETYPE_OFFSET: {
			timelib_unixtime2gmt(tm, tm->sse + tm->z + (tm->dst * 3600));

			goto cleanup;
		}

		case TIMELIB_ZONETYPE_ID: {
			int32_t  offset = 0;

			timelib_get_time_zone_offset_info(tm->sse, tm->tz_info, &offset, NULL, NULL);
			timelib_unixtime2gmt(tm, tm->sse + offset);

			goto cleanup;
		}

		default:
			timelib_unixtime2gmt(tm, tm->sse);
			goto cleanup;
	}
cleanup:
	tm->sse = sse;
	tm->is_localtime = 1;
	tm->have_zone = 1;
	tm->z = z;
	tm->dst = dst;
}

void timelib_unixtime2local(timelib_time *tm, timelib_sll ts)
{
	timelib_time_offset *gmt_offset;
	timelib_tzinfo      *tz = tm->tz_info;

	switch (tm->zone_type) {
		case TIMELIB_ZONETYPE_ABBR:
		case TIMELIB_ZONETYPE_OFFSET: {
			int z = tm->z;
			signed int dst = tm->dst;

			timelib_unixtime2gmt(tm, ts + tm->z + (tm->dst * 3600));

			tm->sse = ts;
			tm->z = z;
			tm->dst = dst;
			break;
		}

		case TIMELIB_ZONETYPE_ID:
			gmt_offset = timelib_get_time_zone_info(ts, tz);
			timelib_unixtime2gmt(tm, ts + gmt_offset->offset);

			/* we need to reset the sse here as unixtime2gmt modifies it */
			tm->sse = ts;
			tm->dst = gmt_offset->is_dst;
			tm->z = gmt_offset->offset;
			tm->tz_info = tz;

			timelib_time_tz_abbr_update(tm, gmt_offset->abbr);
			timelib_time_offset_dtor(gmt_offset);
			break;

		default:
			tm->is_localtime = 0;
			tm->have_zone = 0;
			return;
	}

	tm->is_localtime = 1;
	tm->have_zone = 1;
}

void timelib_set_timezone_from_offset(timelib_time *t, timelib_sll utc_offset)
{
	if (t->tz_abbr) {
		timelib_free(t->tz_abbr);
	}
	t->tz_abbr = NULL;

	t->z = utc_offset;
	t->have_zone = 1;
	t->zone_type = TIMELIB_ZONETYPE_OFFSET;
	t->dst = 0;
	t->tz_info = NULL;
}

void timelib_set_timezone_from_abbr(timelib_time *t, timelib_abbr_info abbr_info)
{
	if (t->tz_abbr) {
		timelib_free(t->tz_abbr);
	}
	t->tz_abbr = timelib_strdup(abbr_info.abbr);

	t->z = abbr_info.utc_offset;
	t->have_zone = 1;
	t->zone_type = TIMELIB_ZONETYPE_ABBR;
	t->dst = abbr_info.dst;
	t->tz_info = NULL;
}

void timelib_set_timezone(timelib_time *t, timelib_tzinfo *tz)
{
	timelib_time_offset *gmt_offset;

	gmt_offset = timelib_get_time_zone_info(t->sse, tz);
	t->z = gmt_offset->offset;
/*
	if (t->dst != gmt_offset->is_dst) {
		printf("ERROR (%d, %d)\n", t->dst, gmt_offset->is_dst);
		exit(1);
	}
*/
	t->dst = gmt_offset->is_dst;
	t->tz_info = tz;
	if (t->tz_abbr) {
		timelib_free(t->tz_abbr);
	}
	t->tz_abbr = timelib_strdup(gmt_offset->abbr);
	timelib_time_offset_dtor(gmt_offset);

	t->have_zone = 1;
	t->zone_type = TIMELIB_ZONETYPE_ID;
}

/* Converts the time stored in the struct to localtime if localtime = true,
 * otherwise it converts it to gmttime. This is only done when necessary
 * of course. */
int timelib_apply_localtime(timelib_time *t, unsigned int localtime)
{
	if (localtime) {
		/* Converting from GMT time to local time */
		TIMELIB_DEBUG(printf("Converting from GMT time to local time\n"););

		/* Check if TZ is set */
		if (!t->tz_info) {
			TIMELIB_DEBUG(printf("E: No timezone configured, can't switch to local time\n"););
			return -1;
		}

		timelib_unixtime2local(t, t->sse);
	} else {
		/* Converting from local time to GMT time */
		TIMELIB_DEBUG(printf("Converting from local time to GMT time\n"););

		timelib_unixtime2gmt(t, t->sse);
	}
	return 0;
}
