/*
 * Copyright (C) 2021, 2022  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"
#include "formats.h"

static struct tm DATETIME_EPOCH_ = {
	.tm_sec   = 0,
	.tm_min   = 0,
	.tm_hour  = 0,
	.tm_mday  = 1,
	.tm_mon   = 0,
	.tm_year  = 70,
	.tm_wday  = 4,
	.tm_yday  = 0,
	.tm_isdst = -1,
};

static void
_datetime_buf_cpy_p(char *dst, const char *src)
{
	for (; *src != '\0'; ++src, ++dst) {
		if (*src == '^') {
			*dst = ' ';
		} else {
			*dst = *src;
		}
	}
	*dst = '\0';
}

static void
_datetime_buf_cpy_f(char *dst, const char *src)
{
	for (; *src != '\0'; ++src, ++dst) {
		if (*src == '^') {
			++src;
		}
		*dst = *src;
	}
	*dst = '\0';
}

static void
_datetime_reset_tm(struct tm *tm)
{
	tm->tm_year  = INT_MIN;
	tm->tm_mon   = INT_MIN;
	tm->tm_mday  = INT_MIN;
	tm->tm_wday  = INT_MIN;
	tm->tm_hour  = INT_MIN;
	tm->tm_min   = INT_MIN;
	tm->tm_sec   = INT_MIN;
	tm->tm_isdst = INT_MIN;
}

static void
_datetime_normalize(struct tm *now_tm, struct tm *arg_tm, time_t *arg_sec)
{
	int wday;

	if (arg_tm->tm_sec == INT_MIN) {
		arg_tm->tm_sec = 0;
	}
	if (arg_tm->tm_mday == INT_MIN && arg_tm->tm_wday == INT_MIN) {
		/* No date specified; try today. */
		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_tm->tm_wday = now_tm->tm_wday;
		*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;
			*arg_sec = mktime(arg_tm);
		}
	} else if (arg_tm->tm_mday == INT_MIN) {
		/* Only a weekday specified; try tomorrow or next week.  Uses
		 * same shortcut as above. */
		wday = arg_tm->tm_wday;
		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_tm->tm_wday = now_tm->tm_wday;
		if (wday <= now_tm->tm_wday) {
			wday += 7;
		}
		*arg_sec = mktime(arg_tm);
		*arg_sec += (60 * 60 * 24) * (wday - now_tm->tm_wday);
	} else if (arg_tm->tm_year == INT_MIN) {
		/* No year specified; try this year. */
		arg_tm->tm_year = now_tm->tm_year;
		*arg_sec = mktime(arg_tm);
		if (*arg_sec <= mktime(now_tm)) {
			/* Specified time already happened this year; use next
			 * year. */
			++arg_tm->tm_year;
			*arg_sec = mktime(arg_tm);
		}
	} else {
		*arg_sec = mktime(arg_tm);
	}
}

int
datetime_parse(struct tm *now_tm, const char *input, time_t *arg_sec)
{
	int        date_fmt_len;
	int        time_fmt_len;
	int        misc_fmt_len;
	int        fmt_len;
	char      *fmt_buf;
	size_t     d;
	size_t     t;
	char      *end;
	struct tm  arg_tm;
	time_t     sec;
	bool       got;

	date_fmt_len = strlen(FORMATS_DATE[0]);
	time_fmt_len = strlen(FORMATS_TIME[0]);
	misc_fmt_len = strlen(FORMATS_MISC[0]);
	fmt_len = date_fmt_len + time_fmt_len;
	if (misc_fmt_len > fmt_len) {
		fmt_len = misc_fmt_len;
	}
	fmt_buf = calloc(fmt_len + 1, sizeof(*fmt_buf));
	if (fmt_buf == NULL) {
		fprintf(stderr, "Failed to allocate buffer: %s\n",
				strerror(errno));
		return -1;
	}

	sec = *arg_sec;  /* GCC is dumb. */
	got = false;
	for (t = 0; t < sizeof(FORMATS_TIME) / sizeof(FORMATS_TIME[0]) ; ++t) {
		_datetime_buf_cpy_p(fmt_buf, FORMATS_TIME[t]);
		_datetime_reset_tm(&arg_tm);
		end = strptime(input, fmt_buf, &arg_tm);
		if (end != NULL && *end == '\0') {
			_datetime_normalize(now_tm, &arg_tm, arg_sec);
			if (datetime_diff_epoch(*arg_sec) >= 0) {
				free(fmt_buf);
				return 0;
			}
			sec = *arg_sec;
			got = true;
		}
	}
	for (d = 0; d < sizeof(FORMATS_DATE) / sizeof(FORMATS_DATE[0]); ++d) {
		if (FORMATS_DATE[d][0] == '\0') {
			break;
		}
		_datetime_buf_cpy_p(fmt_buf, FORMATS_DATE[d]);
		for (t = 0; t < sizeof(FORMATS_TIME) / sizeof(FORMATS_TIME[0]);
				++t) {
			_datetime_buf_cpy_p(fmt_buf + date_fmt_len,
					FORMATS_TIME[t]);
			_datetime_reset_tm(&arg_tm);
			end = strptime(input, fmt_buf, &arg_tm);
			if (end != NULL && *end == '\0') {
				_datetime_normalize(now_tm, &arg_tm, arg_sec);
				if (datetime_diff_epoch(*arg_sec) >= 0) {
					free(fmt_buf);
					return 0;
				}
				sec = *arg_sec;
				got = true;
			}
		}
	}
	for (t = 0; t < sizeof(FORMATS_TIME) / sizeof(FORMATS_TIME[0]); ++t) {
		_datetime_buf_cpy_p(fmt_buf, FORMATS_TIME[t]);
		for (d = 0; d < sizeof(FORMATS_DATE) / sizeof(FORMATS_DATE[0]);
				++d) {
			if (FORMATS_DATE[d][0] == '\0') {
				break;
			}
			_datetime_buf_cpy_p(fmt_buf + time_fmt_len,
					FORMATS_DATE[d]);
			_datetime_reset_tm(&arg_tm);
			end = strptime(input, fmt_buf, &arg_tm);
			if (end != NULL && *end == '\0') {
				_datetime_normalize(now_tm, &arg_tm, arg_sec);
				if (datetime_diff_epoch(*arg_sec) >= 0) {
					free(fmt_buf);
					return 0;
				}
				sec = *arg_sec;
				got = true;
			}
		}
	}
	for (d = 0; d < sizeof(FORMATS_MISC) / sizeof(FORMATS_MISC[0]) ; ++d) {
		_datetime_buf_cpy_p(fmt_buf, FORMATS_MISC[d]);
		_datetime_reset_tm(&arg_tm);
		end = strptime(input, fmt_buf, &arg_tm);
		if (end != NULL && *end == '\0') {
			_datetime_normalize(now_tm, &arg_tm, arg_sec);
			if (datetime_diff_epoch(*arg_sec) >= 0) {
				free(fmt_buf);
				return 0;
			}
			sec = *arg_sec;
			got = true;
		}
	}

	if (got == true) {
		*arg_sec = sec;
		free(fmt_buf);
		return 0;
	} else {
		fputs("Unknown date format\n", stderr);
		free(fmt_buf);
		return -1;
	}
}

static void
_datetime_copy_collapse(char *buf, const char *fmt)
{
	int  buf_i;
	int  l;
	bool was_space;
	int  i;

	buf_i = 0;
	l = strlen(fmt);
	was_space = true;
	for (i = 0; i < l; ++i) {
		if (isspace(fmt[i]) != 0) {
			if (was_space == false) {
				buf[buf_i++] = ' ';
				was_space = true;
			}
		} else {
			buf[buf_i++] = fmt[i];
			was_space = false;
		}
	}
	if (buf_i > 0) {
		buf[buf_i - 1] = '\0';
	} else {
		buf[0] = '\0';
	}
}

static int
_datetime_strftime(const char *fmts[], const struct tm *tm, char **out,
		size_t *buf_sz, char **buf, size_t *i)
{
	int resized;

	if (*i == 0) {
		*buf_sz = strlen(fmts[0]) + 1;
		*buf = calloc(*buf_sz, sizeof(**buf));
		if (*buf == NULL) {
			fprintf(stderr, "Failed to allocate buffer: %s\n",
					strerror(errno));
			return -1;
		}
		*out = calloc(*buf_sz, sizeof(**out));
		if (*out == NULL) {
			fprintf(stderr, "Failed to allocate buffer: %s\n",
					strerror(errno));
			return -1;
		}
	}

	if (fmts[*i][0] == '\0') {
		++*i;
	}

	_datetime_buf_cpy_f(*out, fmts[*i]);

	resized = 0;
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wformat-nonliteral"
	while (strftime(*buf, *buf_sz, *out, tm) == 0) {
#pragma GCC diagnostic pop
		++*buf_sz;
		*buf = realloc(*buf, *buf_sz * sizeof(**buf));
		if (*buf == NULL) {
			fprintf(stderr, "Failed to allocate buffer: %s\n",
					strerror(errno));
			return -1;
		}
		resized = 1;
	}
	if (resized > 0) {
		*out = realloc(*out, *buf_sz * sizeof(**out));
		if (*out == NULL) {
			fprintf(stderr, "Failed to allocate buffer: %s\n",
					strerror(errno));
			return -1;
		}
	}

	_datetime_copy_collapse(*out, *buf);
	++*i;

	return 1;
}

int
datetime_strftime_date(const struct tm *tm, char **out, size_t *buf_sz,
		char **buf, size_t *i)
{
	if (*i >= sizeof(FORMATS_DATE) / sizeof(FORMATS_DATE[0])) {
		if (*out != NULL) {
			free(*out);
		}
		if (*buf != NULL) {
			free(*buf);
		}
		return 0;
	}

	return _datetime_strftime(FORMATS_DATE, tm, out, buf_sz, buf, i);
}

int
datetime_strftime_time(const struct tm *tm, char **out, size_t *buf_sz,
		char **buf, size_t *i)
{
	if (*i >= sizeof(FORMATS_TIME) / sizeof(FORMATS_TIME[0])) {
		if (*out != NULL) {
			free(*out);
		}
		if (*buf != NULL) {
			free(*buf);
		}
		return 0;
	}

	return _datetime_strftime(FORMATS_TIME, tm, out, buf_sz, buf, i);
}

int
datetime_strftime_misc(const struct tm *tm, char **out, size_t *buf_sz,
		char **buf, size_t *i)
{
	if (*i >= sizeof(FORMATS_MISC) / sizeof(FORMATS_MISC[0])) {
		if (*out != NULL) {
			free(*out);
		}
		if (*buf != NULL) {
			free(*buf);
		}
		return 0;
	}

	return _datetime_strftime(FORMATS_MISC, tm, out, buf_sz, buf, i);
}

double
datetime_diff_epoch(time_t t)
{
	time_t epoch;

	epoch = timegm(&DATETIME_EPOCH_);

	return difftime(t, epoch);
}