/*
 * UNG's Not GNU
 *
 * Copyright (c) 2023, Jakob Kaivo <jkk@ung.org>
 *
 * 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.
 */

#define _POSIX_C_SOURCE 200809L
#include <locale.h>
#include <regex.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

static void optional_zero(size_t n, char buf[static n], char spec, struct tm *tm)
{
	char fmt[] = { '%', spec, '\0' };
	strftime(buf, n, fmt, tm);
	if (buf[0] != '0') {
		return;
	}

	spec = buf[1];
	snprintf(buf, n, "0?%c", spec);
}

int main(int argc, char *argv[])
{
	setlocale(LC_ALL, "");

	int c;
	while ((c = getopt(argc, argv, "")) != -1) {
		switch (c) {
		/* portable applications should not use operands */
		default:
			return 1;
		}
	}

	FILE *f = fopen("calendar", "r");
	if (f == NULL) {
		perror("calendar: couldn't open calendar file");
		return 1;
	}

	regex_t re[12] = { { 0 } };
	time_t now = time(NULL);
	struct tm *tm = localtime(&now);
	size_t nregs = 2;	/* 1 for today, 1 for tomorrow */
	switch (tm->tm_wday) {
	case 5: /* Friday, extend another day */
		nregs += 1;
		/* FALLTHRU */
	case 6: /* Saturday, extend one day */
		nregs += 1;
		/* FALLTHRU */
	default:
		break;
	}

	const long SECONDS_PER_DAY = 60 * 60 * 24;
	const int REFLAGS = REG_ICASE | REG_NOSUB | REG_EXTENDED;
	for (size_t i = 0; i < nregs; i += 1) {
		char dom[4];
		optional_zero(sizeof(dom), dom, 'd', tm);

		char mon[4];
		optional_zero(sizeof(mon), mon, 'm', tm);

		char buf[64];
		strftime(buf, sizeof(buf), "((%b.?|%B) +|", tm);
		strcat(buf, mon);
		strcat(buf, "/)");
		strcat(buf, dom);
		if (regcomp(re + i, buf, REFLAGS) != 0) {
			perror(buf);
			return 1;
		}

		now += SECONDS_PER_DAY;
		tm = localtime(&now);
	}

	char line[1024];
	while (fgets(line, sizeof(line), f) != NULL) {
		for (size_t i = 0; i < nregs; i++) {
			if (regexec(re + i, line, 0, NULL, 0) == 0) {
				fputs(line, stdout);
				continue;
			}
		}
	}
}