/*
 * Copyright (c) 2009 Norman Golisz <ng@zcat.de>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <stdio.h>
#include <stdlib.h>

inline int calc_golden_num(int);
int calc_easter_date(register int, register int);
int convert_num(char *);
void print_date(int, int);

char *usage_str = "usage: %s <year> || <from_year to_year>\n";

inline int calc_golden_num(year)
	int year;
{
	return year % 19 + 1;
}

int calc_easter_date(year, gnum)
	register int year;
	register int gnum;
{
	int sc, lc, p, d, t;

	if (year <= 1752) {
		d = (year + (year / 4) + 5) % 7;
		p = (3 - (11 * gnum) - 7) % 30;
	} else {
		d = (year + (year / 4) - (year / 100) + (year / 400)) % 7;
		sc = (year - 1600) / 100 - (year - 1600) / 400;
		lc = (((year - 1400) / 100) * 8) / 25;
		p = (3 - 11 * gnum + sc - lc) % 30;
		
		if (p < 0)
			p += 30;
	}

	if (p == 29 || (p == 28 && gnum > 11))
		p--;

	if (d < 0)
		d += 7;

	t = (4 - p - d) % 7;

	if (t < 0)
		t += 7;

	return p + t + 1;
}

int convert_num(s)
	char *s;
{
	return (int)strtol(s, NULL, 10);
}

void print_date(year, edate)
	int year;
	int edate;
{
	printf("%i-%.2i-%.2i\n", year, (edate < 11) ? 3 : 4,
			(edate < 11) ? edate + 21 : edate - 10);
}

int main(argc, argv)
	int argc;
	char **argv;
{
	if (argc < 2 || argc > 3) {
		fprintf(stderr, usage_str, argv[0]);
		exit(EXIT_FAILURE);
	}

	if (argc == 2) {
		int year, gnum, edate;

		year = convert_num(argv[1]);
		gnum = calc_golden_num(year);
		edate = calc_easter_date(year, gnum);
		print_date(year, edate);
	} else {
		int fyear, tyear, gnum, edate, i;

		fyear = convert_num(argv[1]);
		tyear = convert_num(argv[2]);

		if (tyear < fyear) {
			fprintf(stderr, usage_str, argv[0]);
			exit(EXIT_FAILURE);
		}

		for (i = fyear; i <= tyear; i++) {
			gnum = calc_golden_num(i);
			edate = calc_easter_date(i, gnum);
			print_date(i, edate);
		}
	}

	return EXIT_SUCCESS;
}