/*
 * Copyright (c) 1989 The Regents of the University of California.
 * All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Kim Letkeman.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by the University of
 *      California, Berkeley and its contributors.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */
/*
 * Slightly modified for Linux by Rob Hooft (hooft@EMBL-Heidelberg.DE)
 */

#ifdef NOT_MODIFIED
#ifndef lint
char copyright[] =
"@(#) Copyright (c) 1989 The Regents of the University of California.\n\
 All rights reserved.\n";
#endif /* not lint */

#ifndef lint
char sccsid[] = "@(#)cal.c	5.2 (Berkeley) 4/19/91";
#endif /* not lint */
#endif

#include <sys/types.h>
#include <sys/time.h>
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <getopt.h>
#include <string.h>
#include "cal.h"

#define	THURSDAY		4	/* for reformation */
#define	SATURDAY 		6	/* 1 Jan 1 was a Saturday */

#define	FIRST_MISSING_DAY 	639787	/* 3 Sep 1752 */
#define	NUMBER_MISSING_DAYS 	11	/* 11 day correction */

#define	MAXDAYS			42	/* max slots in a month array */
#define	SPACE			-1	/* used in day array */

const int days_in_month[2][13] =
{
  {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
  {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31},
};

const int sep1752[MAXDAYS] =
{
  SPACE, SPACE, 1, 2, 14, 15, 16,
  17, 18, 19, 20, 21, 22, 23,
  24, 25, 26, 27, 28, 29, 30,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
}, j_sep1752[MAXDAYS] =
{
  SPACE, SPACE, 245, 246, 258, 259, 260,
  261, 262, 263, 264, 265, 266, 267,
  268, 269, 270, 271, 272, 273, 274,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
}, empty[MAXDAYS] =
{
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
  SPACE, SPACE, SPACE, SPACE, SPACE, SPACE, SPACE,
};

const char *month_names[12] =
{
  "January", "February", "March", "April", "May", "June",
  "July", "August", "September", "October", "November", "December",
};

const char *day_headings = " S  M Tu  W Th  F  S";
const char *j_day_headings = "  S   M  Tu   W  Th   F   S";

/* leap year -- account for gregorian reformation in 1752 */
#define	leap_year(yr) \
	((yr) <= 1752 ? !((yr) % 4) : \
	(!((yr) % 4) && ((yr) % 100)) || !((yr) % 400))

/* number of centuries since 1700, not inclusive */
#define	centuries_since_1700(yr) \
	((yr) > 1700 ? (yr) / 100 - 17 : 0)

/* number of centuries since 1700 whose modulo of 400 is 0 */
#define	quad_centuries_since_1700(yr) \
	((yr) > 1600 ? ((yr) - 1600) / 400 : 0)

/* number of leap years between year 1 and this year, not inclusive */
#define	leap_years_since_year_1(yr) \
	((yr) / 4 - centuries_since_1700(yr) + quad_centuries_since_1700(yr))

static int julian;


void
main (int argc, char **argv)
{
  extern int optind;
  struct tm *local_time;
  time_t now, time ();
  int ch, month, year, yflag;

  yflag = 0;
  while ((ch = getopt (argc, argv, "jy")) != EOF)
    switch (ch)
      {
      case 'j':
	julian = 1;
	break;
      case 'y':
	yflag = 1;
	break;
      case '?':
      default:
	usage ();
      }
  argc -= optind;
  argv += optind;

  month = 0;
  switch (argc)
    {
    case 2:
      if ((month = atoi (*argv++)) <= 0 || month > 12)
	{
	  (void) fprintf (stderr,
			  "cal: illegal month value: use 0-12\n");
	  exit (1);
	}
      /* FALLTHROUGH */
    case 1:
      if ((year = atoi (*argv)) <= 0 || year > 9999)
	{
	  (void) fprintf (stderr,
			  "cal: illegal year value: use 0-9999\n");
	  exit (1);
	}
      break;
    case 0:
      (void) time (&now);
      local_time = localtime (&now);
      year = local_time->tm_year + 1900;
      if (!yflag)
	month = local_time->tm_mon + 1;
      break;
    default:
      usage ();
    }

  if (month)
    monthly (month, year);
  else if (julian)
    j_yearly (year);
  else
    yearly (year);
  exit (0);
}

#define	DAY_LEN		3	/* 3 spaces per day */
#define	J_DAY_LEN	4	/* 4 spaces per day */
#define	WEEK_LEN	20	/* 7 * 3 - one space at the end */
#define	J_WEEK_LEN	27	/* 7 * 4 - one space at the end */
#define	HEAD_SEP	2	/* spaces between day headings */
#define	J_HEAD_SEP	2

void
monthly (int month, int year)
{
  int col, row;
  char *p;
  int len, days[MAXDAYS];
  char lineout[30];

  day_array (month, year, days);
  len = sprintf (lineout, "%s %d", month_names[month - 1], year);
  (void) printf ("%*s%s\n%s\n",
		 ((julian ? J_WEEK_LEN : WEEK_LEN) - len) / 2, "",
		 lineout, julian ? j_day_headings : day_headings);
  for (row = 0; row < 6; row++)
    {
      for (col = 0, p = lineout; col < 7; col++,
	   p += julian ? J_DAY_LEN : DAY_LEN)
	ascii_day (p, days[row * 7 + col]);
      *p = '\0';
      (void) printf ("%s\n", lineout);
    }
}

void
j_yearly (int year)
{
  int col, *dp, i, month, row, which_cal;
  char *p;
  int days[12][MAXDAYS];
  char lineout[80];

  (void) sprintf (lineout, "%d", year);
  center (lineout, J_WEEK_LEN * 2 + J_HEAD_SEP, 0);
  (void) printf ("\n\n");
  for (i = 0; i < 12; i++)
    day_array (i + 1, year, days[i]);
  (void) memset (lineout, ' ', sizeof (lineout));
  for (month = 0; month < 12; month += 2)
    {
      center (month_names[month], J_WEEK_LEN, J_HEAD_SEP);
      center (month_names[month + 1], J_WEEK_LEN, 0);
      (void) printf ("\n%s%*s%s\n", j_day_headings, J_HEAD_SEP, "",
		     j_day_headings);
      for (row = 0; row < 6; row++)
	{
	  for (which_cal = 0; which_cal < 2; which_cal++)
	    {
	      p = lineout + which_cal * (J_WEEK_LEN + 2);
	      dp = &days[month + which_cal][row * 7];
	      for (col = 0; col < 7; col++, p += J_DAY_LEN)
		ascii_day (p, *dp++);
	    }
	  *p /*(lineout + J_HEAD_SEP + 2 * J_WEEK_LEN) */  = '\0';
	  (void) printf ("%s\n", lineout);
	}
    }
  (void) printf ("\n");
}

void
yearly (int year)
{
  int col, *dp, i, month, row, which_cal;
  char *p;
  int days[12][MAXDAYS];
  char lineout[80];

  (void) sprintf (lineout, "%d", year);
  center (lineout, WEEK_LEN * 3 + HEAD_SEP * 2, 0);
  (void) printf ("\n\n");
  for (i = 0; i < 12; i++)
    day_array (i + 1, year, days[i]);
  (void) memset (lineout, ' ', sizeof (lineout));
  for (month = 0; month < 12; month += 3)
    {
      center (month_names[month], WEEK_LEN, HEAD_SEP);
      center (month_names[month + 1], WEEK_LEN, HEAD_SEP);
      center (month_names[month + 2], WEEK_LEN, 0);
      (void) printf ("\n%s%*s%s%*s%s\n", day_headings, HEAD_SEP,
		     "", day_headings, HEAD_SEP, "", day_headings);
      for (row = 0; row < 6; row++)
	{
	  for (which_cal = 0; which_cal < 3; which_cal++)
	    {
	      p = lineout + which_cal * (WEEK_LEN + 2);
	      dp = &days[month + which_cal][row * 7];
	      for (col = 0; col < 7; col++, p += DAY_LEN)
		ascii_day (p, *dp++);
	    }
	  *p = '\0';
	  (void) printf ("%s\n", lineout);
	}
    }
  (void) printf ("\n");
}

/*
 * day_array --
 *      Fill in an array of 42 integers with a calendar.  Assume for a moment
 *      that you took the (maximum) 6 rows in a calendar and stretched them
 *      out end to end.  You would have 42 numbers or spaces.  This routine
 *      builds that array for any month from Jan. 1 through Dec. 9999.
 */
void
day_array (int month, int year, int *days)
{
  int day, dw, dm;

  if (month == 9 && year == 1752)
    {
      bcopy (julian ? j_sep1752 : sep1752,
	     days, MAXDAYS * sizeof (int));
      return;
    }
  bcopy (empty, days, MAXDAYS * sizeof (int));
  dm = days_in_month[leap_year (year)][month];
  dw = day_in_week (1, month, year);
  day = julian ? day_in_year (1, month, year) : 1;
  while (dm--)
    days[dw++] = day++;
}

/*
 * day_in_year --
 *      return the 1 based day number within the year
 */
int
day_in_year (int day, int month, int year)
{
  int i, leap;

  leap = leap_year (year);
  for (i = 1; i < month; i++)
    day += days_in_month[leap][i];
  return (day);
}

/*
 * day_in_week
 *      return the 0 based day number for any date from 1 Jan. 1 to
 *      31 Dec. 9999.  Assumes the Gregorian reformation eliminates
 *      3 Sep. 1752 through 13 Sep. 1752.  Returns Thursday for all
 *      missing days.
 */
int
day_in_week (int day, int month, int year)
{
  long temp;

  temp = (long) (year - 1) * 365 + leap_years_since_year_1 (year - 1)
    + day_in_year (day, month, year);
  if (temp < FIRST_MISSING_DAY)
    return ((temp - 1 + SATURDAY) % 7);
  if (temp >= (FIRST_MISSING_DAY + NUMBER_MISSING_DAYS))
    return (((temp - 1 + SATURDAY) - NUMBER_MISSING_DAYS) % 7);
  return (THURSDAY);
}

void
ascii_day (char *p, int day)
{
  int display, val;
  static char *aday[] =
  {
    "",
    " 1", " 2", " 3", " 4", " 5", " 6", " 7",
    " 8", " 9", "10", "11", "12", "13", "14",
    "15", "16", "17", "18", "19", "20", "21",
    "22", "23", "24", "25", "26", "27", "28",
    "29", "30", "31",
  };

  if (day == SPACE)
    {
      memset (p, ' ', julian ? J_DAY_LEN : DAY_LEN);
      return;
    }
  if (julian)
    {
      if ((val = day / 100))
	{
	  day %= 100;
	  *p++ = val + '0';
	  display = 1;
	}
      else
	{
	  *p++ = ' ';
	  display = 0;
	}
      val = day / 10;
      if (val || display)
	*p++ = val + '0';
      else
	*p++ = ' ';
      *p++ = day % 10 + '0';
    }
  else
    {
      *p++ = aday[day][0];
      *p++ = aday[day][1];
    }
  *p = ' ';
}

void
center (const char *str, int len, int separate)
{
  len -= strlen (str);
  (void) printf ("%*s%s%*s", len / 2, "", str, len / 2 + len % 2, "");
  if (separate)
    (void) printf ("%*s", separate, "");
}

volatile void
usage ()
{
  (void) fprintf (stderr, "usage: cal [-jy] [[month] year]\n");
  exit (1);
}
