/* Input: */

/* Date as a 4-tuple */

/* It's an encoded day of week,year,encoded month,day of month */

/* Sunday=0, Monday=1, Tuesday=2, Wednesday=3, Thursday=4, Friday=5, Saturday=6 */

/* January=0, February=1, March=2, April=3, May=4, June=5 */
/* July=6, August=7, September=8, October=9, November=10, December=11 */

/* 0,2017,0,15 represents Sunday 2017 January 15 */

/* 1,2018,1,19 represents Monday 2018 February 19 */

/* Output: */

/* The month and year of the first occurrence of Friday the 13th that occurs after the input date */

/* You may assume that the user's input is valid. */

/* fri13.tc - 1/18/17 - tct */
// updated on 9/13/24

int gday_of_week,gyear,gmonth,gday
int is_a_leap_year

split int t(0);char s(0),d(0) [
 int y,ix,tx,sl,ds;ds=strlen(d);t(0)=s;sl=strlen(s)
 while (sl-tx) [
  ix=index(s+tx,sl-tx,d,ds)
  tx=tx+ix+ds-1;y=y+1;t(y)=s+tx;s(tx-ds)=0
  ]
 return y
 ]

leap_year int year [
 if (year%400==0) return 1
 else if (year%100==0) return 0
 else if (year%4==0) return 1
 else return 0
 ]

fix_g [ /* catch the illegals */
 if (gday==32) [
  if (gmonth==11) [
   gmonth=0;gday=1;gyear=gyear+1;is_a_leap_year=leap_year(gyear)
   ]
 else [
  gmonth=gmonth+1;gday=1
  ]
 ]
 else if (gday==31) [
  if ((gmonth==3)+(gmonth==5)+(gmonth==8)+(gmonth==10)) [gmonth=gmonth+1;gday=1;]
  ]
 else if (gday==30) [
  if (gmonth==1) [
   if (is_a_leap_year) [gmonth=2;gday=1]
   ]
  ]
 else if (gday==29) [
  if (gmonth==1) [
   if (is_a_leap_year==0) [gmonth=2;gday=1]
   ]
  ]
 ]

main [
 pl "enter day_of_week (0 thru 6 Sun thru Sat) : ";gday_of_week=gn
 pl "enter year (e.g. 2024) : ";gyear=gn
 pl "enter month (0 thru 11 Jan thru Dec) : ";gmonth=gn
 pl "enter day (1 thru 31) : ";gday=gn
 fri13
 ]

fri13 [
 int month_name(12)
 int day_of_week_name(7)
 char foo(100),bar(100)
 strcpy(foo,"Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec,")
 split month_name,foo,","
 strcpy(bar,"Sunday,Monday,Tuesday,Wednesday,Thursday,Friday,Saturday,")
 split day_of_week_name,bar,","
 pl "Start date: "
 ps day_of_week_name(gday_of_week);putchar ' ';ps month_name(gmonth);pn gday;pn gyear
 gday=gday+1;gday_of_week=gday_of_week+1;gday_of_week=gday_of_week%7;
 if ((gday==32)*(gmonth==11)) [gday=1;gmonth=0;gyear=gyear+1]
 is_a_leap_year=leap_year(gyear)

 while (((gday_of_week==5)*(gday==13))==0) [ /* main loop */
  gday=gday+1;
  fix_g
  gday_of_week=gday_of_week+1;gday_of_week=gday_of_week%7;
  ]

 pl "The next Friday the thirteenth occurs in "
 ps month_name(gmonth);pn gyear
 ]