#include pps/library.tc
#include pps/lrblib.tc

// find the next date that contains the same day number on the same day of
// week as the input date

// ref: http://primepuzzle.com/tc/next_c_doc.html

// a useful calendar site is http://5ko.free.fr/en/year.php?y=1776

leap 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
 ]

next int dow,month,day,year [
 int i,month_n(12),day_of_week_n(7),db(12),da(36),index,work_day,verbose
 char foo(100),bar(100)
 strcpy foo,"Jan,Feb,Mar,Apr,May,Jun,Jul,Aug,Sep,Oct,Nov,Dec,"
 strcpy bar,"Sun,Mon,Tue,Wed,Thu,Fri,Sat,"
 split month_n,foo,",";split day_of_week_n,bar,","
 printf "%c%s %s %d",10,day_of_week_n(dow),month_n(month),day,year
 db(0)=31;db(1)=28;db(2)=31;db(3)=30;db(4)=31;db(5)=30
 db(6)=31;db(7)=31;db(8)=30;db(9)=31;db(10)=30;db(11)=31
// load up 3 years of data. adjust for leap years
 while i<36 [
  da(i)=db(i%12)
  i=i+1
  ]
 i=0
 while i<3 [
  if (leap(year+i)) da(1+12*i)=29
  i=i+1
  ]
 index=month+1;work_day=dow;verbose=1
 if verbose printf "%c%d %d",10,month,work_day
 while 1 [ // main loop
  work_day=(work_day+da(index-1))%7
  if verbose printf "%c%d %d",10,index,work_day
  if work_day==dow // needs to be right day of week
   if (da(index)>=day) break // needs to be a legal month
  index=index+1
  ] // end main loop
 printf "%c%s %d%c",10,month_n(index%12),(year+index/12),10
 ]

main [
 int dow,month,day,year
 printf "%cnext_c.tc - 7/6/19 - lrb%c",10,10
 printf "%cdow (0=Sunday, 1=Monday, etc.) : ",10;dow=gn
 printf "month (0=January, 1=February, etc.) : ";month=gn
 printf "day (1..31) : ";day=gn
 printf "year (e.g. 2019) : ";year=gn
 next dow,month,day,year
 ]