/* POSIX arvelie.c
 *
 * a simple program to convert dates to arvelie.
 * read more: https://wiki.xxiivv.com/site/arvelie.html
 */

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <unistd.h>

void usage();
int main(int argc, char* argv[]);

void
usage()
{
  fprintf(stderr, "usage: arvelie [-d YYYY-MM-DD]\n");
  exit(EXIT_FAILURE);
}

int
main(int argc, char* argv[])
{
  time_t t = -1;
  char* inputDate = NULL;

  int opt;
  while	((opt = getopt(argc, argv, ":d:")) != -1) {
    switch (opt) {
    case 'd':
      inputDate = optarg;
      break;
    case '?':
      usage();
      break;
    case ':':
      usage();
      break;
    default:
      usage();
    }
  }

  if (inputDate != NULL) {
    struct tm tm = {0};
    strptime(inputDate, "%Y-%m-%d", &tm);
    t = mktime(&tm);
  } else {
    t = time(NULL);
  }
  
  struct tm* date = localtime(&t);
  
  int yday = date->tm_yday;
  int year = date->tm_year % 100;
  char month = (yday < 364) ? (char)65 + (yday / 14) : '+';
  int day = yday % 14;

  printf("%02d%c%02d\n", year, month, day);
  exit(EXIT_SUCCESS);
}