/* date.c - Don Yang (uguu.org)

   Date functions.

   05/27/12
                                                                           */

#include<stdio.h>
#include<string.h>
#include<time.h>

/* Moon phase labels for GetMoonPhase */
static const char *label[8] =
{
   "new moon",
   "waxing crescent",
   "first quarter",
   "waxing gibbous",
   "full moon",
   "waning gibbous",
   "last quarter",
   "waning crescent"
};

/* Return moon phase for a particular timestamp */
static int GetMoonPhase(int t)
{
   const int synodic_period = (int)(29.530589 * 86400);
   t -= 434928;
   return ((t % synodic_period) * 8) / synodic_period;
}

int main(int argc, char **argv)
{
   struct tm t;
   time_t s;
   int i;

   /* Initialize time info */
   s = time(NULL);
   memcpy(&t, localtime(&s), sizeof(t));
   printf("%04d-%02d-%02d %02d:%02d:%02d\n",
          t.tm_year + 1900, t.tm_mon + 1, t.tm_mday,
          t.tm_hour, t.tm_min, t.tm_sec);
   t.tm_hour = t.tm_min = t.tm_sec = 0;

   if( argc == 1 )
   {
      /* Get moon phase for today */
      s = mktime(&t);
      printf("Today=%04d-%02d-%02d: %d %s\n",
             t.tm_year + 1900, t.tm_mon + 1, t.tm_mday,
             (int)s, label[GetMoonPhase((int)s)]);
      return 0;
   }

   for(i = 1; i < argc; i++)
   {
      /* Get moon phase for dates specified on command line arguments */
      if( sscanf(argv[i], "%d-%d-%d", &t.tm_year, &t.tm_mon, &t.tm_mday) == 3 )
      {
         printf("%04d-%02d-%02d: ", t.tm_year, t.tm_mon, t.tm_mday);
         t.tm_year -= 1900;
         t.tm_mon--;
         s = mktime(&t);
         if( s == (time_t)-1 )
         {
            puts("invalid");
            continue;
         }
         printf("%d %s\n", (int)s, label[GetMoonPhase((int)s)]);
      }
   }

   return 0;
}