/* mdate.c

mods:
   lrl 930719: cleaned up the code a little
   lrl 910815: Added "h" option to displacement. 
               Corrected problem where, with a format specified with
               no displacement, mdate would think the format was a
               date string.    
*/

#include <stdio.h>
#include <string.h>
#include <sys/types.h>

#define SYSOK 0
#define SYSERR 1

int isleap(int year)
{
    int leap;

    leap = 0;
    if ( (year % 4 ) == 0) 
       leap = 1;
    if ( (year % 100 ) == 0) 
       leap = 0;
    if ( (year % 400 ) == 0) 
       leap = 1;
    if ( (year % 4000 ) == 0) 
       leap = 0;
 
    return leap;
}
      
time_t timeparse(char *sdate)
{
   int i;
   char savch;
   char *spnt, *allmons, *oztime;
   char *getenv(char *vv);
   time_t thyme;
   char tzone[4];
   static int monlen[] = { 0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };
   int month, day, year, hour, minute, second;

   spnt = sdate;

   /* first, find the beginning of the string by finding the first non-blank
      character */
   while ( (*spnt == ' ') && (*spnt != NULL) ) spnt++;

   /* if this is a digit, then we are using the mmddhhnn[[cc]yy] format */
   if (isdigit( (int)*spnt))
   {
      tzone[0] = '?' ; tzone[1] = '?' ; tzone[2] = '?' ; tzone[3] = NULL;

      /* get the month */
      month = 0;
      for ( i = 0; i < 2; i++ )
      {  
          if (isdigit( (int)*spnt))
          {
              month = month * 10 + (*spnt - '0');
          }
          else
          {
              fprintf(stderr," Bad date string: %s \n",sdate);
              fprintf(stderr," The month is bad. \n");
              exit(SYSERR);
          }
          spnt++;
      }
   
      /* get the day of the month */
      day = 0;
      for ( i = 0; i < 2; i++ )
      {  
          if (isdigit( (int)*spnt))
          {
              day = day * 10 + (*spnt - '0');
          }
          else
          {
              fprintf(stderr," Bad date string: %s \n",sdate);
              fprintf(stderr," The day of the month is bad. \n");
              exit(SYSERR);
          }
          spnt++;
      }
   
      /* get the hour of the day */
      hour = 0;
      for ( i = 0; i < 2; i++ )
      {  
          if (isdigit( (int)*spnt))
          {
              hour = hour * 10 + (*spnt - '0');
          }
          else
          {
              fprintf(stderr," Bad date string: %s \n",sdate);
              fprintf(stderr," The hour of the day is bad. \n");
              exit(SYSERR);
          }
          spnt++;
      }
   
      /* get the minute of the hour */
      minute = 0;
      for ( i = 0; i < 2; i++ )
      {  
          if (isdigit( (int)*spnt))
          {
              minute = minute * 10 + (*spnt - '0');
          }
          else
          {
              fprintf(stderr," Bad date string: %s \n",sdate);
              fprintf(stderr," The minute of the hour is bad. \n");
              exit(SYSERR);
          }
          spnt++;
      }
   
      /* get the second of the minute to 0 */
      second = 0;

      if (*spnt != NULL)
      {
         /* get the year */
         year = 0;
         for ( i = 0; i < 2; i++ )
         {  
             if (isdigit( (int)*spnt))
             {
                 year = year * 10 + (*spnt - '0');
             }
             else
             {
                 fprintf(stderr," Bad date string: %s \n",sdate);
                 fprintf(stderr," The year is bad. \n");
                 exit(SYSERR);
             }
             spnt++;
         }

         /* but wait--is there more? */
         if (*spnt != NULL)   /* full 4 digits in the year? */
         {
            /* get the rest of the year */
            for ( i = 0; i < 2; i++ )
            {  
                if (isdigit( (int)*spnt))
                {
                    year = year * 10 + (*spnt - '0');
                }
                else
                {
                    fprintf(stderr," Bad date string: %s \n",sdate);
                    fprintf(stderr," The year is bad. \n");
                    exit(SYSERR);
                }
                spnt++;
            }
         }
         else
         {
            year = year + 1900;  /* only two digits in the year */
            if ( year < 1920 )
               year = year + 100;   /* remain valid past the year 2000 */
         }
      }
      else
      {      /* no year--complain */
          fprintf(stderr," Bad date string: %s \n",sdate);
          fprintf(stderr," The year must be specified. \n");
          exit(SYSERR);
      }
   }
   else
   {     /* the full string format must have been used */
  
      /* This should be one of the days of the week. Save the 4rth char and
         replace it with NULL, terminating a (tentative) day-of-the-week
         string, which can then be checked against all the days of the week. */
      allmons = strdup("SunMonTueWedThuFriSat");
      i = 0;
      while ( (strncmp(&allmons[3*i],spnt,3) != 0) && (i < 7)) i++;
      if ( i < 7 )
      {
   
         /* Advance to the next field, which should be the month */
         while ( (*spnt != ' ')  &&  (*spnt != NULL)) spnt++;
         while ( (*spnt == ' ')  &&  (*spnt != NULL)) spnt++;
   
      }
         /* if no match was made, this is probably an error, but we
            will just assume that the user got lazy and simply did not
            include a day of the week. */ 
   
      /* Now find out which day of the month we are using */
      allmons = strdup("JanFebMarAprMayJunJulAugSepOctNovDec");
      i = 0;
      while ( (strncmp(&allmons[3*i],spnt,3) != 0) && (i < 12)) i++;
      if ( i < 12 )
      {
         month = i + 1;
      }
      else
      {
         fprintf(stderr," Bad date string: %s \n",sdate);
         fprintf(stderr," The month must be in the form Jan, Feb, etc.\n");
         exit(SYSERR);
      }
   
   
      /* scan forward to the day of the month */
      while ( (*spnt != ' ')  &&  (*spnt != NULL)) spnt++;
      while ( (*spnt == ' ')  &&  (*spnt != NULL)) spnt++;
   
      /* get the day of the month */
      day = 0;
      while ( isdigit( (int)*spnt) )
      {
         day = day * 10 + ( *spnt - '0' );
         spnt++;
      }
      if (*spnt != ' ')
      {
         fprintf(stderr," Bad date string: %s \n",sdate);
         fprintf(stderr," The day of the month is bad. \n");
         exit(SYSERR);
      }
   
      /* scan forward to the time of day */
      while ( (*spnt != ' ')  &&  (*spnt != NULL)) spnt++;
      while ( (*spnt == ' ')  &&  (*spnt != NULL)) spnt++;
   
      /* get the time of day */
      hour = 0;
      for ( i = 0; i < 2; i++ )
      {  
          if (isdigit( (int)*spnt))
          {
              hour = hour * 10 + (*spnt - '0');
          }
          else
          {
              fprintf(stderr," Bad date string: %s \n",sdate);
              fprintf(stderr," The hour of the day is bad. \n");
              exit(SYSERR);
          }
          spnt++;
      }
      if (*spnt != ':')
      {
         fprintf(stderr," Bad date string: %s \n",sdate);
         fprintf(stderr," The first time separator is bad. \n");
         exit(SYSERR);
      }
      spnt++;

      /* get the minute of the hour */
      minute = 0;
      for ( i = 0; i < 2; i++ )
      {  
          if (isdigit( (int)*spnt))
          {
              minute = minute * 10 + (*spnt - '0');
          }
          else
          {
              fprintf(stderr," Bad date string: %s \n",sdate);
              fprintf(stderr," The minute of the hour is bad. \n");
              exit(SYSERR);
          }
          spnt++;
      }
      if (*spnt != ':')
      {
         fprintf(stderr," Bad date string: %s \n",sdate);
         fprintf(stderr," The second time separator is bad. \n");
         exit(SYSERR);
      }
      spnt++;
   
      /* get the second of the minute */
      second = 0;
      for ( i = 0; i < 2; i++ )
      {  
          if (isdigit( (int)*spnt))
          {
              second = second * 10 + (*spnt - '0');
          }
          else
          {
              fprintf(stderr," Bad date string: %s \n",sdate);
              fprintf(stderr," The second of the minute is bad. \n");
              exit(SYSERR);
          }
          spnt++;
      }
      if (*spnt != ' ')
      {
         fprintf(stderr," Bad date string: %s \n",sdate);
         fprintf(stderr," There should be a space after the time. \n");
         exit(SYSERR);
      }
   
      /* scan forward to the time zone */
      while ( (*spnt != ' ')  &&  (*spnt != NULL)) spnt++;
      while ( (*spnt == ' ')  &&  (*spnt != NULL)) spnt++;
     
      /* get the time zone */
      strncpy(tzone,spnt,3);
      tzone[3] = NULL;

      /* skip ahead to the year */
      while ( (*spnt != NULL &&  ! isdigit( (int)*spnt) ) ) 
          spnt++;
   
      /* get the year */
      year = 0;
      for ( i = 0; i < 4; i++ )
      {  
          if (isdigit( (int)*spnt))
          {
              year = year * 10 + (*spnt - '0');
          }
          else
          {
              fprintf(stderr," Bad date string: %s \n",sdate);
              fprintf(stderr," The year is bad.\n");
              exit(SYSERR);
          }
          spnt++;
      }
   }  

   /* ok, at this point, we have the year, month, day, hour, minute, and second.
      now we need to combine these into the number of seconds since 
      00:00:00 GMT, January 1, 1970 */

   thyme = 0;

   /* First, add in all the seconds which have passed until the
      beginning of the desired year */
   for ( i = 1970; i < year; i++ )  
       thyme +=  ( 365 + ( isleap(i) ? 1 : 0)  ) * 24 * 3600;

   /* Next, add in all the seconds which have passed until the beginning
      of the desired month */
   for ( i = 1; i < month; i++ )
   {
       thyme += monlen[i] * 24 * 3600;

       /* take care of Feb 29 */
       if (isleap(year) && (i == 2))
          thyme += 24 * 3600;
   }

   /* next, add in the time of the day */
   thyme += (  ((day-1) * 24 + hour) * 60 + minute ) * 60 + second; 

   /* Now we have to shift our time to GMT */
   /* we cannot recognize all the timezones in the world, but
      we can at least try to deal with the one being used here */
   if ( (oztime = getenv("TZ")) != NULL)
   {

      spnt = oztime;

      /* scan until we hit a digit */
      while ( (! isdigit( (int)*spnt))  &&  (*spnt != NULL)) spnt++;
      if (*spnt != NULL)
      {
         hour = 0;
         minute = 0;
         second = 0;

         /* get the hour correction time */
         while (isdigit( (int)*spnt)) 
         {
            hour = hour * 10 + (*spnt - '0');
            spnt++;
         }

         /* are minutes specified as well? */
         if (*spnt == ':')  
         {
            spnt++;

            /* get the minute correction time */
            while (isdigit( (int)*spnt)) 
            {
               minute = minute * 10 + (*spnt - '0');
               spnt++;
            }

            /* are seconds specified as well? */
            if (*spnt == ':')  
            {
               spnt++;

               /* get the second correction time */
               while (isdigit( (int)*spnt)) 
               {
                  second = second * 10 + (*spnt - '0');
                  spnt++;
               }
            }
         }
   
      }
      else
      {
         fprintf(stderr
         ," timeparse: cannot make sense of the TZ environment variable.\n");
         exit(SYSERR);
      }

      /* check to make sure the time zone matches what we were given */
      if ( strncmp(tzone,"???",3) == 0 )
      {
         for (i=0; i<3; i++) 
             tzone[i] = oztime[i];
      }
      if ( strncmp(oztime,tzone,3) == 0 ) 
      {
         thyme += (hour * 60 + minute) * 60 + second;
      }
      else if ( strncmp(spnt,tzone,3) == 0 )
      {
         thyme += ( (hour-1) * 60 + minute) * 60 + second;
      }
      else
      {
         fprintf(stderr,"timeparse: The time zone specified did not match the TZ enviroment variable\n");
         exit(SYSERR);
      }
   }
   else
   {
      fprintf(stderr," timeparse: Unable to obtain present time zone.\n");
      fprintf(stderr," Assuming GMT.\n");
   }

   return thyme;
}


main(int argc, char **argv)
{
    int i;
    char prtim[30];
    time_t time(), svtime, *ptime;
    char *inarg, *fmt;
    int numdays, numhours, numminutes, digit, togo;

    /* first, set up defaults */
    numdays = 0;    /* no days ahead or behind */
    numhours = 0;
    numminutes = 0;
    svtime = time(0);   /* use current time */

    /* get each cmd line argument */
    i = 1;
    togo = argc - 1;

    if ( togo > 0 ) 
    {
       /* displacement field? */
       if ( (argv[i][0] == '+' ) || (argv[i][0] == '-' ) )
       {
           inarg = argv[i] + 1;
           while (*inarg != NULL) 
           {
              digit = *inarg - '0';
              if ((digit >= 0) && (digit <= 9))
              {
                 numdays = numdays*10 + digit;
              }
              else if ( digit == ('h'-'0') )
              {  /* numdays is hhmm instead of the number of days */
                 numminutes =  numdays % 100  ;
                 numhours = numdays / 100  + numminutes / 60 ;
                 numminutes = numminutes % 60 ;
                 numdays = numhours / 24 ;
                 numhours = numhours % 24 ;
              }
              else
              {
                 fprintf(stderr,"Improper day-delta specification: %s \n"
                         ,argv[i]);
                 fprintf(stderr," Usage:\n");
                 fprintf(stderr,"  mdate [ +n | -n [ date [ format ] ] ] \n");
                 exit(SYSERR);
              }
              inarg++;
           }
 
           if (argv[i][0] == '-') 
           {
              numdays = 0 - numdays;
              numhours = 0 - numhours;
              numminutes = 0 - numminutes;
           }

           i++;
           togo--;

         }
     }

     if ( togo > 0 )
     {
        /* the date specifier string */
        svtime = timeparse(argv[i]);

        i++;
        togo--;

     }

     if (togo > 0 )
     {
         fmt = argv[i];

         i++;
         togo--;
     }
     else
     {
         fmt = "%a %b %e %H:%M:%S %Z %Y%n";
     }

    /* now add in a correction for day-delta */
    svtime +=  ( (numdays * 24 + numhours) * 60 + numminutes ) * 60;

    ptime = &svtime;
    (void) cftime(prtim,fmt,ptime);
    printf("%s",prtim);
   
    return SYSOK; 
}