/*
 * Adjust the EXIF timestamp of a series of photos.
 * This uses exiftool to access the EXIF data.
 *
 * Usage: $0 offset Photos...
 *
 * offset is a time offset in the form ±DD:HH:MM:SS
 *
 * $Id: resetdate.c,v 1.5 2012/10/11 01:01:43 grog Exp $
 */
#include <ctype.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/file.h>
#include <sys/param.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>

void usage (char *me)
{
  printf ("Usage:\n\n"
          "%s [-n] offset Photos...\n"
          " -n means \"show but don't do\"\n"
          "offset is a time offset in the form [-][[DD]:HH]:MM:SS\n"
          "at least M and S must be specified\n",
          me );
  exit (1);
}

int main (int argc, char *argv [])
{
  int sign = 1;                                 /* positive until proven otherwise */
  char *c;
  /*
   * Parameters passed as offset.  The meaning depends on the number; see below.
   */
  int P [4];
  int fields;                                   /* number of fields in offset */
  time_t offset;                                /* offset to add to time */
  int arg;
  char command [PATH_MAX + 80];                 /* command to hand to system() */
#define BUFSIZE 1024
  char buf [BUFSIZE + 1];                       /* result read from child */
  FILE *child;
  char *filename;                               /* name of current file */
  struct tm create_date;                        /* creation date of current file */
  struct stat filestat;                         /* and current status */
  struct timeval new_times [2];                 /* adjusted time */
  int dummy = 0;                                /* 1 to just show instead of doing it */
  char *me = argv [0];                          /* this could change */

  if (argc < 2)
    usage (me);
  if (! strcmp (argv [1], "-n"))
  {
    dummy = 1;                                  /* just print stuff out */
    argv++;                                     /* shift */
    argc--;
  }
  if (argc < 2)                                 /* we need two args left overr */
    usage (me);
  c = argv [1];                                 /* offset */
  if (*c == '-')                                /* negative change */
  {
    sign = -1;
    c++;
  }
  else if (*c == '+')                           /* redundant positive */
    c++;
  else if (! isdigit (*c))
    usage (argv [0]);
  /*
   * We can have up to 4 fields here.  If they're all there, they have the
   * meanings implied in the parameter list.  Otherwise we have to reshuffle.
   */
  fields = sscanf (c, "%d:%d:%d:%d", &P [0], &P [1], &P [2], &P [3]);
  switch (fields)
  {
  default:
    usage (argv [0]);

  case 4:                                       /* all present and accounted for */
    offset = P [0] * 86400 + P [1] * 3600 + P [2] * 60 + P [3]; /* D H M S */
    break;

  case 3:                                       /* H:M:S */
    offset = P [0] * 3600 + P [1] * 60 + P [2];
    break;

  case 2:                                       /* M:S only */
    offset = (P [0] * 60 + P [1]);
    break;
  }
  offset *= sign;
  new_times [1].tv_usec = 0;                    /* currently no sub-second component */
  new_times [2].tv_usec = 0;                    /* currently no sub-second component */
  /* How I hate these date conversion functions! */
  create_date.tm_zone = NULL;
  create_date.tm_isdst = -1;                    /* try to guess based on date */

  for (arg = 2; arg < argc; arg++)              /* each photo */
  {
    filename = argv [arg];
    if (stat (filename, &filestat) < 0)
      fprintf (stderr, "Can't stat %s: %s (%d)\n", filename, strerror (errno), errno);
    else if (! S_ISREG (filestat.st_mode))
      fprintf (stderr, "%s is not a file\n", filename);
    else
    {
      sprintf (command, "exiftool -DateTimeOriginal %s", filename);
      child = popen (command, "r");
      if (! child)
      {
        fprintf (stderr, "Can't start %s\n", command);
        exit (1);
      }
      buf [0] = '\0';                           /* in case we read nothing */
      fread (buf, BUFSIZE, 1, child);
      if (ferror (child))
      {
        fprintf (stderr, "Can't read child: %s (%d)\n", strerror (errno), errno);
        exit (1);
      }

      /*
       * We now should have a line of the format:
       *
       * Create Date                     : 2011:04:02 09:23:56
       *
       * For now, strip everything up to and including first :
       */
      c = buf;
      while (*c && (*c != ':'))
        c++;
      while (*c && ((*c == ':') || (*c == ' ')))
        c++;
      if (! strptime (c, "%Y:%m:%d %T", &create_date))
        fprintf (stderr, "Can't parse date '%s' for %s\n", c, filename);
      else
      {
        new_times [0].tv_sec = mktime (&create_date) + offset; /* adjust time */
        /* We don't change the subsecond values. */
        new_times [0].tv_usec = filestat.st_atim.tv_nsec / 1000;
        new_times [1].tv_usec = filestat.st_mtim.tv_nsec / 1000;
        strftime (buf, BUFSIZE, "%Y:%m:%d %T", localtime (&new_times [0].tv_sec));
        sprintf (command,
                 "exiftool -overwrite_original_in_place "
                 "-DateTimeOriginal=\"%s\" "
                 "-CreateDate=\"%s\" "
                 "-ModifyDate=\"%s\" %s  ",
                 buf,
                 buf,
                 buf,
                 filename );
        puts (command);
        if (! dummy)
        {
          system (command);
          new_times [1].tv_sec = new_times [0].tv_sec; /* for utimes call */
          if (utimes (filename, new_times) < 0) /* set modification timestamp too */
            fprintf (stderr,
                     "Can't set modification timestamp for %s: %s (%d)\n",
                     filename,
                     strerror (errno),
                     errno );
        }
      }
      pclose (child);
    }
  }
  return 0;
}