/* Print From: and Subject: fields of messages in a standard Unix mailbox. */

#include <stdio.h>
#include <string.h>
#include <strings.h>
#include <stdlib.h>
#include <ctype.h>

#define buflen 10000
#define fieldlen 39

void trim (char *s) {
  if (s != NULL) {
    size_t l = strlen (s);
    while (l > 0) {
      l--;
      if (isspace (s[l]))
        s[l] = '\0';
      else
        return;
    }
  }
}

int main (int argc, char **argv) {
  char buf[buflen], from[fieldlen+1], subj[fieldlen+1];
  FILE *fp;
  switch (argc) {
  case 1:
    fp = stdin;
    break;
  case 2:
    fp = fopen (argv[1], "r");
    if (!fp) {
      perror (argv[1]);
      exit (-1);
    }
    break;
  default:
    fprintf (stderr, "$Id: skim_std_mailbox.c 257 2006-06-01 14:39:47Z flaterco $\n");
    fprintf (stderr, "Usage:  skim [filename]\n");
    exit (-1);
  }
  from[fieldlen] = subj[fieldlen] = '\0';
  while (1) {
    from[0] = subj[0] = '\0';
    while (1) {
      if (fgets (buf, buflen, fp) == NULL) {
        printf ("%39s %-39s\n", from, subj);
        exit(0);
      }
      trim (buf);
      if (buf[0] == '\0')
        break;
      if (!strncasecmp (buf, "From: ", 6))
        strncpy (from, buf+6, fieldlen);
      else if (!strncasecmp (buf, "Subject: ", 9))
        strncpy (subj, buf+9, fieldlen);
    }
    printf ("%39s %-39s\n", from, subj);
    do {
      if (fgets (buf, buflen, fp) == NULL)
        exit (0);
    } while (strncmp (buf, "From ", 5));
  }
}