# include <stdio.h>
# include <unistd.h>
# include <stdlib.h>
# include <fcntl.h>
# include <sys/stat.h>
# include <string.h>

char * usage = "Usage: %s hashfile overflowfile\n";
const int table_length = 19;
const int record_length = 31;

int hash(char string[], int len) {
   int i, s;

   s = i = 0;
   while((i < len) && (string[i] != '\0')) {
      s = (s * 10 + string[i]) % table_length;
      i++;
   }
   return (s);
}

int write_at_pos(int fd, int pos, char buffer[record_length]) {
/* returns -1 on error, 0 on success, 1 if pos occupied */
    char ch[2];
    if(lseek(fd,pos*record_length,SEEK_SET) <0) {
        perror("lseek");
        return -1;
    }
    if (read(fd,ch,1) < 1) {
       perror("read");
       return -1;
    }
    if (ch[0] != '\0')
       return 1;
    if(lseek(fd,-1,SEEK_CUR) <0) {
        perror("lseek");
        return -1;
    }

    if (write(fd,buffer,record_length) < record_length) {
        perror("write");
        return -1;
    }
    return 0;
}

int append_of(int fd, char buffer[record_length]) {
    if (write(fd,buffer,record_length) < record_length) {
       perror("write");
       return -1;
    }
    return 0;
}

   
int main(int argc, char * argv[]) {
   int hfd, ofd, i;
   char name[record_length];
   char empty[record_length];

   char buffer[record_length]; /*including null-byte */

   if (argc != 3) {
      fprintf(stderr, usage, argv[0]);
      exit(1);
   }

   for(i=0; i< record_length; i++)
       empty[i]='\0';

   printf("File Size: %d\n", table_length * record_length);
   if( (hfd = open(argv[1], O_RDWR | O_CREAT | O_TRUNC, 0644)) < 0) {
      perror("open");
      exit(2);
   }
   if( (ofd = open(argv[2], O_RDWR | O_CREAT | O_TRUNC | O_APPEND, 0644)) < 0) {
      perror("open");
      exit(2);
   }

   /* prepare hashfile: */
   /* fill with table_length * record_length zeros */

   for(i=0; i < table_length; i++) 
      if( write(hfd, empty, record_length) < record_length) {
         perror("write");
         exit(3);
      }

    /* read from stdin: */


    memcpy(name,empty,record_length);
    while( fgets(name, record_length,stdin) != NULL) {
       /* replace \n by \0:*/
       for(i=0; (i < record_length) && (name[i] != '\n'); i++)
                 ;
       if (i < record_length)
             name[i] = '\0';

       printf("Test: %s -> %d\n", name, hash(name, strlen(name)));
       memcpy(buffer,name,record_length);
       switch (write_at_pos(hfd,hash(name,strlen(name)),buffer)) {
          case -1: perror("write_at_pos");
                   exit(4);
          case 1 : fprintf(stderr,"Collossion\n");
                   if (append_of(ofd,buffer) < 0) {
                      fprintf(stderr, "ERROR\n");
                      exit(8);
                   }
                   break;
          default: /*success*/
       }
       memcpy(name,empty,record_length);
    }


exit(0);
}