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

const char default_input[] = "/proc/net/dev";

int main(int argc, const char **argv) {
  const char *input = default_input;

  /* "usage" */
  if (argc < 2) {
    printf("Warning: no file specified, defaulting to %s\n", default_input);
  } else {
    input = argv[1];
    printf("Info: using %s as specified\n", argv[1]);
  }
  
  int file = open(input, 0);
  if (file < 0) {
    printf("Error: unable to open %s: %s\n", input, strerror(errno));
    return 1;
  } else {
    ssize_t ret;
    ssize_t current = 0;
    ssize_t extra = 0;

    printf("Info: %s opened successfully\n", input);

    /* this is ugly but oh well */
    #define bufsize (8000)

    char buf[bufsize+1] = "";
    while ((ret = read(file, buf, bufsize)) > 0) {
      printf("Read: %u\n", ret);
      char *newline = strchr(buf, '\n');
      if (newline) {
        current += (newline-buf);
        *newline = '\0';
        extra = ret-(newline-buf+1);
        printf("Found newline: %u char-long line: with %u extra chars:\n%s\n", current, extra, buf);
        lseek(file, -extra, SEEK_CUR);
        current = 0;
      }
    }
    printf("Final position: %u\n", lseek(file, 0, SEEK_CUR)); 
    close(file);
  }

  return 0;
}