#include <stdbool.h>
#include <stdio.h>
#include <signal.h>
#include <unistd.h>

int usage(char *argv0) {
  printf("Usage: %s [-ai] [file ...]\n", argv0);
  return 2;
}

int main(int argc, char *argv[]){
  int opt;
  bool append = false;
  bool iflag = false;
  while ((opt = getopt(argc, argv, ":ai")) != -1) {
    switch (opt) {
      case 'a':
        append = true;
        break;
      case 'i':
        iflag = true;
        break;
      case '?':
        fprintf(stderr, "%s: invalid option -- '%c'\n", argv[0], optopt);
        return usage(argv[0]);
    }
  }

  if (iflag && signal(SIGINT, SIG_IGN) == SIG_ERR) {} // FIXME

  int arg = optind;
  void *buf[BUFSIZ];
  FILE *file;
  ssize_t n;

  while ((n = read(0, buf, sizeof(buf))) > 0) {
    optind = arg;
    if (optind < argc) {
      for (; optind < argc; optind++) {
        file = fopen(argv[optind], append ? "w" : "a+");
        fwrite(buf, BUFSIZ, 1, file);
        fclose(file);
        append = true;
      }
    } else {
      fwrite(buf, BUFSIZ, 1, stdout);
    }
  }
  return 0;
}