#include <arpa/inet.h>
#include <errno.h>
#include <net/if.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <bpf/bpf.h>
#include <bpf/libbpf.h>
#include <linux/if_link.h>

int main(int argc, char **argv) {
  if (argc != 2) {
    fprintf(stderr, "Usage: %s <iface>\n", argv[0]);
    return 1;
  }

  const char *const iface = argv[1];

  int ifindex = if_nametoindex(iface);
  if (!ifindex) {
    perror("if_nametoindex");
    return 1;
  }

  struct bpf_object *obj;
  int prog_fd;
  const char *const xdp_file = "xdp_udp_handler.o";

  obj = bpf_object__open_file(xdp_file, NULL);
  if (!obj) {
    fprintf(stderr, "Error opening BPF object file: `%s'\n", xdp_file);
    return 1;
  }

  if (bpf_object__load(obj)) {
    fprintf(stderr, "Error loading BPF object\n");
    return 1;
  }

  struct bpf_program *const prog =
      bpf_object__find_program_by_name(obj, "xdp_udp_handler");
  if (!prog) {
    fprintf(stderr, "Couldn't find program\n");
    return 1;
  }

  prog_fd = bpf_program__fd(prog);
  if (prog_fd < 0) {
    fprintf(stderr, "Invalid program FD\n");
    return 1;
  }

  printf("Attaching BPF program in driver (native) mode..\n");
  if (bpf_xdp_attach(ifindex, prog_fd,
                     XDP_FLAGS_UPDATE_IF_NOEXIST | XDP_FLAGS_DRV_MODE,
                     NULL) < 0) {
    perror("bpf_xdp_attach");
    printf("Attaching BPF program in kernel mode..\n");
    if (bpf_xdp_attach(ifindex, prog_fd, XDP_FLAGS_UPDATE_IF_NOEXIST, NULL) <
        0) {
      perror("bpf_xdp_attach");
      return 1;
    }
  }

  printf("XDP program loaded\n");
  return 0;
}