#include "postgres.h"
#include "fmgr.h"
#include "utils/builtins.h"
#include <arpa/inet.h>
#include <sys/socket.h>
#include <netdb.h>
#include <sys/types.h>

PG_MODULE_MAGIC;


PG_FUNCTION_INFO_V1(rdns_lookup);
Datum rdns_lookup(PG_FUNCTION_ARGS) {
  struct in_addr iaddr;
  char host[512];
  struct sockaddr_in sa;
  int r;
  char* ip = text_to_cstring(PG_GETARG_TEXT_PP(0));

  memset(&iaddr, 0, sizeof(struct in_addr));
  memset(&sa, 0, sizeof(struct sockaddr_in));
  memset(host, 0, 512);

  inet_aton(ip, &iaddr);

  sa.sin_family = AF_INET;
  sa.sin_addr = iaddr;

  r = getnameinfo((struct sockaddr*)(&sa), sizeof(struct sockaddr_in), host, 512, 0, 0, NI_NAMEREQD);
  if (r == EAI_NONAME)
    PG_RETURN_NULL();
  if (r) {
    ereport(ERROR, (errcode(ERRCODE_SYSTEM_ERROR), errmsg("getnameinfo failed! %s", gai_strerror(r))));
  }

  PG_RETURN_TEXT_P(cstring_to_text(host));
}

PG_FUNCTION_INFO_V1(circular_rdns_lookup);
Datum circular_rdns_lookup(PG_FUNCTION_ARGS) {
  struct in_addr iaddr;
  char host[512];
  struct sockaddr_in sa;
  int r;
  struct addrinfo hint;
  struct addrinfo* results;
  char* ip = text_to_cstring(PG_GETARG_TEXT_PP(0));
  struct addrinfo* c;

  memset(&iaddr, 0, sizeof(struct in_addr));
  memset(&sa, 0, sizeof(struct sockaddr_in));
  memset(host, 0, 512);
  memset(&hint, 0, sizeof(struct addrinfo));

  inet_aton(ip, &iaddr);

  sa.sin_family = AF_INET;
  sa.sin_addr = iaddr;

  r = getnameinfo((struct sockaddr*)(&sa), sizeof(struct sockaddr_in), host, 512, 0, 0, NI_NAMEREQD);
  if (r == EAI_NONAME)
    PG_RETURN_NULL();
  if (r) {
    ereport(NOTICE, (errcode(ERRCODE_SYSTEM_ERROR), errmsg("getnameinfo failed for IP `%s`, %s", ip, gai_strerror(r))));
    PG_RETURN_NULL();
  }

  hint.ai_family = AF_INET;

  r = getaddrinfo(host, 0, &hint, &results);
  if (r) {
    ereport(NOTICE, (errcode(ERRCODE_SYSTEM_ERROR), errmsg("getaddrinfo failed for host `%s`, %s", host, gai_strerror(r))));
    PG_RETURN_NULL();
  }

  c = results;
  while (c) {
    struct addrinfo* current = c;
    c = current->ai_next;
    if (current->ai_family != AF_INET)
      continue;

    if (((struct sockaddr_in*)current->ai_addr)->sin_addr.s_addr == iaddr.s_addr) {
      freeaddrinfo(results);
      PG_RETURN_TEXT_P(cstring_to_text(host));
    }
  }

  freeaddrinfo(results);
  PG_RETURN_NULL();
}