#include <unistd.h>

#include "byte.h"
#include "dnsresolv.h"
#include "env.h"
#include "readclose.h"
#include "str.h"
#include "taia.h"

/**
  @file dns_rcrw.c
  @author djb
  @ref ucspi-tcp
  @brief DNS receive rewrite
*/

static stralloc data = {0};

static int init(stralloc *rules)
{
  char host[256];
  const char *x;
  int i;
  int j;
  int k;

  if (!stralloc_copys(rules, "")) return DNS_MEM;

  x = env_get("DNSREWRITEFILE");
  if (!x) x = "/etc/dnsrewrite";

  i = openreadclose(x, &data, 64);
  if (i == -1) return DNS_INT;

  if (i) {
    if (!stralloc_append(&data, "\n")) return DNS_MEM;
    i = 0;
    for (j = 0; j < data.len; ++j)
      if (data.s[j] == '\n') {
        if (!stralloc_catb(rules, data.s + i, j - i)) return DNS_MEM;
        while (rules->len) {
          if (rules->s[rules->len - 1] != ' ')
            if (rules->s[rules->len - 1] != '\t')
              if (rules->s[rules->len - 1] != '\r') break;
          --rules->len;
        }
        if (!stralloc_0(rules)) return DNS_MEM;
        i = j + 1;
      }
    return 0;
  }

  x = env_get("LOCALDOMAIN");
  if (x) {
    if (!stralloc_copys(&data, x)) return DNS_MEM;
    if (!stralloc_append(&data, " ")) return DNS_MEM;
    if (!stralloc_copys(rules, "?:")) return DNS_MEM;
    i = 0;
    for (j = 0; j < data.len; ++j) {
      if (data.s[j] == ' ') {
        if (!stralloc_cats(rules, "+.")) return DNS_MEM;
        if (!stralloc_catb(rules, data.s + i, j - i)) return DNS_MEM;
        i = j + 1;
      }
    }
    if (!stralloc_0(rules)) return DNS_MEM;
    if (!stralloc_cats(rules, "*.:")) return DNS_MEM;
    if (!stralloc_0(rules)) return DNS_MEM;
    return 0;
  }

  i = openreadclose("/etc/resolv.conf", &data, 64);
  if (i == -1) return DNS_INT;

  if (i) {
    if (!stralloc_append(&data, "\n")) return DNS_MEM;
    i = 0;
    for (j = 0; j < data.len; ++j) {
      if (data.s[j] == '\n') {
        if (byte_equal("search ", 7, data.s + i) || byte_equal("search\t", 7, data.s + i)
            || byte_equal("domain ", 7, data.s + i) || byte_equal("domain\t", 7, data.s + i))
        {
          if (!stralloc_copys(rules, "?:")) return DNS_MEM;
          i += 7;
          while (i < j) {
            k = byte_chr(data.s + i, j - i, ' ');
            k = byte_chr(data.s + i, k, '\t');
            if (!k) {
              ++i;
              continue;
            }
            if (!stralloc_cats(rules, "+.")) return DNS_MEM;
            if (!stralloc_catb(rules, data.s + i, k)) return DNS_MEM;
            i += k;
          }
          if (!stralloc_0(rules)) return DNS_MEM;
          if (!stralloc_cats(rules, "*.:")) return DNS_MEM;
          if (!stralloc_0(rules)) return DNS_MEM;
          return 0;
        }
        i = j + 1;
      }
    }
  }

  host[0] = 0;
  if (gethostname(host, sizeof(host)) == -1) return DNS_ERR;
  host[(sizeof(host)) - 1] = 0;
  i = str_chr(host, '.');
  if (host[i]) {
    if (!stralloc_copys(rules, "?:")) return DNS_MEM;
    if (!stralloc_cats(rules, host + i)) return DNS_MEM;
    if (!stralloc_0(rules)) return DNS_MEM;
  }
  if (!stralloc_cats(rules, "*.:")) return DNS_MEM;
  if (!stralloc_0(rules)) return DNS_MEM;

  return 0;
}

static int ok = 0;
static unsigned int uses;
static struct taia deadline;
static stralloc rules = {0}; /* defined if ok */

int dns_resolvconfrewrite(stralloc *out)
{
  struct taia now;

  taia_now(&now);
  if (taia_less(&deadline, &now)) ok = 0;
  if (!uses) ok = 0;

  if (!ok) {
    if (init(&rules) < 0) return DNS_INT;
    taia_uint(&deadline, 600);
    taia_add(&deadline, &now, &deadline);
    uses = 10000;
    ok = 1;
  }

  --uses;
  if (!stralloc_copy(out, &rules)) return DNS_MEM;
  return 0;
}