#include <ftw.h>
#include <dirent.h>
#include <sys/stat.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include <limits.h>
#include <pthread.h>
#include "libc.h"

struct history {
  struct history* chain;
  dev_t dev;
  ino_t ino;
  int level;
  int base;
};

#undef dirfd
#define dirfd(d) (*(int*)d)

static int do_nftw(char* path,
                   int (*fn)(const char*, const struct stat*, int, struct FTW*),
                   int fd_limit,
                   int flags,
                   struct history* h) {
  size_t l = strlen(path), j = l && path[l - 1] == '/' ? l - 1 : l;
  struct stat st;
  struct history new;
  int type;
  int r;
  struct FTW lev;
  char* name;

  if ((flags & FTW_PHYS) ? lstat(path, &st) : stat(path, &st) < 0) {
    if (!(flags & FTW_PHYS) && errno == ENOENT && !lstat(path, &st))
      type = FTW_SLN;
    else if (errno != EACCES)
      return -1;
    else
      type = FTW_NS;
  } else if (S_ISDIR(st.st_mode)) {
    if (access(path, R_OK) < 0)
      type = FTW_DNR;
    else if (flags & FTW_DEPTH)
      type = FTW_DP;
    else
      type = FTW_D;
  } else if (S_ISLNK(st.st_mode)) {
    if (flags & FTW_PHYS)
      type = FTW_SL;
    else
      type = FTW_SLN;
  } else {
    type = FTW_F;
  }

  if ((flags & FTW_MOUNT) && h && st.st_dev != h->dev)
    return 0;

  new.chain = h;
  new.dev = st.st_dev;
  new.ino = st.st_ino;
  new.level = h ? h->level + 1 : 0;
  new.base = l + 1;

  lev.level = new.level;
  lev.base = h ? h->base : (name = strrchr(path, '/')) ? name - path : 0;

  if (!(flags & FTW_DEPTH) && (r = fn(path, &st, type, &lev)))
    return r;

  for (; h; h = h->chain)
    if (h->dev == st.st_dev && h->ino == st.st_ino)
      return 0;

  if ((type == FTW_D || type == FTW_DP) && fd_limit) {
    DIR* d = opendir(path);
    if (d) {
      struct dirent* de;
      while ((de = readdir(d))) {
        if (de->d_name[0] == '.' &&
            (!de->d_name[1] || (de->d_name[1] == '.' && !de->d_name[2])))
          continue;
        if (strlen(de->d_name) >= PATH_MAX - l) {
          errno = ENAMETOOLONG;
          closedir(d);
          return -1;
        }
        path[j] = '/';
        strcpy(path + j + 1, de->d_name);
        if ((r = do_nftw(path, fn, fd_limit - 1, flags, &new))) {
          closedir(d);
          return r;
        }
      }
      closedir(d);
    } else if (errno != EACCES) {
      return -1;
    }
  }

  path[l] = 0;
  if ((flags & FTW_DEPTH) && (r = fn(path, &st, type, &lev)))
    return r;

  return 0;
}

int nftw(const char* path,
         int (*fn)(const char*, const struct stat*, int, struct FTW*),
         int fd_limit,
         int flags) {
  int r, cs;
  size_t l;
  char pathbuf[PATH_MAX + 1];

  if (fd_limit <= 0)
    return 0;

  l = strlen(path);
  if (l > PATH_MAX) {
    errno = ENAMETOOLONG;
    return -1;
  }
  memcpy(pathbuf, path, l + 1);

  pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
  r = do_nftw(pathbuf, fn, fd_limit, flags, NULL);
  pthread_setcancelstate(cs, 0);
  return r;
}