/*
 * Dirent interface for Microsoft Visual Studio
 *
 * Copyright (C) 1998-2019 Toni Ronkko
 * This file is part of dirent.  Dirent may be freely distributed
 * under the MIT license.  For all details and documentation, see
 * https://github.com/tronkko/dirent
 */
#ifndef DIRENT_H
#define DIRENT_H

/* Hide warnings about unreferenced local functions */
#if defined(__clang__)
#	pragma clang diagnostic ignored "-Wunused-function"
#elif defined(_MSC_VER)
#	pragma warning(disable:4505)
#elif defined(__GNUC__)
#	pragma GCC diagnostic ignored "-Wunused-function"
#endif

/*
 * Include windows.h without Windows Sockets 1.1 to prevent conflicts with
 * Windows Sockets 2.0.
 */
#ifndef WIN32_LEAN_AND_MEAN
#	define WIN32_LEAN_AND_MEAN
#endif
#include <windows.h>

#include <stdio.h>
#include <stdarg.h>
#include <wchar.h>
#include <string.h>
#include <stdlib.h>
#include <malloc.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <ctype.h>

/* Indicates that d_type field is available in dirent structure */
#define _DIRENT_HAVE_D_TYPE

/* Indicates that d_namlen field is available in dirent structure */
#define _DIRENT_HAVE_D_NAMLEN

/* Entries missing from MSVC 6.0 */
#if !defined(FILE_ATTRIBUTE_DEVICE)
#	define FILE_ATTRIBUTE_DEVICE 0x40
#endif

/* File type and permission flags for stat(), general mask */
#if !defined(S_IFMT)
#	define S_IFMT _S_IFMT
#endif

/* Directory bit */
#if !defined(S_IFDIR)
#	define S_IFDIR _S_IFDIR
#endif

/* Character device bit */
#if !defined(S_IFCHR)
#	define S_IFCHR _S_IFCHR
#endif

/* Pipe bit */
#if !defined(S_IFFIFO)
#	define S_IFFIFO _S_IFFIFO
#endif

/* Regular file bit */
#if !defined(S_IFREG)
#	define S_IFREG _S_IFREG
#endif

/* Read permission */
#if !defined(S_IREAD)
#	define S_IREAD _S_IREAD
#endif

/* Write permission */
#if !defined(S_IWRITE)
#	define S_IWRITE _S_IWRITE
#endif

/* Execute permission */
#if !defined(S_IEXEC)
#	define S_IEXEC _S_IEXEC
#endif

/* Pipe */
#if !defined(S_IFIFO)
#	define S_IFIFO _S_IFIFO
#endif

/* Block device */
#if !defined(S_IFBLK)
#	define S_IFBLK 0
#endif

/* Link
 * S_IFLNK is not defined in Windows's `stat.h`, so we define it here.
 * In Windows's `stat.h`, file type macros (S_IFDIR, S_IFREG...) are defined
 * bitmasks, except that they are NOT on Linux. So long as S_* & ~S_IFMT == 0,
 * as is the case in Linux, the S_IS*(mode) macros works fine. */
#if !defined(S_IFLNK)
#	define S_IFLNK (S_IFMT & 0XCCCCCCCC)
#endif

/* Socket */
#if !defined(S_IFSOCK)
#	define S_IFSOCK 0
#endif

/* Read user permission */
#if !defined(S_IRUSR)
#	define S_IRUSR S_IREAD
#endif

/* Write user permission */
#if !defined(S_IWUSR)
#	define S_IWUSR S_IWRITE
#endif

/* Execute user permission */
#if !defined(S_IXUSR)
#	define S_IXUSR 0
#endif

/* Read group permission */
#if !defined(S_IRGRP)
#	define S_IRGRP 0
#endif

/* Write group permission */
#if !defined(S_IWGRP)
#	define S_IWGRP 0
#endif

/* Execute group permission */
#if !defined(S_IXGRP)
#	define S_IXGRP 0
#endif

/* Read others permission */
#if !defined(S_IROTH)
#	define S_IROTH 0
#endif

/* Write others permission */
#if !defined(S_IWOTH)
#	define S_IWOTH 0
#endif

/* Execute others permission */
#if !defined(S_IXOTH)
#	define S_IXOTH 0
#endif

/* Maximum length of file name */
#if !defined(PATH_MAX)
#	define PATH_MAX MAX_PATH
#endif
#if !defined(FILENAME_MAX)
#	define FILENAME_MAX MAX_PATH
#endif
#if !defined(NAME_MAX)
#	define NAME_MAX FILENAME_MAX
#endif

/* File type flags for d_type */
#define DT_UNKNOWN 0
#define DT_REG S_IFREG
#define DT_DIR S_IFDIR
#define DT_FIFO S_IFIFO
#define DT_SOCK S_IFSOCK
#define DT_CHR S_IFCHR
#define DT_BLK S_IFBLK
#define DT_LNK S_IFLNK

/* Macros for converting between st_mode and d_type */
#define IFTODT(mode) ((mode) & S_IFMT)
#define DTTOIF(type) (type)

/*
 * File type macros.  Note that block devices, sockets and links cannot be
 * distinguished on Windows and the macros S_ISBLK, S_ISSOCK and S_ISLNK are
 * only defined for compatibility.  These macros should always return false
 * on Windows.
 */
#if !defined(S_ISFIFO)
#	define S_ISFIFO(mode) (((mode) & S_IFMT) == S_IFIFO)
#endif
#if !defined(S_ISDIR)
#	define S_ISDIR(mode) (((mode) & S_IFMT) == S_IFDIR)
#endif
#if !defined(S_ISREG)
#	define S_ISREG(mode) (((mode) & S_IFMT) == S_IFREG)
#endif
#if !defined(S_ISLNK)
#	define S_ISLNK(mode) (((mode) & S_IFMT) == S_IFLNK)
#endif
#if !defined(S_ISSOCK)
#	define S_ISSOCK(mode) (((mode) & S_IFMT) == S_IFSOCK)
#endif
#if !defined(S_ISCHR)
#	define S_ISCHR(mode) (((mode) & S_IFMT) == S_IFCHR)
#endif
#if !defined(S_ISBLK)
#	define S_ISBLK(mode) (((mode) & S_IFMT) == S_IFBLK)
#endif

/* Return the exact length of the file name without zero terminator */
#define _D_EXACT_NAMLEN(p) ((p)->d_namlen)

/* Return the maximum size of a file name */
#define _D_ALLOC_NAMLEN(p) ((PATH_MAX)+1)


#ifdef __cplusplus
extern "C" {
#endif


/* Wide-character version */
struct _wdirent {
	/* Always zero */
	long d_ino;

	/* Position of next file in a directory stream */
	long d_off;

	/* Structure size */
	unsigned short d_reclen;

	/* Length of name without \0 */
	size_t d_namlen;

	/* File type */
	int d_type;

	/* File name */
	wchar_t d_name[PATH_MAX+1];
};
typedef struct _wdirent _wdirent;

struct _WDIR {
	/* Current directory entry */
	struct _wdirent ent;

	/* Private file data */
	WIN32_FIND_DATAW data;

	/* True if data is valid */
	int cached;

	/* True if next entry is invalid */
	int invalid;

	/* Win32 search handle */
	HANDLE handle;

	/* Initial directory name */
	wchar_t *patt;
};
typedef struct _WDIR _WDIR;

/* Multi-byte character version */
struct dirent {
	/* Always zero */
	long d_ino;

	/* Position of next file in a directory stream */
	long d_off;

	/* Structure size */
	unsigned short d_reclen;

	/* Length of name without \0 */
	size_t d_namlen;

	/* File type */
	int d_type;

	/* File name */
	char d_name[PATH_MAX+1];
};
typedef struct dirent dirent;

struct DIR {
	struct dirent ent;
	struct _WDIR *wdirp;
};
typedef struct DIR DIR;


/* Dirent functions */
static DIR *opendir(const char *dirname);
static _WDIR *_wopendir(const wchar_t *dirname);

static struct dirent *readdir(DIR *dirp);
static struct _wdirent *_wreaddir(_WDIR *dirp);

static int readdir_r(
	DIR *dirp, struct dirent *entry, struct dirent **result);
static int _wreaddir_r(
	_WDIR *dirp, struct _wdirent *entry, struct _wdirent **result);

static int closedir(DIR *dirp);
static int _wclosedir(_WDIR *dirp);

static void rewinddir(DIR *dirp);
static void _wrewinddir(_WDIR *dirp);

static long telldir(DIR *dirp);
static long _wtelldir(_WDIR *dirp);

static void seekdir(DIR *dirp, long loc);
static void _wseekdir(_WDIR *dirp, long loc);

static int scandir(const char *dirname, struct dirent ***namelist,
	int (*filter)(const struct dirent*),
	int (*compare)(const struct dirent**, const struct dirent**));

static int alphasort(const struct dirent **a, const struct dirent **b);

static int versionsort(const struct dirent **a, const struct dirent **b);

static int strverscmp(const char *a, const char *b);

/* For compatibility with Symbian */
#define wdirent _wdirent
#define WDIR _WDIR
#define wopendir _wopendir
#define wreaddir _wreaddir
#define wclosedir _wclosedir
#define wrewinddir _wrewinddir
#define wtelldir _wtelldir
#define wseekdir _wseekdir

/* Compatibility with older Microsoft compilers and non-Microsoft compilers */
#if !defined(_MSC_VER) || _MSC_VER < 1400
#	define wcstombs_s dirent_wcstombs_s
#	define mbstowcs_s dirent_mbstowcs_s
#endif

/* Optimize dirent_set_errno() away on modern Microsoft compilers */
#if defined(_MSC_VER) && _MSC_VER >= 1400
#	define dirent_set_errno _set_errno
#endif


/* Internal utility functions */
static WIN32_FIND_DATAW *dirent_first(_WDIR *dirp);
static WIN32_FIND_DATAW *dirent_next(_WDIR *dirp);
static long dirent_hash(WIN32_FIND_DATAW *datap);

#if !defined(_MSC_VER) || _MSC_VER < 1400
static int dirent_mbstowcs_s(
	size_t *pReturnValue, wchar_t *wcstr, size_t sizeInWords,
	const char *mbstr, size_t count);
#endif

#if !defined(_MSC_VER) || _MSC_VER < 1400
static int dirent_wcstombs_s(
	size_t *pReturnValue, char *mbstr, size_t sizeInBytes,
	const wchar_t *wcstr, size_t count);
#endif

#if !defined(_MSC_VER) || _MSC_VER < 1400
static void dirent_set_errno(int error);
#endif


/*
 * Open directory stream DIRNAME for read and return a pointer to the
 * internal working area that is used to retrieve individual directory
 * entries.
 */
static _WDIR *
_wopendir(const wchar_t *dirname)
{
	wchar_t *p;

	/* Must have directory name */
	if (dirname == NULL || dirname[0] == '\0') {
		dirent_set_errno(ENOENT);
		return NULL;
	}

	/* Allocate new _WDIR structure */
	_WDIR *dirp = (_WDIR*) malloc(sizeof(struct _WDIR));
	if (!dirp)
		return NULL;

	/* Reset _WDIR structure */
	dirp->handle = INVALID_HANDLE_VALUE;
	dirp->patt = NULL;
	dirp->cached = 0;
	dirp->invalid = 0;

	/*
	 * Compute the length of full path plus zero terminator
	 *
	 * Note that on WinRT there's no way to convert relative paths
	 * into absolute paths, so just assume it is an absolute path.
	 */
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
	/* Desktop */
	DWORD n = GetFullPathNameW(dirname, 0, NULL, NULL);
#else
	/* WinRT */
	size_t n = wcslen(dirname);
#endif

	/* Allocate room for absolute directory name and search pattern */
	dirp->patt = (wchar_t*) malloc(sizeof(wchar_t) * n + 16);
	if (dirp->patt == NULL)
		goto exit_closedir;

	/*
	 * Convert relative directory name to an absolute one.  This
	 * allows rewinddir() to function correctly even when current
	 * working directory is changed between opendir() and rewinddir().
	 *
	 * Note that on WinRT there's no way to convert relative paths
	 * into absolute paths, so just assume it is an absolute path.
	 */
#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
	/* Desktop */
	n = GetFullPathNameW(dirname, n, dirp->patt, NULL);
	if (n <= 0)
		goto exit_closedir;
#else
	/* WinRT */
	wcsncpy_s(dirp->patt, n+1, dirname, n);
#endif

	/* Append search pattern \* to the directory name */
	p = dirp->patt + n;
	switch (p[-1]) {
	case '\\':
	case '/':
	case ':':
		/* Directory ends in path separator, e.g. c:\temp\ */
		/*NOP*/;
		break;

	default:
		/* Directory name doesn't end in path separator */
		*p++ = '\\';
	}
	*p++ = '*';
	*p = '\0';

	/* Open directory stream and retrieve the first entry */
	if (!dirent_first(dirp))
		goto exit_closedir;

	/* Success */
	return dirp;

	/* Failure */
exit_closedir:
	_wclosedir(dirp);
	return NULL;
}

/*
 * Read next directory entry.
 *
 * Returns pointer to static directory entry which may be overwritten by
 * subsequent calls to _wreaddir().
 */
static struct _wdirent *
_wreaddir(_WDIR *dirp)
{
	/*
	 * Read directory entry to buffer.  We can safely ignore the return
	 * value as entry will be set to NULL in case of error.
	 */
	struct _wdirent *entry;
	(void) _wreaddir_r(dirp, &dirp->ent, &entry);

	/* Return pointer to statically allocated directory entry */
	return entry;
}

/*
 * Read next directory entry.
 *
 * Returns zero on success.  If end of directory stream is reached, then sets
 * result to NULL and returns zero.
 */
static int
_wreaddir_r(
	_WDIR *dirp, struct _wdirent *entry, struct _wdirent **result)
{
	/* Validate directory handle */
	if (!dirp || dirp->handle == INVALID_HANDLE_VALUE || !dirp->patt) {
		dirent_set_errno(EBADF);
		*result = NULL;
		return -1;
	}

	/* Read next directory entry */
	WIN32_FIND_DATAW *datap = dirent_next(dirp);
	if (!datap) {
		/* Return NULL to indicate end of directory */
		*result = NULL;
		return /*OK*/0;
	}

	/*
	 * Copy file name as wide-character string.  If the file name is too
	 * long to fit in to the destination buffer, then truncate file name
	 * to PATH_MAX characters and zero-terminate the buffer.
	 */
	size_t i = 0;
	while (i < PATH_MAX && datap->cFileName[i] != 0) {
		entry->d_name[i] = datap->cFileName[i];
		i++;
	}
	entry->d_name[i] = 0;

	/* Length of file name excluding zero terminator */
	entry->d_namlen = i;

	/* Determine file type */
	DWORD attr = datap->dwFileAttributes;
	if ((attr & FILE_ATTRIBUTE_DEVICE) != 0)
		entry->d_type = DT_CHR;
#ifdef FILE_ATTRIBUTE_REPARSE_POINT
	/* A Windows link to directory is both symlink (reparse point) and
	 * directory. Symlink takes precedence, just as Linux does. */
	else if ((attr & FILE_ATTRIBUTE_REPARSE_POINT))
		entry->d_type = DT_LNK;
#endif
	else if ((attr & FILE_ATTRIBUTE_DIRECTORY) != 0)
		entry->d_type = DT_DIR;
	else
		entry->d_type = DT_REG;

	/* Read the next directory entry to cache */
	datap = dirent_next(dirp);
	if (datap) {
		/* Compute 31-bit hash of the next directory entry */
		entry->d_off = dirent_hash(datap);

		/* Push the next directory entry back to cache */
		dirp->cached = 1;
	} else {
		/* End of directory stream */
		entry->d_off = (long) ((~0UL) >> 1);
	}

	/* Reset other fields */
	entry->d_ino = 0;
	entry->d_reclen = sizeof(struct _wdirent);

	/* Set result address */
	*result = entry;
	return /*OK*/0;
}

/*
 * Close directory stream opened by opendir() function.  This invalidates the
 * DIR structure as well as any directory entry read previously by
 * _wreaddir().
 */
static int
_wclosedir(_WDIR *dirp)
{
	if (!dirp) {
		dirent_set_errno(EBADF);
		return /*failure*/-1;
	}

	/*
	 * Release search handle if we have one.  Being able to handle
	 * partially initialized _WDIR structure allows us to use this
	 * function to handle errors occuring within _wopendir.
	 */
	if (dirp->handle != INVALID_HANDLE_VALUE) {
		FindClose(dirp->handle);
	}

	/*
	 * Release search pattern.  Note that we don't need to care if
	 * dirp->patt is NULL or not: function free is guaranteed to act
	 * appropriately.
	 */
	free(dirp->patt);

	/* Release directory structure */
	free(dirp);
	return /*success*/0;
}

/*
 * Rewind directory stream such that _wreaddir() returns the very first
 * file name again.
 */
static void _wrewinddir(_WDIR* dirp)
{
	/* Check directory pointer */
	if (!dirp || dirp->handle == INVALID_HANDLE_VALUE || !dirp->patt)
		return;

	/* Release existing search handle */
	FindClose(dirp->handle);

	/* Open new search handle */
	dirent_first(dirp);
}

/* Get first directory entry */
static WIN32_FIND_DATAW *
dirent_first(_WDIR *dirp)
{
	/* Open directory and retrieve the first entry */
	dirp->handle = FindFirstFileExW(
		dirp->patt, FindExInfoStandard, &dirp->data,
		FindExSearchNameMatch, NULL, 0);
	if (dirp->handle == INVALID_HANDLE_VALUE)
		goto error;

	/* A directory entry is now waiting in memory */
	dirp->cached = 1;
	return &dirp->data;

error:
	/* Failed to open directory: no directory entry in memory */
	dirp->cached = 0;
	dirp->invalid = 1;

	/* Set error code */
	DWORD errorcode = GetLastError();
	switch (errorcode) {
	case ERROR_ACCESS_DENIED:
		/* No read access to directory */
		dirent_set_errno(EACCES);
		break;

	case ERROR_DIRECTORY:
		/* Directory name is invalid */
		dirent_set_errno(ENOTDIR);
		break;

	case ERROR_PATH_NOT_FOUND:
	default:
		/* Cannot find the file */
		dirent_set_errno(ENOENT);
	}
	return NULL;
}

/* Get next directory entry */
static WIN32_FIND_DATAW *
dirent_next(_WDIR *dirp)
{
	/* Return NULL if seek position was invalid */
	if (dirp->invalid)
		return NULL;

	/* Is the next directory entry already in cache? */
	if (dirp->cached) {
		/* Yes, a valid directory entry found in memory */
		dirp->cached = 0;
		return &dirp->data;
	}

	/* Read the next directory entry from stream */
	if (FindNextFileW(dirp->handle, &dirp->data) == FALSE) {
		/* End of directory stream */
		return NULL;
	}

	/* Success */
	return &dirp->data;
}

/*
 * Compute 31-bit hash of file name.
 *
 * See djb2 at http://www.cse.yorku.ca/~oz/hash.html
 */
static long
dirent_hash(WIN32_FIND_DATAW *datap)
{
	unsigned long hash = 5381;
	unsigned long c;
	const wchar_t *p = datap->cFileName;
	const wchar_t *e = p + MAX_PATH;
	while (p != e && (c = *p++) != 0) {
		hash = (hash << 5) + hash + c;
	}

	return (long) (hash & ((~0UL) >> 1));
}

/* Open directory stream using plain old C-string */
static DIR *opendir(const char *dirname)
{
	/* Must have directory name */
	if (dirname == NULL || dirname[0] == '\0') {
		dirent_set_errno(ENOENT);
		return NULL;
	}

	/* Allocate memory for DIR structure */
	struct DIR *dirp = (DIR*) malloc(sizeof(struct DIR));
	if (!dirp)
		return NULL;

	/* Convert directory name to wide-character string */
	wchar_t wname[PATH_MAX + 1];
	size_t n;
	int error = mbstowcs_s(&n, wname, PATH_MAX + 1, dirname, PATH_MAX+1);
	if (error)
		goto exit_failure;

	/* Open directory stream using wide-character name */
	dirp->wdirp = _wopendir(wname);
	if (!dirp->wdirp)
		goto exit_failure;

	/* Success */
	return dirp;

	/* Failure */
exit_failure:
	free(dirp);
	return NULL;
}

/* Read next directory entry */
static struct dirent *
readdir(DIR *dirp)
{
	/*
	 * Read directory entry to buffer.  We can safely ignore the return
	 * value as entry will be set to NULL in case of error.
	 */
	struct dirent *entry;
	(void) readdir_r(dirp, &dirp->ent, &entry);

	/* Return pointer to statically allocated directory entry */
	return entry;
}

/*
 * Read next directory entry into called-allocated buffer.
 *
 * Returns zero on success.  If the end of directory stream is reached, then
 * sets result to NULL and returns zero.
 */
static int
readdir_r(
	DIR *dirp, struct dirent *entry, struct dirent **result)
{
	/* Read next directory entry */
	WIN32_FIND_DATAW *datap = dirent_next(dirp->wdirp);
	if (!datap) {
		/* No more directory entries */
		*result = NULL;
		return /*OK*/0;
	}

	/* Attempt to convert file name to multi-byte string */
	size_t n;
	int error = wcstombs_s(
		&n, entry->d_name, PATH_MAX + 1,
		datap->cFileName, PATH_MAX + 1);

	/*
	 * If the file name cannot be represented by a multi-byte string, then
	 * attempt to use old 8+3 file name.  This allows the program to
	 * access files although file names may seem unfamiliar to the user.
	 *
	 * Be ware that the code below cannot come up with a short file name
	 * unless the file system provides one.  At least VirtualBox shared
	 * folders fail to do this.
	 */
	if (error && datap->cAlternateFileName[0] != '\0') {
		error = wcstombs_s(
			&n, entry->d_name, PATH_MAX + 1,
			datap->cAlternateFileName, PATH_MAX + 1);
	}

	if (!error) {
		/* Length of file name excluding zero terminator */
		entry->d_namlen = n - 1;

		/* Determine file type */
		DWORD attr = datap->dwFileAttributes;
		if ((attr & FILE_ATTRIBUTE_DEVICE) != 0)
			entry->d_type = DT_CHR;
#ifdef FILE_ATTRIBUTE_REPARSE_POINT
		/* A Windows link to directory is both symlink (reparse point) and
		 * directory. Symlink takes precedence, just as Linux does. */
		else if ((attr & FILE_ATTRIBUTE_REPARSE_POINT))
			entry->d_type = DT_LNK;
#endif
		else if ((attr & FILE_ATTRIBUTE_DIRECTORY) != 0)
			entry->d_type = DT_DIR;
		else
			entry->d_type = DT_REG;

		/* Get offset of next file */
		datap = dirent_next(dirp->wdirp);
		if (datap) {
			/* Compute 31-bit hash of the next directory entry */
			entry->d_off = dirent_hash(datap);

			/* Push the next directory entry back to cache */
			dirp->wdirp->cached = 1;
		} else {
			/* End of directory stream */
			entry->d_off = (long) ((~0UL) >> 1);
		}

		/* Reset fields */
		entry->d_ino = 0;
		entry->d_reclen = sizeof(struct dirent);
	} else {
		/*
		 * Cannot convert file name to multi-byte string so construct
		 * an erroneous directory entry and return that.  Note that
		 * we cannot return NULL as that would stop the processing
		 * of directory entries completely.
		 */
		entry->d_name[0] = '?';
		entry->d_name[1] = '\0';
		entry->d_namlen = 1;
		entry->d_type = DT_UNKNOWN;
		entry->d_ino = 0;
		entry->d_off = -1;
		entry->d_reclen = 0;
	}

	/* Return pointer to directory entry */
	*result = entry;
	return /*OK*/0;
}

/* Close directory stream */
static int
closedir(DIR *dirp)
{
	int ok;

	if (!dirp)
		goto exit_failure;

	/* Close wide-character directory stream */
	ok = _wclosedir(dirp->wdirp);
	dirp->wdirp = NULL;

	/* Release multi-byte character version */
	free(dirp);
	return ok;

exit_failure:
	/* Invalid directory stream */
	dirent_set_errno(EBADF);
	return /*failure*/-1;
}

/* Rewind directory stream to beginning */
static void
rewinddir(DIR *dirp)
{
	if (!dirp)
		return;

	/* Rewind wide-character string directory stream */
	_wrewinddir(dirp->wdirp);
}

/* Get position of directory stream */
static long
_wtelldir(_WDIR *dirp)
{
	if (!dirp || dirp->handle == INVALID_HANDLE_VALUE) {
		dirent_set_errno(EBADF);
		return /*failure*/-1;
	}

	/* Read next file entry */
	WIN32_FIND_DATAW *datap = dirent_next(dirp);
	if (!datap) {
		/* End of directory stream */
		return (long) ((~0UL) >> 1);
	}

	/* Store file entry to cache for readdir() */
	dirp->cached = 1;

	/* Return the 31-bit hash code to be used as stream position */
	return dirent_hash(datap);
}

/* Get position of directory stream */
static long
telldir(DIR *dirp)
{
	if (!dirp) {
		dirent_set_errno(EBADF);
		return -1;
	}

	return _wtelldir(dirp->wdirp);
}

/* Seek directory stream to offset */
static void
_wseekdir(_WDIR *dirp, long loc)
{
	if (!dirp)
		return;

	/* Directory must be open */
	if (dirp->handle == INVALID_HANDLE_VALUE)
		goto exit_failure;

	/* Ensure that seek position is valid */
	if (loc < 0)
		goto exit_failure;

	/* Restart directory stream from the beginning */
	FindClose(dirp->handle);
	if (!dirent_first(dirp))
		goto exit_failure;

	/* Reset invalid flag so that we can read from the stream again */
	dirp->invalid = 0;

	/*
	 * Read directory entries from the beginning until the hash matches a
	 * file name.  Be ware that hash code is only 31 bits longs and
	 * duplicates are possible: the hash code cannot return the position
	 * with 100.00% accuracy! Moreover, the method is slow for large
	 * directories.
	 */
	long hash;
	do {
		/* Read next directory entry */
		WIN32_FIND_DATAW *datap = dirent_next(dirp);
		if (!datap) {
			/*
			 * End of directory stream was reached before finding
			 * the requested location.  Perhaps the file in
			 * question was deleted or moved out of the directory.
			 */
			goto exit_failure;
		}

		/* Does the file name match the hash? */
		hash = dirent_hash(datap);
	} while (hash != loc);

	/*
	 * File name matches the hash!  Push the directory entry back to cache
	 * from where next readdir() will return it.
	 */
	dirp->cached = 1;
	dirp->invalid = 0;
	return;

exit_failure:
	/* Ensure that readdir will return NULL */
	dirp->invalid = 1;
}

/* Seek directory stream to offset */
static void
seekdir(DIR *dirp, long loc)
{
	if (!dirp)
		return;

	_wseekdir(dirp->wdirp, loc);
}

/* Scan directory for entries */
static int
scandir(
	const char *dirname, struct dirent ***namelist,
	int (*filter)(const struct dirent*),
	int (*compare)(const struct dirent**, const struct dirent**))
{
	int result;

	/* Open directory stream */
	DIR *dir = opendir(dirname);
	if (!dir) {
		/* Cannot open directory */
		return /*Error*/ -1;
	}

	/* Read directory entries to memory */
	struct dirent *tmp = NULL;
	struct dirent **files = NULL;
	size_t size = 0;
	size_t allocated = 0;
	while (1) {
		/* Allocate room for a temporary directory entry */
		if (!tmp) {
			tmp = (struct dirent*) malloc(sizeof(struct dirent));
			if (!tmp)
				goto exit_failure;
		}

		/* Read directory entry to temporary area */
		struct dirent *entry;
		if (readdir_r(dir, tmp, &entry) != /*OK*/0)
			goto exit_failure;

		/* Stop if we already read the last directory entry */
		if (entry == NULL)
			goto exit_success;

		/* Determine whether to include the entry in results */
		if (filter && !filter(tmp))
			continue;

		/* Enlarge pointer table to make room for another pointer */
		if (size >= allocated) {
			/* Compute number of entries in the new table */
			size_t num_entries = size * 2 + 16;

			/* Allocate new pointer table or enlarge existing */
			void *p = realloc(files, sizeof(void*) * num_entries);
			if (!p)
				goto exit_failure;

			/* Got the memory */
			files = (dirent**) p;
			allocated = num_entries;
		}

		/* Store the temporary entry to ptr table */
		files[size++] = tmp;
		tmp = NULL;
	}

exit_failure:
	/* Release allocated entries */
	for (size_t i = 0; i < size; i++) {
		free(files[i]);
	}

	/* Release the pointer table */
	free(files);
	files = NULL;

	/* Exit with error code */
	result = /*error*/ -1;
	goto exit_status;

exit_success:
	/* Sort directory entries */
	qsort(files, size, sizeof(void*),
		(int (*) (const void*, const void*)) compare);

	/* Pass pointer table to caller */
	if (namelist)
		*namelist = files;

	/* Return the number of directory entries read */
	result = (int) size;

exit_status:
	/* Release temporary directory entry, if we had one */
	free(tmp);

	/* Close directory stream */
	closedir(dir);
	return result;
}

/* Alphabetical sorting */
static int
alphasort(const struct dirent **a, const struct dirent **b)
{
	return strcoll((*a)->d_name, (*b)->d_name);
}

/* Sort versions */
static int
versionsort(const struct dirent **a, const struct dirent **b)
{
	return strverscmp((*a)->d_name, (*b)->d_name);
}

/* Compare strings */
static int
strverscmp(const char *a, const char *b)
{
	size_t i = 0;
	size_t j;

	/* Find first difference */
	while (a[i] == b[i]) {
		if (a[i] == '\0') {
			/* No difference */
			return 0;
		}
		++i;
	}

	/* Count backwards and find the leftmost digit */
	j = i;
	while (j > 0 && isdigit(a[j-1])) {
		--j;
	}

	/* Determine mode of comparison */
	if (a[j] == '0' || b[j] == '0') {
		/* Find the next non-zero digit */
		while (a[j] == '0' && a[j] == b[j]) {
			j++;
		}

		/* String with more digits is smaller, e.g 002 < 01 */
		if (isdigit(a[j])) {
			if (!isdigit(b[j])) {
				return -1;
			}
		} else if (isdigit(b[j])) {
			return 1;
		}
	} else if (isdigit(a[j]) && isdigit(b[j])) {
		/* Numeric comparison */
		size_t k1 = j;
		size_t k2 = j;

		/* Compute number of digits in each string */
		while (isdigit(a[k1])) {
			k1++;
		}
		while (isdigit(b[k2])) {
			k2++;
		}

		/* Number with more digits is bigger, e.g 999 < 1000 */
		if (k1 < k2)
			return -1;
		else if (k1 > k2)
			return 1;
	}

	/* Alphabetical comparison */
	return (int) ((unsigned char) a[i]) - ((unsigned char) b[i]);
}

/* Convert multi-byte string to wide character string */
#if !defined(_MSC_VER) || _MSC_VER < 1400
static int
dirent_mbstowcs_s(
	size_t *pReturnValue, wchar_t *wcstr,
	size_t sizeInWords, const char *mbstr, size_t count)
{
	/* Older Visual Studio or non-Microsoft compiler */
	size_t n = mbstowcs(wcstr, mbstr, sizeInWords);
	if (wcstr && n >= count)
		return /*error*/ 1;

	/* Zero-terminate output buffer */
	if (wcstr && sizeInWords) {
		if (n >= sizeInWords)
			n = sizeInWords - 1;
		wcstr[n] = 0;
	}

	/* Length of multi-byte string with zero terminator */
	if (pReturnValue) {
		*pReturnValue = n + 1;
	}

	/* Success */
	return 0;
}
#endif

/* Convert wide-character string to multi-byte string */
#if !defined(_MSC_VER) || _MSC_VER < 1400
static int
dirent_wcstombs_s(
	size_t *pReturnValue, char *mbstr,
	size_t sizeInBytes, const wchar_t *wcstr, size_t count)
{
	/* Older Visual Studio or non-Microsoft compiler */
	size_t n = wcstombs(mbstr, wcstr, sizeInBytes);
	if (mbstr && n >= count)
		return /*error*/1;

	/* Zero-terminate output buffer */
	if (mbstr && sizeInBytes) {
		if (n >= sizeInBytes) {
			n = sizeInBytes - 1;
		}
		mbstr[n] = '\0';
	}

	/* Length of resulting multi-bytes string WITH zero-terminator */
	if (pReturnValue) {
		*pReturnValue = n + 1;
	}

	/* Success */
	return 0;
}
#endif

/* Set errno variable */
#if !defined(_MSC_VER) || _MSC_VER < 1400
static void
dirent_set_errno(int error)
{
	/* Non-Microsoft compiler or older Microsoft compiler */
	errno = error;
}
#endif

#ifdef __cplusplus
}
#endif
#endif /*DIRENT_H*/