// SPDX-License-Identifier: LGPL-3.0-or-later

/* OS extensions for Lua, module implementation.
 *
 * Copyright: 2022, The DoubleFourteen Code Forge
 * Author: Lorenzo Cogotti
 */

/**
 * Operating System eXtension module.
 *
 * @license LGPL-3.0-or-later
 * @copyright 2022, The DoubleFourteen Code Forge
 * @author Lorenzo Cogotti
 * @module osx
 */

#include "xconf.h"
#include "osx.h"
#include "osx_dir.h"
#include "luacompat.h"

#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"

#include <assert.h>
#include <errno.h>
#include <stdbool.h>
#include <stdlib.h>
#include <string.h>

#ifdef _WIN32
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/locking.h>
#include <direct.h>
#include <fcntl.h>
#include <windows.h>
#include <io.h>
#include <share.h>
#include <limits.h>

typedef struct __stat64 os_stat_type;

#ifndef S_ISDIR
#define S_ISDIR(mode) ((mode)&_S_IFDIR)
#endif
#ifndef S_ISREG
#define S_ISREG(mode) ((mode)&_S_IFREG)
#endif

#define fileno(fh) _fileno(fh)
#define stat(path, buf) _stat64(path, buf)
#define fstat(fd, buf) _fstat64(fd, buf)
#define mkdir(path, mode) _mkdir(path)
#define getcwd(buf, len) _getcwd(buf, len)
#define chdir(path) _chdir(path)
#define getdrive() _getdrive()
#define chdrive(drive) _chdrive(drive)

#ifndef _O_WTEXT
#define _O_WTEXT 0x10000
#endif
#ifndef _O_U16TEXT
#define _O_U16TEXT 0x20000
#endif
#ifndef _O_U8TEXT
#define _O_U8TEXT 0x40000
#endif
#define setmode(fd, mode) _setmode(fd, mode)

static int truncate(const char *path, __int64 size)
{
    int fd;

    if (_sopen_s(&fd, path, _O_WRONLY|_O_BINARY|_O_NOINHERIT, _SH_DENYRW, 0) != 0)
        return -1;

    int ec = _chsize_s(fd, size);
    _close(fd);

    return ec;
}

#define ftruncate(fd, size) _chsize_s(fd, size)
#define isatty(fd) _isatty(fd)
#define fsync(fd) _commit(fd)

static int flocking(FILE *fh, int mode, __int64 ofs, __int64 len)
{
    if (ofs < 0 || len < 0 || len > LONG_MAX) {
        errno = ERANGE;
        return -1;
    }

    _lock_file(fh);
    if (_fseeki64(fh, ofs, SEEK_SET) != 0)
        goto fail;

    if (len == 0) {
        // NOTE: seek may flush write buffers, so file length must be taken now
        len = _filelengthi64(_fileno(fh));
        if (len < 0)
            goto fail;

        len -= ofs;
        if (len < 0)
            len = 0;
        if (len > LONG_MAX) {
            errno = ERANGE;
            goto fail;
        }
    }

    if (_locking(_fileno(fh), mode, len) != 0)
        goto fail;

    _unlock_file(fh);
    return 0;

fail:
    _unlock_file(fh);
    return -1;
}

#else
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

typedef struct stat os_stat_type;

#define _O_BINARY 0
#define _O_TEXT 0
#define _O_WTEXT 0
#define _O_U16TEXT 0
#define _O_U8TEXT 0

static inline int getdrive(void) { return 0; }

static inline int chdrive(int drive)
{
    (void) drive;

    errno = ENOTSUP;
    return -1;
}

static inline int setmode(int fd, int mode)
{
    (void) fd, (void) mode;

    errno = ENOTSUP;
    return -1;
}

#define _LK_NBRLCK F_RDLCK
#define _LK_NBLCK F_WRLCK
#define _LK_UNLCK F_UNLCK

static int flocking(FILE *fh, int mode, off_t ofs, off_t len)
{
    if (ofs < 0 || len < 0) {
        errno = ERANGE;
        return -1;
    }

    flockfile(fh);

    if (fseeko(fh, ofs, SEEK_SET) != 0)
        goto fail;

    struct flock lk = {
        .l_whence = SEEK_SET,
        .l_type = mode,
        .l_start = ofs,
        .l_len = len  // NOTE: 0 has special meaning
    };
    if (fcntl(fileno(fh), F_SETLK, &lk) != 0)
        goto fail;

    funlockfile(fh);
    return 0;

fail:
    funlockfile(fh);
    return -1;
}
#endif

#ifdef __linux__
#define fadvise(fd, advice) posix_fadvise(fd, 0, 0, advice)
#else
// Stub posix_fadvise()
#define POSIX_FADV_NORMAL 0
#define POSIX_FADV_SEQUENTIAL 0
#define POSIX_FADV_RANDOM 0
#define POSIX_FADV_NOREUSE 0

static inline int fadvise(int fd, int advice)
{
    (void) fd, (void) advice;

    errno = ENOTSUP;
    return -1;
}
#endif

static int os_pusherror(lua_State *L, const char *path)
{
    int err = errno;

    lua_pushboolean(L, false);

    if (path)
        lua_pushfstring(L, "%s: %s",  path, strerror(err));
    else
        lua_pushstring(L, strerror(err));

    lua_pushinteger(L, err);
    return 3;
}

static int os_pushfail(lua_State *L, const char *path)
{
    int err = errno;

    luaL_pushfail(L);

    if (path)
        lua_pushfstring(L, "%s: %s", path, strerror(err));
    else
        lua_pushstring(L, strerror(err));

    lua_pushinteger(L, err);
    return 3;
}

static int os_result(lua_State *L, int ec, const char *path)
{
    if (ec == 0) {
        lua_pushboolean(L, true);
        return 1;
    }

    return os_pusherror(L, path);
}

static df_os_dir *todir(lua_State *L)
{
    df_os_dir *dir = luaL_checkudata(L, 1, DF_LUA_DIRHANDLE);
    if (dir->closeflag)
        luaL_error(L, "attempt to use a closed directory");

    return dir;
}

static bool os_dir_filter(lua_State *L, const char *name)
{
    // Preserve errno across filter calls
    int err = errno;

        lua_pushvalue(L, 2);
        lua_pushstring(L, name);
        lua_call(L, 1, 1);

    errno = err;

    bool result = lua_toboolean(L, -1);
    lua_pop(L, 1);

    return result;
}

static int os_dir_close(lua_State *L)
{
    df_os_dir *dir = todir(L);

    os_closedir(dir->hn);
    dir->closeflag = true;
    return 0;
}

static int os_dir_tostring(lua_State *L)
{
    df_os_dir *dir = luaL_checkudata(L, 1, DF_LUA_DIRHANDLE);

    if (dir->closeflag) {
        lua_pushliteral(L, "directory (closed)");
    } else {
        df_os_dirhn hn = dir->hn;
        void *p;

#ifdef _WIN32
        p = (void *) hn->dirh;
#else
        p = hn;
#endif
        lua_pushfstring(L, "directory (%p)", p);
    }
    return 1;
}

static int os_dir_readdir(lua_State *L)
{
    df_os_dir *dir = todir(L);

    errno = 0;

    const char *filename = os_readdir(dir->hn);
    if (!filename)
        return (errno == 0) ? 0 : os_pusherror(L, NULL);

    lua_pushstring(L, filename);
    return 1;
}

static int os_dir_dolistfiles(lua_State *L, bool closeflag, const char *path)
{
    df_os_dir *dir = todir(L);
    bool dofilter = false;

    if (!lua_isnoneornil(L, 2)) {
        luaL_checktype(L, 2, LUA_TFUNCTION);
        dofilter = true;
    }

    char *filename;
    int i = 1;

    lua_newtable(L);

    errno = 0;
    while ((filename = os_readdir(dir->hn)) != NULL) {
        if (strcmp(filename, ".") == 0 || strcmp(filename, "..") == 0)
            continue;
        if (dofilter && !os_dir_filter(L, filename))
            continue;

        lua_pushinteger(L, i++);
        lua_pushstring(L, filename);
        lua_settable(L, -3);
    }

    int err = errno;
    if (closeflag)
        os_dir_close(L);
    if (err != 0) {
        errno = err;
        return os_pushfail(L, path);
    }
    return 1;
}

static int os_dir_listfiles(lua_State *L)
{
    return os_dir_dolistfiles(L, false, NULL);
}

static int os_dir_gc(lua_State *L)
{
    df_os_dir *dir = luaL_checkudata(L, 1, DF_LUA_DIRHANDLE);

    if (!dir->closeflag)
        os_dir_close(L);

    return 0;
}

/**
 * Open a directory.
 *
 * @string path path to the directory to be opened
 * @treturn[1] Dir handle to the newly opened directory
 * @error[2] error message
 * @treturn[2] int system error code
 * @function opendir
 */
static int os_dir_open(lua_State *L)
{
    const char *path = luaL_checkstring(L, 1);

    df_os_dir *dir = lua_newuserdata(L, sizeof(*dir));

    dir->hn = os_opendir(path);
    dir->closeflag = false;
    if (!dir->hn)
        return os_pushfail(L, path);

    luaL_setmetatable(L, DF_LUA_DIRHANDLE);
    return 1;
}

static int os_dir_iter(lua_State *L);

/**
 * Iterate directory.
 *
 * Enumerates directory contents one filename at a time, '.' and '..' are
 * filtered out. Function is intended to control a for loop.
 *
 * @string path path to directory to be traversed
 * @treturn string next file in directory
 * @raise error if the directory could not be opened, or an error occurs during its traversal.
 * @function dir
 */
static int os_dir(lua_State *L)
{
    lua_pushcfunction(L, os_dir_open);
    lua_pushvalue(L, 1);
    lua_call(L, 1, 2);
    if (lua_isnil(L, -2))
        lua_error(L);

    lua_pop(L, 1);

    lua_pushcclosure(L, os_dir_iter, 2);
    return 1;
}

static int os_dir_iter(lua_State *L)
{
    const char *path = lua_tostring(L, lua_upvalueindex(1));
    df_os_dir *dir = lua_touserdata(L, lua_upvalueindex(2));
    const char *filename;

    errno = 0;

nextfilename:
    filename = os_readdir(dir->hn);
    if (!filename) {
        // Error or end of directory
        if (errno != 0)
            luaL_error(L, lua_pushfstring(L, "%s: %s", path, strerror(errno)));

        return 0;
    }

    // Skip dot and dotdot
    if (strcmp(filename, ".") == 0 || strcmp(filename, "..") == 0)
        goto nextfilename;

    // New directory entry
    lua_pushstring(L, filename);
    return 1;
}

/**
 * List directory contents.
 *
 * @string path path to directory to be listed
 * @tparam[opt] function filter a function taking a filename string and returning
 * a boolean to accept/reject each entry
 * @treturn[1] {string,...} array of filenames within the directory,
 * excluding '.' and '..'
 * @error[2] error message
 * @treturn[2] int system error code
 * @function listfiles
 */
static int os_listfiles(lua_State *L)
{
    const char *path = luaL_checkstring(L, 1);
    if (lua_isnone(L, 2))
        lua_pushnil(L);

    lua_pushcfunction(L, os_dir_open);
    lua_pushvalue(L, 1);
    lua_call(L, 1, 2);
    if (lua_isnil(L, -2))
        lua_error(L);

    lua_copy(L, -2, 1);
    lua_pop(L, 2);

    return os_dir_dolistfiles(L, true, path);
}

/**
 * File info returned on success by @{stat}.
 *
 * @string type file type, either of 'regular', 'directory', or 'other', for
 * regular files, directories and any other file respectively
 * @int mtime last modified time in seconds since Unix Epoch, only available for
 * 'regular' and 'directory'
 * @int size file size in bytes, only available for 'regular' files
 * @table FileStat
 */

/**
 * Get file info.
 *
 * @tparam ?string|File f path or opened file handle
 * @treturn[1] FileStat on success
 * @error[2] error message
 * @treturn[2] int system error code
 * @function stat
 */
static int os_stat(lua_State *L)
{
    const char *path = NULL;
    os_stat_type buf;
    int ec;

    if (lua_isstring(L, 1)) {
        path = lua_tostring(L, 1);
        ec = stat(path, &buf);
    } else {
        luaL_Stream *stream = luaL_checkudata(L, 1, LUA_FILEHANDLE);
        ec = fstat(fileno(stream->f), &buf);
    }
    if (ec != 0)
        return os_pushfail(L, path);

    lua_createtable(L, 0, 3);
    if (S_ISREG(buf.st_mode)) {
        lua_pushliteral(L, "regular");
        lua_setfield(L, -2, "type");
        lua_pushinteger(L, buf.st_size);
        lua_setfield(L, -2, "size");
        lua_pushinteger(L, (lua_Integer) buf.st_mtime);
        lua_setfield(L, -2, "mtime");
    } else if (S_ISDIR(buf.st_mode)) {
        lua_pushliteral(L, "directory");
        lua_setfield(L, -2, "type");
        lua_pushinteger(L, (lua_Integer) buf.st_mtime);
        lua_setfield(L, -2, "mtime");
    } else {
        lua_pushstring(L, "other");
        lua_setfield(L, -2, "type");
    }
    return 1;
}

/**
 * Create a new directory.
 *
 * @string path path to the directory to be created
 * @treturn[1] bool true on success and a new directory is created at path
 * @treturn[2] bool false on failure (note: directory may already exist)
 * @treturn[2] string error message
 * @treturn[2] int system error code
 * @function mkdir
 */
static int os_mkdir(lua_State *L)
{
    const char *path = luaL_checkstring(L, 1);

    int ec = mkdir(path, 0666);
    return os_result(L, ec, path);
}

/**
 * Get process current working directory.
 *
 * @treturn[1] string path to current working directory on success
 * @error[2] error message
 * @treturn[2] int system error code
 * @function getcwd
 */
static int os_getcwd(lua_State *L)
{
#if LUA_VERSION_NUM >= 502
    luaL_Buffer buf;
    char *p;
    size_t size = 128;

    luaL_buffinit(L, &buf);
    while (true) {
        p = luaL_prepbuffsize(&buf, size);
        if (getcwd(p, size))
            break;  // got working directory

        if (errno != ERANGE)
            return os_pusherror(L, NULL);

        size <<= 1;
        if (size == 0) {
            // PARANOID
            errno = ERANGE;
            return os_pusherror(L, NULL);
        }
    }

    luaL_pushresultsize(&buf, strlen(p));
    return 1;
#else
    // Unfortunately this leaks memory if Lua ever decides to longjmp().
    // After 12 years since Lua 5.2 introduction,
    // that's what we get with LuaJIT.
    char *buf = NULL;
    size_t size = 128;

    while (true) {
        char *p = realloc(buf, size);
        if (!p)
            goto fail;

        buf = p;
        if (getcwd(buf, size))
            break;  // got working directory

        if (errno != ERANGE)
            goto fail;

        size <<= 1;
        if (size == 0) {
            // PARANOID
            errno = ERANGE;
            goto fail;
        }
    }

    lua_pushstring(L, buf);
    free(buf);
    return 1;

fail:
    free(buf);
    return os_pusherror(L, NULL);
#endif
}

/**
 * Change process current working directory.
 *
 * @string path path to the new working directory
 * @treturn[1] boolean true on success
 * @treturn[2] boolean false on failure
 * @treturn[2] string error message
 * @treturn[2] int system error code
 * @function chdir
 */ 
static int os_chdir(lua_State *L)
{
    const char *path = luaL_checkstring(L, 1);

    int ec = chdir(path);
    return os_result(L, ec, path);
}

/**
 * Get the active drive letter.
 *
 * @treturn[1] string the current drive letter on systems supporting multiple drives
 * (e.g. Windows), an empty string otherwise
 * @error[2] error message
 * @treturn[2] int system error code
 * @function getdrive
 */
static int os_getdrive(lua_State *L)
{
    errno = 0;

    int drive = getdrive();
    if (drive == 0) {
        if (errno != 0)
            return os_pusherror(L, NULL);

        lua_pushliteral(L, "");
        return 1;
    }

    char letter = 'A' + drive - 1;

    lua_pushlstring(L, &letter, 1);
    return 1;
}

/**
 * Change active drive.
 *
 * May only succeed on systems with multiple drives (e.g. Windows).
 * On any other system this function always fail with an appropriate error.
 *
 * @string drive new drive letter (e.g. 'A', 'C', 'D')
 * @treturn[1] bool true on success
 * @treturn[2] bool false on failure
 * @treturn[2] string error message
 * @treturn[2] int system error code
 * @function chdrive
 */
static int os_chdrive(lua_State *L)
{
    size_t len;
    const char *s = luaL_checklstring(L, 1, &len);
    if (len != 1)
        luaL_argerror(L, 1, "invalid drive");

    int drive = *s - 'A' + 1;
    if (drive < 1 || drive > 26)
        luaL_argerror(L, 1, "invalid drive");

    int ec = chdrive(drive);
    return os_result(L, ec, NULL);
}

/**
 * Set file mode.
 *
 * May only succeed on systems where multiple file mode exist (e.g. Windows),
 * will always fail anywhere else (e.g. Unix).
 * Typically such error can be ignored.
 *
 * @tparam File f a file opened for read
 * @string mode new mode for file, either of 'binary', 'text', 'u8text',
 * 'u16text' or 'wtext'
 * @treturn[1] bool true on success
 * @treturn[2] bool false on failure
 * @treturn[2] string error message
 * @treturn[2] int system error code
 * @function setmode
 */
static int os_setmode(lua_State *L)
{
    static const char *modes[] = {
        "binary",
        "text",
        "u8text",
        "u16text",
        "wtext",
        NULL
    };
    static const int imodes[] = {
        _O_BINARY,
        _O_TEXT,
        _O_U8TEXT,
        _O_U16TEXT,
        _O_WTEXT
    };

    luaL_Stream *stream = luaL_checkudata(L, 1, LUA_FILEHANDLE);
    int i = luaL_checkoption(L, 2, NULL, modes);

    int ec = setmode(fileno(stream->f), imodes[i]);
    return os_result(L, ec, NULL);
}

/**
 * Change file size.
 *
 * @tparam ?string|File f path or file opened for write
 * @int size new file size in bytes
 * @treturn[1] bool true on success
 * @treturn[2] bool false on failure
 * @treturn[2] string error string
 * @treturn[2] int system error code
 * @function chsize
 */
static int os_chsize(lua_State *L)
{
    lua_Integer size = luaL_checkinteger(L, 2);
    if (size < 0)
        size = 0;

    const char *path = NULL;
    int ec;

    if (lua_isstring(L, 1)) {
        path = lua_tostring(L, 1);
        ec = truncate(path, size);
    } else {
        luaL_Stream *stream = luaL_checkudata(L, 1, LUA_FILEHANDLE);
        ec = ftruncate(fileno(stream->f), size);
    }

    return os_result(L, ec, path);
}

/**
 * Advise kernel on file access pattern.
 *
 * @tparam File f a file opened for read
 * @string advise read access pattern (either of: 'normal', 'sequential', 'random', 'noreuse')
 * @treturn[1] boolean true on success
 * @treturn[2] boolean false on failure
 * @treturn[2] string error message
 * @treturn[2] int system error code
 * @function fadvise
 */
static int os_fadvise(lua_State *L)
{
    static const char *hints[] = {
        "normal",
        "sequential",
        "random",
        "noreuse",
        NULL
    };
    static const int ihints[] = {
        POSIX_FADV_NORMAL,
        POSIX_FADV_SEQUENTIAL,
        POSIX_FADV_RANDOM,
        POSIX_FADV_NOREUSE
    };

    luaL_Stream *stream = luaL_checkudata(L, 1, LUA_FILEHANDLE);
    int i = luaL_checkoption(L, 2, NULL, hints);

    int ec = fadvise(fileno(stream->f), ihints[i]);
    return os_result(L, ec, NULL);
}

/**
 * Test whether an opened file handle references a character device (TTY).
 *
 * @tparam File f an opened file handle
 * @treturn boolean true if file references a character device, false otherwise.
 * @function isatty
 */
static int os_isatty(lua_State *L)
{
    luaL_Stream *stream = luaL_checkudata(L, 1, LUA_FILEHANDLE);

    int ec = isatty(fileno(stream->f));
    lua_pushboolean(L, ec != 0);
    return 1;
}

/**
 * Commit any pending write to disk.
 *
 * @tparam File f a file opened for write
 * @treturn[1] boolean true on success
 * @treturn[2] boolean false on failure
 * @treturn[2] string error message
 * @treturn[2] int system error code
 * @function commit
 */
static int os_commit(lua_State *L)
{
    luaL_Stream *stream = luaL_checkudata(L, 1, LUA_FILEHANDLE);

    int ec = fsync(fileno(stream->f));
    return os_result(L, ec, NULL);
}

/**
 * Place or remove a read (shared) or write (exclusive) lock to a file.
 *
 * @tparam File f a file opened with appropriate mode for the requested lock
 * @string mode lock mode, any of 'r' (read), 'w' (write), 'u' (release lock)
 * @int[opt=0] start initial offset for the requested section
 * @int[optchain=0] len length of the requested section, 0 has a special meaning,
 * indicating the whole file starting from the initial offset
 * @treturn[1] boolean true on success
 * @treturn[2] boolean false on failure
 * @treturn[2] string error message
 * @treturn[2] int system error code
 * @function locking
 */
static int os_locking(lua_State *L)
{
    static const char *modes[] = { "r", "w", "u", NULL };
    static const int imodes[] = { _LK_NBRLCK, _LK_NBLCK, _LK_UNLCK };

    luaL_Stream *stream = luaL_checkudata(L, 1, LUA_FILEHANDLE);
    int i = luaL_checkoption(L, 2, NULL, modes);
    lua_Integer ofs = luaL_optinteger(L, 3, 0);
    lua_Integer len = luaL_optinteger(L, 4, 0);

    int ec = flocking(stream->f, imodes[i], ofs, len);
    return os_result(L, ec, NULL);
}

/**
 * preferred path separator char: '\\' on Windows, '/' anywhere else
 *
 * @string sep
 */

/**
 * Directory handle.
 *
 * Allows convenient file traversal on directories.
 * Entries traversal order is system-specific, and may not be ordered at all.
 * Provides metamethods: __gc to close directories on garbage collect,
 * __close (on Lua 5.4) to close directories automatically, and __tostring for
 * adequate formatting.
 *
 * @type Dir
 */

/**
 * Read next directory entry.
 *
 * @treturn[1] string next filename in directory, '.' and '..' are also returned
 * @error[2] error message on failure
 * @treturn[2] int system error code
 * @raise error message when attempting to read from a closed directory
 * @function readdir
 */

/**
 * Read and filter subsequent directory entries.
 *
 * @tparam[opt] function filter a function taking a filename string and returning
 * a boolean to accept/reject each entry
 * @treturn[1] {string,...} subsequent filtered contents, '.' and '..' are always filtered out.
 * @error[2] error message on failure
 * @treturn[2] int system error code
 * @raise error message when attempting to read from a closed directory
 * @function listfiles
 */

/**
 * Close opened directory.
 *
 * @raise error message when closing a directory twice
 * @function close
 */

static void createmeta(lua_State *L)
{
    static const luaL_Reg metameth[] = {
        { "__index", NULL },  // placeholder
        { "__tostring", os_dir_tostring },
        { "__gc", os_dir_gc },
#if LUA_VERSION_NUM >= 504
        { "__close", os_dir_gc},
#endif
        { NULL, NULL }
    };
    static const luaL_Reg meth[] = {
        { "readdir", os_dir_readdir },
        { "listfiles", os_dir_listfiles },
        { "close", os_dir_close },
        { NULL, NULL }
    };

    luaL_newmetatable(L, DF_LUA_DIRHANDLE);
    luaL_setfuncs(L, metameth, 0);
    luaL_newlibtable(L, meth);
    luaL_setfuncs(L, meth, 0);
    lua_setfield(L, -2, "__index");
    lua_pop(L, 1);
}

DF_OSXMOD_API int luaopen_osx(lua_State *L)
{
    static const luaL_Reg funcs[] = {
        { "opendir", os_dir_open },
        { "dir", os_dir },
        { "listfiles", os_listfiles },
        { "stat", os_stat },
        { "mkdir", os_mkdir },
        { "getcwd", os_getcwd },
        { "chdir", os_chdir },
        { "getdrive", os_getdrive },
        { "chdrive", os_chdrive },
        { "setmode", os_setmode },
        { "chsize", os_chsize },
        { "fadvise", os_fadvise },
        { "isatty", os_isatty },
        { "commit", os_commit },
        { "locking", os_locking },
        { NULL, NULL }
    };

    createmeta(L);
    luaL_newlib(L, funcs);

    lua_createtable(L, 0, 1);
    luaL_requiref(L, LUA_OSLIBNAME, luaopen_os, false);
    lua_setfield(L, -2, "__index");
    lua_setmetatable(L, -2);

#ifdef _WIN32
    lua_pushliteral(L, "\\");
#else
    lua_pushliteral(L, "/");
#endif
    lua_setfield(L, -2, "sep");

    return 1;
}