/***
Send message to a message queue
@function msgsnd
@int id message queue identifier returned by @{msgget}
@int type arbitrary message type
@string message content
@int[opt=0] flags optionally `IPC_NOWAIT`
@treturn int 0, if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see msgsnd(2)
 */
static int
Pmsgsnd(lua_State *L)
{
	void *ud;
	lua_Alloc lalloc = lua_getallocf(L, &ud);
	struct {
		long mtype;
		char mtext[0];
	} *msg;
	size_t len;
	size_t msgsz;
	ssize_t r;

	int msgid = checkint(L, 1);
	long msgtype = checklong(L, 2);
	const char *msgp = luaL_checklstring(L, 3, &len);
	int msgflg = optint(L, 4, 0);

	checknargs(L, 4);

	msgsz = sizeof(long) + len;

	if ((msg = lalloc(ud, NULL, 0, msgsz)) == NULL)
		return pusherror(L, "lalloc");

	msg->mtype = msgtype;
	memcpy(msg->mtext, msgp, len);

	r = msgsnd(msgid, msg, msgsz, msgflg);
	lua_pushinteger(L, r);

	lalloc(ud, msg, msgsz, 0);

	return (r == -1 ? pusherror(L, NULL) : 1);
}

/***
change process priority
@function nice
@int inc adds inc to the nice value for the calling process
@treturn[1] int new nice value, if successful
@return[2] nil
@return[2] string error message
@treturn[2] int errnum
@see nice(2)
*/
static int
Pnice(lua_State *L)
{
	int inc = checkint(L, 1);
	checknargs(L, 1);
	return pushresult(L, nice(inc), "nice");
}

/***
Get a value for a configuration option for a filename.
@function pathconf
@string path optional
@int key one of `_PC_LINK_MAX`, `_PC_MAX_CANON`, `_PC_NAME_MAX`,
  `_PC_PIPE_BUF`, `_PC_CHOWN_RESTRICTED`, `_PC_NO_TRUNC` or
  `_PC_VDISABLE`
@treturn int associated path configuration value
@see pathconf(3)
@usage
  local unistd = require "posix.unistd"
  for a, b in pairs (unistd.pathconf "/dev/tty") do print(a, b) end
*/
static int
Ppathconf(lua_State *L)
{
	const char *path = luaL_checkstring(L, 1);
	checknargs(L, 2);
	return pushintresult(pathconf(path, checkint(L, 2)));
}

/***
Parse command-line options.
@function getopt
@param arg command line arguments
@string opts short option specifier
@int[opt=0] opterr index of the option with an error
@int[opt=1] optind index of the next unprocessed option
@treturn option iterator, returning 3 values
@see getopt(3)
@see getopt.lua
@usage
local getopt = require "posix.getopt".getopt
for opt, opterr, i in getopt (arg, "ho:v", opterr, i) do
  process (arg, opterr, i)
end
*/
static int
Pgetopt(lua_State *L)
{
	int argc, i;
	const char *optstring;
	char **argv;

	checknargs(L, 4);
	checktype(L, 1, LUA_TTABLE, "list");
	optstring = luaL_checkstring(L, 2);
	opterr = optint(L, 3, 0);
	optind = optint(L, 4, 1);

	argc = (int)lua_objlen(L, 1) + 1;

	lua_pushinteger(L, argc);
	lua_pushstring(L, optstring);

	argv = lua_newuserdata(L, (argc + 1) * sizeof(char *));
	argv[argc] = NULL;
	for (i = 0; i < argc; i++)
	{
		lua_pushinteger(L, i);
		lua_gettable(L, 1);
		argv[i] = (char *)luaL_checkstring(L, -1);
	}

	/* Push remaining upvalues, and make and push closure. */
	lua_pushcclosure(L, iter_getopt, 3 + argc);

	return 1;
}

/***
Test whether a file descriptor refers to a terminal.
@function isatty
@int fd file descriptor to act on
@treturn[1] int `1` if *fd* is open and refers to a terminal, if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see isatty(3)
*/
static int
Pisatty(lua_State *L)
{
	int fd = checkint(L, 1);
	checknargs(L, 1);
	return pushresult(L, isatty(fd) == 0 ? -1 : 1, "isatty");
}

/***
Synchronize a file's in-core state with storage device.
@function fsync
@int fd
@treturn[1] int `0`, if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see fsync(2)
@see sync
*/
static int
Pfsync(lua_State *L)
{
  int fd = checkint(L, 1);
  checknargs(L, 1);
  return pushresult(L, fsync(fd), NULL);
}

/***
Get list of supplementary group ids.
@function getgroups
@see getgroups(2)
@treturn table group id
*/
static int
Pgetgroups(lua_State *L)
{
	int n_group_slots = getgroups(0, NULL);
	checknargs(L, 0);

	if (n_group_slots < 0)
		return pusherror(L, NULL);
	else if (n_group_slots == 0)
		lua_newtable(L);
	else
	{
		gid_t  *group;
		int     n_groups;
		int     i;

		group = lua_newuserdata(L, sizeof(*group) * n_group_slots);

		n_groups = getgroups(n_group_slots, group);
		if (n_groups < 0)
			return pusherror(L, NULL);

		lua_createtable(L, n_groups, 0);
		for (i = 0; i < n_groups; i++)
		{
			lua_pushinteger(L, group[i]);
			lua_rawseti(L, -2, i + 1);
		}
	}

	return 1;
}

/***
Close an open file descriptor.
@function close
@int fd file descriptor to act on
@treturn[1] int `0` if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see close(2)
@usage
  local unistd = require "posix.unistd"
  local ok, errmsg = unistd.close (log)
  if not ok then error (errmsg) end
*/
static int
Pclose(lua_State *L)
{
	int fd = checkint(L, 1);
	checknargs(L, 1);
	return pushresult(L, close(fd), NULL);
}

static int
runexec(lua_State *L, int use_shell)
{
	char **argv;
	const char *path = luaL_checkstring(L, 1);
	int i, n;
	checknargs(L, 2);

	if (lua_type(L, 2) != LUA_TTABLE)
		argtypeerror(L, 2, "table");

	n = lua_objlen(L, 2);
	argv = lua_newuserdata(L, (n + 2) * sizeof(char*));

	/* Set argv[0], defaulting to command */
	argv[0] = (char*) path;
	lua_pushinteger(L, 0);
	lua_gettable(L, 2);
	if (lua_type(L, -1) == LUA_TSTRING)
		argv[0] = (char*)lua_tostring(L, -1);
	else
		lua_pop(L, 1);

	/* Read argv[1..n] from table. */
	for (i=1; i<=n; i++)
	{
		lua_pushinteger(L, i);
		lua_gettable(L, 2);
		argv[i] = (char*)lua_tostring(L, -1);
	}
	argv[n+1] = NULL;

	(use_shell ? execvp : execv) (path, argv);
	return pusherror(L, path);
}

/***
Name of a terminal device.
@function ttyname
@see ttyname(3)
@int[opt=0] fd file descriptor to process
@return string name
*/
static int
Pttyname(lua_State *L)
{
	int fd=optint(L, 1, 0);
	checknargs(L, 1);
	return pushstringresult(ttyname(fd));
}

/***
Schedule an alarm signal.
@function alarm
@int seconds number of seconds to send SIGALRM in
@return int number of seconds remaining in previous alarm or `0`
@see alarm(2)
@usage
  local unistd = require "posix.unistd"
  seconds = unistd.alarm(10)
*/
static int
Palarm(lua_State *L)
{
	int seconds = checkint(L, 1);
	checknargs(L, 1);
	return pushintresult(alarm(seconds));
}

/***
Commit buffer cache to disk.
@function sync
@see fsync
@see sync(2)
*/
static int
Psync(lua_State *L)
{
	checknargs(L, 0);
	sync();
	return 0;
}

/***
Sleep for a number of seconds.
@function sleep
@int seconds minimum numebr of seconds to sleep
@treturn[1] int `0` if the requested time has elapsed
@treturn[2] int unslept seconds remaining, if interrupted
@see sleep(3)
@see posix.time.nanosleep
*/
static int
Psleep(lua_State *L)
{
	unsigned int seconds = checkint(L, 1);
	checknargs(L, 1);
	return pushintresult(sleep(seconds));
}

/***
Set the uid, euid, gid, egid, sid or pid & gid.
@function setpid
@string what one of 'u', 'U', 'g', 'G', 's', 'p' (upper-case means "effective")
@int id (uid, gid or pid for every value of `what` except 's')
@int[opt] gid (only for `what` value 'p')
@treturn[1] int `0`, if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see setuid(2)
@see seteuid(2)
@see setgid(2)
@see setegid(2)
@see setsid(2)
@see setpgid(2)
*/
static int
Psetpid(lua_State *L)
{
	const char *what=luaL_checkstring(L, 1);
	checknargs(L, *what == 'p' ? 3 : 2);
	switch (*what)
	{
		case 'U':
			return pushresult(L, seteuid(mygetuid(L, 2)), NULL);
		case 'u':
			return pushresult(L, setuid(mygetuid(L, 2)), NULL);
		case 'G':
			return pushresult(L, setegid(mygetgid(L, 2)), NULL);
		case 'g':
			return pushresult(L, setgid(mygetgid(L, 2)), NULL);
		case 's':
			return pushresult(L, setsid(), NULL);
		case 'p':
		{
			pid_t pid  = checkint(L, 2);
			pid_t pgid = checkint(L, 3);
			return pushresult(L, setpgid(pid,pgid), NULL);
		}
		default:
			badoption(L, 1, "id", *what);
			return 0;
	}
}

/***
Create a unique temporary directory.
@function mkdtemp
@string templ pattern that ends in six 'X' characters
@treturn[1] string path to directory, if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see mkdtemp(3)
*/
static int
Pmkdtemp(lua_State *L)
{
#if defined LPOSIX_2008_COMPLIANT
	const char *path = luaL_checkstring(L, 1);
	size_t path_len = strlen(path) + 1;
	void *ud;
	lua_Alloc lalloc;
	char *tmppath;
	char *r;
	checknargs(L, 1);
	lalloc = lua_getallocf(L, &ud);

	if ((tmppath = lalloc(ud, NULL, 0, path_len)) == NULL)
		return pusherror(L, "lalloc");
	strcpy(tmppath, path);

	if ((r = mkdtemp(tmppath)))
		lua_pushstring(L, tmppath);
	lalloc(ud, tmppath, path_len, 0);
	return (r == NULL) ? pusherror(L, path) : 1;
#else
	return binding_notimplemented(L, "mkdtemp", "C");
#endif
}

/***
Remove a directory.
@function rmdir
@string path file to act on
@treturn[1] int `0`, if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see rmdir(2)
*/
static int
Prmdir(lua_State *L)
{
	const char *path = luaL_checkstring(L, 1);
	checknargs(L, 1);
	return pushresult(L, rmdir(path), path);
}

/***
Receive message from a message queue
@function msgrcv
@int id message queue identifier returned by @{msgget}
@int size maximum message size
@int type message type (optional, default - 0)
@int[opt=0] flags bitwise OR of zero or more of `IPC_NOWAIT`, `MSG_EXCEPT`
  and `MSG_NOERROR`
@treturn[1] int message type from @{msgsnd}
@treturn[1] string message text, if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see msgrcv(2)
 */
static int
Pmsgrcv(lua_State *L)
{
	int msgid = checkint(L, 1);
	size_t msgsz = checkint(L, 2);
	long msgtyp = optint(L, 3, 0);
	int msgflg = optint(L, 4, 0);

	void *ud;
	lua_Alloc lalloc;
	struct {
		long mtype;
		char mtext[0];
	} *msg;

	checknargs(L, 4);
	lalloc = lua_getallocf(L, &ud);

	if ((msg = lalloc(ud, NULL, 0, msgsz)) == NULL)
		return pusherror(L, "lalloc");

	int res = msgrcv(msgid, msg, msgsz, msgtyp, msgflg);
	if (res != -1)
	{
		lua_pushinteger(L, msg->mtype);
		lua_pushlstring(L, msg->mtext, res - sizeof(long));
	}
	lalloc(ud, msg, msgsz, 0);

	return (res == -1) ? pusherror(L, NULL) : 2;
}

/***
Change the name or location of a file
@function rename
@tparam string oldpath
@tparam string newpath
@treturn[1] int `0` if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see rename(2)
@usage
local ok, errmsg = P.rename (oldpath, newpath)
if not ok then error (errmsg) end
*/
static int
Prename(lua_State *L)	/** rename(oldpath, newpath) */
{
	const char *oldpath = luaL_checkstring(L, 1);
	const char *newpath = luaL_checkstring(L, 2);
	checknargs(L, 2);
	return pushresult(L, rename(oldpath, newpath), NULL);
}

/***
Write bytes to a file.
@function write
@int fd the file descriptor to act on
@string buf containing bytes to write
@treturn[1] int number of bytes written, if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see write(2)
*/
static int
Pwrite(lua_State *L)
{
	int fd = checkint(L, 1);
	const char *buf = luaL_checkstring(L, 2);
	checknargs(L, 2);
	return pushresult(L, write(fd, buf, lua_objlen(L, 2)), NULL);
}

/***
Duplicate one open file descriptor to another.
If *newfd* references an open file already, it is closed before being
reallocated to *fd*.
@function dup2
@int fd an open file descriptor to act on
@int newfd new descriptor to duplicate *fd*
@treturn[1] int new file descriptor, if successful
@return[2] nil
@treturn[2] string error message
@treturn[2] int errnum
@see dup2(2)
*/
static int
Pdup2(lua_State *L)
{
	int fd = checkint(L, 1);
	int newfd = checkint(L, 2);
	checknargs(L, 2);
	return pushresult(L, dup2(fd, newfd), NULL);
}