// For some fucking reason, libuv hasn't implemented lseek() (WHY??)
// Here, a sync version is implemented (as i cannot be bothered with callbacks)

#include <errno.h>
#include <lauxlib.h>
#include <lua.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>

#ifdef _WIN32
	#include <io.h>
	#include <windows.h>
	#define off_t LONGLONG
	#define _LARGEFILE_SOURCE
#endif

static int luafunc_seek(lua_State *ctx) {

	int fd = lua_tointeger(ctx, 1);
	off_t offset = lua_isnoneornil(ctx, 2) ? 0 : luaL_checkinteger(ctx, 2);

	int whence = SEEK_CUR;
	if (!lua_isnoneornil(ctx, 3)) {
		const char *swhence = luaL_checkstring(ctx, 3);
		if (!strcmp(swhence, "set")) {
			whence = SEEK_SET;
		}
		else if (!strcmp(swhence, "cur")) {
			whence = SEEK_CUR;
		}
		else if (!strcmp(swhence, "end")) {
			whence = SEEK_END;
		}
		else {
			luaL_typeerror(ctx, 3, "'set', 'cur' or 'end'");
		}
	}

	#ifdef _WIN32
		HANDLE fh;
		LARGE_INTEGER new_offset;

		fh = (HANDLE)_get_osfhandle(fd);
		if (fh == (HANDLE)-1) {
			errno = EBADF;
			return -1;
		}

		DWORD method;
		switch (whence) {
		case SEEK_SET:
			method = FILE_BEGIN;
			break;
		case SEEK_CUR:
			method = FILE_CURRENT;
			break;
		case SEEK_END:
			method = FILE_END;
			break;
		default:
			errno = EINVAL;
			return -1;
		}

		LARGE_INTEGER distance;
		distance.QuadPart = offset;

		if (!SetFilePointerEx(fh, distance, &new_offset, method)) {
			lua_pushnil(ctx);
			lua_pushstring(ctx, strerror(EINVAL));
			return 2;
		}

		off_t offs = new_offset.QuadPart;
	#else
		off_t offs = lseek(fd, offset, whence);
		if (offs < 0) {
			lua_pushnil(ctx);
			lua_pushstring(ctx, strerror(errno));
			return 2;
		}
	#endif

	lua_pushinteger(ctx, offs);
	return 1;
}

int luaopen_seek(lua_State *ctx) {
	lua_pushcfunction(ctx, luafunc_seek);
	return 1;
}