#include	<sys/stat.h>
#include	<dirent.h>
#include	<limits.h>
#include	<string.h>
#include	<termios.h>
#include	<unistd.h>
#include	<stdlib.h>

struct devdir {
	struct devdir	*d_next;
	char			*d_name;
};

static struct devdir	*head;
static struct devdir	*tail;
static char				pathname[_POSIX_PATH_MAX + 1];

static void
add(char *dirname)
{
	struct devdir	*ddp;
	int				len;

	len = strlen(dirname);

	/*
	 * Skip ., .., and /dev/fd.
	 */
	if ((dirname[len-1] == '.') && (dirname[len-2] == '/' ||
	  (dirname[len-2] == '.' && dirname[len-3] == '/')))
		return;
	if (strcmp(dirname, "/dev/fd") == 0)
		return;
	ddp = malloc(sizeof(struct devdir));
	if (ddp == NULL)
		return;

	ddp->d_name = strdup(dirname);
	if (ddp->d_name == NULL) {
		free(ddp);
		return;
	}
	ddp->d_next = NULL;
	if (tail == NULL) {
		head = ddp;
		tail = ddp;
	} else {
		tail->d_next = ddp;
		tail = ddp;
	}
}

static void
cleanup(void)
{
	struct devdir	*ddp, *nddp;

	ddp = head;
	while (ddp != NULL) {
		nddp = ddp->d_next;
		free(ddp->d_name);
		free(ddp);
		ddp = nddp;
	}
	head = NULL;
	tail = NULL;
}

static char *
searchdir(char *dirname, struct stat *fdstatp)
{
	struct stat		devstat;
	DIR				*dp;
	int				devlen;
	struct dirent	*dirp;

	strcpy(pathname, dirname);
	if ((dp = opendir(dirname)) == NULL)
		return(NULL);
	strcat(pathname, "/");
	devlen = strlen(pathname);
	while ((dirp = readdir(dp)) != NULL) {
		strncpy(pathname + devlen, dirp->d_name,
		  _POSIX_PATH_MAX - devlen);

		/*
		 * Skip aliases.
		 */
		if (strcmp(pathname, "/dev/stdin") == 0 ||
		  strcmp(pathname, "/dev/stdout") == 0 ||
		  strcmp(pathname, "/dev/stderr") == 0)
			continue;
		if (stat(pathname, &devstat) < 0)
			continue;
		if (S_ISDIR(devstat.st_mode)) {
			add(pathname);
			continue;
		}
		if (devstat.st_ino == fdstatp->st_ino &&
		  devstat.st_dev == fdstatp->st_dev) {	/* found a match */
			closedir(dp);
			return(pathname);
		}
	}

	closedir(dp);
	return(NULL);
}

char *
ttyname(int fd)
{
	struct stat		fdstat;
	struct devdir	*ddp;
	char			*rval;

	if (isatty(fd) == 0)
		return(NULL);
	if (fstat(fd, &fdstat) < 0)
		return(NULL);
	if (S_ISCHR(fdstat.st_mode) == 0)
		return(NULL);

	rval = searchdir("/dev", &fdstat);
	if (rval == NULL) {
		for (ddp = head; ddp != NULL; ddp = ddp->d_next)
			if ((rval = searchdir(ddp->d_name, &fdstat)) != NULL)
				break;
	}

	cleanup();
	return(rval);
}