#include <u.h>
#include <libc.h>
#include <fcall.h>

#define DBG(s)
#define MAXDEPTH	100

static void namedev(Dir*);
static int  samefile(Dir*, Dir*);
static int  crossedmnt(char*);

char *
getwd(char *s , int size) 
{
	Dir *p, db[MAXDEPTH], root;
	int depth, l;
	char *x, *v;

	x = s;
	if(dirstat("/", &root) < 0) {
		strcpy(s, "stat of / failed");
		return 0;
	}

	for(depth = 0; depth < MAXDEPTH; depth++) {
		p = &db[depth];
		if(dirstat(".", p) < 0) {
			strcpy(s, "stat of . failed");
			return 0;
		}

		DBG(print("stat: %s %lux\n", p->name, p->qid);)

		if(samefile(p, &root)) {
			depth--;
			break;
		}

		if(depth > 1 && samefile(p, &db[depth-1])) {
			p->name[0] = '#';
			p->name[1] = p->type;
			p->name[2] = '\0';
			break;
		}

		if(crossedmnt(p->name))
			namedev(p);

		if(chdir("..") < 0) {
			strcpy(s, "chdir .. failed");
			return 0;
		}
	}

	while(depth >= 0) {
		v = db[depth--].name;
		if(v[0] == '.' && v[1] == '\0')
			continue;
		if(v[0] != '#')
			*x++ = '/';
		l = strlen(v);
		size -= l+1;
		if(size <= 0) {
			strcpy(s, "buffer too small");
			return 0;
		}
		strcpy(x, v);
		x += l;
	}
	if(x == s){
		*x++ = '/';
		*x = 0;
	}
	DBG(print("chdir %s\n", s);)
	if(chdir(s) < 0) {
		strcpy(s, "failed to return to .");
		return 0;
	}
	return s;
}

/*
 * In cases where we have no valid name from the stat we must search .. for an
 * entry which leads back to our current depth. This happens in three ways:
 * when crossing a mount point or when we are in a dev which uses devgen in the
 * kernel to fill in the stat buffer or when we are at slash of a mounted file system
 */
static void
namedev(Dir *p)
{
	Dir dirb, tdirb;
	char buf[DIRLEN*50], sd[NAMELEN*2];
	int fd, n;
	char *t, *e;

	fd = open("..", OREAD);
	if(fd < 0)
		return;

	for(;;) {
		n = read(fd, buf, sizeof(buf));
		if(n <= 0)
			return;
		e = &buf[n];

		for(t = buf; t < e; t += DIRLEN) {
			convM2D(t, &dirb);
			if((dirb.qid.path&CHDIR) == 0)
				continue;
			sprint(sd, "../%s/.", dirb.name);
			if(dirstat(sd, &tdirb) < 0)
				continue;

			if(samefile(&tdirb, p) == 0)
				continue;
			close(fd);
			DBG(print("%s->%s\n", p->name, dirb.name);)
			strcpy(p->name, dirb.name);
			return;
		}
	}
	close(fd);
}

static int
samefile(Dir *a, Dir *b)
{
	if(a->type != b->type)
		return 0;
	if(a->dev != b->dev)
		return 0;
	if(a->qid.path != b->qid.path)
		return 0;
	return 1;
}

/*
 * returns true if we must establish a child which derives the current directory name
 * after stat has failed to account for devices and the mount table
 */
int
crossedmnt(char *elem)
{
	char junk[DIRLEN];

	if((elem[0] == '.' || elem[0] == '/') && elem[1] == '\0')
		return 1;

	sprint(junk, "../%s", elem);
	if(stat(junk, junk) < 0)
		return 1;

	return 0;
}