/*
 * DNS referrals give two main fields: the path to connect to in
 * /Netbios-host-name/share-name/path... form and a network
 * address of how to find this path of the form domain.dom.
 *
 * The domain.dom is resolved in XP/Win2k etc using AD to do
 * a lookup (this is a consensus view, I don't think anyone
 * has proved it).  I cannot do this as AD needs Kerberos and
 * LDAP which I don't have.
 *
 * Instead I just use the NetBios names passed in the paths
 * and assume that the servers are in the same DNS domain as me
 * and have their DNS hostname set the same as their netbios
 * called-name; thankfully this always seems to be the case (so far).
 *
 * I have not added support for starting another instance of
 * cifs to connect to other servers referenced in DFS links,
 * this is not a problem for me and I think it hides a load
 * of problems of its own wrt plan9's private namespaces.
 *
 * The proximity of my test server (AD enabled) is always 0 but some
 * systems may report more meaningful values.  The expiry time is
 * similarly zero, so I guess at 5 mins.
 *
 * If the redirection points to a "hidden" share (i.e., its name
 * ends in a $) then the type of the redirection is 0 (unknown) even
 * though it is a CIFS share.
 *
 * It would be nice to add a check for which subnet a server is on
 * so our first choice is always the the server on the same subnet
 * as us which replies to a ping (i.e., is up).  This could short-
 * circuit the tests as the a server on the same subnet will always
 * be the fastest to get to.
 *
 * If I set Flags2_DFS then I don't see DFS links, I just get
 * path not found (?!).
 *
 * If I do a QueryFileInfo of a DFS link point (IE when I'am doing a walk)
 * Then I just see a directory, its not until I try to walk another level
 * That I get  "IO reparse tag not handled" error rather than
 * "Path not covered".
 *
 * If I check the extended attributes of the QueryFileInfo in walk() then I can
 * see this is a reparse point and so I can get the referral.  The only
 * problem here is that samba and the like may not support this.
 */
#include <u.h>
#include <libc.h>
#include <fcall.h>
#include <thread.h>
#include <libsec.h>
#include <ctype.h>
#include <9p.h>
#include "cifs.h"

#define SINT_MAX	0x7fffffff

typedef struct Dfscache Dfscache;
struct Dfscache {
	Dfscache*next;		/* next entry */
	char	*src;
	char	*host;
	char	*share;
	char	*path;
	long	expiry;		/* expiry time in sec */
	long	rtt;		/* round trip time, nsec */
	int	prox;		/* proximity, lower = closer */
};

Dfscache *Cache;

int
dfscacheinfo(Fmt *f)
{
	long ex;
	Dfscache *cp;

	for(cp = Cache; cp; cp = cp->next){
		ex = cp->expiry - time(nil);
		if(ex < 0)
			ex = -1;
		fmtprint(f, "%-42s %6ld %8.1f %4d %-16s %-24s %s\n",
			cp->src, ex, (double)cp->rtt/1000.0L, cp->prox,
			cp->host, cp->share, cp->path);
	}
	return 0;
}

char *
trimshare(char *s)
{
	char *p;
	static char name[128];

	strncpy(name, s, sizeof(name));
	name[sizeof(name)-1] = 0;
	if((p = strrchr(name, '$')) != nil && p[1] == 0)
		*p = 0;
	return name;
}

static Dfscache *
lookup(char *opath, int *exact)
{
	char *path;
	int len, n, m;
	Dfscache *cp, *best;

	*exact = 0;

	len = 0;
	best = nil;
	path = opath;
	m = strlen(opath);
	for(cp = Cache; cp; cp = cp->next){
		n = strlen(cp->src);
		if(n < len || cistrncmp(path, cp->src, n) != 0 ||
		    path[n] != 0 && path[n] != '/')
			continue;
		best = cp;
		len = n;
		if(n == m){
			*exact = 1;
			break;
		}
	}
	return best;
}

char *
mapfile(char *opath)
{
	int exact;
	char *p, *path;
	Dfscache *cp;
	static char npath[MAX_DFS_PATH];

	path = opath;
	if((cp = lookup(path, &exact)) != nil){
		snprint(npath, sizeof npath, "/%s%s%s%s", cp->share,
			*cp->path? "/": "", cp->path, path + strlen(cp->src));
		path = npath;
	}

	if((p = strchr(path+1, '/')) == nil)
		p = "/";
	if(Debug && strstr(Debug, "dfs") != nil)
		print("mapfile src=%q => dst=%q\n", opath, p);
	return p;
}

int
mapshare(char *path, Share **osp)
{
	int i, exact;
	char *try, *tail[] = { "", "$" };
	Dfscache *cp;
	Share *sp;

	if((cp = lookup(path, &exact)) == nil)
		return 0;

	for(sp = Shares; sp < Shares+Nshares; sp++)
		if(cistrcmp(cp->share, trimshare(sp->name)) == 0){
			if(Debug && strstr(Debug, "dfs") != nil)
				print("mapshare, already connected, src=%q => dst=%q\n",
					path, sp->name);
			*osp = sp;
			return 0;
		}
	/*
	 * Try to autoconnect to share if it is not known.  Note even if you
	 * didn't specify any shares and let the system autoconnect you may
	 * not already have the share you need as RAP (which we use) throws
	 * away names > 12 chars long.  If we where to use RPC then this block
	 * of code would be less important, though it would still be useful
	 * to catch Shares added since cifs(1) was started.
	 */
	sp = Shares + Nshares;
	for(i = 0; i < 2; i++){
		try = smprint("%s%s", cp->share, tail[i]);
		if(CIFStreeconnect(Sess, Sess->cname, try, sp) == 0){
			sp->name = try;
			*osp = sp;
			Nshares++;
			if(Debug && strstr(Debug, "dfs") != nil)
				print("mapshare connected, src=%q dst=%q\n",
					path, cp->share);
			return 0;
		}
		free(try);
	}

	if(Debug && strstr(Debug, "dfs") != nil)
		print("mapshare failed src=%s\n", path);
	return -1;
}

/*
 * Rtt_tol is the fractional tollerance for RTT comparisons.
 * If a later (further down the list) host's RTT is less than
 * 1/Rtt_tol better than my current best then I don't bother
 * with it.  This biases me towards entries at the top of the list
 * which Active Directory has already chosen for me and prevents
 * noise in RTTs from pushing me to more distant machines.
 */
static int
remap(Dfscache *cp, Refer *re)
{
	int n;
	long rtt;
	char *p, *a[4];
	enum {
		Hostname = 1,
		Shre = 2,
		Path = 3,
		Rtt_tol = 10,
	};

	if(Debug && strstr(Debug, "dfs") != nil)
		print("	remap %s\n", re->addr);

	for(p = re->addr; *p; p++)
		if(*p == '\\')
			*p = '/';

	if(cp->prox < re->prox){
		if(Debug && strstr(Debug, "dfs") != nil)
			print("	remap %d < %d\n", cp->prox, re->prox);
		return -1;
	}
	if((n = getfields(re->addr, a, sizeof(a), 0, "/")) < 3){
		if(Debug && strstr(Debug, "dfs") != nil)
			print("	remap nfields=%d\n", n);
		return -1;
	}
	if((rtt = ping(a[Hostname], Dfstout)) == -1){
		if(Debug && strstr(Debug, "dfs") != nil)
			print("	remap ping failed\n");
		return -1;
	}
	if(cp->rtt < rtt && (rtt/labs(rtt-cp->rtt)) < Rtt_tol){
		if(Debug && strstr(Debug, "dfs") != nil)
			print("	remap bad ping %ld < %ld && %ld < %d\n",
				cp->rtt, rtt, (rtt/labs(rtt-cp->rtt)), Rtt_tol);
		return -1;
	}

	if(n < 4)
		a[Path] = "";
	if(re->ttl == 0)
		re->ttl = 60*5;

	free(cp->host);
	free(cp->share);
	free(cp->path);
	cp->rtt = rtt;
	cp->prox = re->prox;
	cp->expiry = time(nil)+re->ttl;
	cp->host = estrdup9p(a[Hostname]);
	cp->share = estrdup9p(trimshare(a[Shre]));
	cp->path = estrdup9p(a[Path]);
	if(Debug && strstr(Debug, "dfs") != nil)
		print("	remap ping OK prox=%d host=%s share=%s path=%s\n",
			cp->prox, cp->host, cp->share, cp->path);
	return 0;
}

static int
redir1(Session *s, char *path, Dfscache *cp, int level)
{
	Refer retab[16], *re;
	int n, gflags, used, found;

	if(level > 8)
		return -1;

	if((n = T2getdfsreferral(s, &Ipc, path, &gflags, &used, retab,
	    nelem(retab))) == -1)
		return -1;

	if(! (gflags & DFS_HEADER_ROOT))
		used = SINT_MAX;

	found = 0;
	for(re = retab; re < retab+n; re++){
		if(Debug && strstr(Debug, "dfs") != nil)
			print("referal level=%d prox=%d path=%q addr=%q\n",
				level, re->prox, re->path, re->addr);

		if(gflags & DFS_HEADER_STORAGE){
			if(remap(cp, re) == 0)
				found = 1;
		} else{
			if(redir1(s, re->addr, cp, level+1) != -1)  /* ???? */
				found = 1;
		}
		free(re->addr);
		free(re->path);
	}

	if(Debug && strstr(Debug, "dfs") != nil)
		print("referal level=%d path=%q found=%d used=%d\n",
			level, path, found, used);
	if(!found)
		return -1;
	return used;
}

/*
 * We can afford to ignore the used count returned by redir
 * because of the semantics of 9p - we always walk to directories
 * ome and we a time and we always walk before any other file operations
 */
int
redirect(Session *s, Share *sp, char *path)
{
	int exact;
	char *unc;
	Dfscache *cp;

	if(Debug && strstr(Debug, "dfs") != nil)
		print("redirect name=%q path=%q\n", sp->name, path);

	cp = lookup(path, &exact);
	if(cp && exact){
		if(cp->expiry >= time(nil)){	/* cache hit */
			if(Debug && strstr(Debug, "dfs") != nil)
				print("redirect cache=hit src=%q => share=%q path=%q\n",
					cp->src, cp->share, cp->path);
			return 0;

		} else{				/* cache hit, but entry stale */
			cp->rtt = SINT_MAX;
			cp->prox = SINT_MAX;

			unc = smprint("//%s/%s/%s%s%s", s->auth->windom,
				cp->share, cp->path, *cp->path? "/": "",
				path + strlen(cp->src) + 1);
			if(unc == nil)
				sysfatal("no memory: %r");
			if(redir1(s, unc, cp, 1) == -1){
				if(Debug && strstr(Debug, "dfs") != nil)
					print("redirect refresh failed unc=%q\n",
						unc);
				free(unc);
				return -1;
			}
			free(unc);
			if(Debug && strstr(Debug, "dfs") != nil)
				print("redirect refresh cache=stale src=%q => share=%q path=%q\n",
					cp->src, cp->share, cp->path);
			return 0;
		}
	}

	/* in-exact match or complete miss */
	if(cp)
		unc = smprint("//%s/%s/%s%s%s", s->auth->windom, cp->share,
			cp->path, *cp->path? "/": "", path + strlen(cp->src) + 1);
	else
		unc = smprint("//%s%s", s->auth->windom, path);
	if(unc == nil)
		sysfatal("no memory: %r");

	cp = emalloc9p(sizeof(Dfscache));
	memset(cp, 0, sizeof(Dfscache));
	cp->rtt = SINT_MAX;
	cp->prox = SINT_MAX;

	if(redir1(s, unc, cp, 1) == -1){
		if(Debug && strstr(Debug, "dfs") != nil)
			print("redirect new failed unc=%q\n", unc);
		free(unc);
		free(cp);
		return -1;
	}
	free(unc);

	cp->src = estrdup9p(path);
	cp->next = Cache;
	Cache = cp;
	if(Debug && strstr(Debug, "dfs") != nil)
		print("redirect cache=miss src=%q => share=%q path=%q\n",
			cp->src, cp->share, cp->path);
	return 0;
}