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

void
rot13(char *p, int n)
{
	char *ep;

	for(ep=p+n; p<ep; p++)
		if(isalpha(*p))
			if(tolower(*p) <= 'm')
				*p += 13;
			else
				*p -= 13;
}

int isdir[65536];
void
filter(int rd, int wr)
{
	char buf[MAXMSG+MAXFDATA], wbuf[MAXMSG+MAXFDATA];
	Fcall f;
	long n;

	while(n=sizeof buf, getS(rd, buf, &f, &n) == nil){
		if(f.type == Ropen)
			isdir[f.fid] = f.qid.path&CHDIR;
		if((f.type == Twrite || f.type == Rread) && !isdir[f.fid])
			rot13(f.data, f.count);
		n = convS2M(&f, wbuf);
		write(wr, wbuf, n);
	}
	postnote(PNGROUP, getpid(), "spanish inquisition"); /* nobody expects this */
}

void
main(int argc, char **argv)
{
	int sfd, p[2];

	rfork(RFNOTEG);

	if(argc != 1+2){
		fprint(2, "usage: rot13fs service-in mountpoint\n");
		exits("usage");
	}

	if((sfd = open(argv[1], ORDWR)) < 0)
		sysfatal("cannot open %s: %r\n", argv[1]);

	if(pipe(p) < 0)
		sysfatal("pipe fails: %r\n");

	switch(rfork(RFNAMEG|RFPROC|RFFDG|RFMEM)){
	case -1:
		sysfatal("rfork fails: %r\n");
	case 0:
		close(p[0]);
		switch(fork()){
		case -1:
			sysfatal("rfork fails: %r\n");
		case 0:
			filter(sfd, p[1]);
			break;
		default:
			filter(p[1], sfd);
			break;
		}
		_exits(0);
	default:
		close(p[1]);
		if(amount(p[0], argv[2], MREPL, "") < 0)
			sysfatal("mount fails: %r\n");
		exits(0);
	}
}