implement Rot13;

include "sys.m"; sys: Sys;
include "draw.m";

Rot13: module
{
	init:	fn(ctxt: ref Draw->Context, argv: list of string);
};

stdout: ref Sys->FD;
tab: array of int;

init(nil: ref Draw->Context, args: list of string)
{
	sys = load Sys Sys->PATH;
	stdout = sys->fildes(1);
	inittab();
	args = tl args;
	if(args == nil)
		args = "-" :: nil;
	for(; args != nil; args = tl args){
		file := hd args;
		if(file != "-"){
			fd := sys->open(file, Sys->OREAD);
			if(fd == nil){
				sys->fprint(sys->fildes(2), "rot13: cannot open %s: %r\n", file);
				raise "fail:bad open";
			}
			rot13cat(fd, file);
		}else
			rot13cat(sys->fildes(0), "<stdin>");
	}
}

inittab()
{
	tab = array[256] of int;
	for(i := 0; i < 256; i++)
		tab[i] = i;

	for(i = 'a'; i <= 'z'; i++)
		tab[i] = (((i - 'a') + 13) % 26) + 'a';
	for(i = 'A'; i <= 'Z'; i++)
		tab[i] = (((i - 'A') + 13) % 26) + 'A';
}


rot13(s: string): string
{
	for(i := 0; i < len s; i++) {
		if(s[i] < 256)
			s[i] = tab[s[i]];
	}
	return s;
}

rot13cat(fd: ref Sys->FD, file: string)
{
	buf := array[Sys->ATOMICIO] of byte;

	while((n := sys->read(fd, buf, len buf)) > 0) {
		obuf := array of byte (rot13(string buf));
		if(sys->write(stdout, obuf, n) < n) {
			sys->fprint(sys->fildes(2), "rot13: write error: %r\n");
			raise "fail:write error";
		}
	}
	if(n < 0) {
		sys->fprint(sys->fildes(2), "rot13: error reading %s: %r\n", file);
		raise "fail:read error";
	}
}