use warnings;
use strict;

die "Usage: $0 INFILE\n" unless @ARGV==1;
my $INFILE = shift @ARGV;

use constant { STATE_IDLE=>0, STATE_BEGIN=>1, STATE_INBLOCK=>2 };

open my $fh, '<', $INFILE or die "$INFILE: $!";
my %found;
my $state = STATE_IDLE;
my $curnum;
for my $pass (1..2) {
	while (<$fh>) {
		chomp;
		my $out = 1;
		if ($state==STATE_IDLE) {
			if (/^\s*(?:foo\s+)?ref\s+(\d+)\s*$/) { $out=!$found{$1} }
			elsif (/^begin$/) { $state=STATE_BEGIN }
			else { die "unexpected in state $state: $_" }
		}
		elsif ($state==STATE_BEGIN) {
			if (/^\s*(\d+)\s*$/) { $curnum=$1; $state=STATE_INBLOCK }
			else { die "unexpected in state $state: $_" }
		}
		elsif ($state==STATE_INBLOCK) {
			if (/^end$/) { $state=STATE_IDLE }
			elsif (/bar/) { $found{$curnum}=1 }
		}
		else { die "bad state $state" }
		print $_, "\n" if $pass==2 && $out;
	}
	die "unexpected state at eof: $state" unless $state==STATE_IDLE;
	seek $fh, 0, 0 or die "seek $INFILE: $!";
}
close $fh;