#!/usr/bin/perl

use File::Temp qw/ :mktemp  /;

sub usage() {
    print "usage: cat diff | $0 old new old new old new...\n";
    exit(1);
}

my @subs;

sub filter($) {
    my $line = shift();

    foreach my $sub (@subs) {
	$line =~ s/$sub->[0]/$sub->[1]/g;
    }

    # remove the first char
    $line =~ s/^[ +-]//;

    return $line;
}

($oldfh, $oldfile) = mkstemp("/tmp/oldXXXXX");
($newfh, $newfile) = mkstemp("/tmp/newXXXXX");

while (my $param1 = shift()) {
    my $param2 = shift;

    if ($param2 =~ /^$/) {
	usage();
    }
    push @subs, [$param1, $param2];
}

while (<>) {
    my $line = $_;

    if ($line =~ /^(---|\+\+\+)/) {
	next;
    }

    my $output = filter($line);
    if ($line =~ /^-/) {
	print $oldfh $output;
	next;
    }
    if ($line =~ /^\+/) {
	print $newfh $output;
	next;
    }
    print $oldfh $output;
    print $newfh $output;
}

system("diff -uw $oldfile $newfile");

unlink($oldfile);
unlink($newfile);