use File::Find;
use URI::URL;

$DIR = shift || die "usage: $0 base [start]\n";
die "missing $DIR" unless -d $DIR;

$START = shift || $DIR;
die "missing $START" unless -d $START;

find ( \&fixup, $START );

sub fixup {

    return unless /.html$/;
    my $filename = $File::Find::name;
    my $BASE = $filename;
    $BASE =~ s,[^/]+$,,;
    die "$file exists " if -e "$filename.orig";
    local @ARGV = $filename;
    local $^I = ".orig";
    warn "@ARGV\n";

    while (<>) {
	s{
	    ( 
		(HREF \s* = \s*) 
		(['"]) 
		($DIR.*?) 
		\3
	    )
	}{
	    my ($all, $first, $quote, $file) = ($1, $2, $3, $4);
	    if ( index($file, $DIR) == 0 ) {
		my $rel = url("file:$file", "file:$BASE")->rel();
		$rel =~ s/#$//;
		$first . $quote . $rel . $quote;
	    } else {
		$all;
	    } 
	}sgex;

    } continue {
	print;
    }

}