#!/usr/bin/env perl

use English;
$INPLACE_EDIT=1;


our $prevn;

BEGIN {
    $prevn = 0;
    print STDERR "<h1>Contents</h1>\n<ul>\n";
}

while (<>)
{
        if (m{
            <h([123])\s+id="           # 1. hn
               ([^"]+)                 # 3. id
            ">
            (                          # 4. header
                (<code>[^(]+)?.+?      # 5. label
            )
            </h\1>
        }x) {
            my ($hn, $id, $val, $label) = ($1, $2, $3, $4);

            if ($prevn) {
                if ($hn != $prevn) {
                    print STDERR $hn > $prevn
                        ? $hn - $prevn > 1
                        ? "<ul><li><ul>" : "<ul>\n" : $prevn - $hn > 1
                        ? "</li></ul></li></ul></li>\n" : "</li></ul></li>\n";
                    $prevn = $hn;
                } else {
                    print STDERR "</li>\n"
                }
            } else {
                $prevn = $hn;
            }
            print STDERR qq{<li><a href="#$id">$val</a>};

            $_ = qq{<h$hn id="$id">$val</h$hn>\n};
        }
}
continue
{print}

END { print STDERR "</li>\n</ul>\n" }