#!/usr/bin/perl

use strict;
use HTML::Template;

my $template = "
        <ul>
                <TMPL_LOOP tree>
                <li><TMPL_VAR value> (depth=<TMPL_VAR depth>)
                    <TMPL_LOOP open><ul></TMPL_LOOP>
                        <TMPL_IF close>
                                <TMPL_LOOP close>
                                        </li></ul>
                                        <TMPL_IF __LAST__></li></TMPL_IF>
                                </TMPL_LOOP>
                        <TMPL_ELSE>
                                <TMPL_UNLESS open>
                                        </li>
                                </TMPL_UNLESS>
                        </TMPL_IF>
                </TMPL_LOOP>
        </ul>
";

my $tree = [
        { 'value' => 'a',    'depth' => 1 },
        { 'value' => 'b',    'depth' => 1 },
        { 'value' => 'b1',   'depth' => 2 },
        { 'value' => 'b2',   'depth' => 2 },
        { 'value' => 'c',    'depth' => 1 },
        { 'value' => 'c1',   'depth' => 2 },
        { 'value' => 'c1.1', 'depth' => 3 },
        { 'value' => 'd',    'depth' => 1 }
];

for my $i (0 .. $#$tree) {
        my $delta;
        if (defined($tree->[$i+1])) {
                $delta = $tree->[$i+1]->{'depth'} - $tree->[$i]->{'depth'};
        }
        else {
                $delta = - $tree->[$i]->{'depth'};
        }

        if ($delta > 0) {
                push(@{$tree->[$i]->{'open'}},{}) for (1 .. $delta);
        }
        elsif ($delta < 0) {
                push(@{$tree->[$i]->{'close'}},{}) for ($delta .. -1);
        }
}

my $html_template = HTML::Template->new(
        scalarref => \$template,
        loop_context_vars => 1);

$html_template->param('tree' => $tree);
print $html_template->output;