#!/usr/bin/perl

use strict;
use warnings;
use Scalar::Util qw/weaken/;

my $root_elem = { };

my @indent_levels = (-1);
my $pos_in_tree = $root_elem;

while (my $line = <>) {
	chomp $line;
	$line =~ s/^\s*//;
	my $indent_part = $&;
	$indent_part =~ s/\t/q{ } x 8/ge;
	my $cur_indent_len = length $indent_part;
	
	my $new_elem = { name => $line };
		
	while ($cur_indent_len < $indent_levels[-1]) {
		pop @indent_levels;
		$pos_in_tree = $pos_in_tree->{parent};
		die <<"_E" if scalar @indent_levels == 1;
Indent level underflow
at line $., containing "$line".
_E
		die <<"_E" if $cur_indent_len > $indent_levels[-1];
Indent level mismatch:
$cur_indent_len should be $indent_levels[-1]
at line $., containing "$line".
_E
	}

	if ($cur_indent_len > $indent_levels[-1]) {
		push @indent_levels, $cur_indent_len;
		$new_elem->{parent} = $pos_in_tree;
	} else {
		$new_elem->{parent}
			= $pos_in_tree->{parent};
	}

	weaken($new_elem->{parent});
	push @{$new_elem->{parent}{children}}, $new_elem;
	$pos_in_tree = $new_elem;
}

use Data::Dumper;
$Data::Dumper::Purity = 1;

my $new_tree;
eval Data::Dumper->Dump([$root_elem], ["new_tree"]);
die "Error in data loading: $@" if $@;
print Data::Dumper->Dump([$new_tree], ["new_tree"]);