<?php
class Node
{
    private $data = array();
    private $offset = 0;
    private $meta_count = 0;
    private $child_count = 0;
    private $meta = array();
    private $children = /* Node */array();

    public function __construct($data, $offset)
    {
        $this->data = $data;
        $this->offset = $offset;
    }

    protected function get_length():int
    {
        $length = 2; //Identifiers
        $length += $this->meta_count;

        foreach ($this->children as $child)
        {
            $length += $child->get_length();
        }

        return $length;
    }

    public function parse_data()
    {
        $this->child_count = $this->data[$this->offset];
        $this->meta_count = $this->data[$this->offset+1];

        $offset = $this->offset+2;

        for($i=0;$i<$this->child_count;$i++)
        {
            $node = new Node($this->data, $offset);
            $this->children[] = $node;
            $node->parse_data();
            $offset += $node->get_length();
        }

        $this->meta = array_slice($this->data, $offset, $this->meta_count);

    }

    public function get_meta_sum():int //Part 1
    {
        $sum = array_sum($this->meta);

        foreach ($this->children as $child)
        {
            $sum += $child->get_meta_sum();
        }

        return $sum;
    }

    public function get_meta_sum_indexed():int //Part 2
    {
        $sum = 0;

        if($this->child_count>0)
        {
            foreach ($this->meta as $m)
            {
                if($m < 1) continue;

                if(isset($this->children[$m-1]))
                {
                    $sum += $this->children[$m-1]->get_meta_sum_indexed();
                }
            }
        } else {
            $sum = array_sum($this->meta);
        }

        return $sum;
    }

}

$input = file_get_contents('input.txt');

$data = explode(' ', $input);

$node = new Node($data, 0);
$node->parse_data();

echo 'Part 1: '. $node->get_meta_sum() . PHP_EOL;
echo 'Part 2: '. $node->get_meta_sum_indexed() . PHP_EOL;