website-archive/hackcal/index.php

<?php
header('Content-Type: application/json');
$period = max(filter_input(INPUT_GET, 'period', FILTER_VALIDATE_INT, array('options' => array('min_range' => 1, 'max_range' => 12))), 1);
echo file_get_contents("https://hackcal.ctbk.de/?period=".$period);