<?php

# Requirements
require_once '../include/config.php';

# Caching
if (!file_exists($cachefile) || (filemtime($cachefile) + $cachetime < time())) {
    $context = stream_context_create(['http' => ['timeout' => 10]]);
    $ical_str = @file_get_contents($ical_url, false, $context);

    if ($ical_str !== false && strpos($ical_str, 'BEGIN:VCALENDAR') !== false) {
        file_put_contents($cachefile, $ical_str);
    }
}

if (file_exists($cachefile)) {
   $content = file_get_contents($cachefile);

   // Replace X-WR-CALNAME
   $content = preg_replace('/X-WR-CALNAME:.*(\r\n|\n|\r)/i', "X-WR-CALNAME:" . $ical_name . "\r\n", $content);

   // Remove all ORGANIZER
   $content = preg_replace('/^ORGANIZER[:;].*(?:\r?\n[\t ].*)*(\r?\n)?/mi', '', $content);

   // Filter CATEGORIES
   $exclude = $_GET['exclude'] ?? '';

   if ($exclude && strlen($exclude) < 32 && preg_match('/^[a-zA-Z0-9_|-]+$/', $exclude)) {

      $parts = explode('|', $exclude);
      $safe_parts = array_map(function($part) {
         return preg_quote(trim($part), '/');
      }, $parts);
      $safe_exclude = implode('|', $safe_parts);

      $filtered_content = preg_replace('/BEGIN:VEVENT(?!(?:(?!END:VEVENT)[\s\S])*CATEGORIES:(?:(?!' . $safe_exclude . ')[\s\S])*?(?:\r?\n|;))(?:(?!END:VEVENT)[\s\S])*END:VEVENT(?:\r?\n)?/ms', '', $content);

      if ($filtered_content !== null) {
         $content = $filtered_content;
      }
   }

   header('Content-Type: text/calendar; charset=utf-8');
   header('Content-Disposition: attachment; filename="' . $ical_file . '"');
   header('Content-Description: File Transfer');
   header('Cache-Control: public, max-age=120, must-revalidate');
   header('Content-Length: ' . strlen($content));

   echo $content;
   exit;
} else {
   die("File not found.");
}