Add handler to serve filtered ics file

cache/index.php

@@ -0,0 +1,53 @@
+<?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.");
+}