Discovery: STUB: Add ExpireTimestampConverter.

collabora_online.services.yml

@@ -4,6 +4,7 @@ services:
   logger.channel.collabora_online:
     parent: logger.channel_base
     arguments: ['cool']
+  Drupal\collabora_online\ExpireTimestampConverter: {}
   Drupal\collabora_online\Discovery\CollaboraDiscoveryFetcherInterface:
     class: Drupal\collabora_online\Discovery\CollaboraDiscoveryFetcher
   Drupal\collabora_online\Discovery\CachingDiscoveryFetcher:

src/Time/ExpireTimestampConverter.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\collabora_online\Time;
+
+use Drupal\Component\Datetime\TimeInterface;
+use Drupal\Core\Cache\Cache;
+
+/**
+ * Service to convert between expire timestamp and cache max-age value.
+ */
+class ExpireTimestampConverter {
+
+  public function __construct(
+    protected readonly TimeInterface $time,
+  ) {}
+
+  public function getExpireTimestamp(int $max_age): int {
+    if ($max_age === Cache::PERMANENT) {
+      return Cache::PERMANENT;
+    }
+    return $max_age + $this->time->getRequestTime();
+  }
+
+  public function getMaxAge(int $expire): int {
+    if ($expire === Cache::PERMANENT) {
+      return Cache::PERMANENT;
+    }
+    return $expire - $this->time->getRequestTime();
+  }
+
+}