refactor: replace custom CRM with Monica fork

app/Http/Controllers/DAV/Backend/CalDAV/AbstractCalDAVBackend.php

@@ -0,0 +1,42 @@
+<?php
+
+namespace App\Http\Controllers\DAV\Backend\CalDAV;
+
+use Sabre\DAV\Server as SabreServer;
+use Sabre\CalDAV\Plugin as CalDAVPlugin;
+use Sabre\DAV\Sync\Plugin as DAVSyncPlugin;
+use App\Http\Controllers\DAV\Backend\IDAVBackend;
+use App\Http\Controllers\DAV\Backend\SyncDAVBackend;
+use App\Http\Controllers\DAV\DAVACL\PrincipalBackend;
+
+abstract class AbstractCalDAVBackend implements ICalDAVBackend, IDAVBackend
+{
+    use SyncDAVBackend;
+
+    /**
+     * Get description array.
+     *
+     * @return array
+     */
+    public function getDescription()
+    {
+        $token = DAVSyncPlugin::SYNCTOKEN_PREFIX.$this->refreshSyncToken(null)->id;
+
+        return [
+            'id' => $this->backendUri(),
+            'uri' => $this->backendUri(),
+            'principaluri' => PrincipalBackend::getPrincipalUser($this->user),
+            '{DAV:}sync-token'  => $token,
+            '{'.SabreServer::NS_SABREDAV.'}sync-token' => $token,
+            '{'.CalDAVPlugin::NS_CALENDARSERVER.'}getctag' => $token,
+        ];
+    }
+
+    /**
+     * Get the new exported version of the object.
+     *
+     * @param  mixed  $obj
+     * @return string
+     */
+    abstract protected function refreshObject($obj): string;
+}