feat: harmonize mailbox messages

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

lib/Stores/MessageStore.php

@@ -145,6 +145,25 @@ class MessageStore
         return $uids;
     }
 
+    /**
+     * List the flags of every message cached for a mailbox.
+     *
+     * @return array<int, list<string>> set flags keyed by UID
+     */
+    public function flags(string $serviceId, string $mailbox, int $uidValidity): array
+    {
+        $cursor = $this->dataStore->selectCollection(self::COLLECTION_NAME)->find(
+            ['sid' => $serviceId, 'mailbox' => $mailbox, 'uidValidity' => $uidValidity],
+            ['projection' => ['uid' => 1, 'flags' => 1]],
+        );
+
+        $flags = [];
+        foreach ($cursor as $document) {
+            $flags[(int) $document['uid']] = array_values(array_map('strval', (array) ($document['flags'] ?? [])));
+        }
+        return $flags;
+    }
+
     /**
      * Replace the flags of a message.
      *