internal: incomplete vault systems behind feature flag (#2340)

packages/services/src/Domain/Singleton/SingletonManagerInterface.ts

@@ -0,0 +1,26 @@
+import { DecryptedItemInterface, ItemContent, Predicate, PredicateInterface } from '@standardnotes/models'
+import { ContentType } from '@standardnotes/common'
+
+export interface SingletonManagerInterface {
+  findSingleton<T extends DecryptedItemInterface>(
+    contentType: ContentType,
+    predicate: PredicateInterface<T>,
+  ): T | undefined
+
+  findOrCreateContentTypeSingleton<
+    C extends ItemContent = ItemContent,
+    T extends DecryptedItemInterface<C> = DecryptedItemInterface<C>,
+  >(
+    contentType: ContentType,
+    createContent: ItemContent,
+  ): Promise<T>
+
+  findOrCreateSingleton<
+    C extends ItemContent = ItemContent,
+    T extends DecryptedItemInterface<C> = DecryptedItemInterface<C>,
+  >(
+    predicate: Predicate<T>,
+    contentType: ContentType,
+    createContent: ItemContent,
+  ): Promise<T>
+}