Adds logic around downloading stories

ts/util/shouldDownloadStory.ts

@@ -0,0 +1,23 @@
+// Copyright 2022 Signal Messenger, LLC
+// SPDX-License-Identifier: AGPL-3.0-only
+
+import type { ConversationAttributesType } from '../model-types.d';
+
+import dataInterface from '../sql/Client';
+
+const MAX_NUM_STORIES_TO_PREFETCH = 5;
+
+export async function shouldDownloadStory(
+  conversation: ConversationAttributesType
+): Promise<boolean> {
+  if (!conversation.hasPostedStory) {
+    return true;
+  }
+
+  const [storyReads, storyCounts] = await Promise.all([
+    dataInterface.countStoryReadsByConversation(conversation.id),
+    dataInterface.getStoryCount(conversation.id),
+  ]);
+
+  return storyReads > 0 && storyCounts <= MAX_NUM_STORIES_TO_PREFETCH;
+}