fix(splash): reuse latest chat message preview

src/lib/chat/splash_latest_message.ts

@@ -1,9 +1,47 @@
 "use client";
 
 import { getChatRepository } from "@/data/repositories/chat_repository";
+import {
+  resolveChatCacheOwnerKey,
+  type ChatCacheIdentityResolver,
+} from "@/data/repositories/chat_cache_identity";
 import { Result, type Result as ResultT } from "@/utils";
 
-import { getSplashLatestMessagePreview } from "./splash_latest_message_preview";
+import type { SplashLatestMessageCache } from "./splash_latest_message_cache";
+import { getLatestSplashMessagePreview } from "./splash_latest_message_preview";
+
+export interface LoadSplashLatestMessagePreviewInput {
+  cache: SplashLatestMessageCache;
+  fetchPreview?: () => Promise<ResultT<string | null>>;
+  resolveIdentity?: ChatCacheIdentityResolver;
+}
+
+export async function resolveSplashLatestMessageCacheIdentity(): Promise<
+  string | null
+> {
+  const result = await resolveChatCacheOwnerKey();
+  return Result.isOk(result) ? result.data : null;
+}
+
+export async function loadSplashLatestMessagePreview({
+  cache,
+  fetchPreview = fetchSplashLatestMessagePreview,
+  resolveIdentity = resolveChatCacheOwnerKey,
+}: LoadSplashLatestMessagePreviewInput): Promise<ResultT<string | null>> {
+  const identityResult = await resolveIdentity();
+  const identity = Result.isOk(identityResult) ? identityResult.data : null;
+
+  if (identity) {
+    const cached = cache.get(identity);
+    if (cached) return Result.ok(cached.message);
+  }
+
+  const result = await fetchPreview();
+  if (identity && Result.isOk(result)) {
+    cache.set(identity, result.data);
+  }
+  return result;
+}
 
 export async function fetchSplashLatestMessagePreview(): Promise<
   ResultT<string | null>
@@ -11,6 +49,5 @@ export async function fetchSplashLatestMessagePreview(): Promise<
   const result = await getChatRepository().getHistory(1, 0);
   if (Result.isErr(result)) return Result.err(result.error);
 
-  const latestMessage = result.data.messages.at(-1) ?? null;
-  return Result.ok(getSplashLatestMessagePreview(latestMessage));
+  return Result.ok(getLatestSplashMessagePreview(result.data.messages));
 }