a

src/lib/stores/cache/messages.ts

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+import { getMessageById } from "$lib/api/message";
+import { isErrorResponse, type Message } from "$lib/types";
+import { get, writable, type Writable } from "svelte/store";
+
+const messagesCache: Writable<Map<number, Message>> = writable(new Map<number, Message>());
+
+const runningCaches = new Set();
+
+export function addMessageToCache(message: Message) {
+    messagesCache.update((messages) => messages.set(message.id, message));
+}
+
+export async function getCachedMessage(messageId: number): Promise<Message | null> {
+    const cached = get(messagesCache).get(messageId);
+
+    if (cached)
+        return cached;
+
+    if (runningCaches.has(messageId))
+        return await new Promise((resolve) => {
+            messagesCache.subscribe((users) => {
+
+                const user = users.get(messageId);
+                if (user) {
+                    runningCaches.delete(messageId);
+                    resolve(user);
+                }
+            });
+        });
+
+    runningCaches.add(messageId);
+
+    const response = await getMessageById(messageId);
+    if (isErrorResponse(response))
+        return null;
+
+    const message = response as Message;
+
+    addMessageToCache(message);
+
+    return message;
+}