From 8a078acaa6aa795e80346f7fef5ddf60b7aefc66 Mon Sep 17 00:00:00 2001
From: Ayaan Zaidi <hi@obviy.us>
Date: Thu, 23 Apr 2026 14:19:41 +0530
Subject: [PATCH] perf(telegram): bound forum metadata cache

---
 extensions/telegram/src/bot/helpers.test.ts | 14 +++++++++
 extensions/telegram/src/bot/helpers.ts      | 34 ++++++++++++++++++---
 2 files changed, 44 insertions(+), 4 deletions(-)

diff --git a/extensions/telegram/src/bot/helpers.test.ts b/extensions/telegram/src/bot/helpers.test.ts
index c78cb595cc0..12d0550fcb7 100644
--- a/extensions/telegram/src/bot/helpers.test.ts
+++ b/extensions/telegram/src/bot/helpers.test.ts
@@ -74,6 +74,20 @@ describe("resolveTelegramForumFlag", () => {
     expect(getChat).toHaveBeenCalledTimes(1);
   });
 
+  it("refreshes cached forum metadata from explicit Telegram updates", async () => {
+    const getChat = vi.fn(async () => ({ is_forum: true }));
+    const params = {
+      chatId: -100654,
+      chatType: "supergroup" as const,
+      isGroup: true,
+      getChat,
+    };
+    await expect(resolveTelegramForumFlag(params)).resolves.toBe(true);
+    await expect(resolveTelegramForumFlag({ ...params, isForum: false })).resolves.toBe(false);
+    await expect(resolveTelegramForumFlag(params)).resolves.toBe(false);
+    expect(getChat).toHaveBeenCalledTimes(1);
+  });
+
   it("returns false when forum lookup is unavailable", async () => {
     const getChat = vi.fn(async () => {
       throw new Error("lookup failed");
diff --git a/extensions/telegram/src/bot/helpers.ts b/extensions/telegram/src/bot/helpers.ts
index 2a2f8effaed..89ddbff4518 100644
--- a/extensions/telegram/src/bot/helpers.ts
+++ b/extensions/telegram/src/bot/helpers.ts
@@ -40,7 +40,26 @@ export {
 };
 
 const TELEGRAM_GENERAL_TOPIC_ID = 1;
-const telegramForumFlagByChatId = new Map<string, boolean>();
+const TELEGRAM_FORUM_FLAG_CACHE_MAX_CHATS = 1024;
+const TELEGRAM_FORUM_FLAG_CACHE_TTL_MS = 10 * 60_000;
+const telegramForumFlagByChatId = new Map<string, { expiresAtMs: number; isForum: boolean }>();
+
+function cacheTelegramForumFlag(chatId: string | number, isForum: boolean, nowMs = Date.now()) {
+  const cacheKey = String(chatId);
+  if (
+    !telegramForumFlagByChatId.has(cacheKey) &&
+    telegramForumFlagByChatId.size >= TELEGRAM_FORUM_FLAG_CACHE_MAX_CHATS
+  ) {
+    const oldestKey = telegramForumFlagByChatId.keys().next().value;
+    if (oldestKey !== undefined) {
+      telegramForumFlagByChatId.delete(oldestKey);
+    }
+  }
+  telegramForumFlagByChatId.set(cacheKey, {
+    expiresAtMs: nowMs + TELEGRAM_FORUM_FLAG_CACHE_TTL_MS,
+    isForum,
+  });
+}
 
 function hadUnsafeTelegramText(raw: unknown, sanitized: string): boolean {
   return typeof raw === "string" && raw.trim().length > 0 && sanitized.trim().length === 0;
@@ -67,19 +86,26 @@ export async function resolveTelegramForumFlag(params: {
   getChat?: TelegramGetChat;
 }): Promise<boolean> {
   if (typeof params.isForum === "boolean") {
+    if (params.isGroup && params.chatType === "supergroup") {
+      cacheTelegramForumFlag(params.chatId, params.isForum);
+    }
     return params.isForum;
   }
   if (!params.isGroup || params.chatType !== "supergroup" || !params.getChat) {
     return false;
   }
   const cacheKey = String(params.chatId);
+  const nowMs = Date.now();
   const cached = telegramForumFlagByChatId.get(cacheKey);
-  if (cached !== undefined) {
-    return cached;
+  if (cached && cached.expiresAtMs > nowMs) {
+    return cached.isForum;
+  }
+  if (cached) {
+    telegramForumFlagByChatId.delete(cacheKey);
   }
   try {
     const resolved = extractTelegramForumFlag(await params.getChat(params.chatId)) === true;
-    telegramForumFlagByChatId.set(cacheKey, resolved);
+    cacheTelegramForumFlag(params.chatId, resolved, nowMs);
     return resolved;
   } catch {
     return false;