Telegram: persist polling update offsets

Closes #739

src/telegram/update-offset-store.ts

@@ -0,0 +1,89 @@
+import crypto from "node:crypto";
+import fs from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+
+import { resolveStateDir } from "../config/paths.js";
+
+const STORE_VERSION = 1;
+
+type TelegramUpdateOffsetState = {
+  version: number;
+  lastUpdateId: number | null;
+};
+
+function normalizeAccountId(accountId?: string) {
+  const trimmed = accountId?.trim();
+  if (!trimmed) return "default";
+  return trimmed.replace(/[^a-z0-9._-]+/gi, "_");
+}
+
+function resolveTelegramUpdateOffsetPath(
+  accountId?: string,
+  env: NodeJS.ProcessEnv = process.env,
+): string {
+  const stateDir = resolveStateDir(env, os.homedir);
+  const normalized = normalizeAccountId(accountId);
+  return path.join(stateDir, "telegram", `update-offset-${normalized}.json`);
+}
+
+function safeParseState(raw: string): TelegramUpdateOffsetState | null {
+  try {
+    const parsed = JSON.parse(raw) as TelegramUpdateOffsetState;
+    if (parsed?.version !== STORE_VERSION) return null;
+    if (
+      parsed.lastUpdateId !== null &&
+      typeof parsed.lastUpdateId !== "number"
+    ) {
+      return null;
+    }
+    return parsed;
+  } catch {
+    return null;
+  }
+}
+
+export async function readTelegramUpdateOffset(params: {
+  accountId?: string;
+  env?: NodeJS.ProcessEnv;
+}): Promise<number | null> {
+  const filePath = resolveTelegramUpdateOffsetPath(
+    params.accountId,
+    params.env,
+  );
+  try {
+    const raw = await fs.readFile(filePath, "utf-8");
+    const parsed = safeParseState(raw);
+    return parsed?.lastUpdateId ?? null;
+  } catch (err) {
+    const code = (err as { code?: string }).code;
+    if (code === "ENOENT") return null;
+    return null;
+  }
+}
+
+export async function writeTelegramUpdateOffset(params: {
+  accountId?: string;
+  updateId: number;
+  env?: NodeJS.ProcessEnv;
+}): Promise<void> {
+  const filePath = resolveTelegramUpdateOffsetPath(
+    params.accountId,
+    params.env,
+  );
+  const dir = path.dirname(filePath);
+  await fs.mkdir(dir, { recursive: true, mode: 0o700 });
+  const tmp = path.join(
+    dir,
+    `${path.basename(filePath)}.${crypto.randomUUID()}.tmp`,
+  );
+  const payload: TelegramUpdateOffsetState = {
+    version: STORE_VERSION,
+    lastUpdateId: params.updateId,
+  };
+  await fs.writeFile(tmp, `${JSON.stringify(payload, null, 2)}\n`, {
+    encoding: "utf-8",
+  });
+  await fs.chmod(tmp, 0o600);
+  await fs.rename(tmp, filePath);
+}