Self-repairing message counter

ts/util/incrementMessageCounter.ts

@@ -1,16 +1,57 @@
 // Copyright 2021 Signal Messenger, LLC
 // SPDX-License-Identifier: AGPL-3.0-only
 
-import { debounce } from 'lodash';
+import { debounce, isNumber } from 'lodash';
+
+import { strictAssert } from './assert';
+import Data from '../sql/Client';
 
 let receivedAtCounter: number | undefined;
 
-export function incrementMessageCounter(): number {
-  if (!receivedAtCounter) {
-    receivedAtCounter =
-      Number(localStorage.getItem('lastReceivedAtCounter')) || Date.now();
+export async function initializeMessageCounter(): Promise<void> {
+  strictAssert(
+    receivedAtCounter === undefined,
+    'incrementMessageCounter: already initialized'
+  );
+
+  const storedCounter = Number(localStorage.getItem('lastReceivedAtCounter'));
+  const dbCounter = await Data.getMaxMessageCounter();
+
+  if (isNumber(dbCounter) && isNumber(storedCounter)) {
+    window.log.info(
+      'initializeMessageCounter: picking max of db/stored counters'
+    );
+    receivedAtCounter = Math.max(dbCounter, storedCounter);
+
+    if (receivedAtCounter !== storedCounter) {
+      window.log.warn(
+        'initializeMessageCounter: mismatch between db/stored counters'
+      );
+    }
+  } else if (isNumber(storedCounter)) {
+    window.log.info('initializeMessageCounter: picking stored counter');
+    receivedAtCounter = storedCounter;
+  } else if (isNumber(dbCounter)) {
+    window.log.info(
+      'initializeMessageCounter: picking fallback counter from the database'
+    );
+    receivedAtCounter = dbCounter;
+  } else {
+    window.log.info('initializeMessageCounter: defaulting to Date.now()');
+    receivedAtCounter = Date.now();
   }
 
+  if (storedCounter !== receivedAtCounter) {
+    localStorage.setItem('lastReceivedAtCounter', String(receivedAtCounter));
+  }
+}
+
+export function incrementMessageCounter(): number {
+  strictAssert(
+    receivedAtCounter !== undefined,
+    'incrementMessageCounter: not initialized'
+  );
+
   receivedAtCounter += 1;
   debouncedUpdateLastReceivedAt();