fix(wallet): one ledger-tip req per pollInterval

WHAT: replaced `delay` operator with `auditTime` operator, which
starts a timer once the first isSettled$ emission, and emits the last
value, ignoring previous ones.
WHY: isSettled$ observable emissions triggered ledger-tip
requests, delayed by pollingInterval.
Flapping isSettled$ caused multiple requests to be done,
because the flapping was delayed.
Throttling is in place for the case where the ledger-tip request is
not resolved yet.

Author: mirceahasegan

packages/wallet/src/services/TipTracker.ts

@@ -5,9 +5,9 @@ import {
   EMPTY,
   Observable,
   Subject,
+  auditTime,
   combineLatest,
   concat,
-  delay,
   distinctUntilChanged,
   exhaustMap,
   filter,
@@ -56,17 +56,19 @@ export class TipTracker extends PersistentDocumentTrackerSubject<Cardano.Tip> {
         // - if it's not settled for maxPollInterval
         combineLatest([
           triggerOrInterval$(syncStatus.isSettled$.pipe(filter((isSettled) => isSettled)), maxPollInterval).pipe(
-            // trigger fetch after some delay once fully synced and online
-            delay(minPollInterval),
+            // Do not allow more than one fetch per minPollInterval.
+            // The first syncStatus starts a minPollInterval timer. Only the latest emission from the minPollInterval
+            // is emitted in case the syncStatus changes multiple times.
+            auditTime(minPollInterval),
             // trigger fetch on start
             startWith(null)
           ),
           connectionStatus$
         ]).pipe(
-          // Throttle syncing by interval, cancel ongoing request on external trigger
           tap(([, connectionStatus]) => {
             logger.debug(connectionStatus === ConnectionStatus.down ? 'Skipping fetch tip' : 'Fetching tip...');
           }),
+          // Throttle syncing by interval, cancel ongoing request on external trigger
           exhaustMap(([, connectionStatus]) =>
             connectionStatus === ConnectionStatus.down
               ? EMPTY

packages/wallet/test/services/TipTracker.test.ts

@@ -2,7 +2,7 @@ import { Cardano } from '@cardano-sdk/core';
 import { ConnectionStatus, TipTracker } from '../../src/services';
 import { InMemoryDocumentStore } from '../../src/persistence';
 import { Milliseconds, SyncStatus } from '../../src';
-import { Observable, firstValueFrom, of } from 'rxjs';
+import { NEVER, Observable, firstValueFrom, of, take, takeUntil, timer } from 'rxjs';
 import { createStubObservable, createTestScheduler } from '@cardano-sdk/util-dev';
 import { dummyLogger } from 'ts-log';
 
@@ -15,6 +15,8 @@ const mockTips = {
   y: { hash: 'hy' }
 } as unknown as Record<string, Cardano.Tip>;
 
+const trueFalse = { f: false, t: true };
+
 describe('TipTracker', () => {
   const pollInterval: Milliseconds = 1; // delays emission after trigger
   let store: InMemoryDocumentStore<Cardano.Tip>;
@@ -26,6 +28,48 @@ describe('TipTracker', () => {
     connectionStatus$ = of(ConnectionStatus.up);
   });
 
+  it('calls the provider as soon as subscribed', () => {
+    createTestScheduler().run(({ cold, expectObservable }) => {
+      const provider$ = createStubObservable<Cardano.Tip>(cold('a|', mockTips));
+      const tracker$ = new TipTracker({
+        connectionStatus$,
+        logger,
+        maxPollInterval: Number.MAX_VALUE,
+        minPollInterval: pollInterval,
+        provider$,
+        store,
+        syncStatus: { isSettled$: NEVER } as unknown as SyncStatus
+      });
+      expectObservable(tracker$.asObservable().pipe(take(1))).toBe('(a|)', mockTips);
+    });
+  });
+
+  it('LW-11686 ignores multiple syncStatus emissions during pollInterval', () => {
+    const poll: Milliseconds = 3;
+    const sync = '-ttt-t----|';
+    const tipT = 'a---b---c-|';
+    // a-b--c-d|
+    createTestScheduler().run(({ cold, expectObservable }) => {
+      const syncStatus: Partial<SyncStatus> = { isSettled$: cold(sync, trueFalse) };
+      const provider$ = createStubObservable<Cardano.Tip>(
+        cold('(a|)', mockTips),
+        cold('(b|)', mockTips),
+        cold('(c|)', mockTips),
+        cold('(d|)', mockTips)
+      );
+      const tracker$ = new TipTracker({
+        connectionStatus$,
+        logger,
+        maxPollInterval: Number.MAX_VALUE,
+        minPollInterval: poll,
+        provider$,
+        store,
+        syncStatus: syncStatus as SyncStatus
+      });
+      expectObservable(tracker$.asObservable().pipe(takeUntil(timer(10)))).toBe(tipT, mockTips);
+    });
+  });
+
   it('calls the provider immediately, only emitting distinct values, with throttling', () => {
     createTestScheduler().run(({ cold, expectObservable }) => {
       const syncStatus: Partial<SyncStatus> = { isSettled$: cold('---a---bc--d|') };
@@ -48,7 +92,7 @@ describe('TipTracker', () => {
     });
   });
 
-  it('starting offline, then coming online should subscribe to provider immediatelly for initial fetch', () => {
+  it('starting offline, then coming online should subscribe to provider immediately for initial fetch', () => {
     createTestScheduler().run(({ cold, hot, expectObservable, expectSubscriptions }) => {
       const connectionStatusOffOn$ = hot('d--u----|', {
         d: ConnectionStatus.down,