Optimize heartbeat retrievals (#2590)

packages/api-derive/src/imOnline/receivedHeartbeats.ts

@@ -13,6 +13,25 @@ import { BN_ZERO } from '@polkadot/util';
 
 import { memo } from '../util';
 
+function mapResult ([result, validators, heartbeats, numBlocks]: [DeriveHeartbeats, AccountId[], Option<Bytes>[], u32[]]): DeriveHeartbeats {
+  validators.forEach((validator, index): void => {
+    const validatorId = validator.toString();
+    const blockCount = numBlocks[index];
+    const hasMessage = !heartbeats[index].isEmpty;
+    const prev = result[validatorId];
+
+    if (!prev || prev.hasMessage !== hasMessage || !prev.blockCount.eq(blockCount)) {
+      result[validatorId] = {
+        blockCount,
+        hasMessage,
+        isOnline: hasMessage || blockCount.gt(BN_ZERO)
+      };
+    }
+  });
+
+  return result;
+}
+
 /**
  * @description Return a boolean array indicating whether the passed accounts had received heartbeats in the current session
  */
@@ -20,8 +39,9 @@ export function receivedHeartbeats (instanceId: string, api: ApiInterfaceRx): ()
   return memo(instanceId, (): Observable<DeriveHeartbeats> =>
     api.query.imOnline?.receivedHeartbeats
       ? api.derive.staking.overview().pipe(
-        switchMap(({ currentIndex, validators }): Observable<[AccountId[], Option<Bytes>[], u32[]]> =>
+        switchMap(({ currentIndex, validators }): Observable<[DeriveHeartbeats, AccountId[], Option<Bytes>[], u32[]]> =>
           combineLatest([
+            of({}),
             of(validators),
             api.query.imOnline.receivedHeartbeats.multi<Option<Bytes>>(
               validators.map((_address, index) => [currentIndex, index])),
@@ -29,16 +49,8 @@ export function receivedHeartbeats (instanceId: string, api: ApiInterfaceRx): ()
               validators.map((address) => [currentIndex, address]))
           ])
         ),
-        map(([validators, heartbeats, numBlocks]): DeriveHeartbeats =>
-          validators.reduce((result: DeriveHeartbeats, validator, index): DeriveHeartbeats => ({
-            ...result,
-            [validator.toString()]: {
-              blockCount: numBlocks[index],
-              hasMessage: !heartbeats[index].isEmpty,
-              isOnline: !heartbeats[index].isEmpty || numBlocks[index].gt(BN_ZERO)
-            }
-          }), {})
-        )
+        map(mapResult)
       )
-      : of({}));
+      : of({})
+  );
 }