Expand types, add type guards, flesh out futures position example

src/util/type-guards.ts

@@ -0,0 +1,73 @@
+import {
+  WsAccountSnapshotUMCBL,
+  WsBaseEvent,
+  WSPositionSnapshotUMCBL,
+  WsSnapshotAccountEvent,
+  WsSnapshotChannelEvent,
+  WsSnapshotPositionsEvent,
+} from '../types';
+
+/** TypeGuard: event has a string "action" property */
+function isWsEvent(event: unknown): event is WsBaseEvent {
+  return (
+    typeof event === 'object' &&
+    event &&
+    typeof event['action'] === 'string' &&
+    event['data']
+  );
+}
+
+/** TypeGuard: event has "action === snapshot" */
+function isWsSnapshotEvent(event: unknown): event is WsBaseEvent<'snapshot'> {
+  return isWsEvent(event) && event.action === 'snapshot';
+}
+
+/** TypeGuard: event has a string channel name */
+function isWsChannelEvent(event: WsBaseEvent): event is WsSnapshotChannelEvent {
+  if (
+    typeof event['arg'] === 'object' &&
+    event.arg &&
+    typeof event?.arg['channel'] === 'string'
+  ) {
+    return true;
+  }
+  return false;
+}
+
+/** TypeGuard: event is an account update (balance) */
+export function isWsAccountSnapshotEvent(
+  event: unknown
+): event is WsSnapshotAccountEvent {
+  return (
+    isWsSnapshotEvent(event) &&
+    isWsChannelEvent(event) &&
+    event.arg.channel === 'account' &&
+    Array.isArray(event.data)
+  );
+}
+
+/** TypeGuard: event is a positions update */
+export function isWsPositionsSnapshotEvent(
+  event: unknown
+): event is WsSnapshotPositionsEvent {
+  return (
+    isWsSnapshotEvent(event) &&
+    isWsChannelEvent(event) &&
+    event.arg.channel === 'positions' &&
+    Array.isArray(event.data)
+  );
+}
+
+/** TypeGuard: event is a UMCBL account update (balance) */
+export function isWsFuturesAccountSnapshotEvent(
+  event: unknown
+): event is WsAccountSnapshotUMCBL {
+  return isWsAccountSnapshotEvent(event) && event.arg.instType === 'umcbl';
+}
+
+/** TypeGuard: event is a UMCBL positions update */
+export function isWsFuturesPositionsSnapshotEvent(
+  event: unknown
+): event is WSPositionSnapshotUMCBL {
+  return isWsPositionsSnapshotEvent(event) && event.arg.instType === 'umcbl';
+}