Use custom websocket to avoid needing admin privileges.

src/camera-manager/frigate/event-watcher.ts

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+import { HomeAssistant } from '@dermotduffy/custom-card-helpers';
+import { FrigateEventChange, frigateEventChangeSchema } from './types';
+
+export interface FrigateEventWatcherRequest {
+  instanceID: string;
+  matcher?(event: FrigateEventChange): boolean;
+  callback(event: FrigateEventChange): void;
+}
+
+export interface FrigateEventWatcherSubscriptionInterface {
+  subscribe(hass: HomeAssistant, request: FrigateEventWatcherRequest): Promise<void>;
+  unsubscribe(callback: FrigateEventWatcherRequest): void;
+}
+
+type SubscriptionUnsubscribe = () => Promise<void>;
+
+export class FrigateEventWatcher implements FrigateEventWatcherSubscriptionInterface {
+  protected _requests: FrigateEventWatcherRequest[] = [];
+  protected _unsubscribeCallback: Record<string, SubscriptionUnsubscribe> = {};
+
+  public async subscribe(
+    hass: HomeAssistant,
+    request: FrigateEventWatcherRequest,
+  ): Promise<void> {
+    const shouldSubscribe = !this._hasSubscribers(request.instanceID);
+    this._requests.push(request);
+    if (shouldSubscribe) {
+      this._unsubscribeCallback[request.instanceID] =
+        await hass.connection.subscribeMessage<string>(
+          (data) => this._receiveHandler(request.instanceID, data),
+          { type: 'frigate/events/subscribe', instance_id: request.instanceID },
+        );
+    }
+  }
+
+  public async unsubscribe(request: FrigateEventWatcherRequest): Promise<void> {
+    this._requests = this._requests.filter(
+      (existingRequest) => existingRequest !== request,
+    );
+
+    if (!this._hasSubscribers(request.instanceID)) {
+      await this._unsubscribeCallback[request.instanceID]();
+      delete this._unsubscribeCallback[request.instanceID];
+    }
+  }
+
+  protected _hasSubscribers(instanceID: string): boolean {
+    return !!this._requests.filter((request) => request.instanceID === instanceID)
+      .length;
+  }
+
+  protected _receiveHandler(instanceID: string, data: string): void {
+    let json: unknown;
+    try {
+      json = JSON.parse(data);
+    } catch (e) {
+      console.warn('Received non-JSON payload as Frigate event', data);
+      return;
+    }
+
+    const parsedEvent = frigateEventChangeSchema.safeParse(json);
+    if (!parsedEvent.success) {
+      console.warn('Received malformed Frigate event from Home Assistant', data);
+      return;
+    }
+
+    for (const request of this._requests) {
+      if (
+        request.instanceID === instanceID &&
+        (!request.matcher || request.matcher(parsedEvent.data))
+      ) {
+        request.callback(parsedEvent.data);
+      }
+    }
+  }
+}