make clients of sse service observable

src/homepage.ts

@@ -1,8 +1,8 @@
-import { API_HA_DeskPosition } from "./homeassistant";
-import { TidalGetCurrent } from "./tidal";
+import { type API_HA_DeskPosition } from "./homeassistant";
+import { type TidalGetCurrent } from "./tidal";
 
 export type FullInformation = {
 	ha_desk_position: API_HA_DeskPosition | null;
 	ha_temp: string | null;
 	tidal_current: TidalGetCurrent | null;
-}
+};

src/sse.ts

@@ -4,22 +4,51 @@ import { logInfo } from "./logger.js";
 export type SseClient = {
 	id: UUID;
 	send: (data: SseEvent) => void;
-}
+};
 
 export type SseEvent = {
 	type: string;
 	data?: unknown;
 	message?: string;
-}
+};
+
+export type SseClientChangeEvent = {
+	type: "add" | "remove";
+	clientId: string;
+	clientCount: number;
+};
+
+export type SseClientChangeCallback = (event: SseClientChangeEvent) => void;
 
 export class SseService {
 	private clients: Map<string, SseClient> = new Map();
+	private clientChangeCallbacks: SseClientChangeCallback[] = [];
+
+	onClientChange(callback: SseClientChangeCallback): () => void {
+		this.clientChangeCallbacks.push(callback);
+		return () => {
+			this.clientChangeCallbacks = this.clientChangeCallbacks.filter(
+				(cb) => cb !== callback,
+			);
+		};
+	}
+
+	private emitClientChange(event: SseClientChangeEvent): void {
+		for (const callback of this.clientChangeCallbacks) {
+			callback(event);
+		}
+	}
 
 	addClient(client: SseClient): void {
 		this.clients.set(client.id, client);
 		logInfo(
 			`SSE client connected: ${client.id}. Total clients: ${this.clients.size}`,
 		);
+		this.emitClientChange({
+			type: "add",
+			clientId: client.id,
+			clientCount: this.clients.size,
+		});
 	}
 
 	removeClient(clientId: string): void {
@@ -27,12 +56,17 @@ export class SseService {
 		logInfo(
 			`SSE client disconnected: ${clientId}. Total clients: ${this.clients.size}`,
 		);
+		this.emitClientChange({
+			type: "remove",
+			clientId,
+			clientCount: this.clients.size,
+		});
 	}
 
 	notifyClients(event: SseEvent): void {
 		for (const client of this.clients.values()) {
-	    client.send(event);
-	  }
+			client.send(event);
+		}
 	}
 
 	getClientCount(): number {