Added the api definition and required interfaces also added the addObserver and removeObserver methods.

Author: Samruddhi90

packages/remote-config/src/api.ts

@@ -22,7 +22,10 @@ import {
   LogLevel as RemoteConfigLogLevel,
   RemoteConfig,
   Value,
-  RemoteConfigOptions
+  RemoteConfigOptions,
+  ConfigUpdateObserver,
+  Unsubscribe,
+  ConfigUpdate
 } from './public_types';
 import { RemoteConfigAbortSignal } from './client/remote_config_fetch_client';
 import {
@@ -351,3 +354,22 @@ export async function setCustomSignals(
     );
   }
 }
+/**
+ * Registers a real-time listener for Remote Config updates.
+ *
+ * @param remoteConfig - The {@link RemoteConfig} instance.
+ * @param observer - The {@link ConfigUpdateObserver} to be notified of config updates.
+ * @returns An {@link Unsubscribe} function to remove the listener.
+ *
+ * @public
+ */
+export function onConfigUpdate(
+  remoteConfig: RemoteConfig,
+  observer: ConfigUpdateObserver
+): Unsubscribe {
+  const rc = getModularInstance(remoteConfig) as RemoteConfigImpl;
+  rc._realtimeHandler.addObserver(observer);
+  return () => {
+    rc._realtimeHandler.removeObserver(observer);
+  }
+};

packages/remote-config/src/client/realtime_handler.ts

@@ -0,0 +1,35 @@
+
+import { ConfigUpdateObserver } from "../public_types";
+export class RealtimeHandler {
+    constructor() {
+
+    } 
+    private observers: Set<ConfigUpdateObserver> = new Set<ConfigUpdateObserver>();
+    begineRealtime(){
+        //if observers are present, start the realtime updates
+        if (this.observers.size > 0) {
+           
+        }
+    }
+    /**
+     * Adds an observer to the realtime updates.
+     * @param observer The observer to add.
+     */
+    addObserver(observer: ConfigUpdateObserver) {
+        this.observers.add(observer);
+        console.log("observer added:", this.observers);
+
+        this.begineRealtime();
+    }
+    /**
+     * Removes an observer from the realtime updates.
+     * @param observer The observer to remove.
+     * @returns true if the observer was removed, false if it was not found.
+     */
+    removeObserver(observer: ConfigUpdateObserver) {
+        if (this.observers.has(observer)) {
+            console.log("observer remove:", this.observers);
+            return this.observers.delete(observer);
+        }
+    }
+}

packages/remote-config/src/public_types.ts

@@ -15,8 +15,7 @@
  * limitations under the License.
  */
 
-import { FirebaseApp } from '@firebase/app';
-
+import { FirebaseApp, FirebaseError } from '@firebase/app';
 /**
  * The Firebase Remote Config service interface.
  *
@@ -217,3 +216,39 @@ declare module '@firebase/component' {
     'remote-config': RemoteConfig;
   }
 }
+
+/**
+ * Observer interface for receiving real-time Remote Config update notifications.
+ *
+ * @public
+ */
+export interface ConfigUpdateObserver {
+    // Called when a new ConfigUpdate is available.
+    next: (configUpdate: ConfigUpdate) => void;
+
+    // Called if an error occurs during the stream.
+    error: (error: FirebaseError) => void;
+
+    // Called when the stream is gracefully terminated.
+    complete: () => void;
+}
+
+/**
+ * A function that unsubscribes from a real-time event stream.
+ *
+ * @public
+ */
+export type Unsubscribe = () => void;
+
+/**
+ * Contains information about which keys have been updated.
+ * 
+ * @public
+ */
+export interface ConfigUpdate {
+  /**
+   * Parameter keys whose values have been updated from the currently activated values.
+   * Includes keys that are added, deleted, or whose value, value source, or metadata has changed.
+   */
+  readonly updatedKeys: string[]
+}

packages/remote-config/src/register.ts

@@ -37,6 +37,7 @@ import { ErrorCode, ERROR_FACTORY } from './errors';
 import { RemoteConfig as RemoteConfigImpl } from './remote_config';
 import { IndexedDbStorage, InMemoryStorage } from './storage/storage';
 import { StorageCache } from './storage/storage_cache';
+import { RealtimeHandler } from './client/realtime_handler';
 // This needs to be in the same file that calls `getProvider()` on the component
 // or it will get tree-shaken out.
 import '@firebase/installations';
@@ -107,12 +108,15 @@ export function registerRemoteConfig(): void {
       logger
     );
 
+    const realtimehandler = new RealtimeHandler();
+
     const remoteConfigInstance = new RemoteConfigImpl(
       app,
       cachingClient,
       storageCache,
       storage,
-      logger
+      logger,
+      realtimehandler
     );
 
     // Starts warming cache.

packages/remote-config/src/remote_config.ts

@@ -25,7 +25,7 @@ import { StorageCache } from './storage/storage_cache';
 import { RemoteConfigFetchClient } from './client/remote_config_fetch_client';
 import { Storage } from './storage/storage';
 import { Logger } from '@firebase/logger';
-
+import { RealtimeHandler } from './client/realtime_handler';
 const DEFAULT_FETCH_TIMEOUT_MILLIS = 60 * 1000; // One minute
 const DEFAULT_CACHE_MAX_AGE_MILLIS = 12 * 60 * 60 * 1000; // Twelve hours.
 
@@ -83,6 +83,10 @@ export class RemoteConfig implements RemoteConfigType {
     /**
      * @internal
      */
-    readonly _logger: Logger
+    readonly _logger: Logger,
+    /**
+     * @internal
+     */
+    readonly _realtimeHandler: RealtimeHandler
   ) {}
 }