index.js

/**
 * Copyright 2023 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import {initializeApp} from "firebase-admin/app";
import {getAuth} from "firebase-admin/auth";
import {getDatabase} from "firebase-admin/database";
import {getMessaging} from "firebase-admin/messaging";
import {log, warn} from "firebase-functions/logger";
import {onValueWritten} from "firebase-functions/v2/database";

initializeApp();
const auth = getAuth();
const db = getDatabase();
const messaging = getMessaging();

/**
 * Triggers when a user gets a new follower and sends a notification. Followers
 * add a flag to `/followers/{followedUid}/{followerUid}`. Users save their
 * device notification tokens to
 * `/users/{followedUid}/notificationTokens/{notificationToken}`.
 */
export const sendFollowerNotification = onValueWritten(
    "/followers/{followedUid}/{followerUid}",
    async (event) => {
      // If un-follow we exit the function.
      if (!event.data.after.val()) {
        log(`User ${event.params.followerUid} unfollowed` +
            ` user ${event.params.followedUid} :(`);
        return;
      }

      log(`User ${event.params.followerUid} is now following` +
         ` user ${event.params.followedUid}`);
      const tokensRef =
        db.ref(`/users/${event.params.followedUid}/notificationTokens`);
      const notificationTokens = await tokensRef.get();
      if (!notificationTokens.hasChildren()) {
        log("There are no tokens to send notifications to.");
        return;
      }

      log(`There are ${notificationTokens.numChildren()} tokens` +
          " to send notifications to.");
      const followerProfile = await auth.getUser(event.params.followerUid);

      // Notification details.
      const notification = {
        title: "You have a new follower!",
        body: (followerProfile.displayName ?? "Someone") +
                " is now following you.",
        image: followerProfile.photoURL ?? "",
      };

      // Send notifications to all tokens.
      const messages = [];
      notificationTokens.forEach((child) => {
        messages.push({
          token: child.key,
          notification: notification,
        });
      });
      const batchResponse = await messaging.sendEach(messages);

      if (batchResponse.failureCount < 1) {
        // Messages sent sucessfully. We're done!
        log("Messages sent.");
        return;
      }
      warn(`${batchResponse.failureCount} messages weren't sent.`,
          batchResponse);

      // Clean up the tokens that are not registered any more.
      for (let i = 0; i < batchResponse.responses.length; i++) {
        const errorCode = batchResponse.responses[i].error?.code;
        const errorMessage = batchResponse.responses[i].error?.message;
        if ((errorCode === "messaging/invalid-registration-token") ||
            (errorCode === "messaging/registration-token-not-registered") ||
            (errorCode === "messaging/invalid-argument" &&
              errorMessage ===
              "The registration token is not a valid FCM registration token")) {
          log(`Removing invalid token: ${messages[i].token}`);
          await tokensRef.child(messages[i].token).remove();
        }
      }
    });