// Copyright 2024 Google LLC

//

// 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.

// This is a generated sample, using the typeless sample bot. Please

// look for the source TypeScript sample (.ts) for modifications.

'use strict';

/**

* This sample demonstrates how to perform basic operations on

* subscriptions with the Google Cloud Pub/Sub API.

*

* For more information, see the README.md under /pubsub and the documentation

* at https://cloud.google.com/pubsub/docs.

*/

// sample-metadata:

// title: Optimistic Subscribe

// description: Listens for messages from a subscription, creating it if needed.

// usage: node optimisticSubscribe.js <subscription-name-or-id> <topic-name-or-id> [timeout-in-seconds]

// [START pubsub_optimistic_subscribe]

/**

* TODO(developer): Uncomment these variables before running the sample.

*/

// const subscriptionNameOrId = 'YOUR_SUBSCRIPTION_NAME_OR_ID';

// const topicNameOrId = 'YOUR_TOPIC_NAME_OR_ID';

// const timeout = 60;

// Imports the Google Cloud client library

const {PubSub} = require('@google-cloud/pubsub');

// Creates a client; cache this for further use

const pubSubClient = new PubSub();

function optimisticSubscribe(subscriptionNameOrId, topicNameOrId, timeout) {

// Try using an existing subscription

let subscription = pubSubClient.subscription(subscriptionNameOrId);

// Create an event handler to handle messages

let messageCount = 0;

const messageHandler = message => {

console.log(`Received message ${message.id}:`);

console.log(`\tData: ${message.data}`);

console.log(`\tAttributes: ${message.attributes}`);

messageCount += 1;

// "Ack" (acknowledge receipt of) the message

message.ack();

};

// Set an error handler so that we're notified if the subscription doesn't

// already exist.

subscription.on('error', async e => {

// Resource Not Found

if (e.code === 5) {

console.log('Subscription not found, creating it');

await pubSubClient.createSubscription(

topicNameOrId,

subscriptionNameOrId,

);

// Refresh our subscriber object and re-attach the message handler.

subscription = pubSubClient.subscription(subscriptionNameOrId);

subscription.on('message', messageHandler);

}

});

// Listen for new messages until timeout is hit; this will attempt to

// open the actual subscriber streams. If it fails, the error handler

// above will be called.

subscription.on('message', messageHandler);

// Wait a while for the subscription to run. (Part of the sample only.)

setTimeout(() => {

subscription.removeListener('message', messageHandler);

console.log(`${messageCount} message(s) received.`);

}, timeout * 1000);

}

// [END pubsub_optimistic_subscribe]

function main(

subscriptionNameOrId = 'YOUR_SUBSCRIPTION_NAME_OR_ID',

topicNameOrId = 'YOUR_TOPIC_NAME_OR_ID',

timeout = 60,

) {

timeout = Number(timeout);

optimisticSubscribe(subscriptionNameOrId, topicNameOrId, timeout);

}

main(...process.argv.slice(2));