docs: add ST recipe for user re-engagement email

[DOCS-1127]: https://hasurahq.atlassian.net/browse/DOCS-1127?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

PR-URL: https://github.com/hasura/graphql-engine-mono/pull/10376
GitOrigin-RevId: 8ef692770f58ebb8e719d3f5a5bbd9b073e0022a

docs/docs/scheduled-triggers/recipes/abandoned-cart.mdx

@@ -9,6 +9,7 @@ keywords:
   - abandoned cart
   - reminder
   - automated
+sidebar_position: 4
 ---
 
 import Tabs from '@theme/Tabs';

docs/docs/scheduled-triggers/recipes/check-expiration.mdx

@@ -10,6 +10,7 @@ keywords:
   - expiration
   - coupon
   - automated
+sidebar_position: 2
 ---
 
 import Tabs from '@theme/Tabs';

docs/docs/scheduled-triggers/recipes/daily-summary-email.mdx

@@ -10,7 +10,7 @@ keywords:
   - daily
   - summary
   - automated
-sidebar_position: 2
+sidebar_position: 3
 ---
 
 import Tabs from '@theme/Tabs';

docs/docs/scheduled-triggers/recipes/index.mdx

@@ -44,7 +44,13 @@ will help you to implement your own custom logic for triggering any event which
 
 In e-commerce applications, it's a common practice to remind customers about the items they may have added to
 their carts, but then left without checking out. These are generally known as "abandoned carts". Recalling
-customers in this eay can help to improve egangement and conversion rates. This recipe demonstrates how to send a
+customers in this eay can help to improve engagement and conversion rates. This recipe demonstrates how to send a
 gentle email reminder to customers about their carts 24 hours after they added items but didn't complete the purchase.
-The principles used in this example can guide you to design your own custom logic for triggering any event based on a
- time interval. [Check it out](/scheduled-triggers/recipes/abandoned-cart.mdx)!
+The principles used in this example can guide you to design your own custom logic for triggering any event based on 
+a time interval. [Check it out](/scheduled-triggers/recipes/abandoned-cart.mdx)!
+
+ ### User re-engagement email
+
+In applications with a notification system, it's common to send a re-engagement email to users who have not logged in
+for a certain period of time. This recipe shows how to send a re-engagement email to users who have not logged in for
+over a week. [Check it out](/scheduled-triggers/recipes/user-reengagement-email.mdx)!

docs/docs/scheduled-triggers/recipes/user-reengagement-email.mdx

@@ -0,0 +1,302 @@
+---
+title: Using Schedule Triggers for Sending a user re-engagement email
+description: Succinct, tested, and reusable code recipes for common use cases in Hasura.
+sidebar_label: User re-engagement Email
+keywords:
+  - hasura
+  - docs
+  - recipes
+  - scheduled triggers
+  - re-engagement
+  - automated
+sidebar_position: 5
+---
+
+import Tabs from '@theme/Tabs';
+import TabItem from '@theme/TabItem';
+import Thumbnail from '@site/src/components/Thumbnail';
+import SampleAppBlock from '@site/src/components/SampleAppBlock';
+
+# Send a User Re-engagement Email
+
+## Introduction
+
+Scheduled Triggers allows you to schedule business, or other logic to occur at specific times or intervals. In this
+guide, we'll explore how to use Scheduled Triggers to send an email to users if they haven't been active in over a week.
+We'll do this by executing this trigger every morning and seeing which users' `last_seen` property is older than a week.
+If it is, we'll send them an email persuading them to come back to our app.
+
+<SampleAppBlock dependent />
+
+## Prerequisites
+
+Before getting started, ensure that you have the following in place:
+
+- The docs e-commerce sample app deployed to Hasura Cloud.
+- A working SMTP server or email-sending service that you can integrate with to send emails.
+
+:::info Tunneling your webhook endpoint from your local machine
+
+If you plan on using a webhook endpoint hosted on your own machine, ensure that you have a tunneling service such as
+[ngrok](https://ngrok.com/) set up so that your Cloud Project can communicate with your local machine.
+
+:::
+
+## Our model
+
+When sending transactional emails such as this, there are three fundamental components to consider:
+
+- **Your data source**: In your database, which table contains the value that you want to use to determine whether or
+  not to send the email?
+- **Your querying logic**: In your webhook, how will you query your database to determine whether or not to send the
+  email? How will you return information so that you have the correct data to include in the email?
+- **Your email templating**: How will you generate and send the email containing the information you want to send?
+
+Our sample app's database contains, among others, a `users` table that contains a `last_seen` property. We'll use this
+property to determine whether or not to send the email. We'll query the database to find all users whose `last_seen`
+property is older than a week. Then, we'll send an email to each of those users.
+
+## Step 1: Create the Scheduled Event
+
+Head to the Hasura Console of your project and navigate to the "Events" tab. From there, click on the `Cron Triggers`
+item in the sidebar. Then, click `Create`:
+
+<Thumbnail
+  src="/img/scheduled-triggers/scheduled-triggers_getting-started-guide_2.18.0_click-create.png"
+  alt="Hasura Scheduled Trigger architecture"
+  width="1000"
+/>
+
+## Step 2: Configure the Scheduled Event
+
+First, provide a name for your trigger, e.g., `user_reengagement_email`. Then, enter a webhook URL that will be called
+when the event is triggered. This webhook will be responsible for sending the re-engagement emails and can be hosted
+anywhere, and written in any language, you like.
+
+The route on our webhook we'll use is `/user-reengagement-email`. Below, we'll see what this looks like with a service
+like [ngrok](https://ngrok.com/), but the format will follow this template:
+
+```text
+https://<your-webhook-url>/user-reengagement-email
+```
+
+:::info Tunneling your webhook endpoint to your local machine
+
+You'll need to use a tunneling service such as [ngrok](https://ngrok.com/) to expose a webhook endpoint running on your
+local machine to the internet and Hasura Cloud. This will give you a public URL that will forward requests to your local
+machine and the server which we'll configure below.
+
+You'll need to modify your webhook URL to use the public URL provided by ngrok.
+
+After installing ngrok and
+[authenticating](https://ngrok.com/docs/secure-tunnels/ngrok-agent/tunnel-authtokens/#:~:text=Once%20you've%20signed%20up,make%20installing%20the%20authtoken%20simple.),
+you can do this by running:
+
+```bash
+ngrok http 4000
+```
+
+Then, copy the `Forwarding` value for use in our webhook 🎉
+
+:::
+
+Next, we'll configure the cron expression that will trigger the event. In this example, we want to send requests at 9:00
+AM every morning. We can do that with the following cron expression:
+
+```
+0 9 * * *
+```
+
+Our trigger must also have a payload. This payload will be sent to the webhook endpoint when the event is triggered. We
+don't have to include any data in the payload, but we can if we want to. In this example, we'll simply send a
+`trigger_type` property categorizing the event as a `daily_recap_email`. In the `Payload` section, enter the following:
+
+```json
+{
+  "trigger_type": "user_reengagement_email"
+}
+```
+
+Under `Advanced Settings`, we can configure the headers that will be sent with the request. We'll add an
+`authentication` header to prevent abuse of the endpoint and ensure that only Hasura can trigger the event. Set the
+`Key` as `secret-authorization-string` and the `Value` as `super_secret_string_123`.
+
+<Thumbnail
+  src="/img/scheduled-triggers/scheduled-triggers_recipes_review-request_auth-header.png"
+  alt="Hasura Scheduled Trigger architecture"
+  width="1000"
+/>
+
+Also, change the `Request Transform Options` to `POST` so that the payload is sent in the request body.
+
+Finally, click the `Add Cron Trigger` button to create the Scheduled Event.
+
+## Step 3: Create a webhook to handle the request
+
+Whenever a cron job is triggered, Hasura will send a request to the webhook URL you provided. In this example, we're
+simply going to send a `POST` request. Our webhook will parse the request, ensure the header is correct, and then query
+the database to determine which users will receive an email.
+
+Below, we've written an example of webhook in JavaScript. As we established earlier, this runs on port `4000`. If you're
+attempting to run this locally, follow the instructions below. If you're running this in a hosted environment, use this
+code as a guide to write your own webhook.
+
+Init a new project with `npm init` and install the following dependencies:
+
+```bash
+npm install express nodemailer
+```
+
+<details>
+<summary>
+Then, create a new file called <code>index.js</code> and add the following code:
+</summary>
+
+```javascript
+const express = require('express');
+const nodemailer = require('nodemailer');
+
+const app = express();
+
+// Create a Nodemailer transporter using Ethereal email service
+// Ideally, this configuration would be stored somewhere else
+nodemailer.createTestAccount((err, account) => {
+  if (err) {
+    console.error('Failed to create a testing account. ' + err.message);
+    return process.exit(1);
+  }
+
+  // If all goes as planned, here's the console telling us we're 👍
+  console.log('Credentials obtained, listening on the webhook...');
+
+  // Create a transporter object for nodemailer
+  const transporter = nodemailer.createTransport({
+    host: 'smtp.ethereal.email',
+    port: 587,
+    secure: false,
+    auth: {
+      user: account.user,
+      pass: account.pass,
+    },
+  });
+
+  // Function to fetch inactive users
+  async function getInactiveUsers(oneWeekAgo) {
+    const response = await fetch('<YOUR_CLOUD_PROJECT_ENDPOINT>', {
+      method: 'POST',
+      headers: {
+        'Content-Type': 'application/json',
+        'x-hasura-admin-secret': '<YOUR_ADMIN_SECRET>',
+      },
+      body: JSON.stringify({
+        query: `
+          query InactiveUsersQuery($oneWeekAgo: timestamptz!) {
+            users(where: {last_seen: {_lt: $oneWeekAgo}}) {
+              id
+              name
+              email
+            }
+          }
+        `,
+        variables: {
+          oneWeekAgo: oneWeekAgo.toISOString(),
+        },
+      }),
+    });
+
+    const { data } = await response.json();
+    return data.users;
+  }
+
+  // Function to send emails to inactive users
+  async function sendInactiveUserEmails(transporter, inactiveUsers) {
+    for (const user of inactiveUsers) {
+      // Create a message object
+      const message = {
+        from: 'SuperStore.com <sender@SuperStore.com>',
+        to: `${user.name} <${user.email}>`,
+        subject: `We miss you, ${user.name.split(' ')[0]}!`,
+        text: `Hi ${
+          user.name.split(' ')[0]
+        }, it's been over one week since you last logged in. Come back and do things!`,
+      };
+
+      // Send the message using the Nodemailer transporter
+      const info = await transporter.sendMail(message);
+
+      // Log the message info
+      console.log(`\nMessage sent to ${user.name}: ${nodemailer.getTestMessageUrl(info)}`);
+    }
+  }
+
+  // Our route for the webhook
+  app.post('/user-reengagement-email', async (req, res) => {
+    // confirm the auth header is correct — ideally, you'd keep the secret in an environment variable
+    const authHeader = req.headers['secret-authorization-string'];
+    if (authHeader !== 'super_secret_string_123') {
+      return res.status(401).json({
+        message: 'Unauthorized',
+      });
+    }
+
+    // Calculate the date one week ago
+    const oneWeekAgo = new Date();
+    oneWeekAgo.setDate(oneWeekAgo.getDate() - 7);
+
+    // Fetch the list of users who haven't logged in for over one week
+    const inactiveUsers = await getInactiveUsers(oneWeekAgo);
+
+    // Send emails to inactive users
+    await sendInactiveUserEmails(transporter, inactiveUsers);
+
+    // Return a JSON response to the client
+    res.json({
+      message: 'Inactive user emails sent!',
+    });
+  });
+
+  // Start the server
+  app.listen(4000, () => {
+    console.log('Server started on port 4000');
+  });
+});
+```
+
+</details>
+
+You can run the server by running `node index.js` in your terminal. If you see the message
+`Webhook server is running on port 4000`, you're good to go!
+
+## Step 4: Test the setup
+
+First, let's update one of the users in our database to have a `last_seen` property that is older than a week. In the
+Hasura Console, navigate to the `Data` tab and click on the `users` table. Then, click on the `Modify` tab and update
+the `last_seen` property of one of the users to be older than a week:
+
+```plaintext
+YYYY-MM-DDTHH:MM:SS.SSSZ
+```
+
+:::info Timestamp formatting
+
+The format above is the [ISO 8601 format](https://www.iso.org/iso-8601-date-and-time-format.html). Enter the year,
+month, day, hour, minute, second, and millisecond of the date you want to set. For example, if you want to set the date
+to `2023-10-10`, you would enter `2023-10-10T00:00:00.000Z`.
+
+:::
+
+With your server running, Hasura should start hitting our endpoint. As we set our cron expression to `0 9 * * *`, the
+webhook will be triggered at 9:00 AM every day. We don't want to wait that long to test it. For now, update the
+expression to `* * * * *` to trigger the webhook every minute. Then, check out your invocation logs in the Hasura
+Console to verify that the webhook was triggered successfully and your terminal to see the outputted information and
+link to a handy email 🎉
+
+<Thumbnail
+  src="/img/scheduled-triggers/scheduled-triggers_recipes_review-terminal.png"
+  alt="Hasura Scheduled Trigger architecture"
+  width="1000"
+/>
+
+Feel free to customize the webhook implementation based on your specific requirements and chosen email sending service.
+Remember to handle error scenarios, implement necessary validations, and add appropriate security measures to your
+webhook endpoint.