Leetcode Daily Question Telegram Bot

Warning
End of Maintenance Notice (2023-10-29):
Visit https://t.me/LeetcodeQustionOfToday/720 for more information.

Fetch question of today from Leetcode's GraphQL API and send it to Telegram channel.

Development Notes

Tech Stack

• Python 3
• Serverless
• AWS Lambda
• AWS CloudFormation - Used by Serverless when doing deployment
• AWS CloudWatch - Automatically Setup by Serverless when doing deployment
• AWS S3 - Used by Serverless when doing deployment

Note:
Both Lambda, CloudWatch, and CloudFormation has free tier provided. However for AWS S3, it has only has free tier for limited time.

To check the tier limit, head to https://aws.amazon.com/free/. It is recommended to setup a billing alert by following the documentation on https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/tracking-free-tier-usage.html.

Development Setup

Prerequisites

• Node.js 14 installed
• Python 3 installed
• virtualenv installed

Prepare serverless environment

NPM

npm install serverless@3 --global
npm install

Yarn

yarn global add serverless@3
yarn

Setup Python Virtual Environments

# Create a new virtual environment
virtualenv venv --python=python3

# Activate virtual environment created
. venv/bin/activate

# Install dependencies listed in requirements.txt
pip install -r requirements.txt

Setup Bot to send message

Save a copy of .env and name it as .env.local, place your Telegram bot token and Telegram Chat ID in the configuration file.

Note: Environment variables are used instead of ConfigParser provided by Python since by default AWS Lambda will encrypt environment variables using KMS, and we don't want to store tokens using plain text.

1. How to get a Telegram bot token

1. In Telegram, search for the user @BotFather.
2. Use the command \newbot and choose a name and username for your bot.
3. @BotFather will return you the token of the bot created. Remember to keep it safe!

2. How to get a Telegram chat ID

1. Send a /start command to the telegram bot created in the previous step
2. Visit https://api.telegram.org/bot<BOT_TOKEN>/getUpdates
3. Look at the API response, result[0]['message']['chat']['id'] should contains ID of the chat. Remember to copy the - prefix if exists.

3. Test if Bot token and Chat ID is correct or not

Open Terminal, run the following command. You will need to replace <BOT_TOKEN> and <CHAT_ID> with the one you get in previous steps.

curl -X POST "https://api.telegram.org/bot<BOT_TOKEN>/sendMessage" -d "chat_id=<CHAT_ID>&text=Hello World"

Deployment

Create named AWS profile (for first time deployment)

1. Create new user on AWS, with "Programmatic access"
2. Assign permission to user by "Attaching existing policies directly"
   • In the official Serverless blog, they have introduced serverless-policy generator to help you generate IAM policies.
3. Configure new AWS credientials to use newly created user

   aws configure --profile <PROFILE_NAME>

Deploy to Lambda

# Load environment variables
. load-environment-variables.sh

# Deploy to AWS Lambda using serverless cli
serverless deploy --aws-profile <PROFILE_NAME>

Settings

Add / Edit bot messages

All messages are stored in app/messages.txt, and will be randomly picked when handler is triggered. To update the message sets, simply edit and save the file. Re-deployment is needed for changes to take effect.

Add / Edit stickers

All sticker IDs are stored in app/stickers.txt, and will be randomly picked when handler is triggered. To update the sticker sets, you will need to get the sticker ID by sending stickers to the created bot. Visit https://api.telegram.org/bot<BOT_TOKEN>/getUpdates, stickers ID can be found in the API reponse node result[n]['message']['sticker']['file_id']. Re-deployment is needed for changes to take effect.

Edit bot schedule

Open serverless.yml, edit functions['cron']['schedule']. Syntax reference: https://docs.aws.amazon.com/lambda/latest/dg/services-cloudwatchevents-expressions.html

Test

Testing the handler

Run the following command inside virtual environment:

# Load environment variables
. load-environment-variables.sh

# Execute handler
serverless invoke local -f cron

Others

Delete deployed Lambda function

serverless remove --aws-profile <PROFILE_NAME>