Tutorial: Building a Verifiable, Automated Daily Lottery with Hardhat and Chronos

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Tutorial: Deploy and Verify an Automated Daily Lottery with Hardhat & Chronos

Hello Helios Community!

Here is a quick-start guide to deploying a fully automated, decentralized daily lottery on the Helios Testnet.

This tutorial shows you how to use Hardhat to deploy and verify a smart contract, and then use Chronos, the native scheduling service, to have it automatically draw a winner every 24 hours. The full source code is available on GitHub for those who want to dive deeper.

Quick Start Guide

This guide will get you up and running in minutes.

1. Prerequisites

  • Node.js (v18 or later)
  • MetaMask browser extension
  • A wallet funded with testnet HLS from the Helios Faucet.

2. Setup

First, clone the project repository and install the necessary dependencies.

git clone https://github.com/azrim/helios-lottery.git

cd helios-lottery

npm install

Next, configure your environment file. This will store your private key for deploying the contract.

cp .env.example .env

Now, open the new .env file and add your MetaMask private key.

3. Compile & Deploy

Run the following commands to compile and then deploy the AutomatedDailyLottery smart contract to the Helios Testnet.

  • Compile the contract
    • npx hardhat compile
  • Deploy the contract
    • npx hardhat run scripts/deploy.js --network helios_testnet

    After deployment, the script will print the new contract's address. Copy this address for the next steps.

    4. Verify the Smart Contract

    Verifying your contract on a block explorer is a crucial step that builds trust and transparency.

    Run the helper script to generate the necessary verification files. The script will prompt you to enter the contract address you just copied.

    npx hardhat run scripts/extract-input.js

    This script creates an output directory containing a verify-input.json file and a detailed markdown tutorial named verify-smart-contracts.md. Open the markdown file and follow the simple steps to verify your contract on the Helios Explorer.

    5. Schedule the Task with Chronos

    Now that your contract is verified, you can tell Chronos to call the drawWinner function every 24 hours.

    1. Open the file scripts/schedule.js.
    2. Replace the placeholder YOUR_DEPLOYED_CONTRACT_ADDRESS with your actual contract address.
    3. Run the scheduling script:
    npx hardhat run scripts/schedule.js --network helios_testnet

    This script calls the Chronos precompile to register the automated task and saves the cronId and cronWallet address to your contract for easy on-chain verification.

    How to Verify Your Automated Task

    You can get on-chain proof that your task is scheduled and funded.

    1. Go to the Helios Explorer and search for your deployed lottery contract address.
    2. Select the "Read Contract" tab.
    3. Find the getCronTaskInfo function and click "Query".

    You will see the cronId, the cronWallet address, and a cronWalletBalance of 1 HLS (in wei). This confirms the task is scheduled!

    Successfully deploying and scheduling a Chronos task also earns you XP on the testnet!

    Chronos Deploy Achievement XP Notification
    Chronos Deploy Achievement XP Notification929×231 25 KB

    That's it! Your fully automated and verified DApp is now running on Helios.

    For a more detailed, step-by-step guide on how this was built from scratch, you can check out the full README.md on GitHub.

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