Hoelee Smart Contract - Automate Lottery

📚 A Learning Project

Note from Hoelee 👋 — This is part of my journey exploring Web 3.0 / blockchain development. I'm a hands-on self-taught developer learning Solidity and smart-contract engineering by building real, working projects — not just following tutorials. This lottery contract is one of my practice builds: it walks through the full modern Web3 stack end-to-end, from writing the contract, to testing it (Hardhat and Foundry), to deploying and verifying on a public testnet with Chainlink automation. Consider it my learning project note — documenting what I'm studying, how I build, and the standards I hold myself to. It grows as I learn. 🚀

Grand Porject Overview

This Project Smart Contract Created With

1. Solidity Contract + Hardhat + node.js for Test
2. Solidity Contract & Test + Foundry

Hardhat Project

A fully functional Smart Contract wrriten with solidity, node.js and using Hardhat to show usage of all kinds of standard development features, including:

• running blockchain node in localhost - hardhat & ganache
• solidity prettier code beautifier setup
• standard of developing Smart Contract with solidity
• standard of developing node.js script to use hardhat library efficiently
• check gas fee & gas price in real-time, with usage of coverage
• auto verify contract on Etherscan.io
• creating automate test cases - unit test & staging test
• creating tasks etc.
• refactor codes to reduce gas fee
• write code in best practice, with usage of solhint
• prettier solidity & node.js code
• gitea version control

This project mainly to keep as a reference for future Web 3.0 Developments.

Read More in Hardhat Project's Note Page.

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Foundry Project

Same Lottery Project, Use Of Solidity to test smart contract, ensure high coverage of function correctness. Feature included:

• Modular Enable Test In Multiple Networks With Different Conditions
• Local Network Using Of Anvil + Mock VRF (Verifiable Randomness Function)
• Testnet Use of Latest V2.5 Chainlink VRF Subscription With Consumer Subscription
• Use of Custom LinkToken on Sepolia Testnet
• Smart Contract Test With High Coverage To Ensure Correctness
• Private Key Encrypted With Keystore, Safer Usage With Password
• Smart Contract Layer-2 Ready (ZKsync)

Read More In Foundry Project's Note Page.

Success Deploy & Verified Smart Contract In Sepolia Testnet

0xc2022b56eBC140B5FebCf9FBaB14c17db4C315C4 https://sepolia.etherscan.io/address/0xc2022b56eBC140B5FebCf9FBaB14c17db4C315C4#code Via deploy.js https://sepolia.etherscan.io/address/0x3a827C119e1D746bb3C7bcbbf95c55246C8CcBdd#code Via yarn hardhat deploy --network sepolia

Public Reported Hacked Code References:

This website is records of all kind previous hacked smart contract:

https://rekt.news/leaderboard/

1. Understanding Of Known Vulnerabilities

• Reentrancy Attack
  • Locked with modifier while running withdraw function
  • Update variable immediately before call external function
• Integer Overflow / Underflow
  • Use compiler version >0.8.0 have check in place
• Front-Running
  • Use average gas fee / off peak times
  • Use commit-reveal schema
  • Use submarine send

2. Other Explored Features

1. Generate Random Words
   • Create subscription at https://vrf.chain.link/ (MetaMask #1)
   • Add Fund To The Created Subsciption Contract (MetaMask #2)
   • Add Consumer
     • Get Subscription ID
     • Open Remix To Prepare Deploy Consumer Contract https://docs.chain.link/vrf/v2-5/migration-from-v2
     • Change To Correct gwei limit hash address at https://docs.chain.link/vrf/v2/subscription/supported-networks
     • Adjust Setting - random words count, confirmation blocks etc.
     • Insert Subscription ID - v2 is uint64 BUT v2.5 is uint256
     • Deploy And Get hash address (MetaMask #3)
     • Insert in chainlink consumer (Metamask #4)
   • Ready to use, record down the consumer contract address
2. New Time Based Trigger Automation Through Chainlink UpKeep
   • Same As VRF Subscription, V2.5 Optional Reduced Steps
   • Setup At https://automation.chain.link/
   • After Subscription Created, Funded, & Setup Interval:
     • VRFCoordinator will call checkUpkeep(bytes memory checkData)
     • checkUpkeep true will call internal contract performUpkeep(bytes calldata performData)

3. Looking Web 3.0 Developer For Your Project?

👨💻 About Hoelee — I'm actively exploring Web 3.0 and blockchain development while continuing my work in web development and self-hosting. I'm a dedicated, self-motivated learner who picks projects apart, understands how they work, and ships real code — not just concepts.

Mr Hoelee is welcoming a 💼 Web 3.0 / blockchain Remote Job — especially entry/junior roles, internships, or a learning-oriented opportunity where I can grow and contribute. Let's talk! Contact me immediately via WhatsApp +601****5290

Or you can email me@hoelee.com now. Thanks.

Check out my portfolio at hoelee.com to see more of what I build.

4. Like this project?

If you are feeling generous, buy me a coffee! - buymeacoffee.com/hoelee