A Fair Smart Contract Raffle

A decentralized and automated raffle system built on blockchain technology, utilizing Chainlink VRF for verifiable randomness and Chainlink Automation for trustless execution.

Overview

This project implements a fully automated raffle system where:

• Users can enter by paying a set entrance fee
• A winner is automatically and fairly selected at regular intervals
• Uses Chainlink VRF (Verifiable Random Function) for provably fair winner selection
• Leverages Chainlink Automation for automatic draws
• Implements a robust testing suite

Features

• Fair Entry System: Fixed entrance fee required to participate
• Automated Execution: No manual intervention needed for picking winners
• Verifiable Randomness: Chainlink VRF v2.5 ensures provably fair winner selection
• Time-Based Draws: Configurable intervals between raffles
• Transparent: Fully verifiable on-chain logic
• State Management: Proper handling of raffle states (OPEN and CALCULATING)
• Gas Efficient: Optimized for minimal gas consumption

Technical Details

Contract Architecture

The project consists of several key contracts:

• Raffle.sol: Main contract implementing the raffle logic
• DeployRaffle.s.sol: Script for deploying the raffle
• HelperConfig.s.sol: Configuration management for different networks
• Interactions.s.sol: Helper scripts for contract interactions

Key Dependencies

• Solidity ^0.8.19
• Chainlink VRF V2.5
• Forge/Foundry for testing and deployment
• Solmate for optimized contract implementations

Testing

Comprehensive test suite available in test/unit/RaffleTest.t.sol, covering:

• Initialization states
• Entry conditions
• Player recording
• Event emissions
• State transitions
• Upkeep checks
• Winner selection

Getting Started

Prerequisites

• Foundry installed
• Node.js and npm (for additional tooling)
• An RPC URL for deployment
• LINK tokens for VRF funding (on mainnet/testnet)

Installation

1. Clone the repository:

git clone <your-repo-url>
cd raffle-contract

2. Install dependencies:

forge install

3. Compile contracts:

forge build

4. Run tests:

forge test

Deployment

1. Set up your environment variables:

cp .env.example .env
# Fill in your environment variables

2. Deploy to a network:

forge script script/DeployRaffle.s.sol --rpc-url <your_rpc_url> --private-key <your_private_key>

Usage

Entering the Raffle

Users can enter the raffle by calling the enterRaffle() function with the required entrance fee:

raffle.enterRaffle{value: entranceFee}()

Checking Raffle Status

Several view functions are available:

• getEntranceFee(): Get the required entrance fee
• getRaffleState(): Check if raffle is OPEN or CALCULATING
• getPlayer(uint256 index): Get player at specific index
• getNumberOfPlayers(): Get total number of players

Security Considerations

• Implements CEI (Checks-Effects-Interactions) pattern
• Uses custom errors for gas efficiency
• Proper access control mechanisms
• Comprehensive error handling
• VRF v2.5 for secure randomness

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Author

Saksham Gupta

Acknowledgments

• Chainlink VRF team for randomness solution
• Foundry team for development framework