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https://github.com/aalbacetef/solidity-lottery

Simple Lottery implementation in Solidity w/ Hardhat and Viem.
https://github.com/aalbacetef/solidity-lottery

ethereum evm hardhat solidity solidity-contracts viem web3

Last synced: 22 days ago
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Simple Lottery implementation in Solidity w/ Hardhat and Viem.

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README 

        
# Lottery Smart Contract Project



This project implements a lottery system as a Solidity smart contract. The contract is meant to be a **toy project/demo** and is not intended for production use. 



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## Features



- **Lottery Participation**:

  - Users can purchase lottery tickets with ETH.

  - Ticket numbers are uniquely generated for each participant.

  - Ensures fairness and prevents duplicate ticket assignments.



- **Winning and Prize Distribution**:

  - The lottery owner sets a winning number to conclude the game.

  - Participants with tickets matching the winning number (or partial matches) are rewarded based on a multi-tiered prize structure.

  - Winners can claim their prizes via the contract.



- **Ownership**:

  - Ownership can be securely transferred to another address.

  - Owners receive fees collected from ticket sales.



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## Important Notes



This project is **for educational purposes only**. The current implementation of randomness uses a simple `_randMod` function based on `keccak256`, `block.timestamp`, and other deterministic inputs. This method is **not secure for production use**, as it can be manipulated by miners or other network participants. 



For a production-ready lottery system, consider integrating an external randomness oracle, such as [Chainlink VRF](https://chain.link/vrf).



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## Smart Contract Overview



### Constructor



The constructor initializes the lottery with the following parameters:



- `_pricePerTicket`: Price of each ticket (in wei).

- `_ticketDigitLength`: Number of digits in ticket numbers.

- `_fees`: Amount deducted per ticket as fees for the owner.

- `_nonce`: Seed for random number generation.

- `_maxRetries`: Maximum retries for ensuring unique ticket numbers.

- `_prizeBrackets`: Percentage of the prize pool allocated to winners in each bracket.



### Key Functions



- **`buyTicket(uint numTickets)`**: Purchases tickets by sending ETH. Each ticket is uniquely generated and linked to the buyer.



- **`setWinningNumber(uint number)`**: Sets the winning number and finalizes the lottery. Only the contract owner can call this function.



- **`withdraw()`**: 

  - **For the owner**: Withdraws the accumulated owner's balance.

  - **For winners**: Allows withdrawal of their prize amounts.



- **`ticketsForAddress(address participant)`**: Returns all tickets owned by a given address. Non-owners can only view their own tickets.



- **`transferOwnership(address newOwner)`**: Transfers contract ownership to a specified address. Can only be executed by the owner.



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## Events



- `PoolIncreased(uint amount)`: Emitted when the lottery pool grows due to ticket sales.

- `LotteryOver(uint drawnDigit)`: Emitted when the winning number is set and the lottery concludes.

- `OwnershipChanged(address from, address to)`: Emitted when the owner of the lottery is changed.



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## Security Considerations



- **Randomness**: The current `_randMod` function is not secure. It is advised to replace this with a secure randomness oracle for any non-demo implementation.

- **Access Control**: Owner-restricted functions ensure key operations are limited to the intended party.

- **Withdrawal Safety**: Users can only withdraw their rightful balances, preventing malicious withdrawals.



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## Other Improvements 



Aside from moving to something like [Chainlink VRF](https://chain.link/vrf), other things that could be added are:



- mechanism for canceling the Lottery

- mechanism for starting a new round

- ways to allow for refunds

- validation on the passed in prize brackets