CharityRaffle

An Ethereum Smart Contract CharityRaffle. Currently only on RINKEBY @0x9328495624a11061075F0C7AfE90BAD20b323C23

NOT TO BE USED ON MAINNET (see Warnings)

Description

This smart contract is used to create a raffle for a charity.

Raffle Details

A raffle is composed of:

• An identifier (id- sequential number, 1 indexed)
• A name (name- string)
• A beneficiary, the one to which the procedes of the raffle will be paid (beneficiary- address)
• An start date (startTime- uint256 unix timestamp)
• An end date (endTime- uint256 unix timestamp)
• A ticket price (ticketPrice- uint256 in wei)
• A ticket count, the number of purchased tickets (ticketCount- uint256)
• The ticket balance of all the ticket owners (ticketBalances- address => uint256)
• A list of ticket owners, used for itteration (ticketOwners- address[])
• A state of the raffle (state- uint8)
  • Open: 0
  • SelectingWinner: 1
  • Finished: 2
  • Expired: 3
• A bool to track if the winnings have been paid out (paidOut- bool)

Raffle Rules

1. Anyone can make a new raffle
2. Anyone can buy tickets for any open raffle, and this can be for multiple raffles
3. Tickets are only refundable if the raffle expires, this means that the beneficiary has not claimed the raffle a week after it's end
4. The beneficiary can only end the raffle after the end time

Functions

CreateRaffle

CreateRaffle(string memory _raffleName, uint256 _ticketPrice, uint256 _raffleLength) public returns(uint256 raffleId) This function takes in the name of the raffle (a string), the ticket price (in WEI), and the length of the raffle (in seconds). Warning: The raffle start and end times are based on when the transaction is mined.

BuyTickets

BuyTickets(uint256 raffleId, uint256 _ticketCount) public payable The function used to buy tickets for a raffle. The functions takes in the raffleId and the number of tickets to purchase. The raffle must be open to purchase tickets (the state must be open and the time must be within the raffle time). You must buy at least 1 ticket and the value transfered must be at least the ticket price.

TicketRefund

TicketRefund(uint256 raffleId) public This function is used to refund the tickets you have purchased if the raffle expires. The function takes in the raffleId and will transfer the ticket owner the value of all the tickets they bought.

ClaimRaffle

ClaimRaffle(uint256 raffleId) public This is the function called by the beneficiary to claim the raffle. The function takes the id of the raffle being claimed. Contract must have enough LINK token to pay out the raffle since it will be using the Chainlink VRF system to pick the winner. The function dose not instantly transfer the funds or set the winner as the VRF needs to respond. The VRF will call fulfillRandomness which will transfer the funds and set the winner.

CollectChange

CollectChange() public onlyOwner returns (uint256) This is a function that can be run by the contract owner to collect the change that is left over from ticket purchases that overpay.

GetRaffleInfo, GetRaffleTicketInfo

GetRaffleInfo(uint256 _id) public view returns (string memory name, address payable beneficiary, address payable winner, uint256 startTime, uint256 endTime) and GetRaffleTicketInfo(uint256 _id) public view returns (string memory name, uint256 startTime, uint256 endTime, uint256 ticketCount, uint256 ticketPrice) These functions are used to get the raffle information for a given raffleId. These two functions are split up since a single function wasnt able to return all the information.

GetRaffleBalance

GetRaffleBalance(uint256 _id, address owner) public view returns (uint256 balance) This function is used to get the balance of a raffle for a given owner.

Other Global Variables

RaffleCount

The number of raffles, uses the openzeppelin counter.

expirationPeriod

The number of seconds before a raffle expires (by design should be a week).

linkTokenAddress, linkFee, VRFKeyHash

These are the addresses of the LINK token on the given network, the LINK fee needed to call the VRF, and the VRF key hash. Read more at https://docs.chain.link/docs/chainlink-vrf/.

Contract Dependencies

• Chainlink VRF to generate randomness for the winner.
• OpenZepplin Counters to get raffle Ids.
• OpenZepplin Access Control to track the owner for change collection.

Brownie Setup

• Install all the dependencies in requirements.txt using pip install -r requirements.txt (preferably using a virtual environment)
• Add a .env file to /brownie with in it:
  • An infura key for easy network access in WEB3_INFURA_PROJECT_ID
  • An etherscan API tokoen for contract verification in ETHERSCAN_TOKEN
• cd brownie && brownie compile to compile the smart contract
• Use brownie test to test the smart contract.
• Use brownie run scripts\deploy.py to deploy the smart contract to a local network. (Add the --network NETWORKNAME flag to deploy it to a real network).

Interacton with the frontend

If you want to use this smart contract with a frontend, I have made one at https://github.com/SuperZooper3/charity-raffle-front-end. There is a running version at https://eth-charity-raffle.herokuapp.com/.

If you want to test the frontend locally with this smart contract, make sure to put the two repositories in the same directory. Ex: ...\Blockchain: -> charity-raffle-front-end -> CharityRaffle

Futre Improvements

• Add an automatic NFT given out to the winner as some kind of a prize.
• Let raffles be created for beneciaries other than the raffle creator.
• Let raffle creators add other NFT or ERC20 tokens as raffle prizes.
• Accept ERC20 tokens for raffles.

Warnings

This contract has not been audited and it is my first real smart contract so I do not expect it to be perfect. It has been tested extensively and is working as intended on a local machine and on the Rinkeby Testnet but might not work on other networks. It comes as is with no warranty and is not intended for use in production.

Known issues:

• Because of the selection system's O(n) cost, if there are too many entrants, the selection could fail
• If the VRF fails to respond, the system's actions are unspecified