Lottery-Contract

Hardhat Smart Contract Lottery System

Key Components

Chainlink VRF (Verifiable Random Function)

• Ensures that the random number used to select the winner is provably random and tamper-proof.

Chainlink Keepers

• Automates the execution of the contract based on predefined conditions (e.g., time intervals).

State Variables

Chainlink VRF Variables

• i_vrfCoordinatorV2: Address of the VRFCoordinatorV2 contract.
• i_subscriptionId: Subscription ID for Chainlink VRF.
• i_gasLane: Maximum gas price for the callback request.
• i_callbackGasLimit: Maximum gas to be used for the callback.
• REQUEST_CONFIRMATIONS: Number of confirmations required before the VRF response is considered.
• NUM_WORDS: Number of random words requested.

Lottery Variables

• i_interval: Time interval for each raffle draw.
• i_entranceFee: Fee to enter the raffle.
• s_lastTimeStamp: Timestamp of the last raffle draw.
• s_recentWinner: Address of the most recent winner.
• s_players: List of players in the current raffle.
• s_raffleState: State of the raffle (OPEN or CALCULATING).

Events

• RequestedRaffleWinner(uint256 indexed requestId): Emitted when a random winner is requested.
• RaffleEnter(address indexed player): Emitted when a player enters the raffle.
• WinnerPicked(address indexed player): Emitted when a winner is picked.

Functions

Constructor

• Initializes the contract with the necessary parameters and sets the initial state of the raffle to OPEN.

enterRaffle

• Allows users to enter the raffle by sending the required entrance fee.
• Adds the player's address to the s_players array.
• Emits the RaffleEnter event.

checkUpkeep

• Called by Chainlink Keepers to check if the upkeep (i.e., selecting a winner) is needed.
• Returns true if the time interval has passed, the raffle is open, there are players, and the contract has a balance.

performUpkeep

• Called by Chainlink Keepers when checkUpkeep returns true.
• Initiates the random number request to Chainlink VRF.
• Sets the raffle state to CALCULATING.
• Emits the RequestedRaffleWinner event.

fulfillRandomWords

• Callback function called by Chainlink VRF with the random number.
• Uses the random number to select a winner from the s_players array.
• Resets the raffle state to OPEN, clears the players array, updates the last timestamp, and transfers the contract balance to the winner.
• Emits the WinnerPicked event.

Error Handling

Custom Errors

• Raffle__UpkeepNotNeeded: Thrown when upkeep is not needed.
• Raffle__TransferFailed: Thrown when the transfer to the winner fails.
• Raffle__SendMoreToEnterRaffle: Thrown when the sent ETH is less than the entrance fee.
• Raffle__RaffleNotOpen: Thrown when the raffle is not open.
• Raffle__NotEnoughETHEntered: Thrown when not enough ETH is sent to enter the raffle.

Getter Functions

• getRaffleState
• getNumWords
• getRequestConfirmations
• getRecentWinner
• getPlayer
• getLastTimeStamp
• getInterval
• getEntranceFee
• getNumberOfPlayers

Functions to retrieve the state and configuration of the raffle.

Summary

This contract ensures a fair and automated raffle system by leveraging Chainlink's VRF for randomness and Keepers for automation. Users can participate by sending ETH, and the contract will automatically select a winner at defined intervals, transferring the accumulated prize to the winner. The use of custom errors and events helps in monitoring and debugging the contract's operation.