Lottery (solidity)

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

contract Lottery{
    address public owner;
    uint256 public ticketPrice;
    uint256 public totalCommission;
    uint256 public lotteryEndTime;
    bool public lotteryActive;
    uint256 private ticketCounter;
    uint256 public winningTicket;

    mapping(address => uint256[]) public tickets;
    mapping(uint256 => address) public ticketOwners;
    address[] public players;

    constructor(){
        owner= msg.sender;
        lotteryActive= false;
        ticketCounter= 0;
        winningTicket= 0;
    }
    modifier onlyOwner(){
        require(msg.sender== owner,"Not the contract owner");
        _;
    }
    modifier whenLotteryActive(){
        require(lotteryActive,"Lottery is not active");
        _;
    }
    modifier whenLotteryEnded(){
        require(block.timestamp>= lotteryEndTime,"Lottery hasnot ended yet");
        _;
    }
    //function to start the lottery
    function startLottery(uint256 _ticketPrice, uint256 _durationInSeconds) public onlyOwner() {
        require(!lotteryActive,"A lottery is already active");
        ticketPrice = _ticketPrice;
        lotteryActive = true;
        lotteryEndTime = block.timestamp + _durationInSeconds;
        winningTicket= 0;
    }
    //functions to buy a tickets(10 tickets at a time not more than that)
    function buyTickets(uint256 _numTickets) public payable whenLotteryActive(){
        require(block.timestamp < lotteryEndTime,"Lottery has ended");
        require(_numTickets > 0 && _numTickets <=10,"Can buy 1-10 tickets only");
        require(msg.value == _numTickets * ticketPrice, "Incorrect payement");

        if (tickets[msg.sender].length == 0){
            players.push(msg.sender);
        }
        for (uint256 i =0; i < _numTickets; i++){
            ticketCounter++;
            tickets[msg.sender].push(ticketCounter);
            ticketOwners[ticketCounter] = msg.sender;
        }
    }
    //function to end the lottery by the owner and pick the random number for winner
    function endLottery() public onlyOwner whenLotteryActive whenLotteryEnded{
        require(ticketCounter > 0,"No tickets sold");

        //Generate a random winning ticket
        winningTicket = uint256(keccak256(abi.encodePacked(block.timestamp, block.prevrandao, ticketCounter))) % ticketCounter + 1; 

        //Determine the winner
        address winner = ticketOwners[winningTicket];

        //calculate prize distribution
        uint256 prize = address(this).balance * 90/100;
        uint256 commission = address(this).balance - prize;
        totalCommission += commission;

        //transfer prize to winner
        payable(winner).transfer(prize);

        // Reset the lottery
        delete players;
        lotteryActive = false;
    }
    //function for the owner to withdraw the total commisiion
    function withdrawCommission(uint amount) public onlyOwner{
        require(amount > 0 && amount <= totalCommission,"Withdraw amount should be greated than zero");
        payable(owner).transfer(amount);
        totalCommission -= amount;
    }
    function getPlayerTickets(address _player) public view returns(uint256[] memory){
        return tickets[_player];
    }
    //view function to check the winning tickets
    function getWinningTickets() public view returns(uint256){
        require(!lotteryActive,"Lottery is still active");
        return winningTicket;
    }
    //view function to check the contract balance
    function getContractbalance() public view returns(uint256){
        return address(this).balance;
    }

}

🎲 Smart Contract: Lottery (Explained)

📜 License and Version

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.13;

• License: The contract is unlicensed, meaning it’s not open-source unless stated otherwise.
• Solidity version: Compatible with version 0.8.13 or higher.

---

🏛️ State Variables

address public owner;
uint256 public ticketPrice;
uint256 public totalCommission;
uint256 public lotteryEndTime;
bool public lotteryActive;
uint256 private ticketCounter;
uint256 public winningTicket;

• owner: The person who deployed the contract (admin).
• ticketPrice: Cost of one lottery ticket.
• totalCommission: Earnings retained by the owner (10% of total funds).
• lotteryEndTime: Timestamp when lottery ends.
• lotteryActive: Tracks if a lottery is ongoing.
• ticketCounter: Unique counter for ticket IDs.
• winningTicket: The randomly selected winning ticket number.

---

👥 Mappings and Arrays

mapping(address => uint256[]) public tickets;
mapping(uint256 => address) public ticketOwners;
address[] public players;

• tickets: Maps a player’s address to a list of their ticket numbers.
• ticketOwners: Maps each ticket number to its owner.
• players: List of all unique players who bought at least one ticket.

---

🛠️ Constructor: Sets the Contract Owner

constructor(){
    owner= msg.sender;
    lotteryActive= false;
    ticketCounter= 0;
    winningTicket= 0;
}

• Runs once when the contract is deployed.
• Initializes the owner and sets default values.

---

🔐 Modifiers: Access Control

modifier onlyOwner() { ... }
modifier whenLotteryActive() { ... }
modifier whenLotteryEnded() { ... }

• onlyOwner: Restricts function to owner/admin.
• whenLotteryActive: Ensures a lottery is ongoing.
• whenLotteryEnded: Ensures the lottery duration has passed.

---

🚀 Start the Lottery

function startLottery(uint256 _ticketPrice, uint256 _durationInSeconds) public onlyOwner { ... }

• Starts a new lottery.
• Owner sets:
  • Ticket price
  • Duration (in seconds)
• Resets the winning ticket.

---

🎟️ Buy Lottery Tickets

function buyTickets(uint256 _numTickets) public payable whenLotteryActive { ... }

• Buy 1 to 10 tickets at once.
• Validates correct payment (_numTickets * ticketPrice).
• Adds buyer to players if it’s their first time.
• Mints new tickets and assigns them.

---

🛑 End the Lottery and Pick Winner

function endLottery() public onlyOwner whenLotteryActive whenLotteryEnded { ... }

• Can only be called after lottery duration ends.
• Generates a random winner using:

uint256(keccak256(abi.encodePacked(block.timestamp, block.prevrandao, ticketCounter))) % ticketCounter + 1;

• 90% of funds go to the winner.
• 10% goes to the owner as commission.
• Resets the state for the next lottery.

---

💵 Withdraw Commission (Owner Only)

function withdrawCommission(uint amount) public onlyOwner { ... }

• Lets the owner withdraw earned commissions.

---

👁️ View Player Tickets

function getPlayerTickets(address _player) public view returns(uint256[] memory)

• Returns all ticket numbers owned by a player.

---

🏆 View Winning Ticket

function getWinningTickets() public view returns(uint256)

• Only callable after lottery ends.
• Returns the winning ticket number.

---

💰 View Contract Balance

function getContractbalance() public view returns(uint256)

• Shows the current balance (ETH) held by the contract.

---

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🎲 Lottery Contract Overview

This smart contract allows users to participate in a decentralized lottery where:

• Players buy tickets using ETH.
• A random winner is selected after the deadline.
• The winner receives 90% of the pot.
• The owner collects a 10% commission.

---

🔐 Admin Controls:

• Start and end the lottery.
• Set ticket price and duration.
• Withdraw commission after lottery ends.

---

💡 How Randomness Works:

The winner is picked using:

keccak256(abi.encodePacked(block.timestamp, block.prevrandao, ticketCounter))

This creates a pseudo-random hash based on:

• The time
• A blockchain randomness source
• Ticket count

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💳 Rules:

• Buy up to 10 tickets per transaction
• Must pay exact amount: ticketPrice * number of tickets
• One winner per round