Introduction

This guide will show you how to write the lottery contract showcased during ZENCON.

Hardhat Configuration

require("@nomicfoundation/hardhat-toolbox");
let privateKey = 'test test test test test test test test test test test test';

/** @type import('hardhat/config').HardhatUserConfig */
module.exports = {
  networks: {
    zeniq: {
      url: "https://smart.zeniq.network:9545",
      chainId: 383414847825,
      accounts: [privateKey]
    }
  },
  solidity: {
    version: "0.8.19",
    settings: {
      optimizer: {
        enabled: true,
        runs: 200
      }
    }
  },
}

Lottery Contract

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.19;

import "@openzeppelin/contracts/access/Ownable.sol";

contract Lottery is Ownable {
    address[] public players;
    address public lastWinner;
    uint256 public winningPrize;
    mapping(address => bool) public hasEntered;

    event PlayerEntered(address indexed player);
    event WinnerPicked(address indexed winner, uint256 amount);

    // Function to enter the lottery (Função para participar na loteria)
    function enter() public {
        require(!hasEntered[msg.sender], "You have already entered the lottery");

        players.push(msg.sender);
        emit PlayerEntered(msg.sender);
        hasEntered[msg.sender] = true;
    }

    // Function to set the winning prize (Função para definir o prêmio inicial)
    function setWinningPrize() public payable onlyOwner {
        require(winningPrize == 0, "Winning prize has already been set");
        require(msg.value > 0, "Initial prize must be greater than 0");

        winningPrize = msg.value;
    }

    // Function to pick a winner (Função para escolher um vencedor)
    function pickWinner() public onlyOwner {
        require(players.length > 0, "No players in the lottery");
        require(winningPrize > 0, "Winning prize not set");

        // Generate a pseudo-random number using last block and current time (Gerar um número pseudo-aleatório usando o último bloco e o horário atual)
        uint256 randomNumber = uint256(keccak256(abi.encodePacked(block.prevrandao, block.timestamp, players)));

        // Pick a winner based on the random number (Escolher um vencedor com base no número aleatório)
        address winner = players[randomNumber % players.length];

        // Transfer the winning prize to the winner (Transferir o prêmio acumulado para o vencedor)
        payable(winner).transfer(winningPrize);

        // Reset participant status
        for (uint256 i = 0; i < players.length; i++) {
         hasEntered[players[i]] = false;
        }

        // Reset the list of players and winning prize (Resetar a lista de participantes e o prêmio acumulado)
        delete players;
        winningPrize = 0;

        emit WinnerPicked(winner, winningPrize);
        lastWinner = winner;
    }

    // Function to get the list of players (Função para obter a lista de participantes)
    function getPlayers() public view returns (address[] memory) {
        return players;
    }
}

Deploying the Contract

// We require the Hardhat Runtime Environment explicitly here. This is optional
// but useful for running the script in a standalone fashion through `node <script>`.
//
// You can also run a script with `npx hardhat run <script>`. If you do that, Hardhat
// will compile your contracts, add the Hardhat Runtime Environment's members to the
// global scope, and execute the script.
const hre = require("hardhat");

async function main() {
  const lottery = await hre.ethers.deployContract("Lottery");

  await lottery.waitForDeployment();

  console.log(`Lottery contract address`, lottery.target);
}

// We recommend this pattern to be able to use async/await everywhere
// and properly handle errors.
main().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});