lottery.sol

// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.0;

// Lottery implements simple lottery contract.
// In this contract, the enter function allows players to enter the lottery
// by sending a positive value to the contract, which is added to the jackpot total.
// The random function generates a random index within the bounds of the players
// array length, using the current block timestamp, difficulty, and array length.
//
// The pickWinner function selects the winner by calling the random function and
// transferring the entire jackpot to the winner's address. 
// Finally, the players array and the jackpot total are reset for the next lottery.
contract Lottery {
  uint public jackpot;
  address[] public players;

  // enter the given amount to the lottery pool
  function enter() public payable {
    require(msg.value > 0, "You must enter with a positive value");
    players.push(msg.sender);
    jackpot += msg.value;
  }

  // playersExist checks if there are some player in the list
  function playersExist() public view returns (bool exist) {
    exist = players.length >= 2;
  }

  // random choses a random winner
  function random() private view returns (uint) {
    return uint(keccak256(abi.encodePacked(block.timestamp, block.difficulty, players.length))) % players.length;
  }

  // pickWinner picks a random winner and transfer funds to them
  function pickWinner() public {
    require(players.length >= 2, "Not enough players entered the lottery");
    uint randomIndex = random();
    address payable winner = payable(players[randomIndex]);
    winner.transfer(jackpot);
    delete players;
    jackpot = 0;
  }
}