Programming Language Constructs Final Project

合約地址: 0xbee0e72afae3727b66b07ae894e961618be1c028d3c5a808a737df8ae84895e2

Code































































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

contract Lottery {
    address[] public players;
    address public recentWinner;

    address private _owner;
    uint256 private _totalMoney;
    uint256 public entranceFee;

    // 建立onlyOwner的modifier
    modifier onlyOwner(){
        require (msg.sender==_owner, "This action can only be activated by the owner");
        _;
    }
    // 定義enum
    enum LOTTERY_STATE{
        CLOSED,
        OPEN,
        DRAWING
    }
    // 宣告enum
    LOTTERY_STATE state;

    constructor()  {
        _owner=msg.sender;
        state=LOTTERY_STATE.CLOSED;
        _totalMoney=0;
    }

    function enter() public payable{
        require(state==LOTTERY_STATE.OPEN, "Lottery isn't open!");
        require(msg.value>=entranceFee, "You don't have enough money!");
        _totalMoney+=msg.value;
        players.push(msg.sender);
    }

    function startLottery(uint256 setEntranceFee) public onlyOwner(){
        require(state!=LOTTERY_STATE.OPEN, "Lottery is already open!");
        state=LOTTERY_STATE.OPEN;
        entranceFee=setEntranceFee;
    }

    function endLottery() public onlyOwner(){
        require(state!=LOTTERY_STATE.CLOSED, "Action not applicable");
        state=LOTTERY_STATE.DRAWING;

        uint256 indexOfWinner = uint256(
            keccak256(
                abi.encodePacked(msg.sender, block.difficulty, block.timestamp)
            )
        )%players.length;

        (bool success, )=payable(players[indexOfWinner]).call{value: _totalMoney}("");
        require(success, "Transaction failed");
        _totalMoney=0;
        recentWinner=players[indexOfWinner];
        delete players;
        state=LOTTERY_STATE.CLOSED;
    }
}

功能實作說明

constructor

將變數初始化、設定莊家為部署合約的人。

enter

首先檢查樂透狀態、交易發起人的金額是否可支付入場費，兩條件皆符合才將其加入參加者名冊。

startLottery

先透過onlyOwner() modifier確認交易發起人為莊家後才准許執行後續動作。一開始確認樂透不是開放狀態以避免重複開場，接著才將樂透狀態設為開放，並透過此函式設定入場費。