pragma solidity ^0.6.2;

contract Ico {
    
    mapping(address => uint256) amountMap; // 每個用戶眾籌數(shù)量
    uint256 public totalErc20Amount;    // 總分發(fā)的ERC20數(shù)量
    uint256 public totalEthAmount;   // 眾籌的總ETH數(shù)量
    uint256 public minValue = 1 ether;    // 最小金額限制
    address payable owner;      // 眾籌發(fā)起人
    bool status;    // 眾籌狀態(tài)
    ERC20 erc20;
    
    constructor() public{
        owner = msg.sender;
        status = true;
    }
    // 眾籌ETH
    function crowdFunding() public payable{
        require(status,"crowd funding is close");       // 確保還在眾籌階段
        require(msg.value >= minValue,"crowd funding value must be > 1 ether");
        amountMap[msg.sender] += msg.value;     // 用戶眾籌金額增加記錄賬本
        uint256 beforeTotalEthAmount = totalEthAmount;  // 用來防止溢出攻擊
        totalEthAmount += msg.value;    // 總眾籌資產(chǎn)增加
        assert(beforeTotalEthAmount <= totalEthAmount); // 防止溢出攻擊
    }
    // 項目方獲取眾籌資產(chǎn)
    function turnOutEth(uint256 _value,address _ercContractAddress) public onlyOwner{
        owner.transfer(address(this).balance);   // 所有眾籌ETH轉(zhuǎn)入項目方錢包地址
        erc20 = ERC20(_ercContractAddress);     // 初始化ERC20代幣合約
        bool success = erc20.transferFrom(owner,address(this),_value);  // 項目方轉(zhuǎn)入ERC20代幣
        require(success,"transferFrom is fail");    // 確保轉(zhuǎn)賬成功
        totalErc20Amount = _value;  // 更新用戶總分配ERC20數(shù)量
        status = false;         // 眾籌結(jié)束
    }
    //  領(lǐng)取代幣
    function turnOutErc() public{
        require(!status,"crowd funding is not close");  // 確保眾籌結(jié)束
        uint256 turnOutAmount = amountMap[msg.sender] * totalErc20Amount / totalEthAmount; // 計算單個用戶能得到的ERC20數(shù)量
        bool success = erc20.transfer(msg.sender,turnOutAmount);      // 轉(zhuǎn)出ERC20給用戶
        require(success,"transfer is fail");        // 確保轉(zhuǎn)賬成功
        amountMap[msg.sender] = 0;  // 預(yù)防重復(fù)領(lǐng)取
    }
    //  僅限管理員操作
    modifier onlyOwner(){
        require(msg.sender == owner, "No authority");
        _;
    }
}
interface ERC20{
    function transfer(address,uint256) external returns(bool);
    function transferFrom(address,address,uint256) external returns(bool);
}