pragma solidity 0.6.2;


// ETH-USDT
contract MakerDao{

    using SafeMath for uint256;

    uint256 serviceCharge = 5;  // 1 DAI 借贷一天的手续费
    uint256 loanMortgageRate = 300; // 抵押率
    uint256 intervalTime = 86400; // 手续费结算周期
    uint256 closePositionMortgageRate = 150; // 可平仓抵押率

    ERC20 daiErc20;    // DAI ERC20合约对象
    ERC20 mkrErc20;     // MKR ERC20合约对象
    Oracle oracle;      // 预言机对象（MakerDao是由14个节点传输价格取平均值获得的ETH/USDT价格）

    struct Loan{
        uint256 time;   // 借贷时间
        uint256 ethAmount;  // 质押ETH数量
        uint256 daiAmount;  // 借款DAI数量
    }

    mapping(address => Loan) loanMapping;

    constructor(address daiContractAddress,address oracleContractAddress,address mkrContractAddress) public{
        daiErc20 = ERC20(daiContractAddress);
        mkrErc20 = ERC20(mkrContractAddress);
        oracle = Oracle(oracleContractAddress);
    }
    // 抵押ETH获取DAI
    function exchange() public payable{
        // 质押ETH金额不能为0
        require(msg.value > 0,"eth value is not zero");
        Loan memory loan = loanMapping[msg.sender];
        // 确定没有未完成的借贷单
        require(loan.time == 0,"loan is existence");
        // 获取预言机ETH/USDT价格
        uint256 price= oracle.getDaiPrice();
        // 根据ETH数量，以及抵押率计算可以贷DAI的数量
        uint256 daiAmount = msg.value.mul(price).mul(100).div(loanMortgageRate);
        daiErc20.transfer(msg.sender,daiAmount);
        loanMapping[msg.sender] = Loan(now,msg.value,daiAmount);
    }

    // 还款 (手续费用MKR来支付)
    function repayment() public{
        Loan memory loan = loanMapping[msg.sender];
        require(daiErc20.balanceOf(msg.sender) >= loan.daiAmount,"dai balance is not nought");
        // 贷款周期（天）
        uint256 day = (now.sub(loan.time)).div(intervalTime);
        // 利息用MKR结算
        uint256 mkrAmount = serviceCharge.mul(loan.daiAmount).mul(day).div(10000);
        require(mkrErc20.balanceOf(msg.sender) >= mkrAmount,"mkr balance is not nought");
        require(daiErc20.transferFrom(msg.sender,address(this),loan.daiAmount),"dai transferFrom is error");
        require(mkrErc20.transferFrom(msg.sender,address(this),mkrAmount),"mkr transferFrom is error");
        msg.sender.transfer(loan.ethAmount);

        loanMapping[msg.sender] = Loan(0,0,0);
    }
    // 平仓
    function closePosition(address addr) public{
        Loan memory loan = loanMapping[addr];
        // 确定借贷单还未完成
        require(loan.time > 0,"loan is existence");
        // 获取预言机ETH/USDT价格
        uint256 price= oracle.getDaiPrice();
        // 确保抵押率已经达到平仓线
        require(loan.daiAmount.mul(100).div(loan.ethAmount.mul(price)) <= closePositionMortgageRate,"loan mortgage rate is too large");
        require(daiErc20.transferFrom(msg.sender,address(this),loan.daiAmount),"dai transferFrom is error");
        // 借贷天数
        uint256 day = (now.sub(loan.time)).div(intervalTime);
        // 利息
        uint256 mkrAmount = serviceCharge.mul(loan.daiAmount).mul(day).div(10000);
        require(mkrErc20.transferFrom(msg.sender,address(this),mkrAmount),"mkr transferFrom is error");
        msg.sender.transfer(loan.ethAmount);

        loanMapping[addr] = Loan(0,0,0);
    }
    // 补仓
    function replenishment() public payable{
        require(msg.value > 0,"eth value is not zero");
        Loan memory loan = loanMapping[msg.sender];
        require(loan.ethAmount > 0,"loan is existence");
        loanMapping[msg.sender] = Loan(loan.time,loan.ethAmount.add(msg.value),loan.daiAmount);
    }


}

interface Oracle{
    function getDaiPrice() external returns(uint256);
}
interface ERC20 {
    function balanceOf(address account) external view returns (uint256);
    function transfer(address recipient, uint256 amount) external;
    function transferFrom(address sender, address recipient, uint256 amount) external view returns(bool);
}
library SafeMath {
    int256 constant private INT256_MIN = -2**255;
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b);
        return c;
    }
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b > 0);
        uint256 c = a / b;
        return c;
    }
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b <= a);
        uint256 c = a - b;

        return c;
    }
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a);

        return c;
    }
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        require(b != 0);
        return a % b;
    }
}