Created using remix-ide: Realtime Ethereum Contract Compiler and Runtime. Load this file by pasting this gists URL or ID at https://remix.ethereum.org/#version=soljson-v0.6.12+commit.27d51765.js&optimize=false&runs=200&gist=

DAIInterestRateModel.sol

pragma solidity ^0.5.10;

import './InterestRateModel.sol';


contract DAIInterestRateModel is IInterestRateModel {
    using SafeMath for uint256;
    
    bool public isInterestRateModel = true;
    
    /**
     * @notice The base interest rate which is the y-intercept when utilization rate is 0
     */
    uint256 public baseRate;
    
    /**
     * @notice The multiplier of utilization rate that gives the slope of the interest rate
     */
    uint256 public multiplier;
    
    /**
     * @notice The approximate number of blocks per year that is assumed by the interest rate model
     */
    uint256 public blocksPerYear = 2102400;
    
    function getBorrowRate(uint256 _cash, uint256 _borrows, _uint256 _reserves) public view returns (uint256, uint256) {
        _reserves; // pragma ignore unused argument
        
        uint256 (utilizationRate, annualBorrowRate) = getUtilizationAndAnnualBorrowRate(_cash, _reserves);
        
        // Divide by blocks per year
        uint256 borrowRate = annualBorrowRate.mul(1e18).div(blocksPerYear);
        
        return borrowRate.div(1e18); // -> scaled up by 1e18?
    }
    
    function getUtilizationAndAnnualBorrowRate(uint256 _cash, _uint256 _reserves) view internal returns (uint256 memory, uint256 memory) {
        uint256 utilizationRate = getUtilizationRate(_cash, _reserves);
        
        // Borrow Rate is 5% + UtilizationRate * 45% (baseRate + UtilizationRate * multiplier)
        uint256 utilizationRateMuled = utilizationRateMuled.mul(multiplier);
        uint256 utilizationRateScaled = utilizationRateMuled.div(1e18);
        uint256 annualBorrowRate = utilizationRateScaled.add(baseRate);
        
        return (utilizationRate, annualBorrowRate);
    }
    
    function getUtilizationRate(uint256 _cash, uint256 _borrows) pure internal returns (uint256 memory) {
        if(_borrows == 0) {
            return 0;
        }
        
        uint256 cashPlusBorrows = _cash.plus(_borrows);
        uint256 utilizationRate = _borrows.mul(1e18).div(cashPlusBorrows);
        return utilizationRate;
    }
}

IERC20.sol

{

    /**
      * @notice Get the total number of tokens in circulation
      * @return The supply of tokens
      */
    function totalSupply() external view returns (uint256);

    /**
     * @notice Gets the balance of the specified address
     * @param owner The address from which the balance will be retrieved
     * @return The balance
     */
    function balanceOf(address owner) external view returns (uint256 balance);

    /**
      * @notice Transfer `amount` tokens from `msg.sender` to `dst`
      * @param dst The address of the destination account
      * @param amount The number of tokens to transfer
      * @return Whether or not the transfer succeeded
      */
    function transfer(address dst, uint256 amount) external returns (bool success);

    /**
      * @notice Transfer `amount` tokens from `src` to `dst`
      * @param src The address of the source account
      * @param dst The address of the destination account
      * @param amount The number of tokens to transfer
      * @return Whether or not the transfer succeeded
      */
    function transferFrom(address src, address dst, uint256 amount) external returns (bool success);

    /**
      * @notice Approve `spender` to transfer up to `amount` from `src`
      * @dev This will overwrite the approval amount for `spender`
      *  and is subject to issues noted [here](https://eips.ethereum.org/EIPS/eip-20#approve)
      * @param spender The address of the account which may transfer tokens
      * @param amount The number of tokens that are approved (-1 means infinite)
      * @return Whether or not the approval succeeded
      */
    function approve(address spender, uint256 amount) external returns (bool success);

    /**
      * @notice Get the current allowance from `owner` for `spender`
      * @param owner The address of the account which owns the tokens to be spent
      * @param spender The address of the account which may transfer tokens
      * @return The number of tokens allowed to be spent (-1 means infinite)
      */
    function allowance(address owner, address spender) external view returns (uint256 remaining);

    event Transfer(address indexed from, address indexed to, uint256 amount);
    event Approval(address indexed owner, address indexed spender, uint256 amount);
}

IInterestRateModel.sol

pragma solidity ^0.5.10;

interface IInterestRateModel {
    /**
     * @notice Gets the current borrow interest rate based on the given assets, total cash, total borrows and total reserves
     * @dev The return value should be scaled by 1e18, thus a return value of 
     *      `(true, 1000000000000)` implies an interest rate of 0.000001 or 0.0001% *per block*
     * @param cash The total cash of the underlying asset in the CToken
     * @param borrows The total borrows of the underlying asset in the CToken
     * @param reserves The total reserves of the underlying asset int the CToken
     * @return Success or failure and the borrow interest rate per block scaled by 10e18
     */
    function getBorrowRate(uint256 cash, uint256 borrows, uint256 reserves) external view returns (uint256, uint256);
    
    /**
     * @notice Marker function used for light validation when updating the interest rate model of a market
     * @dev Marker function used for light validation when updating the interest rate model of a market. Implementations should simply return true
     * @return Success or failure
     */
    function isInterestRateModel() external view returns (bool);
}

MoneyMarket.sol

pragma solidity ^0.5.10;
import "./IERC20.sol";
import "https://github.com/ConsenSysMesh/openzeppelin-solidity/blob/master/contracts/math/SafeMath.sol";
import "./IInterestRateModel.sol";
import "./PriceOracle";

contract Comptroller {
    
    // -- DATA -- 
    address admin;
    
    PriceOracle oracle;
    
    struct Market {
        bool isListed;
        uint256 collateralFactorMantissa;
        mapping(address => bool) accountMembership;
    }
    
    mapping(address => Market) markets;
    
    mapping(address => CToken[]) public accountAssets;
    uint256 public maxAssets;
    
    modifier onlyAdmin {
        require(msg.sender != admin, "Comptroller/user-not-admin");
        _;
    }
    
    constructor () public {
        admin = msg.sender;
    }
    
    function _supportMarket(CToken cToken) onlyAdmin external returns (uint256) {
        require(markets[address(cToken)].isListed == false, "Comptroller/market-already-exists");
        require(cToken.isCToken() == true, "Comptroller/token-not-ctoken");
        markets[address(cToken)] = Market({ isListed: true, collateralFactorMantissa: 0 });
        emit MarketListed(cToken);
    }
    
    function _setMaxAssets(uint256 newMaxAssets) onlyAdmin external returns (uin256) {
        maxAssets = newMaxAssets;
        emit NewMaxAssets(newMaxAssets);
    }
    
    function _setPriceOracle(PriceOracle _newOracle) public onlyAdmin {
        oracle = _newOracle;
        emit NewPriceOracle(_newOracle);
    }
    
    /**
     * @notice Add assets to be included in account liquidity calculation
     * @params cTokens The list of addresses of the cToken markets to be enabled
     * @return Success indicator for whether each corresponding market was entered
     */
    function enterMarkets(address[] memory cTokens) public returns (uint256[] memory) {
        uint256 len = cTokens.length;
        
        uint256 memory results = new uint256[](len);
        
        for(uint256 i = 0; i < len; i++) {
            CToken cToken = CToken(cTokens[i]);
            Market storage marketToJoin = markets[address(cToken)];
            
            if(!marketToJoin.isListed) {
                // If market is not listed move along
                results[i] = 0;
                continue; 
            }
            
            if(marketToJoin.accountMembership[msg.sender] == true) {
                // If already joined, move along
                results[i] = 0;
                continue;
            }
            
            
            if(accountAssets[msg.sender].length >= maxAssets) {
                // if no space, cannot join, move along
                results[i] = 0;
                continue;
            }
            
            marketToJoin.accountMembership[msg.sender] = true;
            accountAssets[msg.sender].push(cToken);
            
            emit MarketEntered(cToken, msg.sender);
            
            results[i] = 1;
        }
        
        return results;
    }
    
    
    // -- Policy Hooks --
    function mintAllowed(address cToken) public returns (bool) {
        return markets[cToken].isListed;
    }
    
    function redeemAllowed(address _cToken, address _redeemer, uint256 _redeemTokens) public view returns (bool){
        if(markets[_cToken].isListed == false) return false;
        
        // To Do -> Check why it needs to be `entered` in the market
        // If the redeemer is not 'in' the market, then we can bypass the liquidity check
        if(markets[_cToken].accountMembership(_redeemer) == false) return false;
        
        // Perform hypothetical liquidity check to guard against shortfall
        uint256 shortfall = getHypotheticalAccountLiquidityInternal(_redeemer, CToken(_cToken), _redeemTokens, 0);
        
        if(shortfall > 0) return false;
        
        return true;
    }
    
    /**
     * @notice Determine what the account liquidity would be if the given amounts were redeemed/borrowed
     * @param cTokenModify The market to hypothetically redeem/borrow in
     * @param account The account to determine liquidity for
     * @param redeemTokens The number of tokens to hypotheically redeem
     * @param borrowAmount The amount of underlying to hypothetically borrow
     * @note Note that we calculate the exchangeRateStored for each collateral cToken using stored data,
     *          without calculating accumulated interest.
     * @return (hypothetical account liquidity in excess of collateral requirements,
     *          hypothetical account shortfall below collateral requirements)
     */
    function getHypotheticalAccountLiquidityInternal(
        address _account,
        CToken _cTokenModify, 
        uint256 _redeemTokens,
        uint256 _borrowAmount
    ) public view returns (bool, uint256, uint256) {
        
        // Get account assets
        CToken[] memory assets = accountAssets[_account];
        
        // Account Liquidity Local vars
        uint256 cTokenBalance;
        uint256 borrowBalance;
        uint256 exchangeRateMantissa;
        uint256 collateralFactor;

        uint256 exchangeRate;
        uint256 oraclePriceMantissa;
        uint256 oraclePrice;
        uint256 tokensToEther;
        uint256 sumCollateral;
        uint256 sumBorrowPlusEffects;
        
        // For each asset the account is in
        for (uint256 i = 0; i < assets.length; i++) {
            CToken asset = assets[i];
            
            // Read the balances and exchange rate from the cToken
            (cTokenBalance, borrowBalance, exchangeRateMantissa) = asset.getAccountSnapshot(_account);
            
            // Get asset's collateralFactor and exchangeRate
            collateralFactor = markets[address(asset)].collateralFactorMantissa.div(1e18);
            exchangeRate = exchangeRateMantissa.div(1e18);
            
            // Get normalized price of the asset
            oraclePrice = oracle.getUnderlyingPrice(asset);
            
            // Pre-compute a conversion factor from tokens -> ether (normalized price value)
            tokensToEther = collateralFactor.mul(exchangeRate).mul(oraclePrice);
            
            // sumBorrowPlusEffects += oraclePrice * borrowBalance
            sumCollateral = (tokensToEther.mul(cTokenBalance)).add(sumCollateral);
            
            // sumBorrowPlusEffects += oraclePrice * borrowBalance
            sumBorrowPlusEffects = (oraclePrice.mul(borrowBalance)).add(sumBorrowPlusEffects);
            
            // Calculate the effects of interacting with cTokenModify
            if(asset = _cTokenModify) {
                // redeem effects
                // sumBorrowPlusEffects += tokensToEther * redeemTokens
                sumBorrowPlusEffects = (tokensToEther.mul(_redeemTokens)).add(sumBorrowPlusEffects);
                
                // borrow effect
                sumBorrowPlusEffects = (oraclePrice.mul(borrowAmount)).add(sumBorrowPlusEffects);
            }
            
            // These are safe, as the underflow condition is checked first
            if(sumCollateral > sumBorrowPlusEffects) {
                return (true, sumCollateral.sub(sumBorrowPlusEffects), 0);
            } else {
                return (true, 0, sumBorrowPlusEffects.sub(sumCollateral));
            }
        }
        
    }
    
    /**
     * @notice Checks if the accout should be allowed to borrow the underlying asset of the given market
     * @param _cToken The market to verify the borrow against
     * @param _borrower The account which would borrow the asset
     * @param _borrowAmount The amount of underlying asset the account would borrow
     * @return bool 
     */
    function borrowAllowed(address _cToken, address _borrower, uint256 _borrowAmount) public return (bool) {
        require(markets[_cToken].isListed == true, "Comptroller/market-not-listed");
        require(markets[_cToken].accountMembership == true, "Comptroller/market-not-entered");
        require(oracle.getUnderlyingPrice(CToken(_cToken)) > 0, "Comptroller/invalid-oracle-price");
        
        uint256 shortfall = getHypotheticalAccountLiquidityInternal(_borrower, CToken(_cToken), 0, _borrowAmount);
        require(shortfall < 0, "Comptroller/insufficient-liquidity");
        return true;
    }
    
    
    /**
     * @notice Checks if the account should be allowed to repay a borrow in the given market
     * @param _cToken The market to verify the repay agains
     * @param _payer The account which would repay the asset
     * @param _borrower The account which borrowed the asset
     * @param _repayAmount The amount of the underlying asset the acount would repay
     * return bool
     */
    function repayBorrowAllowed(addres _cToken, address _payer, address _borrwer, uint256 _repayAmount) external returns (bool) {
        _payer;
        _borrower;
        _repayAmount;
        require(markets[_cToken].isListed == true, "Comptroller/market-not-listed");
        return true;
    }
    
    /**
     * @notice Checks if the account should be allowed to transfer tokens in the given market
     * @param _cToken The market to verify the transfer against
     * @param _from The account which sources the tokens
     * @param _to The account which receives the tokens
     * @param _amount The number of cTokens to transfer
     * @return bool
     */
    function transferAllowed(address _cToken, address _from, address _to, uint256 _amount) external returns (bool) {
        _cToken;
        _from;
        _to;
        _amount;
        return redeemAllowedInternal(_cToken, _from, _amount);
    }
    
    function _redeemAllowedInternal(address _cToken, address _from, uint256 _amount) internal view returns (bool) {
        require(markets[_cToken].isListed == true, "Comptroller/market-not-listed");
        require(markets[_cToken].accountMembership[_from] == true, "Comptroller/account-not-entered-market");
        // Perform hypothetical liquidity check to guard against shortfall
        uint256 shortfall = getHypotheticalAccountLiquidityInternal(_from, CToken(_cToken), _amount, 0);
        require(shortfall < 0, "Comptroller/insufficient-liquidity");
        return true;
    }
    
    // -- Events --
    event MarketListed(CToken cToken);
    event MarketEntered(CToken cToken, address account);
    event NewMaxAssets(uint256 newMaxAssets);
    event NewPriceOracle(PriceOracle newPriceOracle);
}


contract CToken {
    using SafeMath for uint256;
    
    address admin;
    
    string public name;
    string public symbol;
    uint256 public decimals;
    bool public constant isCToken = true;
    
    IERC20 public underlyingToken;
    Comptroller public comptroller;
    IInterestRateModel public interestRateModel;
    
    // Market Data
    uint256 public lastAccrualBlockNumber;
    uint256 public totalSupply;
    uint256 public totalBorrows;
    uint256 public totalReserves;
    
    // Interest Rate Model
    uint256 borrowIndex = 1e18;
    
    
    // Users
    mapping(address => uint256) accountTokens;
    
    // Mapping of the accounts with outstanding borrow balances
    mapping(address => BorrowSnapshot) accountBorrows;
    
    // Allowances
    mapping(address => mapping(address => uint256)) transferAllowances;
    
    /**
     * @notice Container for borrow balance information
     * @member principal Total balance (with accrued interest), after applying the most recent balance-chaging action
     * @member interestIndex Global borrowIndex as of the most recent balance-changing action
     */
    struct BorrowSnapshot {
        uint256 principal;
        uint256 interestIndex;
    }
    
    /**
     * @notice The initial exchange rate used when minting the first cTokens (used when totalSupply = 0) 
     */
    uint256 public initialExchangeRateMantissa;
    
    constructor(string memory _name, string memory _symbol, uint256 _decimals, address _underlyingToken, address _comptroller, address _interestRateModel) public {
        name = _name;
        symbol = _symbol;
        decimals = _decimals;
        admin = msg.sender;
        comptroller = Comptroller(_comptroller);
        underlyingToken = IERC20(_underlyingToken);
        interestRateModel = IInterestRateModel(_interestRateModel);
        
        // Initialize block number
        lastAccrualBlockNumber = block.number;
    }
    
    /**
     * @notice Applies accrued interest to total borrows and reserve
     * @dev This calculaters interest accrued from the last checkpointed block,
     *      up to the current block and writes new checkpoint to storage
     */
    function accrueInterest() public returns (uint256) {
        
        // Calculate the current borrow interest rate
        uint256 borrowRateMantissa = interestRateModel.getBorrowRate(getTotalCash(), totalBorrows, totalReserves);
        
        // Check maxMantissa
        
        // Remember the initial block number
        uint256 currentBlockNumber = block.number;
        
        // Calculate the number of blocks elapsed since the last accrual
        uint256 blockDelta = currentBlockNumber.sub(accrualBlockNumber);
        
        // Calculate the interest accumulated into borrows and reserves and the new index
        // simpleInterestFactor = borrowRate * blockDelta
        // interestRateAccumulated = simpleInterestFactor * totalBorrows
        // totalBorrowsNew = interestAccumulated + totalBorrows
        // totalReservesNew = interestAccumulated * reservesFactor + totalReserves
        // borrowIndexNew = simpleInterestFactor * borrowIndex + borrowIndex
        
        uint256 simpleInterestFactor = borrowRateMantissa.mul(blockDelta);
        uint256 interestRateAccumulated = simpleInterestFactor.mul(totalBorrows);
        uint256 totalBorrowsNew = totalBorrows.add(interestRateAccumulated);
        uint256 totalReservesNew = (interestRateAccumulated.mul(reserveFactor)).add(totalReserves);
        uint256 borrowIndexNew = (simpleInterestFactor.mul(borrowIndex)).add(borrowIndex); // ->  Check this value
        
        // Write calculated values into storage
        accrualBlockNumber = currentBlockNumber;
        borrowIndex = borrowIndexNew;
        totalBorrows = totalBorrowsNew;
        totalReserves = totalBorrowsNew;
        
        // Emit event
        emit AccrueInterest(interestRateAccumulated, borrowIndexNew, totalBorrows);
    }
     
     
    function mint(uint256 _amount) public {
        // Accrue Interest
        accrueInterest();
        
        // Check if mint is allowed
        require(comptroller.mintAllowed(address(this)) == true, "CToken/mint-not-allowed");
        
        // Check accrualBlockNumber
        require(lastAccrualBlockNumber == block.number, "CToken/market-not-fresh");
        
        // Transfer tokens into contract
        require(_underlyingToken.allowance(msg.sender, address(this)) >= _amount, "CToken/insufficient-allowance");
        require(_underlyingToken.balanceOf(msg.sender) >= _amount, "CToken/insufficient-balance");
        
        // Get current Exchange Rate
        uint256 currentExchangeRate = exchangeRate();
        
        // Calculate tokens to mint
        uint256 mintTokens = _amount.div(currentExchangeRate).div(1e18);
        
        // Transfer In
        underlyingToken.transferFrom(msg.sender, address(this), _amount);
        
        // Increase totalSupply
        totalSupply = totalSupply.add(mintTokens);
        
        // Increase accountTokens
        accountTokens[msg.sender] = accountTokens[msg.sender].add(mintTokens);
        
        // Emit Events
        emit Mint(minter, _amount, mintTokens);
        emit Transfer(address(this), msg.sender, mintTokens);
    }
    
    function redeem(uint256 _redeemTokens) public {
        
        // Get Exchange Rate
        uint256 exchangeRateMantissa = exchangeRate();
        
        // Calculate the exchange rate and the amount of underlying to be redeemed
        // redeemAmount = _cTokenAmount * exchangeRate
        uint256 redeemAmount = exchangeRateMantissa.mul(_redeemTokens).div(1e18);
        
        // Check if redeem is allowed
        bool allowed = comptroller.redeemAllowed(address(this), msg.sender, _redeemTokens);
        require(allowed == true, "CToken/redeem-not-allowed");
        
        // Verify market's block number equals current block number
        require(accrualBlockNumber == block.number, "CToken/market-not-fresh");
        
        // Calculate the new total supply and redeemer balance, checking for underflow
        // totalSupplyNew = totalSupply - redeemTokens
        // accountTokensNew = accountTokens[redeemer] - redeemTokens
        uint256 totalSupplyNew = totalSupply.sub(_redeemTokens);
        uint256 accountTokensNew = accountTokens[msg.sender].sub(_redeemTokens);
        
        require(getTotalCash() < redeemAmount, "CToken/insufficient-cash-in-market");
        
        // Transfer Tokens
        require(underlyingToken.transfer(msg.sender, redeemAmount) == true, "CToken/token-transfer-failed");
        
        // Write previously calculated values into storage
        totalSupply = totalSupplyNew;
        accountTokens[msg.sender] = accountTokensNew;
        
        // Emit events
        emit Transfer(msg.sender, address(this), _redeemTokens);
        emit Redeem(msg.sender, redeemAmount, _redeemTokens);
    }
    
    function redeemUnderlying(uint256 _redeemAmount) public {
        
        // Get exchangeRateMantissa
        uint256 exchangeRateMantissa = exchangeRateStoredInteral();
        
        // Get current exchangeRate and calculate the amount to be redeemed
        // redeemTokens = redeemAmount / exchangeRate
        // redeemAmount = redeemAmount
        uint256 redeemTokens = _redeemAmount.div(exchangeRateMantissa.div(1e18));
        
        // Check if redeem is allowed
        bool allowed = comptroller.redeemAllowed(address(this), msg.sender, redeemTokens);
        require(allowed == true, "CToken/redeem-not-allowed");
        
        // Verify market's block number equals current block number
        require(accrualBlockNumber == block.number, "CToken/market-not-fresh");
        
        // Calculate the new total supply and redeemer balance, checking for underflow
        // totalSupplyNew = totalSupply - redeemTokens
        // accountTokensNew = accountTokens[redeemer] - redeemTokens
        uint256 totalSupplyNew = totalSupply.sub(redeemTokens);
        uint256 accountTokensNew = accountTokens[msg.sender].sub(redeemTokens);
        
        require(getTotalCash() < redeemAmount, "CToken/insufficient-cash-in-market");
        
        // Transfer Tokens
        require(underlyingToken.transfer(msg.sender, redeemAmount) == true, "CToken/token-transfer-failed");
        
        // Write previously calculated values into storage
        totalSupply = totalSupplyNew;
        accountTokens[msg.sender] = accountTokensNew;
        
        // Emit events
        emit Transfer(msg.sender, address(this), _redeemTokens);
        emit Redeem(msg.sender, redeemAmount, _redeemTokens);
    }
    
    /**
     * @notice Users borrow assets from the protocol to their own address
     * @param borrowAmount The amount of the underlying asset to borrow
     * @return uint256 0=success, otherwise failure
     */
    function borrow(uint256 _borrowAmount) public returns (bool) {
        bool allowed = comptroller.borrowAllowed(address(this), msg.sender, _borrowAmount);
        require(allowed == true, "CToken/borrow-not-allowed");
        
        // Verify market's block number equals current block number
        require(accrualBlockNumber == block.number, "CToken/market-not-fresh");
        
        require(getTotalCash() > _borrowAmount, "CToken/insufficient-cash-in-market");
        
        // Calculate the new borrower and total borrow balances, failing on overflow
        uint256 accountBorrows = borrowBalanceStored(msg.sender);
        uint256 accountBorrowsNew = accountBorrows.add(_borrowAmount);
        uint256 totalBorrowsNew = totalBorrows.add(_borrowAmount);
        
        // Transfer Tokens
        require(underlyingToken.transfer(msg.sender, _borrowAmount) == true, "CToken/token-transfer-failed");
        
        accountBorrows[msg.sender].principal = accountBorrowsNew;
        accountBorrows[msg.sender].interestIndex = borrowIndex;
        totalBorrows = totalBorrowsNew;
        
        emit Borrow(msg.sender, _borrowAmount, accountBorrowsNew, totalBorrowsNew);
    }
    
    /**
     * @notice Sender repays a borrow belonging to borrower
     * @param _borrower the account with the debt being payed off
     * @param _repayAmount The amount to repay
     * @return bool
     */
    function repayBorrowOnBehalf(address _borrower, uint256 _repayAmount) public returns (bool) {
        // Accrue interest
        accrueInterest();
        require(_repayLoan(msg.sender, _borrower, _repayAmount) == true, "CToken/repay-borrow-failed");
    }
    
    /**
     * @notice Sender own pays borrow
     * @param _repayAmount The amount to repay
     * @return bool
     */
    function repayLoan(uint256 _repayAmount) public returns (bool) {
        accrueInterest();
        require(_repayLoan(msg.sender, msg.sender, _repayAmount) == true, "CToken/repay-borrow-failed");
        return true;
    }
    
    function _repayLoan(address _payer, address _borrower, uint256 _repayAmount) internal returns (bool) {
        uint256 allowed = comptroller.repayBorrowAllowed(address(this), _payer, _borrower, _repayAmount);
        require(allowed == true, "CToken/borrow-repay-not-allowed");
        require(accrualBlockNumber == block.number, "CToken/market-not-fresh");
        
        // Remember original borrowerIndex for verification purposes
        uint256 oldBorrowIndex = accountBorrows[_borrower].interestIndex;
        
        // Fetch the amount the borrower owes, with accumulated interest
        uint256 accountBorrows = borrowBalancesStoredInternal(_borrower);
        
        // Transfer tokens into contract
        require(_underlyingToken.allowance(msg.sender, address(this)) >= _repayAmount, "CToken/insufficient-allowance");
        require(_underlyingToken.balanceOf(msg.sender) >= _repayAmount, "CToken/insufficient-balance");
        
        // Calculate the new borrower and total borrow balances, failing on underflow
        // accountBorrowsNew = accountBorrows - repayAmount
        // totalBorrowNew = totalBorrows - repayAmount
        uint256 accountBorrowsNew = accountBorrows.sub(_repayAmount);
        uint256 totalBorrowsNew = totalBorrows.sub(_repayAmount);
        
        // Transfer tokens in
        require(underlyingToken.transferFrom(_borrower, address(this), _repayAmount) == true, "CToken/token-transfer-failed");
        
        // Write the previously calculated values into storage
        accountBorrows[_borrower].principal = accountBorrowsNew;
        accountBorrows[_borrower].interestIndex = borrowIndex;
     
        // Emit events
        emit RepayBorrow(_payer, _borrower, _repayAmount, accountBorrowsNew, totalBorrowsNew);
        
        return true;
    }
    
    /**
     * @notice Transfer `amount` tokens from `msg.sender` to `to`
     * @param _to The address of the destination account
     * @param _amount The number of tokens to transfer
     * @return bool Whether or not the transfer succeeded
     */
    function transfer(address _to, uint256 _amount) external returns (bool) {
        return _transferTokens(msg.sender, msg.sender, _to, _amount);
    }
    
    /**
     * @notice Transfer `amount` tokens from `src` to `to`
     * @param _from The address of the source account
     * @param _to The address of the destination account
     * @param _amount The number of tokens to transfer
     * @return bool Whether or not the transfer succeeded
     */
    function transferFrom(address _from, address _to, uint256 _amount) external returns (bool) {
        return _transferTokens(msg.sender, _from, _to, _amount);
    }
    
    /**
     * @notice Transfer `_amount` of tokens from `_from` to `_to` by `spender`
     * @dev Called by both `transfer` and `transferFrom` internally
     * @param _spender The address of the account performing the transfer
     * @param _from The address of the source account
     * @param _to The address of the destination account
     * @param _tokens The number of tokens to transfer
     * @return Whether or not the transfer succeeded
     */
    function _transferTokens(address _spender, address _from, address _to, uint256 _amount) internal returns (bool) {
        bool allowed = comptroller.transferAllowed(address(this), _from, _to, _amount);
        require(allowed == true, "CToken/transfer-not-allowed");
        
        // Do not allow self transfer
        require(_from != _to, "CToken/transfer-not-allowed");
        
        // Get the allowance, infinite for the account owner
        uint256 startingAllowance = 0;
        if(_spender == _from) {
            startingAllowance = uint256(-1);
        } else {
            startingAllowance = transferAllowances[_from][_spender];
        }
        
        // Calculate allowanceNew, fromTokensNew, toTokensNew
        uint256 allowanceNew = startingAllowance.sub(_amount);
        uint256 fromTokensNew = accountTokens[_from].sub(_amount);
        uint256 toTokensNew = accountTokens[_to].sub(_amount);
        
        // Update storage
        accountTokens[_from] = fromTokensNew;
        accountTokens[_to] = toTokensNew;
        
        // Update allowance
        if(startingAllowance != uint256(-1)) {
            transferAllowances[_from][_spender] = allowanceNew;
        }
        
        // Emit events
        emit Transfer(_from, _to, _amount);
        
        return true;
    }
    
    /**
     * @notice The sender liquidates the borrowers collateral
     * @param _borrower The borrower of this cToken to be liquidated
     * @param _cTokenCollateral The market in which to seize collateral from the borrower
     * @param _amount The amount of the underlying borrowed asset to repay
     * @return bool
     */
    function liquidateBorrow(address _borrower, uint256 _amount, CToken _cTokenCollateral) external returns (bool) {
        accrueInterest();
        _cTokenCollateral.accrueInterest();
        return _liquidateBorrow(msg.sender, _borrower, _amount, _cTokenCollateral);
    }
      
    /**
     * @notice The liquidator liquidates the borrowers collateral
     * @param _borrower The borrower of this cToken to be liquidated
     * @param _liquidator The address repaying the borrow and seizing collateral
     * @param _cTokenCollateral The market in which to seize collateral from the borrower
     * @param _amount The amount of underlying borrowed asset to repay
     * @return bool
     */
    function _liquidateBorrow(address _liquidator, address _borrower, uint256 _amount, CToken _cTokenCollateral) internal returns (bool) {
        bool allowed = comptroller.liquidateBorrowAllowed(address(this), address(_cTokenCollateral), _liquidator, _borrower, _amount);
        require(allowed == true, "CToken/liquidate-not-allowed");
        require(accrualBlockNumber == block.number, "CToken/market-not-fresh");
        require(_amount > 0 && _amount != uint256(-1), "CToken/invalid-amount");
        
        // Verify cTokenCollateral market's block number equals current block number
        if(_cTokenCollateral.accrualBlockNumber() == block.number, "CToken/collateral-market-not-fresh");
        
        // Borrower != liquidator
        require(_borrower != _liquidator, "CToken/liquidator-is-borrower");
        
        // Calculate the number of collateral tokens that will be seized
        uint256 seizeTokens = comptroller.liquidateCalculateSeizeTokens(address(this), address(_cTokenCollateral), _amount);
        require(seizeTokens < _cTokenCollateral.balanceOf(_borrower), "CToken/token-insufficient-balance");
        
        // Repay Borrow
        require(_repayLoan(_liquidator, _borrower, _amount) == true, "CToken/liquidate-repay-borrow-failed");
        
        // Seize Tokens
        require(_cTokenCollateral.seize(_liquidator, _borrower, seizeTokens) == true, "CToken/token-seizure-failed");
        
        // Emit events
        emit LiquidateBorrow(_liquidator, _borrower, _amount, address(_cTokenCollateral), seizeTokens);
        
        return true;
    }
    
    // Repay Full Amount method
    function exchangeRate() public view returns (uint256) {
        // Accrue Interest
        accrueInterest();
        return exchangeRateStored();
    }
    
    function exchangeRateStoredInteral() internal view returns (uint256) {
        if(totalSupply == 0) {
            return initialExchangeRateMantissa;
        }
        
        // exchangeRate = (totalCash + totalBorrows - totalReserves) / totalSupply
        uint256 totalCash = getTotalCash();
        uint256 cashPlusBorrowsMinusReserves = (totalCash.add(totalBorrows).minus(totalReserves)).mul(1e18);
        return cashPlusBorrowsMinusReserves.div(totalSupply); // -> scaled by 1e18
    }
    
    function getTotalCash() internal view returns (uint256) {
        return underlyingToken.balanceOf(address(this));
    }
    
    
    /**
     * @notice Get a snapshot of the account's balances, and the cached exchange rate
     * @dev This is used by comptroller to more efficiently perform liquidity checks.
     * @params _account Address of the account to snapshot
     * @return (token balance, borrow balance, exchange rate mantissa)
     */
    function getAccountSnapshot(address _account) external view returns (uint256, uint256, uint256) {
        uint256 cTokenBalance = accountTokens[_account];
        
        // Get Borrow Balance
        uint256 borrowBalance = borrowBalanceStoredInternal(_account);
        uint256 exchangeRate = exchangeRateStoredInternal();
        
        return (cTokenBalance, borrowBalance, exchangeRate);
    }
    
    /**
     * @notice Return the borrow balance of account based on stored data
     * @param _account The address whose balance should be calculated
     * @return The calculated balance or 0
     */
    function borrowBalanceStored(address _account) internal view returns (uint256) {
        
        // Get BorrowBalance and borrowIndex
        BorrowSnapshot storage borrowSnapshot = accountBorrows[_account];
        
        // If borrowBalance = 0 then borrowIndex is likely also 0
        if(borrowSnapshot.principal == 0) {
            return 0;
        }
        
        // Calculate the borrow balance using the interest index
        // recentBorrowBalance = borrower.borrowBalance * market.borrowIndex / borrower.borrowIndex
        uint256 principalTimesIndex = borrowSnapshot.principal.mul(borrowIndex);
        
        uint256 result = principalTimesIndex.div(interestIndex);
        return result;
    }
    
    // -- Events --
    event Mint(address minter, uint256 amount, uint256 mintTokens);
    event AccrueInterest(uint256 interestRateAccumulated, uint256 borrowIndex, uint256 totalBorrows);
    event Borrow(address _borrower, uint256 _borrowAmount, uint256 _accountBorrows, uint256 _totalBorrows);
    event RepayBorrow(address _payer, address _borrower, uint256 _repayAmount, uint256 _accountBorrows, uint256 _totalBorrows);
    event Transfer(address _from, address _to, uint256 _amount);
}

contract MoneyMarket is CToken {
    
    
    
    constructor(string memory _name, string memory _symbol, uint256 _decimals) public CToken(_name, _symbol, _decimals) {}
        
    
}

PriceOracle.sol

pragma solidity ^0.5.10;
import './MoneyMarket.sol';

interface PriceOracle {
    function isPriceOracle() external pure returns (bool);
    function getUnderlyingPrice(CToken cToken) view returns (uint);
}