CTokenCash.sol

// SPDX-License-Identifier: BSD-3-Clause
pragma solidity ^0.8.10;

import "../cErc20Delegate/ComptrollerInterface.sol";
import "../cErc20Delegate/ErrorReporter.sol";
import "../cErc20Delegate/EIP20Interface.sol";
import "../cErc20Delegate/InterestRateModel.sol";
import "../cErc20Delegate/ExponentialNoError.sol";
import "./CTokenInterfacesModifiedCash.sol";

/**
 * @title Ondo's CToken Contract for CASH
 * @notice Abstract base for CTokens w/underlying as CASH tokens
 * @dev Does KYC checks on key functions
 * @author Compound + Ondo
 */
abstract contract CTokenCash is
  CTokenInterface,
  ExponentialNoError,
  TokenErrorReporter
{
  /**
   * @notice Initialize the money market
   * @param comptroller_ The address of the Comptroller
   * @param interestRateModel_ The address of the interest rate model
   * @param initialExchangeRateMantissa_ The initial exchange rate, scaled by 1e18
   * @param name_ EIP-20 name of this token
   * @param symbol_ EIP-20 symbol of this token
   * @param decimals_ EIP-20 decimal precision of this token
   * @param kycRegistry_ KYC Registry contract address
   * @param kycRequirementGroup_ KYC Requirement group to check KYC status
   *                             against
   */
  function initialize(
    ComptrollerInterface comptroller_,
    InterestRateModel interestRateModel_,
    uint initialExchangeRateMantissa_,
    string memory name_,
    string memory symbol_,
    uint8 decimals_,
    address kycRegistry_,
    uint256 kycRequirementGroup_
  ) public {
    require(msg.sender == admin, "only admin may initialize the market");
    require(
      accrualBlockNumber == 0 && borrowIndex == 0,
      "market may only be initialized once"
    );

    // Set initial exchange rate
    initialExchangeRateMantissa = initialExchangeRateMantissa_;
    require(
      initialExchangeRateMantissa > 0,
      "initial exchange rate must be greater than zero."
    );

    // Set the comptroller
    uint err = _setComptroller(comptroller_);
    require(err == NO_ERROR, "setting comptroller failed");

    // Initialize block number and borrow index (block number mocks depend on comptroller being set)
    accrualBlockNumber = getBlockNumber();
    borrowIndex = mantissaOne;

    // Set the interest rate model (depends on block number / borrow index)
    err = _setInterestRateModelFresh(interestRateModel_);
    require(err == NO_ERROR, "setting interest rate model failed");

    name = name_;
    symbol = symbol_;
    decimals = decimals_;

    // The counter starts true to prevent changing it from zero to non-zero (i.e. smaller cost/refund)
    _notEntered = true;

    // Initialize KYCRegistryClient
    _setKYCRegistry(kycRegistry_);
    _setKYCRequirementGroup(kycRequirementGroup_);
  }

  /**
   * @notice Transfer `tokens` tokens from `src` to `dst` by `spender`
   * @dev Called by both `transfer` and `transferFrom` internally
   * @param spender The address of the account performing the transfer
   * @param src The address of the source account
   * @param dst The address of the destination account
   * @param tokens The number of tokens to transfer
   * @return 0 if the transfer succeeded, else revert
   */
  function transferTokens(
    address spender,
    address src,
    address dst,
    uint tokens
  ) internal returns (uint) {
    /* Revert if KYC not valid */
    require(_getKYCStatus(spender), "Spender not KYC'd");
    require(_getKYCStatus(src), "Source not KYC'd");
    require(_getKYCStatus(dst), "Destination not KYC'd");

    /* Fail if transfer not allowed */
    uint allowed = comptroller.transferAllowed(address(this), src, dst, tokens);
    if (allowed != 0) {
      revert TransferComptrollerRejection(allowed);
    }

    /* Do not allow self-transfers */
    if (src == dst) {
      revert TransferNotAllowed();
    }

    /* Get the allowance, infinite for the account owner */
    uint startingAllowance = 0;
    if (spender == src) {
      startingAllowance = type(uint).max;
    } else {
      startingAllowance = transferAllowances[src][spender];
    }

    /* Do the calculations, checking for {under,over}flow */
    uint allowanceNew = startingAllowance - tokens;
    uint srcTokensNew = accountTokens[src] - tokens;
    uint dstTokensNew = accountTokens[dst] + tokens;

    /////////////////////////
    // EFFECTS & INTERACTIONS
    // (No safe failures beyond this point)

    accountTokens[src] = srcTokensNew;
    accountTokens[dst] = dstTokensNew;

    /* Eat some of the allowance (if necessary) */
    if (startingAllowance != type(uint).max) {
      transferAllowances[src][spender] = allowanceNew;
    }

    /* We emit a Transfer event */
    emit Transfer(src, dst, tokens);

    // unused function
    // comptroller.transferVerify(address(this), src, dst, tokens);

    return NO_ERROR;
  }

  /**
   * @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 override nonReentrant returns (bool) {
    return transferTokens(msg.sender, msg.sender, dst, amount) == NO_ERROR;
  }

  /**
   * @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 override nonReentrant returns (bool) {
    return transferTokens(msg.sender, src, dst, amount) == NO_ERROR;
  }

  /**
   * @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 (uint256.max means infinite)
   * @return Whether or not the approval succeeded
   */
  function approve(
    address spender,
    uint256 amount
  ) external override returns (bool) {
    address src = msg.sender;
    transferAllowances[src][spender] = amount;
    emit Approval(src, spender, amount);
    return true;
  }

  /**
   * @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 override returns (uint256) {
    return transferAllowances[owner][spender];
  }

  /**
   * @notice Get the token balance of the `owner`
   * @param owner The address of the account to query
   * @return The number of tokens owned by `owner`
   */
  function balanceOf(address owner) external view override returns (uint256) {
    return accountTokens[owner];
  }

  /**
   * @notice Get the underlying balance of the `owner`
   * @dev This also accrues interest in a transaction
   * @param owner The address of the account to query
   * @return The amount of underlying owned by `owner`
   */
  function balanceOfUnderlying(address owner) external override returns (uint) {
    Exp memory exchangeRate = Exp({mantissa: exchangeRateCurrent()});
    return mul_ScalarTruncate(exchangeRate, accountTokens[owner]);
  }

  /**
   * @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.
   * @param account Address of the account to snapshot
   * @return (possible error, token balance, borrow balance, exchange rate mantissa)
   */
  function getAccountSnapshot(
    address account
  ) external view override returns (uint, uint, uint, uint) {
    return (
      NO_ERROR,
      accountTokens[account],
      borrowBalanceStoredInternal(account),
      exchangeRateStoredInternal()
    );
  }

  /**
   * @dev Function to simply retrieve block number
   *  This exists mainly for inheriting test contracts to stub this result.
   */
  function getBlockNumber() internal view virtual returns (uint) {
    return block.number;
  }

  /**
   * @notice Returns the current per-block borrow interest rate for this cToken
   * @return The borrow interest rate per block, scaled by 1e18
   */
  function borrowRatePerBlock() external view override returns (uint) {
    return
      interestRateModel.getBorrowRate(
        getCashPrior(),
        totalBorrows,
        totalReserves
      );
  }

  /**
   * @notice Returns the current per-block supply interest rate for this cToken
   * @return The supply interest rate per block, scaled by 1e18
   */
  function supplyRatePerBlock() external view override returns (uint) {
    return
      interestRateModel.getSupplyRate(
        getCashPrior(),
        totalBorrows,
        totalReserves,
        reserveFactorMantissa
      );
  }

  /**
   * @notice Returns the current total borrows plus accrued interest
   * @return The total borrows with interest
   */
  function totalBorrowsCurrent() external override nonReentrant returns (uint) {
    accrueInterest();
    return totalBorrows;
  }

  /**
   * @notice Accrue interest to updated borrowIndex and then calculate account's borrow balance using the updated borrowIndex
   * @param account The address whose balance should be calculated after updating borrowIndex
   * @return The calculated balance
   */
  function borrowBalanceCurrent(
    address account
  ) external override nonReentrant returns (uint) {
    accrueInterest();
    return borrowBalanceStored(account);
  }

  /**
   * @notice Return the borrow balance of account based on stored data
   * @param account The address whose balance should be calculated
   * @return The calculated balance
   */
  function borrowBalanceStored(
    address account
  ) public view override returns (uint) {
    return borrowBalanceStoredInternal(account);
  }

  /**
   * @notice Return the borrow balance of account based on stored data
   * @param account The address whose balance should be calculated
   * @return (error code, the calculated balance or 0 if error code is non-zero)
   */
  function borrowBalanceStoredInternal(
    address account
  ) internal view returns (uint) {
    /* Get borrowBalance and borrowIndex */
    BorrowSnapshot storage borrowSnapshot = accountBorrows[account];

    /* If borrowBalance = 0 then borrowIndex is likely also 0.
     * Rather than failing the calculation with a division by 0, we immediately return 0 in this case.
     */
    if (borrowSnapshot.principal == 0) {
      return 0;
    }

    /* Calculate new borrow balance using the interest index:
     *  recentBorrowBalance = borrower.borrowBalance * market.borrowIndex / borrower.borrowIndex
     */
    uint principalTimesIndex = borrowSnapshot.principal * borrowIndex;
    return principalTimesIndex / borrowSnapshot.interestIndex;
  }

  /**
   * @notice Accrue interest then return the up-to-date exchange rate
   * @return Calculated exchange rate scaled by 1e18
   */
  function exchangeRateCurrent() public override nonReentrant returns (uint) {
    accrueInterest();
    return exchangeRateStored();
  }

  /**
   * @notice Calculates the exchange rate from the underlying to the cToken
   * @dev This function does not accrue interest before calculating the exchange rate
   * @return Calculated exchange rate scaled by 1e18
   */
  function exchangeRateStored() public view override returns (uint) {
    return exchangeRateStoredInternal();
  }

  /**
   * @notice Calculates the exchange rate from the underlying to the cToken
   * @dev This function does not accrue interest before calculating the exchange rate
   * @return calculated exchange rate scaled by 1e18
   */
  function exchangeRateStoredInternal() internal view virtual returns (uint) {
    uint _totalSupply = totalSupply;
    if (_totalSupply == 0) {
      /*
       * If there are no tokens minted:
       *  exchangeRate = initialExchangeRate
       */
      return initialExchangeRateMantissa;
    } else {
      /*
       * Otherwise:
       *  exchangeRate = (totalCash + totalBorrows - totalReserves) / totalSupply
       */
      uint totalCash = getCashPrior();
      uint cashPlusBorrowsMinusReserves = totalCash +
        totalBorrows -
        totalReserves;
      uint exchangeRate = (cashPlusBorrowsMinusReserves * expScale) /
        _totalSupply;

      return exchangeRate;
    }
  }

  /**
   * @notice Get cash balance of this cToken in the underlying asset
   * @return The quantity of underlying asset owned by this contract
   */
  function getCash() external view override returns (uint) {
    return getCashPrior();
  }

  /**
   * @notice Applies accrued interest to total borrows and reserves
   * @dev This calculates interest accrued from the last checkpointed block
   *   up to the current block and writes new checkpoint to storage.
   */
  function accrueInterest() public virtual override returns (uint) {
    /* Remember the initial block number */
    uint currentBlockNumber = getBlockNumber();
    uint accrualBlockNumberPrior = accrualBlockNumber;

    /* Short-circuit accumulating 0 interest */
    if (accrualBlockNumberPrior == currentBlockNumber) {
      return NO_ERROR;
    }

    /* Read the previous values out of storage */
    uint cashPrior = getCashPrior();
    uint borrowsPrior = totalBorrows;
    uint reservesPrior = totalReserves;
    uint borrowIndexPrior = borrowIndex;

    /* Calculate the current borrow interest rate */
    uint borrowRateMantissa = interestRateModel.getBorrowRate(
      cashPrior,
      borrowsPrior,
      reservesPrior
    );
    require(
      borrowRateMantissa <= borrowRateMaxMantissa,
      "borrow rate is absurdly high"
    );

    /* Calculate the number of blocks elapsed since the last accrual */
    uint blockDelta = currentBlockNumber - accrualBlockNumberPrior;

    /*
     * Calculate the interest accumulated into borrows and reserves and the new index:
     *  simpleInterestFactor = borrowRate * blockDelta
     *  interestAccumulated = simpleInterestFactor * totalBorrows
     *  totalBorrowsNew = interestAccumulated + totalBorrows
     *  totalReservesNew = interestAccumulated * reserveFactor + totalReserves
     *  borrowIndexNew = simpleInterestFactor * borrowIndex + borrowIndex
     */

    Exp memory simpleInterestFactor = mul_(
      Exp({mantissa: borrowRateMantissa}),
      blockDelta
    );
    uint interestAccumulated = mul_ScalarTruncate(
      simpleInterestFactor,
      borrowsPrior
    );
    uint totalBorrowsNew = interestAccumulated + borrowsPrior;
    uint totalReservesNew = mul_ScalarTruncateAddUInt(
      Exp({mantissa: reserveFactorMantissa}),
      interestAccumulated,
      reservesPrior
    );
    uint borrowIndexNew = mul_ScalarTruncateAddUInt(
      simpleInterestFactor,
      borrowIndexPrior,
      borrowIndexPrior
    );

    /////////////////////////
    // EFFECTS & INTERACTIONS
    // (No safe failures beyond this point)

    /* We write the previously calculated values into storage */
    accrualBlockNumber = currentBlockNumber;
    borrowIndex = borrowIndexNew;
    totalBorrows = totalBorrowsNew;
    totalReserves = totalReservesNew;

    /* We emit an AccrueInterest event */
    emit AccrueInterest(
      cashPrior,
      interestAccumulated,
      borrowIndexNew,
      totalBorrowsNew
    );

    return NO_ERROR;
  }

  /**
   * @notice Sender supplies assets into the market and receives cTokens in exchange
   * @dev Accrues interest whether or not the operation succeeds, unless reverted
   * @param mintAmount The amount of the underlying asset to supply
   */
  function mintInternal(uint mintAmount) internal nonReentrant {
    accrueInterest();
    // mintFresh emits the actual Mint event if successful and logs on errors, so we don't need to
    mintFresh(msg.sender, mintAmount);
  }

  /**
   * @notice User supplies assets into the market and receives cTokens in exchange
   * @dev Assumes interest has already been accrued up to the current block
   * @param minter The address of the account which is supplying the assets
   * @param mintAmount The amount of the underlying asset to supply
   */
  function mintFresh(address minter, uint mintAmount) internal {
    /* Revert if minter not KYC'd */
    require(_getKYCStatus(minter), "Minter not KYC'd");

    /* Fail if mint not allowed */
    uint allowed = comptroller.mintAllowed(address(this), minter, mintAmount);
    if (allowed != 0) {
      revert MintComptrollerRejection(allowed);
    }

    /* Verify market's block number equals current block number */
    if (accrualBlockNumber != getBlockNumber()) {
      revert MintFreshnessCheck();
    }

    Exp memory exchangeRate = Exp({mantissa: exchangeRateStoredInternal()});

    /////////////////////////
    // EFFECTS & INTERACTIONS
    // (No safe failures beyond this point)

    /*
     *  We call `doTransferIn` for the minter and the mintAmount.
     *  Note: The cToken must handle variations between ERC-20 and ETH underlying.
     *  `doTransferIn` reverts if anything goes wrong, since we can't be sure if
     *  side-effects occurred. The function returns the amount actually transferred,
     *  in case of a fee. On success, the cToken holds an additional `actualMintAmount`
     *  of cash.
     */
    uint actualMintAmount = doTransferIn(minter, mintAmount);

    /*
     * We get the current exchange rate and calculate the number of cTokens to be minted:
     *  mintTokens = actualMintAmount / exchangeRate
     */

    uint mintTokens = div_(actualMintAmount, exchangeRate);

    /*
     * We calculate the new total supply of cTokens and minter token balance, checking for overflow:
     *  totalSupplyNew = totalSupply + mintTokens
     *  accountTokensNew = accountTokens[minter] + mintTokens
     * And write them into storage
     */
    totalSupply = totalSupply + mintTokens;
    accountTokens[minter] = accountTokens[minter] + mintTokens;

    /* We emit a Mint event, and a Transfer event */
    emit Mint(minter, actualMintAmount, mintTokens);
    emit Transfer(address(this), minter, mintTokens);

    /* We call the defense hook */
    // unused function
    // comptroller.mintVerify(address(this), minter, actualMintAmount, mintTokens);
  }

  /**
   * @notice Sender redeems cTokens in exchange for the underlying asset
   * @dev Accrues interest whether or not the operation succeeds, unless reverted
   * @param redeemTokens The number of cTokens to redeem into underlying
   */
  function redeemInternal(uint redeemTokens) internal nonReentrant {
    accrueInterest();
    // redeemFresh emits redeem-specific logs on errors, so we don't need to
    redeemFresh(payable(msg.sender), redeemTokens, 0);
  }

  /**
   * @notice Sender redeems cTokens in exchange for a specified amount of underlying asset
   * @dev Accrues interest whether or not the operation succeeds, unless reverted
   * @param redeemAmount The amount of underlying to receive from redeeming cTokens
   */
  function redeemUnderlyingInternal(uint redeemAmount) internal nonReentrant {
    accrueInterest();
    // redeemFresh emits redeem-specific logs on errors, so we don't need to
    redeemFresh(payable(msg.sender), 0, redeemAmount);
  }

  /**
   * @notice User redeems cTokens in exchange for the underlying asset
   * @dev Assumes interest has already been accrued up to the current block
   * @param redeemer The address of the account which is redeeming the tokens
   * @param redeemTokensIn The number of cTokens to redeem into underlying (only one of redeemTokensIn or redeemAmountIn may be non-zero)
   * @param redeemAmountIn The number of underlying tokens to receive from redeeming cTokens (only one of redeemTokensIn or redeemAmountIn may be non-zero)
   */
  function redeemFresh(
    address payable redeemer,
    uint redeemTokensIn,
    uint redeemAmountIn
  ) internal {
    /* Revert if redeemer not KYC'd */
    require(_getKYCStatus(redeemer), "Redeemer not KYC'd");

    require(
      redeemTokensIn == 0 || redeemAmountIn == 0,
      "one of redeemTokensIn or redeemAmountIn must be zero"
    );

    /* exchangeRate = invoke Exchange Rate Stored() */
    Exp memory exchangeRate = Exp({mantissa: exchangeRateStoredInternal()});

    uint redeemTokens;
    uint redeemAmount;
    /* If redeemTokensIn > 0: */
    if (redeemTokensIn > 0) {
      /*
       * We calculate the exchange rate and the amount of underlying to be redeemed:
       *  redeemTokens = redeemTokensIn
       *  redeemAmount = redeemTokensIn x exchangeRateCurrent
       */
      redeemTokens = redeemTokensIn;
      redeemAmount = mul_ScalarTruncate(exchangeRate, redeemTokensIn);
    } else {
      /*
       * We get the current exchange rate and calculate the amount to be redeemed:
       *  redeemTokens = redeemAmountIn / exchangeRate
       *  redeemAmount = redeemAmountIn
       */
      redeemTokens = div_(redeemAmountIn, exchangeRate);
      redeemAmount = redeemAmountIn;
    }

    /* Fail if redeem not allowed */
    uint allowed = comptroller.redeemAllowed(
      address(this),
      redeemer,
      redeemTokens
    );
    if (allowed != 0) {
      revert RedeemComptrollerRejection(allowed);
    }

    /* Verify market's block number equals current block number */
    if (accrualBlockNumber != getBlockNumber()) {
      revert RedeemFreshnessCheck();
    }

    /* Fail gracefully if protocol has insufficient cash */
    if (getCashPrior() < redeemAmount) {
      revert RedeemTransferOutNotPossible();
    }

    /////////////////////////
    // EFFECTS & INTERACTIONS
    // (No safe failures beyond this point)

    /*
     * We write the previously calculated values into storage.
     *  Note: Avoid token reentrancy attacks by writing reduced supply before external transfer.
     */
    totalSupply = totalSupply - redeemTokens;
    accountTokens[redeemer] = accountTokens[redeemer] - redeemTokens;

    /*
     * We invoke doTransferOut for the redeemer and the redeemAmount.
     *  Note: The cToken must handle variations between ERC-20 and ETH underlying.
     *  On success, the cToken has redeemAmount less of cash.
     *  doTransferOut reverts if anything goes wrong, since we can't be sure if side effects occurred.
     */
    doTransferOut(redeemer, redeemAmount);

    /* We emit a Transfer event, and a Redeem event */
    emit Transfer(redeemer, address(this), redeemTokens);
    emit Redeem(redeemer, redeemAmount, redeemTokens);

    /* We call the defense hook */
    comptroller.redeemVerify(
      address(this),
      redeemer,
      redeemAmount,
      redeemTokens
    );
  }

  /**
   * @notice Sender borrows assets from the protocol to their own address
   * @param borrowAmount The amount of the underlying asset to borrow
   */
  function borrowInternal(uint borrowAmount) internal nonReentrant {
    accrueInterest();
    // borrowFresh emits borrow-specific logs on errors, so we don't need to
    borrowFresh(payable(msg.sender), borrowAmount);
  }

  /**
   * @notice Users borrow assets from the protocol to their own address
   * @param borrowAmount The amount of the underlying asset to borrow
   */
  function borrowFresh(address payable borrower, uint borrowAmount) internal {
    /* Revert if borrower not KYC'd */
    require(_getKYCStatus(borrower), "Borrower not KYC'd");

    /* Fail if borrow not allowed */
    uint allowed = comptroller.borrowAllowed(
      address(this),
      borrower,
      borrowAmount
    );
    if (allowed != 0) {
      revert BorrowComptrollerRejection(allowed);
    }

    /* Verify market's block number equals current block number */
    if (accrualBlockNumber != getBlockNumber()) {
      revert BorrowFreshnessCheck();
    }

    /* Fail gracefully if protocol has insufficient underlying cash */
    if (getCashPrior() < borrowAmount) {
      revert BorrowCashNotAvailable();
    }

    /*
     * We calculate the new borrower and total borrow balances, failing on overflow:
     *  accountBorrowNew = accountBorrow + borrowAmount
     *  totalBorrowsNew = totalBorrows + borrowAmount
     */
    uint accountBorrowsPrev = borrowBalanceStoredInternal(borrower);
    uint accountBorrowsNew = accountBorrowsPrev + borrowAmount;
    uint totalBorrowsNew = totalBorrows + borrowAmount;

    /////////////////////////
    // EFFECTS & INTERACTIONS
    // (No safe failures beyond this point)

    /*
         * We write the previously calculated values into storage.
         *  Note: Avoid token reentrancy attacks by writing increased borrow before external transfer.
        `*/
    accountBorrows[borrower].principal = accountBorrowsNew;
    accountBorrows[borrower].interestIndex = borrowIndex;
    totalBorrows = totalBorrowsNew;

    /*
     * We invoke doTransferOut for the borrower and the borrowAmount.
     *  Note: The cToken must handle variations between ERC-20 and ETH underlying.
     *  On success, the cToken borrowAmount less of cash.
     *  doTransferOut reverts if anything goes wrong, since we can't be sure if side effects occurred.
     */
    doTransferOut(borrower, borrowAmount);

    /* We emit a Borrow event */
    emit Borrow(borrower, borrowAmount, accountBorrowsNew, totalBorrowsNew);
  }

  /**
   * @notice Sender repays their own borrow
   * @param repayAmount The amount to repay, or -1 for the full outstanding amount
   */
  function repayBorrowInternal(uint repayAmount) internal nonReentrant {
    accrueInterest();
    // repayBorrowFresh emits repay-borrow-specific logs on errors, so we don't need to
    repayBorrowFresh(msg.sender, msg.sender, repayAmount);
  }

  /**
   * @notice Sender repays a borrow belonging to borrower
   * @param borrower the account with the debt being payed off
   * @param repayAmount The amount to repay, or -1 for the full outstanding amount
   */
  function repayBorrowBehalfInternal(
    address borrower,
    uint repayAmount
  ) internal nonReentrant {
    accrueInterest();
    // repayBorrowFresh emits repay-borrow-specific logs on errors, so we don't need to
    repayBorrowFresh(msg.sender, borrower, repayAmount);
  }

  /**
   * @notice Borrows are repaid by another user (possibly the borrower).
   * @param payer the account paying off the borrow
   * @param borrower the account with the debt being payed off
   * @param repayAmount the amount of underlying tokens being returned, or -1 for the full outstanding amount
   * @return (uint) the actual repayment amount.
   */
  function repayBorrowFresh(
    address payer,
    address borrower,
    uint repayAmount
  ) internal returns (uint) {
    /* Revert if not KYC'd */
    require(_getKYCStatus(payer), "Payer not KYC'd");
    require(_getKYCStatus(borrower), "Borrower not KYC'd");

    /* Fail if repayBorrow not allowed */
    uint allowed = comptroller.repayBorrowAllowed(
      address(this),
      payer,
      borrower,
      repayAmount
    );
    if (allowed != 0) {
      revert RepayBorrowComptrollerRejection(allowed);
    }

    /* Verify market's block number equals current block number */
    if (accrualBlockNumber != getBlockNumber()) {
      revert RepayBorrowFreshnessCheck();
    }

    /* We fetch the amount the borrower owes, with accumulated interest */
    uint accountBorrowsPrev = borrowBalanceStoredInternal(borrower);

    /* If repayAmount == -1, repayAmount = accountBorrows */
    uint repayAmountFinal = repayAmount == type(uint).max
      ? accountBorrowsPrev
      : repayAmount;

    /////////////////////////
    // EFFECTS & INTERACTIONS
    // (No safe failures beyond this point)

    /*
     * We call doTransferIn for the payer and the repayAmount
     *  Note: The cToken must handle variations between ERC-20 and ETH underlying.
     *  On success, the cToken holds an additional repayAmount of cash.
     *  doTransferIn reverts if anything goes wrong, since we can't be sure if side effects occurred.
     *   it returns the amount actually transferred, in case of a fee.
     */
    uint actualRepayAmount = doTransferIn(payer, repayAmountFinal);

    /*
     * We calculate the new borrower and total borrow balances, failing on underflow:
     *  accountBorrowsNew = accountBorrows - actualRepayAmount
     *  totalBorrowsNew = totalBorrows - actualRepayAmount
     */
    uint accountBorrowsNew = accountBorrowsPrev - actualRepayAmount;
    uint totalBorrowsNew = totalBorrows - actualRepayAmount;

    /* We write the previously calculated values into storage */
    accountBorrows[borrower].principal = accountBorrowsNew;
    accountBorrows[borrower].interestIndex = borrowIndex;
    totalBorrows = totalBorrowsNew;

    /* We emit a RepayBorrow event */
    emit RepayBorrow(
      payer,
      borrower,
      actualRepayAmount,
      accountBorrowsNew,
      totalBorrowsNew
    );

    return actualRepayAmount;
  }

  /**
   * @notice The sender liquidates the borrowers collateral.
   *  The collateral seized is transferred to the liquidator.
   * @param borrower The borrower of this cToken to be liquidated
   * @param cTokenCollateral The market in which to seize collateral from the borrower
   * @param repayAmount The amount of the underlying borrowed asset to repay
   */
  function liquidateBorrowInternal(
    address borrower,
    uint repayAmount,
    CTokenInterface cTokenCollateral
  ) internal nonReentrant {
    accrueInterest();

    uint error = cTokenCollateral.accrueInterest();
    if (error != NO_ERROR) {
      // accrueInterest emits logs on errors, but we still want to log the fact that an attempted liquidation failed
      revert LiquidateAccrueCollateralInterestFailed(error);
    }

    // liquidateBorrowFresh emits borrow-specific logs on errors, so we don't need to
    liquidateBorrowFresh(msg.sender, borrower, repayAmount, cTokenCollateral);
  }

  /**
   * @notice The liquidator liquidates the borrowers collateral.
   *  The collateral seized is transferred to the liquidator.
   * @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 repayAmount The amount of the underlying borrowed asset to repay
   */
  function liquidateBorrowFresh(
    address liquidator,
    address borrower,
    uint repayAmount,
    CTokenInterface cTokenCollateral
  ) internal {
    /* Fail if liquidate not allowed */
    uint allowed = comptroller.liquidateBorrowAllowed(
      address(this),
      address(cTokenCollateral),
      liquidator,
      borrower,
      repayAmount
    );
    if (allowed != 0) {
      revert LiquidateComptrollerRejection(allowed);
    }

    /* Verify market's block number equals current block number */
    if (accrualBlockNumber != getBlockNumber()) {
      revert LiquidateFreshnessCheck();
    }

    /* Verify cTokenCollateral market's block number equals current block number */
    if (cTokenCollateral.accrualBlockNumber() != getBlockNumber()) {
      revert LiquidateCollateralFreshnessCheck();
    }

    /* Fail if borrower = liquidator */
    if (borrower == liquidator) {
      revert LiquidateLiquidatorIsBorrower();
    }

    /* Fail if repayAmount = 0 */
    if (repayAmount == 0) {
      revert LiquidateCloseAmountIsZero();
    }

    /* Fail if repayAmount = -1 */
    if (repayAmount == type(uint).max) {
      revert LiquidateCloseAmountIsUintMax();
    }

    /* Fail if repayBorrow fails */
    uint actualRepayAmount = repayBorrowFresh(
      liquidator,
      borrower,
      repayAmount
    );

    /////////////////////////
    // EFFECTS & INTERACTIONS
    // (No safe failures beyond this point)

    /* We calculate the number of collateral tokens that will be seized */
    (uint amountSeizeError, uint seizeTokens) = comptroller
      .liquidateCalculateSeizeTokens(
        address(this),
        address(cTokenCollateral),
        actualRepayAmount
      );
    require(
      amountSeizeError == NO_ERROR,
      "LIQUIDATE_COMPTROLLER_CALCULATE_AMOUNT_SEIZE_FAILED"
    );

    /* Revert if borrower collateral token balance < seizeTokens */
    require(
      cTokenCollateral.balanceOf(borrower) >= seizeTokens,
      "LIQUIDATE_SEIZE_TOO_MUCH"
    );

    // If this is also the collateral, run seizeInternal to avoid re-entrancy, otherwise make an external call
    if (address(cTokenCollateral) == address(this)) {
      seizeInternal(address(this), liquidator, borrower, seizeTokens);
    } else {
      require(
        cTokenCollateral.seize(liquidator, borrower, seizeTokens) == NO_ERROR,
        "token seizure failed"
      );
    }

    /* We emit a LiquidateBorrow event */
    emit LiquidateBorrow(
      liquidator,
      borrower,
      actualRepayAmount,
      address(cTokenCollateral),
      seizeTokens
    );
  }

  /**
   * @notice Transfers collateral tokens (this market) to the liquidator.
   * @dev Will fail unless called by another cToken during the process of liquidation.
   *  Its absolutely critical to use msg.sender as the borrowed cToken and not a parameter.
   * @param liquidator The account receiving seized collateral
   * @param borrower The account having collateral seized
   * @param seizeTokens The number of cTokens to seize
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function seize(
    address liquidator,
    address borrower,
    uint seizeTokens
  ) external override nonReentrant returns (uint) {
    seizeInternal(msg.sender, liquidator, borrower, seizeTokens);

    return NO_ERROR;
  }

  /**
   * @notice Transfers collateral tokens (this market) to the liquidator.
   * @dev Called only during an in-kind liquidation, or by liquidateBorrow during the liquidation of another cToken.
   *  Its absolutely critical to use msg.sender as the seizer cToken and not a parameter.
   * @param seizerToken The contract seizing the collateral (i.e. borrowed cToken)
   * @param liquidator The account receiving seized collateral
   * @param borrower The account having collateral seized
   * @param seizeTokens The number of cTokens to seize
   */
  function seizeInternal(
    address seizerToken,
    address liquidator,
    address borrower,
    uint seizeTokens
  ) internal {
    /* Revert if not KYC'd */
    require(_getKYCStatus(liquidator), "Liquidator not KYC'd");
    require(_getKYCStatus(borrower), "Borrower not KYC'd");

    /* Fail if seize not allowed */
    uint allowed = comptroller.seizeAllowed(
      address(this),
      seizerToken,
      liquidator,
      borrower,
      seizeTokens
    );
    if (allowed != 0) {
      revert LiquidateSeizeComptrollerRejection(allowed);
    }

    /* Fail if borrower = liquidator */
    if (borrower == liquidator) {
      revert LiquidateSeizeLiquidatorIsBorrower();
    }

    /*
     * We calculate the new borrower and liquidator token balances, failing on underflow/overflow:
     *  borrowerTokensNew = accountTokens[borrower] - seizeTokens
     *  liquidatorTokensNew = accountTokens[liquidator] + seizeTokens
     */
    uint protocolSeizeTokens = mul_(
      seizeTokens,
      Exp({mantissa: protocolSeizeShareMantissa})
    );
    uint liquidatorSeizeTokens = seizeTokens - protocolSeizeTokens;
    Exp memory exchangeRate = Exp({mantissa: exchangeRateStoredInternal()});
    uint protocolSeizeAmount = mul_ScalarTruncate(
      exchangeRate,
      protocolSeizeTokens
    );
    uint totalReservesNew = totalReserves + protocolSeizeAmount;

    /////////////////////////
    // EFFECTS & INTERACTIONS
    // (No safe failures beyond this point)

    /* We write the calculated values into storage */
    totalReserves = totalReservesNew;
    totalSupply = totalSupply - protocolSeizeTokens;
    accountTokens[borrower] = accountTokens[borrower] - seizeTokens;
    accountTokens[liquidator] =
      accountTokens[liquidator] +
      liquidatorSeizeTokens;

    /* Emit a Transfer event */
    emit Transfer(borrower, liquidator, liquidatorSeizeTokens);
    emit Transfer(borrower, address(this), protocolSeizeTokens);
    emit ReservesAdded(address(this), protocolSeizeAmount, totalReservesNew);
  }

  /*** Admin Functions ***/

  /**
   * @notice Begins transfer of admin rights. The newPendingAdmin must call `_acceptAdmin` to finalize the transfer.
   * @dev Admin function to begin change of admin. The newPendingAdmin must call `_acceptAdmin` to finalize the transfer.
   * @param newPendingAdmin New pending admin.
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function _setPendingAdmin(
    address payable newPendingAdmin
  ) external override returns (uint) {
    // Check caller = admin
    if (msg.sender != admin) {
      revert SetPendingAdminOwnerCheck();
    }

    // Save current value, if any, for inclusion in log
    address oldPendingAdmin = pendingAdmin;

    // Store pendingAdmin with value newPendingAdmin
    pendingAdmin = newPendingAdmin;

    // Emit NewPendingAdmin(oldPendingAdmin, newPendingAdmin)
    emit NewPendingAdmin(oldPendingAdmin, newPendingAdmin);

    return NO_ERROR;
  }

  /**
   * @notice Accepts transfer of admin rights. msg.sender must be pendingAdmin
   * @dev Admin function for pending admin to accept role and update admin
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function _acceptAdmin() external override returns (uint) {
    // Check caller is pendingAdmin and pendingAdmin ≠ address(0)
    if (msg.sender != pendingAdmin || msg.sender == address(0)) {
      revert AcceptAdminPendingAdminCheck();
    }

    // Save current values for inclusion in log
    address oldAdmin = admin;
    address oldPendingAdmin = pendingAdmin;

    // Store admin with value pendingAdmin
    admin = pendingAdmin;

    // Clear the pending value
    pendingAdmin = payable(address(0));

    emit NewAdmin(oldAdmin, admin);
    emit NewPendingAdmin(oldPendingAdmin, pendingAdmin);

    return NO_ERROR;
  }

  /**
   * @notice Sets a new comptroller for the market
   * @dev Admin function to set a new comptroller
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function _setComptroller(
    ComptrollerInterface newComptroller
  ) public override returns (uint) {
    // Check caller is admin
    if (msg.sender != admin) {
      revert SetComptrollerOwnerCheck();
    }

    ComptrollerInterface oldComptroller = comptroller;
    // Ensure invoke comptroller.isComptroller() returns true
    require(newComptroller.isComptroller(), "marker method returned false");

    // Set market's comptroller to newComptroller
    comptroller = newComptroller;

    // Emit NewComptroller(oldComptroller, newComptroller)
    emit NewComptroller(oldComptroller, newComptroller);

    return NO_ERROR;
  }

  /**
   * @notice accrues interest and sets a new reserve factor for the protocol using _setReserveFactorFresh
   * @dev Admin function to accrue interest and set a new reserve factor
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function _setReserveFactor(
    uint newReserveFactorMantissa
  ) external override nonReentrant returns (uint) {
    accrueInterest();
    // _setReserveFactorFresh emits reserve-factor-specific logs on errors, so we don't need to.
    return _setReserveFactorFresh(newReserveFactorMantissa);
  }

  /**
   * @notice Sets a new reserve factor for the protocol (*requires fresh interest accrual)
   * @dev Admin function to set a new reserve factor
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function _setReserveFactorFresh(
    uint newReserveFactorMantissa
  ) internal returns (uint) {
    // Check caller is admin
    if (msg.sender != admin) {
      revert SetReserveFactorAdminCheck();
    }

    // Verify market's block number equals current block number
    if (accrualBlockNumber != getBlockNumber()) {
      revert SetReserveFactorFreshCheck();
    }

    // Check newReserveFactor ≤ maxReserveFactor
    if (newReserveFactorMantissa > reserveFactorMaxMantissa) {
      revert SetReserveFactorBoundsCheck();
    }

    uint oldReserveFactorMantissa = reserveFactorMantissa;
    reserveFactorMantissa = newReserveFactorMantissa;

    emit NewReserveFactor(oldReserveFactorMantissa, newReserveFactorMantissa);

    return NO_ERROR;
  }

  /**
   * @notice Accrues interest and reduces reserves by transferring from msg.sender
   * @param addAmount Amount of addition to reserves
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function _addReservesInternal(
    uint addAmount
  ) internal nonReentrant returns (uint) {
    accrueInterest();

    // _addReservesFresh emits reserve-addition-specific logs on errors, so we don't need to.
    _addReservesFresh(addAmount);
    return NO_ERROR;
  }

  /**
   * @notice Add reserves by transferring from caller
   * @dev Requires fresh interest accrual
   * @param addAmount Amount of addition to reserves
   * @return (uint, uint) An error code (0=success, otherwise a failure (see ErrorReporter.sol for details)) and the actual amount added, net token fees
   */
  function _addReservesFresh(uint addAmount) internal returns (uint, uint) {
    // totalReserves + actualAddAmount
    uint totalReservesNew;
    uint actualAddAmount;

    // We fail gracefully unless market's block number equals current block number
    if (accrualBlockNumber != getBlockNumber()) {
      revert AddReservesFactorFreshCheck(actualAddAmount);
    }

    /////////////////////////
    // EFFECTS & INTERACTIONS
    // (No safe failures beyond this point)

    /*
     * We call doTransferIn for the caller and the addAmount
     *  Note: The cToken must handle variations between ERC-20 and ETH underlying.
     *  On success, the cToken holds an additional addAmount of cash.
     *  doTransferIn reverts if anything goes wrong, since we can't be sure if side effects occurred.
     *  it returns the amount actually transferred, in case of a fee.
     */

    actualAddAmount = doTransferIn(msg.sender, addAmount);

    totalReservesNew = totalReserves + actualAddAmount;

    // Store reserves[n+1] = reserves[n] + actualAddAmount
    totalReserves = totalReservesNew;

    /* Emit NewReserves(admin, actualAddAmount, reserves[n+1]) */
    emit ReservesAdded(msg.sender, actualAddAmount, totalReservesNew);

    /* Return (NO_ERROR, actualAddAmount) */
    return (NO_ERROR, actualAddAmount);
  }

  /**
   * @notice Accrues interest and reduces reserves by transferring to admin
   * @param reduceAmount Amount of reduction to reserves
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function _reduceReserves(
    uint reduceAmount
  ) external override nonReentrant returns (uint) {
    accrueInterest();
    // _reduceReservesFresh emits reserve-reduction-specific logs on errors, so we don't need to.
    return _reduceReservesFresh(reduceAmount);
  }

  /**
   * @notice Reduces reserves by transferring to admin
   * @dev Requires fresh interest accrual
   * @param reduceAmount Amount of reduction to reserves
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function _reduceReservesFresh(uint reduceAmount) internal returns (uint) {
    // totalReserves - reduceAmount
    uint totalReservesNew;

    // Check caller is admin
    if (msg.sender != admin) {
      revert ReduceReservesAdminCheck();
    }

    // We fail gracefully unless market's block number equals current block number
    if (accrualBlockNumber != getBlockNumber()) {
      revert ReduceReservesFreshCheck();
    }

    // Fail gracefully if protocol has insufficient underlying cash
    if (getCashPrior() < reduceAmount) {
      revert ReduceReservesCashNotAvailable();
    }

    // Check reduceAmount ≤ reserves[n] (totalReserves)
    if (reduceAmount > totalReserves) {
      revert ReduceReservesCashValidation();
    }

    /////////////////////////
    // EFFECTS & INTERACTIONS
    // (No safe failures beyond this point)

    totalReservesNew = totalReserves - reduceAmount;

    // Store reserves[n+1] = reserves[n] - reduceAmount
    totalReserves = totalReservesNew;

    // doTransferOut reverts if anything goes wrong, since we can't be sure if side effects occurred.
    doTransferOut(admin, reduceAmount);

    emit ReservesReduced(admin, reduceAmount, totalReservesNew);

    return NO_ERROR;
  }

  /**
   * @notice accrues interest and updates the interest rate model using _setInterestRateModelFresh
   * @dev Admin function to accrue interest and update the interest rate model
   * @param newInterestRateModel the new interest rate model to use
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function _setInterestRateModel(
    InterestRateModel newInterestRateModel
  ) public override returns (uint) {
    accrueInterest();
    // _setInterestRateModelFresh emits interest-rate-model-update-specific logs on errors, so we don't need to.
    return _setInterestRateModelFresh(newInterestRateModel);
  }

  /**
   * @notice updates the interest rate model (*requires fresh interest accrual)
   * @dev Admin function to update the interest rate model
   * @param newInterestRateModel the new interest rate model to use
   * @return uint 0=success, otherwise a failure (see ErrorReporter.sol for details)
   */
  function _setInterestRateModelFresh(
    InterestRateModel newInterestRateModel
  ) internal returns (uint) {
    // Used to store old model for use in the event that is emitted on success
    InterestRateModel oldInterestRateModel;

    // Check caller is admin
    if (msg.sender != admin) {
      revert SetInterestRateModelOwnerCheck();
    }

    // We fail gracefully unless market's block number equals current block number
    if (accrualBlockNumber != getBlockNumber()) {
      revert SetInterestRateModelFreshCheck();
    }

    // Track the market's current interest rate model
    oldInterestRateModel = interestRateModel;

    // Ensure invoke newInterestRateModel.isInterestRateModel() returns true
    require(
      newInterestRateModel.isInterestRateModel(),
      "marker method returned false"
    );

    // Set the interest rate model to newInterestRateModel
    interestRateModel = newInterestRateModel;

    // Emit NewMarketInterestRateModel(oldInterestRateModel, newInterestRateModel)
    emit NewMarketInterestRateModel(oldInterestRateModel, newInterestRateModel);

    return NO_ERROR;
  }

  /*** KYC ***/

  /**
   * @notice Update KYC group of the contract for which
   *         accounts are checked against
   *
   * @param _kycRequirementGroup The new KYC requirement group
   */
  function setKYCRequirementGroup(uint256 _kycRequirementGroup) external {
    require(msg.sender == admin, "Only admin can set KYC requirement group");
    _setKYCRequirementGroup(_kycRequirementGroup);
  }

  /**
   * @notice Sets the KYC registry requirement group for this
   *         client to check kyc status for
   *
   * @param _kycRequirementGroup The new KYC group
   */
  function _setKYCRequirementGroup(uint256 _kycRequirementGroup) internal {
    uint256 oldKYCLevel = kycRequirementGroup;
    kycRequirementGroup = _kycRequirementGroup;
    emit KYCRequirementGroupSet(oldKYCLevel, _kycRequirementGroup);
  }

  /**
   * @notice Update KYC registry address
   *
   * @param _kycRegistry The new KYC registry address
   */
  function setKYCRegistry(address _kycRegistry) external {
    require(msg.sender == admin, "Only admin can set KYC registry");
    _setKYCRegistry(_kycRegistry);
  }

  /**
   * @notice Sets the KYC registry address for this client
   *
   * @param _kycRegistry The new KYC registry address
   */
  function _setKYCRegistry(address _kycRegistry) internal {
    require(_kycRegistry != address(0), "KYC registry cannot be zero address");
    address oldKYCRegistry = address(kycRegistry);
    kycRegistry = IKYCRegistry(_kycRegistry);
    emit KYCRegistrySet(oldKYCRegistry, _kycRegistry);
  }

  /**
   * @notice Checks whether an address has been KYC'd
   *
   * @param account The address to check
   */
  function _getKYCStatus(address account) internal view returns (bool) {
    return kycRegistry.getKYCStatus(kycRequirementGroup, account);
  }

  /*** Safe Token ***/

  /**
   * @notice Gets balance of this contract in terms of the underlying
   * @dev This excludes the value of the current message, if any
   * @return The quantity of underlying owned by this contract
   */
  function getCashPrior() internal view virtual returns (uint);

  /**
   * @dev Performs a transfer in, reverting upon failure. Returns the amount actually transferred to the protocol, in case of a fee.
   *  This may revert due to insufficient balance or insufficient allowance.
   */
  function doTransferIn(
    address from,
    uint amount
  ) internal virtual returns (uint);

  /**
   * @dev Performs a transfer out, ideally returning an explanatory error code upon failure rather than reverting.
   *  If caller has not called checked protocol's balance, may revert due to insufficient cash held in the contract.
   *  If caller has checked protocol's balance, and verified it is >= amount, this should not revert in normal conditions.
   */
  function doTransferOut(address payable to, uint amount) internal virtual;

  /*** Reentrancy Guard ***/

  /**
   * @dev Prevents a contract from calling itself, directly or indirectly.
   */
  modifier nonReentrant() {
    require(_notEntered, "re-entered");
    _notEntered = false;
    _;
    _notEntered = true; // get a gas-refund post-Istanbul
  }
}