// File: @openzeppelin/contracts/token/ERC20/IERC20.sol

pragma solidity ^0.5.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP. Does not include
 * the optional functions; to access them see {ERC20Detailed}.
 */
interface IERC20 {
    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

// File: @openzeppelin/contracts/math/SafeMath.sol

pragma solidity ^0.5.0;

/**
 * @dev Wrappers over Solidity's arithmetic operations with added overflow
 * checks.
 *
 * Arithmetic operations in Solidity wrap on overflow. This can easily result
 * in bugs, because programmers usually assume that an overflow raises an
 * error, which is the standard behavior in high level programming languages.
 * `SafeMath` restores this intuition by reverting the transaction when an
 * operation overflows.
 *
 * Using this library instead of the unchecked operations eliminates an entire
 * class of bugs, so it's recommended to use it always.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        uint256 c = a + b;
        require(c >= a, "SafeMath: addition overflow");

        return c;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return sub(a, b, "SafeMath: subtraction overflow");
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     * - Subtraction cannot overflow.
     *
     * _Available since v2.4.0._
     */
    function sub(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b <= a, errorMessage);
        uint256 c = a - b;

        return c;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
        // benefit is lost if 'b' is also tested.
        // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
        if (a == 0) {
            return 0;
        }

        uint256 c = a * b;
        require(c / a == b, "SafeMath: multiplication overflow");

        return c;
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return div(a, b, "SafeMath: division by zero");
    }

    /**
     * @dev Returns the integer division of two unsigned integers. Reverts with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        // Solidity only automatically asserts when dividing by 0
        require(b > 0, errorMessage);
        uint256 c = a / b;
        // assert(a == b * c + a % b); // There is no case in which this doesn't hold

        return c;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return mod(a, b, "SafeMath: modulo by zero");
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * Reverts with custom message when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     * - The divisor cannot be zero.
     *
     * _Available since v2.4.0._
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}

// File: @openzeppelin/contracts/utils/Address.sol

pragma solidity ^0.5.5;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * This test is non-exhaustive, and there may be false-negatives: during the
     * execution of a contract's constructor, its address will be reported as
     * not containing a contract.
     *
     * IMPORTANT: It is unsafe to assume that an address for which this
     * function returns false is an externally-owned account (EOA) and not a
     * contract.
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies in extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != 0x0 && codehash != accountHash);
    }

    /**
     * @dev Converts an `address` into `address payable`. Note that this is
     * simply a type cast: the actual underlying value is not changed.
     *
     * _Available since v2.4.0._
     */
    function toPayable(address account) internal pure returns (address payable) {
        return address(uint160(account));
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     *
     * _Available since v2.4.0._
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-call-value
        (bool success, ) = recipient.call.value(amount)("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }
}

// File: @openzeppelin/contracts/token/ERC20/SafeERC20.sol

pragma solidity ^0.5.0;




/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for ERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    function safeApprove(IERC20 token, address spender, uint256 value) internal {
        // safeApprove should only be called when setting an initial allowance,
        // or when resetting it to zero. To increase and decrease it, use
        // 'safeIncreaseAllowance' and 'safeDecreaseAllowance'
        // solhint-disable-next-line max-line-length
        require((value == 0) || (token.allowance(address(this), spender) == 0),
            "SafeERC20: approve from non-zero to non-zero allowance"
        );
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, value));
    }

    function safeIncreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).add(value);
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    function safeDecreaseAllowance(IERC20 token, address spender, uint256 value) internal {
        uint256 newAllowance = token.allowance(address(this), spender).sub(value, "SafeERC20: decreased allowance below zero");
        callOptionalReturn(token, abi.encodeWithSelector(token.approve.selector, spender, newAllowance));
    }

    /**
     * @dev Imitates a Solidity high-level call (i.e. a regular function call to a contract), relaxing the requirement
     * on the return value: the return value is optional (but if data is returned, it must not be false).
     * @param token The token targeted by the call.
     * @param data The call data (encoded using abi.encode or one of its variants).
     */
    function callOptionalReturn(IERC20 token, bytes memory data) private {
        // We need to perform a low level call here, to bypass Solidity's return data size checking mechanism, since
        // we're implementing it ourselves.

        // A Solidity high level call has three parts:
        //  1. The target address is checked to verify it contains contract code
        //  2. The call itself is made, and success asserted
        //  3. The return value is decoded, which in turn checks the size of the returned data.
        // solhint-disable-next-line max-line-length
        require(address(token).isContract(), "SafeERC20: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = address(token).call(data);
        require(success, "SafeERC20: low-level call failed");

        if (returndata.length > 0) { // Return data is optional
            // solhint-disable-next-line max-line-length
            require(abi.decode(returndata, (bool)), "SafeERC20: ERC20 operation did not succeed");
        }
    }
}

// File: @openzeppelin/contracts/GSN/Context.sol

pragma solidity ^0.5.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
contract Context {
    // Empty internal constructor, to prevent people from mistakenly deploying
    // an instance of this contract, which should be used via inheritance.
    constructor () internal { }
    // solhint-disable-previous-line no-empty-blocks

    function _msgSender() internal view returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

// File: @openzeppelin/contracts/ownership/Ownable.sol

pragma solidity ^0.5.0;

/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor () internal {
        _owner = _msgSender();
        emit OwnershipTransferred(address(0), _owner);
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(isOwner(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Returns true if the caller is the current owner.
     */
    function isOwner() public view returns (bool) {
        return _msgSender() == _owner;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public onlyOwner {
        emit OwnershipTransferred(_owner, address(0));
        _owner = address(0);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public onlyOwner {
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     */
    function _transferOwnership(address newOwner) internal {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// File: contracts/interfaces/CERC20.sol

pragma solidity 0.5.11;

interface CERC20 {
  function mint(uint256 mintAmount) external returns (uint256);
  function redeem(uint256 redeemTokens) external returns (uint256);
  function exchangeRateStored() external view returns (uint256);
  function supplyRatePerBlock() external view returns (uint256);

  function borrowRatePerBlock() external view returns (uint256);
  function totalReserves() external view returns (uint256);
  function getCash() external view returns (uint256);
  function totalBorrows() external view returns (uint256);
  function reserveFactorMantissa() external view returns (uint256);
  function interestRateModel() external view returns (address);
}

// File: contracts/interfaces/ILendingProtocol.sol

pragma solidity 0.5.11;

interface ILendingProtocol {
  function mint() external returns (uint256);
  function redeem(address account) external returns (uint256);
  function nextSupplyRate(uint256 amount) external view returns (uint256);
  function nextSupplyRateWithParams(uint256[] calldata params) external view returns (uint256);
  function getAPR() external view returns (uint256);
  function getPriceInToken() external view returns (uint256);
  function token() external view returns (address);
  function underlying() external view returns (address);
}

// File: contracts/interfaces/WhitePaperInterestRateModel.sol

pragma solidity 0.5.11;

interface WhitePaperInterestRateModel {
  function getBorrowRate(uint256 cash, uint256 borrows, uint256 _reserves) external view returns (uint256, uint256);
  function getSupplyRate(uint256 cash, uint256 borrows, uint256 reserves, uint256 reserveFactorMantissa) external view returns (uint256);
  function multiplier() external view returns (uint256);
  function baseRate() external view returns (uint256);
  function blocksPerYear() external view returns (uint256);
  function dsrPerBlock() external view returns (uint256);
}

// File: contracts/wrappers/IdleCompound.sol

/**
 * @title: Compound wrapper
 * @summary: Used for interacting with Compound. Has
 *           a common interface with all other protocol wrappers.
 *           This contract holds assets only during a tx, after tx it should be empty
 * @author: William Bergamo, idle.finance
 */
pragma solidity 0.5.11;







contract IdleCompound is ILendingProtocol, Ownable {
  using SafeERC20 for IERC20;
  using SafeMath for uint256;

  // protocol token (cToken) address
  address public token;
  // underlying token (token eg DAI) address
  address public underlying;
  address public idleToken;

  /**
   * @param _token : cToken address
   * @param _underlying : underlying token (eg DAI) address
   */
  constructor(address _token, address _underlying) public {
    require(_token != address(0) && _underlying != address(0), 'COMP: some addr is 0');

    token = _token;
    underlying = _underlying;
  }

  /**
   * Throws if called by any account other than IdleToken contract.
   */
  modifier onlyIdle() {
    require(msg.sender == idleToken, "Ownable: caller is not IdleToken contract");
    _;
  }

  // onlyOwner
  /**
   * sets idleToken address
   * NOTE: can be called only once. It's not on the constructor because we are deploying this contract
   *       after the IdleToken contract
   * @param _idleToken : idleToken address
   */
  function setIdleToken(address _idleToken)
    external onlyOwner {
      require(idleToken == address(0), "idleToken addr already set");
      require(_idleToken != address(0), "_idleToken addr is 0");
      idleToken = _idleToken;
  }
  // end onlyOwner

  /**
   * Calculate next supply rate for Compound, given an `_amount` supplied (last array param)
   * and all other params supplied. See `info_compound.md` for more info
   * on calculations.
   *
   * @param params : array with all params needed for calculation (see below)
   * @return : yearly net rate
   */
  function nextSupplyRateWithParams(uint256[] memory params)
    public view
    returns (uint256) {
      /*
        This comment is a reference for params name
        This gives stack too deep so check implementation below

        uint256 j = params[0]; // 10 ** 18;
        uint256 a = params[1]; // white.baseRate(); // from WhitePaper
        uint256 b = params[2]; // cToken.totalBorrows();
        uint256 c = params[3]; // white.multiplier(); // from WhitePaper
        uint256 d = params[4]; // cToken.totalReserves();
        uint256 e = params[5]; // j.sub(cToken.reserveFactorMantissa());
        uint256 s = params[6]; // cToken.getCash();
        uint256 k = params[7]; // white.blocksPerYear();
        uint256 f = params[8]; // 100;
        uint256 x = params[9]; // newAmountSupplied;

        // q = ((((a + (b*c)/(b + s + x)) / k) * e * b / (s + x + b - d)) / j) * k * f -> to get yearly rate
        nextRate = a.add(b.mul(c).div(b.add(s).add(x))).div(k).mul(e).mul(b).div(
          s.add(x).add(b).sub(d)
        ).div(j).mul(k).mul(f); // to get the yearly rate
      */

      // (b*c)/(b + s + x)
      uint256 inter1 = params[2].mul(params[3]).div(params[2].add(params[6]).add(params[9]));
      // (s + x + b - d)
      uint256 inter2 = params[6].add(params[9]).add(params[2]).sub(params[4]);
      // ((a + (b*c)/(b + s + x)) / k) * e
      uint256 inter3 = params[1].add(inter1).div(params[7]).mul(params[5]);
      // ((((a + (b*c)/(b + s + x)) / k) * e * b / (s + x + b - d)) / j) * k * f
      return inter3.mul(params[2]).div(inter2).div(params[0]).mul(params[7]).mul(params[8]);
  }

  /**
   * Calculate next supply rate for Compound, given an `_amount` supplied
   *
   * @param _amount : new underlying amount supplied (eg DAI)
   * @return : yearly net rate
   */
  function nextSupplyRate(uint256 _amount)
    external view
    returns (uint256) {
      CERC20 cToken = CERC20(token);
      WhitePaperInterestRateModel white = WhitePaperInterestRateModel(cToken.interestRateModel());
      uint256[] memory params = new uint256[](10);

      params[0] = 10**18; // j
      params[1] = white.baseRate(); // a
      params[2] = cToken.totalBorrows(); // b
      params[3] = white.multiplier(); // c
      params[4] = cToken.totalReserves(); // d
      params[5] = params[0].sub(cToken.reserveFactorMantissa()); // e
      params[6] = cToken.getCash(); // s
      params[7] = white.blocksPerYear(); // k
      params[8] = 100; // f
      params[9] = _amount; // x

      // q = ((((a + (b*c)/(b + s + x)) / k) * e * b / (s + x + b - d)) / j) * k * f -> to get yearly rate
      return nextSupplyRateWithParams(params);
  }

  /**
   * @return current price of cToken in underlying
   */
  function getPriceInToken()
    external view
    returns (uint256) {
      return CERC20(token).exchangeRateStored();
  }

  /**
   * @return apr : current yearly net rate
   */
  function getAPR()
    external view
    returns (uint256 apr) {
      CERC20 cToken = CERC20(token);
      WhitePaperInterestRateModel white = WhitePaperInterestRateModel(cToken.interestRateModel());
      uint256 cRate = cToken.supplyRatePerBlock(); // interest % per block
      apr = cRate.mul(white.blocksPerYear()).mul(100);
  }

  /**
   * Gets all underlying tokens in this contract and mints cTokens
   * tokens are then transferred to msg.sender
   * NOTE: underlying tokens needs to be sended here before calling this
   *
   * @return cTokens minted
   */
  function mint()
    external onlyIdle
    returns (uint256 cTokens) {
      uint256 balance = IERC20(underlying).balanceOf(address(this));
      if (balance == 0) {
        return cTokens;
      }
      // approve the transfer to cToken contract
      IERC20(underlying).safeIncreaseAllowance(token, balance);
      // get a handle for the corresponding cToken contract
      CERC20 _cToken = CERC20(token);
      // mint the cTokens and assert there is no error
      require(_cToken.mint(balance) == 0, "Error minting");
      // cTokens are now in this contract
      cTokens = IERC20(token).balanceOf(address(this));
      // transfer them to the caller
      IERC20(token).safeTransfer(msg.sender, cTokens);
  }

  /**
   * Gets all cTokens in this contract and redeems underlying tokens.
   * underlying tokens are then transferred to `_account`
   * NOTE: cTokens needs to be sended here before calling this
   *
   * @return underlying tokens redeemd
   */
  function redeem(address _account)
    external onlyIdle
    returns (uint256 tokens) {
      // Funds needs to be sended here before calling this
      CERC20 _cToken = CERC20(token);
      IERC20 _underlying = IERC20(underlying);
      // redeem all underlying sent in this contract
      require(_cToken.redeem(IERC20(token).balanceOf(address(this))) == 0, "Something went wrong when redeeming in cTokens");

      tokens = _underlying.balanceOf(address(this));
      _underlying.safeTransfer(_account, tokens);
  }
}