pragma solidity 0.5.16;


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);
}

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;
    }
}

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");
    }
}

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");
        }
    }
}

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;
    }
}

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;
    }
}

interface CHAI {
  function dai(address usr) external returns (uint wad);
  // wad is denominated in dai
  function join(address dst, uint wad) external;
  // wad is denominated in (1/chi) * dai
  function exit(address src, uint wad) external;
}

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);
  function availableLiquidity() external view returns (uint256);
}

interface PotLike {
  function chi() external view returns (uint256);
  function rho() external view returns (uint256);
  function dsr() external view returns (uint256);
  function join(uint256) external;
  function exit(uint256) external;
}

contract DSMath {
   function _add(uint x, uint y) internal pure returns (uint z) {
       require((z = x + y) >= x);
   }
   function _mul(uint x, uint y) internal pure returns (uint z) {
       require(y == 0 || (z = x * y) / y == x);
   }

   uint constant RAY = 10 ** 27;

   function rmul(uint x, uint y) internal pure returns (uint z) {
       z = _add(_mul(x, y), RAY / 2) / RAY;
   }

   // This famous algorithm is called "exponentiation by squaring"
   // and calculates x^n with x as fixed-point and n as regular unsigned.
   //
   // It's O(log n), instead of O(n) for naive repeated multiplication.
   //
   // These facts are why it works:
   //
   //  If n is even, then x^n = (x^2)^(n/2).
   //  If n is odd,  then x^n = x * x^(n-1),
   //   and applying the equation for even x gives
   //    x^n = x * (x^2)^((n-1) / 2).
   //
   //  Also, EVM division is flooring and
   //    floor[(n-1) / 2] = floor[n / 2].
   //
   /* function rpow(uint x, uint n) internal pure returns (uint z) {
       z = n % 2 != 0 ? x : RAY;

       for (n /= 2; n != 0; n /= 2) {
           x = rmul(x, x);

           if (n % 2 != 0) {
               z = rmul(z, x);
           }
       }
   } */

  // https://github.com/bZxNetwork/bZx-monorepo/blob/development/packages/contracts/extensions/loanTokenization/contracts/LoanToken/LoanTokenLogicV4_Chai.sol#L1591
   function rpow(
       uint256 x,
       uint256 n,
       uint256 base)
       public
       pure
       returns (uint256 z)
   {
       assembly {
           switch x case 0 {switch n case 0 {z := base} default {z := 0}}
           default {
               switch mod(n, 2) case 0 { z := base } default { z := x }
               let half := div(base, 2)  // for rounding.
               for { n := div(n, 2) } n { n := div(n,2) } {
                   let xx := mul(x, x)
                   if iszero(eq(div(xx, x), x)) { revert(0,0) }
                   let xxRound := add(xx, half)
                   if lt(xxRound, xx) { revert(0,0) }
                   x := div(xxRound, base)
                   if mod(n,2) {
                       let zx := mul(z, x)
                       if and(iszero(iszero(x)), iszero(eq(div(zx, x), z))) { revert(0,0) }
                       let zxRound := add(zx, half)
                       if lt(zxRound, zx) { revert(0,0) }
                       z := div(zxRound, base)
                   }
               }
           }
       }
   }
}

contract IdleDSR is ILendingProtocol, Ownable, DSMath {
  using SafeERC20 for IERC20;
  using SafeMath for uint256;

  // protocol token (CHAI) address
  address public token;
  // underlying token (token eg DAI) address
  address public underlying;
  address public idleToken;
  uint256 public constant secondsInAYear = 31536000;
  PotLike public pot = PotLike(0x197E90f9FAD81970bA7976f33CbD77088E5D7cf7);

  /**
   * @param _token : CHAI address
   * @param _underlying : underlying token (eg DAI) address
   */
  constructor(address _token, address _underlying) public {
    require(_token != address(0) && _underlying != address(0), 'DSR: some addr is 0');

    token = _token;
    underlying = _underlying;
    IERC20(_underlying).safeApprove(_token, uint256(-1));
  }

  /**
   * Throws if called by any account other than IdleToken contract.
   */
  modifier onlyIdle() {
    require(msg.sender == idleToken, "Ownable: caller is not IdleToken");
    _;
  }

  // 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 CHAI, given an `_amount` supplied (last array param)
   * and all other params supplied. See `info_compound.md` for more info
   * on calculations.
   *
   * @param : not used
   * @return : yearly net rate
   */
  function nextSupplyRateWithParams(uint256[] calldata)
    external view
    returns (uint256) {
    return nextSupplyRate(0);
  }

  /**
   * Calculate next supply rate for CHAI, given an `_amount` supplied
   *
   * @param : new underlying amount supplied (eg DAI)
   * @return : yearly net rate
   */
  function nextSupplyRate(uint256)
    public view
    returns (uint256) {
    return pot.dsr().sub(RAY).mul(secondsInAYear).div(10**9).mul(100);
  }

  /**
   * @return current price of chaiToken in underlying
   */
  function getPriceInToken()
    external view
    returns (uint256) {
    return _chaiPrice();
  }

  function _chaiPrice() internal view returns (uint256){
    uint256 rho = pot.rho();
    uint256 chi = pot.chi();
    if (now > rho) {
      chi = rmul(rpow(pot.dsr(), now - rho, RAY), chi);
    }
    return chi.div(10**9);
  }


  /**
   * @return apr : current yearly net rate
   */
  function getAPR()
    external view
    returns (uint256 apr) {
    return nextSupplyRate(0);
  }

  /**
   * Gets all underlying tokens in this contract and mints chaiTokens
   * tokens are then transferred to msg.sender
   * NOTE: underlying tokens needs to be sended here before calling this
   *
   * @return chaiTokens minted
   */
  function mint()
    external onlyIdle
    returns (uint256 chaiTokens) {
      uint256 balance = IERC20(underlying).balanceOf(address(this));
      if (balance == 0) {
        return chaiTokens;
      }
      CHAI(token).join(msg.sender, balance);
      chaiTokens = balance.mul(10**18).div(_chaiPrice());
  }

  /**
   * Gets all chaiTokens in this contract and redeems underlying tokens.
   * underlying tokens are then transferred to `_account`
   * NOTE: chaiTokens needs to be sended here before calling this
   *
   * @return underlying tokens redeemd
   */
  function redeem(address _account)
    external onlyIdle
    returns (uint256 tokens) {
      uint256 balance = IERC20(token).balanceOf(address(this));
      CHAI(token).exit(address(this), balance);
      IERC20 _underlying = IERC20(underlying);
      tokens = _underlying.balanceOf(address(this));
      _underlying.safeTransfer(_account, tokens);
  }

  function availableLiquidity() external view returns (uint256) {
    return uint256(-1);
  }
}