// File: /Users/tam/Work/kazamio/CoFiX/contracts/CoFiXControllerV2.sol



// SPDX-License-Identifier: GPL-3.0-or-later
pragma solidity 0.6.12;

import "@openzeppelin/contracts/math/SafeMath.sol";
import "./lib/ABDKMath64x64.sol";
import "./interface/INest_3_OfferPrice.sol";
import "./interface/ICoFiXKTable.sol";
import "./lib/TransferHelper.sol";
import "./interface/ICoFiXController.sol";
import "./interface/INest_3_VoteFactory.sol";
import "./interface/ICoFiXPair.sol";
import "./interface/ICoFiXFactory.sol";

// Controller contract to call NEST Oracle for prices, managed by governance
// Governance role of this contract should be the `Timelock` contract, which is further managed by a multisig contract
contract CoFiXControllerV2 is ICoFiXController {  // ctrl-v2: change contract name to avoid truffle complaint

    using SafeMath for uint256;

    enum CoFiX_OP { QUERY, MINT, BURN, SWAP_WITH_EXACT, SWAP_FOR_EXACT } // operations in CoFiX

    uint256 constant public AONE = 1 ether;
    uint256 constant public K_BASE = 1E8;
    uint256 constant public NAVPS_BASE = 1E18; // NAVPS (Net Asset Value Per Share), need accuracy
    uint256 internal T = 600; // ctrl-v2: V1 (900) -> V2 (600)
    uint256 internal K_EXPECTED_VALUE = 0.005*1E8; // ctrl-v2: V1 (0.0025) -> V2 (0.005)
    // impact cost params
    uint256 constant internal C_BUYIN_ALPHA = 25700000000000; // α=2.570e-05*1e18
    uint256 constant internal C_BUYIN_BETA = 854200000000; // β=8.542e-07*1e18
    uint256 constant internal C_SELLOUT_ALPHA = 117100000000000; // α=-1.171e-04*1e18
    uint256 constant internal C_SELLOUT_BETA = 838600000000; // β=8.386e-07*1e18

    mapping(address => uint32[3]) internal KInfoMap; // gas saving, index [0] is k vlaue, index [1] is updatedAt, index [2] is theta
    mapping(address => bool) public callerAllowed;

    INest_3_VoteFactory public immutable voteFactory;

    // managed by governance
    address public governance;
    address public immutable nestToken;
    address public immutable factory;
    address public kTable;
    uint256 public timespan = 14;
    uint256 public kRefreshInterval = 5 minutes;
    uint256 public DESTRUCTION_AMOUNT = 0 ether; // from nest oracle
    int128 public MAX_K0 = 0xCCCCCCCCCCCCD00; // (0.05*2**64).toString(16)
    int128 public GAMMA = 0x8000000000000000; // (0.5*2**64).toString(16)

    modifier onlyGovernance() {
        require(msg.sender == governance, "CoFiXCtrl: !governance");
        _;
    }

    constructor(address _voteFactory, address _nest, address _factory, address _kTable) public {
        governance = msg.sender;
        voteFactory = INest_3_VoteFactory(address(_voteFactory));
        nestToken = _nest;
        factory = _factory;
        kTable = _kTable;

        // add previous pair as caller
        ICoFiXFactory cFactory = ICoFiXFactory(_factory);
        uint256 pairCnt = cFactory.allPairsLength();
        for (uint256 i = 0; i < pairCnt; i++) {
            address pair = cFactory.allPairs(i);
            callerAllowed[pair] = true;
        }
    }

    receive() external payable {}

    /* setters for protocol governance */
    function setGovernance(address _new) external onlyGovernance {
        governance = _new;
        emit NewGovernance(_new);
    }

    function setKTable(address _kTable) external onlyGovernance {
        kTable = _kTable;
        emit NewKTable(_kTable);
    }    

    function setTimespan(uint256 _timeSpan) external onlyGovernance {
        timespan = _timeSpan;
        emit NewTimespan(_timeSpan);
    }

    function setKRefreshInterval(uint256 _interval) external onlyGovernance {
        kRefreshInterval = _interval;
        emit NewKRefreshInterval(_interval);
    }

    function setOracleDestructionAmount(uint256 _amount) external onlyGovernance {
        DESTRUCTION_AMOUNT = _amount;
    }

    function setTLimit(uint256 _T) external onlyGovernance { // ctrl-v2: new setter for T
        T = _T;
    }

    function setK(address token, uint32 k) external onlyGovernance { // ctrl-v2: new setter for K, adjustable by governance
        K_EXPECTED_VALUE = uint256(k);
        emit NewK(token, k); // new event for setting K
    }

    function setTheta(address token, uint32 theta) external onlyGovernance {
        KInfoMap[token][2] = theta;
        emit NewTheta(token, theta);
    }

    // Activate on NEST Oracle, should not be called twice for the same nest oracle
    function activate() external onlyGovernance {
        // address token, address from, address to, uint value
        TransferHelper.safeTransferFrom(nestToken, msg.sender, address(this), DESTRUCTION_AMOUNT);
        address oracle = voteFactory.checkAddress("nest.v3.offerPrice");
        // address token, address to, uint value
        TransferHelper.safeApprove(nestToken, oracle, DESTRUCTION_AMOUNT);
        INest_3_OfferPrice(oracle).activation(); // nest.transferFrom will be called
        TransferHelper.safeApprove(nestToken, oracle, 0); // ensure safety
    }

    function addCaller(address caller) external override {
        require(msg.sender == factory || msg.sender == governance, "CoFiXCtrl: only factory or gov");
        callerAllowed[caller] = true;
    }

    // Calc variance of price and K in CoFiX is very expensive
    // We use expected value of K based on statistical calculations here to save gas
    // In the near future, NEST could provide the variance of price directly. We will adopt it then.
    // We can make use of `data` bytes in the future
    function queryOracle(address token, uint8 op, bytes memory data) external override payable returns (uint256 _k, uint256 _ethAmount, uint256 _erc20Amount, uint256 _blockNum, uint256 _theta) {
        require(callerAllowed[msg.sender], "CoFiXCtrl: caller not allowed");
        (_ethAmount, _erc20Amount, _blockNum) = getLatestPrice(token);
        CoFiX_OP cop = CoFiX_OP(op);
        uint256 impactCost;
        if (cop == CoFiX_OP.SWAP_WITH_EXACT) {
            impactCost = calcImpactCostFor_SWAP_WITH_EXACT(token, data, _ethAmount, _erc20Amount);
        } else if (cop == CoFiX_OP.SWAP_FOR_EXACT) {
            revert("disabled experimental feature!"); // ctrl-v2: disable swapForExact function
         } else if (cop == CoFiX_OP.BURN) {
            impactCost = calcImpactCostFor_BURN(token, data, _ethAmount, _erc20Amount);
        }
        _k = K_EXPECTED_VALUE.add(impactCost); // ctrl-v2: adjustable K + impactCost is the final K
        _theta = KInfoMap[token][2];
        return (_k, _ethAmount, _erc20Amount, _blockNum, _theta);
    }

    function calcImpactCostFor_BURN(address token, bytes memory data, uint256 ethAmount, uint256 erc20Amount) public view returns (uint256 impactCost) {
        // bytes memory data = abi.encode(msg.sender, outToken, to, liquidity);
        (, address outToken, , uint256 liquidity) = abi.decode(data, (address, address, address, uint256));
        // calc real vol by liquidity * np
        uint256 navps = ICoFiXPair(msg.sender).getNAVPerShare(ethAmount, erc20Amount); // pair call controller, msg.sender is pair
        uint256 vol = liquidity.mul(navps).div(NAVPS_BASE);
        if (outToken != token) {
            // buy in ETH, outToken is ETH
            return impactCostForBuyInETH(vol);
        }
        // sell out liquidity, outToken is token, take this as sell out ETH and get token
        return impactCostForSellOutETH(vol);
    }

    function calcImpactCostFor_SWAP_WITH_EXACT(address token, bytes memory data, uint256 ethAmount, uint256 erc20Amount) public pure returns (uint256 impactCost) {
        (, address outToken, , uint256 amountIn) = abi.decode(data, (address, address, address, uint256));
        if (outToken != token) {
            // buy in ETH, outToken is ETH, amountIn is token
            // convert to amountIn in ETH
            uint256 vol = uint256(amountIn).mul(ethAmount).div(erc20Amount);
            return impactCostForBuyInETH(vol);
        }
        // sell out ETH, amountIn is ETH
        return impactCostForSellOutETH(amountIn);
    }

    function calcImpactCostFor_SWAP_FOR_EXACT(address token, bytes memory data, uint256 ethAmount, uint256 erc20Amount) public pure returns (uint256 impactCost) {
        (, address outToken, uint256 amountOutExact,) = abi.decode(data, (address, address, uint256, address));
        if (outToken != token) {
            // buy in ETH, outToken is ETH, amountOutExact is ETH
            return impactCostForBuyInETH(amountOutExact);
        }
        // sell out ETH, amountIn is ETH, amountOutExact is token
        // convert to amountOutExact in ETH
        uint256 vol = uint256(amountOutExact).mul(ethAmount).div(erc20Amount);
        return impactCostForSellOutETH(vol);
    }

    // impact cost
    // - C = 0, if VOL < 500
    // - C = α + β * VOL, if VOL >= 500

    // α=2.570e-05，β=8.542e-07
    function impactCostForBuyInETH(uint256 vol) public pure returns (uint256 impactCost) {
        if (vol < 500 ether) {
            return 0;
        }
        // return C_BUYIN_ALPHA.add(C_BUYIN_BETA.mul(vol).div(1e18)).mul(1e8).div(1e18);
        return C_BUYIN_ALPHA.add(C_BUYIN_BETA.mul(vol).div(1e18)).div(1e10); // combine mul div
    }

    // α=-1.171e-04，β=8.386e-07
    function impactCostForSellOutETH(uint256 vol) public pure returns (uint256 impactCost) {
        if (vol < 500 ether) {
            return 0;
        }
        // return (C_SELLOUT_BETA.mul(vol).div(1e18)).sub(C_SELLOUT_ALPHA).mul(1e8).div(1e18);
        return (C_SELLOUT_BETA.mul(vol).div(1e18)).sub(C_SELLOUT_ALPHA).div(1e10); // combine mul div
    }

    function getKInfo(address token) external view returns (uint32 k, uint32 updatedAt, uint32 theta) {
        k = uint32(K_EXPECTED_VALUE); // ctrl-v2: load from storage instead of constant value
        updatedAt = uint32(block.timestamp);
        theta = KInfoMap[token][2];
    }

    function getLatestPrice(address token) internal returns (uint256 _ethAmount, uint256 _erc20Amount, uint256 _blockNum) {
        uint256 _balanceBefore = address(this).balance;
        address oracle = voteFactory.checkAddress("nest.v3.offerPrice");
        uint256[] memory _rawPriceList = INest_3_OfferPrice(oracle).updateAndCheckPriceList{value: msg.value}(token, 1);
        require(_rawPriceList.length == 3, "CoFiXCtrl: bad price len");
        // validate T
        uint256 _T = block.number.sub(_rawPriceList[2]).mul(timespan);
        require(_T < T, "CoFiXCtrl: oralce price outdated"); // ctrl-v2: adjustable T
        uint256 oracleFeeChange = msg.value.sub(_balanceBefore.sub(address(this).balance));
        if (oracleFeeChange > 0) TransferHelper.safeTransferETH(msg.sender, oracleFeeChange);
        return (_rawPriceList[0], _rawPriceList[1], _rawPriceList[2]);
        // return (K_EXPECTED_VALUE, _rawPriceList[0], _rawPriceList[1], _rawPriceList[2], KInfoMap[token][2]);
    }
    
    // ctrl-v2: remove unused code bellow according to PeckShield's advice
}
// File: /Users/tam/Work/kazamio/CoFiX/contracts/interface/ICoFiXController.sol



// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity 0.6.12;

interface ICoFiXController {

    event NewK(address token, int128 K, int128 sigma, uint256 T, uint256 ethAmount, uint256 erc20Amount, uint256 blockNum, uint256 tIdx, uint256 sigmaIdx, int128 K0);
    event NewGovernance(address _new);
    event NewOracle(address _priceOracle);
    event NewKTable(address _kTable);
    event NewTimespan(uint256 _timeSpan);
    event NewKRefreshInterval(uint256 _interval);
    event NewKLimit(int128 maxK0);
    event NewGamma(int128 _gamma);
    event NewTheta(address token, uint32 theta);
    event NewK(address token, uint32 k);

    function addCaller(address caller) external;

    function queryOracle(address token, uint8 op, bytes memory data) external payable returns (uint256 k, uint256 ethAmount, uint256 erc20Amount, uint256 blockNum, uint256 theta);
}
// File: /Users/tam/Work/kazamio/CoFiX/contracts/interface/ICoFiXERC20.sol



// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity 0.6.12;

interface ICoFiXERC20 {
    event Approval(address indexed owner, address indexed spender, uint value);
    event Transfer(address indexed from, address indexed to, uint value);

    // function name() external pure returns (string memory);
    // function symbol() external pure returns (string memory);
    function decimals() external pure returns (uint8);
    function totalSupply() external view returns (uint);
    function balanceOf(address owner) external view returns (uint);
    function allowance(address owner, address spender) external view returns (uint);

    function approve(address spender, uint value) external returns (bool);
    function transfer(address to, uint value) external returns (bool);
    function transferFrom(address from, address to, uint value) external returns (bool);

    function DOMAIN_SEPARATOR() external view returns (bytes32);
    function PERMIT_TYPEHASH() external pure returns (bytes32);
    function nonces(address owner) external view returns (uint);

    function permit(address owner, address spender, uint value, uint deadline, uint8 v, bytes32 r, bytes32 s) external;
}

// File: /Users/tam/Work/kazamio/CoFiX/contracts/interface/ICoFiXFactory.sol



// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity 0.6.12;

interface ICoFiXFactory {
    // All pairs: {ETH <-> ERC20 Token}
    event PairCreated(address indexed token, address pair, uint256);
    event NewGovernance(address _new);
    event NewController(address _new);
    event NewFeeReceiver(address _new);
    event NewFeeVaultForLP(address token, address feeVault);
    event NewVaultForLP(address _new);
    event NewVaultForTrader(address _new);
    event NewVaultForCNode(address _new);

    /// @dev Create a new token pair for trading
    /// @param  token the address of token to trade
    /// @return pair the address of new token pair
    function createPair(
        address token
        )
        external
        returns (address pair);

    function getPair(address token) external view returns (address pair);
    function allPairs(uint256) external view returns (address pair);
    function allPairsLength() external view returns (uint256);

    function getTradeMiningStatus(address token) external view returns (bool status);
    function setTradeMiningStatus(address token, bool status) external;
    function getFeeVaultForLP(address token) external view returns (address feeVault); // for LPs
    function setFeeVaultForLP(address token, address feeVault) external;

    function setGovernance(address _new) external;
    function setController(address _new) external;
    function setFeeReceiver(address _new) external;
    function setVaultForLP(address _new) external;
    function setVaultForTrader(address _new) external;
    function setVaultForCNode(address _new) external;
    function getController() external view returns (address controller);
    function getFeeReceiver() external view returns (address feeReceiver); // For CoFi Holders
    function getVaultForLP() external view returns (address vaultForLP);
    function getVaultForTrader() external view returns (address vaultForTrader);
    function getVaultForCNode() external view returns (address vaultForCNode);
}
// File: /Users/tam/Work/kazamio/CoFiX/contracts/interface/ICoFiXKTable.sol



// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity 0.6.12;

interface ICoFiXKTable {
    function setK0(uint256 tIdx, uint256 sigmaIdx, int128 k0) external;
    function setK0InBatch(uint256[] memory tIdxs, uint256[] memory sigmaIdxs, int128[] memory k0s) external;
    function getK0(uint256 tIdx, uint256 sigmaIdx) external view returns (int128);
}
// File: /Users/tam/Work/kazamio/CoFiX/contracts/interface/ICoFiXPair.sol



// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity 0.6.12;
import './ICoFiXERC20.sol';

interface ICoFiXPair is ICoFiXERC20 {

    struct OraclePrice {
        uint256 ethAmount;
        uint256 erc20Amount;
        uint256 blockNum;
        uint256 K;
        uint256 theta;
    }

    // All pairs: {ETH <-> ERC20 Token}
    event Mint(address indexed sender, uint amount0, uint amount1);
    event Burn(address indexed sender, address outToken, uint outAmount, address indexed to);
    event Swap(
        address indexed sender,
        uint amountIn,
        uint amountOut,
        address outToken,
        address indexed to
    );
    event Sync(uint112 reserve0, uint112 reserve1);

    function MINIMUM_LIQUIDITY() external pure returns (uint);
    function factory() external view returns (address);
    function token0() external view returns (address);
    function token1() external view returns (address);
    function getReserves() external view returns (uint112 reserve0, uint112 reserve1);

    function mint(address to) external payable returns (uint liquidity, uint oracleFeeChange);
    function burn(address outToken, address to) external payable returns (uint amountOut, uint oracleFeeChange);
    function swapWithExact(address outToken, address to) external payable returns (uint amountIn, uint amountOut, uint oracleFeeChange, uint256[4] memory tradeInfo);
    function swapForExact(address outToken, uint amountOutExact, address to) external payable returns (uint amountIn, uint amountOut, uint oracleFeeChange, uint256[4] memory tradeInfo);
    function skim(address to) external;
    function sync() external;

    function initialize(address, address, string memory, string memory) external;

    /// @dev get Net Asset Value Per Share
    /// @param  ethAmount ETH side of Oracle price {ETH <-> ERC20 Token}
    /// @param  erc20Amount Token side of Oracle price {ETH <-> ERC20 Token}
    /// @return navps The Net Asset Value Per Share (liquidity) represents
    function getNAVPerShare(uint256 ethAmount, uint256 erc20Amount) external view returns (uint256 navps);
}

// File: /Users/tam/Work/kazamio/CoFiX/contracts/interface/INest_3_OfferPrice.sol



// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity 0.6.12;

interface INest_3_OfferPrice {
    function transfer(address to, uint value) external returns (bool);

    /**
    * @dev Update and check the latest price
    * @param tokenAddress Token address
    * @return ethAmount ETH amount
    * @return erc20Amount Erc20 amount
    * @return blockNum Price block
    */
    function updateAndCheckPriceNow(address tokenAddress) external payable returns(uint256 ethAmount, uint256 erc20Amount, uint256 blockNum);

    /**
    * @dev Update and check the effective price list
    * @param tokenAddress Token address
    * @param num Number of prices to check
    * @return uint256[] price list
    */
    function updateAndCheckPriceList(address tokenAddress, uint256 num) external payable returns (uint256[] memory);

    // Activate the price checking function
    function activation() external;

    // Check the minimum ETH cost of obtaining the price
    function checkPriceCostLeast(address tokenAddress) external view returns(uint256);

    // Check the maximum ETH cost of obtaining the price
    function checkPriceCostMost(address tokenAddress) external view returns(uint256);

    // Check the cost of a single price data
    function checkPriceCostSingle(address tokenAddress) external view returns(uint256);

    // Check whether the price-checking functions can be called
    function checkUseNestPrice(address target) external view returns (bool);

    // Check whether the address is in the blocklist
    function checkBlocklist(address add) external view returns(bool);

    // Check the amount of NEST to destroy to call prices
    function checkDestructionAmount() external view returns(uint256);

    // Check the waiting time to start calling prices
    function checkEffectTime() external view returns (uint256);
}
// File: /Users/tam/Work/kazamio/CoFiX/contracts/interface/INest_3_VoteFactory.sol



// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity 0.6.12;

interface INest_3_VoteFactory {
    // 查询地址
	function checkAddress(string calldata name) external view returns (address contractAddress);
    // _offerPrice = Nest_3_OfferPrice(address(voteFactoryMap.checkAddress("nest.v3.offerPrice")));
}
// File: /Users/tam/Work/kazamio/CoFiX/contracts/lib/ABDKMath64x64.sol



// SPDX-License-Identifier: Copyright © 2019 by ABDK Consulting

/*
 * ABDK Math 64.64 Smart Contract Library.  Copyright © 2019 by ABDK Consulting.
 * Author: Mikhail Vladimirov <mikhail.vladimirov@gmail.com>
 */
pragma solidity 0.6.12;

/**
 * Smart contract library of mathematical functions operating with signed
 * 64.64-bit fixed point numbers.  Signed 64.64-bit fixed point number is
 * basically a simple fraction whose numerator is signed 128-bit integer and
 * denominator is 2^64.  As long as denominator is always the same, there is no
 * need to store it, thus in Solidity signed 64.64-bit fixed point numbers are
 * represented by int128 type holding only the numerator.
 */
library ABDKMath64x64 {
  /**
   * @dev Minimum value signed 64.64-bit fixed point number may have. 
   */
  int128 private constant MIN_64x64 = -0x80000000000000000000000000000000;

  /**
   * @dev Maximum value signed 64.64-bit fixed point number may have. 
   */
  int128 private constant MAX_64x64 = 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF;

  /**
   * Convert signed 256-bit integer number into signed 64.64-bit fixed point
   * number.  Revert on overflow.
   *
   * @param x signed 256-bit integer number
   * @return signed 64.64-bit fixed point number
   */
  function fromInt (int256 x) internal pure returns (int128) {
    require (x >= -0x8000000000000000 && x <= 0x7FFFFFFFFFFFFFFF);
    return int128 (x << 64);
  }

  /**
   * Convert signed 64.64 fixed point number into signed 64-bit integer number
   * rounding down.
   *
   * @param x signed 64.64-bit fixed point number
   * @return signed 64-bit integer number
   */
  function toInt (int128 x) internal pure returns (int64) {
    return int64 (x >> 64);
  }

  /**
   * Convert unsigned 256-bit integer number into signed 64.64-bit fixed point
   * number.  Revert on overflow.
   *
   * @param x unsigned 256-bit integer number
   * @return signed 64.64-bit fixed point number
   */
  function fromUInt (uint256 x) internal pure returns (int128) {
    require (x <= 0x7FFFFFFFFFFFFFFF);
    return int128 (x << 64);
  }

  /**
   * Convert signed 64.64 fixed point number into unsigned 64-bit integer
   * number rounding down.  Revert on underflow.
   *
   * @param x signed 64.64-bit fixed point number
   * @return unsigned 64-bit integer number
   */
  function toUInt (int128 x) internal pure returns (uint64) {
    require (x >= 0);
    return uint64 (x >> 64);
  }

  /**
   * Convert signed 128.128 fixed point number into signed 64.64-bit fixed point
   * number rounding down.  Revert on overflow.
   *
   * @param x signed 128.128-bin fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function from128x128 (int256 x) internal pure returns (int128) {
    int256 result = x >> 64;
    require (result >= MIN_64x64 && result <= MAX_64x64);
    return int128 (result);
  }

  /**
   * Convert signed 64.64 fixed point number into signed 128.128 fixed point
   * number.
   *
   * @param x signed 64.64-bit fixed point number
   * @return signed 128.128 fixed point number
   */
  function to128x128 (int128 x) internal pure returns (int256) {
    return int256 (x) << 64;
  }

  /**
   * Calculate x + y.  Revert on overflow.
   *
   * @param x signed 64.64-bit fixed point number
   * @param y signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function add (int128 x, int128 y) internal pure returns (int128) {
    int256 result = int256(x) + y;
    require (result >= MIN_64x64 && result <= MAX_64x64);
    return int128 (result);
  }

  /**
   * Calculate x - y.  Revert on overflow.
   *
   * @param x signed 64.64-bit fixed point number
   * @param y signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function sub (int128 x, int128 y) internal pure returns (int128) {
    int256 result = int256(x) - y;
    require (result >= MIN_64x64 && result <= MAX_64x64);
    return int128 (result);
  }

  /**
   * Calculate x * y rounding down.  Revert on overflow.
   *
   * @param x signed 64.64-bit fixed point number
   * @param y signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function mul (int128 x, int128 y) internal pure returns (int128) {
    int256 result = int256(x) * y >> 64;
    require (result >= MIN_64x64 && result <= MAX_64x64);
    return int128 (result);
  }

  /**
   * Calculate x * y rounding towards zero, where x is signed 64.64 fixed point
   * number and y is signed 256-bit integer number.  Revert on overflow.
   *
   * @param x signed 64.64 fixed point number
   * @param y signed 256-bit integer number
   * @return signed 256-bit integer number
   */
  function muli (int128 x, int256 y) internal pure returns (int256) {
    if (x == MIN_64x64) {
      require (y >= -0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF &&
        y <= 0x1000000000000000000000000000000000000000000000000);
      return -y << 63;
    } else {
      bool negativeResult = false;
      if (x < 0) {
        x = -x;
        negativeResult = true;
      }
      if (y < 0) {
        y = -y; // We rely on overflow behavior here
        negativeResult = !negativeResult;
      }
      uint256 absoluteResult = mulu (x, uint256 (y));
      if (negativeResult) {
        require (absoluteResult <=
          0x8000000000000000000000000000000000000000000000000000000000000000);
        return -int256 (absoluteResult); // We rely on overflow behavior here
      } else {
        require (absoluteResult <=
          0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF);
        return int256 (absoluteResult);
      }
    }
  }

  /**
   * Calculate x * y rounding down, where x is signed 64.64 fixed point number
   * and y is unsigned 256-bit integer number.  Revert on overflow.
   *
   * @param x signed 64.64 fixed point number
   * @param y unsigned 256-bit integer number
   * @return unsigned 256-bit integer number
   */
  function mulu (int128 x, uint256 y) internal pure returns (uint256) {
    if (y == 0) return 0;

    require (x >= 0);

    uint256 lo = (uint256 (x) * (y & 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF)) >> 64;
    uint256 hi = uint256 (x) * (y >> 128);

    require (hi <= 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF);
    hi <<= 64;

    require (hi <=
      0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF - lo);
    return hi + lo;
  }

  /**
   * Calculate x / y rounding towards zero.  Revert on overflow or when y is
   * zero.
   *
   * @param x signed 64.64-bit fixed point number
   * @param y signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function div (int128 x, int128 y) internal pure returns (int128) {
    require (y != 0);
    int256 result = (int256 (x) << 64) / y;
    require (result >= MIN_64x64 && result <= MAX_64x64);
    return int128 (result);
  }

  /**
   * Calculate x / y rounding towards zero, where x and y are signed 256-bit
   * integer numbers.  Revert on overflow or when y is zero.
   *
   * @param x signed 256-bit integer number
   * @param y signed 256-bit integer number
   * @return signed 64.64-bit fixed point number
   */
  function divi (int256 x, int256 y) internal pure returns (int128) {
    require (y != 0);

    bool negativeResult = false;
    if (x < 0) {
      x = -x; // We rely on overflow behavior here
      negativeResult = true;
    }
    if (y < 0) {
      y = -y; // We rely on overflow behavior here
      negativeResult = !negativeResult;
    }
    uint128 absoluteResult = divuu (uint256 (x), uint256 (y));
    if (negativeResult) {
      require (absoluteResult <= 0x80000000000000000000000000000000);
      return -int128 (absoluteResult); // We rely on overflow behavior here
    } else {
      require (absoluteResult <= 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF);
      return int128 (absoluteResult); // We rely on overflow behavior here
    }
  }

  /**
   * Calculate x / y rounding towards zero, where x and y are unsigned 256-bit
   * integer numbers.  Revert on overflow or when y is zero.
   *
   * @param x unsigned 256-bit integer number
   * @param y unsigned 256-bit integer number
   * @return signed 64.64-bit fixed point number
   */
  function divu (uint256 x, uint256 y) internal pure returns (int128) {
    require (y != 0);
    uint128 result = divuu (x, y);
    require (result <= uint128 (MAX_64x64));
    return int128 (result);
  }

  /**
   * Calculate -x.  Revert on overflow.
   *
   * @param x signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function neg (int128 x) internal pure returns (int128) {
    require (x != MIN_64x64);
    return -x;
  }

  /**
   * Calculate |x|.  Revert on overflow.
   *
   * @param x signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function abs (int128 x) internal pure returns (int128) {
    require (x != MIN_64x64);
    return x < 0 ? -x : x;
  }

  /**
   * Calculate 1 / x rounding towards zero.  Revert on overflow or when x is
   * zero.
   *
   * @param x signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function inv (int128 x) internal pure returns (int128) {
    require (x != 0);
    int256 result = int256 (0x100000000000000000000000000000000) / x;
    require (result >= MIN_64x64 && result <= MAX_64x64);
    return int128 (result);
  }

  /**
   * Calculate arithmetics average of x and y, i.e. (x + y) / 2 rounding down.
   *
   * @param x signed 64.64-bit fixed point number
   * @param y signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function avg (int128 x, int128 y) internal pure returns (int128) {
    return int128 ((int256 (x) + int256 (y)) >> 1);
  }

  /**
   * Calculate geometric average of x and y, i.e. sqrt (x * y) rounding down.
   * Revert on overflow or in case x * y is negative.
   *
   * @param x signed 64.64-bit fixed point number
   * @param y signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function gavg (int128 x, int128 y) internal pure returns (int128) {
    int256 m = int256 (x) * int256 (y);
    require (m >= 0);
    require (m <
        0x4000000000000000000000000000000000000000000000000000000000000000);
    return int128 (sqrtu (uint256 (m), uint256 (x) + uint256 (y) >> 1));
  }

  /**
   * Calculate x^y assuming 0^0 is 1, where x is signed 64.64 fixed point number
   * and y is unsigned 256-bit integer number.  Revert on overflow.
   *
   * @param x signed 64.64-bit fixed point number
   * @param y uint256 value
   * @return signed 64.64-bit fixed point number
   */
  function pow (int128 x, uint256 y) internal pure returns (int128) {
    uint256 absoluteResult;
    bool negativeResult = false;
    if (x >= 0) {
      absoluteResult = powu (uint256 (x) << 63, y);
    } else {
      // We rely on overflow behavior here
      absoluteResult = powu (uint256 (uint128 (-x)) << 63, y);
      negativeResult = y & 1 > 0;
    }

    absoluteResult >>= 63;

    if (negativeResult) {
      require (absoluteResult <= 0x80000000000000000000000000000000);
      return -int128 (absoluteResult); // We rely on overflow behavior here
    } else {
      require (absoluteResult <= 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF);
      return int128 (absoluteResult); // We rely on overflow behavior here
    }
  }

  /**
   * Calculate sqrt (x) rounding down.  Revert if x < 0.
   *
   * @param x signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function sqrt (int128 x) internal pure returns (int128) {
    require (x >= 0);
    return int128 (sqrtu (uint256 (x) << 64, 0x10000000000000000));
  }

  /**
   * Calculate binary logarithm of x.  Revert if x <= 0.
   *
   * @param x signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function log_2 (int128 x) internal pure returns (int128) {
    require (x > 0);

    int256 msb = 0;
    int256 xc = x;
    if (xc >= 0x10000000000000000) { xc >>= 64; msb += 64; }
    if (xc >= 0x100000000) { xc >>= 32; msb += 32; }
    if (xc >= 0x10000) { xc >>= 16; msb += 16; }
    if (xc >= 0x100) { xc >>= 8; msb += 8; }
    if (xc >= 0x10) { xc >>= 4; msb += 4; }
    if (xc >= 0x4) { xc >>= 2; msb += 2; }
    if (xc >= 0x2) msb += 1;  // No need to shift xc anymore

    int256 result = msb - 64 << 64;
    uint256 ux = uint256 (x) << 127 - msb;
    for (int256 bit = 0x8000000000000000; bit > 0; bit >>= 1) {
      ux *= ux;
      uint256 b = ux >> 255;
      ux >>= 127 + b;
      result += bit * int256 (b);
    }

    return int128 (result);
  }

  /**
   * Calculate natural logarithm of x.  Revert if x <= 0.
   *
   * @param x signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function ln (int128 x) internal pure returns (int128) {
    require (x > 0);

    return int128 (
        uint256 (log_2 (x)) * 0xB17217F7D1CF79ABC9E3B39803F2F6AF >> 128);
  }

  /**
   * Calculate binary exponent of x.  Revert on overflow.
   *
   * @param x signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function exp_2 (int128 x) internal pure returns (int128) {
    require (x < 0x400000000000000000); // Overflow

    if (x < -0x400000000000000000) return 0; // Underflow

    uint256 result = 0x80000000000000000000000000000000;

    if (x & 0x8000000000000000 > 0)
      result = result * 0x16A09E667F3BCC908B2FB1366EA957D3E >> 128;
    if (x & 0x4000000000000000 > 0)
      result = result * 0x1306FE0A31B7152DE8D5A46305C85EDEC >> 128;
    if (x & 0x2000000000000000 > 0)
      result = result * 0x1172B83C7D517ADCDF7C8C50EB14A791F >> 128;
    if (x & 0x1000000000000000 > 0)
      result = result * 0x10B5586CF9890F6298B92B71842A98363 >> 128;
    if (x & 0x800000000000000 > 0)
      result = result * 0x1059B0D31585743AE7C548EB68CA417FD >> 128;
    if (x & 0x400000000000000 > 0)
      result = result * 0x102C9A3E778060EE6F7CACA4F7A29BDE8 >> 128;
    if (x & 0x200000000000000 > 0)
      result = result * 0x10163DA9FB33356D84A66AE336DCDFA3F >> 128;
    if (x & 0x100000000000000 > 0)
      result = result * 0x100B1AFA5ABCBED6129AB13EC11DC9543 >> 128;
    if (x & 0x80000000000000 > 0)
      result = result * 0x10058C86DA1C09EA1FF19D294CF2F679B >> 128;
    if (x & 0x40000000000000 > 0)
      result = result * 0x1002C605E2E8CEC506D21BFC89A23A00F >> 128;
    if (x & 0x20000000000000 > 0)
      result = result * 0x100162F3904051FA128BCA9C55C31E5DF >> 128;
    if (x & 0x10000000000000 > 0)
      result = result * 0x1000B175EFFDC76BA38E31671CA939725 >> 128;
    if (x & 0x8000000000000 > 0)
      result = result * 0x100058BA01FB9F96D6CACD4B180917C3D >> 128;
    if (x & 0x4000000000000 > 0)
      result = result * 0x10002C5CC37DA9491D0985C348C68E7B3 >> 128;
    if (x & 0x2000000000000 > 0)
      result = result * 0x1000162E525EE054754457D5995292026 >> 128;
    if (x & 0x1000000000000 > 0)
      result = result * 0x10000B17255775C040618BF4A4ADE83FC >> 128;
    if (x & 0x800000000000 > 0)
      result = result * 0x1000058B91B5BC9AE2EED81E9B7D4CFAB >> 128;
    if (x & 0x400000000000 > 0)
      result = result * 0x100002C5C89D5EC6CA4D7C8ACC017B7C9 >> 128;
    if (x & 0x200000000000 > 0)
      result = result * 0x10000162E43F4F831060E02D839A9D16D >> 128;
    if (x & 0x100000000000 > 0)
      result = result * 0x100000B1721BCFC99D9F890EA06911763 >> 128;
    if (x & 0x80000000000 > 0)
      result = result * 0x10000058B90CF1E6D97F9CA14DBCC1628 >> 128;
    if (x & 0x40000000000 > 0)
      result = result * 0x1000002C5C863B73F016468F6BAC5CA2B >> 128;
    if (x & 0x20000000000 > 0)
      result = result * 0x100000162E430E5A18F6119E3C02282A5 >> 128;
    if (x & 0x10000000000 > 0)
      result = result * 0x1000000B1721835514B86E6D96EFD1BFE >> 128;
    if (x & 0x8000000000 > 0)
      result = result * 0x100000058B90C0B48C6BE5DF846C5B2EF >> 128;
    if (x & 0x4000000000 > 0)
      result = result * 0x10000002C5C8601CC6B9E94213C72737A >> 128;
    if (x & 0x2000000000 > 0)
      result = result * 0x1000000162E42FFF037DF38AA2B219F06 >> 128;
    if (x & 0x1000000000 > 0)
      result = result * 0x10000000B17217FBA9C739AA5819F44F9 >> 128;
    if (x & 0x800000000 > 0)
      result = result * 0x1000000058B90BFCDEE5ACD3C1CEDC823 >> 128;
    if (x & 0x400000000 > 0)
      result = result * 0x100000002C5C85FE31F35A6A30DA1BE50 >> 128;
    if (x & 0x200000000 > 0)
      result = result * 0x10000000162E42FF0999CE3541B9FFFCF >> 128;
    if (x & 0x100000000 > 0)
      result = result * 0x100000000B17217F80F4EF5AADDA45554 >> 128;
    if (x & 0x80000000 > 0)
      result = result * 0x10000000058B90BFBF8479BD5A81B51AD >> 128;
    if (x & 0x40000000 > 0)
      result = result * 0x1000000002C5C85FDF84BD62AE30A74CC >> 128;
    if (x & 0x20000000 > 0)
      result = result * 0x100000000162E42FEFB2FED257559BDAA >> 128;
    if (x & 0x10000000 > 0)
      result = result * 0x1000000000B17217F7D5A7716BBA4A9AE >> 128;
    if (x & 0x8000000 > 0)
      result = result * 0x100000000058B90BFBE9DDBAC5E109CCE >> 128;
    if (x & 0x4000000 > 0)
      result = result * 0x10000000002C5C85FDF4B15DE6F17EB0D >> 128;
    if (x & 0x2000000 > 0)
      result = result * 0x1000000000162E42FEFA494F1478FDE05 >> 128;
    if (x & 0x1000000 > 0)
      result = result * 0x10000000000B17217F7D20CF927C8E94C >> 128;
    if (x & 0x800000 > 0)
      result = result * 0x1000000000058B90BFBE8F71CB4E4B33D >> 128;
    if (x & 0x400000 > 0)
      result = result * 0x100000000002C5C85FDF477B662B26945 >> 128;
    if (x & 0x200000 > 0)
      result = result * 0x10000000000162E42FEFA3AE53369388C >> 128;
    if (x & 0x100000 > 0)
      result = result * 0x100000000000B17217F7D1D351A389D40 >> 128;
    if (x & 0x80000 > 0)
      result = result * 0x10000000000058B90BFBE8E8B2D3D4EDE >> 128;
    if (x & 0x40000 > 0)
      result = result * 0x1000000000002C5C85FDF4741BEA6E77E >> 128;
    if (x & 0x20000 > 0)
      result = result * 0x100000000000162E42FEFA39FE95583C2 >> 128;
    if (x & 0x10000 > 0)
      result = result * 0x1000000000000B17217F7D1CFB72B45E1 >> 128;
    if (x & 0x8000 > 0)
      result = result * 0x100000000000058B90BFBE8E7CC35C3F0 >> 128;
    if (x & 0x4000 > 0)
      result = result * 0x10000000000002C5C85FDF473E242EA38 >> 128;
    if (x & 0x2000 > 0)
      result = result * 0x1000000000000162E42FEFA39F02B772C >> 128;
    if (x & 0x1000 > 0)
      result = result * 0x10000000000000B17217F7D1CF7D83C1A >> 128;
    if (x & 0x800 > 0)
      result = result * 0x1000000000000058B90BFBE8E7BDCBE2E >> 128;
    if (x & 0x400 > 0)
      result = result * 0x100000000000002C5C85FDF473DEA871F >> 128;
    if (x & 0x200 > 0)
      result = result * 0x10000000000000162E42FEFA39EF44D91 >> 128;
    if (x & 0x100 > 0)
      result = result * 0x100000000000000B17217F7D1CF79E949 >> 128;
    if (x & 0x80 > 0)
      result = result * 0x10000000000000058B90BFBE8E7BCE544 >> 128;
    if (x & 0x40 > 0)
      result = result * 0x1000000000000002C5C85FDF473DE6ECA >> 128;
    if (x & 0x20 > 0)
      result = result * 0x100000000000000162E42FEFA39EF366F >> 128;
    if (x & 0x10 > 0)
      result = result * 0x1000000000000000B17217F7D1CF79AFA >> 128;
    if (x & 0x8 > 0)
      result = result * 0x100000000000000058B90BFBE8E7BCD6D >> 128;
    if (x & 0x4 > 0)
      result = result * 0x10000000000000002C5C85FDF473DE6B2 >> 128;
    if (x & 0x2 > 0)
      result = result * 0x1000000000000000162E42FEFA39EF358 >> 128;
    if (x & 0x1 > 0)
      result = result * 0x10000000000000000B17217F7D1CF79AB >> 128;

    result >>= 63 - (x >> 64);
    require (result <= uint256 (MAX_64x64));

    return int128 (result);
  }

  /**
   * Calculate natural exponent of x.  Revert on overflow.
   *
   * @param x signed 64.64-bit fixed point number
   * @return signed 64.64-bit fixed point number
   */
  function exp (int128 x) internal pure returns (int128) {
    require (x < 0x400000000000000000); // Overflow

    if (x < -0x400000000000000000) return 0; // Underflow

    return exp_2 (
        int128 (int256 (x) * 0x171547652B82FE1777D0FFDA0D23A7D12 >> 128));
  }

  /**
   * Calculate x / y rounding towards zero, where x and y are unsigned 256-bit
   * integer numbers.  Revert on overflow or when y is zero.
   *
   * @param x unsigned 256-bit integer number
   * @param y unsigned 256-bit integer number
   * @return unsigned 64.64-bit fixed point number
   */
  function divuu (uint256 x, uint256 y) private pure returns (uint128) {
    require (y != 0);

    uint256 result;

    if (x <= 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF)
      result = (x << 64) / y;
    else {
      uint256 msb = 192;
      uint256 xc = x >> 192;
      if (xc >= 0x100000000) { xc >>= 32; msb += 32; }
      if (xc >= 0x10000) { xc >>= 16; msb += 16; }
      if (xc >= 0x100) { xc >>= 8; msb += 8; }
      if (xc >= 0x10) { xc >>= 4; msb += 4; }
      if (xc >= 0x4) { xc >>= 2; msb += 2; }
      if (xc >= 0x2) msb += 1;  // No need to shift xc anymore

      result = (x << 255 - msb) / ((y - 1 >> msb - 191) + 1);
      require (result <= 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF);

      uint256 hi = result * (y >> 128);
      uint256 lo = result * (y & 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF);

      uint256 xh = x >> 192;
      uint256 xl = x << 64;

      if (xl < lo) xh -= 1;
      xl -= lo; // We rely on overflow behavior here
      lo = hi << 128;
      if (xl < lo) xh -= 1;
      xl -= lo; // We rely on overflow behavior here

      assert (xh == hi >> 128);

      result += xl / y;
    }

    require (result <= 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF);
    return uint128 (result);
  }

  /**
   * Calculate x^y assuming 0^0 is 1, where x is unsigned 129.127 fixed point
   * number and y is unsigned 256-bit integer number.  Revert on overflow.
   *
   * @param x unsigned 129.127-bit fixed point number
   * @param y uint256 value
   * @return unsigned 129.127-bit fixed point number
   */
  function powu (uint256 x, uint256 y) private pure returns (uint256) {
    if (y == 0) return 0x80000000000000000000000000000000;
    else if (x == 0) return 0;
    else {
      int256 msb = 0;
      uint256 xc = x;
      if (xc >= 0x100000000000000000000000000000000) { xc >>= 128; msb += 128; }
      if (xc >= 0x10000000000000000) { xc >>= 64; msb += 64; }
      if (xc >= 0x100000000) { xc >>= 32; msb += 32; }
      if (xc >= 0x10000) { xc >>= 16; msb += 16; }
      if (xc >= 0x100) { xc >>= 8; msb += 8; }
      if (xc >= 0x10) { xc >>= 4; msb += 4; }
      if (xc >= 0x4) { xc >>= 2; msb += 2; }
      if (xc >= 0x2) msb += 1;  // No need to shift xc anymore

      int256 xe = msb - 127;
      if (xe > 0) x >>= xe;
      else x <<= -xe;

      uint256 result = 0x80000000000000000000000000000000;
      int256 re = 0;

      while (y > 0) {
        if (y & 1 > 0) {
          result = result * x;
          y -= 1;
          re += xe;
          if (result >=
            0x8000000000000000000000000000000000000000000000000000000000000000) {
            result >>= 128;
            re += 1;
          } else result >>= 127;
          if (re < -127) return 0; // Underflow
          require (re < 128); // Overflow
        } else {
          x = x * x;
          y >>= 1;
          xe <<= 1;
          if (x >=
            0x8000000000000000000000000000000000000000000000000000000000000000) {
            x >>= 128;
            xe += 1;
          } else x >>= 127;
          if (xe < -127) return 0; // Underflow
          require (xe < 128); // Overflow
        }
      }

      if (re > 0) result <<= re;
      else if (re < 0) result >>= -re;

      return result;
    }
  }

  /**
   * Calculate sqrt (x) rounding down, where x is unsigned 256-bit integer
   * number.
   *
   * @param x unsigned 256-bit integer number
   * @return unsigned 128-bit integer number
   */
  function sqrtu (uint256 x, uint256 r) private pure returns (uint128) {
    if (x == 0) return 0;
    else {
      require (r > 0);
      while (true) {
        uint256 rr = x / r;
        if (r == rr || r + 1 == rr) return uint128 (r);
        else if (r == rr + 1) return uint128 (rr);
        r = r + rr + 1 >> 1;
      }
    }
  }
}

// File: /Users/tam/Work/kazamio/CoFiX/contracts/lib/TransferHelper.sol



// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity 0.6.12;

// helper methods for interacting with ERC20 tokens and sending ETH that do not consistently return true/false
library TransferHelper {
    function safeApprove(address token, address to, uint value) internal {
        // bytes4(keccak256(bytes('approve(address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0x095ea7b3, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: APPROVE_FAILED');
    }

    function safeTransfer(address token, address to, uint value) internal {
        // bytes4(keccak256(bytes('transfer(address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0xa9059cbb, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: TRANSFER_FAILED');
    }

    function safeTransferFrom(address token, address from, address to, uint value) internal {
        // bytes4(keccak256(bytes('transferFrom(address,address,uint256)')));
        (bool success, bytes memory data) = token.call(abi.encodeWithSelector(0x23b872dd, from, to, value));
        require(success && (data.length == 0 || abi.decode(data, (bool))), 'TransferHelper: TRANSFER_FROM_FAILED');
    }

    function safeTransferETH(address to, uint value) internal {
        (bool success,) = to.call{value:value}(new bytes(0));
        require(success, 'TransferHelper: ETH_TRANSFER_FAILED');
    }
}

// File: @openzeppelin/contracts/math/SafeMath.sol



// SPDX-License-Identifier: MIT

pragma solidity ^0.6.0;

/**
 * @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.
     */
    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.
     */
    function div(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        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.
     */
    function mod(uint256 a, uint256 b, string memory errorMessage) internal pure returns (uint256) {
        require(b != 0, errorMessage);
        return a % b;
    }
}