Contract Source Code:

// SPDX-License-Identifier: MIT

pragma solidity 0.6.12;

/**
 * @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;
    }
}
pragma solidity 0.6.12;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
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);
}
pragma solidity 0.6.12;

contract Governable {
    address public gov;

    constructor() public {
        gov = msg.sender;
    }

    modifier onlyGov() {
        require(msg.sender == gov, "Governable: forbidden");
        _;
    }

    function setGov(address _gov) external onlyGov {
        gov = _gov;
    }
}
pragma solidity 0.6.12;

interface IVaultUtils {
    function updateCumulativeFundingRate(address _collateralToken, address _indexToken) external returns (bool);
    function validateIncreasePosition(address _account, address _collateralToken, address _indexToken, uint256 _sizeDelta, bool _isLong) external view;
    function validateDecreasePosition(address _account, address _collateralToken, address _indexToken, uint256 _collateralDelta, uint256 _sizeDelta, bool _isLong, address _receiver) external view;
    function validateLiquidation(address _account, address _collateralToken, address _indexToken, bool _isLong, bool _raise) external view returns (uint256, uint256);
    function getEntryFundingRate(address _collateralToken, address _indexToken, bool _isLong) external view returns (uint256);
    function getPositionFee(address _account, address _collateralToken, address _indexToken, bool _isLong, uint256 _sizeDelta) external view returns (uint256);
    function getFundingFee(address _account, address _collateralToken, address _indexToken, bool _isLong, uint256 _size, uint256 _entryFundingRate) external view returns (uint256);
    function getBuyUsdgFeeBasisPoints(address _token, uint256 _usdgAmount) external view returns (uint256);
    function getSellUsdgFeeBasisPoints(address _token, uint256 _usdgAmount) external view returns (uint256);
    function getSwapFeeBasisPoints(address _tokenIn, address _tokenOut, uint256 _usdgAmount) external view returns (uint256);
    function getFeeBasisPoints(address _token, uint256 _usdgDelta, uint256 _feeBasisPoints, uint256 _taxBasisPoints, bool _increment) external view returns (uint256);
}
pragma solidity 0.6.12;

interface IVault {
    function isInitialized() external view returns (bool);
    function isSwapEnabled() external view returns (bool);
    function isLeverageEnabled() external view returns (bool);

    function setVaultUtils(IVaultUtils _vaultUtils) external;
    function setError(uint256 _errorCode, string calldata _error) external;

    function router() external view returns (address);
    function usdg() external view returns (address);
    function gov() external view returns (address);

    function whitelistedTokenCount() external view returns (uint256);
    function maxLeverage() external view returns (uint256);

    function minProfitTime() external view returns (uint256);
    function hasDynamicFees() external view returns (bool);
    function fundingInterval() external view returns (uint256);
    function totalTokenWeights() external view returns (uint256);
    function getTargetUsdgAmount(address _token) external view returns (uint256);

    function inManagerMode() external view returns (bool);
    function inPrivateLiquidationMode() external view returns (bool);

    function maxGasPrice() external view returns (uint256);

    function approvedRouters(address _account, address _router) external view returns (bool);
    function isLiquidator(address _account) external view returns (bool);
    function isManager(address _account) external view returns (bool);

    function minProfitBasisPoints(address _token) external view returns (uint256);
    function tokenBalances(address _token) external view returns (uint256);
    function lastFundingTimes(address _token) external view returns (uint256);

    function setMaxLeverage(uint256 _maxLeverage) external;
    function setInManagerMode(bool _inManagerMode) external;
    function setManager(address _manager, bool _isManager) external;
    function setIsSwapEnabled(bool _isSwapEnabled) external;
    function setIsLeverageEnabled(bool _isLeverageEnabled) external;
    function setMaxGasPrice(uint256 _maxGasPrice) external;
    function setUsdgAmount(address _token, uint256 _amount) external;
    function setBufferAmount(address _token, uint256 _amount) external;
    function setMaxGlobalShortSize(address _token, uint256 _amount) external;
    function setInPrivateLiquidationMode(bool _inPrivateLiquidationMode) external;
    function setLiquidator(address _liquidator, bool _isActive) external;

    function setFundingRate(uint256 _fundingInterval, uint256 _fundingRateFactor, uint256 _stableFundingRateFactor) external;

    function setFees(
        uint256 _taxBasisPoints,
        uint256 _stableTaxBasisPoints,
        uint256 _mintBurnFeeBasisPoints,
        uint256 _swapFeeBasisPoints,
        uint256 _stableSwapFeeBasisPoints,
        uint256 _marginFeeBasisPoints,
        uint256 _liquidationFeeUsd,
        uint256 _minProfitTime,
        bool _hasDynamicFees
    ) external;

    function setTokenConfig(
        address _token,
        uint256 _tokenDecimals,
        uint256 _redemptionBps,
        uint256 _minProfitBps,
        uint256 _maxUsdgAmount,
        bool _isStable,
        bool _isShortable
    ) external;

    function setPriceFeed(address _priceFeed) external;
    function withdrawFees(address _token, address _receiver) external returns (uint256);

    function directPoolDeposit(address _token) external;
    function buyUSDG(address _token, address _receiver) external returns (uint256);
    function sellUSDG(address _token, address _receiver) external returns (uint256);
    function swap(address _tokenIn, address _tokenOut, address _receiver) external returns (uint256);
    function increasePosition(address _account, address _collateralToken, address _indexToken, uint256 _sizeDelta, bool _isLong) external;
    function decreasePosition(address _account, address _collateralToken, address _indexToken, uint256 _collateralDelta, uint256 _sizeDelta, bool _isLong, address _receiver) external returns (uint256);
    function validateLiquidation(address _account, address _collateralToken, address _indexToken, bool _isLong, bool _raise) external view returns (uint256, uint256);
    function liquidatePosition(address _account, address _collateralToken, address _indexToken, bool _isLong, address _feeReceiver) external;
    function tokenToUsdMin(address _token, uint256 _tokenAmount) external view returns (uint256);

    function priceFeed() external view returns (address);
    function fundingRateFactor() external view returns (uint256);
    function stableFundingRateFactor() external view returns (uint256);
    function cumulativeFundingRates(address _token) external view returns (uint256);
    function getNextFundingRate(address _token) external view returns (uint256);
    function getFeeBasisPoints(address _token, uint256 _usdgDelta, uint256 _feeBasisPoints, uint256 _taxBasisPoints, bool _increment) external view returns (uint256);

    function liquidationFeeUsd() external view returns (uint256);
    function taxBasisPoints() external view returns (uint256);
    function stableTaxBasisPoints() external view returns (uint256);
    function mintBurnFeeBasisPoints() external view returns (uint256);
    function swapFeeBasisPoints() external view returns (uint256);
    function stableSwapFeeBasisPoints() external view returns (uint256);
    function marginFeeBasisPoints() external view returns (uint256);

    function allWhitelistedTokensLength() external view returns (uint256);
    function allWhitelistedTokens(uint256) external view returns (address);
    function whitelistedTokens(address _token) external view returns (bool);
    function stableTokens(address _token) external view returns (bool);
    function shortableTokens(address _token) external view returns (bool);
    function feeReserves(address _token) external view returns (uint256);
    function globalShortSizes(address _token) external view returns (uint256);
    function globalShortAveragePrices(address _token) external view returns (uint256);
    function maxGlobalShortSizes(address _token) external view returns (uint256);
    function tokenDecimals(address _token) external view returns (uint256);
    function tokenWeights(address _token) external view returns (uint256);
    function guaranteedUsd(address _token) external view returns (uint256);
    function poolAmounts(address _token) external view returns (uint256);
    function bufferAmounts(address _token) external view returns (uint256);
    function reservedAmounts(address _token) external view returns (uint256);
    function usdgAmounts(address _token) external view returns (uint256);
    function maxUsdgAmounts(address _token) external view returns (uint256);
    function getRedemptionAmount(address _token, uint256 _usdgAmount) external view returns (uint256);
    function getMaxPrice(address _token) external view returns (uint256);
    function getMinPrice(address _token) external view returns (uint256);

    function getDelta(address _indexToken, uint256 _size, uint256 _averagePrice, bool _isLong, uint256 _lastIncreasedTime) external view returns (bool, uint256);
    function getPosition(address _account, address _collateralToken, address _indexToken, bool _isLong) external view returns (uint256, uint256, uint256, uint256, uint256, uint256, bool, uint256);
}
pragma solidity 0.6.12;

contract VaultUtils is IVaultUtils, Governable {
    using SafeMath for uint256;

    struct Position {
        uint256 size;
        uint256 collateral;
        uint256 averagePrice;
        uint256 entryFundingRate;
        uint256 reserveAmount;
        int256 realisedPnl;
        uint256 lastIncreasedTime;
    }

    IVault public vault;

    uint256 public constant BASIS_POINTS_DIVISOR = 10000;
    uint256 public constant FUNDING_RATE_PRECISION = 1000000;

    constructor(IVault _vault) public {
        vault = _vault;
    }

    function updateCumulativeFundingRate(address /* _collateralToken */, address /* _indexToken */) public override returns (bool) {
        return true;
    }

    function validateIncreasePosition(address /* _account */, address /* _collateralToken */, address /* _indexToken */, uint256 /* _sizeDelta */, bool /* _isLong */) external override view {
        // no additional validations
    }

    function validateDecreasePosition(address /* _account */, address /* _collateralToken */, address /* _indexToken */ , uint256 /* _collateralDelta */, uint256 /* _sizeDelta */, bool /* _isLong */, address /* _receiver */) external override view {
        // no additional validations
    }

    function getPosition(address _account, address _collateralToken, address _indexToken, bool _isLong) internal view returns (Position memory) {
        IVault _vault = vault;
        Position memory position;
        {
            (uint256 size, uint256 collateral, uint256 averagePrice, uint256 entryFundingRate, /* reserveAmount */, /* realisedPnl */, /* hasProfit */, uint256 lastIncreasedTime) = _vault.getPosition(_account, _collateralToken, _indexToken, _isLong);
            position.size = size;
            position.collateral = collateral;
            position.averagePrice = averagePrice;
            position.entryFundingRate = entryFundingRate;
            position.lastIncreasedTime = lastIncreasedTime;
        }
        return position;
    }

    function validateLiquidation(address _account, address _collateralToken, address _indexToken, bool _isLong, bool _raise) public view override returns (uint256, uint256) {
        Position memory position = getPosition(_account, _collateralToken, _indexToken, _isLong);
        IVault _vault = vault;

        (bool hasProfit, uint256 delta) = _vault.getDelta(_indexToken, position.size, position.averagePrice, _isLong, position.lastIncreasedTime);
        uint256 marginFees = getFundingFee(_account, _collateralToken, _indexToken, _isLong, position.size, position.entryFundingRate);
        marginFees = marginFees.add(getPositionFee(_account, _collateralToken, _indexToken, _isLong, position.size));

        if (!hasProfit && position.collateral < delta) {
            if (_raise) { revert("Vault: losses exceed collateral"); }
            return (1, marginFees);
        }

        uint256 remainingCollateral = position.collateral;
        if (!hasProfit) {
            remainingCollateral = position.collateral.sub(delta);
        }

        if (remainingCollateral < marginFees) {
            if (_raise) { revert("Vault: fees exceed collateral"); }
            // cap the fees to the remainingCollateral
            return (1, remainingCollateral);
        }

        if (remainingCollateral < marginFees.add(_vault.liquidationFeeUsd())) {
            if (_raise) { revert("Vault: liquidation fees exceed collateral"); }
            return (1, marginFees);
        }

        if (remainingCollateral.mul(_vault.maxLeverage()) < position.size.mul(BASIS_POINTS_DIVISOR)) {
            if (_raise) { revert("Vault: maxLeverage exceeded"); }
            return (2, marginFees);
        }

        return (0, marginFees);
    }

    function getEntryFundingRate(address _collateralToken, address /* _indexToken */, bool /* _isLong */) public override view returns (uint256) {
        return vault.cumulativeFundingRates(_collateralToken);
    }

    function getPositionFee(address /* _account */, address /* _collateralToken */, address /* _indexToken */, bool /* _isLong */, uint256 _sizeDelta) public override view returns (uint256) {
        if (_sizeDelta == 0) { return 0; }
        uint256 afterFeeUsd = _sizeDelta.mul(BASIS_POINTS_DIVISOR.sub(vault.marginFeeBasisPoints())).div(BASIS_POINTS_DIVISOR);
        return _sizeDelta.sub(afterFeeUsd);
    }

    function getFundingFee(address /* _account */, address _collateralToken, address /* _indexToken */, bool /* _isLong */, uint256 _size, uint256 _entryFundingRate) public override view returns (uint256) {
        if (_size == 0) { return 0; }

        uint256 fundingRate = vault.cumulativeFundingRates(_collateralToken).sub(_entryFundingRate);
        if (fundingRate == 0) { return 0; }

        return _size.mul(fundingRate).div(FUNDING_RATE_PRECISION);
    }

    function getBuyUsdgFeeBasisPoints(address _token, uint256 _usdgAmount) public override view returns (uint256) {
        return getFeeBasisPoints(_token, _usdgAmount, vault.mintBurnFeeBasisPoints(), vault.taxBasisPoints(), true);
    }

    function getSellUsdgFeeBasisPoints(address _token, uint256 _usdgAmount) public override view returns (uint256) {
        return getFeeBasisPoints(_token, _usdgAmount, vault.mintBurnFeeBasisPoints(), vault.taxBasisPoints(), false);
    }

    function getSwapFeeBasisPoints(address _tokenIn, address _tokenOut, uint256 _usdgAmount) public override view returns (uint256) {
        bool isStableSwap = vault.stableTokens(_tokenIn) && vault.stableTokens(_tokenOut);
        uint256 baseBps = isStableSwap ? vault.stableSwapFeeBasisPoints() : vault.swapFeeBasisPoints();
        uint256 taxBps = isStableSwap ? vault.stableTaxBasisPoints() : vault.taxBasisPoints();
        uint256 feesBasisPoints0 = getFeeBasisPoints(_tokenIn, _usdgAmount, baseBps, taxBps, true);
        uint256 feesBasisPoints1 = getFeeBasisPoints(_tokenOut, _usdgAmount, baseBps, taxBps, false);
        // use the higher of the two fee basis points
        return feesBasisPoints0 > feesBasisPoints1 ? feesBasisPoints0 : feesBasisPoints1;
    }

    // cases to consider
    // 1. initialAmount is far from targetAmount, action increases balance slightly => high rebate
    // 2. initialAmount is far from targetAmount, action increases balance largely => high rebate
    // 3. initialAmount is close to targetAmount, action increases balance slightly => low rebate
    // 4. initialAmount is far from targetAmount, action reduces balance slightly => high tax
    // 5. initialAmount is far from targetAmount, action reduces balance largely => high tax
    // 6. initialAmount is close to targetAmount, action reduces balance largely => low tax
    // 7. initialAmount is above targetAmount, nextAmount is below targetAmount and vice versa
    // 8. a large swap should have similar fees as the same trade split into multiple smaller swaps
    function getFeeBasisPoints(address _token, uint256 _usdgDelta, uint256 _feeBasisPoints, uint256 _taxBasisPoints, bool _increment) public override view returns (uint256) {
        if (!vault.hasDynamicFees()) { return _feeBasisPoints; }

        uint256 initialAmount = vault.usdgAmounts(_token);
        uint256 nextAmount = initialAmount.add(_usdgDelta);
        if (!_increment) {
            nextAmount = _usdgDelta > initialAmount ? 0 : initialAmount.sub(_usdgDelta);
        }

        uint256 targetAmount = vault.getTargetUsdgAmount(_token);
        if (targetAmount == 0) { return _feeBasisPoints; }

        uint256 initialDiff = initialAmount > targetAmount ? initialAmount.sub(targetAmount) : targetAmount.sub(initialAmount);
        uint256 nextDiff = nextAmount > targetAmount ? nextAmount.sub(targetAmount) : targetAmount.sub(nextAmount);

        // action improves relative asset balance
        if (nextDiff < initialDiff) {
            uint256 rebateBps = _taxBasisPoints.mul(initialDiff).div(targetAmount);
            return rebateBps > _feeBasisPoints ? 0 : _feeBasisPoints.sub(rebateBps);
        }

        uint256 averageDiff = initialDiff.add(nextDiff).div(2);
        if (averageDiff > targetAmount) {
            averageDiff = targetAmount;
        }
        uint256 taxBps = _taxBasisPoints.mul(averageDiff).div(targetAmount);
        return _feeBasisPoints.add(taxBps);
    }
}