// SPDX-License-Identifier: MIT

pragma solidity >=0.6.2 <0.8.0;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is 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.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        // solhint-disable-next-line no-inline-assembly
        assembly { size := extcodesize(account) }
        return size > 0;
    }

    /**
     * @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].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        // solhint-disable-next-line avoid-low-level-calls, avoid-call-value
        (bool success, ) = recipient.call{ value: amount }("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain`call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
      return functionCall(target, data, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data, string memory errorMessage) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(address target, bytes memory data, uint256 value, string memory errorMessage) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        require(isContract(target), "Address: call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.call{ value: value }(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data, string memory errorMessage) internal view returns (bytes memory) {
        require(isContract(target), "Address: static call to non-contract");

        // solhint-disable-next-line avoid-low-level-calls
        (bool success, bytes memory returndata) = target.staticcall(data);
        return _verifyCallResult(success, returndata, errorMessage);
    }

    function _verifyCallResult(bool success, bytes memory returndata, string memory errorMessage) private pure returns(bytes memory) {
        if (success) {
            return returndata;
        } else {
            // Look for revert reason and bubble it up if present
            if (returndata.length > 0) {
                // The easiest way to bubble the revert reason is using memory via assembly

                // solhint-disable-next-line no-inline-assembly
                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// SPDX-License-Identifier: LGPL-3.0-or-later
pragma solidity >=0.6.8;

library AllowListVerifierHelper {
    /// @dev Value returned by a call to `isAllowed` if the check
    /// was successful. The value is defined as:
    /// bytes4(keccak256("isAllowed(address,uint256,bytes)"))
    bytes4 internal constant MAGICVALUE = 0x19a05a7e;
}

///
/// @dev Standardized interface for an allowList manager for easyAuction
/// The interface was inspired by EIP-1271
interface AllowListVerifier {
    /// @dev Should return whether the a specific user has access to an auction
    /// by returning the magic value from AllowListVerifierHelper
    function isAllowed(
        address user,
        uint256 auctionId,
        bytes calldata callData
    ) external view returns (bytes4);
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/*
 * @dev Provides information about the current execution context, including the
 * sender of the transaction and its data. While these are generally available
 * via msg.sender and msg.data, they should not be accessed in such a direct
 * manner, since when dealing with GSN meta-transactions the account sending and
 * paying for execution may not be the actual sender (as far as an application
 * is concerned).
 *
 * This contract is only required for intermediate, library-like contracts.
 */
abstract contract Context {
    function _msgSender() internal view virtual returns (address payable) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes memory) {
        this; // silence state mutability warning without generating bytecode - see https://github.com/ethereum/solidity/issues/2691
        return msg.data;
    }
}

pragma solidity >=0.6.8;
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC20/SafeERC20.sol";
import "./libraries/IterableOrderedOrderSet.sol";
import "@openzeppelin/contracts/math/Math.sol";
import "@openzeppelin/contracts/math/SafeMath.sol";
import "./libraries/IdToAddressBiMap.sol";
import "./libraries/SafeCast.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "./interfaces/AllowListVerifier.sol";

contract EasyAuction is Ownable {
    using SafeERC20 for IERC20;
    using SafeMath for uint64;
    using SafeMath for uint96;
    using SafeMath for uint256;
    using SafeCast for uint256;
    using IterableOrderedOrderSet for IterableOrderedOrderSet.Data;
    using IterableOrderedOrderSet for bytes32;
    using IdToAddressBiMap for IdToAddressBiMap.Data;

    modifier atStageOrderPlacement(uint256 auctionId) {
        require(
            block.timestamp < auctionData[auctionId].auctionEndDate,
            "no longer in order placement phase"
        );
        _;
    }

    modifier atStageOrderPlacementAndCancelation(uint256 auctionId) {
        require(
            block.timestamp < auctionData[auctionId].orderCancellationEndDate,
            "no longer in order placement and cancelation phase"
        );
        _;
    }

    modifier atStageSolutionSubmission(uint256 auctionId) {
        {
            uint256 auctionEndDate = auctionData[auctionId].auctionEndDate;
            require(
                auctionEndDate != 0 &&
                    block.timestamp >= auctionEndDate &&
                    auctionData[auctionId].clearingPriceOrder == bytes32(0),
                "Auction not in solution submission phase"
            );
        }
        _;
    }

    modifier atStageFinished(uint256 auctionId) {
        require(
            auctionData[auctionId].clearingPriceOrder != bytes32(0),
            "Auction not yet finished"
        );
        _;
    }

    event NewSellOrder(
        uint256 indexed auctionId,
        uint64 indexed userId,
        uint96 buyAmount,
        uint96 sellAmount
    );
    event CancellationSellOrder(
        uint256 indexed auctionId,
        uint64 indexed userId,
        uint96 buyAmount,
        uint96 sellAmount
    );
    event ClaimedFromOrder(
        uint256 indexed auctionId,
        uint64 indexed userId,
        uint96 buyAmount,
        uint96 sellAmount
    );
    event NewUser(uint64 indexed userId, address indexed userAddress);
    event NewAuction(
        uint256 indexed auctionId,
        IERC20 indexed _auctioningToken,
        IERC20 indexed _biddingToken,
        uint256 orderCancellationEndDate,
        uint256 auctionEndDate,
        uint64 userId,
        uint96 _auctionedSellAmount,
        uint96 _minBuyAmount,
        uint256 minimumBiddingAmountPerOrder,
        uint256 minFundingThreshold,
        address allowListContract,
        bytes allowListData
    );
    event AuctionCleared(
        uint256 indexed auctionId,
        uint96 soldAuctioningTokens,
        uint96 soldBiddingTokens,
        bytes32 clearingPriceOrder
    );
    event UserRegistration(address indexed user, uint64 userId);

    struct AuctionData {
        IERC20 auctioningToken;
        IERC20 biddingToken;
        uint256 orderCancellationEndDate;
        uint256 auctionEndDate;
        bytes32 initialAuctionOrder;
        uint256 minimumBiddingAmountPerOrder;
        uint256 interimSumBidAmount;
        bytes32 interimOrder;
        bytes32 clearingPriceOrder;
        uint96 volumeClearingPriceOrder;
        bool minFundingThresholdNotReached;
        bool isAtomicClosureAllowed;
        uint256 feeNumerator;
        uint256 minFundingThreshold;
    }
    mapping(uint256 => IterableOrderedOrderSet.Data) internal sellOrders;
    mapping(uint256 => AuctionData) public auctionData;
    mapping(uint256 => address) public auctionAccessManager;
    mapping(uint256 => bytes) public auctionAccessData;

    IdToAddressBiMap.Data private registeredUsers;
    uint64 public numUsers;
    uint256 public auctionCounter;

    constructor() public Ownable() {}

    uint256 public feeNumerator = 0;
    uint256 public constant FEE_DENOMINATOR = 1000;
    uint64 public feeReceiverUserId = 1;

    function setFeeParameters(
        uint256 newFeeNumerator,
        address newfeeReceiverAddress
    ) public onlyOwner() {
        require(
            newFeeNumerator <= 15,
            "Fee is not allowed to be set higher than 1.5%"
        );
        // caution: for currently running auctions, the feeReceiverUserId is changing as well.
        feeReceiverUserId = getUserId(newfeeReceiverAddress);
        feeNumerator = newFeeNumerator;
    }

    // @dev: function to intiate a new auction
    // Warning: In case the auction is expected to raise more than
    // 2^96 units of the biddingToken, don't start the auction, as
    // it will not be settlable. This corresponds to about 79
    // billion DAI.
    //
    // Prices between biddingToken and auctioningToken are expressed by a
    // fraction whose components are stored as uint96.
    function initiateAuction(
        IERC20 _auctioningToken,
        IERC20 _biddingToken,
        uint256 orderCancellationEndDate,
        uint256 auctionEndDate,
        uint96 _auctionedSellAmount,
        uint96 _minBuyAmount,
        uint256 minimumBiddingAmountPerOrder,
        uint256 minFundingThreshold,
        bool isAtomicClosureAllowed,
        address accessManagerContract,
        bytes memory accessManagerContractData
    ) public returns (uint256) {
        // withdraws sellAmount + fees
        _auctioningToken.safeTransferFrom(
            msg.sender,
            address(this),
            _auctionedSellAmount.mul(FEE_DENOMINATOR.add(feeNumerator)).div(
                FEE_DENOMINATOR
            ) //[0]
        );
        require(_auctionedSellAmount > 0, "cannot auction zero tokens");
        require(_minBuyAmount > 0, "tokens cannot be auctioned for free");
        require(
            minimumBiddingAmountPerOrder > 0,
            "minimumBiddingAmountPerOrder is not allowed to be zero"
        );
        require(
            orderCancellationEndDate <= auctionEndDate,
            "time periods are not configured correctly"
        );
        require(
            auctionEndDate > block.timestamp,
            "auction end date must be in the future"
        );
        auctionCounter = auctionCounter.add(1);
        sellOrders[auctionCounter].initializeEmptyList();
        uint64 userId = getUserId(msg.sender);
        auctionData[auctionCounter] = AuctionData(
            _auctioningToken,
            _biddingToken,
            orderCancellationEndDate,
            auctionEndDate,
            IterableOrderedOrderSet.encodeOrder(
                userId,
                _minBuyAmount,
                _auctionedSellAmount
            ),
            minimumBiddingAmountPerOrder,
            0,
            IterableOrderedOrderSet.QUEUE_START,
            bytes32(0),
            0,
            false,
            isAtomicClosureAllowed,
            feeNumerator,
            minFundingThreshold
        );
        auctionAccessManager[auctionCounter] = accessManagerContract;
        auctionAccessData[auctionCounter] = accessManagerContractData;
        emit NewAuction(
            auctionCounter,
            _auctioningToken,
            _biddingToken,
            orderCancellationEndDate,
            auctionEndDate,
            userId,
            _auctionedSellAmount,
            _minBuyAmount,
            minimumBiddingAmountPerOrder,
            minFundingThreshold,
            accessManagerContract,
            accessManagerContractData
        );
        return auctionCounter;
    }

    function placeSellOrders(
        uint256 auctionId,
        uint96[] memory _minBuyAmounts,
        uint96[] memory _sellAmounts,
        bytes32[] memory _prevSellOrders,
        bytes calldata allowListCallData
    ) external atStageOrderPlacement(auctionId) returns (uint64 userId) {
        return
            _placeSellOrders(
                auctionId,
                _minBuyAmounts,
                _sellAmounts,
                _prevSellOrders,
                allowListCallData,
                msg.sender
            );
    }

    function placeSellOrdersOnBehalf(
        uint256 auctionId,
        uint96[] memory _minBuyAmounts,
        uint96[] memory _sellAmounts,
        bytes32[] memory _prevSellOrders,
        bytes calldata allowListCallData,
        address orderSubmitter
    ) external atStageOrderPlacement(auctionId) returns (uint64 userId) {
        return
            _placeSellOrders(
                auctionId,
                _minBuyAmounts,
                _sellAmounts,
                _prevSellOrders,
                allowListCallData,
                orderSubmitter
            );
    }

    function _placeSellOrders(
        uint256 auctionId,
        uint96[] memory _minBuyAmounts,
        uint96[] memory _sellAmounts,
        bytes32[] memory _prevSellOrders,
        bytes calldata allowListCallData,
        address orderSubmitter
    ) internal returns (uint64 userId) {
        {
            address allowListManger = auctionAccessManager[auctionId];
            if (allowListManger != address(0)) {
                require(
                    AllowListVerifier(allowListManger).isAllowed(
                        orderSubmitter,
                        auctionId,
                        allowListCallData
                    ) == AllowListVerifierHelper.MAGICVALUE,
                    "user not allowed to place order"
                );
            }
        }
        {
            (
                ,
                uint96 buyAmountOfInitialAuctionOrder,
                uint96 sellAmountOfInitialAuctionOrder
            ) = auctionData[auctionId].initialAuctionOrder.decodeOrder();
            for (uint256 i = 0; i < _minBuyAmounts.length; i++) {
                require(
                    _minBuyAmounts[i].mul(buyAmountOfInitialAuctionOrder) <
                        sellAmountOfInitialAuctionOrder.mul(_sellAmounts[i]),
                    "limit price not better than mimimal offer"
                );
            }
        }
        uint256 sumOfSellAmounts = 0;
        userId = getUserId(orderSubmitter);
        uint256 minimumBiddingAmountPerOrder =
            auctionData[auctionId].minimumBiddingAmountPerOrder;
        for (uint256 i = 0; i < _minBuyAmounts.length; i++) {
            require(
                _minBuyAmounts[i] > 0,
                "_minBuyAmounts must be greater than 0"
            );
            // orders should have a minimum bid size in order to limit the gas
            // required to compute the final price of the auction.
            require(
                _sellAmounts[i] > minimumBiddingAmountPerOrder,
                "order too small"
            );
            if (
                sellOrders[auctionId].insert(
                    IterableOrderedOrderSet.encodeOrder(
                        userId,
                        _minBuyAmounts[i],
                        _sellAmounts[i]
                    ),
                    _prevSellOrders[i]
                )
            ) {
                sumOfSellAmounts = sumOfSellAmounts.add(_sellAmounts[i]);
                emit NewSellOrder(
                    auctionId,
                    userId,
                    _minBuyAmounts[i],
                    _sellAmounts[i]
                );
            }
        }
        auctionData[auctionId].biddingToken.safeTransferFrom(
            msg.sender,
            address(this),
            sumOfSellAmounts
        ); //[1]
    }

    function cancelSellOrders(uint256 auctionId, bytes32[] memory _sellOrders)
        public
        atStageOrderPlacementAndCancelation(auctionId)
    {
        uint64 userId = getUserId(msg.sender);
        uint256 claimableAmount = 0;
        for (uint256 i = 0; i < _sellOrders.length; i++) {
            // Note: we keep the back pointer of the deleted element so that
            // it can be used as a reference point to insert a new node.
            bool success =
                sellOrders[auctionId].removeKeepHistory(_sellOrders[i]);
            if (success) {
                (
                    uint64 userIdOfIter,
                    uint96 buyAmountOfIter,
                    uint96 sellAmountOfIter
                ) = _sellOrders[i].decodeOrder();
                require(
                    userIdOfIter == userId,
                    "Only the user can cancel his orders"
                );
                claimableAmount = claimableAmount.add(sellAmountOfIter);
                emit CancellationSellOrder(
                    auctionId,
                    userId,
                    buyAmountOfIter,
                    sellAmountOfIter
                );
            }
        }
        auctionData[auctionId].biddingToken.safeTransfer(
            msg.sender,
            claimableAmount
        ); //[2]
    }

    function precalculateSellAmountSum(
        uint256 auctionId,
        uint256 iterationSteps
    ) public atStageSolutionSubmission(auctionId) {
        (, , uint96 auctioneerSellAmount) =
            auctionData[auctionId].initialAuctionOrder.decodeOrder();
        uint256 sumBidAmount = auctionData[auctionId].interimSumBidAmount;
        bytes32 iterOrder = auctionData[auctionId].interimOrder;

        for (uint256 i = 0; i < iterationSteps; i++) {
            iterOrder = sellOrders[auctionId].next(iterOrder);
            (, , uint96 sellAmountOfIter) = iterOrder.decodeOrder();
            sumBidAmount = sumBidAmount.add(sellAmountOfIter);
        }

        require(
            iterOrder != IterableOrderedOrderSet.QUEUE_END,
            "reached end of order list"
        );

        // it is checked that not too many iteration steps were taken:
        // require that the sum of SellAmounts times the price of the last order
        // is not more than initially sold amount
        (, uint96 buyAmountOfIter, uint96 sellAmountOfIter) =
            iterOrder.decodeOrder();
        require(
            sumBidAmount.mul(buyAmountOfIter) <
                auctioneerSellAmount.mul(sellAmountOfIter),
            "too many orders summed up"
        );

        auctionData[auctionId].interimSumBidAmount = sumBidAmount;
        auctionData[auctionId].interimOrder = iterOrder;
    }

    function settleAuctionAtomically(
        uint256 auctionId,
        uint96[] memory _minBuyAmount,
        uint96[] memory _sellAmount,
        bytes32[] memory _prevSellOrder,
        bytes calldata allowListCallData
    ) public atStageSolutionSubmission(auctionId) {
        require(
            auctionData[auctionId].isAtomicClosureAllowed,
            "not allowed to settle auction atomically"
        );
        require(
            _minBuyAmount.length == 1 && _sellAmount.length == 1,
            "Only one order can be placed atomically"
        );
        uint64 userId = getUserId(msg.sender);
        require(
            auctionData[auctionId].interimOrder.smallerThan(
                IterableOrderedOrderSet.encodeOrder(
                    userId,
                    _minBuyAmount[0],
                    _sellAmount[0]
                )
            ),
            "precalculateSellAmountSum is already too advanced"
        );
        _placeSellOrders(
            auctionId,
            _minBuyAmount,
            _sellAmount,
            _prevSellOrder,
            allowListCallData,
            msg.sender
        );
        settleAuction(auctionId);
    }

    // @dev function settling the auction and calculating the price
    function settleAuction(uint256 auctionId)
        public
        atStageSolutionSubmission(auctionId)
        returns (bytes32 clearingOrder)
    {
        (
            uint64 auctioneerId,
            uint96 minAuctionedBuyAmount,
            uint96 fullAuctionedAmount
        ) = auctionData[auctionId].initialAuctionOrder.decodeOrder();

        uint256 currentBidSum = auctionData[auctionId].interimSumBidAmount;
        bytes32 currentOrder = auctionData[auctionId].interimOrder;
        uint256 buyAmountOfIter;
        uint256 sellAmountOfIter;
        uint96 fillVolumeOfAuctioneerOrder = fullAuctionedAmount;
        // Sum order up, until fullAuctionedAmount is fully bought or queue end is reached
        do {
            bytes32 nextOrder = sellOrders[auctionId].next(currentOrder);
            if (nextOrder == IterableOrderedOrderSet.QUEUE_END) {
                break;
            }
            currentOrder = nextOrder;
            (, buyAmountOfIter, sellAmountOfIter) = currentOrder.decodeOrder();
            currentBidSum = currentBidSum.add(sellAmountOfIter);
        } while (
            currentBidSum.mul(buyAmountOfIter) <
                fullAuctionedAmount.mul(sellAmountOfIter)
        );

        if (
            currentBidSum > 0 &&
            currentBidSum.mul(buyAmountOfIter) >=
            fullAuctionedAmount.mul(sellAmountOfIter)
        ) {
            // All considered/summed orders are sufficient to close the auction fully
            // at price between current and previous orders.
            uint256 uncoveredBids =
                currentBidSum.sub(
                    fullAuctionedAmount.mul(sellAmountOfIter).div(
                        buyAmountOfIter
                    )
                );

            if (sellAmountOfIter >= uncoveredBids) {
                //[13]
                // Auction fully filled via partial match of currentOrder
                uint256 sellAmountClearingOrder =
                    sellAmountOfIter.sub(uncoveredBids);
                auctionData[auctionId]
                    .volumeClearingPriceOrder = sellAmountClearingOrder
                    .toUint96();
                currentBidSum = currentBidSum.sub(uncoveredBids);
                clearingOrder = currentOrder;
            } else {
                //[14]
                // Auction fully filled via price strictly between currentOrder and the order
                // immediately before. For a proof, see the security-considerations.md
                currentBidSum = currentBidSum.sub(sellAmountOfIter);
                clearingOrder = IterableOrderedOrderSet.encodeOrder(
                    0,
                    fullAuctionedAmount,
                    currentBidSum.toUint96()
                );
            }
        } else {
            // All considered/summed orders are not sufficient to close the auction fully at price of last order //[18]
            // Either a higher price must be used or auction is only partially filled

            if (currentBidSum > minAuctionedBuyAmount) {
                //[15]
                // Price higher than last order would fill the auction
                clearingOrder = IterableOrderedOrderSet.encodeOrder(
                    0,
                    fullAuctionedAmount,
                    currentBidSum.toUint96()
                );
            } else {
                //[16]
                // Even at the initial auction price, the auction is partially filled
                clearingOrder = IterableOrderedOrderSet.encodeOrder(
                    0,
                    fullAuctionedAmount,
                    minAuctionedBuyAmount
                );
                fillVolumeOfAuctioneerOrder = currentBidSum
                    .mul(fullAuctionedAmount)
                    .div(minAuctionedBuyAmount)
                    .toUint96();
            }
        }
        auctionData[auctionId].clearingPriceOrder = clearingOrder;

        if (auctionData[auctionId].minFundingThreshold > currentBidSum) {
            auctionData[auctionId].minFundingThresholdNotReached = true;
        }
        processFeesAndAuctioneerFunds(
            auctionId,
            fillVolumeOfAuctioneerOrder,
            auctioneerId,
            fullAuctionedAmount
        );
        emit AuctionCleared(
            auctionId,
            fillVolumeOfAuctioneerOrder,
            uint96(currentBidSum),
            clearingOrder
        );
        // Gas refunds
        auctionAccessManager[auctionId] = address(0);
        delete auctionAccessData[auctionId];
        auctionData[auctionId].initialAuctionOrder = bytes32(0);
        auctionData[auctionId].interimOrder = bytes32(0);
        auctionData[auctionId].interimSumBidAmount = uint256(0);
        auctionData[auctionId].minimumBiddingAmountPerOrder = uint256(0);
    }

    function claimFromParticipantOrder(
        uint256 auctionId,
        bytes32[] memory orders
    )
        public
        atStageFinished(auctionId)
        returns (
            uint256 sumAuctioningTokenAmount,
            uint256 sumBiddingTokenAmount
        )
    {
        for (uint256 i = 0; i < orders.length; i++) {
            // Note: we don't need to keep any information about the node since
            // no new elements need to be inserted.
            require(
                sellOrders[auctionId].remove(orders[i]),
                "order is no longer claimable"
            );
        }
        AuctionData memory auction = auctionData[auctionId];
        (, uint96 priceNumerator, uint96 priceDenominator) =
            auction.clearingPriceOrder.decodeOrder();
        (uint64 userId, , ) = orders[0].decodeOrder();
        bool minFundingThresholdNotReached =
            auctionData[auctionId].minFundingThresholdNotReached;
        for (uint256 i = 0; i < orders.length; i++) {
            (uint64 userIdOrder, uint96 buyAmount, uint96 sellAmount) =
                orders[i].decodeOrder();
            require(
                userIdOrder == userId,
                "only allowed to claim for same user"
            );
            if (minFundingThresholdNotReached) {
                //[10]
                sumBiddingTokenAmount = sumBiddingTokenAmount.add(sellAmount);
            } else {
                //[23]
                if (orders[i] == auction.clearingPriceOrder) {
                    //[25]
                    sumAuctioningTokenAmount = sumAuctioningTokenAmount.add(
                        auction
                            .volumeClearingPriceOrder
                            .mul(priceNumerator)
                            .div(priceDenominator)
                    );
                    sumBiddingTokenAmount = sumBiddingTokenAmount.add(
                        sellAmount.sub(auction.volumeClearingPriceOrder)
                    );
                } else {
                    if (orders[i].smallerThan(auction.clearingPriceOrder)) {
                        //[17]
                        sumAuctioningTokenAmount = sumAuctioningTokenAmount.add(
                            sellAmount.mul(priceNumerator).div(priceDenominator)
                        );
                    } else {
                        //[24]
                        sumBiddingTokenAmount = sumBiddingTokenAmount.add(
                            sellAmount
                        );
                    }
                }
            }
            emit ClaimedFromOrder(auctionId, userId, buyAmount, sellAmount);
        }
        sendOutTokens(
            auctionId,
            sumAuctioningTokenAmount,
            sumBiddingTokenAmount,
            userId
        ); //[3]
    }

    function processFeesAndAuctioneerFunds(
        uint256 auctionId,
        uint256 fillVolumeOfAuctioneerOrder,
        uint64 auctioneerId,
        uint96 fullAuctionedAmount
    ) internal {
        uint256 feeAmount =
            fullAuctionedAmount.mul(auctionData[auctionId].feeNumerator).div(
                FEE_DENOMINATOR
            ); //[20]
        if (auctionData[auctionId].minFundingThresholdNotReached) {
            sendOutTokens(
                auctionId,
                fullAuctionedAmount.add(feeAmount),
                0,
                auctioneerId
            ); //[4]
        } else {
            //[11]
            (, uint96 priceNumerator, uint96 priceDenominator) =
                auctionData[auctionId].clearingPriceOrder.decodeOrder();
            uint256 unsettledAuctionTokens =
                fullAuctionedAmount.sub(fillVolumeOfAuctioneerOrder);
            uint256 auctioningTokenAmount =
                unsettledAuctionTokens.add(
                    feeAmount.mul(unsettledAuctionTokens).div(
                        fullAuctionedAmount
                    )
                );
            uint256 biddingTokenAmount =
                fillVolumeOfAuctioneerOrder.mul(priceDenominator).div(
                    priceNumerator
                );
            sendOutTokens(
                auctionId,
                auctioningTokenAmount,
                biddingTokenAmount,
                auctioneerId
            ); //[5]
            sendOutTokens(
                auctionId,
                feeAmount.mul(fillVolumeOfAuctioneerOrder).div(
                    fullAuctionedAmount
                ),
                0,
                feeReceiverUserId
            ); //[7]
        }
    }

    function sendOutTokens(
        uint256 auctionId,
        uint256 auctioningTokenAmount,
        uint256 biddingTokenAmount,
        uint64 userId
    ) internal {
        address userAddress = registeredUsers.getAddressAt(userId);
        if (auctioningTokenAmount > 0) {
            auctionData[auctionId].auctioningToken.safeTransfer(
                userAddress,
                auctioningTokenAmount
            );
        }
        if (biddingTokenAmount > 0) {
            auctionData[auctionId].biddingToken.safeTransfer(
                userAddress,
                biddingTokenAmount
            );
        }
    }

    function registerUser(address user) public returns (uint64 userId) {
        numUsers = numUsers.add(1).toUint64();
        require(
            registeredUsers.insert(numUsers, user),
            "User already registered"
        );
        userId = numUsers;
        emit UserRegistration(user, userId);
    }

    function getUserId(address user) public returns (uint64 userId) {
        if (registeredUsers.hasAddress(user)) {
            userId = registeredUsers.getId(user);
        } else {
            userId = registerUser(user);
            emit NewUser(userId, user);
        }
    }

    function getSecondsRemainingInBatch(uint256 auctionId)
        public
        view
        returns (uint256)
    {
        if (auctionData[auctionId].auctionEndDate < block.timestamp) {
            return 0;
        }
        return auctionData[auctionId].auctionEndDate.sub(block.timestamp);
    }

    function containsOrder(uint256 auctionId, bytes32 order)
        public
        view
        returns (bool)
    {
        return sellOrders[auctionId].contains(order);
    }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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 ^0.6.0;

///////////////////////////////////////////////////////////////////////////////////////////////////////////
// Contract does not have test coverage, as it was nearly copied from:
// https://github.com/gnosis/solidity-data-structures/blob/master/contracts/libraries/IdToAddressBiMap.sol
// The only change is uint16 -> uint64
///////////////////////////////////////////////////////////////////////////////////////////////////////////

library IdToAddressBiMap {
    struct Data {
        mapping(uint64 => address) idToAddress;
        mapping(address => uint64) addressToId;
    }

    function hasId(Data storage self, uint64 id) internal view returns (bool) {
        return self.idToAddress[id + 1] != address(0);
    }

    function hasAddress(Data storage self, address addr)
        internal
        view
        returns (bool)
    {
        return self.addressToId[addr] != 0;
    }

    function getAddressAt(Data storage self, uint64 id)
        internal
        view
        returns (address)
    {
        require(hasId(self, id), "Must have ID to get Address");
        return self.idToAddress[id + 1];
    }

    function getId(Data storage self, address addr)
        internal
        view
        returns (uint64)
    {
        require(hasAddress(self, addr), "Must have Address to get ID");
        return self.addressToId[addr] - 1;
    }

    function insert(
        Data storage self,
        uint64 id,
        address addr
    ) internal returns (bool) {
        require(addr != address(0), "Cannot insert zero address");
        require(id != uint64(-1), "Cannot insert max uint64");
        // Ensure bijectivity of the mappings
        if (
            self.addressToId[addr] != 0 ||
            self.idToAddress[id + 1] != address(0)
        ) {
            return false;
        }
        self.idToAddress[id + 1] = addr;
        self.addressToId[addr] = id + 1;
        return true;
    }
}

pragma solidity >=0.6.8;

import "@openzeppelin/contracts/math/SafeMath.sol";

library IterableOrderedOrderSet {
    using SafeMath for uint96;
    using IterableOrderedOrderSet for bytes32;

    // represents smallest possible value for an order under comparison of fn smallerThan()
    bytes32 internal constant QUEUE_START =
        0x0000000000000000000000000000000000000000000000000000000000000001;
    // represents highest possible value for an order under comparison of fn smallerThan()
    bytes32 internal constant QUEUE_END =
        0xffffffffffffffffffffffffffffffffffffffff000000000000000000000001;

    /// The struct is used to implement a modified version of a doubly linked
    /// list with sorted elements. The list starts from QUEUE_START to
    /// QUEUE_END, and each node keeps track of its predecessor and successor.
    /// Nodes can be added or removed.
    ///
    /// `next` and `prev` have a different role. The list is supposed to be
    /// traversed with `next`. If `next` is empty, the node is not part of the
    /// list. However, `prev` might be set for elements that are not in the
    /// list, which is why it should not be used for traversing. Having a `prev`
    /// set for elements not in the list is used to keep track of the history of
    /// the position in the list of a removed element.
    struct Data {
        mapping(bytes32 => bytes32) nextMap;
        mapping(bytes32 => bytes32) prevMap;
    }

    struct Order {
        uint64 owner;
        uint96 buyAmount;
        uint96 sellAmount;
    }

    function initializeEmptyList(Data storage self) internal {
        self.nextMap[QUEUE_START] = QUEUE_END;
        self.prevMap[QUEUE_END] = QUEUE_START;
    }

    function isEmpty(Data storage self) internal view returns (bool) {
        return self.nextMap[QUEUE_START] == QUEUE_END;
    }

    function insert(
        Data storage self,
        bytes32 elementToInsert,
        bytes32 elementBeforeNewOne
    ) internal returns (bool) {
        (, , uint96 denominator) = decodeOrder(elementToInsert);
        require(denominator != uint96(0), "Inserting zero is not supported");
        require(
            elementToInsert != QUEUE_START && elementToInsert != QUEUE_END,
            "Inserting element is not valid"
        );
        if (contains(self, elementToInsert)) {
            return false;
        }
        if (
            elementBeforeNewOne != QUEUE_START &&
            self.prevMap[elementBeforeNewOne] == bytes32(0)
        ) {
            return false;
        }
        if (!elementBeforeNewOne.smallerThan(elementToInsert)) {
            return false;
        }

        // `elementBeforeNewOne` might have been removed during the time it
        // took to the transaction calling this function to be mined, so
        // the new order cannot be appended directly to this. We follow the
        // history of previous links backwards until we find an element in
        // the list from which to start our search.
        // Note that following the link backwards returns elements that are
        // before `elementBeforeNewOne` in sorted order.
        while (self.nextMap[elementBeforeNewOne] == bytes32(0)) {
            elementBeforeNewOne = self.prevMap[elementBeforeNewOne];
        }

        // `elementBeforeNewOne` belongs now to the linked list. We search the
        // largest entry that is smaller than the element to insert.
        bytes32 previous;
        bytes32 current = elementBeforeNewOne;
        do {
            previous = current;
            current = self.nextMap[current];
        } while (current.smallerThan(elementToInsert));
        // Note: previous < elementToInsert < current
        self.nextMap[previous] = elementToInsert;
        self.prevMap[current] = elementToInsert;
        self.prevMap[elementToInsert] = previous;
        self.nextMap[elementToInsert] = current;

        return true;
    }

    /// The element is removed from the linked list, but the node retains
    /// information on which predecessor it had, so that a node in the chain
    /// can be reached by following the predecessor chain of deleted elements.
    function removeKeepHistory(Data storage self, bytes32 elementToRemove)
        internal
        returns (bool)
    {
        if (!contains(self, elementToRemove)) {
            return false;
        }
        bytes32 previousElement = self.prevMap[elementToRemove];
        bytes32 nextElement = self.nextMap[elementToRemove];
        self.nextMap[previousElement] = nextElement;
        self.prevMap[nextElement] = previousElement;
        self.nextMap[elementToRemove] = bytes32(0);
        return true;
    }

    /// Remove an element from the chain, clearing all related storage.
    /// Note that no elements should be inserted using as a reference point a
    /// node deleted after calling `remove`, since an element in the `prev`
    /// chain might be missing.
    function remove(Data storage self, bytes32 elementToRemove)
        internal
        returns (bool)
    {
        bool result = removeKeepHistory(self, elementToRemove);
        if (result) {
            self.prevMap[elementToRemove] = bytes32(0);
        }
        return result;
    }

    function contains(Data storage self, bytes32 value)
        internal
        view
        returns (bool)
    {
        if (value == QUEUE_START) {
            return false;
        }
        // Note: QUEUE_END is not contained in the list since it has no
        // successor.
        return self.nextMap[value] != bytes32(0);
    }

    // @dev orders are ordered by
    // 1. their price - buyAmount/sellAmount
    // 2. by the sellAmount
    // 3. their userId,
    function smallerThan(bytes32 orderLeft, bytes32 orderRight)
        internal
        pure
        returns (bool)
    {
        (
            uint64 userIdLeft,
            uint96 priceNumeratorLeft,
            uint96 priceDenominatorLeft
        ) = decodeOrder(orderLeft);
        (
            uint64 userIdRight,
            uint96 priceNumeratorRight,
            uint96 priceDenominatorRight
        ) = decodeOrder(orderRight);

        if (
            priceNumeratorLeft.mul(priceDenominatorRight) <
            priceNumeratorRight.mul(priceDenominatorLeft)
        ) return true;
        if (
            priceNumeratorLeft.mul(priceDenominatorRight) >
            priceNumeratorRight.mul(priceDenominatorLeft)
        ) return false;

        if (priceNumeratorLeft < priceNumeratorRight) return true;
        if (priceNumeratorLeft > priceNumeratorRight) return false;
        require(
            userIdLeft != userIdRight,
            "user is not allowed to place same order twice"
        );
        if (userIdLeft < userIdRight) {
            return true;
        }
        return false;
    }

    function first(Data storage self) internal view returns (bytes32) {
        require(!isEmpty(self), "Trying to get first from empty set");
        return self.nextMap[QUEUE_START];
    }

    function next(Data storage self, bytes32 value)
        internal
        view
        returns (bytes32)
    {
        require(value != QUEUE_END, "Trying to get next of last element");
        bytes32 nextElement = self.nextMap[value];
        require(
            nextElement != bytes32(0),
            "Trying to get next of non-existent element"
        );
        return nextElement;
    }

    function decodeOrder(bytes32 _orderData)
        internal
        pure
        returns (
            uint64 userId,
            uint96 buyAmount,
            uint96 sellAmount
        )
    {
        // Note: converting to uint discards the binary digits that do not fit
        // the type.
        userId = uint64(uint256(_orderData) >> 192);
        buyAmount = uint96(uint256(_orderData) >> 96);
        sellAmount = uint96(uint256(_orderData));
    }

    function encodeOrder(
        uint64 userId,
        uint96 buyAmount,
        uint96 sellAmount
    ) internal pure returns (bytes32) {
        return
            bytes32(
                (uint256(userId) << 192) +
                    (uint256(buyAmount) << 96) +
                    uint256(sellAmount)
            );
    }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Standard math utilities missing in the Solidity language.
 */
library Math {
    /**
     * @dev Returns the largest of two numbers.
     */
    function max(uint256 a, uint256 b) internal pure returns (uint256) {
        return a >= b ? a : b;
    }

    /**
     * @dev Returns the smallest of two numbers.
     */
    function min(uint256 a, uint256 b) internal pure returns (uint256) {
        return a < b ? a : b;
    }

    /**
     * @dev Returns the average of two numbers. The result is rounded towards
     * zero.
     */
    function average(uint256 a, uint256 b) internal pure returns (uint256) {
        // (a + b) / 2 can overflow, so we distribute
        return (a / 2) + (b / 2) + ((a % 2 + b % 2) / 2);
    }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "../GSN/Context.sol";
/**
 * @dev Contract module which provides a basic access control mechanism, where
 * there is an account (an owner) that can be granted exclusive access to
 * specific functions.
 *
 * By default, the owner account will be the one that deploys the contract. This
 * can later be changed with {transferOwnership}.
 *
 * This module is used through inheritance. It will make available the modifier
 * `onlyOwner`, which can be applied to your functions to restrict their use to
 * the owner.
 */
abstract 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 {
        address msgSender = _msgSender();
        _owner = msgSender;
        emit OwnershipTransferred(address(0), msgSender);
    }

    /**
     * @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(_owner == _msgSender(), "Ownable: caller is not the 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 virtual 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 virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        emit OwnershipTransferred(_owner, newOwner);
        _owner = newOwner;
    }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @dev Wrappers over Solidity's uintXX/intXX casting operators with added overflow
 * checks.
 *
 * Logic was copied and modified from here: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/SafeCast.sol
 */
library SafeCast {
    function toUint96(uint256 value) internal pure returns (uint96) {
        require(value < 2**96, "SafeCast: value doesn't fit in 96 bits");
        return uint96(value);
    }

    function toUint64(uint256 value) internal pure returns (uint64) {
        require(value < 2**64, "SafeCast: value doesn't fit in 64 bits");
        return uint64(value);
    }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

import "./IERC20.sol";
import "../../math/SafeMath.sol";
import "../../utils/Address.sol";

/**
 * @title SafeERC20
 * @dev Wrappers around ERC20 operations that throw on failure (when the token
 * contract returns false). Tokens that return no value (and instead revert or
 * throw on failure) are also supported, non-reverting calls are assumed to be
 * successful.
 * To use this library you can add a `using SafeERC20 for IERC20;` statement to your contract,
 * which allows you to call the safe operations as `token.safeTransfer(...)`, etc.
 */
library SafeERC20 {
    using SafeMath for uint256;
    using Address for address;

    function safeTransfer(IERC20 token, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transfer.selector, to, value));
    }

    function safeTransferFrom(IERC20 token, address from, address to, uint256 value) internal {
        _callOptionalReturn(token, abi.encodeWithSelector(token.transferFrom.selector, from, to, value));
    }

    /**
     * @dev Deprecated. This function has issues similar to the ones found in
     * {IERC20-approve}, and its usage is discouraged.
     *
     * Whenever possible, use {safeIncreaseAllowance} and
     * {safeDecreaseAllowance} instead.
     */
    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. We use {Address.functionCall} to perform this call, which verifies that
        // the target address contains contract code and also asserts for success in the low-level call.

        bytes memory returndata = address(token).functionCall(data, "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");
        }
    }
}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0 <0.8.0;

/**
 * @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;
    }
}

{
  "compilationTarget": {
    "contracts/EasyAuction.sol": "EasyAuction"
  },
  "evmVersion": "istanbul",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs",
    "useLiteralContent": true
  },
  "optimizer": {
    "enabled": false,
    "runs": 200
  },
  "remappings": []
}