// File: contracts/wyvern/WyvernExchange.sol



/*

  << Project Wyvern Exchange >>

*/

pragma solidity 0.4.23;

import "./exchange/Exchange.sol";

/**
 * @title WyvernExchange
 * @author Project Wyvern Developers
 */
contract WyvernExchange is Exchange {
    string public constant name = "Project Wyvern Exchange";

    string public constant version = "2.2";

    string public constant codename = "Lambton Worm";

    /**
     * @dev Initialize a WyvernExchange instance
     * @param registryAddress Address of the registry instance which this Exchange instance will use
     * @param tokenAddress Address of the token used for protocol fees
     */
    constructor(
        ProxyRegistry registryAddress,
        TokenTransferProxy tokenTransferProxyAddress,
        ERC20 tokenAddress,
        address protocolFeeAddress
    ) public {
        registry = registryAddress;
        tokenTransferProxy = tokenTransferProxyAddress;
        exchangeToken = tokenAddress;
        protocolFeeRecipient = protocolFeeAddress;
        owner = msg.sender;
    }
}

// File: contracts/wyvern/exchange/Exchange.sol



/*
  
  Exchange contract. This is an outer contract with public or convenience functions and includes no state-modifying functions.
 
*/

pragma solidity 0.4.23;

import "./ExchangeCore.sol";

/**
 * @title Exchange
 * @author Project Wyvern Developers
 */
contract Exchange is ExchangeCore {
    /**
     * @dev Call guardedArrayReplace - library function exposed for testing.
     */
    function guardedArrayReplace(
        bytes array,
        bytes desired,
        bytes mask
    ) public pure returns (bytes) {
        ArrayUtils.guardedArrayReplace(array, desired, mask);
        return array;
    }

    /**
     * Test copy byte array
     *
     * @param arrToCopy Array to copy
     * @return byte array
     */
    function testCopy(bytes arrToCopy) public pure returns (bytes) {
        bytes memory arr = new bytes(arrToCopy.length);
        uint256 index;
        assembly {
            index := add(arr, 0x20)
        }
        ArrayUtils.unsafeWriteBytes(index, arrToCopy);
        return arr;
    }

    /**
     * Test write address to bytes
     *
     * @param addr Address to write
     * @return byte array
     */
    function testCopyAddress(address addr) public pure returns (bytes) {
        bytes memory arr = new bytes(0x14);
        uint256 index;
        assembly {
            index := add(arr, 0x20)
        }
        ArrayUtils.unsafeWriteAddress(index, addr);
        return arr;
    }

    /**
     * @dev Call calculateFinalPrice - library function exposed for testing.
     */
    function calculateFinalPrice(
        SaleKindInterface.Side side,
        SaleKindInterface.SaleKind saleKind,
        uint256 basePrice,
        uint256 extra,
        uint256 listingTime,
        uint256 expirationTime
    ) public view returns (uint256) {
        return
            SaleKindInterface.calculateFinalPrice(
                side,
                saleKind,
                basePrice,
                extra,
                listingTime,
                expirationTime
            );
    }

    /**
     * @dev Call hashOrder - Solidity ABI encoding limitation workaround, hopefully temporary.
     */
    function hashOrder_(
        address[7] addrs,
        uint256[9] uints,
        FeeMethod feeMethod,
        SaleKindInterface.Side side,
        SaleKindInterface.SaleKind saleKind,
        AuthenticatedProxy.HowToCall howToCall,
        bytes calldata,
        bytes replacementPattern,
        bytes staticExtradata
    ) public pure returns (bytes32) {
        return
            hashOrder(
                Order(
                    addrs[0],
                    addrs[1],
                    addrs[2],
                    uints[0],
                    uints[1],
                    uints[2],
                    uints[3],
                    addrs[3],
                    feeMethod,
                    side,
                    saleKind,
                    addrs[4],
                    howToCall,
                    calldata,
                    replacementPattern,
                    addrs[5],
                    staticExtradata,
                    ERC20(addrs[6]),
                    uints[4],
                    uints[5],
                    uints[6],
                    uints[7],
                    uints[8]
                )
            );
    }

    /**
     * @dev Call hashToSign - Solidity ABI encoding limitation workaround, hopefully temporary.
     */
    function hashToSign_(
        address[7] addrs,
        uint256[9] uints,
        FeeMethod feeMethod,
        SaleKindInterface.Side side,
        SaleKindInterface.SaleKind saleKind,
        AuthenticatedProxy.HowToCall howToCall,
        bytes calldata,
        bytes replacementPattern,
        bytes staticExtradata
    ) public pure returns (bytes32) {
        return
            hashToSign(
                Order(
                    addrs[0],
                    addrs[1],
                    addrs[2],
                    uints[0],
                    uints[1],
                    uints[2],
                    uints[3],
                    addrs[3],
                    feeMethod,
                    side,
                    saleKind,
                    addrs[4],
                    howToCall,
                    calldata,
                    replacementPattern,
                    addrs[5],
                    staticExtradata,
                    ERC20(addrs[6]),
                    uints[4],
                    uints[5],
                    uints[6],
                    uints[7],
                    uints[8]
                )
            );
    }

    /**
     * @dev Call validateOrderParameters - Solidity ABI encoding limitation workaround, hopefully temporary.
     */
    function validateOrderParameters_(
        address[7] addrs,
        uint256[9] uints,
        FeeMethod feeMethod,
        SaleKindInterface.Side side,
        SaleKindInterface.SaleKind saleKind,
        AuthenticatedProxy.HowToCall howToCall,
        bytes calldata,
        bytes replacementPattern,
        bytes staticExtradata
    ) public view returns (bool) {
        Order memory order = Order(
            addrs[0],
            addrs[1],
            addrs[2],
            uints[0],
            uints[1],
            uints[2],
            uints[3],
            addrs[3],
            feeMethod,
            side,
            saleKind,
            addrs[4],
            howToCall,
            calldata,
            replacementPattern,
            addrs[5],
            staticExtradata,
            ERC20(addrs[6]),
            uints[4],
            uints[5],
            uints[6],
            uints[7],
            uints[8]
        );
        return validateOrderParameters(order);
    }

    /**
     * @dev Call validateOrder - Solidity ABI encoding limitation workaround, hopefully temporary.
     */
    function validateOrder_(
        address[7] addrs,
        uint256[9] uints,
        FeeMethod feeMethod,
        SaleKindInterface.Side side,
        SaleKindInterface.SaleKind saleKind,
        AuthenticatedProxy.HowToCall howToCall,
        bytes calldata,
        bytes replacementPattern,
        bytes staticExtradata,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public view returns (bool) {
        Order memory order = Order(
            addrs[0],
            addrs[1],
            addrs[2],
            uints[0],
            uints[1],
            uints[2],
            uints[3],
            addrs[3],
            feeMethod,
            side,
            saleKind,
            addrs[4],
            howToCall,
            calldata,
            replacementPattern,
            addrs[5],
            staticExtradata,
            ERC20(addrs[6]),
            uints[4],
            uints[5],
            uints[6],
            uints[7],
            uints[8]
        );
        return validateOrder(hashToSign(order), order, Sig(v, r, s));
    }

    /**
     * @dev Call approveOrder - Solidity ABI encoding limitation workaround, hopefully temporary.
     */
    function approveOrder_(
        address[7] addrs,
        uint256[9] uints,
        FeeMethod feeMethod,
        SaleKindInterface.Side side,
        SaleKindInterface.SaleKind saleKind,
        AuthenticatedProxy.HowToCall howToCall,
        bytes calldata,
        bytes replacementPattern,
        bytes staticExtradata,
        bool orderbookInclusionDesired
    ) public {
        Order memory order = Order(
            addrs[0],
            addrs[1],
            addrs[2],
            uints[0],
            uints[1],
            uints[2],
            uints[3],
            addrs[3],
            feeMethod,
            side,
            saleKind,
            addrs[4],
            howToCall,
            calldata,
            replacementPattern,
            addrs[5],
            staticExtradata,
            ERC20(addrs[6]),
            uints[4],
            uints[5],
            uints[6],
            uints[7],
            uints[8]
        );
        return approveOrder(order, orderbookInclusionDesired);
    }

    /**
     * @dev Call cancelOrder - Solidity ABI encoding limitation workaround, hopefully temporary.
     */
    function cancelOrder_(
        address[7] addrs,
        uint256[9] uints,
        FeeMethod feeMethod,
        SaleKindInterface.Side side,
        SaleKindInterface.SaleKind saleKind,
        AuthenticatedProxy.HowToCall howToCall,
        bytes calldata,
        bytes replacementPattern,
        bytes staticExtradata,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) public {
        return
            cancelOrder(
                Order(
                    addrs[0],
                    addrs[1],
                    addrs[2],
                    uints[0],
                    uints[1],
                    uints[2],
                    uints[3],
                    addrs[3],
                    feeMethod,
                    side,
                    saleKind,
                    addrs[4],
                    howToCall,
                    calldata,
                    replacementPattern,
                    addrs[5],
                    staticExtradata,
                    ERC20(addrs[6]),
                    uints[4],
                    uints[5],
                    uints[6],
                    uints[7],
                    uints[8]
                ),
                Sig(v, r, s)
            );
    }

    /**
     * @dev Call calculateCurrentPrice - Solidity ABI encoding limitation workaround, hopefully temporary.
     */
    function calculateCurrentPrice_(
        address[7] addrs,
        uint256[9] uints,
        FeeMethod feeMethod,
        SaleKindInterface.Side side,
        SaleKindInterface.SaleKind saleKind,
        AuthenticatedProxy.HowToCall howToCall,
        bytes calldata,
        bytes replacementPattern,
        bytes staticExtradata
    ) public view returns (uint256) {
        return
            calculateCurrentPrice(
                Order(
                    addrs[0],
                    addrs[1],
                    addrs[2],
                    uints[0],
                    uints[1],
                    uints[2],
                    uints[3],
                    addrs[3],
                    feeMethod,
                    side,
                    saleKind,
                    addrs[4],
                    howToCall,
                    calldata,
                    replacementPattern,
                    addrs[5],
                    staticExtradata,
                    ERC20(addrs[6]),
                    uints[4],
                    uints[5],
                    uints[6],
                    uints[7],
                    uints[8]
                )
            );
    }

    /**
     * @dev Call ordersCanMatch - Solidity ABI encoding limitation workaround, hopefully temporary.
     */
    function ordersCanMatch_(
        address[14] addrs,
        uint256[18] uints,
        uint8[8] feeMethodsSidesKindsHowToCalls,
        bytes calldataBuy,
        bytes calldataSell,
        bytes replacementPatternBuy,
        bytes replacementPatternSell,
        bytes staticExtradataBuy,
        bytes staticExtradataSell
    ) public view returns (bool) {
        Order memory buy = Order(
            addrs[0],
            addrs[1],
            addrs[2],
            uints[0],
            uints[1],
            uints[2],
            uints[3],
            addrs[3],
            FeeMethod(feeMethodsSidesKindsHowToCalls[0]),
            SaleKindInterface.Side(feeMethodsSidesKindsHowToCalls[1]),
            SaleKindInterface.SaleKind(feeMethodsSidesKindsHowToCalls[2]),
            addrs[4],
            AuthenticatedProxy.HowToCall(feeMethodsSidesKindsHowToCalls[3]),
            calldataBuy,
            replacementPatternBuy,
            addrs[5],
            staticExtradataBuy,
            ERC20(addrs[6]),
            uints[4],
            uints[5],
            uints[6],
            uints[7],
            uints[8]
        );
        Order memory sell = Order(
            addrs[7],
            addrs[8],
            addrs[9],
            uints[9],
            uints[10],
            uints[11],
            uints[12],
            addrs[10],
            FeeMethod(feeMethodsSidesKindsHowToCalls[4]),
            SaleKindInterface.Side(feeMethodsSidesKindsHowToCalls[5]),
            SaleKindInterface.SaleKind(feeMethodsSidesKindsHowToCalls[6]),
            addrs[11],
            AuthenticatedProxy.HowToCall(feeMethodsSidesKindsHowToCalls[7]),
            calldataSell,
            replacementPatternSell,
            addrs[12],
            staticExtradataSell,
            ERC20(addrs[13]),
            uints[13],
            uints[14],
            uints[15],
            uints[16],
            uints[17]
        );
        return ordersCanMatch(buy, sell);
    }

    /**
     * @dev Return whether or not two orders' calldata specifications can match
     * @param buyCalldata Buy-side order calldata
     * @param buyReplacementPattern Buy-side order calldata replacement mask
     * @param sellCalldata Sell-side order calldata
     * @param sellReplacementPattern Sell-side order calldata replacement mask
     * @return Whether the orders' calldata can be matched
     */
    function orderCalldataCanMatch(
        bytes buyCalldata,
        bytes buyReplacementPattern,
        bytes sellCalldata,
        bytes sellReplacementPattern
    ) public pure returns (bool) {
        if (buyReplacementPattern.length > 0) {
            ArrayUtils.guardedArrayReplace(
                buyCalldata,
                sellCalldata,
                buyReplacementPattern
            );
        }
        if (sellReplacementPattern.length > 0) {
            ArrayUtils.guardedArrayReplace(
                sellCalldata,
                buyCalldata,
                sellReplacementPattern
            );
        }
        return ArrayUtils.arrayEq(buyCalldata, sellCalldata);
    }

    /**
     * @dev Call calculateMatchPrice - Solidity ABI encoding limitation workaround, hopefully temporary.
     */
    function calculateMatchPrice_(
        address[14] addrs,
        uint256[18] uints,
        uint8[8] feeMethodsSidesKindsHowToCalls,
        bytes calldataBuy,
        bytes calldataSell,
        bytes replacementPatternBuy,
        bytes replacementPatternSell,
        bytes staticExtradataBuy,
        bytes staticExtradataSell
    ) public view returns (uint256) {
        Order memory buy = Order(
            addrs[0],
            addrs[1],
            addrs[2],
            uints[0],
            uints[1],
            uints[2],
            uints[3],
            addrs[3],
            FeeMethod(feeMethodsSidesKindsHowToCalls[0]),
            SaleKindInterface.Side(feeMethodsSidesKindsHowToCalls[1]),
            SaleKindInterface.SaleKind(feeMethodsSidesKindsHowToCalls[2]),
            addrs[4],
            AuthenticatedProxy.HowToCall(feeMethodsSidesKindsHowToCalls[3]),
            calldataBuy,
            replacementPatternBuy,
            addrs[5],
            staticExtradataBuy,
            ERC20(addrs[6]),
            uints[4],
            uints[5],
            uints[6],
            uints[7],
            uints[8]
        );
        Order memory sell = Order(
            addrs[7],
            addrs[8],
            addrs[9],
            uints[9],
            uints[10],
            uints[11],
            uints[12],
            addrs[10],
            FeeMethod(feeMethodsSidesKindsHowToCalls[4]),
            SaleKindInterface.Side(feeMethodsSidesKindsHowToCalls[5]),
            SaleKindInterface.SaleKind(feeMethodsSidesKindsHowToCalls[6]),
            addrs[11],
            AuthenticatedProxy.HowToCall(feeMethodsSidesKindsHowToCalls[7]),
            calldataSell,
            replacementPatternSell,
            addrs[12],
            staticExtradataSell,
            ERC20(addrs[13]),
            uints[13],
            uints[14],
            uints[15],
            uints[16],
            uints[17]
        );
        return calculateMatchPrice(buy, sell);
    }

    /**
     * @dev Call atomicMatch - Solidity ABI encoding limitation workaround, hopefully temporary.
     */
    function atomicMatch_(
        address[14] addrs,
        uint256[18] uints,
        uint8[8] feeMethodsSidesKindsHowToCalls,
        bytes calldataBuy,
        bytes calldataSell,
        bytes replacementPatternBuy,
        bytes replacementPatternSell,
        bytes staticExtradataBuy,
        bytes staticExtradataSell,
        uint8[2] vs,
        bytes32[5] rssMetadata
    ) public payable {
        return
            atomicMatch(
                Order(
                    addrs[0],
                    addrs[1],
                    addrs[2],
                    uints[0],
                    uints[1],
                    uints[2],
                    uints[3],
                    addrs[3],
                    FeeMethod(feeMethodsSidesKindsHowToCalls[0]),
                    SaleKindInterface.Side(feeMethodsSidesKindsHowToCalls[1]),
                    SaleKindInterface.SaleKind(
                        feeMethodsSidesKindsHowToCalls[2]
                    ),
                    addrs[4],
                    AuthenticatedProxy.HowToCall(
                        feeMethodsSidesKindsHowToCalls[3]
                    ),
                    calldataBuy,
                    replacementPatternBuy,
                    addrs[5],
                    staticExtradataBuy,
                    ERC20(addrs[6]),
                    uints[4],
                    uints[5],
                    uints[6],
                    uints[7],
                    uints[8]
                ),
                Sig(vs[0], rssMetadata[0], rssMetadata[1]),
                Order(
                    addrs[7],
                    addrs[8],
                    addrs[9],
                    uints[9],
                    uints[10],
                    uints[11],
                    uints[12],
                    addrs[10],
                    FeeMethod(feeMethodsSidesKindsHowToCalls[4]),
                    SaleKindInterface.Side(feeMethodsSidesKindsHowToCalls[5]),
                    SaleKindInterface.SaleKind(
                        feeMethodsSidesKindsHowToCalls[6]
                    ),
                    addrs[11],
                    AuthenticatedProxy.HowToCall(
                        feeMethodsSidesKindsHowToCalls[7]
                    ),
                    calldataSell,
                    replacementPatternSell,
                    addrs[12],
                    staticExtradataSell,
                    ERC20(addrs[13]),
                    uints[13],
                    uints[14],
                    uints[15],
                    uints[16],
                    uints[17]
                ),
                Sig(vs[1], rssMetadata[2], rssMetadata[3]),
                rssMetadata[4]
            );
    }
}

// File: contracts/wyvern/exchange/ExchangeCore.sol



/*

  Decentralized digital asset exchange. Supports any digital asset that can be represented on the Ethereum blockchain (i.e. - transferred in an Ethereum transaction or sequence of transactions).

  Let us suppose two agents interacting with a distributed ledger have utility functions preferencing certain states of that ledger over others.
  Aiming to maximize their utility, these agents may construct with their utility functions along with the present ledger state a mapping of state transitions (transactions) to marginal utilities.
  Any composite state transition with positive marginal utility for and enactable by the combined permissions of both agents thus is a mutually desirable trade, and the trustless 
  code execution provided by a distributed ledger renders the requisite atomicity trivial.

  Relative to this model, this instantiation makes two concessions to practicality:
  - State transition preferences are not matched directly but instead intermediated by a standard of tokenized value.
  - A small fee can be charged in WYV for order settlement in an amount configurable by the frontend hosting the orderbook.

  Solidity presently possesses neither a first-class functional typesystem nor runtime reflection (ABI encoding in Solidity), so we must be a bit clever in implementation and work at a lower level of abstraction than would be ideal.

  We elect to utilize the following structure for the initial version of the protocol:
  - Buy-side and sell-side orders each provide calldata (bytes) - for a sell-side order, the state transition for sale, for a buy-side order, the state transition to be bought.
    Along with the calldata, orders provide `replacementPattern`: a bytemask indicating which bytes of the calldata can be changed (e.g. NFT destination address).
    When a buy-side and sell-side order are matched, the desired calldatas are unified, masked with the bytemasks, and checked for agreement.
    This alone is enough to implement common simple state transitions, such as "transfer my CryptoKitty to any address" or "buy any of this kind of nonfungible token".
  - Orders (of either side) can optionally specify a static (no state modification) callback function, which receives configurable data along with the actual calldata as a parameter.
    Although it requires some encoding acrobatics, this allows for arbitrary transaction validation functions.
    For example, a buy-sider order could express the intent to buy any CryptoKitty with a particular set of characteristics (checked in the static call),
    or a sell-side order could express the intent to sell any of three ENS names, but not two others.
    Use of the EVM's STATICCALL opcode, added in Ethereum Metropolis, allows the static calldata to be safely specified separately and thus this kind of matching to happen correctly
    - that is to say, wherever the two (transaction => bool) functions intersect.

  Future protocol versions may improve upon this structure in capability or usability according to protocol user feedback demand, with upgrades enacted by the Wyvern DAO.
 
*/

pragma solidity 0.4.23;

import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";
import "openzeppelin-solidity/contracts/math/SafeMath.sol";
import "openzeppelin-solidity/contracts/ownership/Ownable.sol";

import "../registry/ProxyRegistry.sol";
import "../registry/TokenTransferProxy.sol";
import "../registry/AuthenticatedProxy.sol";
import "../common/ArrayUtils.sol";
import "../common/ReentrancyGuarded.sol";
import "./SaleKindInterface.sol";

/**
 * @title ExchangeCore
 * @author Project Wyvern Developers
 */
contract ExchangeCore is ReentrancyGuarded, Ownable {
    /* The token used to pay exchange fees. */
    ERC20 public exchangeToken;

    /* User registry. */
    ProxyRegistry public registry;

    /* Token transfer proxy. */
    TokenTransferProxy public tokenTransferProxy;

    /* Cancelled / finalized orders, by hash. */
    mapping(bytes32 => bool) public cancelledOrFinalized;

    /* Orders verified by on-chain approval (alternative to ECDSA signatures so that smart contracts can place orders directly). */
    mapping(bytes32 => bool) public approvedOrders;

    /* For split fee orders, minimum required protocol maker fee, in basis points. Paid to owner (who can change it). */
    uint256 public minimumMakerProtocolFee = 0;

    /* For split fee orders, minimum required protocol taker fee, in basis points. Paid to owner (who can change it). */
    uint256 public minimumTakerProtocolFee = 0;

    /* Recipient of protocol fees. */
    address public protocolFeeRecipient;

    /* Fee method: protocol fee or split fee. */
    enum FeeMethod {
        ProtocolFee,
        SplitFee
    }

    /* Inverse basis point. */
    uint256 public constant INVERSE_BASIS_POINT = 10000;

    /* An ECDSA signature. */
    struct Sig {
        /* v parameter */
        uint8 v;
        /* r parameter */
        bytes32 r;
        /* s parameter */
        bytes32 s;
    }

    /* An order on the exchange. */
    struct Order {
        /* Exchange address, intended as a versioning mechanism. */
        address exchange;
        /* Order maker address. */
        address maker;
        /* Order taker address, if specified. */
        address taker;
        /* Maker relayer fee of the order, unused for taker order. */
        uint256 makerRelayerFee;
        /* Taker relayer fee of the order, or maximum taker fee for a taker order. */
        uint256 takerRelayerFee;
        /* Maker protocol fee of the order, unused for taker order. */
        uint256 makerProtocolFee;
        /* Taker protocol fee of the order, or maximum taker fee for a taker order. */
        uint256 takerProtocolFee;
        /* Order fee recipient or zero address for taker order. */
        address feeRecipient;
        /* Fee method (protocol token or split fee). */
        FeeMethod feeMethod;
        /* Side (buy/sell). */
        SaleKindInterface.Side side;
        /* Kind of sale. */
        SaleKindInterface.SaleKind saleKind;
        /* Target. */
        address target;
        /* HowToCall. */
        AuthenticatedProxy.HowToCall howToCall;
        /* Calldata. */
        bytes calldata;
        /* Calldata replacement pattern, or an empty byte array for no replacement. */
        bytes replacementPattern;
        /* Static call target, zero-address for no static call. */
        address staticTarget;
        /* Static call extra data. */
        bytes staticExtradata;
        /* Token used to pay for the order, or the zero-address as a sentinel value for Ether. */
        address paymentToken;
        /* Base price of the order (in paymentTokens). */
        uint256 basePrice;
        /* Auction extra parameter - minimum bid increment for English auctions, starting/ending price difference. */
        uint256 extra;
        /* Listing timestamp. */
        uint256 listingTime;
        /* Expiration timestamp - 0 for no expiry. */
        uint256 expirationTime;
        /* Order salt, used to prevent duplicate hashes. */
        uint256 salt;
    }

    event OrderApprovedPartOne(
        bytes32 indexed hash,
        address exchange,
        address indexed maker,
        address taker,
        uint256 makerRelayerFee,
        uint256 takerRelayerFee,
        uint256 makerProtocolFee,
        uint256 takerProtocolFee,
        address indexed feeRecipient,
        FeeMethod feeMethod,
        SaleKindInterface.Side side,
        SaleKindInterface.SaleKind saleKind,
        address target
    );
    event OrderApprovedPartTwo(
        bytes32 indexed hash,
        AuthenticatedProxy.HowToCall howToCall,
        bytes calldata,
        bytes replacementPattern,
        address staticTarget,
        bytes staticExtradata,
        address paymentToken,
        uint256 basePrice,
        uint256 extra,
        uint256 listingTime,
        uint256 expirationTime,
        uint256 salt,
        bool orderbookInclusionDesired
    );
    event OrderCancelled(bytes32 indexed hash);
    event OrdersMatched(
        bytes32 buyHash,
        bytes32 sellHash,
        address indexed maker,
        address indexed taker,
        uint256 price,
        bytes32 indexed metadata
    );

    /**
     * @dev Change the minimum maker fee paid to the protocol (owner only)
     * @param newMinimumMakerProtocolFee New fee to set in basis points
     */
    function changeMinimumMakerProtocolFee(uint256 newMinimumMakerProtocolFee)
        public
        onlyOwner
    {
        minimumMakerProtocolFee = newMinimumMakerProtocolFee;
    }

    /**
     * @dev Change the minimum taker fee paid to the protocol (owner only)
     * @param newMinimumTakerProtocolFee New fee to set in basis points
     */
    function changeMinimumTakerProtocolFee(uint256 newMinimumTakerProtocolFee)
        public
        onlyOwner
    {
        minimumTakerProtocolFee = newMinimumTakerProtocolFee;
    }

    /**
     * @dev Change the protocol fee recipient (owner only)
     * @param newProtocolFeeRecipient New protocol fee recipient address
     */
    function changeProtocolFeeRecipient(address newProtocolFeeRecipient)
        public
        onlyOwner
    {
        protocolFeeRecipient = newProtocolFeeRecipient;
    }

    /**
     * @dev Transfer tokens
     * @param token Token to transfer
     * @param from Address to charge fees
     * @param to Address to receive fees
     * @param amount Amount of protocol tokens to charge
     */
    function transferTokens(
        address token,
        address from,
        address to,
        uint256 amount
    ) internal {
        if (amount > 0) {
            require(tokenTransferProxy.transferFrom(token, from, to, amount));
        }
    }

    /**
     * @dev Charge a fee in protocol tokens
     * @param from Address to charge fees
     * @param to Address to receive fees
     * @param amount Amount of protocol tokens to charge
     */
    function chargeProtocolFee(
        address from,
        address to,
        uint256 amount
    ) internal {
        transferTokens(exchangeToken, from, to, amount);
    }

    /**
     * @dev Execute a STATICCALL (introduced with Ethereum Metropolis, non-state-modifying external call)
     * @param target Contract to call
     * @param calldata Calldata (appended to extradata)
     * @param extradata Base data for STATICCALL (probably function selector and argument encoding)
     * @return The result of the call (success or failure)
     */
    function staticCall(
        address target,
        bytes memory calldata,
        bytes memory extradata
    ) public view returns (bool result) {
        bytes memory combined = new bytes(calldata.length + extradata.length);
        uint256 index;
        assembly {
            index := add(combined, 0x20)
        }
        index = ArrayUtils.unsafeWriteBytes(index, extradata);
        ArrayUtils.unsafeWriteBytes(index, calldata);
        assembly {
            result := staticcall(
                gas,
                target,
                add(combined, 0x20),
                mload(combined),
                mload(0x40),
                0
            )
        }
        return result;
    }

    /**
     * Calculate size of an order struct when tightly packed
     *
     * @param order Order to calculate size of
     * @return Size in bytes
     */
    function sizeOf(Order memory order) internal pure returns (uint256) {
        return ((0x14 * 7) +
            (0x20 * 9) +
            4 +
            order.calldata.length +
            order.replacementPattern.length +
            order.staticExtradata.length);
    }

    /**
     * @dev Hash an order, returning the canonical order hash, without the message prefix
     * @param order Order to hash
     * @return Hash of order
     */
    function hashOrder(Order memory order)
        internal
        pure
        returns (bytes32 hash)
    {
        /* Unfortunately abi.encodePacked doesn't work here, stack size constraints. */
        uint256 size = sizeOf(order);
        bytes memory array = new bytes(size);
        uint256 index;
        assembly {
            index := add(array, 0x20)
        }
        index = ArrayUtils.unsafeWriteAddress(index, order.exchange);
        index = ArrayUtils.unsafeWriteAddress(index, order.maker);
        index = ArrayUtils.unsafeWriteAddress(index, order.taker);
        index = ArrayUtils.unsafeWriteUint(index, order.makerRelayerFee);
        index = ArrayUtils.unsafeWriteUint(index, order.takerRelayerFee);
        index = ArrayUtils.unsafeWriteUint(index, order.makerProtocolFee);
        index = ArrayUtils.unsafeWriteUint(index, order.takerProtocolFee);
        index = ArrayUtils.unsafeWriteAddress(index, order.feeRecipient);
        index = ArrayUtils.unsafeWriteUint8(index, uint8(order.feeMethod));
        index = ArrayUtils.unsafeWriteUint8(index, uint8(order.side));
        index = ArrayUtils.unsafeWriteUint8(index, uint8(order.saleKind));
        index = ArrayUtils.unsafeWriteAddress(index, order.target);
        index = ArrayUtils.unsafeWriteUint8(index, uint8(order.howToCall));
        index = ArrayUtils.unsafeWriteBytes(index, order.calldata);
        index = ArrayUtils.unsafeWriteBytes(index, order.replacementPattern);
        index = ArrayUtils.unsafeWriteAddress(index, order.staticTarget);
        index = ArrayUtils.unsafeWriteBytes(index, order.staticExtradata);
        index = ArrayUtils.unsafeWriteAddress(index, order.paymentToken);
        index = ArrayUtils.unsafeWriteUint(index, order.basePrice);
        index = ArrayUtils.unsafeWriteUint(index, order.extra);
        index = ArrayUtils.unsafeWriteUint(index, order.listingTime);
        index = ArrayUtils.unsafeWriteUint(index, order.expirationTime);
        index = ArrayUtils.unsafeWriteUint(index, order.salt);
        assembly {
            hash := keccak256(add(array, 0x20), size)
        }
        return hash;
    }

    /**
     * @dev Hash an order, returning the hash that a client must sign, including the standard message prefix
     * @param order Order to hash
     * @return Hash of message prefix and order hash per Ethereum format
     */
    function hashToSign(Order memory order) internal pure returns (bytes32) {
        return keccak256("\x19Ethereum Signed Message:\n32", hashOrder(order));
    }

    /**
     * @dev Assert an order is valid and return its hash
     * @param order Order to validate
     * @param sig ECDSA signature
     */
    function requireValidOrder(Order memory order, Sig memory sig)
        internal
        view
        returns (bytes32)
    {
        bytes32 hash = hashToSign(order);
        require(validateOrder(hash, order, sig));
        return hash;
    }

    /**
     * @dev Validate order parameters (does *not* check signature validity)
     * @param order Order to validate
     */
    function validateOrderParameters(Order memory order)
        internal
        view
        returns (bool)
    {
        /* Order must be targeted at this protocol version (this Exchange contract). */
        if (order.exchange != address(this)) {
            return false;
        }

        /* Order must possess valid sale kind parameter combination. */
        if (
            !SaleKindInterface.validateParameters(
                order.saleKind,
                order.expirationTime
            )
        ) {
            return false;
        }

        /* If using the split fee method, order must have sufficient protocol fees. */
        if (
            order.feeMethod == FeeMethod.SplitFee &&
            (order.makerProtocolFee < minimumMakerProtocolFee ||
                order.takerProtocolFee < minimumTakerProtocolFee)
        ) {
            return false;
        }

        return true;
    }

    /**
     * @dev Validate a provided previously approved / signed order, hash, and signature.
     * @param hash Order hash (already calculated, passed to avoid recalculation)
     * @param order Order to validate
     * @param sig ECDSA signature
     */
    function validateOrder(
        bytes32 hash,
        Order memory order,
        Sig memory sig
    ) internal view returns (bool) {
        /* Not done in an if-conditional to prevent unnecessary ecrecover evaluation, which seems to happen even though it should short-circuit. */

        /* Order must have valid parameters. */
        if (!validateOrderParameters(order)) {
            return false;
        }

        /* Order must have not been canceled or already filled. */
        if (cancelledOrFinalized[hash]) {
            return false;
        }

        /* Order authentication. Order must be either:
        /* (a) previously approved */
        if (approvedOrders[hash]) {
            return true;
        }

        /* or (b) ECDSA-signed by maker. */
        if (ecrecover(hash, sig.v, sig.r, sig.s) == order.maker) {
            return true;
        }

        return false;
    }

    /**
     * @dev Approve an order and optionally mark it for orderbook inclusion. Must be called by the maker of the order
     * @param order Order to approve
     * @param orderbookInclusionDesired Whether orderbook providers should include the order in their orderbooks
     */
    function approveOrder(Order memory order, bool orderbookInclusionDesired)
        internal
    {
        /* CHECKS */

        /* Assert sender is authorized to approve order. */
        require(msg.sender == order.maker);

        /* Calculate order hash. */
        bytes32 hash = hashToSign(order);

        /* Assert order has not already been approved. */
        require(!approvedOrders[hash]);

        /* EFFECTS */

        /* Mark order as approved. */
        approvedOrders[hash] = true;

        /* Log approval event. Must be split in two due to Solidity stack size limitations. */
        {
            emit OrderApprovedPartOne(
                hash,
                order.exchange,
                order.maker,
                order.taker,
                order.makerRelayerFee,
                order.takerRelayerFee,
                order.makerProtocolFee,
                order.takerProtocolFee,
                order.feeRecipient,
                order.feeMethod,
                order.side,
                order.saleKind,
                order.target
            );
        }
        {
            emit OrderApprovedPartTwo(
                hash,
                order.howToCall,
                order.calldata,
                order.replacementPattern,
                order.staticTarget,
                order.staticExtradata,
                order.paymentToken,
                order.basePrice,
                order.extra,
                order.listingTime,
                order.expirationTime,
                order.salt,
                orderbookInclusionDesired
            );
        }
    }

    /**
     * @dev Cancel an order, preventing it from being matched. Must be called by the maker of the order
     * @param order Order to cancel
     * @param sig ECDSA signature
     */
    function cancelOrder(Order memory order, Sig memory sig) internal {
        /* CHECKS */

        /* Calculate order hash. */
        bytes32 hash = requireValidOrder(order, sig);

        /* Assert sender is authorized to cancel order. */
        require(msg.sender == order.maker);

        /* EFFECTS */

        /* Mark order as cancelled, preventing it from being matched. */
        cancelledOrFinalized[hash] = true;

        /* Log cancel event. */
        emit OrderCancelled(hash);
    }

    /**
     * @dev Calculate the current price of an order (convenience function)
     * @param order Order to calculate the price of
     * @return The current price of the order
     */
    function calculateCurrentPrice(Order memory order)
        internal
        view
        returns (uint256)
    {
        return
            SaleKindInterface.calculateFinalPrice(
                order.side,
                order.saleKind,
                order.basePrice,
                order.extra,
                order.listingTime,
                order.expirationTime
            );
    }

    /**
     * @dev Calculate the price two orders would match at, if in fact they would match (otherwise fail)
     * @param buy Buy-side order
     * @param sell Sell-side order
     * @return Match price
     */
    function calculateMatchPrice(Order memory buy, Order memory sell)
        internal
        view
        returns (uint256)
    {
        /* Calculate sell price. */
        uint256 sellPrice = SaleKindInterface.calculateFinalPrice(
            sell.side,
            sell.saleKind,
            sell.basePrice,
            sell.extra,
            sell.listingTime,
            sell.expirationTime
        );

        /* Calculate buy price. */
        uint256 buyPrice = SaleKindInterface.calculateFinalPrice(
            buy.side,
            buy.saleKind,
            buy.basePrice,
            buy.extra,
            buy.listingTime,
            buy.expirationTime
        );

        /* Require price cross. */
        require(buyPrice >= sellPrice);

        /* Maker/taker priority. */
        return sell.feeRecipient != address(0) ? sellPrice : buyPrice;
    }

    /**
     * @dev Execute all ERC20 token / Ether transfers associated with an order match (fees and buyer => seller transfer)
     * @param buy Buy-side order
     * @param sell Sell-side order
     */
    function executeFundsTransfer(Order memory buy, Order memory sell)
        internal
        returns (uint256)
    {
        /* Only payable in the special case of unwrapped Ether. */
        if (sell.paymentToken != address(0)) {
            require(msg.value == 0);
        }

        /* Calculate match price. */
        uint256 price = calculateMatchPrice(buy, sell);

        /* If paying using a token (not Ether), transfer tokens. This is done prior to fee payments to that a seller will have tokens before being charged fees. */
        if (price > 0 && sell.paymentToken != address(0)) {
            transferTokens(sell.paymentToken, buy.maker, sell.maker, price);
        }

        /* Amount that will be received by seller (for Ether). */
        uint256 receiveAmount = price;

        /* Amount that must be sent by buyer (for Ether). */
        uint256 requiredAmount = price;

        /* Determine maker/taker and charge fees accordingly. */
        if (sell.feeRecipient != address(0)) {
            /* Sell-side order is maker. */

            /* Assert taker fee is less than or equal to maximum fee specified by buyer. */
            require(sell.takerRelayerFee <= buy.takerRelayerFee);

            if (sell.feeMethod == FeeMethod.SplitFee) {
                /* Assert taker fee is less than or equal to maximum fee specified by buyer. */
                require(sell.takerProtocolFee <= buy.takerProtocolFee);

                /* Maker fees are deducted from the token amount that the maker receives. Taker fees are extra tokens that must be paid by the taker. */

                if (sell.makerRelayerFee > 0) {
                    uint256 makerRelayerFee = SafeMath.div(
                        SafeMath.mul(sell.makerRelayerFee, price),
                        INVERSE_BASIS_POINT
                    );
                    if (sell.paymentToken == address(0)) {
                        receiveAmount = SafeMath.sub(
                            receiveAmount,
                            makerRelayerFee
                        );
                        sell.feeRecipient.transfer(makerRelayerFee);
                    } else {
                        transferTokens(
                            sell.paymentToken,
                            sell.maker,
                            sell.feeRecipient,
                            makerRelayerFee
                        );
                    }
                }

                if (sell.takerRelayerFee > 0) {
                    uint256 takerRelayerFee = SafeMath.div(
                        SafeMath.mul(sell.takerRelayerFee, price),
                        INVERSE_BASIS_POINT
                    );
                    if (sell.paymentToken == address(0)) {
                        requiredAmount = SafeMath.add(
                            requiredAmount,
                            takerRelayerFee
                        );
                        sell.feeRecipient.transfer(takerRelayerFee);
                    } else {
                        transferTokens(
                            sell.paymentToken,
                            buy.maker,
                            sell.feeRecipient,
                            takerRelayerFee
                        );
                    }
                }

                if (sell.makerProtocolFee > 0) {
                    uint256 makerProtocolFee = SafeMath.div(
                        SafeMath.mul(sell.makerProtocolFee, price),
                        INVERSE_BASIS_POINT
                    );
                    if (sell.paymentToken == address(0)) {
                        receiveAmount = SafeMath.sub(
                            receiveAmount,
                            makerProtocolFee
                        );
                        protocolFeeRecipient.transfer(makerProtocolFee);
                    } else {
                        transferTokens(
                            sell.paymentToken,
                            sell.maker,
                            protocolFeeRecipient,
                            makerProtocolFee
                        );
                    }
                }

                if (sell.takerProtocolFee > 0) {
                    uint256 takerProtocolFee = SafeMath.div(
                        SafeMath.mul(sell.takerProtocolFee, price),
                        INVERSE_BASIS_POINT
                    );
                    if (sell.paymentToken == address(0)) {
                        requiredAmount = SafeMath.add(
                            requiredAmount,
                            takerProtocolFee
                        );
                        protocolFeeRecipient.transfer(takerProtocolFee);
                    } else {
                        transferTokens(
                            sell.paymentToken,
                            buy.maker,
                            protocolFeeRecipient,
                            takerProtocolFee
                        );
                    }
                }
            } else {
                /* Charge maker fee to seller. */
                chargeProtocolFee(
                    sell.maker,
                    sell.feeRecipient,
                    sell.makerRelayerFee
                );

                /* Charge taker fee to buyer. */
                chargeProtocolFee(
                    buy.maker,
                    sell.feeRecipient,
                    sell.takerRelayerFee
                );
            }
        } else {
            /* Buy-side order is maker. */

            /* Assert taker fee is less than or equal to maximum fee specified by seller. */
            require(buy.takerRelayerFee <= sell.takerRelayerFee);

            if (sell.feeMethod == FeeMethod.SplitFee) {
                /* The Exchange does not escrow Ether, so direct Ether can only be used to with sell-side maker / buy-side taker orders. */
                require(sell.paymentToken != address(0));

                /* Assert taker fee is less than or equal to maximum fee specified by seller. */
                require(buy.takerProtocolFee <= sell.takerProtocolFee);

                if (buy.makerRelayerFee > 0) {
                    makerRelayerFee = SafeMath.div(
                        SafeMath.mul(buy.makerRelayerFee, price),
                        INVERSE_BASIS_POINT
                    );
                    transferTokens(
                        sell.paymentToken,
                        buy.maker,
                        buy.feeRecipient,
                        makerRelayerFee
                    );
                }

                if (buy.takerRelayerFee > 0) {
                    takerRelayerFee = SafeMath.div(
                        SafeMath.mul(buy.takerRelayerFee, price),
                        INVERSE_BASIS_POINT
                    );
                    transferTokens(
                        sell.paymentToken,
                        sell.maker,
                        buy.feeRecipient,
                        takerRelayerFee
                    );
                }

                if (buy.makerProtocolFee > 0) {
                    makerProtocolFee = SafeMath.div(
                        SafeMath.mul(buy.makerProtocolFee, price),
                        INVERSE_BASIS_POINT
                    );
                    transferTokens(
                        sell.paymentToken,
                        buy.maker,
                        protocolFeeRecipient,
                        makerProtocolFee
                    );
                }

                if (buy.takerProtocolFee > 0) {
                    takerProtocolFee = SafeMath.div(
                        SafeMath.mul(buy.takerProtocolFee, price),
                        INVERSE_BASIS_POINT
                    );
                    transferTokens(
                        sell.paymentToken,
                        sell.maker,
                        protocolFeeRecipient,
                        takerProtocolFee
                    );
                }
            } else {
                /* Charge maker fee to buyer. */
                chargeProtocolFee(
                    buy.maker,
                    buy.feeRecipient,
                    buy.makerRelayerFee
                );

                /* Charge taker fee to seller. */
                chargeProtocolFee(
                    sell.maker,
                    buy.feeRecipient,
                    buy.takerRelayerFee
                );
            }
        }

        if (sell.paymentToken == address(0)) {
            /* Special-case Ether, order must be matched by buyer. */
            require(msg.value >= requiredAmount);
            sell.maker.transfer(receiveAmount);
            /* Allow overshoot for variable-price auctions, refund difference. */
            uint256 diff = SafeMath.sub(msg.value, requiredAmount);
            if (diff > 0) {
                buy.maker.transfer(diff);
            }
        }

        /* This contract should never hold Ether, however, we cannot assert this, since it is impossible to prevent anyone from sending Ether e.g. with selfdestruct. */

        return price;
    }

    /**
     * @dev Return whether or not two orders can be matched with each other by basic parameters (does not check order signatures / calldata or perform static calls)
     * @param buy Buy-side order
     * @param sell Sell-side order
     * @return Whether or not the two orders can be matched
     */
    function ordersCanMatch(Order memory buy, Order memory sell)
        internal
        view
        returns (bool)
    {
        return (/* Must be opposite-side. */
        (buy.side == SaleKindInterface.Side.Buy &&
            sell.side == SaleKindInterface.Side.Sell) &&
            /* Must use same fee method. */
            (buy.feeMethod == sell.feeMethod) &&
            /* Must use same payment token. */
            (buy.paymentToken == sell.paymentToken) &&
            /* Must match maker/taker addresses. */
            (sell.taker == address(0) || sell.taker == buy.maker) &&
            (buy.taker == address(0) || buy.taker == sell.maker) &&
            /* One must be maker and the other must be taker (no bool XOR in Solidity). */
            ((sell.feeRecipient == address(0) &&
                buy.feeRecipient != address(0)) ||
                (sell.feeRecipient != address(0) &&
                    buy.feeRecipient == address(0))) &&
            /* Must match target. */
            (buy.target == sell.target) &&
            /* Must match howToCall. */
            (buy.howToCall == sell.howToCall) &&
            /* Buy-side order must be settleable. */
            SaleKindInterface.canSettleOrder(
                buy.listingTime,
                buy.expirationTime
            ) &&
            /* Sell-side order must be settleable. */
            SaleKindInterface.canSettleOrder(
                sell.listingTime,
                sell.expirationTime
            ));
    }

    /**
     * @dev Atomically match two orders, ensuring validity of the match, and execute all associated state transitions. Protected against reentrancy by a contract-global lock.
     * @param buy Buy-side order
     * @param buySig Buy-side order signature
     * @param sell Sell-side order
     * @param sellSig Sell-side order signature
     */
    function atomicMatch(
        Order memory buy,
        Sig memory buySig,
        Order memory sell,
        Sig memory sellSig,
        bytes32 metadata
    ) internal reentrancyGuard {
        /* CHECKS */

        /* Ensure buy order validity and calculate hash if necessary. */
        bytes32 buyHash;
        if (buy.maker == msg.sender) {
            require(validateOrderParameters(buy));
        } else {
            buyHash = requireValidOrder(buy, buySig);
        }

        /* Ensure sell order validity and calculate hash if necessary. */
        bytes32 sellHash;
        if (sell.maker == msg.sender) {
            require(validateOrderParameters(sell));
        } else {
            sellHash = requireValidOrder(sell, sellSig);
        }

        /* Must be matchable. */
        require(ordersCanMatch(buy, sell));

        /* Target must exist (prevent malicious selfdestructs just prior to order settlement). */
        uint256 size;
        address target = sell.target;
        assembly {
            size := extcodesize(target)
        }
        require(size > 0);

        /* Must match calldata after replacement, if specified. */
        if (buy.replacementPattern.length > 0) {
            ArrayUtils.guardedArrayReplace(
                buy.calldata,
                sell.calldata,
                buy.replacementPattern
            );
        }
        if (sell.replacementPattern.length > 0) {
            ArrayUtils.guardedArrayReplace(
                sell.calldata,
                buy.calldata,
                sell.replacementPattern
            );
        }
        require(ArrayUtils.arrayEq(buy.calldata, sell.calldata));

        /* Retrieve delegateProxy contract. */
        OwnableDelegateProxy delegateProxy = registry.proxies(sell.maker);

        /* Proxy must exist. */
        require(delegateProxy != address(0));

        /* Assert implementation. */
        require(
            delegateProxy.implementation() ==
                registry.delegateProxyImplementation()
        );

        /* Access the passthrough AuthenticatedProxy. */
        AuthenticatedProxy proxy = AuthenticatedProxy(delegateProxy);

        /* EFFECTS */

        /* Mark previously signed or approved orders as finalized. */
        if (msg.sender != buy.maker) {
            cancelledOrFinalized[buyHash] = true;
        }
        if (msg.sender != sell.maker) {
            cancelledOrFinalized[sellHash] = true;
        }

        /* INTERACTIONS */

        /* Execute funds transfer and pay fees. */
        uint256 price = executeFundsTransfer(buy, sell);

        /* Execute specified call through proxy. */
        require(proxy.proxy(sell.target, sell.howToCall, sell.calldata));

        /* Static calls are intentionally done after the effectful call so they can check resulting state. */

        /* Handle buy-side static call if specified. */
        if (buy.staticTarget != address(0)) {
            require(
                staticCall(buy.staticTarget, sell.calldata, buy.staticExtradata)
            );
        }

        /* Handle sell-side static call if specified. */
        if (sell.staticTarget != address(0)) {
            require(
                staticCall(
                    sell.staticTarget,
                    sell.calldata,
                    sell.staticExtradata
                )
            );
        }

        /* Log match event. */
        emit OrdersMatched(
            buyHash,
            sellHash,
            sell.feeRecipient != address(0) ? sell.maker : buy.maker,
            sell.feeRecipient != address(0) ? buy.maker : sell.maker,
            price,
            metadata
        );
    }
}

// File: openzeppelin-solidity/contracts/token/ERC20/ERC20.sol



pragma solidity ^0.4.23;

import "./ERC20Basic.sol";


/**
 * @title ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/20
 */
contract ERC20 is ERC20Basic {
  function allowance(address owner, address spender)
    public view returns (uint256);

  function transferFrom(address from, address to, uint256 value)
    public returns (bool);

  function approve(address spender, uint256 value) public returns (bool);
  event Approval(
    address indexed owner,
    address indexed spender,
    uint256 value
  );
}

// File: openzeppelin-solidity/contracts/math/SafeMath.sol



pragma solidity ^0.4.23;


/**
 * @title SafeMath
 * @dev Math operations with safety checks that throw on error
 */
library SafeMath {

  /**
  * @dev Multiplies two numbers, throws on overflow.
  */
  function mul(uint256 a, uint256 b) internal pure returns (uint256 c) {
    // Gas optimization: this is cheaper than asserting 'a' not being zero, but the
    // benefit is lost if 'b' is also tested.
    // See: https://github.com/OpenZeppelin/openzeppelin-solidity/pull/522
    if (a == 0) {
      return 0;
    }

    c = a * b;
    assert(c / a == b);
    return c;
  }

  /**
  * @dev Integer division of two numbers, truncating the quotient.
  */
  function div(uint256 a, uint256 b) internal pure returns (uint256) {
    // assert(b > 0); // Solidity automatically throws when dividing by 0
    // uint256 c = a / b;
    // assert(a == b * c + a % b); // There is no case in which this doesn't hold
    return a / b;
  }

  /**
  * @dev Subtracts two numbers, throws on overflow (i.e. if subtrahend is greater than minuend).
  */
  function sub(uint256 a, uint256 b) internal pure returns (uint256) {
    assert(b <= a);
    return a - b;
  }

  /**
  * @dev Adds two numbers, throws on overflow.
  */
  function add(uint256 a, uint256 b) internal pure returns (uint256 c) {
    c = a + b;
    assert(c >= a);
    return c;
  }
}

// File: openzeppelin-solidity/contracts/ownership/Ownable.sol



pragma solidity ^0.4.23;


/**
 * @title Ownable
 * @dev The Ownable contract has an owner address, and provides basic authorization control
 * functions, this simplifies the implementation of "user permissions".
 */
contract Ownable {
  address public owner;


  event OwnershipRenounced(address indexed previousOwner);
  event OwnershipTransferred(
    address indexed previousOwner,
    address indexed newOwner
  );


  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  constructor() public {
    owner = msg.sender;
  }

  /**
   * @dev Throws if called by any account other than the owner.
   */
  modifier onlyOwner() {
    require(msg.sender == owner);
    _;
  }

  /**
   * @dev Allows the current owner to relinquish control of the contract.
   */
  function renounceOwnership() public onlyOwner {
    emit OwnershipRenounced(owner);
    owner = address(0);
  }

  /**
   * @dev Allows the current owner to transfer control of the contract to a newOwner.
   * @param _newOwner The address to transfer ownership to.
   */
  function transferOwnership(address _newOwner) public onlyOwner {
    _transferOwnership(_newOwner);
  }

  /**
   * @dev Transfers control of the contract to a newOwner.
   * @param _newOwner The address to transfer ownership to.
   */
  function _transferOwnership(address _newOwner) internal {
    require(_newOwner != address(0));
    emit OwnershipTransferred(owner, _newOwner);
    owner = _newOwner;
  }
}

// File: contracts/wyvern/registry/ProxyRegistry.sol



/*

  Proxy registry; keeps a mapping of AuthenticatedProxy contracts and mapping of contracts authorized to access them.  
  
  Abstracted away from the Exchange (a) to reduce Exchange attack surface and (b) so that the Exchange contract can be upgraded without users needing to transfer assets to new proxies.

*/

pragma solidity 0.4.23;

import "openzeppelin-solidity/contracts/ownership/Ownable.sol";

import "./OwnableDelegateProxy.sol";

contract ProxyRegistry is Ownable {
    /* DelegateProxy implementation contract. Must be initialized. */
    address public delegateProxyImplementation;

    /* Authenticated proxies by user. */
    mapping(address => OwnableDelegateProxy) public proxies;

    /* Contracts pending access. */
    mapping(address => uint256) public pending;

    /* Contracts allowed to call those proxies. */
    mapping(address => bool) public contracts;

    /* Delay period for adding an authenticated contract.
       This mitigates a particular class of potential attack on the Wyvern DAO (which owns this registry) - if at any point the value of assets held by proxy contracts exceeded the value of half the WYV supply (votes in the DAO),
       a malicious but rational attacker could buy half the Wyvern and grant themselves access to all the proxy contracts. A delay period renders this attack nonthreatening - given two weeks, if that happened, users would have
       plenty of time to notice and transfer their assets.
    */
    uint256 public DELAY_PERIOD = 2 weeks;

    /**
     * Start the process to enable access for specified contract. Subject to delay period.
     *
     * @dev ProxyRegistry owner only
     * @param addr Address to which to grant permissions
     */
    function startGrantAuthentication(address addr) public onlyOwner {
        require(!contracts[addr] && pending[addr] == 0);
        pending[addr] = now;
    }

    function setContract(address addr) public onlyOwner {
        require(!contracts[addr]);
        contracts[addr] = true;
    }

    /**
     * End the process to nable access for specified contract after delay period has passed.
     *
     * @dev ProxyRegistry owner only
     * @param addr Address to which to grant permissions
     */
    function endGrantAuthentication(address addr) public onlyOwner {
        require(
            !contracts[addr] &&
                pending[addr] != 0 &&
                ((pending[addr] + DELAY_PERIOD) < now)
        );
        pending[addr] = 0;
        contracts[addr] = true;
    }

    /**
     * Revoke access for specified contract. Can be done instantly.
     *
     * @dev ProxyRegistry owner only
     * @param addr Address of which to revoke permissions
     */
    function revokeAuthentication(address addr) public onlyOwner {
        contracts[addr] = false;
    }

    /**
     * Register a proxy contract with this registry
     *
     * @dev Must be called by the user which the proxy is for, creates a new AuthenticatedProxy
     * @return New AuthenticatedProxy contract
     */
    function registerProxy() public returns (OwnableDelegateProxy proxy) {
        require(proxies[msg.sender] == address(0));
        proxy = new OwnableDelegateProxy(
            msg.sender,
            delegateProxyImplementation,
            abi.encodeWithSignature(
                "initialize(address,address)",
                msg.sender,
                address(this)
            )
        );
        proxies[msg.sender] = proxy;
        return proxy;
    }
}

// File: contracts/wyvern/registry/TokenTransferProxy.sol



/*

  Token transfer proxy. Uses the authentication table of a ProxyRegistry contract to grant ERC20 `transferFrom` access.
  This means that users only need to authorize the proxy contract once for all future protocol versions.

*/

pragma solidity 0.4.23;

import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";

import "./ProxyRegistry.sol";

contract TokenTransferProxy {
    /* Authentication registry. */
    ProxyRegistry public registry;

    /**
     * Call ERC20 `transferFrom`
     *
     * @dev Authenticated contract only
     * @param token ERC20 token address
     * @param from From address
     * @param to To address
     * @param amount Transfer amount
     */
    function transferFrom(
        address token,
        address from,
        address to,
        uint256 amount
    ) public returns (bool) {
        require(registry.contracts(msg.sender));
        return ERC20(token).transferFrom(from, to, amount);
    }
}

// File: contracts/wyvern/registry/AuthenticatedProxy.sol



/* 

  Proxy contract to hold access to assets on behalf of a user (e.g. ERC20 approve) and execute calls under particular conditions.

*/

pragma solidity 0.4.23;

import "./ProxyRegistry.sol";
import "../common/TokenRecipient.sol";
import "./proxy/OwnedUpgradeabilityStorage.sol";

/**
 * @title AuthenticatedProxy
 * @author Project Wyvern Developers
 */
contract AuthenticatedProxy is TokenRecipient, OwnedUpgradeabilityStorage {
    /* Whether initialized. */
    bool initialized = false;

    /* Address which owns this proxy. */
    address public user;

    /* Associated registry with contract authentication information. */
    ProxyRegistry public registry;

    /* Whether access has been revoked. */
    bool public revoked;

    /* Delegate call could be used to atomically transfer multiple assets owned by the proxy contract with one order. */
    enum HowToCall {
        Call,
        DelegateCall
    }

    /* Event fired when the proxy access is revoked or unrevoked. */
    event Revoked(bool revoked);

    /**
     * Initialize an AuthenticatedProxy
     *
     * @param addrUser Address of user on whose behalf this proxy will act
     * @param addrRegistry Address of ProxyRegistry contract which will manage this proxy
     */
    function initialize(address addrUser, ProxyRegistry addrRegistry) public {
        require(!initialized);
        initialized = true;
        user = addrUser;
        registry = addrRegistry;
    }

    /**
     * Set the revoked flag (allows a user to revoke ProxyRegistry access)
     *
     * @dev Can be called by the user only
     * @param revoke Whether or not to revoke access
     */
    function setRevoke(bool revoke) public {
        require(msg.sender == user);
        revoked = revoke;
        emit Revoked(revoke);
    }

    /**
     * Execute a message call from the proxy contract
     *
     * @dev Can be called by the user, or by a contract authorized by the registry as long as the user has not revoked access
     * @param dest Address to which the call will be sent
     * @param howToCall Which kind of call to make
     * @param calldata Calldata to send
     * @return Result of the call (success or failure)
     */
    function proxy(
        address dest,
        HowToCall howToCall,
        bytes calldata
    ) public returns (bool result) {
        require(
            msg.sender == user || (!revoked && registry.contracts(msg.sender))
        );
        if (howToCall == HowToCall.Call) {
            result = dest.call(calldata);
        } else if (howToCall == HowToCall.DelegateCall) {
            result = dest.delegatecall(calldata);
        }
        return result;
    }

    /**
     * Execute a message call and assert success
     *
     * @dev Same functionality as `proxy`, just asserts the return value
     * @param dest Address to which the call will be sent
     * @param howToCall What kind of call to make
     * @param calldata Calldata to send
     */
    function proxyAssert(
        address dest,
        HowToCall howToCall,
        bytes calldata
    ) public {
        require(proxy(dest, howToCall, calldata));
    }
}

// File: contracts/wyvern/common/ArrayUtils.sol



/*

  Various functions for manipulating arrays in Solidity.
  This library is completely inlined and does not need to be deployed or linked.

*/

pragma solidity 0.4.23;

import "openzeppelin-solidity/contracts/math/SafeMath.sol";

/**
 * @title ArrayUtils
 * @author Project Wyvern Developers
 */
library ArrayUtils {
    /**
     * Replace bytes in an array with bytes in another array, guarded by a bitmask
     * Efficiency of this function is a bit unpredictable because of the EVM's word-specific model (arrays under 32 bytes will be slower)
     *
     * @dev Mask must be the size of the byte array. A nonzero byte means the byte array can be changed.
     * @param array The original array
     * @param desired The target array
     * @param mask The mask specifying which bits can be changed
     * @return The updated byte array (the parameter will be modified inplace)
     */
    function guardedArrayReplace(
        bytes memory array,
        bytes memory desired,
        bytes memory mask
    ) internal pure {
        require(array.length == desired.length);
        require(array.length == mask.length);

        uint256 words = array.length / 0x20;
        uint256 index = words * 0x20;
        assert(index / 0x20 == words);
        uint256 i;

        for (i = 0; i < words; i++) {
            /* Conceptually: array[i] = (!mask[i] && array[i]) || (mask[i] && desired[i]), bitwise in word chunks. */
            assembly {
                let commonIndex := mul(0x20, add(1, i))
                let maskValue := mload(add(mask, commonIndex))
                mstore(
                    add(array, commonIndex),
                    or(
                        and(not(maskValue), mload(add(array, commonIndex))),
                        and(maskValue, mload(add(desired, commonIndex)))
                    )
                )
            }
        }

        /* Deal with the last section of the byte array. */
        if (words > 0) {
            /* This overlaps with bytes already set but is still more efficient than iterating through each of the remaining bytes individually. */
            i = words;
            assembly {
                let commonIndex := mul(0x20, add(1, i))
                let maskValue := mload(add(mask, commonIndex))
                mstore(
                    add(array, commonIndex),
                    or(
                        and(not(maskValue), mload(add(array, commonIndex))),
                        and(maskValue, mload(add(desired, commonIndex)))
                    )
                )
            }
        } else {
            /* If the byte array is shorter than a word, we must unfortunately do the whole thing bytewise.
               (bounds checks could still probably be optimized away in assembly, but this is a rare case) */
            for (i = index; i < array.length; i++) {
                array[i] =
                    ((mask[i] ^ 0xff) & array[i]) |
                    (mask[i] & desired[i]);
            }
        }
    }

    /**
     * Test if two arrays are equal
     * Source: https://github.com/GNSPS/solidity-bytes-utils/blob/master/contracts/BytesLib.sol
     *
     * @dev Arrays must be of equal length, otherwise will return false
     * @param a First array
     * @param b Second array
     * @return Whether or not all bytes in the arrays are equal
     */
    function arrayEq(bytes memory a, bytes memory b)
        internal
        pure
        returns (bool)
    {
        bool success = true;

        assembly {
            let length := mload(a)

            // if lengths don't match the arrays are not equal
            switch eq(length, mload(b))
            case 1 {
                // cb is a circuit breaker in the for loop since there's
                //  no said feature for inline assembly loops
                // cb = 1 - don't breaker
                // cb = 0 - break
                let cb := 1

                let mc := add(a, 0x20)
                let end := add(mc, length)

                for {
                    let cc := add(b, 0x20)
                    // the next line is the loop condition:
                    // while(uint(mc < end) + cb == 2)
                } eq(add(lt(mc, end), cb), 2) {
                    mc := add(mc, 0x20)
                    cc := add(cc, 0x20)
                } {
                    // if any of these checks fails then arrays are not equal
                    if iszero(eq(mload(mc), mload(cc))) {
                        // unsuccess:
                        success := 0
                        cb := 0
                    }
                }
            }
            default {
                // unsuccess:
                success := 0
            }
        }

        return success;
    }

    /**
     * Unsafe write byte array into a memory location
     *
     * @param index Memory location
     * @param source Byte array to write
     * @return End memory index
     */
    function unsafeWriteBytes(uint256 index, bytes source)
        internal
        pure
        returns (uint256)
    {
        if (source.length > 0) {
            assembly {
                let length := mload(source)
                let end := add(source, add(0x20, length))
                let arrIndex := add(source, 0x20)
                let tempIndex := index
                for {

                } eq(lt(arrIndex, end), 1) {
                    arrIndex := add(arrIndex, 0x20)
                    tempIndex := add(tempIndex, 0x20)
                } {
                    mstore(tempIndex, mload(arrIndex))
                }
                index := add(index, length)
            }
        }
        return index;
    }

    /**
     * Unsafe write address into a memory location
     *
     * @param index Memory location
     * @param source Address to write
     * @return End memory index
     */
    function unsafeWriteAddress(uint256 index, address source)
        internal
        pure
        returns (uint256)
    {
        uint256 conv = uint256(source) << 0x60;
        assembly {
            mstore(index, conv)
            index := add(index, 0x14)
        }
        return index;
    }

    /**
     * Unsafe write uint into a memory location
     *
     * @param index Memory location
     * @param source uint to write
     * @return End memory index
     */
    function unsafeWriteUint(uint256 index, uint256 source)
        internal
        pure
        returns (uint256)
    {
        assembly {
            mstore(index, source)
            index := add(index, 0x20)
        }
        return index;
    }

    /**
     * Unsafe write uint8 into a memory location
     *
     * @param index Memory location
     * @param source uint8 to write
     * @return End memory index
     */
    function unsafeWriteUint8(uint256 index, uint8 source)
        internal
        pure
        returns (uint256)
    {
        assembly {
            mstore8(index, source)
            index := add(index, 0x1)
        }
        return index;
    }
}

// File: contracts/wyvern/common/ReentrancyGuarded.sol



/*

  Simple contract extension to provide a contract-global reentrancy guard on functions.

*/

pragma solidity 0.4.23;

/**
 * @title ReentrancyGuarded
 * @author Project Wyvern Developers
 */
contract ReentrancyGuarded {
    bool reentrancyLock = false;

    /* Prevent a contract function from being reentrant-called. */
    modifier reentrancyGuard() {
        if (reentrancyLock) {
            revert();
        }
        reentrancyLock = true;
        _;
        reentrancyLock = false;
    }
}

// File: contracts/wyvern/exchange/SaleKindInterface.sol



/*

  Abstract over fixed-price sales and Dutch auctions, with the intent of easily supporting additional methods of sale later.

  Separated into a library for convenience, all the functions are inlined.

*/

pragma solidity 0.4.23;

import "openzeppelin-solidity/contracts/math/SafeMath.sol";

/**
 * @title SaleKindInterface
 * @author Project Wyvern Developers
 */
library SaleKindInterface {
    /**
     * Side: buy or sell.
     */
    enum Side {
        Buy,
        Sell
    }

    /**
     * Currently supported kinds of sale: fixed price, Dutch auction.
     * English auctions cannot be supported without stronger escrow guarantees.
     * Future interesting options: Vickrey auction, nonlinear Dutch auctions.
     */
    enum SaleKind {
        FixedPrice,
        DutchAuction
    }

    /**
     * @dev Check whether the parameters of a sale are valid
     * @param saleKind Kind of sale
     * @param expirationTime Order expiration time
     * @return Whether the parameters were valid
     */
    function validateParameters(SaleKind saleKind, uint256 expirationTime)
        internal
        pure
        returns (bool)
    {
        /* Auctions must have a set expiration date. */
        return (saleKind == SaleKind.FixedPrice || expirationTime > 0);
    }

    /**
     * @dev Return whether or not an order can be settled
     * @dev Precondition: parameters have passed validateParameters
     * @param listingTime Order listing time
     * @param expirationTime Order expiration time
     */
    function canSettleOrder(uint256 listingTime, uint256 expirationTime)
        internal
        view
        returns (bool)
    {
        return
            (listingTime < now) &&
            (expirationTime == 0 || now < expirationTime);
    }

    /**
     * @dev Calculate the settlement price of an order
     * @dev Precondition: parameters have passed validateParameters.
     * @param side Order side
     * @param saleKind Method of sale
     * @param basePrice Order base price
     * @param extra Order extra price data
     * @param listingTime Order listing time
     * @param expirationTime Order expiration time
     */
    function calculateFinalPrice(
        Side side,
        SaleKind saleKind,
        uint256 basePrice,
        uint256 extra,
        uint256 listingTime,
        uint256 expirationTime
    ) internal view returns (uint256 finalPrice) {
        if (saleKind == SaleKind.FixedPrice) {
            return basePrice;
        } else if (saleKind == SaleKind.DutchAuction) {
            uint256 diff = SafeMath.div(
                SafeMath.mul(extra, SafeMath.sub(now, listingTime)),
                SafeMath.sub(expirationTime, listingTime)
            );
            if (side == Side.Sell) {
                /* Sell-side - start price: basePrice. End price: basePrice - extra. */
                return SafeMath.sub(basePrice, diff);
            } else {
                /* Buy-side - start price: basePrice. End price: basePrice + extra. */
                return SafeMath.add(basePrice, diff);
            }
        }
    }
}

// File: openzeppelin-solidity/contracts/token/ERC20/ERC20Basic.sol



pragma solidity ^0.4.23;


/**
 * @title ERC20Basic
 * @dev Simpler version of ERC20 interface
 * @dev see https://github.com/ethereum/EIPs/issues/179
 */
contract ERC20Basic {
  function totalSupply() public view returns (uint256);
  function balanceOf(address who) public view returns (uint256);
  function transfer(address to, uint256 value) public returns (bool);
  event Transfer(address indexed from, address indexed to, uint256 value);
}

// File: contracts/wyvern/registry/OwnableDelegateProxy.sol



/*

  WyvernOwnableDelegateProxy

*/

pragma solidity 0.4.23;

import "./ProxyRegistry.sol";
import "./AuthenticatedProxy.sol";
import "./proxy/OwnedUpgradeabilityProxy.sol";

contract OwnableDelegateProxy is OwnedUpgradeabilityProxy {
    constructor(
        address owner,
        address initialImplementation,
        bytes calldata
    ) public {
        setUpgradeabilityOwner(owner);
        _upgradeTo(initialImplementation);
        require(initialImplementation.delegatecall(calldata));
    }
}

// File: contracts/wyvern/registry/proxy/OwnedUpgradeabilityProxy.sol



pragma solidity 0.4.23;

import "./Proxy.sol";
import "./OwnedUpgradeabilityStorage.sol";

/**
 * @title OwnedUpgradeabilityProxy
 * @dev This contract combines an upgradeability proxy with basic authorization control functionalities
 */
contract OwnedUpgradeabilityProxy is Proxy, OwnedUpgradeabilityStorage {
    /**
     * @dev Event to show ownership has been transferred
     * @param previousOwner representing the address of the previous owner
     * @param newOwner representing the address of the new owner
     */
    event ProxyOwnershipTransferred(address previousOwner, address newOwner);

    /**
     * @dev This event will be emitted every time the implementation gets upgraded
     * @param implementation representing the address of the upgraded implementation
     */
    event Upgraded(address indexed implementation);

    /**
     * @dev Upgrades the implementation address
     * @param implementation representing the address of the new implementation to be set
     */
    function _upgradeTo(address implementation) internal {
        require(_implementation != implementation);
        _implementation = implementation;
        emit Upgraded(implementation);
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyProxyOwner() {
        require(msg.sender == proxyOwner());
        _;
    }

    /**
     * @dev Tells the address of the proxy owner
     * @return the address of the proxy owner
     */
    function proxyOwner() public view returns (address) {
        return upgradeabilityOwner();
    }

    /**
     * @dev Allows the current owner to transfer control of the contract to a newOwner.
     * @param newOwner The address to transfer ownership to.
     */
    function transferProxyOwnership(address newOwner) public onlyProxyOwner {
        require(newOwner != address(0));
        emit ProxyOwnershipTransferred(proxyOwner(), newOwner);
        setUpgradeabilityOwner(newOwner);
    }

    /**
     * @dev Allows the upgradeability owner to upgrade the current implementation of the proxy.
     * @param implementation representing the address of the new implementation to be set.
     */
    function upgradeTo(address implementation) public onlyProxyOwner {
        _upgradeTo(implementation);
    }

    /**
     * @dev Allows the upgradeability owner to upgrade the current implementation of the proxy
     * and delegatecall the new implementation for initialization.
     * @param implementation representing the address of the new implementation to be set.
     * @param data represents the msg.data to bet sent in the low level call. This parameter may include the function
     * signature of the implementation to be called with the needed payload
     */
    function upgradeToAndCall(address implementation, bytes data)
        public
        payable
        onlyProxyOwner
    {
        upgradeTo(implementation);
        require(address(this).delegatecall(data));
    }
}

// File: contracts/wyvern/common/TokenRecipient.sol



/*

  Token recipient. Modified very slightly from the example on http://ethereum.org/dao (just to index log parameters).

*/

pragma solidity 0.4.23;

import "openzeppelin-solidity/contracts/token/ERC20/ERC20.sol";

/**
 * @title TokenRecipient
 * @author Project Wyvern Developers
 */
contract TokenRecipient {
    event ReceivedEther(address indexed sender, uint256 amount);
    event ReceivedTokens(
        address indexed from,
        uint256 value,
        address indexed token,
        bytes extraData
    );

    /**
     * @dev Receive tokens and generate a log event
     * @param from Address from which to transfer tokens
     * @param value Amount of tokens to transfer
     * @param token Address of token
     * @param extraData Additional data to log
     */
    function receiveApproval(
        address from,
        uint256 value,
        address token,
        bytes extraData
    ) public {
        ERC20 t = ERC20(token);
        require(t.transferFrom(from, this, value));
        emit ReceivedTokens(from, value, token, extraData);
    }

    /**
     * @dev Receive Ether and generate a log event
     */
    function() public payable {
        emit ReceivedEther(msg.sender, msg.value);
    }
}

// File: contracts/wyvern/registry/proxy/OwnedUpgradeabilityStorage.sol



pragma solidity 0.4.23;

/**
 * @title OwnedUpgradeabilityStorage
 * @dev This contract keeps track of the upgradeability owner
 */
contract OwnedUpgradeabilityStorage {
    // Current implementation
    address internal _implementation;

    // Owner of the contract
    address private _upgradeabilityOwner;

    /**
     * @dev Tells the address of the owner
     * @return the address of the owner
     */
    function upgradeabilityOwner() public view returns (address) {
        return _upgradeabilityOwner;
    }

    /**
     * @dev Sets the address of the owner
     */
    function setUpgradeabilityOwner(address newUpgradeabilityOwner) internal {
        _upgradeabilityOwner = newUpgradeabilityOwner;
    }

    /**
     * @dev Tells the address of the current implementation
     * @return address of the current implementation
     */
    function implementation() public view returns (address) {
        return _implementation;
    }

    /**
     * @dev Tells the proxy type (EIP 897)
     * @return Proxy type, 2 for forwarding proxy
     */
    function proxyType() public pure returns (uint256 proxyTypeId) {
        return 2;
    }
}

// File: contracts/wyvern/registry/proxy/Proxy.sol



pragma solidity 0.4.23;

/**
 * @title Proxy
 * @dev Gives the possibility to delegate any call to a foreign implementation.
 */
contract Proxy {
    /**
     * @dev Tells the address of the implementation where every call will be delegated.
     * @return address of the implementation to which it will be delegated
     */
    function implementation() public view returns (address);

    /**
     * @dev Tells the type of proxy (EIP 897)
     * @return Type of proxy, 2 for upgradeable proxy
     */
    function proxyType() public pure returns (uint256 proxyTypeId);

    /**
     * @dev Fallback function allowing to perform a delegatecall to the given implementation.
     * This function will return whatever the implementation call returns
     */
    function() public payable {
        address _impl = implementation();
        require(_impl != address(0));

        assembly {
            let ptr := mload(0x40)
            calldatacopy(ptr, 0, calldatasize)
            let result := delegatecall(gas, _impl, ptr, calldatasize, 0, 0)
            let size := returndatasize
            returndatacopy(ptr, 0, size)

            switch result
            case 0 {
                revert(ptr, size)
            }
            default {
                return(ptr, size)
            }
        }
    }
}