pragma solidity ^0.4.18;


/**
 * Interface for required functionality in the ERC721 standard
 * for non-fungible tokens.
 *
 * Author: Nadav Hollander (nadav at dharma.io)
 */
contract ERC721 {
    // Function
    function totalSupply() public view returns (uint256 _totalSupply);
    function balanceOf(address _owner) public view returns (uint256 _balance);
    function ownerOf(uint _tokenId) public view returns (address _owner);
    function approve(address _to, uint _tokenId) public;
    function transferFrom(address _from, address _to, uint _tokenId) public;
    function transfer(address _to, uint _tokenId) public;
    function implementsERC721() public view returns (bool _implementsERC721);

    // Events
    event Transfer(address indexed _from, address indexed _to, uint256 _tokenId);
    event Approval(address indexed _owner, address indexed _approved, uint256 _tokenId);
}

/// @title Auction Core
/// @dev Contains models, variables, and internal methods for the auction.
contract ClockAuctionBase {

    // Represents an auction on an NFT
    struct Auction {
        // Address of the NFT
        address nftAddress;
        // Current owner of NFT
        address seller;
        // Price (in wei) at beginning of auction
        uint128 startingPrice;
        // Price (in wei) at end of auction
        uint128 endingPrice;
        // Duration (in seconds) of auction
        uint64 duration;
        // Time when auction started
        // NOTE: 0 if this auction has been concluded
        uint64 startedAt;
    }

    // Cut owner takes on each auction, measured in basis points (1/100 of a percent).
    // Values 0-10,000 map to 0%-100%
    uint256 public ownerCut;

    // Map from token ID to their corresponding auction.
    mapping (address => mapping(uint256 => Auction)) nftToTokenIdToAuction;

    event AuctionCreated(address nftAddress, uint256 tokenId, uint256 startingPrice, uint256 endingPrice, uint256 duration);
    event AuctionSuccessful(address nftAddress, uint256 tokenId, uint256 totalPrice, address winner);
    event AuctionCancelled(address nftAddress, uint256 tokenId);

    /// @dev DON'T give me your money.
    function() external {}

    // Modifiers to check that inputs can be safely stored with a certain
    // number of bits. We use constants and multiple modifiers to save gas.
    modifier canBeStoredWith64Bits(uint256 _value) {
        require(_value <= 18446744073709551615);
        _;
    }

    modifier canBeStoredWith128Bits(uint256 _value) {
        require(_value < 340282366920938463463374607431768211455);
        _;
    }

    /// @dev Returns true if the claimant owns the token.
    /// @param _nft - The address of the NFT.
    /// @param _claimant - Address claiming to own the token.
    /// @param _tokenId - ID of token whose ownership to verify.
    function _owns(address _nft, address _claimant, uint256 _tokenId) internal view returns (bool) {
        ERC721 nonFungibleContract = _getNft(_nft);
        return (nonFungibleContract.ownerOf(_tokenId) == _claimant);
    }

    /// @dev Escrows the NFT, assigning ownership to this contract.
    /// Throws if the escrow fails.
    /// @param _nft - The address of the NFT.
    /// @param _owner - Current owner address of token to escrow.
    /// @param _tokenId - ID of token whose approval to verify.
    function _escrow(address _nft, address _owner, uint256 _tokenId) internal {
        ERC721 nonFungibleContract = _getNft(_nft);

        // it will throw if transfer fails
        nonFungibleContract.transferFrom(_owner, this, _tokenId);
    }

    /// @dev Transfers an NFT owned by this contract to another address.
    /// Returns true if the transfer succeeds.
    /// @param _nft - The address of the NFT.
    /// @param _receiver - Address to transfer NFT to.
    /// @param _tokenId - ID of token to transfer.
    function _transfer(address _nft, address _receiver, uint256 _tokenId) internal {
        ERC721 nonFungibleContract = _getNft(_nft);

        // it will throw if transfer fails
        nonFungibleContract.transfer(_receiver, _tokenId);
    }

    /// @dev Adds an auction to the list of open auctions. Also fires the
    ///  AuctionCreated event.
    /// @param _tokenId The ID of the token to be put on auction.
    /// @param _auction Auction to add.
    function _addAuction(address _nft, uint256 _tokenId, Auction _auction) internal {
        // Require that all auctions have a duration of
        // at least one minute. (Keeps our math from getting hairy!)
        require(_auction.duration >= 1 minutes);

        nftToTokenIdToAuction[_nft][_tokenId] = _auction;
        
        AuctionCreated(
            address(_nft),
            uint256(_tokenId),
            uint256(_auction.startingPrice),
            uint256(_auction.endingPrice),
            uint256(_auction.duration)
        );
    }

    /// @dev Cancels an auction unconditionally.
    function _cancelAuction(address _nft, uint256 _tokenId, address _seller) internal {
        _removeAuction(_nft, _tokenId);
        _transfer(_nft, _seller, _tokenId);
        AuctionCancelled(_nft, _tokenId);
    }

    /// @dev Computes the price and transfers winnings.
    /// Does NOT transfer ownership of token.
    function _bid(address _nft, uint256 _tokenId, uint256 _bidAmount)
        internal
        returns (uint256)
    {
        // Get a reference to the auction struct
        Auction storage auction = nftToTokenIdToAuction[_nft][_tokenId];

        // Explicitly check that this auction is currently live.
        // (Because of how Ethereum mappings work, we can't just count
        // on the lookup above failing. An invalid _tokenId will just
        // return an auction object that is all zeros.)
        require(_isOnAuction(auction));

        // Check that the incoming bid is higher than the current
        // price
        uint256 price = _currentPrice(auction);
        require(_bidAmount >= price);

        // Grab a reference to the seller before the auction struct
        // gets deleted.
        address seller = auction.seller;

        // The bid is good! Remove the auction before sending the fees
        // to the sender so we can't have a reentrancy attack.
        _removeAuction(_nft, _tokenId);

        // Transfer proceeds to seller (if there are any!)
        if (price > 0) {
            //  Calculate the auctioneer's cut.
            // (NOTE: _computeCut() is guaranteed to return a
            //  value <= price, so this subtraction can't go negative.)
            uint256 auctioneerCut = _computeCut(price);
            uint256 sellerProceeds = price - auctioneerCut;

            // NOTE: Doing a transfer() in the middle of a complex
            // method like this is generally discouraged because of
            // reentrancy attacks and DoS attacks if the seller is
            // a contract with an invalid fallback function. We explicitly
            // guard against reentrancy attacks by removing the auction
            // before calling transfer(), and the only thing the seller
            // can DoS is the sale of their own asset! (And if it's an
            // accident, they can call cancelAuction(). )
            seller.transfer(sellerProceeds);
        }

        // Tell the world!
        AuctionSuccessful(_nft, _tokenId, price, msg.sender);

        return price;
    }

    /// @dev Removes an auction from the list of open auctions.
    /// @param _tokenId - ID of NFT on auction.
    function _removeAuction(address _nft, uint256 _tokenId) internal {
        delete nftToTokenIdToAuction[_nft][_tokenId];
    }

    /// @dev Returns true if the NFT is on auction.
    /// @param _auction - Auction to check.
    function _isOnAuction(Auction storage _auction) internal view returns (bool) {
        return (_auction.startedAt > 0);
    }

    /// @dev Returns current price of an NFT on auction. Broken into two
    ///  functions (this one, that computes the duration from the auction
    ///  structure, and the other that does the price computation) so we
    ///  can easily test that the price computation works correctly.
    function _currentPrice(Auction storage _auction)
        internal
        view
        returns (uint256)
    {
        uint256 secondsPassed = 0;
        
        // A bit of insurance against negative values (or wraparound).
        // Probably not necessary (since Ethereum guarnatees that the
        // now variable doesn't ever go backwards).
        if (now > _auction.startedAt) {
            secondsPassed = now - _auction.startedAt;
        }

        return _computeCurrentPrice(
            _auction.startingPrice,
            _auction.endingPrice,
            _auction.duration,
            secondsPassed
        );
    }

    /// @dev Computes the current price of an auction. Factored out
    ///  from _currentPrice so we can run extensive unit tests.
    ///  When testing, make this function public and turn on
    ///  `Current price computation` test suite.
    function _computeCurrentPrice(
        uint256 _startingPrice,
        uint256 _endingPrice,
        uint256 _duration,
        uint256 _secondsPassed
    )
        internal
        pure
        returns (uint256)
    {
        // NOTE: We don't use SafeMath (or similar) in this function because
        //  all of our public functions carefully cap the maximum values for
        //  time (at 64-bits) and currency (at 128-bits). _duration is
        //  also known to be non-zero (see the require() statement in
        //  _addAuction())
        if (_secondsPassed >= _duration) {
            // We've reached the end of the dynamic pricing portion
            // of the auction, just return the end price.
            return _endingPrice;
        } else {
            // Starting price can be higher than ending price (and often is!), so
            // this delta can be negative.
            int256 totalPriceChange = int256(_endingPrice) - int256(_startingPrice);
            
            // This multiplication can't overflow, _secondsPassed will easily fit within
            // 64-bits, and totalPriceChange will easily fit within 128-bits, their product
            // will always fit within 256-bits.
            int256 currentPriceChange = totalPriceChange * int256(_secondsPassed) / int256(_duration);
            
            // currentPriceChange can be negative, but if so, will have a magnitude
            // less that _startingPrice. Thus, this result will always end up positive.
            int256 currentPrice = int256(_startingPrice) + currentPriceChange;
            
            return uint256(currentPrice);
        }
    }

    /// @dev Computes owner's cut of a sale.
    /// @param _price - Sale price of NFT.
    function _computeCut(uint256 _price) internal view returns (uint256) {
        // NOTE: We don't use SafeMath (or similar) in this function because
        //  all of our entry functions carefully cap the maximum values for
        //  currency (at 128-bits), and ownerCut <= 10000 (see the require()
        //  statement in the ClockAuction constructor). The result of this
        //  function is always guaranteed to be <= _price.
        return _price * ownerCut / 10000;
    }

    /// @dev Gets the NFT object from an address, validating that implementsERC721 is true.
    /// @param _nft - Address of the NFT.
    function _getNft(address _nft) internal view returns (ERC721) {
        ERC721 candidateContract = ERC721(_nft);
        //require(candidateContract.implementsERC721());
        return candidateContract;
    }

}

/**
 * @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 OwnershipTransferred(address indexed previousOwner, address indexed newOwner);


  /**
   * @dev The Ownable constructor sets the original `owner` of the contract to the sender
   * account.
   */
  function Ownable() 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 transfer control of the contract to a newOwner.
   * @param newOwner The address to transfer ownership to.
   */
  function transferOwnership(address newOwner) public onlyOwner {
    require(newOwner != address(0));
    OwnershipTransferred(owner, newOwner);
    owner = newOwner;
  }

}

/**
 * @title Pausable
 * @dev Base contract which allows children to implement an emergency stop mechanism.
 */
contract Pausable is Ownable {
  event Pause();
  event Unpause();

  bool public paused = false;


  /**
   * @dev Modifier to make a function callable only when the contract is not paused.
   */
  modifier whenNotPaused() {
    require(!paused);
    _;
  }

  /**
   * @dev Modifier to make a function callable only when the contract is paused.
   */
  modifier whenPaused() {
    require(paused);
    _;
  }

  /**
   * @dev called by the owner to pause, triggers stopped state
   */
  function pause() onlyOwner whenNotPaused public {
    paused = true;
    Pause();
  }

  /**
   * @dev called by the owner to unpause, returns to normal state
   */
  function unpause() onlyOwner whenPaused public {
    paused = false;
    Unpause();
  }
}

/// @title Clock auction for non-fungible tokens.
contract ClockAuction is Pausable, ClockAuctionBase {

    /// @dev Constructor creates a reference to the NFT ownership contract
    ///  and verifies the owner cut is in the valid range.
    /// @param _cut - percent cut the owner takes on each auction, must be
    ///  between 0-10,000.
    function ClockAuction(uint256 _cut) public {
        require(_cut <= 10000);
        ownerCut = _cut;
    }

    /// @dev Remove all Ether from the contract, which is the owner's cuts
    ///  as well as any Ether sent directly to the contract address.
    ///  Always transfers to the NFT contract, but can be called either by
    ///  the owner or the NFT contract.
    function withdrawBalance() external {
        require(
            msg.sender == owner
        );
        msg.sender.transfer(this.balance);
    }

    /// @dev Creates and begins a new auction.
    /// @param _nftAddress - address of a deployed contract implementing
    ///  the Nonfungible Interface.
    /// @param _tokenId - ID of token to auction, sender must be owner.
    /// @param _startingPrice - Price of item (in wei) at beginning of auction.
    /// @param _endingPrice - Price of item (in wei) at end of auction.
    /// @param _duration - Length of time to move between starting
    ///  price and ending price (in seconds).
    /// @param _seller - Seller, if not the message sender
    function createAuction(
        address _nftAddress,
        uint256 _tokenId,
        uint256 _startingPrice,
        uint256 _endingPrice,
        uint256 _duration,
        address _seller
    )
        public
        whenNotPaused
        canBeStoredWith128Bits(_startingPrice)
        canBeStoredWith128Bits(_endingPrice)
        canBeStoredWith64Bits(_duration)
    {
        require(_owns(_nftAddress, msg.sender, _tokenId));
        _escrow(_nftAddress, msg.sender, _tokenId);
        Auction memory auction = Auction(
            _nftAddress,
            _seller,
            uint128(_startingPrice),
            uint128(_endingPrice),
            uint64(_duration),
            uint64(now)
        );
        _addAuction(_nftAddress, _tokenId, auction);
    }

    /// @dev Bids on an open auction, completing the auction and transferring
    ///  ownership of the NFT if enough Ether is supplied.
    /// @param _nftAddress - address of a deployed contract implementing
    ///  the Nonfungible Interface.
    /// @param _tokenId - ID of token to bid on.
    function bid(address _nftAddress, uint256 _tokenId)
        public
        payable
        whenNotPaused
    {
        // _bid will throw if the bid or funds transfer fails
        _bid(_nftAddress, _tokenId, msg.value);
        _transfer(_nftAddress, msg.sender, _tokenId);
    }

    /// @dev Cancels an auction that hasn't been won yet.
    ///  Returns the NFT to original owner.
    /// @notice This is a state-modifying function that can
    ///  be called while the contract is paused.
    /// @param _nftAddress - Address of the NFT.
    /// @param _tokenId - ID of token on auction
    function cancelAuction(address _nftAddress, uint256 _tokenId)
        public
    {
        Auction storage auction = nftToTokenIdToAuction[_nftAddress][_tokenId];
        require(_isOnAuction(auction));
        address seller = auction.seller;
        require(msg.sender == seller);
        _cancelAuction(_nftAddress, _tokenId, seller);
    }

    /// @dev Cancels an auction when the contract is paused.
    ///  Only the owner may do this, and NFTs are returned to
    ///  the seller. This should only be used in emergencies.
    /// @param _nftAddress - Address of the NFT.
    /// @param _tokenId - ID of the NFT on auction to cancel.
    function cancelAuctionWhenPaused(address _nftAddress, uint256 _tokenId)
        whenPaused
        onlyOwner
        public
    {
        Auction storage auction = nftToTokenIdToAuction[_nftAddress][_tokenId];
        require(_isOnAuction(auction));
        _cancelAuction(_nftAddress, _tokenId, auction.seller);
    }

    /// @dev Returns auction info for an NFT on auction.
    /// @param _nftAddress - Address of the NFT.
    /// @param _tokenId - ID of NFT on auction.
    function getAuction(address _nftAddress, uint256 _tokenId)
        public
        view
        returns
    (
        address seller,
        uint256 startingPrice,
        uint256 endingPrice,
        uint256 duration,
        uint256 startedAt
    ) {
        Auction storage auction = nftToTokenIdToAuction[_nftAddress][_tokenId];
        require(_isOnAuction(auction));
        return (
            auction.seller,
            auction.startingPrice,
            auction.endingPrice,
            auction.duration,
            auction.startedAt
        );
    }

    /// @dev Returns the current price of an auction.
    /// @param _nftAddress - Address of the NFT.
    /// @param _tokenId - ID of the token price we are checking.
    function getCurrentPrice(address _nftAddress, uint256 _tokenId)
        public
        view
        returns (uint256)
    {
        Auction storage auction = nftToTokenIdToAuction[_nftAddress][_tokenId];
        require(_isOnAuction(auction));
        return _currentPrice(auction);
    }

}

/// @title Clock auction modified for sale of kitties
contract SaleClockAuction is ClockAuction {

    // Delegate constructor
    function SaleClockAuction(uint256 _cut) public
        ClockAuction(_cut) {}

    /// @dev Creates and begins a new auction.
    /// @param _nftAddress - The address of the NFT.
    /// @param _tokenId - ID of token to auction, sender must be owner.
    /// @param _startingPrice - Price of item (in wei) at beginning of auction.
    /// @param _endingPrice - Price of item (in wei) at end of auction.
    /// @param _duration - Length of auction (in seconds).
    function createAuction(
        address _nftAddress,
        uint256 _tokenId,
        uint256 _startingPrice,
        uint256 _endingPrice,
        uint256 _duration
    )
        public
        canBeStoredWith128Bits(_startingPrice)
        canBeStoredWith128Bits(_endingPrice)
        canBeStoredWith64Bits(_duration)
    {
        address seller = msg.sender;
        _escrow(_nftAddress, seller, _tokenId);
        Auction memory auction = Auction(
            _nftAddress,
            seller,
            uint128(_startingPrice),
            uint128(_endingPrice),
            uint64(_duration),
            uint64(now)
        );
        _addAuction(_nftAddress, _tokenId, auction);
    }

    /// @dev Updates lastSalePrice if seller is the nft contract
    /// Otherwise, works the same as default bid method.
    function bid(address _nftAddress, uint256 _tokenId)
        public
        payable
    {
        // _bid verifies token ID size
        address seller = nftToTokenIdToAuction[_nftAddress][_tokenId].seller;
        uint256 price = _bid(_nftAddress, _tokenId, msg.value);
        _transfer(_nftAddress, msg.sender, _tokenId);
    }
}