Address Details

contract

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.4;

// Importing OpenZeppelin's contracts
import "@openzeppelin/contracts/utils/math/SafeMath.sol";
import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
import "@openzeppelin/contracts/token/ERC721/utils/ERC721Holder.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/access/Ownable.sol";

contract Auction is ERC721Holder, Ownable, ReentrancyGuard {

    using SafeMath for uint256;
    IERC20 private erc20Token;

    // static
    uint256 public immutable floorPrice;
    uint256 public immutable startTime;
    uint256 public immutable endTime;
    address private immutable beneficiary;
    uint256 private immutable tokenIssue;
    uint256 private immutable redeemQty;
    uint private immutable feePercent;

    // state
    bool public canceled;
    bool public ended;
    bool private fundCollected;
    uint256 public highestBindingBid;
    address public highestBidder;
    address[] private bidders;   
    mapping(address => uint256) public fundsByBidder;        
    mapping(address => bool) public rewardCollected;        
    mapping(uint256 => uint256) public tokenRedeemed;
    uint256[] private tokensAllowed;

    // events
    event LogBid(address bidder, uint256 bid, address highestBidder, uint256 highestBid, uint256 highestBindingBid);
    event LogWithdrawal(address withdrawalAccount, uint256 amount);
    event LogCanceled(bool success);
    event LogRefund(address sender, uint256 amount);
    event FundCollected(uint256 merchantFee, uint256 marketplaceFee);
    event TokenCollected(address winner, uint256 tokenId);
    event Received(address sender, uint256 amount);
    event TokenRedeemed(uint tokenId, uint256 redeemedTotal);

    //trigger when deploy
    constructor(IERC20 _erc20Token, address _beneficiary, uint256 _floorPrice, uint256 _startTime, uint256 _endTime, uint256 _tokenIssue, uint256 _feePercent, uint256 _redeemQty)
    {
        require(_startTime > 1000000000, 'Auction start timestamp is not in seconds!');
        require(_endTime > block.timestamp, 'Auction end timestamp can not be the past!');
        require(_beneficiary != address(0x0), 'Beneficiary address is not correct!');
        erc20Token = _erc20Token;
        beneficiary = _beneficiary;
        floorPrice = etherToWei(_floorPrice);
        startTime = _startTime;
        endTime = _endTime;
        tokenIssue = _tokenIssue;
        feePercent = _feePercent;
        redeemQty = _redeemQty;
    }

    // bid on NFD
    function placeBid(uint256 amount) external
        nonReentrant
        onlyAfterStart
        onlyBeforeEnd
        onlyNotCanceled
        onlyNotBeneficiary
    {   
        address _bidder = msg.sender;
        require(erc20Token.balanceOf(_bidder) >= amount, 'Insufficiant ERC20 token balance!'); 
        require(erc20Token.allowance(_bidder, address(this)) >= amount, 'Approve ERC20 tokens first!');      

        // calculate the user's total bid based on the current amount they've sent to the contract
        // plus whatever has been sent with this transaction
        uint newBid = fundsByBidder[_bidder].add(amount);

        // reject payments of less than floor price
        require(newBid >= floorPrice, 'Bid Token amount too low!, amount should be above floor price');

         // if the user isn't even willing to overbid the highest binding bid, there's nothing for us
        // to do except revert the transaction.
        if (newBid <= highestBindingBid) revert('overbid the highest binding bid!');

        // grab the previous highest bid (before updating fundsByBidder, in case msg.sender is the
        // highestBidder and is just increasing their maximum bid).
        uint highestBid = fundsByBidder[highestBidder];

        fundsByBidder[_bidder] = newBid;

        if (newBid <= highestBid) {
            // if the user has overbid the highestBindingBid but not the highestBid, we simply
            // increase the highestBindingBid and leave highestBidder alone.

            // note that this case is impossible if msg.sender == highestBidder because you can never
            // bid less ETH than you've already bid.

            highestBindingBid = min(newBid.add(etherToWei(1)), highestBid);
        } else {
            // if msg.sender is already the highest bidder, they must simply be wanting to raise
            // their maximum bid, in which case we shouldn't increase the highestBindingBid.

            // if the user is NOT highestBidder, and has overbid highestBid completely, we set them
            // as the new highestBidder and recalculate highestBindingBid.

            if (_bidder != highestBidder) {
                highestBidder = _bidder;
                highestBindingBid = min(newBid, highestBid.add(etherToWei(1)));
            }
            highestBid = newBid;
        }                 
               
        // ERC20 token transfer from bidder to current contract address
        erc20Token.transferFrom(_bidder, address(this), amount);
        addNewBidder(_bidder);
        emit LogBid(_bidder, amount, highestBidder, highestBid, highestBindingBid);
    }

    function addNewBidder(address bidder) internal virtual
    {
        bool alreadyBidder; 
        for (uint256 i = 0; i < bidders.length; i++) {
            if(msg.sender == bidders[i]) {alreadyBidder = true; break;}
        }
        if(!alreadyBidder) bidders.push(bidder);
    }

    function min(uint a, uint b)
        private
        pure
        returns (uint)
    {
        if (a < b) return a;
        return b;
    }

    function withdraw() external
        nonReentrant
        onlyHasCanceled
        onlyNotBeneficiary
        onlyBidder
    {
        address withdrawalAccount;
        uint256 withdrawalAmount;        

        withdrawalAccount = _msgSender();
        withdrawalAmount = fundsByBidder[withdrawalAccount];

        require(withdrawalAmount > 0, 'You have already withdrawal your funds!');
        fundsByBidder[withdrawalAccount] -= withdrawalAmount;

        //withdraw the ERC20 tokens paid for bid
        erc20Token.transfer(withdrawalAccount, withdrawalAmount);
        emit LogWithdrawal(withdrawalAccount, withdrawalAmount);
    }

    function getHighestBid() public       
        view returns (uint256)
    {
        return fundsByBidder[highestBidder];
    }

    function getMyBid() public
        view returns (uint256)
    {
        return fundsByBidder[_msgSender()];
    }

    function getAuctionStatus() public
        view returns (string memory )
    {
        if( canceled ) return 'canceled';
        if( block.timestamp > endTime ) return 'ended';
        if( block.timestamp < startTime ) return 'not-started';
        return 'running';
    }

    function getTokenReddemCount(uint256 _tokenId) public
        view returns (uint256)
    {
        return tokenRedeemed[_tokenId];
    }

    function getFeePercent() external 
        onlyOwner      
        view returns (uint256)
    {
        return feePercent;
    }

    function tokenList() external 
        onlyOwner
        onlyCompleted
        view returns (uint256[] memory) 
    {
        return tokensAllowed;
    }

    function bidderList() external 
        onlyOwner
        onlyAfterStart
        view returns (address[] memory) 
    {
        return bidders;
    }

    function winnerList() external
        onlyOwner
        view returns (address[] memory)
    {
        return _winnerList();
    }

    function etherToWei(uint valueEther) internal pure returns (uint)
    {
       return valueEther*(10**18);
    }

    function onERC721Received(
        address,
        address,
        uint256 _tokenId,
        bytes memory
    ) public virtual override returns (bytes4) {

        require(tokenIssue > tokensAllowed.length, 'Token allowance has reached the maximum!');
        tokensAllowed.push(_tokenId);
        return this.onERC721Received.selector;
    }

    function redeemNFD(uint256 _tokenId) external virtual
        onlyOwner
        onlyCompleted
    {   
        bool tokenAllowed;
        for( uint256 i = 0; i < tokensAllowed.length; i++ ) 
        {
            if(tokensAllowed[i] == _tokenId) {
                tokenAllowed = true;
                break;
            }
        }
        require(tokenAllowed, 'Token is not allowed for redeemed!');
        require( redeemQty > tokenRedeemed[_tokenId], "User have reached the maximum allowance!");
        tokenRedeemed[_tokenId] = tokenRedeemed[_tokenId].add(1);
        emit TokenRedeemed( _tokenId,  tokenRedeemed[_tokenId]);        
    }

    function _winnersListPrepare(uint _priceMargin, address[] memory _winners, uint _winnerIndex) internal 
        view 
        returns (address[] memory)
    {        
        uint priceFilter = fundsByBidder[highestBidder].sub(etherToWei(_priceMargin));
        for (uint j = 0; j < bidders.length; j++) {
            if( _winnerIndex == _winners.length ) break;
            address bidder = bidders[j];
            if( fundsByBidder[bidder] >= priceFilter ){
                bool duplicateWinner;
                for (uint k = 0; k <= _winnerIndex; k++) {
                    if( bidder == _winners[k] ) duplicateWinner = true;
                }
                if(!duplicateWinner){                        
                    _winners[_winnerIndex] = bidder;
                    ++_winnerIndex;
                }
            }                
        }
        if( _winnerIndex != _winners.length ) _winnersListPrepare(_priceMargin.add(1), _winners, _winnerIndex);
        return _winners; 
    }

    function _winnerList() internal 
        virtual
        onlyCompleted
        view 
        returns (address[] memory) 
    {        
        require(bidders.length > 0, 'No bidder found, winner list can not be generate!');
        uint256 maxWinners = bidders.length < tokenIssue ? bidders.length : tokenIssue;
        address[] memory winners = new address[](maxWinners); 
        winners[0] = highestBidder;
        if( maxWinners == 1 ) return winners;
        return _winnersListPrepare(1,winners, 1);
    }

    function cancelAuction() external
        nonReentrant
        onlyOwner
        onlyBeforeEnd
        onlyNotCanceled
        returns (bool success)
    {
        canceled = true;
        emit LogCanceled(true);
        return true;
    }

    function refund() external
        nonReentrant
        onlyNotBeneficiary
        onlyCompleted
        onlyBidder
        onlyNonWinner
    {
        uint256 withdrawalAmount = fundsByBidder[_msgSender()];
        require(withdrawalAmount > 0, 'You already have refund back!');
        fundsByBidder[_msgSender()] -= withdrawalAmount;
        
        //refund the ERC20 tokens to bidder, paid for bid but not become winner
        erc20Token.transfer(_msgSender(), withdrawalAmount);
        emit LogRefund(_msgSender(), withdrawalAmount);
    }

    function collectToken(uint _tokenId, address _virtuousToken) external
        nonReentrant
        onlyNotBeneficiary
        onlyCompleted
        onlyWinner
        onlyRewardNotCollected
    {   
        IERC721 virtuousToken = IERC721(_virtuousToken);
        require(virtuousToken.balanceOf(address(this)) > 0, "Caller must own nft");
        require(virtuousToken.ownerOf(_tokenId) == address(this), "You must own the token");
        rewardCollected[_msgSender()] = true;
        virtuousToken.safeTransferFrom(address(this), _msgSender(), _tokenId);
        emit TokenCollected( _msgSender(),  _tokenId);
    }

    function collectFund() external
        nonReentrant
        onlyBeneficiaryOrOwner
        onlyNotCollected
    {   
        address[] memory winners = _winnerList();
        uint256 merchantFund;
        uint256 marketplaceRoyalty;
        for( uint256 i = 0; i < winners.length; i++ ) 
        {   
            address winner = winners[i];
            uint256 amount = fundsByBidder[winner];                   
            uint256 marketplaceFee = amount.div(100).mul(feePercent);
            marketplaceRoyalty = marketplaceRoyalty.add(marketplaceFee);
            uint256 merchantFee = amount.sub(marketplaceFee);
            merchantFund = merchantFund.add(merchantFee);            
            fundsByBidder[winner] -= amount;
        }
        fundCollected = true;
        erc20Token.transfer(beneficiary, merchantFund);
        erc20Token.transfer(owner(), marketplaceRoyalty);
        emit FundCollected(merchantFund, marketplaceRoyalty);
    }

    receive() external payable 
    {
        emit Received(_msgSender(), msg.value);
    }

    fallback() external payable {
        emit Received(_msgSender(), msg.value);
    }

    modifier onlyNotBeneficiary {
        if (_msgSender() == beneficiary) revert('Beneficiary can not perform the action!');
        _;
    }

    modifier onlyBeneficiaryOrOwner {
        require( _msgSender() == beneficiary || _msgSender() == owner(), 'Beneficiary / Owner can only perform the action!');
        _;
    }

    modifier onlyAfterStart {
        if (block.timestamp < startTime) revert('Auction yet not start!');
        _;
    }

    modifier onlyBeforeEnd {
        if (block.timestamp > endTime) revert('Auction already ended!');
        _;
    }

    modifier onlyNotCanceled {
        if (canceled) revert('Auction already canceled!');
        _;
    }

    modifier onlyHasCanceled {
        if (!canceled) revert('Auction is not canceled!');
        _;
    }

    modifier onlyCompleted {
        require(block.timestamp > endTime && !canceled, "Auction is not ended yet!");
        _;
    }

    modifier onlyNotCollected {
        require(!fundCollected, "Funds already collected!");
        _;
    }

    modifier onlyBidder {
        require(fundsByBidder[_msgSender()] > 0, 'You are not a valid bidder!');
        _;
    }

    modifier onlyNonWinner {
        address[] memory winners = _winnerList();
        for( uint256 i = 0; i < winners.length; i++ ) {
            if( _msgSender() == winners[i] ) revert('You are winner, you can not perform this action!');
        }
        _;
    }

    modifier onlyWinner {
        address[] memory winners = _winnerList();
        bool winner;
        for( uint256 i = 0; i < winners.length; i++ ) {
            if( _msgSender() == winners[i] ){ winner = true; break; }
        }
        require(winner, 'You are not a winner!');
        _;
    }

    modifier onlyRewardNotCollected {
        require(!rewardCollected[_msgSender()], 'You have already collected your token!');
        _;
    }
}

contract AuctionFactory is Ownable, ReentrancyGuard {
    address[] public auctions;
    event AuctionCreated(address auctionContract, uint numAuctions, address[] allAuctions);

    function createAuction(IERC20 _erc20Token, address _beneficiary, uint256 _floorPrice, uint256 _startTime, uint256 _endTime, uint256 _tokenIssue, uint256 _feePercent, uint256 _redeemQty) public
        onlyOwner
    {
        Auction newAuction = new Auction(_erc20Token, _beneficiary, _floorPrice, _startTime, _endTime, _tokenIssue, _feePercent, _redeemQty);
        auctions.push(address(newAuction));
        emit AuctionCreated(address(newAuction), auctions.length, auctions);
    }

    function allAuctions() public view returns (address[] memory) {
        return auctions;
    }
} 
        

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (access/Ownable.sol)

pragma solidity ^0.8.0;

import "../utils/Context.sol";

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

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

    /**
     * @dev Initializes the contract setting the deployer as the initial owner.
     */
    constructor() {
        _transferOwnership(_msgSender());
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _transferOwnership(address(0));
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Can only be called by the current owner.
     */
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _transferOwnership(newOwner);
    }

    /**
     * @dev Transfers ownership of the contract to a new account (`newOwner`).
     * Internal function without access restriction.
     */
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (security/ReentrancyGuard.sol)

pragma solidity ^0.8.0;

/**
 * @dev Contract module that helps prevent reentrant calls to a function.
 *
 * Inheriting from `ReentrancyGuard` will make the {nonReentrant} modifier
 * available, which can be applied to functions to make sure there are no nested
 * (reentrant) calls to them.
 *
 * Note that because there is a single `nonReentrant` guard, functions marked as
 * `nonReentrant` may not call one another. This can be worked around by making
 * those functions `private`, and then adding `external` `nonReentrant` entry
 * points to them.
 *
 * TIP: If you would like to learn more about reentrancy and alternative ways
 * to protect against it, check out our blog post
 * https://blog.openzeppelin.com/reentrancy-after-istanbul/[Reentrancy After Istanbul].
 */
abstract contract ReentrancyGuard {
    // Booleans are more expensive than uint256 or any type that takes up a full
    // word because each write operation emits an extra SLOAD to first read the
    // slot's contents, replace the bits taken up by the boolean, and then write
    // back. This is the compiler's defense against contract upgrades and
    // pointer aliasing, and it cannot be disabled.

    // The values being non-zero value makes deployment a bit more expensive,
    // but in exchange the refund on every call to nonReentrant will be lower in
    // amount. Since refunds are capped to a percentage of the total
    // transaction's gas, it is best to keep them low in cases like this one, to
    // increase the likelihood of the full refund coming into effect.
    uint256 private constant _NOT_ENTERED = 1;
    uint256 private constant _ENTERED = 2;

    uint256 private _status;

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and making it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC20/IERC20.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC20 standard as defined in the EIP.
 */
interface IERC20 {
    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);

    /**
     * @dev Returns the amount of tokens in existence.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);

    /**
     * @dev Moves `amount` tokens from the caller's account to `to`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address to, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `from` to `to` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 amount
    ) external returns (bool);
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC721/IERC721.sol)

pragma solidity ^0.8.0;

import "../../utils/introspection/IERC165.sol";

/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
    /**
     * @dev Emitted when `tokenId` token is transferred from `from` to `to`.
     */
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
     */
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
     */
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    /**
     * @dev Returns the number of tokens in ``owner``'s account.
     */
    function balanceOf(address owner) external view returns (uint256 balance);

    /**
     * @dev Returns the owner of the `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function ownerOf(uint256 tokenId) external view returns (address owner);

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        bytes calldata data
    ) external;

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
     * are aware of the ERC721 protocol to prevent tokens from being forever locked.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId
    ) external;

    /**
     * @dev Transfers `tokenId` token from `from` to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) external;

    /**
     * @dev Gives permission to `to` to transfer `tokenId` token to another account.
     * The approval is cleared when the token is transferred.
     *
     * Only a single account can be approved at a time, so approving the zero address clears previous approvals.
     *
     * Requirements:
     *
     * - The caller must own the token or be an approved operator.
     * - `tokenId` must exist.
     *
     * Emits an {Approval} event.
     */
    function approve(address to, uint256 tokenId) external;

    /**
     * @dev Approve or remove `operator` as an operator for the caller.
     * Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
     *
     * Requirements:
     *
     * - The `operator` cannot be the caller.
     *
     * Emits an {ApprovalForAll} event.
     */
    function setApprovalForAll(address operator, bool _approved) external;

    /**
     * @dev Returns the account approved for `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function getApproved(uint256 tokenId) external view returns (address operator);

    /**
     * @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
     *
     * See {setApprovalForAll}
     */
    function isApprovedForAll(address owner, address operator) external view returns (bool);
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (token/ERC721/IERC721Receiver.sol)

pragma solidity ^0.8.0;

/**
 * @title ERC721 token receiver interface
 * @dev Interface for any contract that wants to support safeTransfers
 * from ERC721 asset contracts.
 */
interface IERC721Receiver {
    /**
     * @dev Whenever an {IERC721} `tokenId` token is transferred to this contract via {IERC721-safeTransferFrom}
     * by `operator` from `from`, this function is called.
     *
     * It must return its Solidity selector to confirm the token transfer.
     * If any other value is returned or the interface is not implemented by the recipient, the transfer will be reverted.
     *
     * The selector can be obtained in Solidity with `IERC721Receiver.onERC721Received.selector`.
     */
    function onERC721Received(
        address operator,
        address from,
        uint256 tokenId,
        bytes calldata data
    ) external returns (bytes4);
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC721/utils/ERC721Holder.sol)

pragma solidity ^0.8.0;

import "../IERC721Receiver.sol";

/**
 * @dev Implementation of the {IERC721Receiver} interface.
 *
 * Accepts all token transfers.
 * Make sure the contract is able to use its token with {IERC721-safeTransferFrom}, {IERC721-approve} or {IERC721-setApprovalForAll}.
 */
contract ERC721Holder is IERC721Receiver {
    /**
     * @dev See {IERC721Receiver-onERC721Received}.
     *
     * Always returns `IERC721Receiver.onERC721Received.selector`.
     */
    function onERC721Received(
        address,
        address,
        uint256,
        bytes memory
    ) public virtual override returns (bytes4) {
        return this.onERC721Received.selector;
    }
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/Context.sol)

pragma solidity ^0.8.0;

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

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/introspection/IERC165.sol)

pragma solidity ^0.8.0;

/**
 * @dev Interface of the ERC165 standard, as defined in the
 * https://eips.ethereum.org/EIPS/eip-165[EIP].
 *
 * Implementers can declare support of contract interfaces, which can then be
 * queried by others ({ERC165Checker}).
 *
 * For an implementation, see {ERC165}.
 */
interface IERC165 {
    /**
     * @dev Returns true if this contract implements the interface defined by
     * `interfaceId`. See the corresponding
     * https://eips.ethereum.org/EIPS/eip-165#how-interfaces-are-identified[EIP section]
     * to learn more about how these ids are created.
     *
     * This function call must use less than 30 000 gas.
     */
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}
          

// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.6.0) (utils/math/SafeMath.sol)

pragma solidity ^0.8.0;

// CAUTION
// This version of SafeMath should only be used with Solidity 0.8 or later,
// because it relies on the compiler's built in overflow checks.

/**
 * @dev Wrappers over Solidity's arithmetic operations.
 *
 * NOTE: `SafeMath` is generally not needed starting with Solidity 0.8, since the compiler
 * now has built in overflow checking.
 */
library SafeMath {
    /**
     * @dev Returns the addition of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, with an overflow flag.
     *
     * _Available since v3.4._
     */
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            // Gas optimization: this is cheaper than requiring 'a' not being zero, but the
            // benefit is lost if 'b' is also tested.
            // See: https://github.com/OpenZeppelin/openzeppelin-contracts/pull/522
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

    /**
     * @dev Returns the division of two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers, with a division by zero flag.
     *
     * _Available since v3.4._
     */
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

    /**
     * @dev Returns the addition of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `+` operator.
     *
     * Requirements:
     *
     * - Addition cannot overflow.
     */
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting on
     * overflow (when the result is negative).
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return a - b;
    }

    /**
     * @dev Returns the multiplication of two unsigned integers, reverting on
     * overflow.
     *
     * Counterpart to Solidity's `*` operator.
     *
     * Requirements:
     *
     * - Multiplication cannot overflow.
     */
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator.
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting when dividing by zero.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return a % b;
    }

    /**
     * @dev Returns the subtraction of two unsigned integers, reverting with custom message on
     * overflow (when the result is negative).
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {trySub}.
     *
     * Counterpart to Solidity's `-` operator.
     *
     * Requirements:
     *
     * - Subtraction cannot overflow.
     */
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

    /**
     * @dev Returns the integer division of two unsigned integers, reverting with custom message on
     * division by zero. The result is rounded towards zero.
     *
     * Counterpart to Solidity's `/` operator. Note: this function uses a
     * `revert` opcode (which leaves remaining gas untouched) while Solidity
     * uses an invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }

    /**
     * @dev Returns the remainder of dividing two unsigned integers. (unsigned integer modulo),
     * reverting with custom message when dividing by zero.
     *
     * CAUTION: This function is deprecated because it requires allocating memory for the error
     * message unnecessarily. For custom revert reasons use {tryMod}.
     *
     * Counterpart to Solidity's `%` operator. This function uses a `revert`
     * opcode (which leaves remaining gas untouched) while Solidity uses an
     * invalid opcode to revert (consuming all remaining gas).
     *
     * Requirements:
     *
     * - The divisor cannot be zero.
     */
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}