// File: /contracts/CompetitionETHAsPrize.sol



// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.4;

import "@openzeppelin/contracts/access/AccessControl.sol";
import "@openzeppelin/contracts/token/ERC721/IERC721.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@chainlink/contracts/src/v0.8/VRFConsumerBase.sol";
import "@openzeppelin/contracts/utils/math/Math.sol";

import "./BlackListManager.sol";

/// @title Raffles manager
/// @author Luis Pando
/// @notice It consumes VRF v1 from Chainlink. It has the role
/// "operator" that is the one used by a backend app to make some calls
/// @dev It saves in an ordered array the player wallet and the current
/// entries count. So buying entries has a complexity of O(1)
/// For calculating the winner, from the huge random number generated by Chainlink
/// a normalized random is generated by using the module method, adding 1 to have
/// a random from 1 to entriesCount.
/// So next step is to perform a binary search on the ordered array to get the
/// player O(log n)
/// Example:
/// 0 -> { 1, player1} as player1 buys 1 entry
/// 1 -> {51, player2} as player2 buys 50 entries
/// 2 -> {52, player3} as player3 buys 1 entry
/// 3 -> {53, player4} as player4 buys 1 entry
/// 4 -> {153, player5} as player5 buys 100 entries
/// So the setWinner method performs a binary search on that sorted array to get the upper bound.
/// If the random number generated is 150, the winner is player5. If the random number is 20, winner is player2

contract CompetitionETHAsPrize is
    AccessControl,
    ReentrancyGuard,
    VRFConsumerBase
{
    ////////// CHAINLINK VRF v1 /////////////////
    bytes32 internal keyHash; // chainlink
    uint256 internal fee; // fee paid in LINK to chainlink. 0.1 in Rinkeby, 2 in mainnet

    struct RandomResult {
        uint256 randomNumber; // random number generated by chainlink.
        uint256 nomalizedRandomNumber; // random number % entriesLength + 1. So between 1 and entries.length
    }

    // event sent when the random number is generated by the VRF
    event RandomNumberCreated(
        uint256 indexed idFromMetawin,
        uint256 randomNumber,
        uint256 normalizedRandomNumber
    );

    struct RaffleInfo {
        uint256 id; // raffleId
        uint256 size; // length of the entries array of that raffle
    }

    mapping(uint256 => RandomResult) public requests;
    // map the requestId created by chainlink with the raffle info passed as param when calling getRandomNumber()
    mapping(bytes32 => RaffleInfo) public chainlinkRaffleInfo;

    /////////////// END CHAINKINK VRF V1 //////////////

    // Event sent when the raffle is created by the operator
    event RaffleCreated(uint256 indexed raffleId, uint256 indexed prizeAmount);
    // Event sent when the ETH is staked
    event RaffleStarted(uint256 indexed raffleId, address indexed seller);
    // Event sent when the raffle is finished (either early cashout or successful completion)
    event RaffleEnded(
        uint256 indexed raffleId,
        address indexed winner,
        uint256 amountRaised,
        uint256 randomNumber
    );
    // Event sent when one or more entries are sold (info from the price structure)
    event EntrySold(
        uint256 indexed raffleId,
        address indexed buyer,
        uint256 currentSize,
        uint256 priceStructureId
    );
    // Event sent when a free entry is added by the operator
    event FreeEntry(
        uint256 indexed raffleId,
        address[] buyer,
        uint256 amount,
        uint256 currentSize
    );
    // Event sent when a raffle is asked to cancel by the operator
    event RaffleCancelled(uint256 indexed raffleId, uint256 amountRaised);
    // The raffle is closed successfully and the platform receives the fee
    event FeeTransferredToPlatform(
        uint256 indexed raffleId,
        uint256 amountTransferred
    );
    // When the raffle is asked to be cancelled and 30 days have passed, the operator can call a method
    // to transfer the remaining funds and this event is emitted
    event RemainingFundsTransferred(
        uint256 indexed raffleId,
        uint256 amountInWeis
    );
    // When the raffle is asked to be cancelled and 30 days have not passed yet, the players can call a
    // method to refund the amount spent on the raffle and this event is emitted
    event Refund(
        uint256 indexed raffleId,
        uint256 amountInWeis,
        address indexed player
    );
    event EarlyCashoutTriggered(uint256 indexed raffleId, uint256 amountRaised);
    event SetWinnerTriggered(uint256 indexed raffleId, uint256 amountRaised);
    event StatusChangedInEmergency(uint256 indexed raffleId, uint256 newStatus);
    // Emitted when an entry is cancelled
    event EntryCancelled(uint256 indexed raffleId, uint256 amountOfEntriesCanceled, address player);
    
    /* every raffle has an array of price structure (max size = 5) with the different 
    prices for the different entries bought. The price for 1 entry is different than 
    for 5 entries where there is a discount*/
    struct PriceStructure {
        uint256 id;
        uint256 numEntries;
        uint256 price;
    }
    mapping(uint256 => PriceStructure[5]) public prices;

    // Every raffle has a funding structure.
    struct FundingStructure {
        uint256 minimumFundsInWeis;
        uint256 desiredFundsInWeis;
    }
    mapping(uint256 => FundingStructure) public fundingList;

    // In order to calculate the winner, in this struct is saved for each bought the data
    struct EntriesBought {
        uint256 currentEntriesLength; // current amount of entries bought in the raffle
        address player; // wallet address of the player
    }
    // every raffle has a sorted array of EntriesBought. Each element is created when calling
    // either buyEntry or giveBatchEntriesForFree
    mapping(uint256 => EntriesBought[]) public entriesList;

    // Main raffle data struct
    struct RaffleStruct {
        STATUS status; // status of the raffle. Can be created, accepted, ended, etc
        uint256 maxEntries; // maximum number of entries allowed per user, to avoid abuse
        uint256 amountOfETH; // Amount of ETH of the prize
        address winner; // address of thed winner of the raffle. Address(0) if no winner yet
        uint256 randomNumber; // normalized (0-Entries array size) random number generated by the VRF
        uint256 amountRaised; // funds raised so far in wei
        address seller; // address of the seller of the ETH
        uint256 platformPercentage; // percentage of the funds raised that goes to the platform
        uint256 entriesLength; // to easy frontend, the length of the entries array is saved here
        uint256 cancellingDate;
        address[] collectionWhitelist; // addresses of the required nfts. Will be empty if no NFT is required to buy
        ENTRY_TYPE entryType;
    }
    // The main structure is an array of raffles
    RaffleStruct[] public raffles;

    // Map that contains the number of entries each user has bought, to prevent abuse, and the claiming info
    struct ClaimStruct {
        uint256 numEntriesPerUser;
        uint256 amountSpentInWeis;
        bool claimed;
    }
    mapping(bytes32 => ClaimStruct) public claimsData;

    // Map with the addresses linked to a particular raffle + nft
    mapping(bytes32 => address) public requiredNFTWallets;

    // All the different status a rafVRFCoordinatorfle can have
    enum STATUS {
        CREATED, // the operator creates the raffle
        ACCEPTED, // the seller stakes the eth for the raffle
        EARLY_CASHOUT, // the seller wants to cashout early
        CANCELLED, // the operator cancels the raffle and transfer the remaining funds after 30 days passes
        CLOSING_REQUESTED, // the operator sets a winner
        ENDED, // the raffle is finished, and funds were transferred
        CANCEL_REQUESTED // operator asks to cancel the raffle. Players has 30 days to ask for a refund
    }

    enum ENTRY_TYPE {
        ONLY_DIRECTLY,
        ONLY_EXTERNAL_CONTRACT,
        MIXED
    }

    // The operator role is operated by a backend application
    bytes32 public constant OPERATOR_ROLE = keccak256("OPERATOR");
    // requested by Hamburger. Role for the buy method of the hamburger (only that contract)
    bytes32 public constant MINTERCONTRACT_ROLE = keccak256("MINTERCONTRACT");

    // address of the wallet controlled by the platform that will receive the platform fee
    address payable public destinationWallet =
        payable(0xEda703919A528481F4F11423a728300dCaBF441F);

    // contract that contains the black list
    BlackListManager blackListManager;

    constructor(
        address _blacklistManager,
        address _vrfCoordinator,
        address _linkToken,
        bytes32 _keyHash,
        bool _mainetFee
    )
        VRFConsumerBase(
            _vrfCoordinator, // VRF Coordinator
            _linkToken // LINK Token
        )
    {
        _setupRole(OPERATOR_ROLE, 0x13503B622abC0bD30A7e9687057DF6E8c42Fb928);
        _setupRole(DEFAULT_ADMIN_ROLE, msg.sender);

        keyHash = _keyHash;
        if (_mainetFee == true)
            fee = 2 * 10**18; // in mainnet, the fee must be 2 LINK
        else fee = 0.1 * 10**18; // 0.1 LINK In Rinkeby and Goerli

        blackListManager = BlackListManager(_blacklistManager);
    }

    /// @dev this is the method that will be called by the smart contract to get a random number
    /// @param _id Id of the raffle
    /// @param _entriesSize length of the entries array of that raffle
    /// @return requestId Id generated by chainlink
    function getRandomNumber(uint256 _id, uint256 _entriesSize)
        internal
        returns (bytes32 requestId)
    {
        require(
            LINK.balanceOf(address(this)) >= fee,
            "Not enough LINK - fill contract with faucet"
        );
        bytes32 result = requestRandomness(keyHash, fee);
        // result is the requestId generated by chainlink. It is saved in a map linked to the param id
        chainlinkRaffleInfo[result] = RaffleInfo({id: _id, size: _entriesSize});
        return result;
    }

    /// @dev Callback function used by VRF Coordinator. Is called by chainlink
    /// the random number generated is normalized to the size of the entries array, and an event is
    /// generated, that will be listened by the platform backend to be checked if corresponds to a
    /// member of the MW community, and if true will call transferFunds
    /// @param requestId id generated previously (on method getRandomNumber by chainlink)
    /// @param randomness random number (huge) generated by chainlink
    function fulfillRandomness(bytes32 requestId, uint256 randomness)
        internal
        override
    {
        // randomness is the actual random number. Now extract from the aux map the original param id of the call
        RaffleInfo memory raffleInfo = chainlinkRaffleInfo[requestId];
        // save the random number on the map with the original id as key
        uint256 normalizedRandomNumber = (randomness % raffleInfo.size) + 1;

        RandomResult memory result = RandomResult({
            randomNumber: randomness,
            nomalizedRandomNumber: normalizedRandomNumber
        });

        requests[raffleInfo.id] = result;

        // send the event with the original id and the random number
        emit RandomNumberCreated(
            raffleInfo.id,
            randomness,
            normalizedRandomNumber
        );

        transferFunds(raffleInfo.id, normalizedRandomNumber);
    }

    //////////////////////////////////////////////

    /// @param _desiredFundsInWeis the amount the seller would like to get from the raffle
    /// @param _maxEntriesPerUser To avoid whales, the number of entries an user can have is limited
    /// @param _amountOfETH Amount of ETH of the prize
    /// @param _minimumFundsInWeis The mininum amount required for the raffle to set a winner
    /// @param _prices Array of prices and amount of entries the customer could purchase
    /// @param _commissionInBasicPoints commission for the platform, in basic points
    /// @param _collectionWhitelist array with the required collections to participate in the raffle. Empty if there is no collection
    /// @param _entryType enum with the kind of entry ONLY_DIRECTLY, ONLY_EXTERNAL_CONTRACT or BOTH
    /// @notice Creates a raffle
    /// @dev creates a raffle struct and push it to the raffles array. Some data is stored in the funding data structure
    /// sends an event when finished
    /// @return raffleId
    function createRaffle(
        uint256 _desiredFundsInWeis,
        uint256 _maxEntriesPerUser,
        uint256 _amountOfETH,
        uint256 _minimumFundsInWeis,
        PriceStructure[] calldata _prices,
        uint256 _commissionInBasicPoints,
        address[] calldata _collectionWhitelist,
        ENTRY_TYPE _entryType
    ) external onlyRole(OPERATOR_ROLE) returns (uint256) {
        require(_maxEntriesPerUser > 0, "maxEntries is 0");
        require(_amountOfETH > 0, "Prize is 0");
        require(_commissionInBasicPoints <= 5000, "commission too high");

        RaffleStruct memory raffle = RaffleStruct({
            status: STATUS.CREATED,
            maxEntries: _maxEntriesPerUser,
            amountOfETH: _amountOfETH,
            winner: address(0),
            randomNumber: 0,
            amountRaised: 0,
            seller: msg.sender,
            platformPercentage: _commissionInBasicPoints,
            entriesLength: 0,
            cancellingDate: 0,
            collectionWhitelist: _collectionWhitelist,
            entryType: _entryType
        });

        raffles.push(raffle);

        require(_prices.length > 0, "No prices");

        for (uint256 i = 0; i < _prices.length; i++) {
            require(_prices[i].numEntries > 0, "numEntries is 0");

            PriceStructure memory p = PriceStructure({
                id: _prices[i].id,
                numEntries: _prices[i].numEntries,
                price: _prices[i].price
            });

            prices[raffles.length - 1][i] = p;
        }

        fundingList[raffles.length - 1] = FundingStructure({
            minimumFundsInWeis: _minimumFundsInWeis,
            desiredFundsInWeis: _desiredFundsInWeis
        });

        emit RaffleCreated(raffles.length - 1, _amountOfETH);

        return raffles.length - 1;
    }

    /* * Example of a price structure:
1 ticket 0.02
5 tickets 0.018 (10% discount)
10 tickets 0.16  (20% discount)
25 tickets 0.35  (30% discount) 
50 tickets 0.6 (40% discount)
*/
    /// @param _idRaffle raffleId
    /// @param _id Id of the price structure
    /// @return the price structure of that particular Id + raffle
    /// @dev Returns the price structure, used in the frontend
    function getPriceStructForId(uint256 _idRaffle, uint256 _id)
        internal
        view
        returns (PriceStructure memory)
    {
        for (uint256 i = 0; i < 5; i++) {
            if (prices[_idRaffle][i].id == _id) {
                return prices[_idRaffle][i];
            }
        }
        return PriceStructure({id: 0, numEntries: 0, price: 0});
    }

    /// @param _raffleId Id of the raffle
    /// @dev Anyone can stake. The owner must have approved this contract before. Otherwise will revert when transferring from the owner
    function stakeETH(uint256 _raffleId) external payable nonReentrant {
        RaffleStruct storage raffle = raffles[_raffleId];
        // Check if the raffle is already created
        require(raffle.status == STATUS.CREATED, "Raffle not CREATED");
        // check the amount staked is the correct
        require(raffle.amountOfETH == msg.value, "Prize not staked");

        raffle.status = STATUS.ACCEPTED;
        raffle.seller = msg.sender;

        emit RaffleStarted(_raffleId, msg.sender);
    }

    /// @dev callable by players. Depending on the number of entries assigned to the price structure the player buys (_id parameter)
    /// one or more entries will be assigned to the player.
    /// Also it is checked the maximum number of entries per user is not reached
    /// As the method is payable, in msg.value there will be the amount paid by the user
    /// @notice If the operator set requiredNFTs when creating the raffle, only the owners of nft on that collection can make a call to this method. This will be
    /// used for special raffles
    /// @param _raffleId: id of the raffle
    /// @param _id: id of the price structure
    /// @param _collection: collection of the tokenId used. Not used if there is no required nft on the raffle
    /// @param _tokenIdUsed: id of the token used in private raffles (to avoid abuse can not be reused on the same raffle)
    function buyEntry(
        uint256 _raffleId,
        uint256 _id,
        address _collection,
        uint256 _tokenIdUsed
    ) external payable nonReentrant {
        RaffleStruct storage raffle = raffles[_raffleId];
        require(raffle.seller != msg.sender, "Seller cannot buy");
        require(
            raffle.entryType == ENTRY_TYPE.MIXED ||
                raffle.entryType == ENTRY_TYPE.ONLY_DIRECTLY,
            "Entry type not allowed"
        );
        require(
            blackListManager.isBlackListed(msg.sender) == false,
            "Blacklisted!"
        );
        // if the raffle requires an nft
        if (raffle.collectionWhitelist.length > 0) {
            bool hasRequiredCollection = false;
            for (uint256 i = 0; i < raffle.collectionWhitelist.length; i++) {
                if (raffle.collectionWhitelist[i] == _collection) {
                    hasRequiredCollection = true;
                    break;
                }
            }
            require(
                hasRequiredCollection == true,
                "Not in required collection"
            );
            IERC721 requiredNFT = IERC721(_collection);
            require(
                requiredNFT.ownerOf(_tokenIdUsed) == msg.sender,
                "Not the owner of tokenId"
            );
            bytes32 hashRequiredNFT = keccak256(
                abi.encode(_collection, _raffleId, _tokenIdUsed)
            );
            // check the tokenId has not been using yet in the raffle, to avoid abuse
            if (requiredNFTWallets[hashRequiredNFT] == address(0)) {
                requiredNFTWallets[hashRequiredNFT] = msg.sender;
            } else
                require(
                    requiredNFTWallets[hashRequiredNFT] == msg.sender,
                    "tokenId used"
                );
        }

        require(msg.sender != address(0), "msg.sender is null"); // 37
        require(_id > 0, "howMany is 0");
        require(raffle.status == STATUS.ACCEPTED, "Raffle is not in accepted"); // 1808
        PriceStructure memory priceStruct = getPriceStructForId(_raffleId, _id);
        require(priceStruct.numEntries > 0, "id not supported");
        require(
            msg.value == priceStruct.price,
            "msg.value must be equal to the price"
        ); // 1722

        bytes32 hash = keccak256(abi.encode(msg.sender, _raffleId));
        // check there are enough entries left for this particular user
        require(
            claimsData[hash].numEntriesPerUser + priceStruct.numEntries <=
                raffle.maxEntries,
            "Bought too many entries"
        );

        EntriesBought memory entryBought = EntriesBought({
            player: msg.sender,
            currentEntriesLength: raffle.entriesLength + priceStruct.numEntries
        });
        entriesList[_raffleId].push(entryBought);

        raffle.amountRaised += msg.value; // 6917 gas
        // update the field entriesLength, used in frontend to avoid making extra calls
        raffle.entriesLength = raffle.entriesLength + priceStruct.numEntries;
        //update claim data
        claimsData[hash].numEntriesPerUser += priceStruct.numEntries;
        claimsData[hash].amountSpentInWeis += msg.value;

        emit EntrySold(_raffleId, msg.sender, raffle.entriesLength, _id); // 2377
    }

    // The operator can add free entries to the raffle
    /// @param _raffleId Id of the raffle
    /// @param _freePlayers array of addresses corresponding to the wallet of the users that won a free entrie
    /// @dev only operator can make this call. Assigns a single entry per user, except if that user already reached the max limit of entries per user
    function giveBatchEntriesForFree(
        uint256 _raffleId,
        address[] memory _freePlayers
    ) external nonReentrant onlyRole(OPERATOR_ROLE) {
        require(
            raffles[_raffleId].status == STATUS.ACCEPTED,
            "Raffle is not in accepted"
        );

        uint256 freePlayersLength = _freePlayers.length;
        uint256 validPlayersCount = 0;
        for (uint256 i = 0; i < freePlayersLength; i++) {
            address entry = _freePlayers[i];
            if (
                claimsData[keccak256(abi.encode(entry, _raffleId))]
                    .numEntriesPerUser +
                    1 <=
                raffles[_raffleId].maxEntries
            ) {
                // add a new element to the entriesBought array.
                // as this method only adds 1 entry per call, the amountbought is always 1
                EntriesBought memory entryBought = EntriesBought({
                    player: entry,
                    currentEntriesLength: raffles[_raffleId].entriesLength +
                        i +
                        1
                });
                entriesList[_raffleId].push(entryBought);

                claimsData[keccak256(abi.encode(entry, _raffleId))]
                    .numEntriesPerUser++;

                ++validPlayersCount;
            }
        }

        raffles[_raffleId].entriesLength =
            raffles[_raffleId].entriesLength +
            validPlayersCount;

        emit FreeEntry(
            _raffleId,
            _freePlayers,
            freePlayersLength,
            raffles[_raffleId].entriesLength
        );
    }

    // helper method to get the winner address of a raffle
    /// @param _raffleId Id of the raffle
    /// @param _normalizedRandomNumber Generated by chainlink
    /// @return the wallet that won the raffle
    /// @dev Uses a binary search on the sorted array to retreive the winner
    /// but if the winner candidate is blacklisted, loop through the left looking for
    /// a candidate not blacklisted
    function getWinnerAddressFromRandom(
        uint256 _raffleId,
        uint256 _normalizedRandomNumber
    ) public view returns (address) {
        uint256 position = findUpperBound(
            entriesList[_raffleId],
            _normalizedRandomNumber
        );

        address candidate = entriesList[_raffleId][position].player;
        // general case
        if (candidate != address(0)) return candidate;
        // special case. The user is blacklisted, so try next on the left until find a non-blacklisted
        else {
            bool ended = false;
            uint256 i = position;
            while (
                ended == false && entriesList[_raffleId][i].player == address(0)
            ) {
                if (i == 0) i = entriesList[_raffleId].length - 1;
                else i = i - 1;
                // we came to the beginning without finding a non blacklisted player
                if (i == position) ended == true;
            }
            require(!ended, "All users blacklisted");
            return entriesList[_raffleId][i].player;
        }
    }

    /// @param array sorted array of EntriesBought. CurrentEntriesLength is the numeric field used to sort
    /// @param element uint256 to find. Goes from 1 to entriesLength
    /// @dev based on openzeppelin code (v4.0), modified to use an array of EntriesBought
    /// Searches a sorted array and returns the first index that contains a value greater or equal to element.
    /// If no such index exists (i.e. all values in the array are strictly less than element), the array length is returned. Time complexity O(log n).
    /// array is expected to be sorted in ascending order, and to contain no repeated elements.
    /// https://docs.openzeppelin.com/contracts/3.x/api/utils#Arrays-findUpperBound-uint256---uint256-
    function findUpperBound(EntriesBought[] storage array, uint256 element)
        internal
        view
        returns (uint256)
    {
        if (array.length == 0) {
            return 0;
        }

        uint256 low = 0;
        uint256 high = array.length;

        while (low < high) {
            uint256 mid = Math.average(low, high);

            // Note that mid will always be strictly less than high (i.e. it will be a valid array index)
            // because Math.average rounds down (it does integer division with truncation).
            if (array[mid].currentEntriesLength > element) {
                high = mid;
            } else {
                low = mid + 1;
            }
        }

        // At this point `low` is the exclusive upper bound. We will return the inclusive upper bound.
        if (low > 0 && array[low - 1].currentEntriesLength == element) {
            return low - 1;
        } else {
            return low;
        }
    }

    // The operator can call this method once they receive the event "RandomNumberCreated"
    // triggered by the VRF v1 consumer contract (RandomNumber.sol)
    /// @param _raffleId Id of the raffle
    /// @param _normalizedRandomNumber index of the array that contains the winner of the raffle. Generated by chainlink
    /// @notice it is the method that sets the winner and transfers funds
    /// @dev called by Chainlink callback
    function transferFunds(uint256 _raffleId, uint256 _normalizedRandomNumber)
        internal
        nonReentrant
    {
        RaffleStruct storage raffle = raffles[_raffleId];
        // Only when the raffle has been asked to be closed and the platform
        require(
            raffle.status == STATUS.EARLY_CASHOUT ||
                raffle.status == STATUS.CLOSING_REQUESTED,
            "Raffle in wrong status"
        );

        raffle.randomNumber = _normalizedRandomNumber;
        raffle.winner = getWinnerAddressFromRandom(
            _raffleId,
            _normalizedRandomNumber
        );
        raffle.status = STATUS.ENDED;

        (bool sentPrize, ) = raffle.winner.call{value: raffle.amountOfETH}("");
        require(sentPrize, "Failed to send Ether");

        uint256 amountForPlatform = (raffle.amountRaised *
            raffle.platformPercentage) / 10000;
        uint256 amountForSeller = raffle.amountRaised - amountForPlatform;
        // transfer amount (75%) to the seller.
        (bool sent, ) = raffle.seller.call{value: amountForSeller}("");
        require(sent, "Failed to send Ether");
        // transfer the amount to the platform
        (bool sent2, ) = destinationWallet.call{value: amountForPlatform}("");
        require(sent2, "Failed send Eth to MW");
        emit FeeTransferredToPlatform(_raffleId, amountForPlatform);

        emit RaffleEnded(
            _raffleId,
            raffle.winner,
            raffle.amountRaised,
            _normalizedRandomNumber
        );
    }

    // can be called by the seller at every moment once enough funds has been raised
    /// @param _raffleId Id of the raffle
    /// @notice the seller of the ETH, if the minimum amount has been reached, can call an early cashout, finishing the raffle
    /// @dev it triggers Chainlink VRF1 consumer, and generates a random number that is normalized and checked that corresponds to a MW player
    function earlyCashOut(uint256 _raffleId) external {
        RaffleStruct storage raffle = raffles[_raffleId];
        FundingStructure memory funding = fundingList[_raffleId];

        require(raffle.seller == msg.sender, "Not the seller");
        // Check if the raffle is already accepted
        require(
            raffle.status == STATUS.ACCEPTED,
            "Raffle not in accepted status"
        );
        require(
            raffle.amountRaised >= funding.minimumFundsInWeis,
            "Not enough funds raised"
        );

        raffle.status = STATUS.EARLY_CASHOUT;

        getRandomNumber(_raffleId, raffle.entriesLength);

        emit EarlyCashoutTriggered(_raffleId, raffle.amountRaised);
    }

    /// @param _raffleId Id of the raffle
    /// @notice the operator finish the raffle, if the desired funds has been reached
    /// @dev it triggers Chainlink VRF1 consumer, and generates a random number that is normalized and checked that corresponds to a MW player
    function setWinner(uint256 _raffleId)
        external
        nonReentrant
        onlyRole(OPERATOR_ROLE)
    {
        RaffleStruct storage raffle = raffles[_raffleId];
        FundingStructure storage funding = fundingList[_raffleId];
        // Check if the raffle is already accepted or is called again because early cashout failed
        require(raffle.status == STATUS.ACCEPTED, "Raffle in wrong status");
        require(
            raffle.amountRaised >= funding.minimumFundsInWeis,
            "Not enough funds raised"
        );

        require(
            funding.desiredFundsInWeis <= raffle.amountRaised,
            "Desired funds not raised"
        );
        raffle.status = STATUS.CLOSING_REQUESTED;

        // this call trigers the VRF v1 process from Chainlink
        getRandomNumber(_raffleId, raffle.entriesLength);

        emit SetWinnerTriggered(_raffleId, raffle.amountRaised);
    }

    /// @param _newAddress new address of the platform
    /// @dev Change the wallet of the platform. The one that will receive the platform fee when the raffle is closed.
    /// Only the admin can change this
    function setDestinationAddress(address payable _newAddress)
        external
        onlyRole(DEFAULT_ADMIN_ROLE)
    {
        destinationWallet = _newAddress;
    }

    /// @param _raffleId Id of the raffle
    /// @dev The operator can cancel the raffle. The ETH is sent back to the seller
    /// The raised funds are send to the destination wallet. The buyers will
    /// be refunded offchain in the metawin wallet
    function cancelRaffle(uint256 _raffleId)
        external
        nonReentrant
        onlyRole(OPERATOR_ROLE)
    {
        RaffleStruct storage raffle = raffles[_raffleId];
        //FundingStructure memory funding = fundingList[_raffleId];
        // Dont cancel twice, or cancel an already ended raffle
        require(
            raffle.status != STATUS.ENDED &&
                raffle.status != STATUS.CANCELLED &&
                raffle.status != STATUS.EARLY_CASHOUT &&
                raffle.status != STATUS.CLOSING_REQUESTED &&
                raffle.status != STATUS.CANCEL_REQUESTED,
            "Wrong status"
        );

        // only if the raffle is in accepted status the ETH is staked and could have entries sold
        if (raffle.status == STATUS.ACCEPTED) {
            // transfer eth to the owner
            (bool sentPrize, ) = raffle.seller.call{value: raffle.amountOfETH}(
                ""
            );
            require(sentPrize, "Failed to send Ether");
        }
        raffle.status = STATUS.CANCEL_REQUESTED;
        raffle.cancellingDate = block.timestamp;

        emit RaffleCancelled(_raffleId, raffle.amountRaised);
    }

    /// @param _raffleId Id of the raffle
    /// @dev The player can claim a refund during the first 30 days after the raffle was cancelled
    /// in the map "ClaimsData" it is saves how much the player spent on that raffle, as they could
    /// have bought several entries
    function claimRefund(uint256 _raffleId) external nonReentrant {
        RaffleStruct storage raffle = raffles[_raffleId];
        require(raffle.status == STATUS.CANCEL_REQUESTED, "wrong status");
        require(
            block.timestamp <= raffle.cancellingDate + 30 days,
            "claim time expired"
        );

        ClaimStruct storage claimData = claimsData[
            keccak256(abi.encode(msg.sender, _raffleId))
        ];

        require(claimData.claimed == false, "already refunded");

        raffle.amountRaised = raffle.amountRaised - claimData.amountSpentInWeis;

        claimData.claimed = true;
        (bool sent, ) = msg.sender.call{value: claimData.amountSpentInWeis}("");
        require(sent, "Fail send refund");

        emit Refund(_raffleId, claimData.amountSpentInWeis, msg.sender);
    }

    /// @param _raffleId Id of the raffle
    /// @dev after 30 days after cancelling passes, the operator can transfer to
    /// destinationWallet the remaining funds
    function transferRemainingFunds(uint256 _raffleId)
        external
        nonReentrant
        onlyRole(OPERATOR_ROLE)
    {
        RaffleStruct storage raffle = raffles[_raffleId];
        require(raffle.status == STATUS.CANCEL_REQUESTED, "Wrong status");
        require(
            block.timestamp > raffle.cancellingDate + 30 days,
            "claim too soon"
        );

        raffle.status = STATUS.CANCELLED;

        (bool sent, ) = destinationWallet.call{value: raffle.amountRaised}("");
        require(sent, "Fail send Eth to MW");

        emit RemainingFundsTransferred(_raffleId, raffle.amountRaised);

        raffle.amountRaised = 0;
    }

    /// @param _raffleId Id of the raffle
    /// @return array of entries bougth of that particular raffle
    function getEntriesBought(uint256 _raffleId)
        external
        view
        returns (EntriesBought[] memory)
    {
        return entriesList[_raffleId];
    }

    /// @param _raffleId Id of the raffle
    /// @param _player wallet of the player
    /// @return Claims data of the player on that raffle
    function getClaimData(uint256 _raffleId, address _player)
        external
        view
        returns (ClaimStruct memory)
    {
        return claimsData[keccak256(abi.encode(_player, _raffleId))];
    }

    /// @dev for different reasons player entries should be void
    /// this has a cost in gas, but this makes cheaper in gas the callback from chainlink
    /// This method has to be called for every raffle of the blacklisted player
    /// @param _raffleId Id of the raffle
    /// @param entriesToCancel array that contains the index of the entries to cancel. 0 based
    /// @param _player player who owns the entry to be voided
    function cancelEntry(
        uint256 _raffleId,
        uint256[] calldata entriesToCancel,
        address _player
     ) external onlyRole(OPERATOR_ROLE) {
        uint256 totalEntriesBoughtCancelled = 0;
        for (uint256 i = 0; i < entriesToCancel.length; i++) {
            EntriesBought storage entry = entriesList[_raffleId][
                entriesToCancel[i]
            ];

            require(entry.player == _player, "Entry did not belong to player");

            entry.player = address(0);

            uint256 previousTotalEntriesLength;
            if (entriesToCancel[i] == 0) previousTotalEntriesLength = 0;
            else previousTotalEntriesLength = entriesList[_raffleId][
                entriesToCancel[i]-1].currentEntriesLength;
            totalEntriesBoughtCancelled += entry.currentEntriesLength - previousTotalEntriesLength;
        }
        emit EntryCancelled(_raffleId, totalEntriesBoughtCancelled, _player);
    }

    // Requested by Valerio Di Napoli.
    /// @param _raffleId id of the raffle
    /// @param _amountOfEntries amount of entries. Must be lower than maxEntriesPerUser
    /// @param _player The address of the player
    /// @notice Called by other contract created by Valerio, that minted an NFT and after that call this method
    /// @dev add entries but they are free so no payable
    function createFreeEntriesFromExternalContract(
        uint256 _raffleId,
        uint256 _amountOfEntries,
        address _player
    ) external onlyRole(MINTERCONTRACT_ROLE) nonReentrant {
        // if can buy run this code.
        bytes32 hash = keccak256(abi.encode(_player, _raffleId));

        RaffleStruct storage raffle = raffles[_raffleId];

        require(
            raffle.entryType == ENTRY_TYPE.ONLY_EXTERNAL_CONTRACT ||
                raffle.entryType == ENTRY_TYPE.MIXED,
            "Entry type not allowed"
        );

        EntriesBought memory entryBought = EntriesBought({
            player: _player,
            currentEntriesLength: raffle.entriesLength + _amountOfEntries
        });
        entriesList[_raffleId].push(entryBought);

        // update the field entriesLength.
        raffle.entriesLength += _amountOfEntries;
        //update claim data
        claimsData[hash].numEntriesPerUser += _amountOfEntries;

        address[] memory players = new address[](1);
        players[0] = _player;
        emit FreeEntry(
            _raffleId,
            players,
            _amountOfEntries,
            raffle.entriesLength
        );
    }

    function playerIsBlacklisted(address _player) external view returns (bool) {
        return blackListManager.isBlackListed(_player);
    }

    function raffleNotInAcceptedState(uint256 _raffleId)
        external
        view
        returns (bool)
    {
        RaffleStruct memory raffle = raffles[_raffleId];
        return (raffle.status != STATUS.ACCEPTED);
    }

    function playerIsSeller(address _player, uint256 _raffleId)
        external
        view
        returns (bool)
    {
        RaffleStruct memory raffle = raffles[_raffleId];
        return (raffle.seller == _player);
    }

    function playerReachedMaxEntries(
        address _player,
        uint256 _raffleId,
        uint256 _amountOfEntries
    ) external view returns (bool) {
        RaffleStruct memory raffle = raffles[_raffleId];

        bytes32 hash = keccak256(abi.encode(_player, _raffleId));
        // check there are enough entries left for this particular user
        return (claimsData[hash].numEntriesPerUser + _amountOfEntries >
            raffle.maxEntries);
    }

    /* Requested by Valerio Di Napoli.
    @param _player The address of the player    
    @param _raffleId id of the raffle
    @param _colection Address of the required collection, if any
    @param _tokenIdUsed Id of the token of the required collection the player says he has and want to use in the raffle
    @returns bool if the player can buy or not, and string with the cause of the rejection. "" if can buy
    @notice Method that returns if the user can or cannot buy entries because the player owns an nft in the case or required collections.
    */
    function playerHasRequiredNFTs(
        address _player,
        uint256 _raffleId,
        address _collection,
        uint256 _tokenIdUsed
    ) external view returns (bool canBuy, string memory cause) {
        RaffleStruct memory raffle = raffles[_raffleId];

        // if the raffle requires an nft
        if (raffle.collectionWhitelist.length > 0) {
            bool hasRequiredCollection = false;
            for (uint256 i = 0; i < raffle.collectionWhitelist.length; i++) {
                if (raffle.collectionWhitelist[i] == _collection) {
                    hasRequiredCollection = true;
                    break;
                }
            }
            if (hasRequiredCollection == false)
                return (false, "Not in required collection");

            IERC721 requiredNFT = IERC721(_collection);
            if (requiredNFT.ownerOf(_tokenIdUsed) != _player)
                return (false, "Not the owner of tokenId");
            bytes32 hashRequiredNFT = keccak256(
                abi.encode(_collection, _raffleId, _tokenIdUsed)
            );
            // check the tokenId has not been using yet in the raffle, to avoid abuse
            if (requiredNFTWallets[hashRequiredNFT] != _player)
                return (false, "tokenId used");
        }

        return (true, "");
    }
}

// File: /contracts/BlackListManager.sol



// SPDX-License-Identifier: UNLICENSED
pragma solidity ^0.8.4;

import "@openzeppelin/contracts/access/AccessControl.sol";

/// @title Blacklist manager
/// @author Luis Pando
/// @notice Manages the players that are blacklisted
/// @dev A player is blacklisted for all the raffles at once.
contract BlackListManager is AccessControl {
    bytes32 public constant OPERATOR_ROLE = keccak256("OPERATOR");

    struct BlackListStruct {
        bool blacklisted;   // is blacklisted the user
        uint256 dateBlacklisted; // when was blacklisted for the first time
    }
    // map with the wallet of the player as key
    mapping(address => BlackListStruct) public blackList;

    constructor() {
        _setupRole(OPERATOR_ROLE, msg.sender);
        _setupRole(DEFAULT_ADMIN_ROLE, msg.sender);
    }

    /// @notice Add a player to the blacklist. The blacklist is common for all the raffles
    /// @dev the user could be added and removed from the blacklist several times, but the
    /// field dateBlacklisted will contain the date of when the user was added, even if was removed
    /// @param _player User that has suspicious behaviour and that will be blacklisted
    function addToBlackList(address _player) external onlyRole(OPERATOR_ROLE) {
        BlackListStruct memory blElement = BlackListStruct({
            blacklisted: true,
            dateBlacklisted: block.timestamp
        });
        blackList[_player] = blElement;
    }

    /// @notice remove a player from the blacklist
    /// @param _player that will be removed from the blacklist and will be able to buy entries again
    function removeFromBlackList(address _player)
        external
        onlyRole(OPERATOR_ROLE)
    {
        blackList[_player].blacklisted = false;
    }

    /// @notice returns if a player is in the blacklist
    /// @param _player User to check if blacklisted or not
    /// @return true if the user wallet is in the blacklist. False otherwise
    function isBlackListed(address _player) external view returns (bool) {
        return blackList[_player].blacklisted;
    }

    /// @notice returns the date (if any) when the user was blacklisted for first time
    /// @dev The returned value will exists even if the user was removed from the blacklist
    /// Do not use it without calling isBlacklisted first
    /// @param _player User to return the date when blacklisted
    /// @return a number with the epoch of when the player was blacklisted. 0 if never blacklisted
    function getBlackListedDate(address _player) external view returns (uint256) {
        return blackList[_player].dateBlacklisted;
    }
}

// File: @openzeppelin/contracts/utils/math/Math.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (utils/math/Math.sol)

pragma solidity ^0.8.0;

/**
 * @dev Standard math utilities missing in the Solidity language.
 */
library Math {
    enum Rounding {
        Down, // Toward negative infinity
        Up, // Toward infinity
        Zero // Toward zero
    }

    /**
     * @dev Returns the largest of two numbers.
     */
    function max(uint256 a, uint256 b) internal pure returns (uint256) {
        return a >= b ? a : b;
    }

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

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

    /**
     * @dev Returns the ceiling of the division of two numbers.
     *
     * This differs from standard division with `/` in that it rounds up instead
     * of rounding down.
     */
    function ceilDiv(uint256 a, uint256 b) internal pure returns (uint256) {
        // (a + b - 1) / b can overflow on addition, so we distribute.
        return a == 0 ? 0 : (a - 1) / b + 1;
    }

    /**
     * @notice Calculates floor(x * y / denominator) with full precision. Throws if result overflows a uint256 or denominator == 0
     * @dev Original credit to Remco Bloemen under MIT license (https://xn--2-umb.com/21/muldiv)
     * with further edits by Uniswap Labs also under MIT license.
     */
    function mulDiv(
        uint256 x,
        uint256 y,
        uint256 denominator
    ) internal pure returns (uint256 result) {
        unchecked {
            // 512-bit multiply [prod1 prod0] = x * y. Compute the product mod 2^256 and mod 2^256 - 1, then use
            // use the Chinese Remainder Theorem to reconstruct the 512 bit result. The result is stored in two 256
            // variables such that product = prod1 * 2^256 + prod0.
            uint256 prod0; // Least significant 256 bits of the product
            uint256 prod1; // Most significant 256 bits of the product
            assembly {
                let mm := mulmod(x, y, not(0))
                prod0 := mul(x, y)
                prod1 := sub(sub(mm, prod0), lt(mm, prod0))
            }

            // Handle non-overflow cases, 256 by 256 division.
            if (prod1 == 0) {
                return prod0 / denominator;
            }

            // Make sure the result is less than 2^256. Also prevents denominator == 0.
            require(denominator > prod1);

            ///////////////////////////////////////////////
            // 512 by 256 division.
            ///////////////////////////////////////////////

            // Make division exact by subtracting the remainder from [prod1 prod0].
            uint256 remainder;
            assembly {
                // Compute remainder using mulmod.
                remainder := mulmod(x, y, denominator)

                // Subtract 256 bit number from 512 bit number.
                prod1 := sub(prod1, gt(remainder, prod0))
                prod0 := sub(prod0, remainder)
            }

            // Factor powers of two out of denominator and compute largest power of two divisor of denominator. Always >= 1.
            // See https://cs.stackexchange.com/q/138556/92363.

            // Does not overflow because the denominator cannot be zero at this stage in the function.
            uint256 twos = denominator & (~denominator + 1);
            assembly {
                // Divide denominator by twos.
                denominator := div(denominator, twos)

                // Divide [prod1 prod0] by twos.
                prod0 := div(prod0, twos)

                // Flip twos such that it is 2^256 / twos. If twos is zero, then it becomes one.
                twos := add(div(sub(0, twos), twos), 1)
            }

            // Shift in bits from prod1 into prod0.
            prod0 |= prod1 * twos;

            // Invert denominator mod 2^256. Now that denominator is an odd number, it has an inverse modulo 2^256 such
            // that denominator * inv = 1 mod 2^256. Compute the inverse by starting with a seed that is correct for
            // four bits. That is, denominator * inv = 1 mod 2^4.
            uint256 inverse = (3 * denominator) ^ 2;

            // Use the Newton-Raphson iteration to improve the precision. Thanks to Hensel's lifting lemma, this also works
            // in modular arithmetic, doubling the correct bits in each step.
            inverse *= 2 - denominator * inverse; // inverse mod 2^8
            inverse *= 2 - denominator * inverse; // inverse mod 2^16
            inverse *= 2 - denominator * inverse; // inverse mod 2^32
            inverse *= 2 - denominator * inverse; // inverse mod 2^64
            inverse *= 2 - denominator * inverse; // inverse mod 2^128
            inverse *= 2 - denominator * inverse; // inverse mod 2^256

            // Because the division is now exact we can divide by multiplying with the modular inverse of denominator.
            // This will give us the correct result modulo 2^256. Since the preconditions guarantee that the outcome is
            // less than 2^256, this is the final result. We don't need to compute the high bits of the result and prod1
            // is no longer required.
            result = prod0 * inverse;
            return result;
        }
    }

    /**
     * @notice Calculates x * y / denominator with full precision, following the selected rounding direction.
     */
    function mulDiv(
        uint256 x,
        uint256 y,
        uint256 denominator,
        Rounding rounding
    ) internal pure returns (uint256) {
        uint256 result = mulDiv(x, y, denominator);
        if (rounding == Rounding.Up && mulmod(x, y, denominator) > 0) {
            result += 1;
        }
        return result;
    }

    /**
     * @dev Returns the square root of a number. It the number is not a perfect square, the value is rounded down.
     *
     * Inspired by Henry S. Warren, Jr.'s "Hacker's Delight" (Chapter 11).
     */
    function sqrt(uint256 a) internal pure returns (uint256) {
        if (a == 0) {
            return 0;
        }

        // For our first guess, we get the biggest power of 2 which is smaller than the square root of the target.
        // We know that the "msb" (most significant bit) of our target number `a` is a power of 2 such that we have
        // `msb(a) <= a < 2*msb(a)`.
        // We also know that `k`, the position of the most significant bit, is such that `msb(a) = 2**k`.
        // This gives `2**k < a <= 2**(k+1)` → `2**(k/2) <= sqrt(a) < 2 ** (k/2+1)`.
        // Using an algorithm similar to the msb conmputation, we are able to compute `result = 2**(k/2)` which is a
        // good first aproximation of `sqrt(a)` with at least 1 correct bit.
        uint256 result = 1;
        uint256 x = a;
        if (x >> 128 > 0) {
            x >>= 128;
            result <<= 64;
        }
        if (x >> 64 > 0) {
            x >>= 64;
            result <<= 32;
        }
        if (x >> 32 > 0) {
            x >>= 32;
            result <<= 16;
        }
        if (x >> 16 > 0) {
            x >>= 16;
            result <<= 8;
        }
        if (x >> 8 > 0) {
            x >>= 8;
            result <<= 4;
        }
        if (x >> 4 > 0) {
            x >>= 4;
            result <<= 2;
        }
        if (x >> 2 > 0) {
            result <<= 1;
        }

        // At this point `result` is an estimation with one bit of precision. We know the true value is a uint128,
        // since it is the square root of a uint256. Newton's method converges quadratically (precision doubles at
        // every iteration). We thus need at most 7 iteration to turn our partial result with one bit of precision
        // into the expected uint128 result.
        unchecked {
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            result = (result + a / result) >> 1;
            return min(result, a / result);
        }
    }

    /**
     * @notice Calculates sqrt(a), following the selected rounding direction.
     */
    function sqrt(uint256 a, Rounding rounding) internal pure returns (uint256) {
        uint256 result = sqrt(a);
        if (rounding == Rounding.Up && result * result < a) {
            result += 1;
        }
        return result;
    }
}

// File: @openzeppelin/contracts/utils/introspection/IERC165.sol



// 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);
}

// File: @openzeppelin/contracts/utils/introspection/ERC165.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (utils/introspection/ERC165.sol)

pragma solidity ^0.8.0;

import "./IERC165.sol";

/**
 * @dev Implementation of the {IERC165} interface.
 *
 * Contracts that want to implement ERC165 should inherit from this contract and override {supportsInterface} to check
 * for the additional interface id that will be supported. For example:
 *
 * ```solidity
 * function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
 *     return interfaceId == type(MyInterface).interfaceId || super.supportsInterface(interfaceId);
 * }
 * ```
 *
 * Alternatively, {ERC165Storage} provides an easier to use but more expensive implementation.
 */
abstract contract ERC165 is IERC165 {
    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IERC165).interfaceId;
    }
}

// File: @openzeppelin/contracts/utils/Strings.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (utils/Strings.sol)

pragma solidity ^0.8.0;

/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";
    uint8 private constant _ADDRESS_LENGTH = 20;

    /**
     * @dev Converts a `uint256` to its ASCII `string` decimal representation.
     */
    function toString(uint256 value) internal pure returns (string memory) {
        // Inspired by OraclizeAPI's implementation - MIT licence
        // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

        if (value == 0) {
            return "0";
        }
        uint256 temp = value;
        uint256 digits;
        while (temp != 0) {
            digits++;
            temp /= 10;
        }
        bytes memory buffer = new bytes(digits);
        while (value != 0) {
            digits -= 1;
            buffer[digits] = bytes1(uint8(48 + uint256(value % 10)));
            value /= 10;
        }
        return string(buffer);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        if (value == 0) {
            return "0x00";
        }
        uint256 temp = value;
        uint256 length = 0;
        while (temp != 0) {
            length++;
            temp >>= 8;
        }
        return toHexString(value, length);
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
     */
    function toHexString(uint256 value, uint256 length) internal pure returns (string memory) {
        bytes memory buffer = new bytes(2 * length + 2);
        buffer[0] = "0";
        buffer[1] = "x";
        for (uint256 i = 2 * length + 1; i > 1; --i) {
            buffer[i] = _HEX_SYMBOLS[value & 0xf];
            value >>= 4;
        }
        require(value == 0, "Strings: hex length insufficient");
        return string(buffer);
    }

    /**
     * @dev Converts an `address` with fixed length of 20 bytes to its not checksummed ASCII `string` hexadecimal representation.
     */
    function toHexString(address addr) internal pure returns (string memory) {
        return toHexString(uint256(uint160(addr)), _ADDRESS_LENGTH);
    }
}

// File: @openzeppelin/contracts/utils/Context.sol



// 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;
    }
}

// File: @openzeppelin/contracts/token/ERC721/IERC721.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (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 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);
}

// File: @openzeppelin/contracts/security/ReentrancyGuard.sol



// 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;
    }
}

// File: @openzeppelin/contracts/access/IAccessControl.sol



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

pragma solidity ^0.8.0;

/**
 * @dev External interface of AccessControl declared to support ERC165 detection.
 */
interface IAccessControl {
    /**
     * @dev Emitted when `newAdminRole` is set as ``role``'s admin role, replacing `previousAdminRole`
     *
     * `DEFAULT_ADMIN_ROLE` is the starting admin for all roles, despite
     * {RoleAdminChanged} not being emitted signaling this.
     *
     * _Available since v3.1._
     */
    event RoleAdminChanged(bytes32 indexed role, bytes32 indexed previousAdminRole, bytes32 indexed newAdminRole);

    /**
     * @dev Emitted when `account` is granted `role`.
     *
     * `sender` is the account that originated the contract call, an admin role
     * bearer except when using {AccessControl-_setupRole}.
     */
    event RoleGranted(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Emitted when `account` is revoked `role`.
     *
     * `sender` is the account that originated the contract call:
     *   - if using `revokeRole`, it is the admin role bearer
     *   - if using `renounceRole`, it is the role bearer (i.e. `account`)
     */
    event RoleRevoked(bytes32 indexed role, address indexed account, address indexed sender);

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) external view returns (bool);

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {AccessControl-_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) external view returns (bytes32);

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function grantRole(bytes32 role, address account) external;

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     */
    function revokeRole(bytes32 role, address account) external;

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been granted `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     */
    function renounceRole(bytes32 role, address account) external;
}

// File: @openzeppelin/contracts/access/AccessControl.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.7.0) (access/AccessControl.sol)

pragma solidity ^0.8.0;

import "./IAccessControl.sol";
import "../utils/Context.sol";
import "../utils/Strings.sol";
import "../utils/introspection/ERC165.sol";

/**
 * @dev Contract module that allows children to implement role-based access
 * control mechanisms. This is a lightweight version that doesn't allow enumerating role
 * members except through off-chain means by accessing the contract event logs. Some
 * applications may benefit from on-chain enumerability, for those cases see
 * {AccessControlEnumerable}.
 *
 * Roles are referred to by their `bytes32` identifier. These should be exposed
 * in the external API and be unique. The best way to achieve this is by
 * using `public constant` hash digests:
 *
 * ```
 * bytes32 public constant MY_ROLE = keccak256("MY_ROLE");
 * ```
 *
 * Roles can be used to represent a set of permissions. To restrict access to a
 * function call, use {hasRole}:
 *
 * ```
 * function foo() public {
 *     require(hasRole(MY_ROLE, msg.sender));
 *     ...
 * }
 * ```
 *
 * Roles can be granted and revoked dynamically via the {grantRole} and
 * {revokeRole} functions. Each role has an associated admin role, and only
 * accounts that have a role's admin role can call {grantRole} and {revokeRole}.
 *
 * By default, the admin role for all roles is `DEFAULT_ADMIN_ROLE`, which means
 * that only accounts with this role will be able to grant or revoke other
 * roles. More complex role relationships can be created by using
 * {_setRoleAdmin}.
 *
 * WARNING: The `DEFAULT_ADMIN_ROLE` is also its own admin: it has permission to
 * grant and revoke this role. Extra precautions should be taken to secure
 * accounts that have been granted it.
 */
abstract contract AccessControl is Context, IAccessControl, ERC165 {
    struct RoleData {
        mapping(address => bool) members;
        bytes32 adminRole;
    }

    mapping(bytes32 => RoleData) private _roles;

    bytes32 public constant DEFAULT_ADMIN_ROLE = 0x00;

    /**
     * @dev Modifier that checks that an account has a specific role. Reverts
     * with a standardized message including the required role.
     *
     * The format of the revert reason is given by the following regular expression:
     *
     *  /^AccessControl: account (0x[0-9a-f]{40}) is missing role (0x[0-9a-f]{64})$/
     *
     * _Available since v4.1._
     */
    modifier onlyRole(bytes32 role) {
        _checkRole(role);
        _;
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IAccessControl).interfaceId || super.supportsInterface(interfaceId);
    }

    /**
     * @dev Returns `true` if `account` has been granted `role`.
     */
    function hasRole(bytes32 role, address account) public view virtual override returns (bool) {
        return _roles[role].members[account];
    }

    /**
     * @dev Revert with a standard message if `_msgSender()` is missing `role`.
     * Overriding this function changes the behavior of the {onlyRole} modifier.
     *
     * Format of the revert message is described in {_checkRole}.
     *
     * _Available since v4.6._
     */
    function _checkRole(bytes32 role) internal view virtual {
        _checkRole(role, _msgSender());
    }

    /**
     * @dev Revert with a standard message if `account` is missing `role`.
     *
     * The format of the revert reason is given by the following regular expression:
     *
     *  /^AccessControl: account (0x[0-9a-f]{40}) is missing role (0x[0-9a-f]{64})$/
     */
    function _checkRole(bytes32 role, address account) internal view virtual {
        if (!hasRole(role, account)) {
            revert(
                string(
                    abi.encodePacked(
                        "AccessControl: account ",
                        Strings.toHexString(uint160(account), 20),
                        " is missing role ",
                        Strings.toHexString(uint256(role), 32)
                    )
                )
            );
        }
    }

    /**
     * @dev Returns the admin role that controls `role`. See {grantRole} and
     * {revokeRole}.
     *
     * To change a role's admin, use {_setRoleAdmin}.
     */
    function getRoleAdmin(bytes32 role) public view virtual override returns (bytes32) {
        return _roles[role].adminRole;
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     *
     * May emit a {RoleGranted} event.
     */
    function grantRole(bytes32 role, address account) public virtual override onlyRole(getRoleAdmin(role)) {
        _grantRole(role, account);
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * If `account` had been granted `role`, emits a {RoleRevoked} event.
     *
     * Requirements:
     *
     * - the caller must have ``role``'s admin role.
     *
     * May emit a {RoleRevoked} event.
     */
    function revokeRole(bytes32 role, address account) public virtual override onlyRole(getRoleAdmin(role)) {
        _revokeRole(role, account);
    }

    /**
     * @dev Revokes `role` from the calling account.
     *
     * Roles are often managed via {grantRole} and {revokeRole}: this function's
     * purpose is to provide a mechanism for accounts to lose their privileges
     * if they are compromised (such as when a trusted device is misplaced).
     *
     * If the calling account had been revoked `role`, emits a {RoleRevoked}
     * event.
     *
     * Requirements:
     *
     * - the caller must be `account`.
     *
     * May emit a {RoleRevoked} event.
     */
    function renounceRole(bytes32 role, address account) public virtual override {
        require(account == _msgSender(), "AccessControl: can only renounce roles for self");

        _revokeRole(role, account);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * If `account` had not been already granted `role`, emits a {RoleGranted}
     * event. Note that unlike {grantRole}, this function doesn't perform any
     * checks on the calling account.
     *
     * May emit a {RoleGranted} event.
     *
     * [WARNING]
     * ====
     * This function should only be called from the constructor when setting
     * up the initial roles for the system.
     *
     * Using this function in any other way is effectively circumventing the admin
     * system imposed by {AccessControl}.
     * ====
     *
     * NOTE: This function is deprecated in favor of {_grantRole}.
     */
    function _setupRole(bytes32 role, address account) internal virtual {
        _grantRole(role, account);
    }

    /**
     * @dev Sets `adminRole` as ``role``'s admin role.
     *
     * Emits a {RoleAdminChanged} event.
     */
    function _setRoleAdmin(bytes32 role, bytes32 adminRole) internal virtual {
        bytes32 previousAdminRole = getRoleAdmin(role);
        _roles[role].adminRole = adminRole;
        emit RoleAdminChanged(role, previousAdminRole, adminRole);
    }

    /**
     * @dev Grants `role` to `account`.
     *
     * Internal function without access restriction.
     *
     * May emit a {RoleGranted} event.
     */
    function _grantRole(bytes32 role, address account) internal virtual {
        if (!hasRole(role, account)) {
            _roles[role].members[account] = true;
            emit RoleGranted(role, account, _msgSender());
        }
    }

    /**
     * @dev Revokes `role` from `account`.
     *
     * Internal function without access restriction.
     *
     * May emit a {RoleRevoked} event.
     */
    function _revokeRole(bytes32 role, address account) internal virtual {
        if (hasRole(role, account)) {
            _roles[role].members[account] = false;
            emit RoleRevoked(role, account, _msgSender());
        }
    }
}

// File: @chainlink/contracts/src/v0.8/interfaces/LinkTokenInterface.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

interface LinkTokenInterface {
  function allowance(address owner, address spender) external view returns (uint256 remaining);

  function approve(address spender, uint256 value) external returns (bool success);

  function balanceOf(address owner) external view returns (uint256 balance);

  function decimals() external view returns (uint8 decimalPlaces);

  function decreaseApproval(address spender, uint256 addedValue) external returns (bool success);

  function increaseApproval(address spender, uint256 subtractedValue) external;

  function name() external view returns (string memory tokenName);

  function symbol() external view returns (string memory tokenSymbol);

  function totalSupply() external view returns (uint256 totalTokensIssued);

  function transfer(address to, uint256 value) external returns (bool success);

  function transferAndCall(
    address to,
    uint256 value,
    bytes calldata data
  ) external returns (bool success);

  function transferFrom(
    address from,
    address to,
    uint256 value
  ) external returns (bool success);
}

// File: @chainlink/contracts/src/v0.8/VRFRequestIDBase.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

contract VRFRequestIDBase {
  /**
   * @notice returns the seed which is actually input to the VRF coordinator
   *
   * @dev To prevent repetition of VRF output due to repetition of the
   * @dev user-supplied seed, that seed is combined in a hash with the
   * @dev user-specific nonce, and the address of the consuming contract. The
   * @dev risk of repetition is mostly mitigated by inclusion of a blockhash in
   * @dev the final seed, but the nonce does protect against repetition in
   * @dev requests which are included in a single block.
   *
   * @param _userSeed VRF seed input provided by user
   * @param _requester Address of the requesting contract
   * @param _nonce User-specific nonce at the time of the request
   */
  function makeVRFInputSeed(
    bytes32 _keyHash,
    uint256 _userSeed,
    address _requester,
    uint256 _nonce
  ) internal pure returns (uint256) {
    return uint256(keccak256(abi.encode(_keyHash, _userSeed, _requester, _nonce)));
  }

  /**
   * @notice Returns the id for this request
   * @param _keyHash The serviceAgreement ID to be used for this request
   * @param _vRFInputSeed The seed to be passed directly to the VRF
   * @return The id for this request
   *
   * @dev Note that _vRFInputSeed is not the seed passed by the consuming
   * @dev contract, but the one generated by makeVRFInputSeed
   */
  function makeRequestId(bytes32 _keyHash, uint256 _vRFInputSeed) internal pure returns (bytes32) {
    return keccak256(abi.encodePacked(_keyHash, _vRFInputSeed));
  }
}

// File: @chainlink/contracts/src/v0.8/VRFConsumerBase.sol



// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

import "./interfaces/LinkTokenInterface.sol";

import "./VRFRequestIDBase.sol";

/** ****************************************************************************
 * @notice Interface for contracts using VRF randomness
 * *****************************************************************************
 * @dev PURPOSE
 *
 * @dev Reggie the Random Oracle (not his real job) wants to provide randomness
 * @dev to Vera the verifier in such a way that Vera can be sure he's not
 * @dev making his output up to suit himself. Reggie provides Vera a public key
 * @dev to which he knows the secret key. Each time Vera provides a seed to
 * @dev Reggie, he gives back a value which is computed completely
 * @dev deterministically from the seed and the secret key.
 *
 * @dev Reggie provides a proof by which Vera can verify that the output was
 * @dev correctly computed once Reggie tells it to her, but without that proof,
 * @dev the output is indistinguishable to her from a uniform random sample
 * @dev from the output space.
 *
 * @dev The purpose of this contract is to make it easy for unrelated contracts
 * @dev to talk to Vera the verifier about the work Reggie is doing, to provide
 * @dev simple access to a verifiable source of randomness.
 * *****************************************************************************
 * @dev USAGE
 *
 * @dev Calling contracts must inherit from VRFConsumerBase, and can
 * @dev initialize VRFConsumerBase's attributes in their constructor as
 * @dev shown:
 *
 * @dev   contract VRFConsumer {
 * @dev     constructor(<other arguments>, address _vrfCoordinator, address _link)
 * @dev       VRFConsumerBase(_vrfCoordinator, _link) public {
 * @dev         <initialization with other arguments goes here>
 * @dev       }
 * @dev   }
 *
 * @dev The oracle will have given you an ID for the VRF keypair they have
 * @dev committed to (let's call it keyHash), and have told you the minimum LINK
 * @dev price for VRF service. Make sure your contract has sufficient LINK, and
 * @dev call requestRandomness(keyHash, fee, seed), where seed is the input you
 * @dev want to generate randomness from.
 *
 * @dev Once the VRFCoordinator has received and validated the oracle's response
 * @dev to your request, it will call your contract's fulfillRandomness method.
 *
 * @dev The randomness argument to fulfillRandomness is the actual random value
 * @dev generated from your seed.
 *
 * @dev The requestId argument is generated from the keyHash and the seed by
 * @dev makeRequestId(keyHash, seed). If your contract could have concurrent
 * @dev requests open, you can use the requestId to track which seed is
 * @dev associated with which randomness. See VRFRequestIDBase.sol for more
 * @dev details. (See "SECURITY CONSIDERATIONS" for principles to keep in mind,
 * @dev if your contract could have multiple requests in flight simultaneously.)
 *
 * @dev Colliding `requestId`s are cryptographically impossible as long as seeds
 * @dev differ. (Which is critical to making unpredictable randomness! See the
 * @dev next section.)
 *
 * *****************************************************************************
 * @dev SECURITY CONSIDERATIONS
 *
 * @dev A method with the ability to call your fulfillRandomness method directly
 * @dev could spoof a VRF response with any random value, so it's critical that
 * @dev it cannot be directly called by anything other than this base contract
 * @dev (specifically, by the VRFConsumerBase.rawFulfillRandomness method).
 *
 * @dev For your users to trust that your contract's random behavior is free
 * @dev from malicious interference, it's best if you can write it so that all
 * @dev behaviors implied by a VRF response are executed *during* your
 * @dev fulfillRandomness method. If your contract must store the response (or
 * @dev anything derived from it) and use it later, you must ensure that any
 * @dev user-significant behavior which depends on that stored value cannot be
 * @dev manipulated by a subsequent VRF request.
 *
 * @dev Similarly, both miners and the VRF oracle itself have some influence
 * @dev over the order in which VRF responses appear on the blockchain, so if
 * @dev your contract could have multiple VRF requests in flight simultaneously,
 * @dev you must ensure that the order in which the VRF responses arrive cannot
 * @dev be used to manipulate your contract's user-significant behavior.
 *
 * @dev Since the ultimate input to the VRF is mixed with the block hash of the
 * @dev block in which the request is made, user-provided seeds have no impact
 * @dev on its economic security properties. They are only included for API
 * @dev compatability with previous versions of this contract.
 *
 * @dev Since the block hash of the block which contains the requestRandomness
 * @dev call is mixed into the input to the VRF *last*, a sufficiently powerful
 * @dev miner could, in principle, fork the blockchain to evict the block
 * @dev containing the request, forcing the request to be included in a
 * @dev different block with a different hash, and therefore a different input
 * @dev to the VRF. However, such an attack would incur a substantial economic
 * @dev cost. This cost scales with the number of blocks the VRF oracle waits
 * @dev until it calls responds to a request.
 */
abstract contract VRFConsumerBase is VRFRequestIDBase {
  /**
   * @notice fulfillRandomness handles the VRF response. Your contract must
   * @notice implement it. See "SECURITY CONSIDERATIONS" above for important
   * @notice principles to keep in mind when implementing your fulfillRandomness
   * @notice method.
   *
   * @dev VRFConsumerBase expects its subcontracts to have a method with this
   * @dev signature, and will call it once it has verified the proof
   * @dev associated with the randomness. (It is triggered via a call to
   * @dev rawFulfillRandomness, below.)
   *
   * @param requestId The Id initially returned by requestRandomness
   * @param randomness the VRF output
   */
  function fulfillRandomness(bytes32 requestId, uint256 randomness) internal virtual;

  /**
   * @dev In order to keep backwards compatibility we have kept the user
   * seed field around. We remove the use of it because given that the blockhash
   * enters later, it overrides whatever randomness the used seed provides.
   * Given that it adds no security, and can easily lead to misunderstandings,
   * we have removed it from usage and can now provide a simpler API.
   */
  uint256 private constant USER_SEED_PLACEHOLDER = 0;

  /**
   * @notice requestRandomness initiates a request for VRF output given _seed
   *
   * @dev The fulfillRandomness method receives the output, once it's provided
   * @dev by the Oracle, and verified by the vrfCoordinator.
   *
   * @dev The _keyHash must already be registered with the VRFCoordinator, and
   * @dev the _fee must exceed the fee specified during registration of the
   * @dev _keyHash.
   *
   * @dev The _seed parameter is vestigial, and is kept only for API
   * @dev compatibility with older versions. It can't *hurt* to mix in some of
   * @dev your own randomness, here, but it's not necessary because the VRF
   * @dev oracle will mix the hash of the block containing your request into the
   * @dev VRF seed it ultimately uses.
   *
   * @param _keyHash ID of public key against which randomness is generated
   * @param _fee The amount of LINK to send with the request
   *
   * @return requestId unique ID for this request
   *
   * @dev The returned requestId can be used to distinguish responses to
   * @dev concurrent requests. It is passed as the first argument to
   * @dev fulfillRandomness.
   */
  function requestRandomness(bytes32 _keyHash, uint256 _fee) internal returns (bytes32 requestId) {
    LINK.transferAndCall(vrfCoordinator, _fee, abi.encode(_keyHash, USER_SEED_PLACEHOLDER));
    // This is the seed passed to VRFCoordinator. The oracle will mix this with
    // the hash of the block containing this request to obtain the seed/input
    // which is finally passed to the VRF cryptographic machinery.
    uint256 vRFSeed = makeVRFInputSeed(_keyHash, USER_SEED_PLACEHOLDER, address(this), nonces[_keyHash]);
    // nonces[_keyHash] must stay in sync with
    // VRFCoordinator.nonces[_keyHash][this], which was incremented by the above
    // successful LINK.transferAndCall (in VRFCoordinator.randomnessRequest).
    // This provides protection against the user repeating their input seed,
    // which would result in a predictable/duplicate output, if multiple such
    // requests appeared in the same block.
    nonces[_keyHash] = nonces[_keyHash] + 1;
    return makeRequestId(_keyHash, vRFSeed);
  }

  LinkTokenInterface internal immutable LINK;
  address private immutable vrfCoordinator;

  // Nonces for each VRF key from which randomness has been requested.
  //
  // Must stay in sync with VRFCoordinator[_keyHash][this]
  mapping(bytes32 => uint256) /* keyHash */ /* nonce */
    private nonces;

  /**
   * @param _vrfCoordinator address of VRFCoordinator contract
   * @param _link address of LINK token contract
   *
   * @dev https://docs.chain.link/docs/link-token-contracts
   */
  constructor(address _vrfCoordinator, address _link) {
    vrfCoordinator = _vrfCoordinator;
    LINK = LinkTokenInterface(_link);
  }

  // rawFulfillRandomness is called by VRFCoordinator when it receives a valid VRF
  // proof. rawFulfillRandomness then calls fulfillRandomness, after validating
  // the origin of the call
  function rawFulfillRandomness(bytes32 requestId, uint256 randomness) external {
    require(msg.sender == vrfCoordinator, "Only VRFCoordinator can fulfill");
    fulfillRandomness(requestId, randomness);
  }
}