// SPDX-License-Identifier: MIT
// File: @openzeppelin/contracts/security/ReentrancyGuard.sol


// OpenZeppelin Contracts (last updated v4.8.0) (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() {
        _nonReentrantBefore();
        _;
        _nonReentrantAfter();
    }

    function _nonReentrantBefore() private {
        // On the first call to nonReentrant, _status will be _NOT_ENTERED
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;
    }

    function _nonReentrantAfter() private {
        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

// File: erc-payable-token/contracts/token/ERC1363/IERC1363Receiver.sol



pragma solidity ^0.8.0;

/**
 * @title IERC1363Receiver Interface
 * @author Vittorio Minacori (https://github.com/vittominacori)
 * @dev Interface for any contract that wants to support transferAndCall or transferFromAndCall
 *  from ERC1363 token contracts as defined in
 *  https://eips.ethereum.org/EIPS/eip-1363
 */
interface IERC1363Receiver {
    /**
     * @notice Handle the receipt of ERC1363 tokens
     * @dev Any ERC1363 smart contract calls this function on the recipient
     * after a `transfer` or a `transferFrom`. This function MAY throw to revert and reject the
     * transfer. Return of other than the magic value MUST result in the
     * transaction being reverted.
     * Note: the token contract address is always the message sender.
     * @param spender address The address which called `transferAndCall` or `transferFromAndCall` function
     * @param sender address The address which are token transferred from
     * @param amount uint256 The amount of tokens transferred
     * @param data bytes Additional data with no specified format
     * @return `bytes4(keccak256("onTransferReceived(address,address,uint256,bytes)"))` unless throwing
     */
    function onTransferReceived(
        address spender,
        address sender,
        uint256 amount,
        bytes calldata data
    ) external returns (bytes4);
}

// File: @chainlink/contracts/src/v0.8/interfaces/VRFV2WrapperInterface.sol


pragma solidity ^0.8.0;

interface VRFV2WrapperInterface {
  /**
   * @return the request ID of the most recent VRF V2 request made by this wrapper. This should only
   * be relied option within the same transaction that the request was made.
   */
  function lastRequestId() external view returns (uint256);

  /**
   * @notice Calculates the price of a VRF request with the given callbackGasLimit at the current
   * @notice block.
   *
   * @dev This function relies on the transaction gas price which is not automatically set during
   * @dev simulation. To estimate the price at a specific gas price, use the estimatePrice function.
   *
   * @param _callbackGasLimit is the gas limit used to estimate the price.
   */
  function calculateRequestPrice(uint32 _callbackGasLimit) external view returns (uint256);

  /**
   * @notice Estimates the price of a VRF request with a specific gas limit and gas price.
   *
   * @dev This is a convenience function that can be called in simulation to better understand
   * @dev pricing.
   *
   * @param _callbackGasLimit is the gas limit used to estimate the price.
   * @param _requestGasPriceWei is the gas price in wei used for the estimation.
   */
  function estimateRequestPrice(uint32 _callbackGasLimit, uint256 _requestGasPriceWei) external view returns (uint256);
}

// File: @chainlink/contracts/src/v0.8/interfaces/LinkTokenInterface.sol


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/VRFV2WrapperConsumerBase.sol


pragma solidity ^0.8.0;



/** *******************************************************************************
 * @notice Interface for contracts using VRF randomness through the VRF V2 wrapper
 * ********************************************************************************
 * @dev PURPOSE
 *
 * @dev Create VRF V2 requests without the need for subscription management. Rather than creating
 * @dev and funding a VRF V2 subscription, a user can use this wrapper to create one off requests,
 * @dev paying up front rather than at fulfillment.
 *
 * @dev Since the price is determined using the gas price of the request transaction rather than
 * @dev the fulfillment transaction, the wrapper charges an additional premium on callback gas
 * @dev usage, in addition to some extra overhead costs associated with the VRFV2Wrapper contract.
 * *****************************************************************************
 * @dev USAGE
 *
 * @dev Calling contracts must inherit from VRFV2WrapperConsumerBase. The consumer must be funded
 * @dev with enough LINK to make the request, otherwise requests will revert. To request randomness,
 * @dev call the 'requestRandomness' function with the desired VRF parameters. This function handles
 * @dev paying for the request based on the current pricing.
 *
 * @dev Consumers must implement the fullfillRandomWords function, which will be called during
 * @dev fulfillment with the randomness result.
 */
abstract contract VRFV2WrapperConsumerBase {
  LinkTokenInterface internal immutable LINK;
  VRFV2WrapperInterface internal immutable VRF_V2_WRAPPER;

  /**
   * @param _link is the address of LinkToken
   * @param _vrfV2Wrapper is the address of the VRFV2Wrapper contract
   */
  constructor(address _link, address _vrfV2Wrapper) {
    LINK = LinkTokenInterface(_link);
    VRF_V2_WRAPPER = VRFV2WrapperInterface(_vrfV2Wrapper);
  }

  /**
   * @dev Requests randomness from the VRF V2 wrapper.
   *
   * @param _callbackGasLimit is the gas limit that should be used when calling the consumer's
   *        fulfillRandomWords function.
   * @param _requestConfirmations is the number of confirmations to wait before fulfilling the
   *        request. A higher number of confirmations increases security by reducing the likelihood
   *        that a chain re-org changes a published randomness outcome.
   * @param _numWords is the number of random words to request.
   *
   * @return requestId is the VRF V2 request ID of the newly created randomness request.
   */
  function requestRandomness(
    uint32 _callbackGasLimit,
    uint16 _requestConfirmations,
    uint32 _numWords
  ) internal returns (uint256 requestId) {
    LINK.transferAndCall(
      address(VRF_V2_WRAPPER),
      VRF_V2_WRAPPER.calculateRequestPrice(_callbackGasLimit),
      abi.encode(_callbackGasLimit, _requestConfirmations, _numWords)
    );
    return VRF_V2_WRAPPER.lastRequestId();
  }

  /**
   * @notice fulfillRandomWords handles the VRF V2 wrapper response. The consuming contract must
   * @notice implement it.
   *
   * @param _requestId is the VRF V2 request ID.
   * @param _randomWords is the randomness result.
   */
  function fulfillRandomWords(uint256 _requestId, uint256[] memory _randomWords) internal virtual;

  function rawFulfillRandomWords(uint256 _requestId, uint256[] memory _randomWords) external {
    require(msg.sender == address(VRF_V2_WRAPPER), "only VRF V2 wrapper can fulfill");
    fulfillRandomWords(_requestId, _randomWords);
  }
}

// File: @openzeppelin/contracts/utils/math/Math.sol


// OpenZeppelin Contracts (last updated v4.8.0) (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. If 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)`. This value can be written `msb(a)=2**k` with `k=log2(a)`.
        //
        // This can be rewritten `2**log2(a) <= a < 2**(log2(a) + 1)`
        // → `sqrt(2**k) <= sqrt(a) < sqrt(2**(k+1))`
        // → `2**(k/2) <= sqrt(a) < 2**((k+1)/2) <= 2**(k/2 + 1)`
        //
        // Consequently, `2**(log2(a) / 2)` is a good first approximation of `sqrt(a)` with at least 1 correct bit.
        uint256 result = 1 << (log2(a) >> 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) {
        unchecked {
            uint256 result = sqrt(a);
            return result + (rounding == Rounding.Up && result * result < a ? 1 : 0);
        }
    }

    /**
     * @dev Return the log in base 2, rounded down, of a positive value.
     * Returns 0 if given 0.
     */
    function log2(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >> 128 > 0) {
                value >>= 128;
                result += 128;
            }
            if (value >> 64 > 0) {
                value >>= 64;
                result += 64;
            }
            if (value >> 32 > 0) {
                value >>= 32;
                result += 32;
            }
            if (value >> 16 > 0) {
                value >>= 16;
                result += 16;
            }
            if (value >> 8 > 0) {
                value >>= 8;
                result += 8;
            }
            if (value >> 4 > 0) {
                value >>= 4;
                result += 4;
            }
            if (value >> 2 > 0) {
                value >>= 2;
                result += 2;
            }
            if (value >> 1 > 0) {
                result += 1;
            }
        }
        return result;
    }

    /**
     * @dev Return the log in base 2, following the selected rounding direction, of a positive value.
     * Returns 0 if given 0.
     */
    function log2(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log2(value);
            return result + (rounding == Rounding.Up && 1 << result < value ? 1 : 0);
        }
    }

    /**
     * @dev Return the log in base 10, rounded down, of a positive value.
     * Returns 0 if given 0.
     */
    function log10(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >= 10**64) {
                value /= 10**64;
                result += 64;
            }
            if (value >= 10**32) {
                value /= 10**32;
                result += 32;
            }
            if (value >= 10**16) {
                value /= 10**16;
                result += 16;
            }
            if (value >= 10**8) {
                value /= 10**8;
                result += 8;
            }
            if (value >= 10**4) {
                value /= 10**4;
                result += 4;
            }
            if (value >= 10**2) {
                value /= 10**2;
                result += 2;
            }
            if (value >= 10**1) {
                result += 1;
            }
        }
        return result;
    }

    /**
     * @dev Return the log in base 10, following the selected rounding direction, of a positive value.
     * Returns 0 if given 0.
     */
    function log10(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log10(value);
            return result + (rounding == Rounding.Up && 10**result < value ? 1 : 0);
        }
    }

    /**
     * @dev Return the log in base 256, rounded down, of a positive value.
     * Returns 0 if given 0.
     *
     * Adding one to the result gives the number of pairs of hex symbols needed to represent `value` as a hex string.
     */
    function log256(uint256 value) internal pure returns (uint256) {
        uint256 result = 0;
        unchecked {
            if (value >> 128 > 0) {
                value >>= 128;
                result += 16;
            }
            if (value >> 64 > 0) {
                value >>= 64;
                result += 8;
            }
            if (value >> 32 > 0) {
                value >>= 32;
                result += 4;
            }
            if (value >> 16 > 0) {
                value >>= 16;
                result += 2;
            }
            if (value >> 8 > 0) {
                result += 1;
            }
        }
        return result;
    }

    /**
     * @dev Return the log in base 10, following the selected rounding direction, of a positive value.
     * Returns 0 if given 0.
     */
    function log256(uint256 value, Rounding rounding) internal pure returns (uint256) {
        unchecked {
            uint256 result = log256(value);
            return result + (rounding == Rounding.Up && 1 << (result * 8) < value ? 1 : 0);
        }
    }
}

// File: @openzeppelin/contracts/utils/Strings.sol


// OpenZeppelin Contracts (last updated v4.8.0) (utils/Strings.sol)

pragma solidity ^0.8.0;


/**
 * @dev String operations.
 */
library Strings {
    bytes16 private constant _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) {
        unchecked {
            uint256 length = Math.log10(value) + 1;
            string memory buffer = new string(length);
            uint256 ptr;
            /// @solidity memory-safe-assembly
            assembly {
                ptr := add(buffer, add(32, length))
            }
            while (true) {
                ptr--;
                /// @solidity memory-safe-assembly
                assembly {
                    mstore8(ptr, byte(mod(value, 10), _SYMBOLS))
                }
                value /= 10;
                if (value == 0) break;
            }
            return buffer;
        }
    }

    /**
     * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
     */
    function toHexString(uint256 value) internal pure returns (string memory) {
        unchecked {
            return toHexString(value, Math.log256(value) + 1);
        }
    }

    /**
     * @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] = _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/cryptography/ECDSA.sol


// OpenZeppelin Contracts (last updated v4.8.0) (utils/cryptography/ECDSA.sol)

pragma solidity ^0.8.0;


/**
 * @dev Elliptic Curve Digital Signature Algorithm (ECDSA) operations.
 *
 * These functions can be used to verify that a message was signed by the holder
 * of the private keys of a given address.
 */
library ECDSA {
    enum RecoverError {
        NoError,
        InvalidSignature,
        InvalidSignatureLength,
        InvalidSignatureS,
        InvalidSignatureV // Deprecated in v4.8
    }

    function _throwError(RecoverError error) private pure {
        if (error == RecoverError.NoError) {
            return; // no error: do nothing
        } else if (error == RecoverError.InvalidSignature) {
            revert("ECDSA: invalid signature");
        } else if (error == RecoverError.InvalidSignatureLength) {
            revert("ECDSA: invalid signature length");
        } else if (error == RecoverError.InvalidSignatureS) {
            revert("ECDSA: invalid signature 's' value");
        }
    }

    /**
     * @dev Returns the address that signed a hashed message (`hash`) with
     * `signature` or error string. This address can then be used for verification purposes.
     *
     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:
     * this function rejects them by requiring the `s` value to be in the lower
     * half order, and the `v` value to be either 27 or 28.
     *
     * IMPORTANT: `hash` _must_ be the result of a hash operation for the
     * verification to be secure: it is possible to craft signatures that
     * recover to arbitrary addresses for non-hashed data. A safe way to ensure
     * this is by receiving a hash of the original message (which may otherwise
     * be too long), and then calling {toEthSignedMessageHash} on it.
     *
     * Documentation for signature generation:
     * - with https://web3js.readthedocs.io/en/v1.3.4/web3-eth-accounts.html#sign[Web3.js]
     * - with https://docs.ethers.io/v5/api/signer/#Signer-signMessage[ethers]
     *
     * _Available since v4.3._
     */
    function tryRecover(bytes32 hash, bytes memory signature) internal pure returns (address, RecoverError) {
        if (signature.length == 65) {
            bytes32 r;
            bytes32 s;
            uint8 v;
            // ecrecover takes the signature parameters, and the only way to get them
            // currently is to use assembly.
            /// @solidity memory-safe-assembly
            assembly {
                r := mload(add(signature, 0x20))
                s := mload(add(signature, 0x40))
                v := byte(0, mload(add(signature, 0x60)))
            }
            return tryRecover(hash, v, r, s);
        } else {
            return (address(0), RecoverError.InvalidSignatureLength);
        }
    }

    /**
     * @dev Returns the address that signed a hashed message (`hash`) with
     * `signature`. This address can then be used for verification purposes.
     *
     * The `ecrecover` EVM opcode allows for malleable (non-unique) signatures:
     * this function rejects them by requiring the `s` value to be in the lower
     * half order, and the `v` value to be either 27 or 28.
     *
     * IMPORTANT: `hash` _must_ be the result of a hash operation for the
     * verification to be secure: it is possible to craft signatures that
     * recover to arbitrary addresses for non-hashed data. A safe way to ensure
     * this is by receiving a hash of the original message (which may otherwise
     * be too long), and then calling {toEthSignedMessageHash} on it.
     */
    function recover(bytes32 hash, bytes memory signature) internal pure returns (address) {
        (address recovered, RecoverError error) = tryRecover(hash, signature);
        _throwError(error);
        return recovered;
    }

    /**
     * @dev Overload of {ECDSA-tryRecover} that receives the `r` and `vs` short-signature fields separately.
     *
     * See https://eips.ethereum.org/EIPS/eip-2098[EIP-2098 short signatures]
     *
     * _Available since v4.3._
     */
    function tryRecover(
        bytes32 hash,
        bytes32 r,
        bytes32 vs
    ) internal pure returns (address, RecoverError) {
        bytes32 s = vs & bytes32(0x7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff);
        uint8 v = uint8((uint256(vs) >> 255) + 27);
        return tryRecover(hash, v, r, s);
    }

    /**
     * @dev Overload of {ECDSA-recover} that receives the `r and `vs` short-signature fields separately.
     *
     * _Available since v4.2._
     */
    function recover(
        bytes32 hash,
        bytes32 r,
        bytes32 vs
    ) internal pure returns (address) {
        (address recovered, RecoverError error) = tryRecover(hash, r, vs);
        _throwError(error);
        return recovered;
    }

    /**
     * @dev Overload of {ECDSA-tryRecover} that receives the `v`,
     * `r` and `s` signature fields separately.
     *
     * _Available since v4.3._
     */
    function tryRecover(
        bytes32 hash,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal pure returns (address, RecoverError) {
        // EIP-2 still allows signature malleability for ecrecover(). Remove this possibility and make the signature
        // unique. Appendix F in the Ethereum Yellow paper (https://ethereum.github.io/yellowpaper/paper.pdf), defines
        // the valid range for s in (301): 0 < s < secp256k1n ÷ 2 + 1, and for v in (302): v ∈ {27, 28}. Most
        // signatures from current libraries generate a unique signature with an s-value in the lower half order.
        //
        // If your library generates malleable signatures, such as s-values in the upper range, calculate a new s-value
        // with 0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFEBAAEDCE6AF48A03BBFD25E8CD0364141 - s1 and flip v from 27 to 28 or
        // vice versa. If your library also generates signatures with 0/1 for v instead 27/28, add 27 to v to accept
        // these malleable signatures as well.
        if (uint256(s) > 0x7FFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF5D576E7357A4501DDFE92F46681B20A0) {
            return (address(0), RecoverError.InvalidSignatureS);
        }

        // If the signature is valid (and not malleable), return the signer address
        address signer = ecrecover(hash, v, r, s);
        if (signer == address(0)) {
            return (address(0), RecoverError.InvalidSignature);
        }

        return (signer, RecoverError.NoError);
    }

    /**
     * @dev Overload of {ECDSA-recover} that receives the `v`,
     * `r` and `s` signature fields separately.
     */
    function recover(
        bytes32 hash,
        uint8 v,
        bytes32 r,
        bytes32 s
    ) internal pure returns (address) {
        (address recovered, RecoverError error) = tryRecover(hash, v, r, s);
        _throwError(error);
        return recovered;
    }

    /**
     * @dev Returns an Ethereum Signed Message, created from a `hash`. This
     * produces hash corresponding to the one signed with the
     * https://eth.wiki/json-rpc/API#eth_sign[`eth_sign`]
     * JSON-RPC method as part of EIP-191.
     *
     * See {recover}.
     */
    function toEthSignedMessageHash(bytes32 hash) internal pure returns (bytes32) {
        // 32 is the length in bytes of hash,
        // enforced by the type signature above
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n32", hash));
    }

    /**
     * @dev Returns an Ethereum Signed Message, created from `s`. This
     * produces hash corresponding to the one signed with the
     * https://eth.wiki/json-rpc/API#eth_sign[`eth_sign`]
     * JSON-RPC method as part of EIP-191.
     *
     * See {recover}.
     */
    function toEthSignedMessageHash(bytes memory s) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked("\x19Ethereum Signed Message:\n", Strings.toString(s.length), s));
    }

    /**
     * @dev Returns an Ethereum Signed Typed Data, created from a
     * `domainSeparator` and a `structHash`. This produces hash corresponding
     * to the one signed with the
     * https://eips.ethereum.org/EIPS/eip-712[`eth_signTypedData`]
     * JSON-RPC method as part of EIP-712.
     *
     * See {recover}.
     */
    function toTypedDataHash(bytes32 domainSeparator, bytes32 structHash) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked("\x19\x01", domainSeparator, structHash));
    }
}

// File: @openzeppelin/contracts/utils/Context.sol


// 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/security/Pausable.sol


// OpenZeppelin Contracts (last updated v4.7.0) (security/Pausable.sol)

pragma solidity ^0.8.0;


/**
 * @dev Contract module which allows children to implement an emergency stop
 * mechanism that can be triggered by an authorized account.
 *
 * This module is used through inheritance. It will make available the
 * modifiers `whenNotPaused` and `whenPaused`, which can be applied to
 * the functions of your contract. Note that they will not be pausable by
 * simply including this module, only once the modifiers are put in place.
 */
abstract contract Pausable is Context {
    /**
     * @dev Emitted when the pause is triggered by `account`.
     */
    event Paused(address account);

    /**
     * @dev Emitted when the pause is lifted by `account`.
     */
    event Unpaused(address account);

    bool private _paused;

    /**
     * @dev Initializes the contract in unpaused state.
     */
    constructor() {
        _paused = false;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        _requireNotPaused();
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        _requirePaused();
        _;
    }

    /**
     * @dev Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual returns (bool) {
        return _paused;
    }

    /**
     * @dev Throws if the contract is paused.
     */
    function _requireNotPaused() internal view virtual {
        require(!paused(), "Pausable: paused");
    }

    /**
     * @dev Throws if the contract is not paused.
     */
    function _requirePaused() internal view virtual {
        require(paused(), "Pausable: not paused");
    }

    /**
     * @dev Triggers stopped state.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    function _pause() internal virtual whenNotPaused {
        _paused = true;
        emit Paused(_msgSender());
    }

    /**
     * @dev Returns to normal state.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    function _unpause() internal virtual whenPaused {
        _paused = false;
        emit Unpaused(_msgSender());
    }
}

// File: @openzeppelin/contracts/access/Ownable.sol


// OpenZeppelin Contracts (last updated v4.7.0) (access/Ownable.sol)

pragma solidity ^0.8.0;


/**
 * @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 Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        _checkOwner();
        _;
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if the sender is not the owner.
     */
    function _checkOwner() internal view virtual {
        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);
    }
}

// File: @openzeppelin/contracts/utils/Address.sol


// OpenZeppelin Contracts (last updated v4.8.0) (utils/Address.sol)

pragma solidity ^0.8.1;

/**
 * @dev Collection of functions related to the address type
 */
library Address {
    /**
     * @dev Returns true if `account` is a contract.
     *
     * [IMPORTANT]
     * ====
     * It is unsafe to assume that an address for which this function returns
     * false is an externally-owned account (EOA) and not a contract.
     *
     * Among others, `isContract` will return false for the following
     * types of addresses:
     *
     *  - an externally-owned account
     *  - a contract in construction
     *  - an address where a contract will be created
     *  - an address where a contract lived, but was destroyed
     * ====
     *
     * [IMPORTANT]
     * ====
     * You shouldn't rely on `isContract` to protect against flash loan attacks!
     *
     * Preventing calls from contracts is highly discouraged. It breaks composability, breaks support for smart wallets
     * like Gnosis Safe, and does not provide security since it can be circumvented by calling from a contract
     * constructor.
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize/address.code.length, which returns 0
        // for contracts in construction, since the code is only stored at the end
        // of the constructor execution.

        return account.code.length > 0;
    }

    /**
     * @dev Replacement for Solidity's `transfer`: sends `amount` wei to
     * `recipient`, forwarding all available gas and reverting on errors.
     *
     * https://eips.ethereum.org/EIPS/eip-1884[EIP1884] increases the gas cost
     * of certain opcodes, possibly making contracts go over the 2300 gas limit
     * imposed by `transfer`, making them unable to receive funds via
     * `transfer`. {sendValue} removes this limitation.
     *
     * https://diligence.consensys.net/posts/2019/09/stop-using-soliditys-transfer-now/[Learn more].
     *
     * IMPORTANT: because control is transferred to `recipient`, care must be
     * taken to not create reentrancy vulnerabilities. Consider using
     * {ReentrancyGuard} or the
     * https://solidity.readthedocs.io/en/v0.5.11/security-considerations.html#use-the-checks-effects-interactions-pattern[checks-effects-interactions pattern].
     */
    function sendValue(address payable recipient, uint256 amount) internal {
        require(address(this).balance >= amount, "Address: insufficient balance");

        (bool success, ) = recipient.call{value: amount}("");
        require(success, "Address: unable to send value, recipient may have reverted");
    }

    /**
     * @dev Performs a Solidity function call using a low level `call`. A
     * plain `call` is an unsafe replacement for a function call: use this
     * function instead.
     *
     * If `target` reverts with a revert reason, it is bubbled up by this
     * function (like regular Solidity function calls).
     *
     * Returns the raw returned data. To convert to the expected return value,
     * use https://solidity.readthedocs.io/en/latest/units-and-global-variables.html?highlight=abi.decode#abi-encoding-and-decoding-functions[`abi.decode`].
     *
     * Requirements:
     *
     * - `target` must be a contract.
     * - calling `target` with `data` must not revert.
     *
     * _Available since v3.1._
     */
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, "Address: low-level call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`], but with
     * `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but also transferring `value` wei to `target`.
     *
     * Requirements:
     *
     * - the calling contract must have an ETH balance of at least `value`.
     * - the called Solidity function must be `payable`.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, value, "Address: low-level call with value failed");
    }

    /**
     * @dev Same as {xref-Address-functionCallWithValue-address-bytes-uint256-}[`functionCallWithValue`], but
     * with `errorMessage` as a fallback revert reason when `target` reverts.
     *
     * _Available since v3.1._
     */
    function functionCallWithValue(
        address target,
        bytes memory data,
        uint256 value,
        string memory errorMessage
    ) internal returns (bytes memory) {
        require(address(this).balance >= value, "Address: insufficient balance for call");
        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResultFromTarget(target, success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a static call.
     *
     * _Available since v3.3._
     */
    function functionStaticCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResultFromTarget(target, success, returndata, errorMessage);
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    /**
     * @dev Same as {xref-Address-functionCall-address-bytes-string-}[`functionCall`],
     * but performing a delegate call.
     *
     * _Available since v3.4._
     */
    function functionDelegateCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResultFromTarget(target, success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verify that a low level call to smart-contract was successful, and revert (either by bubbling
     * the revert reason or using the provided one) in case of unsuccessful call or if target was not a contract.
     *
     * _Available since v4.8._
     */
    function verifyCallResultFromTarget(
        address target,
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal view returns (bytes memory) {
        if (success) {
            if (returndata.length == 0) {
                // only check isContract if the call was successful and the return data is empty
                // otherwise we already know that it was a contract
                require(isContract(target), "Address: call to non-contract");
            }
            return returndata;
        } else {
            _revert(returndata, errorMessage);
        }
    }

    /**
     * @dev Tool to verify that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason or using the provided one.
     *
     * _Available since v4.3._
     */
    function verifyCallResult(
        bool success,
        bytes memory returndata,
        string memory errorMessage
    ) internal pure returns (bytes memory) {
        if (success) {
            return returndata;
        } else {
            _revert(returndata, errorMessage);
        }
    }

    function _revert(bytes memory returndata, string memory errorMessage) private pure {
        // Look for revert reason and bubble it up if present
        if (returndata.length > 0) {
            // The easiest way to bubble the revert reason is using memory via assembly
            /// @solidity memory-safe-assembly
            assembly {
                let returndata_size := mload(returndata)
                revert(add(32, returndata), returndata_size)
            }
        } else {
            revert(errorMessage);
        }
    }
}

// File: contracts/ExenoCollection.sol


pragma solidity 0.8.18;







interface IERC20 {
    function allowance(address, address) external view returns(uint256);
    function balanceOf(address) external view returns(uint256);
    function transfer(address, uint256) external;
    function transferFrom(address, address, uint256) external;
}

contract ExenoCollection is
    Ownable,
    Pausable,
    ReentrancyGuard,
    IERC1363Receiver
{
    IERC20 public immutable CORE_TOKEN;
    
    address[5] public SIGNERS;
    
    mapping(address signer => bool status) internal signers;

    mapping(bytes32 nonce => bool status) internal nonces;

    /**
     */
    event Purchase(
        bytes32 indexed id,
        address beneficiary,
        uint256 tier,
        address currency,
        uint256 price,
        uint256 bonus,
        uint256 ticket
    );

    event SignersChanged (
        address[5] signers
    );

    /// Rejected signature when verifing a payload
    error UnauthorizedSigner();

    /// Nonce already used when verifing a payload
    error NonceAlreadyUsed();

    /// Only NFT owner can call `resolve` and only EXN contract can call `onTransferReceived`
    error UnauthorizedCaller();

    /// Allowance is less than the `price` argument when invoking the `buy` method (workaround: set `price` to zero)
    error UndeliveredAllowance(uint256);

    /// Attached native currency amount is less than the `price` argument when invoking the `buy` method (workaround: set `price` to zero)
    error UndeliveredNativePayment(uint256);

    /// Amount send via `transferAndCall` does not match the `price` argument
    error UndeliveredTokenPayment(uint256);

    /// There are not enough EXN tokens in the contract for bonus payout (workaround: set `bonus` to zero)
    error CoreTokenBalanceTooLow(uint256);

    /// Only EXN payment is supported with `transferAndCall`
    error UnsupportedCurrency();

    /// No bonus payout is supported with `transferAndCall`
    error UnsupportedBonus();

    /**
     */
    constructor(
        address coreToken
    )
    {
        CORE_TOKEN = IERC20(coreToken);
    }

    modifier onlyCoreToken() {
        if (msg.sender != address(CORE_TOKEN))
            revert UnauthorizedCaller();
        _;
    }

    /**
     */
    function setSigners(address[5] memory list)
        external onlyOwner
    {
        for (uint8 i = 0; i < 5; i++) {
            signers[SIGNERS[i]] = false;
        }
        for (uint8 i = 0; i < 5; i++) {
            signers[list[i]] = true;
            SIGNERS[i] = list[i];
        }
        emit SignersChanged(list);
    }

    /**
     */
    function buy(
        bytes32 id,             // nonce
        address beneficiary,    // recepient of the new NFT
        uint256 tier,           // tier id, i.e. 1 | 2 | 3
        address currency,       // 0x0000000000000000000000000000000000000000 for native payment or address for other ERC20 tokens
        uint256 price,          // price in currency to be charged for NFT
        uint256 bonus,          // bonus in EXN
        bytes calldata signature
    )
        external payable nonReentrant whenNotPaused
    {
        if (!signers[msg.sender]) {
            _verifySigner(id, _extractSigner(abi.encodePacked(id, beneficiary, tier, currency, price, bonus), signature));
        }
        if (currency != address(0)) {
            if (IERC20(currency).allowance(msg.sender, address(this)) < price)
                revert UndeliveredAllowance(price);
            IERC20(currency).transferFrom(msg.sender, address(this), price);
        } else {
            if (msg.value < price)
                revert UndeliveredNativePayment(price);
        }
        if (bonus > 0) {
            if (CORE_TOKEN.balanceOf(address(this)) < bonus)
                revert CoreTokenBalanceTooLow(bonus);
            CORE_TOKEN.transfer(beneficiary, bonus);
        }
        uint256 ticket = _issueTicket(beneficiary, tier);
        emit Purchase(id, beneficiary, tier, currency, price, bonus, ticket);
    }

    function onTransferReceived(
        address,
        address sender,
        uint256 amount,
        bytes memory data
    ) public override whenNotPaused onlyCoreToken returns(bytes4) {
        (
            bytes32 id,
            address beneficiary,
            uint256 tier,
            address currency,
            uint256 price,
            uint256 bonus,
            bytes memory signature
        ) = abi.decode(data, (bytes32, address, uint256, address, uint256, uint256, bytes));
        if (!signers[sender]) {
            _verifySigner(id, _extractSigner(abi.encodePacked(id, beneficiary, tier, currency, price, bonus), signature));
        }
        if (currency != address(CORE_TOKEN))
            revert UnsupportedCurrency();
        if (bonus > 0)
            revert UnsupportedBonus();
        if (amount < price)
            revert UndeliveredTokenPayment(price);
        uint256 ticket = _issueTicket(beneficiary, tier);
        emit Purchase(id, beneficiary, tier, currency, price, bonus, ticket);
        return IERC1363Receiver(this).onTransferReceived.selector;
    }

    function supportsInterface(bytes4 interfaceId)
        public view virtual returns(bool)
    {
        return interfaceId == type(IERC1363Receiver).interfaceId;
    }

    /**
     */
    function withdrawNative(
        address wallet,
        uint256 amount
    )
        external onlyOwner
    {
        Address.sendValue(payable(wallet), amount);
    }

    function withdrawToken(
        address token,
        address wallet,
        uint256 amount
    )
        external onlyOwner
    {
        IERC20(token).transfer(wallet, amount);
    }

    /**
     */
    function pause()
        external onlyOwner
    {
        _pause();
    }
    
    function unpause()
        external onlyOwner
    {
        _unpause();
    }

    /**
     */
    function getLiquidity()
        external virtual view returns(uint256 native, uint256 core, uint256 payout, uint256 link)
    {
        return (
            address(this).balance,
            CORE_TOKEN.balanceOf(address(this)),
            0,
            0
        );
    }

    function getBalance(address holder)
        external view returns(uint256 native, uint256 core)
    {
        return (
            address(holder).balance,
            CORE_TOKEN.balanceOf(address(holder))
        );
    }

    /**
     */
    function _verifySigner(
        bytes32 id,
        address signer
    )
        internal
    {
        if (!signers[signer])
            revert UnauthorizedSigner();
        if (nonces[id])
            revert NonceAlreadyUsed();
        nonces[id] = true;
    }

    function _issueTicket(
        address,
        uint256
    )
        internal virtual returns(uint256 ticket)
    {}

    function _extractSigner(
        bytes memory message,
        bytes memory signature
    )
        internal pure returns(address)
    {
        return ECDSA.recover(ECDSA.toEthSignedMessageHash(keccak256(message)), signature);
    }
}
// File: @openzeppelin/contracts/utils/introspection/IERC165.sol


// 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


// OpenZeppelin Contracts v4.4.1 (utils/introspection/ERC165.sol)

pragma solidity ^0.8.0;


/**
 * @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/token/ERC1155/IERC1155Receiver.sol


// OpenZeppelin Contracts (last updated v4.5.0) (token/ERC1155/IERC1155Receiver.sol)

pragma solidity ^0.8.0;


/**
 * @dev _Available since v3.1._
 */
interface IERC1155Receiver is IERC165 {
    /**
     * @dev Handles the receipt of a single ERC1155 token type. This function is
     * called at the end of a `safeTransferFrom` after the balance has been updated.
     *
     * NOTE: To accept the transfer, this must return
     * `bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))`
     * (i.e. 0xf23a6e61, or its own function selector).
     *
     * @param operator The address which initiated the transfer (i.e. msg.sender)
     * @param from The address which previously owned the token
     * @param id The ID of the token being transferred
     * @param value The amount of tokens being transferred
     * @param data Additional data with no specified format
     * @return `bytes4(keccak256("onERC1155Received(address,address,uint256,uint256,bytes)"))` if transfer is allowed
     */
    function onERC1155Received(
        address operator,
        address from,
        uint256 id,
        uint256 value,
        bytes calldata data
    ) external returns (bytes4);

    /**
     * @dev Handles the receipt of a multiple ERC1155 token types. This function
     * is called at the end of a `safeBatchTransferFrom` after the balances have
     * been updated.
     *
     * NOTE: To accept the transfer(s), this must return
     * `bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))`
     * (i.e. 0xbc197c81, or its own function selector).
     *
     * @param operator The address which initiated the batch transfer (i.e. msg.sender)
     * @param from The address which previously owned the token
     * @param ids An array containing ids of each token being transferred (order and length must match values array)
     * @param values An array containing amounts of each token being transferred (order and length must match ids array)
     * @param data Additional data with no specified format
     * @return `bytes4(keccak256("onERC1155BatchReceived(address,address,uint256[],uint256[],bytes)"))` if transfer is allowed
     */
    function onERC1155BatchReceived(
        address operator,
        address from,
        uint256[] calldata ids,
        uint256[] calldata values,
        bytes calldata data
    ) external returns (bytes4);
}

// File: @openzeppelin/contracts/token/ERC1155/IERC1155.sol


// OpenZeppelin Contracts (last updated v4.7.0) (token/ERC1155/IERC1155.sol)

pragma solidity ^0.8.0;


/**
 * @dev Required interface of an ERC1155 compliant contract, as defined in the
 * https://eips.ethereum.org/EIPS/eip-1155[EIP].
 *
 * _Available since v3.1._
 */
interface IERC1155 is IERC165 {
    /**
     * @dev Emitted when `value` tokens of token type `id` are transferred from `from` to `to` by `operator`.
     */
    event TransferSingle(address indexed operator, address indexed from, address indexed to, uint256 id, uint256 value);

    /**
     * @dev Equivalent to multiple {TransferSingle} events, where `operator`, `from` and `to` are the same for all
     * transfers.
     */
    event TransferBatch(
        address indexed operator,
        address indexed from,
        address indexed to,
        uint256[] ids,
        uint256[] values
    );

    /**
     * @dev Emitted when `account` grants or revokes permission to `operator` to transfer their tokens, according to
     * `approved`.
     */
    event ApprovalForAll(address indexed account, address indexed operator, bool approved);

    /**
     * @dev Emitted when the URI for token type `id` changes to `value`, if it is a non-programmatic URI.
     *
     * If an {URI} event was emitted for `id`, the standard
     * https://eips.ethereum.org/EIPS/eip-1155#metadata-extensions[guarantees] that `value` will equal the value
     * returned by {IERC1155MetadataURI-uri}.
     */
    event URI(string value, uint256 indexed id);

    /**
     * @dev Returns the amount of tokens of token type `id` owned by `account`.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     */
    function balanceOf(address account, uint256 id) external view returns (uint256);

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {balanceOf}.
     *
     * Requirements:
     *
     * - `accounts` and `ids` must have the same length.
     */
    function balanceOfBatch(address[] calldata accounts, uint256[] calldata ids)
        external
        view
        returns (uint256[] memory);

    /**
     * @dev Grants or revokes permission to `operator` to transfer the caller's tokens, according to `approved`,
     *
     * Emits an {ApprovalForAll} event.
     *
     * Requirements:
     *
     * - `operator` cannot be the caller.
     */
    function setApprovalForAll(address operator, bool approved) external;

    /**
     * @dev Returns true if `operator` is approved to transfer ``account``'s tokens.
     *
     * See {setApprovalForAll}.
     */
    function isApprovedForAll(address account, address operator) external view returns (bool);

    /**
     * @dev Transfers `amount` tokens of token type `id` from `from` to `to`.
     *
     * Emits a {TransferSingle} event.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - If the caller is not `from`, it must have been approved to spend ``from``'s tokens via {setApprovalForAll}.
     * - `from` must have a balance of tokens of type `id` of at least `amount`.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
     * acceptance magic value.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 id,
        uint256 amount,
        bytes calldata data
    ) external;

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {safeTransferFrom}.
     *
     * Emits a {TransferBatch} event.
     *
     * Requirements:
     *
     * - `ids` and `amounts` must have the same length.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155BatchReceived} and return the
     * acceptance magic value.
     */
    function safeBatchTransferFrom(
        address from,
        address to,
        uint256[] calldata ids,
        uint256[] calldata amounts,
        bytes calldata data
    ) external;
}

// File: @openzeppelin/contracts/token/ERC1155/extensions/IERC1155MetadataURI.sol


// OpenZeppelin Contracts v4.4.1 (token/ERC1155/extensions/IERC1155MetadataURI.sol)

pragma solidity ^0.8.0;


/**
 * @dev Interface of the optional ERC1155MetadataExtension interface, as defined
 * in the https://eips.ethereum.org/EIPS/eip-1155#metadata-extensions[EIP].
 *
 * _Available since v3.1._
 */
interface IERC1155MetadataURI is IERC1155 {
    /**
     * @dev Returns the URI for token type `id`.
     *
     * If the `\{id\}` substring is present in the URI, it must be replaced by
     * clients with the actual token type ID.
     */
    function uri(uint256 id) external view returns (string memory);
}

// File: @openzeppelin/contracts/token/ERC1155/ERC1155.sol


// OpenZeppelin Contracts (last updated v4.8.0) (token/ERC1155/ERC1155.sol)

pragma solidity ^0.8.0;







/**
 * @dev Implementation of the basic standard multi-token.
 * See https://eips.ethereum.org/EIPS/eip-1155
 * Originally based on code by Enjin: https://github.com/enjin/erc-1155
 *
 * _Available since v3.1._
 */
contract ERC1155 is Context, ERC165, IERC1155, IERC1155MetadataURI {
    using Address for address;

    // Mapping from token ID to account balances
    mapping(uint256 => mapping(address => uint256)) private _balances;

    // Mapping from account to operator approvals
    mapping(address => mapping(address => bool)) private _operatorApprovals;

    // Used as the URI for all token types by relying on ID substitution, e.g. https://token-cdn-domain/{id}.json
    string private _uri;

    /**
     * @dev See {_setURI}.
     */
    constructor(string memory uri_) {
        _setURI(uri_);
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override(ERC165, IERC165) returns (bool) {
        return
            interfaceId == type(IERC1155).interfaceId ||
            interfaceId == type(IERC1155MetadataURI).interfaceId ||
            super.supportsInterface(interfaceId);
    }

    /**
     * @dev See {IERC1155MetadataURI-uri}.
     *
     * This implementation returns the same URI for *all* token types. It relies
     * on the token type ID substitution mechanism
     * https://eips.ethereum.org/EIPS/eip-1155#metadata[defined in the EIP].
     *
     * Clients calling this function must replace the `\{id\}` substring with the
     * actual token type ID.
     */
    function uri(uint256) public view virtual override returns (string memory) {
        return _uri;
    }

    /**
     * @dev See {IERC1155-balanceOf}.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     */
    function balanceOf(address account, uint256 id) public view virtual override returns (uint256) {
        require(account != address(0), "ERC1155: address zero is not a valid owner");
        return _balances[id][account];
    }

    /**
     * @dev See {IERC1155-balanceOfBatch}.
     *
     * Requirements:
     *
     * - `accounts` and `ids` must have the same length.
     */
    function balanceOfBatch(address[] memory accounts, uint256[] memory ids)
        public
        view
        virtual
        override
        returns (uint256[] memory)
    {
        require(accounts.length == ids.length, "ERC1155: accounts and ids length mismatch");

        uint256[] memory batchBalances = new uint256[](accounts.length);

        for (uint256 i = 0; i < accounts.length; ++i) {
            batchBalances[i] = balanceOf(accounts[i], ids[i]);
        }

        return batchBalances;
    }

    /**
     * @dev See {IERC1155-setApprovalForAll}.
     */
    function setApprovalForAll(address operator, bool approved) public virtual override {
        _setApprovalForAll(_msgSender(), operator, approved);
    }

    /**
     * @dev See {IERC1155-isApprovedForAll}.
     */
    function isApprovedForAll(address account, address operator) public view virtual override returns (bool) {
        return _operatorApprovals[account][operator];
    }

    /**
     * @dev See {IERC1155-safeTransferFrom}.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 id,
        uint256 amount,
        bytes memory data
    ) public virtual override {
        require(
            from == _msgSender() || isApprovedForAll(from, _msgSender()),
            "ERC1155: caller is not token owner or approved"
        );
        _safeTransferFrom(from, to, id, amount, data);
    }

    /**
     * @dev See {IERC1155-safeBatchTransferFrom}.
     */
    function safeBatchTransferFrom(
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    ) public virtual override {
        require(
            from == _msgSender() || isApprovedForAll(from, _msgSender()),
            "ERC1155: caller is not token owner or approved"
        );
        _safeBatchTransferFrom(from, to, ids, amounts, data);
    }

    /**
     * @dev Transfers `amount` tokens of token type `id` from `from` to `to`.
     *
     * Emits a {TransferSingle} event.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - `from` must have a balance of tokens of type `id` of at least `amount`.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
     * acceptance magic value.
     */
    function _safeTransferFrom(
        address from,
        address to,
        uint256 id,
        uint256 amount,
        bytes memory data
    ) internal virtual {
        require(to != address(0), "ERC1155: transfer to the zero address");

        address operator = _msgSender();
        uint256[] memory ids = _asSingletonArray(id);
        uint256[] memory amounts = _asSingletonArray(amount);

        _beforeTokenTransfer(operator, from, to, ids, amounts, data);

        uint256 fromBalance = _balances[id][from];
        require(fromBalance >= amount, "ERC1155: insufficient balance for transfer");
        unchecked {
            _balances[id][from] = fromBalance - amount;
        }
        _balances[id][to] += amount;

        emit TransferSingle(operator, from, to, id, amount);

        _afterTokenTransfer(operator, from, to, ids, amounts, data);

        _doSafeTransferAcceptanceCheck(operator, from, to, id, amount, data);
    }

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_safeTransferFrom}.
     *
     * Emits a {TransferBatch} event.
     *
     * Requirements:
     *
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155BatchReceived} and return the
     * acceptance magic value.
     */
    function _safeBatchTransferFrom(
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    ) internal virtual {
        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");
        require(to != address(0), "ERC1155: transfer to the zero address");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, from, to, ids, amounts, data);

        for (uint256 i = 0; i < ids.length; ++i) {
            uint256 id = ids[i];
            uint256 amount = amounts[i];

            uint256 fromBalance = _balances[id][from];
            require(fromBalance >= amount, "ERC1155: insufficient balance for transfer");
            unchecked {
                _balances[id][from] = fromBalance - amount;
            }
            _balances[id][to] += amount;
        }

        emit TransferBatch(operator, from, to, ids, amounts);

        _afterTokenTransfer(operator, from, to, ids, amounts, data);

        _doSafeBatchTransferAcceptanceCheck(operator, from, to, ids, amounts, data);
    }

    /**
     * @dev Sets a new URI for all token types, by relying on the token type ID
     * substitution mechanism
     * https://eips.ethereum.org/EIPS/eip-1155#metadata[defined in the EIP].
     *
     * By this mechanism, any occurrence of the `\{id\}` substring in either the
     * URI or any of the amounts in the JSON file at said URI will be replaced by
     * clients with the token type ID.
     *
     * For example, the `https://token-cdn-domain/\{id\}.json` URI would be
     * interpreted by clients as
     * `https://token-cdn-domain/000000000000000000000000000000000000000000000000000000000004cce0.json`
     * for token type ID 0x4cce0.
     *
     * See {uri}.
     *
     * Because these URIs cannot be meaningfully represented by the {URI} event,
     * this function emits no events.
     */
    function _setURI(string memory newuri) internal virtual {
        _uri = newuri;
    }

    /**
     * @dev Creates `amount` tokens of token type `id`, and assigns them to `to`.
     *
     * Emits a {TransferSingle} event.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
     * acceptance magic value.
     */
    function _mint(
        address to,
        uint256 id,
        uint256 amount,
        bytes memory data
    ) internal virtual {
        require(to != address(0), "ERC1155: mint to the zero address");

        address operator = _msgSender();
        uint256[] memory ids = _asSingletonArray(id);
        uint256[] memory amounts = _asSingletonArray(amount);

        _beforeTokenTransfer(operator, address(0), to, ids, amounts, data);

        _balances[id][to] += amount;
        emit TransferSingle(operator, address(0), to, id, amount);

        _afterTokenTransfer(operator, address(0), to, ids, amounts, data);

        _doSafeTransferAcceptanceCheck(operator, address(0), to, id, amount, data);
    }

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_mint}.
     *
     * Emits a {TransferBatch} event.
     *
     * Requirements:
     *
     * - `ids` and `amounts` must have the same length.
     * - If `to` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155BatchReceived} and return the
     * acceptance magic value.
     */
    function _mintBatch(
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    ) internal virtual {
        require(to != address(0), "ERC1155: mint to the zero address");
        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, address(0), to, ids, amounts, data);

        for (uint256 i = 0; i < ids.length; i++) {
            _balances[ids[i]][to] += amounts[i];
        }

        emit TransferBatch(operator, address(0), to, ids, amounts);

        _afterTokenTransfer(operator, address(0), to, ids, amounts, data);

        _doSafeBatchTransferAcceptanceCheck(operator, address(0), to, ids, amounts, data);
    }

    /**
     * @dev Destroys `amount` tokens of token type `id` from `from`
     *
     * Emits a {TransferSingle} event.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `from` must have at least `amount` tokens of token type `id`.
     */
    function _burn(
        address from,
        uint256 id,
        uint256 amount
    ) internal virtual {
        require(from != address(0), "ERC1155: burn from the zero address");

        address operator = _msgSender();
        uint256[] memory ids = _asSingletonArray(id);
        uint256[] memory amounts = _asSingletonArray(amount);

        _beforeTokenTransfer(operator, from, address(0), ids, amounts, "");

        uint256 fromBalance = _balances[id][from];
        require(fromBalance >= amount, "ERC1155: burn amount exceeds balance");
        unchecked {
            _balances[id][from] = fromBalance - amount;
        }

        emit TransferSingle(operator, from, address(0), id, amount);

        _afterTokenTransfer(operator, from, address(0), ids, amounts, "");
    }

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_burn}.
     *
     * Emits a {TransferBatch} event.
     *
     * Requirements:
     *
     * - `ids` and `amounts` must have the same length.
     */
    function _burnBatch(
        address from,
        uint256[] memory ids,
        uint256[] memory amounts
    ) internal virtual {
        require(from != address(0), "ERC1155: burn from the zero address");
        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, from, address(0), ids, amounts, "");

        for (uint256 i = 0; i < ids.length; i++) {
            uint256 id = ids[i];
            uint256 amount = amounts[i];

            uint256 fromBalance = _balances[id][from];
            require(fromBalance >= amount, "ERC1155: burn amount exceeds balance");
            unchecked {
                _balances[id][from] = fromBalance - amount;
            }
        }

        emit TransferBatch(operator, from, address(0), ids, amounts);

        _afterTokenTransfer(operator, from, address(0), ids, amounts, "");
    }

    /**
     * @dev Approve `operator` to operate on all of `owner` tokens
     *
     * Emits an {ApprovalForAll} event.
     */
    function _setApprovalForAll(
        address owner,
        address operator,
        bool approved
    ) internal virtual {
        require(owner != operator, "ERC1155: setting approval status for self");
        _operatorApprovals[owner][operator] = approved;
        emit ApprovalForAll(owner, operator, approved);
    }

    /**
     * @dev Hook that is called before any token transfer. This includes minting
     * and burning, as well as batched variants.
     *
     * The same hook is called on both single and batched variants. For single
     * transfers, the length of the `ids` and `amounts` arrays will be 1.
     *
     * Calling conditions (for each `id` and `amount` pair):
     *
     * - When `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * of token type `id` will be  transferred to `to`.
     * - When `from` is zero, `amount` tokens of token type `id` will be minted
     * for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens of token type `id`
     * will be burned.
     * - `from` and `to` are never both zero.
     * - `ids` and `amounts` have the same, non-zero length.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address operator,
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    ) internal virtual {}

    /**
     * @dev Hook that is called after any token transfer. This includes minting
     * and burning, as well as batched variants.
     *
     * The same hook is called on both single and batched variants. For single
     * transfers, the length of the `id` and `amount` arrays will be 1.
     *
     * Calling conditions (for each `id` and `amount` pair):
     *
     * - When `from` and `to` are both non-zero, `amount` of ``from``'s tokens
     * of token type `id` will be  transferred to `to`.
     * - When `from` is zero, `amount` tokens of token type `id` will be minted
     * for `to`.
     * - when `to` is zero, `amount` of ``from``'s tokens of token type `id`
     * will be burned.
     * - `from` and `to` are never both zero.
     * - `ids` and `amounts` have the same, non-zero length.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _afterTokenTransfer(
        address operator,
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    ) internal virtual {}

    function _doSafeTransferAcceptanceCheck(
        address operator,
        address from,
        address to,
        uint256 id,
        uint256 amount,
        bytes memory data
    ) private {
        if (to.isContract()) {
            try IERC1155Receiver(to).onERC1155Received(operator, from, id, amount, data) returns (bytes4 response) {
                if (response != IERC1155Receiver.onERC1155Received.selector) {
                    revert("ERC1155: ERC1155Receiver rejected tokens");
                }
            } catch Error(string memory reason) {
                revert(reason);
            } catch {
                revert("ERC1155: transfer to non-ERC1155Receiver implementer");
            }
        }
    }

    function _doSafeBatchTransferAcceptanceCheck(
        address operator,
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    ) private {
        if (to.isContract()) {
            try IERC1155Receiver(to).onERC1155BatchReceived(operator, from, ids, amounts, data) returns (
                bytes4 response
            ) {
                if (response != IERC1155Receiver.onERC1155BatchReceived.selector) {
                    revert("ERC1155: ERC1155Receiver rejected tokens");
                }
            } catch Error(string memory reason) {
                revert(reason);
            } catch {
                revert("ERC1155: transfer to non-ERC1155Receiver implementer");
            }
        }
    }

    function _asSingletonArray(uint256 element) private pure returns (uint256[] memory) {
        uint256[] memory array = new uint256[](1);
        array[0] = element;

        return array;
    }
}

// File: contracts/ExenoCollectionHub.sol


pragma solidity 0.8.18;





contract ExenoCollectionHub is
    ExenoCollection,
    ERC1155,
    VRFV2WrapperConsumerBase
{
    string public constant name = "Horses Having Horns";
    
    uint16 private constant NUM_OF_CONFIRMATIONS = 3;
    uint32 private constant TIER_RANGE = 10**4;

    IERC20 public immutable PAYOUT_TOKEN;
    IERC20 public immutable LINK_TOKEN;

    address public immutable LINK_WRAPPER;

    string[2] public ENDPOINT;

    Tier[3] public TIERS;

    uint256 internal lastBuyback;

    Request internal lastRequest;

    mapping(uint256 domain => uint256 count) internal sales;

    mapping(address holder => uint256 count) internal holdings;

    mapping(uint256 ticket => Record) internal records;

    mapping(uint256 ticket => Reward) internal rewards;
    
    mapping(uint256 buyback => mapping(uint256 domain => Buyback)) internal buybacks;

    enum Goal {
        MILESTONE, FINAL
    }

    /**
     */
    struct Tier {
        uint256 id;
        uint256 multiplier;
        uint256 limit;
    }

    struct Record {
        uint32 timestamp;
        uint256 tier;
        address holder;
        bool recalled;
    }

    struct Reward {
        uint256 amount;
        bool paid;
    }

    struct Collection {
        uint32 timestamp;
        uint256 tier;
        uint256 ticket;
        uint256 reward;
        bool recalled;
        bool paid;
    }

    struct Request {
        uint256 id;
        uint32 timestamp;
        Goal goal;
        bytes data;
        uint256[] random;
        uint32 gasLimit;
        uint256 price;
        bool status;
    }

    struct Buyback {
        uint32 timestamp;
        uint256 request;
        uint256 random;
        uint256 size;
        uint256 index;
        uint256 ticket;
        address holder;
        uint256 reward;
    }

    /**
     */
    event RequestSent(
        uint256 id,
        uint32 gasLimit,
        uint256 price
    );

    event RequestDeclined(
        uint256 id
    );
    
    event RequestAccepted(
        uint256 id,
        uint256[] random
    );

    event RewardDeclined (
        bytes32 indexed id,
        address holder,
        uint256 amount,
        uint256 ticket
    );

    event RewardAccepted (
        bytes32 indexed id,
        address holder,
        uint256 amount,
        uint256 ticket
    );

    event BuybackResult (
        uint256 indexed id,
        uint256 domain,
        uint256 tier,
        uint256 ticket,
        address holder,
        uint256 reward
    );

    /// Prevents configuring a package outside of 1 | 2 | 3
    error UnsupportedPackageId();
    
    /// Prevents calling the `resolve` method when the ticket has not been recalled
    error UnrecalledTicket();

    /// Prevents calling the `resolve` method when there is no reward associated with a given ticket
    error TicketHasNoReward();

    /// Prevents calling the `resolve` method when reward has already been paid for a given ticket
    error RewardAlreadyPaid();

    /// There are not enough LINK tokens in the contract for randomness request
    error LinkTokenBalanceTooLow(uint256);

    /// There are not enough USDT tokens in the contract for reward payout
    error PaymentTokenBalanceTooLow(uint256);

    /// Unable to mint a new ticket because the limit for a given tier has already been reached
    error TierLimitAlreadyReached();

    /// Not enough tickets have been minted to execute a buyback
    error NotEnoughTicketsInSpace();

    /**
     */
    constructor(
        address coreToken,
        address payoutToken,
        address linkToken,
        address linkWrapper
    )
        ExenoCollection(coreToken)
        ERC1155("")
        VRFV2WrapperConsumerBase(linkToken, linkWrapper)
    {
        PAYOUT_TOKEN = IERC20(payoutToken);
        LINK_TOKEN = IERC20(linkToken);
        LINK_WRAPPER = linkWrapper;
        setTier(1, 1, 5000);
        setTier(2, 4, 3000);
        setTier(3, 10, 2000);
        setEndpoint(["https://nft.exeno.finance/json?id=", ""]);
    }

    modifier onlyHolder(uint256 ticket) {
        if (balanceOf(msg.sender, ticket) == 0)
            revert UnauthorizedCaller();
        _;
    }

    function setTier(
        uint256 id,             // tier id, i.e. 1 | 2 | 3
        uint256 multiplier,     // scaling factor to increase the probability a ticket is selected in a random buyback
        uint256 limit           // limit for the total number of tickets to be issued
    )
        public onlyOwner
    {
        if (id < 1 || id > 3)
            revert UnsupportedPackageId();
        TIERS[id - 1] = Tier(id, multiplier, limit);
    }

    function setEndpoint(string[2] memory endpoint)
        public onlyOwner
    {
        ENDPOINT = endpoint;
    }

    function uri(uint256 id)
        public view override returns(string memory)
    {
        return string(abi.encodePacked(ENDPOINT[0], Strings.toString(id), ENDPOINT[1]));
    }

    function supportsInterface(bytes4 interfaceId)
        public view virtual override(ExenoCollection, ERC1155) returns(bool)
    {
        return super.supportsInterface(interfaceId);
    }

    /**
     */
    function resolve(
        bytes32 id,             // nonce
        uint256 ticket,         // NFT ID, e.g. 10001
        bool accept,            // whether the current holder of the ticket accepts or rejects the reward
        bytes calldata signature
    )
        external nonReentrant whenNotPaused onlyHolder(ticket)
    {
        if (!signers[msg.sender]) {
            _verifySigner(id, _extractSigner(abi.encodePacked(id, ticket, accept), signature));
        }
        if (!records[ticket].recalled)
            revert UnrecalledTicket();
        if (rewards[ticket].paid)
            revert RewardAlreadyPaid();
        uint256 amount = rewards[ticket].amount;
        if (amount == 0)
            revert TicketHasNoReward();
        if (!accept) {
            records[ticket].recalled = false;
            rewards[ticket].amount = 0;
            emit RewardDeclined(id, msg.sender, amount, ticket);
            return;
        }
        if (PAYOUT_TOKEN.balanceOf(address(this)) < amount)
            revert PaymentTokenBalanceTooLow(amount);
        rewards[ticket].paid = true;
        PAYOUT_TOKEN.transfer(msg.sender, amount);
        _safeTransferFrom(msg.sender, owner(), ticket, 1, "");
        emit RewardAccepted(id, msg.sender, amount, ticket);
    }

    /**
     */
    function runMilestoneBuyback(
        uint32 gasLimit,
        uint256[3] memory reward
    )
        external onlyOwner
    {
        _requestRandomness(Goal.MILESTONE, abi.encode(reward), gasLimit, 3);
    }

    function runFinalBuyback(
        uint32 gasLimit,
        uint256 reward
    )
        external onlyOwner
    {
        _requestRandomness(Goal.FINAL, abi.encode(reward), gasLimit, 1);
    }

    /**
     */
    function _issueTicket(
        address beneficiary,
        uint256 tier
    )
        internal override returns(uint256 ticket)
    {
        assert (tier >= 1 && tier <= 3);
        Tier memory p = TIERS[tier - 1];
        assert (p.id == tier);
        if (sales[tier] >= p.limit)
            revert TierLimitAlreadyReached();
        sales[0]++;
        sales[tier]++;
        ticket = tier * TIER_RANGE + sales[tier];
        assert (records[ticket].timestamp == 0);
        records[ticket].timestamp = uint32(block.timestamp);
        assert (records[ticket].tier == 0);
        records[ticket].tier = tier;
        _mint(beneficiary, ticket, 1, "");
        return ticket;
    }

    function _requestRandomness(
        Goal goal,
        bytes memory data,
        uint32 gasLimit,
        uint32 size
    )
        internal
    {
        uint256 price = VRF_V2_WRAPPER.calculateRequestPrice(gasLimit);
        if (LINK_TOKEN.balanceOf(address(this)) < price)
            revert LinkTokenBalanceTooLow(price);
        uint256 id = requestRandomness(gasLimit, NUM_OF_CONFIRMATIONS, size);
        lastRequest = Request({
            id: id,
            timestamp: uint32(block.timestamp),
            goal: goal,
            data: data,
            random: new uint256[](0),
            gasLimit: gasLimit,
            price: price,
            status: false
        });
        emit RequestSent(id, gasLimit, price);
    }

    function fulfillRandomWords(
        uint256 request,
        uint256[] memory random
    )
        internal override
    {
        if (request != lastRequest.id) {
            emit RequestDeclined(request);
            return;
        }
        emit RequestAccepted(request, random);
        lastRequest.random = random;
        lastRequest.status = true;
        if (lastRequest.goal == Goal.MILESTONE) {
            uint256[3] memory reward = abi.decode(lastRequest.data, (uint256[3]));
            if (!_isEmpty(reward)) {
                lastBuyback++;
                for (uint256 i = 0; i < 3; i++) {
                    if (reward[i] > 0) {
                        _buyback(i + 1, request, random[i], reward[i]);
                    }
                }
            }
        } else if (lastRequest.goal == Goal.FINAL) {
            uint256 reward = abi.decode(lastRequest.data, (uint256));
            if (reward > 0) {
                lastBuyback++;
                _buyback(0, request, random[0], abi.decode(lastRequest.data, (uint256)));
            }
        }
    }

    function _buyback(
        uint256 domain,
        uint256 request,
        uint256 random,
        uint256 reward
    )
        internal
    {
        (uint256[] memory space, uint256 size) = getSpace(domain);
        if (size == 0)
            revert NotEnoughTicketsInSpace();
        uint256 index = random % size;
        uint256 ticket = space[index];
        assert (ticket > 0);
        uint256 tier = records[ticket].tier;
        assert (domain == 0 || tier == domain);
        rewards[ticket].amount = reward;
        records[ticket].recalled = true;
        uint32 timestamp = uint32(block.timestamp);
        buybacks[lastBuyback][domain] = Buyback(timestamp, request, random, size, index, ticket, records[ticket].holder, reward);
        emit BuybackResult(lastBuyback, domain, tier, ticket, records[ticket].holder, reward);
    }

    function _afterTokenTransfer(
        address,
        address from,
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory
    )
        internal override
    {
        for (uint256 i = 0; i < ids.length; i++) {
            records[ids[i]].holder = to;
            if (from != address(0)) {
                holdings[from] -= amounts[i];
            }
            if (to != address(0)) {
                holdings[to] += amounts[i];
            }
        }
    }

    function _isDisqualified(uint256 ticket)
        internal view returns(bool)
    {
        return records[ticket].recalled || records[ticket].holder == address(0);
    }

    function _isEmpty(uint256[3] memory input)
        internal pure returns(bool)
    {
        for (uint256 i = 0; i < 3; i++) {
            if (input[i] != 0) {
                return false;
            }
        }
        return true;
    }

    /**
     */
    function getSales(uint256 domain)
        external view returns(uint256)
    {
        return sales[domain];
    }

    function getTickets(address holder)
        public view returns(uint256[] memory list, uint256 size)
    {
        size = holdings[holder];
        list = new uint256[](size);
        uint256 index;
        for (uint256 tier = 1; tier <= 3; tier++) {
            for (uint256 i = 1; i <= sales[tier]; i++) {
                uint256 ticket = tier * TIER_RANGE + i;
                if (balanceOf(holder, ticket) > 0) {
                    list[index++] = ticket;
                }
            }
        }
        return (list, size);
    }

    function getCollection(address holder)
        external view returns(Collection[] memory list, uint256 size)
    {
        (uint256[] memory _tickets, uint256 _size) = getTickets(holder);
        list = new Collection[](_size);
        for (uint256 i = 0; i < _size; i++) {
            list[i] = Collection({
                timestamp: records[_tickets[i]].timestamp,
                tier: records[_tickets[i]].tier,
                ticket: _tickets[i],
                reward: rewards[_tickets[i]].amount,
                recalled: records[_tickets[i]].recalled,
                paid: rewards[_tickets[i]].paid
            });
        }
        return (list, _size);
    }

    function getTicket(uint256 ticket)
        external view returns(uint32 timestamp, uint256 tier, address holder, uint256 reward, bool recalled, bool paid)
    {
        return (records[ticket].timestamp, records[ticket].tier, records[ticket].holder, rewards[ticket].amount, records[ticket].recalled, rewards[ticket].paid);

    }

    function getSpace(uint256 domain)
        public view returns(uint256[] memory space, uint256 size)
    {
        if (domain > 0) {
            for (uint256 i = 1; i <= sales[domain]; i++) {
                uint256 ticket = domain * TIER_RANGE + i;
                if (!_isDisqualified(ticket)) {
                    size++;
                }
            }
            space = new uint256[](size);
            uint256 index;
            for (uint256 i = 1; i <= sales[domain]; i++) {
                uint256 ticket = domain * TIER_RANGE + i;
                if (!_isDisqualified(ticket)) {
                    space[index++] = ticket;
                }
            }
        } else {
            for (uint256 tier = 1; tier <= 3; tier++) {
                for (uint256 i = 1; i <= sales[tier]; i++) {
                    uint256 ticket = tier * TIER_RANGE + i;
                    if (!_isDisqualified(ticket)) {
                        uint256 multiplier = TIERS[records[ticket].tier - 1].multiplier;
                        size += multiplier;
                    }
                }
            }
            space = new uint256[](size);
            uint256 index;
            for (uint256 tier = 1; tier <= 3; tier++) {
                for (uint256 i = 1; i <= sales[tier]; i++) {
                    uint256 ticket = tier * TIER_RANGE + i;
                    if (!_isDisqualified(ticket)) {
                        uint256 multiplier = TIERS[records[ticket].tier - 1].multiplier;
                        for (uint256 n = 0; n < multiplier; n++) {
                            space[index++] = ticket;
                        }
                    }
                }
            }
        }
        return (space, size);
    }

    function getRequest()
        external view returns(
            uint256 request,
            uint32 timestamp,
            uint256[] memory random,
            uint32 gasLimit,
            uint256 price,
            bool status
        )
    {
        return (lastRequest.id, lastRequest.timestamp, lastRequest.random, lastRequest.gasLimit, lastRequest.price, lastRequest.status);
    }

    function getBuyback(uint256 domain)
        external view returns(
            uint256 id,
            uint32 timestamp,
            uint256 request,
            uint256 random,
            uint256 size,
            uint256 index,
            uint256 ticket,
            address holder,
            uint256 reward
        )
    {
        Buyback memory d = buybacks[lastBuyback][domain];
        return (lastBuyback, d.timestamp, d.request, d.random, d.size, d.index, d.ticket, d.holder, d.reward);
    }

    function getBuybacks(uint256 domain)
        external view returns(Buyback[] memory list, uint256 size)
    {
        list = new Buyback[](lastBuyback);
        for (uint256 i = 0; i < lastBuyback; i++) {
            list[i] = buybacks[i + 1][domain];
        }
        return (list, lastBuyback);
    }

    function getLiquidity()
        external override view returns(uint256 native, uint256 core, uint256 payout, uint256 link)
    {
        return (
            address(this).balance,
            CORE_TOKEN.balanceOf(address(this)),
            PAYOUT_TOKEN.balanceOf(address(this)),
            LINK_TOKEN.balanceOf(address(this))
        );
    }

    /**
     */
    function tester(
        uint256 domain,
        uint256 random
    )
        external view returns(uint256 size, uint256 index, uint256 ticket)
    {
        (uint256[] memory space, uint256 _size) = getSpace(domain);
        index = random % _size;
        ticket = space[index];
        return (_size, index, ticket);
    }
}