// SPDX-License-Identifier: MIT

pragma solidity 0.8.3;



// Part: Base64

/// @title Base64
/// @notice Provides a function for encoding some bytes in base64
/// @author Brecht Devos <brecht@loopring.org>
library Base64 {
  bytes internal constant TABLE =
    'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';

  /// @notice Encodes some bytes to the base64 representation
  function encode(bytes memory data) internal pure returns (string memory) {
    uint len = data.length;
    if (len == 0) return '';
    // multiply by 4/3 rounded up
    uint encodedLen = 4 * ((len + 2) / 3);
    // Add some extra buffer at the end
    bytes memory result = new bytes(encodedLen + 32);
    bytes memory table = TABLE;
    assembly {
      let tablePtr := add(table, 1)
      let resultPtr := add(result, 32)
      for {
        let i := 0
      } lt(i, len) {

      } {
        i := add(i, 3)
        let input := and(mload(add(data, i)), 0xffffff)
        let out := mload(add(tablePtr, and(shr(18, input), 0x3F)))
        out := shl(8, out)
        out := add(out, and(mload(add(tablePtr, and(shr(12, input), 0x3F))), 0xFF))
        out := shl(8, out)
        out := add(out, and(mload(add(tablePtr, and(shr(6, input), 0x3F))), 0xFF))
        out := shl(8, out)
        out := add(out, and(mload(add(tablePtr, and(input, 0x3F))), 0xFF))
        out := shl(224, out)
        mstore(resultPtr, out)
        resultPtr := add(resultPtr, 4)
      }
      switch mod(len, 3)
      case 1 {
        mstore(sub(resultPtr, 2), shl(240, 0x3d3d))
      }
      case 2 {
        mstore(sub(resultPtr, 1), shl(248, 0x3d))
      }
      mstore(result, encodedLen)
    }
    return string(result);
  }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/Address

/**
 * @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
     * ====
     */
    function isContract(address account) internal view returns (bool) {
        // This method relies on extcodesize, which returns 0 for contracts in
        // construction, since the code is only stored at the end of the
        // constructor execution.

        uint256 size;
        assembly {
            size := extcodesize(account)
        }
        return size > 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 functionCall(target, data, "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");
        require(isContract(target), "Address: call to non-contract");

        (bool success, bytes memory returndata) = target.call{value: value}(data);
        return verifyCallResult(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) {
        require(isContract(target), "Address: static call to non-contract");

        (bool success, bytes memory returndata) = target.staticcall(data);
        return verifyCallResult(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) {
        require(isContract(target), "Address: delegate call to non-contract");

        (bool success, bytes memory returndata) = target.delegatecall(data);
        return verifyCallResult(success, returndata, errorMessage);
    }

    /**
     * @dev Tool to verifies that a low level call was successful, and revert if it wasn't, either by bubbling the
     * revert reason 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 {
            // 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

                assembly {
                    let returndata_size := mload(returndata)
                    revert(add(32, returndata), returndata_size)
                }
            } else {
                revert(errorMessage);
            }
        }
    }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/Context

/**
 * @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;
    }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/IERC165

/**
 * @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);
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/Initializable

/**
 * @dev This is a base contract to aid in writing upgradeable contracts, or any kind of contract that will be deployed
 * behind a proxy. Since a proxied contract can't have a constructor, it's common to move constructor logic to an
 * external initializer function, usually called `initialize`. It then becomes necessary to protect this initializer
 * function so it can only be called once. The {initializer} modifier provided by this contract will have this effect.
 *
 * TIP: To avoid leaving the proxy in an uninitialized state, the initializer function should be called as early as
 * possible by providing the encoded function call as the `_data` argument to {ERC1967Proxy-constructor}.
 *
 * CAUTION: When used with inheritance, manual care must be taken to not invoke a parent initializer twice, or to ensure
 * that all initializers are idempotent. This is not verified automatically as constructors are by Solidity.
 */
abstract contract Initializable {
    /**
     * @dev Indicates that the contract has been initialized.
     */
    bool private _initialized;

    /**
     * @dev Indicates that the contract is in the process of being initialized.
     */
    bool private _initializing;

    /**
     * @dev Modifier to protect an initializer function from being invoked twice.
     */
    modifier initializer() {
        require(_initializing || !_initialized, "Initializable: contract is already initialized");

        bool isTopLevelCall = !_initializing;
        if (isTopLevelCall) {
            _initializing = true;
            _initialized = true;
        }

        _;

        if (isTopLevelCall) {
            _initializing = false;
        }
    }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/ReentrancyGuard

/**
 * @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 make it call a
     * `private` function that does the actual work.
     */
    modifier nonReentrant() {
        // On the first call to nonReentrant, _notEntered will be true
        require(_status != _ENTERED, "ReentrancyGuard: reentrant call");

        // Any calls to nonReentrant after this point will fail
        _status = _ENTERED;

        _;

        // By storing the original value once again, a refund is triggered (see
        // https://eips.ethereum.org/EIPS/eip-2200)
        _status = _NOT_ENTERED;
    }
}

// Part: Strings

library Strings {
  bytes16 private constant _HEX_SYMBOLS = '0123456789abcdef';

  /**
   * @dev Converts a `uint256` to its ASCII `string` decimal representation.
   */
  function toString(uint value) internal pure returns (string memory) {
    // Inspired by OraclizeAPI's implementation - MIT licence
    // https://github.com/oraclize/ethereum-api/blob/b42146b063c7d6ee1358846c198246239e9360e8/oraclizeAPI_0.4.25.sol

    if (value == 0) {
      return '0';
    }
    uint temp = value;
    uint digits;
    while (temp != 0) {
      digits++;
      temp /= 10;
    }
    bytes memory buffer = new bytes(digits);
    while (value != 0) {
      digits -= 1;
      buffer[digits] = bytes1(uint8(48 + uint(value % 10)));
      value /= 10;
    }
    return string(buffer);
  }

  /**
   * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation.
   */
  function toHexString(uint value) internal pure returns (string memory) {
    if (value == 0) {
      return '0x00';
    }
    uint temp = value;
    uint length = 0;
    while (temp != 0) {
      length++;
      temp >>= 8;
    }
    return toHexString(value, length);
  }

  /**
   * @dev Converts a `uint256` to its ASCII `string` hexadecimal representation with fixed length.
   */
  function toHexString(uint value, uint length) internal pure returns (string memory) {
    bytes memory buffer = new bytes(2 * length + 2);
    buffer[0] = '0';
    buffer[1] = 'x';
    for (uint i = 2 * length + 1; i > 1; --i) {
      buffer[i] = _HEX_SYMBOLS[value & 0xf];
      value >>= 4;
    }
    require(value == 0, 'Strings: hex length insufficient');
    return string(buffer);
  }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/ERC165

/**
 * @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;
    }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/IERC1155

/**
 * @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 be 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;
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/IERC1155Receiver

/**
 * @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.
        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. 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);
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/IERC721

/**
 * @dev Required interface of an ERC721 compliant contract.
 */
interface IERC721 is IERC165 {
    /**
     * @dev Emitted when `tokenId` token is transferred from `from` to `to`.
     */
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables `approved` to manage the `tokenId` token.
     */
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

    /**
     * @dev Emitted when `owner` enables or disables (`approved`) `operator` to manage all of its assets.
     */
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    /**
     * @dev Returns the number of tokens in ``owner``'s account.
     */
    function balanceOf(address owner) external view returns (uint256 balance);

    /**
     * @dev Returns the owner of the `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function ownerOf(uint256 tokenId) external view returns (address owner);

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, checking first that contract recipients
     * are aware of the ERC721 protocol to prevent tokens from being forever locked.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be have been allowed to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId
    ) external;

    /**
     * @dev Transfers `tokenId` token from `from` to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {safeTransferFrom} whenever possible.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) external;

    /**
     * @dev Gives permission to `to` to transfer `tokenId` token to another account.
     * The approval is cleared when the token is transferred.
     *
     * Only a single account can be approved at a time, so approving the zero address clears previous approvals.
     *
     * Requirements:
     *
     * - The caller must own the token or be an approved operator.
     * - `tokenId` must exist.
     *
     * Emits an {Approval} event.
     */
    function approve(address to, uint256 tokenId) external;

    /**
     * @dev Returns the account approved for `tokenId` token.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function getApproved(uint256 tokenId) external view returns (address operator);

    /**
     * @dev Approve or remove `operator` as an operator for the caller.
     * Operators can call {transferFrom} or {safeTransferFrom} for any token owned by the caller.
     *
     * Requirements:
     *
     * - The `operator` cannot be the caller.
     *
     * Emits an {ApprovalForAll} event.
     */
    function setApprovalForAll(address operator, bool _approved) external;

    /**
     * @dev Returns if the `operator` is allowed to manage all of the assets of `owner`.
     *
     * See {setApprovalForAll}
     */
    function isApprovedForAll(address owner, address operator) external view returns (bool);

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If the caller is not `from`, it must be approved to move this token by either {approve} or {setApprovalForAll}.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        bytes calldata data
    ) external;
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/Ownable

/**
 * @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() {
        _setOwner(_msgSender());
    }

    /**
     * @dev Returns the address of the current owner.
     */
    function owner() public view virtual returns (address) {
        return _owner;
    }

    /**
     * @dev Throws if called by any account other than the owner.
     */
    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

    /**
     * @dev Leaves the contract without owner. It will not be possible to call
     * `onlyOwner` functions anymore. Can only be called by the current owner.
     *
     * NOTE: Renouncing ownership will leave the contract without an owner,
     * thereby removing any functionality that is only available to the owner.
     */
    function renounceOwnership() public virtual onlyOwner {
        _setOwner(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");
        _setOwner(newOwner);
    }

    function _setOwner(address newOwner) private {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/Pausable

/**
 * @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 Returns true if the contract is paused, and false otherwise.
     */
    function paused() public view virtual returns (bool) {
        return _paused;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is not paused.
     *
     * Requirements:
     *
     * - The contract must not be paused.
     */
    modifier whenNotPaused() {
        require(!paused(), "Pausable: paused");
        _;
    }

    /**
     * @dev Modifier to make a function callable only when the contract is paused.
     *
     * Requirements:
     *
     * - The contract must be paused.
     */
    modifier whenPaused() {
        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());
    }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/ERC1155Receiver

/**
 * @dev _Available since v3.1._
 */
abstract contract ERC1155Receiver is ERC165, IERC1155Receiver {
    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override(ERC165, IERC165) returns (bool) {
        return interfaceId == type(IERC1155Receiver).interfaceId || super.supportsInterface(interfaceId);
    }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/IERC1155MetadataURI

/**
 * @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);
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/ERC1155

/**
 * @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: balance query for the zero address");
        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 {
        require(_msgSender() != operator, "ERC1155: setting approval status for self");

        _operatorApprovals[_msgSender()][operator] = approved;
        emit ApprovalForAll(_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 owner nor 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: transfer caller is not owner nor 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();

        _beforeTokenTransfer(operator, from, to, _asSingletonArray(id), _asSingletonArray(amount), 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);

        _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);

        _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 `account`.
     *
     * Emits a {TransferSingle} event.
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - If `account` refers to a smart contract, it must implement {IERC1155Receiver-onERC1155Received} and return the
     * acceptance magic value.
     */
    function _mint(
        address account,
        uint256 id,
        uint256 amount,
        bytes memory data
    ) internal virtual {
        require(account != address(0), "ERC1155: mint to the zero address");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, address(0), account, _asSingletonArray(id), _asSingletonArray(amount), data);

        _balances[id][account] += amount;
        emit TransferSingle(operator, address(0), account, id, amount);

        _doSafeTransferAcceptanceCheck(operator, address(0), account, id, amount, data);
    }

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_mint}.
     *
     * 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);

        _doSafeBatchTransferAcceptanceCheck(operator, address(0), to, ids, amounts, data);
    }

    /**
     * @dev Destroys `amount` tokens of token type `id` from `account`
     *
     * Requirements:
     *
     * - `account` cannot be the zero address.
     * - `account` must have at least `amount` tokens of token type `id`.
     */
    function _burn(
        address account,
        uint256 id,
        uint256 amount
    ) internal virtual {
        require(account != address(0), "ERC1155: burn from the zero address");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, account, address(0), _asSingletonArray(id), _asSingletonArray(amount), "");

        uint256 accountBalance = _balances[id][account];
        require(accountBalance >= amount, "ERC1155: burn amount exceeds balance");
        unchecked {
            _balances[id][account] = accountBalance - amount;
        }

        emit TransferSingle(operator, account, address(0), id, amount);
    }

    /**
     * @dev xref:ROOT:erc1155.adoc#batch-operations[Batched] version of {_burn}.
     *
     * Requirements:
     *
     * - `ids` and `amounts` must have the same length.
     */
    function _burnBatch(
        address account,
        uint256[] memory ids,
        uint256[] memory amounts
    ) internal virtual {
        require(account != address(0), "ERC1155: burn from the zero address");
        require(ids.length == amounts.length, "ERC1155: ids and amounts length mismatch");

        address operator = _msgSender();

        _beforeTokenTransfer(operator, account, address(0), ids, amounts, "");

        for (uint256 i = 0; i < ids.length; i++) {
            uint256 id = ids[i];
            uint256 amount = amounts[i];

            uint256 accountBalance = _balances[id][account];
            require(accountBalance >= amount, "ERC1155: burn amount exceeds balance");
            unchecked {
                _balances[id][account] = accountBalance - amount;
            }
        }

        emit TransferBatch(operator, account, address(0), ids, amounts);
    }

    /**
     * @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 `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 _beforeTokenTransfer(
        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;
    }
}

// Part: OpenZeppelin/openzeppelin-contracts@4.3.0/ERC1155Supply

/**
 * @dev Extension of ERC1155 that adds tracking of total supply per id.
 *
 * Useful for scenarios where Fungible and Non-fungible tokens have to be
 * clearly identified. Note: While a totalSupply of 1 might mean the
 * corresponding is an NFT, there is no guarantees that no other token with the
 * same id are not going to be minted.
 */
abstract contract ERC1155Supply is ERC1155 {
    mapping(uint256 => uint256) private _totalSupply;

    /**
     * @dev Total amount of tokens in with a given id.
     */
    function totalSupply(uint256 id) public view virtual returns (uint256) {
        return _totalSupply[id];
    }

    /**
     * @dev Indicates weither any token exist with a given id, or not.
     */
    function exists(uint256 id) public view virtual returns (bool) {
        return ERC1155Supply.totalSupply(id) > 0;
    }

    /**
     * @dev See {ERC1155-_mint}.
     */
    function _mint(
        address account,
        uint256 id,
        uint256 amount,
        bytes memory data
    ) internal virtual override {
        super._mint(account, id, amount, data);
        _totalSupply[id] += amount;
    }

    /**
     * @dev See {ERC1155-_mintBatch}.
     */
    function _mintBatch(
        address to,
        uint256[] memory ids,
        uint256[] memory amounts,
        bytes memory data
    ) internal virtual override {
        super._mintBatch(to, ids, amounts, data);
        for (uint256 i = 0; i < ids.length; ++i) {
            _totalSupply[ids[i]] += amounts[i];
        }
    }

    /**
     * @dev See {ERC1155-_burn}.
     */
    function _burn(
        address account,
        uint256 id,
        uint256 amount
    ) internal virtual override {
        super._burn(account, id, amount);
        _totalSupply[id] -= amount;
    }

    /**
     * @dev See {ERC1155-_burnBatch}.
     */
    function _burnBatch(
        address account,
        uint256[] memory ids,
        uint256[] memory amounts
    ) internal virtual override {
        super._burnBatch(account, ids, amounts);
        for (uint256 i = 0; i < ids.length; ++i) {
            _totalSupply[ids[i]] -= amounts[i];
        }
    }
}

// Part: ProvablyRareGem

/// @title Provably Rare Gems
/// @author Sorawit Suriyakarn (swit.eth / https://twitter.com/nomorebear)
contract ProvablyRareGem is ERC1155Supply, ReentrancyGuard {
  event Create(uint indexed kind);
  event Mine(address indexed miner, uint indexed kind);
  string public constant name = 'Provably Rare Gem';

  struct Gem {
    string name; // Gem name
    string color; // Gem color
    bytes32 entropy; // Additional mining entropy. bytes32(0) means can't mine.
    uint difficulty; // Current difficulity level. Must be non decreasing
    uint gemsPerMine; // Amount of gems to distribute per mine
    uint multiplier; // Difficulty multiplier times 1e4. Must be between 1e4 and 1e10
    address crafter; // Address that can craft gems
    address manager; // Current gem manager
    address pendingManager; // Pending gem manager to be transferred to
  }

  mapping(uint => Gem) public gems;
  mapping(address => uint) public nonce;
  uint public gemCount;

  constructor() ERC1155('GEM') {}

  /// @dev Creates a new gem type. The manager can craft a portion of gems + can premine
  function create(
    string calldata name,
    string calldata color,
    uint difficulty,
    uint gemsPerMine,
    uint multiplier,
    address crafter,
    address manager
  ) external returns (uint) {
    require(difficulty > 0 && difficulty <= 2**128, 'bad difficulty');
    require(gemsPerMine > 0 && gemsPerMine <= 1e6, 'bad gems per mine');
    require(multiplier >= 1e4 && multiplier <= 1e10, 'bad multiplier');
    require(manager != address(0), 'bad manager');
    return _create(name, color, difficulty, gemsPerMine, multiplier, crafter, manager);
  }

  /// @dev Mines new gemstones. Puts kind you want to mine + your salt and tests your luck!
  function mine(uint kind, uint salt) external nonReentrant {
    uint val = luck(kind, salt);
    nonce[msg.sender]++;
    require(kind < gemCount, 'gem kind not exist');
    uint diff = gems[kind].difficulty;
    require(val <= type(uint).max / diff, 'salt not good enough');
    gems[kind].difficulty = (diff * gems[kind].multiplier) / 10000 + 1;
    _mint(msg.sender, kind, gems[kind].gemsPerMine, '');
  }

  /// @dev Updates gem mining entropy. Can be called by gem manager or crafter.
  function updateEntropy(uint kind, bytes32 entropy) external {
    require(kind < gemCount, 'gem kind not exist');
    require(gems[kind].manager == msg.sender || gems[kind].crafter == msg.sender, 'unauthorized');
    gems[kind].entropy = entropy;
  }

  /// @dev Updates gem metadata info. Must only be called by the gem manager.
  function updateGemInfo(
    uint kind,
    string calldata name,
    string calldata color
  ) external {
    require(kind < gemCount, 'gem kind not exist');
    require(gems[kind].manager == msg.sender, 'not gem manager');
    gems[kind].name = name;
    gems[kind].color = color;
  }

  /// @dev Updates gem mining information. Must only be called by the gem manager.
  function updateMiningData(
    uint kind,
    uint difficulty,
    uint multiplier,
    uint gemsPerMine
  ) external {
    require(kind < gemCount, 'gem kind not exist');
    require(gems[kind].manager == msg.sender, 'not gem manager');
    require(difficulty > 0 && difficulty <= 2**128, 'bad difficulty');
    require(multiplier >= 1e4 && multiplier <= 1e10, 'bad multiplier');
    require(gemsPerMine > 0 && gemsPerMine <= 1e6, 'bad gems per mine');
    gems[kind].difficulty = difficulty;
    gems[kind].multiplier = multiplier;
    gems[kind].gemsPerMine = gemsPerMine;
  }

  /// @dev Renounce management ownership for the given gem kinds.
  function renounceManager(uint[] calldata kinds) external {
    for (uint idx = 0; idx < kinds.length; idx++) {
      uint kind = kinds[idx];
      require(kind < gemCount, 'gem kind not exist');
      require(gems[kind].manager == msg.sender, 'not gem manager');
      gems[kind].manager = address(0);
      gems[kind].pendingManager = address(0);
    }
  }

  /// @dev Updates gem crafter. Must only be called by the gem manager.
  function updateCrafter(uint[] calldata kinds, address crafter) external {
    for (uint idx = 0; idx < kinds.length; idx++) {
      uint kind = kinds[idx];
      require(kind < gemCount, 'gem kind not exist');
      require(gems[kind].manager == msg.sender, 'not gem manager');
      gems[kind].crafter = crafter;
    }
  }

  /// @dev Transfers management ownership for the given gem kinds to another address.
  function transferManager(uint[] calldata kinds, address to) external {
    for (uint idx = 0; idx < kinds.length; idx++) {
      uint kind = kinds[idx];
      require(kind < gemCount, 'gem kind not exist');
      require(gems[kind].manager == msg.sender, 'not gem manager');
      gems[kind].pendingManager = to;
    }
  }

  /// @dev Accepts management position for the given gem kinds.
  function acceptManager(uint[] calldata kinds) external {
    for (uint idx = 0; idx < kinds.length; idx++) {
      uint kind = kinds[idx];
      require(kind < gemCount, 'gem kind not exist');
      require(gems[kind].pendingManager == msg.sender, 'not pending manager');
      gems[kind].pendingManager = address(0);
      gems[kind].manager = msg.sender;
    }
  }

  /// @dev Mints gems by crafter. Hopefully, crafter is a good guy. Craft gemsPerMine if amount = 0.
  function craft(
    uint kind,
    uint amount,
    address to
  ) external nonReentrant {
    require(kind < gemCount, 'gem kind not exist');
    require(gems[kind].crafter == msg.sender, 'not gem crafter');
    uint realAmount = amount == 0 ? gems[kind].gemsPerMine : amount;
    _mint(to, kind, realAmount, '');
  }

  /// @dev Returns your luck given salt and gem kind. The smaller the value, the more success chance.
  function luck(uint kind, uint salt) public view returns (uint) {
    require(kind < gemCount, 'gem kind not exist');
    bytes32 entropy = gems[kind].entropy;
    require(entropy != bytes32(0), 'no entropy');
    bytes memory data = abi.encodePacked(
      block.chainid,
      entropy,
      address(this),
      msg.sender,
      kind,
      nonce[msg.sender],
      salt
    );
    return uint(keccak256(data));
  }

  /// @dev Internal function for creating a new gem kind
  function _create(
    string memory name,
    string memory color,
    uint difficulty,
    uint gemsPerMine,
    uint multiplier,
    address crafter,
    address manager
  ) internal returns (uint) {
    uint kind = gemCount++;
    gems[kind] = Gem({
      name: name,
      color: color,
      entropy: bytes32(0),
      difficulty: difficulty,
      gemsPerMine: gemsPerMine,
      multiplier: multiplier,
      crafter: crafter,
      manager: manager,
      pendingManager: address(0)
    });
    emit Create(kind);
    return kind;
  }

  // prettier-ignore
  function uri(uint kind) public view override returns (string memory) {
    require(kind < gemCount, 'gem kind not exist');
    string memory output = string(abi.encodePacked(
        '<svg xmlns="http://www.w3.org/2000/svg" preserveAspectRatio="xMinYMin meet" viewBox="0 0 350 350"><style>.base { fill: ',
        gems[kind].color,
        '; font-family: serif; font-size: 14px; }</style><rect width="100%" height="100%" fill="white" /><text x="10" y="20" class="base">',
        gems[kind].name,
        '</text><text x="10" y="40" class="base">',
        '</text></svg>'
    ));
    string memory json = Base64.encode(bytes(string(abi.encodePacked(
      '{ "name": "',
      gems[kind].name,
      '", ',
      '"description" : ',
      '"Provably Rare Gems", ',
      '"image": "data:image/svg+xml;base64,',
      Base64.encode(bytes(output)),
      '"}'
    ))));
    return string(abi.encodePacked('data:application/json;base64,', json));
  }
}

// Part: ProvablyRareGemV2

/// @title Provably Rare Gems
/// @author Sorawit Suriyakarn (swit.eth / https://twitter.com/nomorebear)
contract ProvablyRareGemV2 is Initializable, ERC1155Supply {
  event Create(uint indexed kind);
  event Mine(address indexed miner, uint indexed kind);
  event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);
  string public name;

  struct Gem {
    string name; // Gem name
    string color; // Gem color
    bytes32 entropy; // Additional mining entropy. bytes32(0) means can't mine.
    uint difficulty; // Current difficulity level. Must be non decreasing
    uint gemsPerMine; // Amount of gems to distribute per mine
    uint multiplier; // Difficulty multiplier times 1e4. Must be between 1e4 and 1e10
    address crafter; // Address that can craft gems
    address manager; // Current gem manager
    address pendingManager; // Pending gem manager to be transferred to
  }

  uint private lock;
  address public owner;
  mapping(uint => Gem) public gems;
  mapping(address => uint) public nonce;
  uint public gemCount;

  constructor() ERC1155('GEM') {}

  modifier nonReentrant() {
    require(lock == 1, '!lock');
    lock = 2;
    _;
    lock = 1;
  }

  modifier onlyOwner() {
    require(owner == msg.sender, '!owner');
    _;
  }

  /// @dev Initializes the contract.
  function initialize() external initializer {
    name = 'Provably Rare Gem';
    lock = 1;
    owner = msg.sender;
    emit OwnershipTransferred(address(0), msg.sender);
  }

  /// @dev Transfers owner.
  /// @param _owner The new owner.
  function transferOwnership(address _owner) external onlyOwner {
    owner = _owner;
    emit OwnershipTransferred(msg.sender, _owner);
  }

  /// @dev Creates a new gem type. The manager can craft a portion of gems + can premine
  function create(
    string calldata name,
    string calldata color,
    uint difficulty,
    uint gemsPerMine,
    uint multiplier,
    address crafter,
    address manager
  ) external returns (uint) {
    require(difficulty > 0 && difficulty <= 2**128, 'bad difficulty');
    require(gemsPerMine > 0 && gemsPerMine <= 1e6, 'bad gems per mine');
    require(multiplier >= 1e4 && multiplier <= 1e10, 'bad multiplier');
    require(manager != address(0), 'bad manager');
    return _create(name, color, difficulty, gemsPerMine, multiplier, crafter, manager);
  }

  /// @dev Mines new gemstones. Puts kind you want to mine + your salt and tests your luck!
  function mine(uint kind, uint salt) external nonReentrant {
    uint val = luck(kind, salt);
    nonce[msg.sender]++;
    require(kind < gemCount, 'gem kind not exist');
    uint diff = gems[kind].difficulty;
    require(val <= type(uint).max / diff, 'salt not good enough');
    gems[kind].difficulty = (diff * gems[kind].multiplier) / 10000 + 1;
    _mint(msg.sender, kind, gems[kind].gemsPerMine, '');
  }

  /// @dev Updates gem mining entropy. Can be called by gem manager or crafter.
  function updateEntropy(uint kind, bytes32 entropy) external {
    require(kind < gemCount, 'gem kind not exist');
    require(gems[kind].manager == msg.sender || gems[kind].crafter == msg.sender, 'unauthorized');
    gems[kind].entropy = entropy;
  }

  /// @dev Updates gem metadata info. Must only be called by the gem manager.
  function updateGemInfo(
    uint kind,
    string calldata name,
    string calldata color
  ) external {
    require(kind < gemCount, 'gem kind not exist');
    require(gems[kind].manager == msg.sender, 'not gem manager');
    gems[kind].name = name;
    gems[kind].color = color;
  }

  /// @dev Updates gem mining information. Must only be called by the gem manager.
  function updateMiningData(
    uint kind,
    uint difficulty,
    uint multiplier,
    uint gemsPerMine
  ) external {
    require(kind < gemCount, 'gem kind not exist');
    require(gems[kind].manager == msg.sender, 'not gem manager');
    require(difficulty > 0 && difficulty <= 2**128, 'bad difficulty');
    require(multiplier >= 1e4 && multiplier <= 1e10, 'bad multiplier');
    require(gemsPerMine > 0 && gemsPerMine <= 1e6, 'bad gems per mine');
    gems[kind].difficulty = difficulty;
    gems[kind].multiplier = multiplier;
    gems[kind].gemsPerMine = gemsPerMine;
  }

  /// @dev Renounce management ownership for the given gem kinds.
  function renounceManager(uint[] calldata kinds) external {
    for (uint idx = 0; idx < kinds.length; idx++) {
      uint kind = kinds[idx];
      require(kind < gemCount, 'gem kind not exist');
      require(gems[kind].manager == msg.sender, 'not gem manager');
      gems[kind].manager = address(0);
      gems[kind].pendingManager = address(0);
    }
  }

  /// @dev Updates gem crafter. Must only be called by the gem manager.
  function updateCrafter(uint[] calldata kinds, address crafter) external {
    for (uint idx = 0; idx < kinds.length; idx++) {
      uint kind = kinds[idx];
      require(kind < gemCount, 'gem kind not exist');
      require(gems[kind].manager == msg.sender, 'not gem manager');
      gems[kind].crafter = crafter;
    }
  }

  /// @dev Transfers management ownership for the given gem kinds to another address.
  function transferManager(uint[] calldata kinds, address to) external {
    for (uint idx = 0; idx < kinds.length; idx++) {
      uint kind = kinds[idx];
      require(kind < gemCount, 'gem kind not exist');
      require(gems[kind].manager == msg.sender, 'not gem manager');
      gems[kind].pendingManager = to;
    }
  }

  /// @dev Accepts management position for the given gem kinds.
  function acceptManager(uint[] calldata kinds) external {
    for (uint idx = 0; idx < kinds.length; idx++) {
      uint kind = kinds[idx];
      require(kind < gemCount, 'gem kind not exist');
      require(gems[kind].pendingManager == msg.sender, 'not pending manager');
      gems[kind].pendingManager = address(0);
      gems[kind].manager = msg.sender;
    }
  }

  /// @dev Mints gems by crafter. Hopefully, crafter is a good guy. Craft gemsPerMine if amount = 0.
  function craft(
    uint kind,
    uint amount,
    address to
  ) external nonReentrant {
    require(kind < gemCount, 'gem kind not exist');
    require(gems[kind].crafter == msg.sender, 'not gem crafter');
    uint realAmount = amount == 0 ? gems[kind].gemsPerMine : amount;
    _mint(to, kind, realAmount, '');
  }

  /// @dev Returns your luck given salt and gem kind. The smaller the value, the more success chance.
  function luck(uint kind, uint salt) public view returns (uint) {
    require(kind < gemCount, 'gem kind not exist');
    bytes32 entropy = gems[kind].entropy;
    require(entropy != bytes32(0), 'no entropy');
    bytes memory data = abi.encodePacked(
      block.chainid,
      entropy,
      address(this),
      msg.sender,
      kind,
      nonce[msg.sender],
      salt
    );
    return uint(keccak256(data));
  }

  /// @dev Internal function for creating a new gem kind
  function _create(
    string memory gemName,
    string memory color,
    uint difficulty,
    uint gemsPerMine,
    uint multiplier,
    address crafter,
    address manager
  ) internal returns (uint) {
    uint kind = gemCount++;
    gems[kind] = Gem({
      name: gemName,
      color: color,
      entropy: bytes32(0),
      difficulty: difficulty,
      gemsPerMine: gemsPerMine,
      multiplier: multiplier,
      crafter: crafter,
      manager: manager,
      pendingManager: address(0)
    });
    emit Create(kind);
    return kind;
  }

  // prettier-ignore
  function uri(uint kind) public view override returns (string memory) {
    require(kind < gemCount, 'gem kind not exist');
    string memory gemName = string(abi.encodePacked(gems[kind].name, ' #', Strings.toString(kind)));
    string memory color = gems[kind].color;
    string memory output = string(abi.encodePacked(
      '<svg id="Layer_1" x="0px" y="0px" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1080 1080" width="350" height="400"><rect x="0" y="0" width="1080" height="1080" fill="#1a1a1a"/><svg id="Layer_1" x="350" y="350" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1080 1080" width="350" height="400"><g transform="translate(0 -25)"><g><polygon class="st0" fill="',
      color,
      '" points="679.25,58.27 400.75,58.27 203.82,255.2 203.82,824.8 400.75,1021.73 679.25,1021.73 876.18,824.8 876.18,255.2"></polygon><g class="st1" opacity="0.3"><path d="M679.25,58.27h-278.5L203.82,255.2v569.6l196.93,196.93h278.5L876.18,824.8V255.2L679.25,58.27z M739.56,709.06 l-116.9,116.9H457.34l-116.9-116.9V370.94l116.9-116.9h165.32l116.9,116.9V709.06z"></path></g><g><g><polygon class="st2" fill="none" stroke-width="10" stroke-miterlimit="10" stroke="#ffffff" points="679.25,58.27 400.75,58.27 203.82,255.2 203.82,824.8 400.75,1021.73 679.25,1021.73 876.18,824.8  876.18,255.2"></polygon><polygon fill="',
      color,
      '" class="st2" stroke-width="10" stroke-miterlimit="10" stroke="#ffffff" points="622.66,254.04 457.34,254.04 340.44,370.94 340.44,709.06 457.34,825.96 622.66,825.96  739.56,709.06 739.56,370.94"></polygon><line class="st2" stroke-width="10" stroke-miterlimit="10" stroke="#ffffff" x1="400.75" y1="58.27" x2="457.34" y2="254.04"></line><line class="st2" stroke-width="10" stroke-miterlimit="10" stroke="#ffffff" x1="679.25" y1="58.27" x2="622.66" y2="254.04"></line><line class="st2" stroke-width="10" stroke-miterlimit="10" stroke="#ffffff" x1="203.82" y1="255.2" x2="340.44" y2="370.94"></line><line class="st2" stroke-width="10" stroke-miterlimit="10" stroke="#ffffff" x1="739.56" y1="370.94" x2="876.18" y2="255.2"></line><line class="st2" stroke-width="10" stroke-miterlimit="10" stroke="#ffffff" x1="739.56" y1="709.06" x2="876.18" y2="824.8"></line><line class="st2" stroke-width="10" stroke-miterlimit="10" stroke="#ffffff" x1="622.66" y1="825.96" x2="679.25" y2="1021.73"></line><line class="st2" stroke-width="10" stroke-miterlimit="10" stroke="#ffffff" x1="457.34" y1="825.96" x2="400.75" y2="1021.73"></line><line class="st2" stroke-width="10" stroke-miterlimit="10" stroke="#ffffff" x1="340.44" y1="709.06" x2="203.82" y2="824.8"></line></g></g></g></g></svg><text x="50%" y="95%" dominant-baseline="middle" text-anchor="middle" font-size="2.5em" fill="#FFFFFF">',
      gemName,
      '</text></svg>'
    ));
    string memory json = Base64.encode(bytes(string(abi.encodePacked(
      '{ "name": "',
      gemName,
      '", ',
      '"description" : ',
      '"Provably Rare Gem is a permissionless on-chain asset for hardcore collectors to mine and collect. Gems must be mined with off-chain Proof-of-Work. The higher the gem rarity, the more difficult it is to be found. Stats and other functionalities are intentionally omitted for others to interpret.", ',
      '"image": "data:image/svg+xml;base64,',
      Base64.encode(bytes(output)),
      '"}'
    ))));
    return string(abi.encodePacked('data:application/json;base64,', json));
  }
}

// Part: LOOTGemCrafter

/// @title LOOT GEM Crafter
/// @author Sorawit Suriyakarn (swit.eth / https://twitter.com/nomorebear)
contract LOOTGemCrafter is Ownable, ReentrancyGuard {
  IERC721 public immutable NFT;
  ProvablyRareGem public immutable GEM;
  uint public immutable FIRST_KIND;

  event Start(bytes32 hashseed);
  event Craft(uint indexed kind, uint amount);
  event Claim(uint indexed id, address indexed claimer);

  bytes32 public hashseed;
  mapping(uint => uint) public crafted;
  mapping(uint => bool) public claimed;

  constructor(IERC721 _nft, ProvablyRareGem _gem) {
    NFT = _nft;
    GEM = _gem;
    FIRST_KIND = _gem.gemCount();
    _gem.create('Amethyst', '#9966CC', 8**2, 64, 10000, address(this), msg.sender);
    _gem.create('Topaz', '#FFC87C', 8**3, 32, 10001, address(this), msg.sender);
    _gem.create('Opal', '#A8C3BC', 8**4, 16, 10005, address(this), msg.sender);
    _gem.create('Sapphire', '#0F52BA', 8**5, 8, 10010, address(this), msg.sender);
    _gem.create('Ruby', '#E0115F', 8**6, 4, 10030, address(this), msg.sender);
    _gem.create('Emerald', '#50C878', 8**7, 2, 10100, address(this), msg.sender);
    _gem.create('Pink Diamond', '#FC74E4', 8**8, 1, 10300, address(this), msg.sender);
    _gem.create('The Dragon Jade', '#00A36C', 8**9, 1, 11000, address(this), msg.sender);
    _gem.create('Azure Skystone', '#348CFC', 8**10, 1, 20000, address(this), msg.sender);
    _gem.create('Scarlet Bloodstone', '#BC1C2C', 8**11, 1, 50000, address(this), msg.sender);
  }

  /// @dev Called once to start the claim and generate hash seed.
  function start() external onlyOwner {
    require(hashseed == bytes32(0), 'already started');
    hashseed = blockhash(block.number - 1);
    for (uint offset = 0; offset < 10; offset++) {
      GEM.updateEntropy(FIRST_KIND + offset, hashseed);
    }
  }

  /// @dev Called by gem manager to craft gems. Can't craft more than 10% of supply.
  function craft(uint kind, uint amount) external nonReentrant onlyOwner {
    require(amount != 0, 'zero amount craft');
    crafted[kind] += amount;
    GEM.craft(kind, amount, msg.sender);
    emit Craft(kind, amount);
    require(crafted[kind] <= GEM.totalSupply(kind) / 10, 'too many crafts');
  }

  /// @dev Returns the list of initial GEM distribution for the given NFT ID.
  function airdrop(uint id) public view returns (uint[4] memory kinds) {
    require(hashseed != bytes32(0), 'not yet started');
    uint[10] memory chances = [uint(1), 1, 3, 6, 10, 20, 30, 100, 300, 1000];
    uint count = 0;
    for (uint idx = 0; idx < 4; idx++) {
      kinds[idx] = FIRST_KIND;
    }
    for (uint offset = 9; offset > 0; offset--) {
      uint seed = uint(keccak256(abi.encodePacked(hashseed, offset, id)));
      if (seed % chances[offset] == 0) {
        kinds[count++] = FIRST_KIND + offset;
      }
      if (count == 4) break;
    }
  }

  /// @dev Called by NFT owners to get a welcome pack of gems. Each NFT ID can claim once.
  function claim(uint id) external nonReentrant {
    _claim(id);
  }

  /// @dev Called by NFT owners to get a welcome pack of gems for multiple NFTs.
  function multiClaim(uint[] calldata ids) external nonReentrant {
    for (uint idx = 0; idx < ids.length; idx++) {
      _claim(ids[idx]);
    }
  }

  function _claim(uint id) internal {
    require(msg.sender == NFT.ownerOf(id), 'not nft owner');
    require(!claimed[id], 'already claimed');
    claimed[id] = true;
    uint[4] memory kinds = airdrop(id);
    for (uint idx = 0; idx < 4; idx++) {
      GEM.craft(kinds[idx], 0, msg.sender);
    }
    emit Claim(id, msg.sender);
  }
}

// File: LOOTGemCrafterV2.sol

/// @title LOOT GEM Crafter
/// @author Sorawit Suriyakarn (swit.eth / https://twitter.com/nomorebear)
contract LOOTGemCrafterV2 is Ownable, ERC1155Receiver, ReentrancyGuard, Pausable {
  IERC721 public immutable NFT;
  ProvablyRareGemV2 public immutable GEM;
  uint public immutable FIRST_KIND;
  bytes32 public immutable hashseed;
  LOOTGemCrafter public immutable old;

  event Craft(uint indexed kind, uint amount);
  event Claim(uint indexed id, address indexed claimer);

  mapping(uint => uint) public crafted;
  mapping(uint => bool) public newClaimed;

  constructor(
    IERC721 _nft,
    ProvablyRareGemV2 _gem,
    LOOTGemCrafter _old
  ) {
    NFT = _nft;
    GEM = _gem;
    old = _old;
    hashseed = _old.hashseed();
    FIRST_KIND = _gem.gemCount();
    ProvablyRareGem oldGem = _old.GEM();
    uint diff;
    (, , , diff, , , , , ) = oldGem.gems(0);
    _gem.create('Amethyst', '#9966CC', diff, 64, 10000, address(this), msg.sender);
    (, , , diff, , , , , ) = oldGem.gems(1);
    _gem.create('Topaz', '#FFC87C', diff, 32, 10001, address(this), msg.sender);
    (, , , diff, , , , , ) = oldGem.gems(2);
    _gem.create('Opal', '#A8C3BC', diff, 16, 10005, address(this), msg.sender);
    (, , , diff, , , , , ) = oldGem.gems(3);
    _gem.create('Sapphire', '#0F52BA', diff, 8, 10010, address(this), msg.sender);
    (, , , diff, , , , , ) = oldGem.gems(4);
    _gem.create('Ruby', '#E0115F', diff, 4, 10030, address(this), msg.sender);
    (, , , diff, , , , , ) = oldGem.gems(5);
    _gem.create('Emerald', '#50C878', diff, 2, 10100, address(this), msg.sender);
    (, , , diff, , , , , ) = oldGem.gems(6);
    _gem.create('Pink Diamond', '#FC74E4', diff, 1, 10300, address(this), msg.sender);
    (, , , diff, , , , , ) = oldGem.gems(7);
    _gem.create('The Dragon Jade', '#00A36C', diff, 1, 11000, address(this), msg.sender);
    (, , , diff, , , , , ) = oldGem.gems(8);
    _gem.create('Azure Skystone', '#348CFC', diff, 1, 20000, address(this), msg.sender);
    (, , , diff, , , , , ) = oldGem.gems(9);
    _gem.create('Scarlet Bloodstone', '#BC1C2C', diff, 1, 50000, address(this), msg.sender);
  }

  /// @dev Pause crafter. Can only be called by owner.
  function pause() external onlyOwner {
    _pause();
  }

  /// @dev Unpause crafter. Can only be called by owner.
  function unpause() external onlyOwner {
    _unpause();
  }

  /// @dev Called once to start the claim and generate hash seed.
  function start() external onlyOwner whenNotPaused {
    for (uint offset = 0; offset < 10; offset++) {
      GEM.updateEntropy(FIRST_KIND + offset, hashseed);
    }
  }

  /// @dev Called by gem manager to craft gems. Can't craft more than 10% of supply.
  function craft(uint kind, uint amount) external nonReentrant onlyOwner whenNotPaused {
    require(amount != 0, 'zero amount craft');
    crafted[kind] += amount;
    GEM.craft(kind, amount, msg.sender);
    emit Craft(kind, amount);
    require(crafted[kind] <= GEM.totalSupply(kind) / 10, 'too many crafts');
  }

  /// @dev Returns the list of initial GEM distribution for the given NFT ID.
  function airdrop(uint id) public view returns (uint[4] memory kinds) {
    require(hashseed != bytes32(0), 'not yet started');
    uint[10] memory chances = [uint(1), 1, 3, 6, 10, 20, 30, 100, 300, 1000];
    uint count = 0;
    for (uint idx = 0; idx < 4; idx++) {
      kinds[idx] = FIRST_KIND;
    }
    for (uint offset = 9; offset > 0; offset--) {
      uint seed = uint(keccak256(abi.encodePacked(hashseed, offset, id)));
      if (seed % chances[offset] == 0) {
        kinds[count++] = FIRST_KIND + offset;
      }
      if (count == 4) break;
    }
  }

  /// @dev Called by NFT owners to get a welcome pack of gems. Each NFT ID can claim once.
  function claim(uint id) external nonReentrant whenNotPaused {
    _claim(id);
  }

  /// @dev Called by NFT owners to get a welcome pack of gems for multiple NFTs.
  function multiClaim(uint[] calldata ids) external nonReentrant whenNotPaused {
    for (uint idx = 0; idx < ids.length; idx++) {
      _claim(ids[idx]);
    }
  }

  /// @dev Returns whether the given NFT ID has already claimed GEMs.
  function claimed(uint id) public view returns (bool) {
    return old.claimed(id) || newClaimed[id];
  }

  function _claim(uint id) internal {
    require(msg.sender == NFT.ownerOf(id), 'not nft owner');
    require(!claimed(id), 'already claimed');
    newClaimed[id] = true;
    uint[4] memory kinds = airdrop(id);
    for (uint idx = 0; idx < 4; idx++) {
      GEM.craft(kinds[idx], 0, msg.sender);
    }
    emit Claim(id, msg.sender);
  }

  function onERC1155Received(
    address operator,
    address from,
    uint id,
    uint value,
    bytes calldata data
  ) external override returns (bytes4) {
    revert('unsupported');
  }

  function onERC1155BatchReceived(
    address operator,
    address from,
    uint[] calldata ids,
    uint[] calldata values,
    bytes calldata data
  ) external override nonReentrant whenNotPaused returns (bytes4) {
    require(msg.sender == address(old.GEM()), 'bad token');
    for (uint idx = 0; idx < ids.length; idx++) {
      uint kind = ids[idx];
      require(kind >= FIRST_KIND && kind < FIRST_KIND + 10, 'bad kind');
      require(values[idx] > 0, 'no value');
      GEM.craft(kind, values[idx], from);
    }
    return this.onERC1155BatchReceived.selector;
  }
}