// File: contracts/Unmasked.sol



// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity ^0.8.4;

import './ERC721B.sol';
import '@openzeppelin/contracts/access/Ownable.sol';
import '@openzeppelin/contracts/utils/cryptography/MerkleProof.sol';
import '@openzeppelin/contracts/utils/Strings.sol';

error InvalidProof();
error OverMaxSupply();
error WrongEtherValue();
error OverMintLimit();
error DoubleClaim();
error SaleNotActive();

contract Unmasked is ERC721B, Ownable {
    using Strings for uint256;

    // OpenSea whitelisting
    address constant proxyRegistryAddress = address(0xa5409ec958C83C3f309868babACA7c86DCB077c1);
    mapping(address => bool) public addressToRegistryDisabled;

    // Merkle whitelisting
    mapping(address => bool) public claimed;
    bytes32 public CLAIM_ROOT;
    bytes32 public WHITELIST_ROOT;

    // collection specific parameters
    string private baseURI;
    string public provenance;
    bool public publicSaleActive;

    uint256 public supply = 3333;
    uint256 public price = 0.06 ether;
    uint256 public price2 = 0.04 ether;
    uint256 constant maxBatchSize = 20;

    constructor() ERC721B('TheUnmasked', 'UNMASKED') {}

    /*///////////////////////////////////////////////////////////////
                          OWNER FUNCTIONS
    //////////////////////////////////////////////////////////////*/

    function withdraw() external onlyOwner {
        uint256 balance = address(this).balance;
        payable(msg.sender).transfer(balance);
    }

    function setClaim(bytes32 _root) external onlyOwner {
        CLAIM_ROOT = _root;
    }

    function setWhitelist(bytes32 _root) external onlyOwner {
        WHITELIST_ROOT = _root;
    }

    function setProvenanceHash(string calldata provenanceHash) external onlyOwner {
        provenance = provenanceHash;
    }

    function setBaseURI(string calldata _baseURI) external onlyOwner {
        baseURI = _baseURI;
    }

    function togglePublicSale() external onlyOwner {
        publicSaleActive = !publicSaleActive;
    }

    function setPrice(uint256 _price, uint256 _price2) external onlyOwner {
        price = _price;
        price2 = _price2;
    }

    function setSupply(uint256 _supply) external onlyOwner {
        supply = _supply;
    }

    /**
     * Reserve NFTs for giveaways
     */
    function reserveUnmasked(uint256 qty) external onlyOwner {
        if ((_owners.length + qty) > supply) revert OverMaxSupply();

        _mint(msg.sender, qty);
    }

    /**
     * Claim function for whitelisted addresses
     */
    function claim(
        address account,
        uint256 qty,
        bytes32[] calldata proof
    ) external {
        if (!_verify(_leaf(account, qty), proof)) revert InvalidProof();
        if ((_owners.length + qty) > supply) revert OverMaxSupply();
        if (claimed[account]) revert DoubleClaim();

        // set claimed to true to prevent double claiming
        claimed[account] = true;

        _mint(account, qty);
    }

    function whitelistMint(uint256 qty, bytes32[] calldata proof) external payable {
        if (!_verify2(_leaf2(msg.sender), proof)) revert InvalidProof();
        if (qty > maxBatchSize) revert OverMintLimit();
        if ((_owners.length + qty) > supply) revert OverMaxSupply();
        if (msg.value < price2 * qty) revert WrongEtherValue();

        _mint(msg.sender, qty);
    }

    function publicMint(uint256 qty) external payable {
        if (!publicSaleActive) revert SaleNotActive();
        if (qty > maxBatchSize) revert OverMintLimit();
        if ((_owners.length + qty) > supply) revert OverMaxSupply();
        if (msg.value < price * qty) revert WrongEtherValue();

        _safeMint(msg.sender, qty);
    }

    /**
        An override to whitelist the OpenSea proxy contract to enable gas-free
        listings. This function returns true if `_operator` is approved to transfer
        items owned by `_owner`.
        @param owner The owner of items to check for transfer ability.
        @param operator The potential transferrer of `_owner`'s items.
    */
    function isApprovedForAll(address owner, address operator) public view override returns (bool) {
        // Whitelist OpenSea proxy contract for easy trading.
        ProxyRegistry proxyRegistry = ProxyRegistry(proxyRegistryAddress);
        if (address(proxyRegistry.proxies(owner)) == operator && !addressToRegistryDisabled[owner]) {
            return true;
        }

        return super.isApprovedForAll(owner, operator);
    }

    /**
     * @notice Allow a user to disable the OpenSea pre-approval if they believe OS to not be secure.
     */
    function toggleRegistryAccess() public virtual {
        addressToRegistryDisabled[msg.sender] = !addressToRegistryDisabled[msg.sender];
    }

    /**
     * @dev See {IERC721Metadata-tokenURI}.
     */
    function tokenURI(uint256 _tokenId) public view override returns (string memory) {
        if (!_exists(_tokenId)) revert URIQueryForNonexistentToken();
        return string(abi.encodePacked(baseURI, Strings.toString(_tokenId)));
    }

    /**
     * @dev See OpenZeppelin MerkleProof.
     */
    function _leaf(address account, uint256 qty) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked(account, qty));
    }

    function _leaf2(address account) internal pure returns (bytes32) {
        return keccak256(abi.encodePacked(account));
    }

    function _verify(bytes32 leaf, bytes32[] memory proof) internal view returns (bool) {
        return MerkleProof.verify(proof, CLAIM_ROOT, leaf);
    }

    function _verify2(bytes32 leaf, bytes32[] memory proof) internal view returns (bool) {
        return MerkleProof.verify(proof, WHITELIST_ROOT, leaf);
    }
}

/**
  @title An OpenSea delegate proxy contract which we include for whitelisting.
  @author OpenSea
*/
contract OwnableDelegateProxy {

}

/**
 * Used to delegate ownership of a contract to another address,
 * to save on unneeded transactions to approve contract use for users
 */
contract ProxyRegistry {
    mapping(address => OwnableDelegateProxy) public proxies;
}

// File: contracts/ERC721B.sol



// SPDX-License-Identifier: GPL-3.0-or-later

pragma solidity ^0.8.4;

import '@openzeppelin/contracts/token/ERC721/IERC721Receiver.sol';

error ApprovalCallerNotOwnerNorApproved();
error ApprovalQueryForNonexistentToken();
error ApproveToCaller();
error ApprovalToCurrentOwner();
error BalanceQueryForZeroAddress();
error MintedQueryForZeroAddress();
error MintToZeroAddress();
error MintZeroQuantity();
error OwnerIndexOutOfBounds();
error OwnerQueryForNonexistentToken();
error TokenIndexOutOfBounds();
error TransferCallerNotOwnerNorApproved();
error TransferFromIncorrectOwner();
error TransferToNonERC721ReceiverImplementer();
error TransferToZeroAddress();
error UnableDetermineTokenOwner();
error UnableGetTokenOwnerByIndex();
error URIQueryForNonexistentToken();

/**
 * Updated, minimalist and gas efficient version of OpenZeppelins ERC721 contract.
 * Includes the Metadata and  Enumerable extension.
 *
 * Assumes serials are sequentially minted starting at 0 (e.g. 0, 1, 2, 3..).
 * Does not support burning tokens
 *
 * @author beskay0x
 * Credits: chiru-labs, solmate, transmissions11, nftchance, squeebo_nft and others
 */

abstract contract ERC721B {
    /*///////////////////////////////////////////////////////////////
                                 EVENTS
    //////////////////////////////////////////////////////////////*/

    event Transfer(address indexed from, address indexed to, uint256 indexed id);

    event Approval(address indexed owner, address indexed spender, uint256 indexed id);

    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    /*///////////////////////////////////////////////////////////////
                          METADATA STORAGE/LOGIC
    //////////////////////////////////////////////////////////////*/

    string public name;

    string public symbol;

    function tokenURI(uint256 tokenId) public view virtual returns (string memory);

    /*///////////////////////////////////////////////////////////////
                          ERC721 STORAGE
    //////////////////////////////////////////////////////////////*/

    // Array which maps token ID to address (index is tokenID)
    address[] internal _owners;

    // Mapping from token ID to approved address
    mapping(uint256 => address) private _tokenApprovals;

    // Mapping from owner to operator approvals
    mapping(address => mapping(address => bool)) private _operatorApprovals;

    /*///////////////////////////////////////////////////////////////
                              CONSTRUCTOR
    //////////////////////////////////////////////////////////////*/

    constructor(string memory _name, string memory _symbol) {
        name = _name;
        symbol = _symbol;
    }

    /*///////////////////////////////////////////////////////////////
                              ERC165 LOGIC
    //////////////////////////////////////////////////////////////*/

    function supportsInterface(bytes4 interfaceId) public view virtual returns (bool) {
        return
            interfaceId == 0x01ffc9a7 || // ERC165 Interface ID for ERC165
            interfaceId == 0x80ac58cd || // ERC165 Interface ID for ERC721
            interfaceId == 0x780e9d63 || // ERC165 Interface ID for ERC721Enumerable
            interfaceId == 0x5b5e139f; // ERC165 Interface ID for ERC721Metadata
    }

    /*///////////////////////////////////////////////////////////////
                       ERC721ENUMERABLE LOGIC
    //////////////////////////////////////////////////////////////*/

    /**
     * @dev See {IERC721Enumerable-totalSupply}.
     */
    function totalSupply() public view returns (uint256) {
        return _owners.length;
    }

    /**
     * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
     * Dont call this function on chain from another smart contract, since it can become quite expensive
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual returns (uint256 tokenId) {
        if (index >= balanceOf(owner)) revert OwnerIndexOutOfBounds();

        uint256 count;
        uint256 qty = _owners.length;
        // Cannot realistically overflow, since we are using uint256
        unchecked {
            for (tokenId; tokenId < qty; tokenId++) {
                if (owner == ownerOf(tokenId)) {
                    if (count == index) return tokenId;
                    else count++;
                }
            }
        }

        revert UnableGetTokenOwnerByIndex();
    }

    /**
     * @dev See {IERC721Enumerable-tokenByIndex}.
     */
    function tokenByIndex(uint256 index) public view virtual returns (uint256) {
        if (index >= totalSupply()) revert TokenIndexOutOfBounds();
        return index;
    }

    /*///////////////////////////////////////////////////////////////
                              ERC721 LOGIC
    //////////////////////////////////////////////////////////////*/

    /**
     * @dev Iterates through _owners array, returns balance of address
     * It is not recommended to call this function from another smart contract
     * as it can become quite expensive -- call this function off chain instead.
     */
    function balanceOf(address owner) public view virtual returns (uint256) {
        if (owner == address(0)) revert BalanceQueryForZeroAddress();

        uint256 count;
        uint256 qty = _owners.length;
        // Cannot realistically overflow, since we are using uint256
        unchecked {
            for (uint256 i; i < qty; i++) {
                if (owner == ownerOf(i)) {
                    count++;
                }
            }
        }
        return count;
    }

    /**
     * @dev See {IERC721-ownerOf}.
     * Gas spent here starts off proportional to the maximum mint batch size.
     * It gradually moves to O(1) as tokens get transferred around in the collection over time.
     */
    function ownerOf(uint256 tokenId) public view virtual returns (address) {
        if (!_exists(tokenId)) revert OwnerQueryForNonexistentToken();

        // Cannot realistically overflow, since we are using uint256
        unchecked {
            for (tokenId; ; tokenId++) {
                if (_owners[tokenId] != address(0)) {
                    return _owners[tokenId];
                }
            }
        }

        revert UnableDetermineTokenOwner();
    }

    /**
     * @dev See {IERC721-approve}.
     */
    function approve(address to, uint256 tokenId) public virtual {
        address owner = ownerOf(tokenId);
        if (to == owner) revert ApprovalToCurrentOwner();

        if (msg.sender != owner && !isApprovedForAll(owner, msg.sender)) revert ApprovalCallerNotOwnerNorApproved();

        _tokenApprovals[tokenId] = to;
        emit Approval(owner, to, tokenId);
    }

    /**
     * @dev See {IERC721-getApproved}.
     */
    function getApproved(uint256 tokenId) public view virtual returns (address) {
        if (!_exists(tokenId)) revert ApprovalQueryForNonexistentToken();

        return _tokenApprovals[tokenId];
    }

    /**
     * @dev See {IERC721-setApprovalForAll}.
     */
    function setApprovalForAll(address operator, bool approved) public virtual {
        if (operator == msg.sender) revert ApproveToCaller();

        _operatorApprovals[msg.sender][operator] = approved;
        emit ApprovalForAll(msg.sender, operator, approved);
    }

    /**
     * @dev See {IERC721-isApprovedForAll}.
     */
    function isApprovedForAll(address owner, address operator) public view virtual returns (bool) {
        return _operatorApprovals[owner][operator];
    }

    /**
     * @dev See {IERC721-transferFrom}.
     */
    function transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) public virtual {
        if (!_exists(tokenId)) revert OwnerQueryForNonexistentToken();
        if (ownerOf(tokenId) != from) revert TransferFromIncorrectOwner();
        if (to == address(0)) revert TransferToZeroAddress();

        bool isApprovedOrOwner = (msg.sender == from ||
            msg.sender == getApproved(tokenId) ||
            isApprovedForAll(from, msg.sender));
        if (!isApprovedOrOwner) revert TransferCallerNotOwnerNorApproved();

        // delete token approvals from previous owner
        delete _tokenApprovals[tokenId];
        _owners[tokenId] = to;

        // if token ID below transferred one isnt set, set it to previous owner
        // if tokenid is zero, skip this to prevent underflow
        if (tokenId > 0 && _owners[tokenId - 1] == address(0)) {
            _owners[tokenId - 1] = from;
        }

        emit Transfer(from, to, tokenId);
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 id
    ) public virtual {
        safeTransferFrom(from, to, id, '');
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 id,
        bytes memory data
    ) public virtual {
        transferFrom(from, to, id);

        if (!_checkOnERC721Received(from, to, id, data)) revert TransferToNonERC721ReceiverImplementer();
    }

    /**
     * @dev Returns whether `tokenId` exists.
     */
    function _exists(uint256 tokenId) internal view virtual returns (bool) {
        return tokenId < _owners.length;
    }

    /**
     * @dev Internal function to invoke {IERC721Receiver-onERC721Received} on a target address.
     * The call is not executed if the target address is not a contract.
     *
     * @param from address representing the previous owner of the given token ID
     * @param to target address that will receive the tokens
     * @param tokenId uint256 ID of the token to be transferred
     * @param _data bytes optional data to send along with the call
     * @return bool whether the call correctly returned the expected magic value
     */
    function _checkOnERC721Received(
        address from,
        address to,
        uint256 tokenId,
        bytes memory _data
    ) private returns (bool) {
        if (to.code.length == 0) return true;

        try IERC721Receiver(to).onERC721Received(msg.sender, from, tokenId, _data) returns (bytes4 retval) {
            return retval == IERC721Receiver(to).onERC721Received.selector;
        } catch (bytes memory reason) {
            if (reason.length == 0) revert TransferToNonERC721ReceiverImplementer();

            assembly {
                revert(add(32, reason), mload(reason))
            }
        }
    }

    /*///////////////////////////////////////////////////////////////
                       INTERNAL MINT LOGIC
    //////////////////////////////////////////////////////////////*/

    /**
     * @dev check if contract confirms token transfer, if not - reverts
     * unlike the standard ERC721 implementation this is only called once per mint,
     * no matter how many tokens get minted, since it is useless to check this
     * requirement several times -- if the contract confirms one token,
     * it will confirm all additional ones too.
     * This saves us around 5k gas per additional mint
     */
    function _safeMint(address to, uint256 qty) internal virtual {
        _safeMint(to, qty, '');
    }

    function _safeMint(
        address to,
        uint256 qty,
        bytes memory data
    ) internal virtual {
        _mint(to, qty);

        if (!_checkOnERC721Received(address(0), to, _owners.length - 1, data))
            revert TransferToNonERC721ReceiverImplementer();
    }

    function _mint(address to, uint256 qty) internal virtual {
        if (to == address(0)) revert MintToZeroAddress();
        if (qty == 0) revert MintZeroQuantity();

        uint256 _currentIndex = _owners.length;

        // Cannot realistically overflow, since we are using uint256
        unchecked {
            for (uint256 i; i < qty - 1; i++) {
                _owners.push();
                emit Transfer(address(0), to, _currentIndex + i);
            }
        }

        // set last index to receiver
        _owners.push(to);
        emit Transfer(address(0), to, _currentIndex + (qty - 1));
    }
}

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



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

pragma solidity ^0.8.0;

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

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

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

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

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

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

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

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

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

// File: @openzeppelin/contracts/utils/cryptography/MerkleProof.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts (last updated v4.5.0) (utils/cryptography/MerkleProof.sol)

pragma solidity ^0.8.0;

/**
 * @dev These functions deal with verification of Merkle Trees proofs.
 *
 * The proofs can be generated using the JavaScript library
 * https://github.com/miguelmota/merkletreejs[merkletreejs].
 * Note: the hashing algorithm should be keccak256 and pair sorting should be enabled.
 *
 * See `test/utils/cryptography/MerkleProof.test.js` for some examples.
 */
library MerkleProof {
    /**
     * @dev Returns true if a `leaf` can be proved to be a part of a Merkle tree
     * defined by `root`. For this, a `proof` must be provided, containing
     * sibling hashes on the branch from the leaf to the root of the tree. Each
     * pair of leaves and each pair of pre-images are assumed to be sorted.
     */
    function verify(
        bytes32[] memory proof,
        bytes32 root,
        bytes32 leaf
    ) internal pure returns (bool) {
        return processProof(proof, leaf) == root;
    }

    /**
     * @dev Returns the rebuilt hash obtained by traversing a Merklee tree up
     * from `leaf` using `proof`. A `proof` is valid if and only if the rebuilt
     * hash matches the root of the tree. When processing the proof, the pairs
     * of leafs & pre-images are assumed to be sorted.
     *
     * _Available since v4.4._
     */
    function processProof(bytes32[] memory proof, bytes32 leaf) internal pure returns (bytes32) {
        bytes32 computedHash = leaf;
        for (uint256 i = 0; i < proof.length; i++) {
            bytes32 proofElement = proof[i];
            if (computedHash <= proofElement) {
                // Hash(current computed hash + current element of the proof)
                computedHash = _efficientHash(computedHash, proofElement);
            } else {
                // Hash(current element of the proof + current computed hash)
                computedHash = _efficientHash(proofElement, computedHash);
            }
        }
        return computedHash;
    }

    function _efficientHash(bytes32 a, bytes32 b) private pure returns (bytes32 value) {
        assembly {
            mstore(0x00, a)
            mstore(0x20, b)
            value := keccak256(0x00, 0x40)
        }
    }
}

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



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

pragma solidity ^0.8.0;

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

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

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

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

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

// File: @openzeppelin/contracts/token/ERC721/IERC721Receiver.sol



// SPDX-License-Identifier: MIT
// OpenZeppelin Contracts v4.4.1 (token/ERC721/IERC721Receiver.sol)

pragma solidity ^0.8.0;

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

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



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

pragma solidity ^0.8.0;

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

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