SNAKESONACHAIN

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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);
            }
        }
    }
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

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

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

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @title Counters
 * @author Matt Condon (@shrugs)
 * @dev Provides counters that can only be incremented, decremented or reset. This can be used e.g. to track the number
 * of elements in a mapping, issuing ERC721 ids, or counting request ids.
 *
 * Include with `using Counters for Counters.Counter;`
 */
library Counters {
    struct Counter {
        // This variable should never be directly accessed by users of the library: interactions must be restricted to
        // the library's function. As of Solidity v0.5.2, this cannot be enforced, though there is a proposal to add
        // this feature: see https://github.com/ethereum/solidity/issues/4637
        uint256 _value; // default: 0
    }

    function current(Counter storage counter) internal view returns (uint256) {
        return counter._value;
    }

    function increment(Counter storage counter) internal {
        unchecked {
            counter._value += 1;
        }
    }

    function decrement(Counter storage counter) internal {
        uint256 value = counter._value;
        require(value > 0, "Counter: decrement overflow");
        unchecked {
            counter._value = value - 1;
        }
    }

    function reset(Counter storage counter) internal {
        counter._value = 0;
    }
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "./IERC165.sol";

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

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "./IERC721.sol";
import "./IERC721Receiver.sol";
import "./extensions/IERC721Metadata.sol";
import "../../utils/Address.sol";
import "../../utils/Context.sol";
import "../../utils/Strings.sol";
import "../../utils/introspection/ERC165.sol";

/**
 * @dev Implementation of https://eips.ethereum.org/EIPS/eip-721[ERC721] Non-Fungible Token Standard, including
 * the Metadata extension, but not including the Enumerable extension, which is available separately as
 * {ERC721Enumerable}.
 */
contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
    using Address for address;
    using Strings for uint256;

    // Token name
    string private _name;

    // Token symbol
    string private _symbol;

    // Mapping from token ID to owner address
    mapping(uint256 => address) private _owners;

    // Mapping owner address to token count
    mapping(address => uint256) private _balances;

    // 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;

    /**
     * @dev Initializes the contract by setting a `name` and a `symbol` to the token collection.
     */
    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override(ERC165, IERC165) returns (bool) {
        return
            interfaceId == type(IERC721).interfaceId ||
            interfaceId == type(IERC721Metadata).interfaceId ||
            super.supportsInterface(interfaceId);
    }

    /**
     * @dev See {IERC721-balanceOf}.
     */
    function balanceOf(address owner) public view virtual override returns (uint256) {
        require(owner != address(0), "ERC721: balance query for the zero address");
        return _balances[owner];
    }

    /**
     * @dev See {IERC721-ownerOf}.
     */
    function ownerOf(uint256 tokenId) public view virtual override returns (address) {
        address owner = _owners[tokenId];
        require(owner != address(0), "ERC721: owner query for nonexistent token");
        return owner;
    }

    /**
     * @dev See {IERC721Metadata-name}.
     */
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    /**
     * @dev See {IERC721Metadata-symbol}.
     */
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev See {IERC721Metadata-tokenURI}.
     */
    function tokenURI(uint256 tokenId) public view virtual override returns (string memory) {
        require(_exists(tokenId), "ERC721Metadata: URI query for nonexistent token");

        string memory baseURI = _baseURI();
        return bytes(baseURI).length > 0 ? string(abi.encodePacked(baseURI, tokenId.toString())) : "";
    }

    /**
     * @dev Base URI for computing {tokenURI}. If set, the resulting URI for each
     * token will be the concatenation of the `baseURI` and the `tokenId`. Empty
     * by default, can be overriden in child contracts.
     */
    function _baseURI() internal view virtual returns (string memory) {
        return "";
    }

    /**
     * @dev See {IERC721-approve}.
     */
    function approve(address to, uint256 tokenId) public virtual override {
        address owner = ERC721.ownerOf(tokenId);
        require(to != owner, "ERC721: approval to current owner");

        require(
            _msgSender() == owner || isApprovedForAll(owner, _msgSender()),
            "ERC721: approve caller is not owner nor approved for all"
        );

        _approve(to, tokenId);
    }

    /**
     * @dev See {IERC721-getApproved}.
     */
    function getApproved(uint256 tokenId) public view virtual override returns (address) {
        require(_exists(tokenId), "ERC721: approved query for nonexistent token");

        return _tokenApprovals[tokenId];
    }

    /**
     * @dev See {IERC721-setApprovalForAll}.
     */
    function setApprovalForAll(address operator, bool approved) public virtual override {
        require(operator != _msgSender(), "ERC721: approve to caller");

        _operatorApprovals[_msgSender()][operator] = approved;
        emit ApprovalForAll(_msgSender(), operator, approved);
    }

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

    /**
     * @dev See {IERC721-transferFrom}.
     */
    function transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) public virtual override {
        //solhint-disable-next-line max-line-length
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");

        _transfer(from, to, tokenId);
    }

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

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        bytes memory _data
    ) public virtual override {
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");
        _safeTransfer(from, to, tokenId, _data);
    }

    /**
     * @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.
     *
     * `_data` is additional data, it has no specified format and it is sent in call to `to`.
     *
     * This internal function is equivalent to {safeTransferFrom}, and can be used to e.g.
     * implement alternative mechanisms to perform token transfer, such as signature-based.
     *
     * Requirements:
     *
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     * - `tokenId` token must exist and be owned by `from`.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function _safeTransfer(
        address from,
        address to,
        uint256 tokenId,
        bytes memory _data
    ) internal virtual {
        _transfer(from, to, tokenId);
        require(_checkOnERC721Received(from, to, tokenId, _data), "ERC721: transfer to non ERC721Receiver implementer");
    }

    /**
     * @dev Returns whether `tokenId` exists.
     *
     * Tokens can be managed by their owner or approved accounts via {approve} or {setApprovalForAll}.
     *
     * Tokens start existing when they are minted (`_mint`),
     * and stop existing when they are burned (`_burn`).
     */
    function _exists(uint256 tokenId) internal view virtual returns (bool) {
        return _owners[tokenId] != address(0);
    }

    /**
     * @dev Returns whether `spender` is allowed to manage `tokenId`.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     */
    function _isApprovedOrOwner(address spender, uint256 tokenId) internal view virtual returns (bool) {
        require(_exists(tokenId), "ERC721: operator query for nonexistent token");
        address owner = ERC721.ownerOf(tokenId);
        return (spender == owner || getApproved(tokenId) == spender || isApprovedForAll(owner, spender));
    }

    /**
     * @dev Safely mints `tokenId` and transfers it to `to`.
     *
     * Requirements:
     *
     * - `tokenId` must not exist.
     * - If `to` refers to a smart contract, it must implement {IERC721Receiver-onERC721Received}, which is called upon a safe transfer.
     *
     * Emits a {Transfer} event.
     */
    function _safeMint(address to, uint256 tokenId) internal virtual {
        _safeMint(to, tokenId, "");
    }

    /**
     * @dev Same as {xref-ERC721-_safeMint-address-uint256-}[`_safeMint`], with an additional `data` parameter which is
     * forwarded in {IERC721Receiver-onERC721Received} to contract recipients.
     */
    function _safeMint(
        address to,
        uint256 tokenId,
        bytes memory _data
    ) internal virtual {
        _mint(to, tokenId);
        require(
            _checkOnERC721Received(address(0), to, tokenId, _data),
            "ERC721: transfer to non ERC721Receiver implementer"
        );
    }

    /**
     * @dev Mints `tokenId` and transfers it to `to`.
     *
     * WARNING: Usage of this method is discouraged, use {_safeMint} whenever possible
     *
     * Requirements:
     *
     * - `tokenId` must not exist.
     * - `to` cannot be the zero address.
     *
     * Emits a {Transfer} event.
     */
    function _mint(address to, uint256 tokenId) internal virtual {
        require(to != address(0), "ERC721: mint to the zero address");
        require(!_exists(tokenId), "ERC721: token already minted");

        _beforeTokenTransfer(address(0), to, tokenId);

        _balances[to] += 1;
        _owners[tokenId] = to;

        emit Transfer(address(0), to, tokenId);
    }

    /**
     * @dev Destroys `tokenId`.
     * The approval is cleared when the token is burned.
     *
     * Requirements:
     *
     * - `tokenId` must exist.
     *
     * Emits a {Transfer} event.
     */
    function _burn(uint256 tokenId) internal virtual {
        address owner = ERC721.ownerOf(tokenId);

        _beforeTokenTransfer(owner, address(0), tokenId);

        // Clear approvals
        _approve(address(0), tokenId);

        _balances[owner] -= 1;
        delete _owners[tokenId];

        emit Transfer(owner, address(0), tokenId);
    }

    /**
     * @dev Transfers `tokenId` from `from` to `to`.
     *  As opposed to {transferFrom}, this imposes no restrictions on msg.sender.
     *
     * Requirements:
     *
     * - `to` cannot be the zero address.
     * - `tokenId` token must be owned by `from`.
     *
     * Emits a {Transfer} event.
     */
    function _transfer(
        address from,
        address to,
        uint256 tokenId
    ) internal virtual {
        require(ERC721.ownerOf(tokenId) == from, "ERC721: transfer of token that is not own");
        require(to != address(0), "ERC721: transfer to the zero address");

        _beforeTokenTransfer(from, to, tokenId);

        // Clear approvals from the previous owner
        _approve(address(0), tokenId);

        _balances[from] -= 1;
        _balances[to] += 1;
        _owners[tokenId] = to;

        emit Transfer(from, to, tokenId);
    }

    /**
     * @dev Approve `to` to operate on `tokenId`
     *
     * Emits a {Approval} event.
     */
    function _approve(address to, uint256 tokenId) internal virtual {
        _tokenApprovals[tokenId] = to;
        emit Approval(ERC721.ownerOf(tokenId), to, tokenId);
    }

    /**
     * @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.isContract()) {
            try IERC721Receiver(to).onERC721Received(_msgSender(), from, tokenId, _data) returns (bytes4 retval) {
                return retval == IERC721Receiver.onERC721Received.selector;
            } catch (bytes memory reason) {
                if (reason.length == 0) {
                    revert("ERC721: transfer to non ERC721Receiver implementer");
                } else {
                    assembly {
                        revert(add(32, reason), mload(reason))
                    }
                }
            }
        } else {
            return true;
        }
    }

    /**
     * @dev Hook that is called before any token transfer. This includes minting
     * and burning.
     *
     * Calling conditions:
     *
     * - When `from` and `to` are both non-zero, ``from``'s `tokenId` will be
     * transferred to `to`.
     * - When `from` is zero, `tokenId` will be minted for `to`.
     * - When `to` is zero, ``from``'s `tokenId` will be burned.
     * - `from` and `to` are never both zero.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 tokenId
    ) internal virtual {}
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../ERC721.sol";
import "./IERC721Enumerable.sol";

/**
 * @dev This implements an optional extension of {ERC721} defined in the EIP that adds
 * enumerability of all the token ids in the contract as well as all token ids owned by each
 * account.
 */
abstract contract ERC721Enumerable is ERC721, IERC721Enumerable {
    // Mapping from owner to list of owned token IDs
    mapping(address => mapping(uint256 => uint256)) private _ownedTokens;

    // Mapping from token ID to index of the owner tokens list
    mapping(uint256 => uint256) private _ownedTokensIndex;

    // Array with all token ids, used for enumeration
    uint256[] private _allTokens;

    // Mapping from token id to position in the allTokens array
    mapping(uint256 => uint256) private _allTokensIndex;

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC721) returns (bool) {
        return interfaceId == type(IERC721Enumerable).interfaceId || super.supportsInterface(interfaceId);
    }

    /**
     * @dev See {IERC721Enumerable-tokenOfOwnerByIndex}.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) public view virtual override returns (uint256) {
        require(index < ERC721.balanceOf(owner), "ERC721Enumerable: owner index out of bounds");
        return _ownedTokens[owner][index];
    }

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

    /**
     * @dev See {IERC721Enumerable-tokenByIndex}.
     */
    function tokenByIndex(uint256 index) public view virtual override returns (uint256) {
        require(index < ERC721Enumerable.totalSupply(), "ERC721Enumerable: global index out of bounds");
        return _allTokens[index];
    }

    /**
     * @dev Hook that is called before any token transfer. This includes minting
     * and burning.
     *
     * Calling conditions:
     *
     * - When `from` and `to` are both non-zero, ``from``'s `tokenId` will be
     * transferred to `to`.
     * - When `from` is zero, `tokenId` will be minted for `to`.
     * - When `to` is zero, ``from``'s `tokenId` will be burned.
     * - `from` cannot be the zero address.
     * - `to` cannot be the zero address.
     *
     * To learn more about hooks, head to xref:ROOT:extending-contracts.adoc#using-hooks[Using Hooks].
     */
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 tokenId
    ) internal virtual override {
        super._beforeTokenTransfer(from, to, tokenId);

        if (from == address(0)) {
            _addTokenToAllTokensEnumeration(tokenId);
        } else if (from != to) {
            _removeTokenFromOwnerEnumeration(from, tokenId);
        }
        if (to == address(0)) {
            _removeTokenFromAllTokensEnumeration(tokenId);
        } else if (to != from) {
            _addTokenToOwnerEnumeration(to, tokenId);
        }
    }

    /**
     * @dev Private function to add a token to this extension's ownership-tracking data structures.
     * @param to address representing the new owner of the given token ID
     * @param tokenId uint256 ID of the token to be added to the tokens list of the given address
     */
    function _addTokenToOwnerEnumeration(address to, uint256 tokenId) private {
        uint256 length = ERC721.balanceOf(to);
        _ownedTokens[to][length] = tokenId;
        _ownedTokensIndex[tokenId] = length;
    }

    /**
     * @dev Private function to add a token to this extension's token tracking data structures.
     * @param tokenId uint256 ID of the token to be added to the tokens list
     */
    function _addTokenToAllTokensEnumeration(uint256 tokenId) private {
        _allTokensIndex[tokenId] = _allTokens.length;
        _allTokens.push(tokenId);
    }

    /**
     * @dev Private function to remove a token from this extension's ownership-tracking data structures. Note that
     * while the token is not assigned a new owner, the `_ownedTokensIndex` mapping is _not_ updated: this allows for
     * gas optimizations e.g. when performing a transfer operation (avoiding double writes).
     * This has O(1) time complexity, but alters the order of the _ownedTokens array.
     * @param from address representing the previous owner of the given token ID
     * @param tokenId uint256 ID of the token to be removed from the tokens list of the given address
     */
    function _removeTokenFromOwnerEnumeration(address from, uint256 tokenId) private {
        // To prevent a gap in from's tokens array, we store the last token in the index of the token to delete, and
        // then delete the last slot (swap and pop).

        uint256 lastTokenIndex = ERC721.balanceOf(from) - 1;
        uint256 tokenIndex = _ownedTokensIndex[tokenId];

        // When the token to delete is the last token, the swap operation is unnecessary
        if (tokenIndex != lastTokenIndex) {
            uint256 lastTokenId = _ownedTokens[from][lastTokenIndex];

            _ownedTokens[from][tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
            _ownedTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index
        }

        // This also deletes the contents at the last position of the array
        delete _ownedTokensIndex[tokenId];
        delete _ownedTokens[from][lastTokenIndex];
    }

    /**
     * @dev Private function to remove a token from this extension's token tracking data structures.
     * This has O(1) time complexity, but alters the order of the _allTokens array.
     * @param tokenId uint256 ID of the token to be removed from the tokens list
     */
    function _removeTokenFromAllTokensEnumeration(uint256 tokenId) private {
        // To prevent a gap in the tokens array, we store the last token in the index of the token to delete, and
        // then delete the last slot (swap and pop).

        uint256 lastTokenIndex = _allTokens.length - 1;
        uint256 tokenIndex = _allTokensIndex[tokenId];

        // When the token to delete is the last token, the swap operation is unnecessary. However, since this occurs so
        // rarely (when the last minted token is burnt) that we still do the swap here to avoid the gas cost of adding
        // an 'if' statement (like in _removeTokenFromOwnerEnumeration)
        uint256 lastTokenId = _allTokens[lastTokenIndex];

        _allTokens[tokenIndex] = lastTokenId; // Move the last token to the slot of the to-delete token
        _allTokensIndex[lastTokenId] = tokenIndex; // Update the moved token's index

        // This also deletes the contents at the last position of the array
        delete _allTokensIndex[tokenId];
        _allTokens.pop();
    }
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

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

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

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

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

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

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

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

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

    /**
     * @dev Safely transfers `tokenId` token from `from` to `to`, 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;
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC721.sol";

/**
 * @title ERC-721 Non-Fungible Token Standard, optional enumeration extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Enumerable is IERC721 {
    /**
     * @dev Returns the total amount of tokens stored by the contract.
     */
    function totalSupply() external view returns (uint256);

    /**
     * @dev Returns a token ID owned by `owner` at a given `index` of its token list.
     * Use along with {balanceOf} to enumerate all of ``owner``'s tokens.
     */
    function tokenOfOwnerByIndex(address owner, uint256 index) external view returns (uint256 tokenId);

    /**
     * @dev Returns a token ID at a given `index` of all the tokens stored by the contract.
     * Use along with {totalSupply} to enumerate all tokens.
     */
    function tokenByIndex(uint256 index) external view returns (uint256);
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

import "../IERC721.sol";

/**
 * @title ERC-721 Non-Fungible Token Standard, optional metadata extension
 * @dev See https://eips.ethereum.org/EIPS/eip-721
 */
interface IERC721Metadata is IERC721 {
    /**
     * @dev Returns the token collection name.
     */
    function name() external view returns (string memory);

    /**
     * @dev Returns the token collection symbol.
     */
    function symbol() external view returns (string memory);

    /**
     * @dev Returns the Uniform Resource Identifier (URI) for `tokenId` token.
     */
    function tokenURI(uint256 tokenId) external view returns (string memory);
}

// SPDX-License-Identifier: MIT

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);
}

// SPDX-License-Identifier: MIT

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() {
        _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);
    }
}

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

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

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

    uint256 private _status;

    constructor() {
        _status = _NOT_ENTERED;
    }

    /**
     * @dev Prevents a contract from calling itself, directly or indirectly.
     * Calling a `nonReentrant` function from another `nonReentrant`
     * function is not supported. It is possible to prevent this from happening
     * by making the `nonReentrant` function external, and 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;
    }
}

pragma solidity >=0.8.0 <0.9.0;
//SPDX-License-Identifier: MIT

import "@openzeppelin/contracts/utils/Strings.sol";
import 'base64-sol/base64.sol';

//import "hardhat/console.sol";

//learn more: https://docs.openzeppelin.com/contracts/3.x/erc721

// GET LISTED ON OPENSEA: https://testnets.opensea.io/get-listed/step-two

library SnakerMaker {

using Strings for uint256;

  struct Snake {
    Color color;
    Color bg_color;
    Color bg_color_2;
    uint256[2] bg_x;
    uint256[2] bg_y;
    string path1;
    string path2;
    uint256 bgIdx;
    uint256 thickIdx;
    uint256 thickness;
    uint256 head;
    uint256 head_mark;
    Color head_mark_color;
    uint256 snakiness_s;
    uint256 snakiness_d;
    uint256 skin_pattern_scale;
    string skin_pattern_freq;
    uint256 skin_pattern_octaves;
  }

  struct Color {
      uint256 hue;
      uint256 saturation;
      uint256 lightness;
  }

  struct Rands {
    uint256[4] x;
    uint256[4] y;
  }

  // Visibility is `public` to enable it being called by other contracts for composition.
  function generateSVGofTokenById(uint256 id) internal pure returns (Snake memory, string memory) {
    string memory seed = Strings.toString(id * 4209);
    Snake memory snk;
    Rands memory randVal;

    // Snake color
    snk.color = randomColor(seed, 0, 359, 40, 100, 20, 60);
    //console.log("rand color %s", toHSLString(snk.color));

    // Head mark color
    snk.head_mark_color = randomColor(string(abi.encodePacked(seed, "HEADCOLOR")), 0, 359, 40, 100, 20, 60);

    // Background
    randVal.x[0] = random(seed, "backzies") % 100;
    //console.log("rand bg %s", randVal.x[0]);
    if (randVal.x[0] < 30) {
      //water
      snk.bgIdx = 0;
      snk.bg_color = randomColor(string(abi.encodePacked(seed, "bgcolor")), 160, 230, 70, 100, 25, 65); 
      snk.bg_color_2.hue = snk.bg_color.hue + 8;
      snk.bg_color_2.lightness = snk.bg_color.lightness - 25;
      snk.bg_color_2.saturation = snk.bg_color.saturation;
    } else if (randVal.x[0] < 60) {
      //desert
      snk.bgIdx = 1;
      snk.bg_x[0] = random(seed, "bgx0") % 250;
      snk.bg_y[0] = random(seed, "bgy0") % 250;
      snk.bg_x[1] = (random(seed, "bgx1") % 250) + 250;
      snk.bg_y[1] = (random(seed, "bgy1") % 250) + 250;
    } else {
      // space
      snk.bg_color = randomColor(string(abi.encodePacked(seed, "bgcolorspace")), 0, 359, 80, 100, 25, 60); 
      snk.bg_x[0] = (random(seed, "bgx0") % 2) + 1;
      snk.bg_y[0] = (random(seed, "bgy0") % 60) + 15;
      snk.bgIdx = 2;
    }    

    // Snake thickness    
    {
    snk.thickIdx = random(seed, "thicc") % 5;
    //console.log("rand thick %s", snk.thickIdx);    

    if (snk.thickIdx < 1) {
      snk.thickness = 12;
      snk.head = 24;
      snk.head_mark = 10;
    } else if (snk.thickIdx < 2) {
      snk.thickness = 21;
      snk.head = 30;
      snk.head_mark = 12;
    } else if (snk.thickIdx < 3) {
      snk.thickness =30;
      snk.head = 39;
      snk.head_mark = 14;
    } else if (snk.thickIdx < 4) {
      snk.thickness = 39;
      snk.head = 42;
      snk.head_mark = 16;
    } else {
      snk.thickness = 48;
      snk.head = 48;
      snk.head_mark = 18;
    } 
    }

    // Snakiness
    snk.snakiness_s = (random(seed, "snakinessS") % 15) + 2;
    //console.log("rand snak %s", snk.snakiness_s);
    snk.snakiness_d = (random(seed, "snakiness__D") % 30) + 20;
    if (snk.snakiness_d < 25) {
      snk.snakiness_d = 0;
    }
    //console.log("rand snakd %s", snk.snakiness_d);

    // Snake pattern
    snk.skin_pattern_scale = (random(seed, "patternscale") % 350) + 50;
    //console.log("rand scale %s", snk.skin_pattern_scale);

    randVal.x[0] = random(seed, "patternfreq") % 6;    
    string[6] memory freq = ["0.02", "0.04", "0.06", "0.08", "0.1", "0.15"];
    snk.skin_pattern_freq = freq[randVal.x[0]];      
    //console.log("rand freq %s", snk.skin_pattern_freq);

    snk.skin_pattern_octaves = (random(seed, "patternoctaves") % 3) + 2;   
    //console.log("rand octaves %s", snk.skin_pattern_octaves);

    // Snake path
    randVal.x[0] = 250;
    randVal.y[0] = randomMaxMin(seed, "ypos0", 300, 470);
    randVal.x[1] = randomMaxMin(seed, "xpos1", 300, 470);
    randVal.y[1] = 250;
    randVal.x[2] = 250;
    randVal.y[2] = randomMaxMin(seed, "ypos2", 30, 200);
    randVal.x[3] = randomMaxMin(seed, "xpos3", 30, 200);
    randVal.y[3] = 250;

    snk.path1 = string(
                abi.encodePacked(
                  'M250 ',
                  Strings.toString(randVal.y[0]),
                  'S',
                  Strings.toString(randVal.x[1]),
                  ',',
                  Strings.toString(randVal.y[0]),
                  ' ',
                  Strings.toString(randVal.x[1]),
                  ',250S',
                  Strings.toString(randVal.x[1]),
                  ',',
                  Strings.toString(randVal.y[2]),
                  ' 250,',
                  Strings.toString(randVal.y[2])
                ));

    snk.path2 = string(
                abi.encodePacked(
                  'M250 ',
                  Strings.toString(randVal.y[2]),
                  'C',
                  Strings.toString(500 - randVal.x[1] ),
                  ',',
                  Strings.toString(randVal.y[2]),
                  ' ',
                  Strings.toString(randVal.x[3])
                  ));

    snk.path2 = string(
                abi.encodePacked(
                  snk.path2,              
                  ',',
                  Strings.toString(randVal.y[2]),
                  ' ',
                  Strings.toString(randVal.x[3]),
                  ',250S',
                  Strings.toString(randVal.x[3]),
                  ',',
                  Strings.toString(randVal.y[0]),
                  ' 250,',
                  Strings.toString(randVal.y[0])
                ));

    //console.log("path1 %s", snk.path1);
    //console.log("path2 %s", snk.path2);

    // backgrounds
    string memory bg;
    if (snk.bgIdx < 1) {
      bg = string(
                abi.encodePacked(
                  '<path fill="',
                  toHSLString(snk.bg_color),
                  '" d="M0 0h500v500H0z"/><pattern id="y" width="40" height="40" patternUnits="userSpaceOnUse"><circle cx="20" cy="20" r="10" fill="',
                  toHSLString(snk.bg_color_2),
                  '" opacity=".2"/></pattern><filter id="m"><feTurbulence type="fractalNoise" baseFrequency=".03" numOctaves="2" seed="5515"/><feDisplacementMap in="SourceGraphic" scale="100"/></filter><g filter="url(#m)"><rect x="-50%" y="-50%" width="200%" height="200%" fill="url(#y)"><animateTransform attributeName="transform" type="translate" dur="5s" values="0,0; 40,40;" repeatCount="indefinite"/></rect></g>'
                )
            );
    } else if (snk.bgIdx < 2) {
      bg = string(
                abi.encodePacked(
                  '<defs><linearGradient id="z" gradientTransform="rotate(90)"><stop offset="5%" stop-color="#e89f00"/><stop offset="95%" stop-color="#e8ba00"/></linearGradient></defs><path fill="#e8ba00" style="filter:url(#x)" d="M0 0h500v500H0z"/><circle cx="',
                  Strings.toString(snk.bg_x[0]),
                  '" cy="',
                  Strings.toString(snk.bg_y[0]),
                  '" r="100" fill="url(#z)" filter="url(#m)"/><circle cx="',
                  Strings.toString(snk.bg_x[1]),
                  '" cy="',
                  Strings.toString(snk.bg_y[1]),
                  '" r="100" fill="url(#z)" filter="url(#m)"/><defs><filter id="x"><feSpecularLighting result="specOut" specularExponent="12" lighting-color="#bbb"><fePointLight x="250" y="-100" z="20"><animate attributeName="x" values="250;375;600" dur="30s" repeatCount="indefinite"/><animate attributeName="y" values="-100;75;250" dur="30s" repeatCount="indefinite"/></fePointLight></feSpecularLighting><feComposite in="SourceGraphic" in2="specOut" operator="arithmetic" k1=".1" k2="1" k3="2"/></filter><filter id="m" filterUnits="userSpaceOnUse"><feTurbulence baseFrequency=".011" type="fractalNoise"/><feDisplacementMap in="SourceGraphic" scale="100"><animate attributeName="scale" begin="0s" dur="3s" values="3000;3400;2700;3200;2800;3000" repeatCount="indefinite"/></feDisplacementMap></filter></defs>'
                )
            );
                } else {
      bg = string(
                abi.encodePacked(
                  '<defs><linearGradient id="z" gradientTransform="rotate(90)"><stop offset="5%"/><stop offset="95%" stop-color="',
                  toHSLString(snk.bg_color),
                  '"/></linearGradient></defs><path fill="#e3eee" d="M0 0h500v500H0z"/><pattern id="x" width="40" height="40" patternUnits="userSpaceOnUse"><circle cx="10" cy="10" r="',
                  Strings.toString(snk.bg_x[0]),
                  '" fill="transparent" stroke="#fcfbe6" opacity=".6"/></pattern><g filter="url(#m)"><rect x="-50%" y="-50%" width="200%" height="200%" fill="url(#x)"><animateTransform attributeName="transform" type="translate" dur="',
                  Strings.toString(snk.bg_y[0]),
                  's" values="0,0; 0,50; 0,0" repeatCount="indefinite"/></rect></g><filter id="n" x="-50%" y="-50%" width="200%" height="200%"><feTurbulence baseFrequency=".08" numOctaves="10" result="lol"/><feDisplacementMap in2="turbulence" in="SourceGraphic" scale="20" xChannelSelector="R" yChannelSelector="G"/><feComposite operator="in" in2="SourceGraphic"/></filter><filter id="m"><feTurbulence type="fractalNoise" baseFrequency=".1" seed="39996"/><feDisplacementMap in="SourceGraphic" xChannelSelector="B" scale="200"/></filter>'
                )
            );                 
    }

    string memory planet = '<circle cx="400" cy="100" r="50" fill="url(#z)"/><circle cx="400" cy="100" r="50" fill="url(#z)" filter="url(#n)"/>';

    // Snake
    string[5] memory snakeParts;
    snakeParts[0] = string(
                    abi.encodePacked(
                    '<defs><path stroke-dasharray="1000" pathLength="1000" fill="none" stroke-linejoin="round" stroke-dashoffset="1000" stroke-linecap="round" stroke-width="',
                    Strings.toString(snk.thickness),
                    '" id="a" d="',
                    snk.path1,
                    '"/><path stroke-dasharray="1000" pathLength="1000" fill="none" stroke-linejoin="round" stroke-dashoffset="0" stroke-linecap="round" stroke-width="',
                    Strings.toString(snk.thickness),
                    '" id="c" d="',
                    snk.path2,
                    '"/><circle cx="0" cy="0" r="',
                    Strings.toString(snk.head),
                    '" id="f"/></defs><use xlink:href="#a" filter="url(#b) url(#S)" stroke="'
                    ));

    snakeParts[1] = string(
                    abi.encodePacked(                
                    snk.bgIdx == 2 ? "#FFF" : "#000",
                    '" opacity="',
                    snk.bgIdx == 2 ? ".3" : ".7",
                    '" transform="translate(6 6)"/><use xlink:href="#c" filter="url(#b) url(#S)" stroke="',
                    snk.bgIdx == 2 ? "#FFF" : "#000",
                    '" opacity="',
                    snk.bgIdx == 2 ? ".3" : ".7",
                    '" transform="translate(6 6)"/><use xlink:href="#a" filter="url(#b)" stroke="'
                    ));

    snakeParts[2] =               
                    string(
                    abi.encodePacked(
                    toHSLString(snk.color),
                    '"/><use xlink:href="#c" filter="url(#b)" stroke="',
                    toHSLString(snk.color),
                    '"/><use xlink:href="#a" filter="url(#d) url(#b)" stroke="',
                    toHSLString(snk.color),
                    '"/><use xlink:href="#c" filter="url(#d) url(#b)" stroke="',
                    toHSLString(snk.color),
                    '"/><g transform="translate(-250 -48)" id="h" filter="url(#b)"><g id="j" opacity="0" transform="translate(170 20)" filter="url(#e)"><line id="line1" x1="30" y1="30" x2="70" y2="30" stroke="red" stroke-width="3" /><line id="line1" x1="30" y1="30" x2="10" y2="10" stroke="red" stroke-width="3" /><line id="line1" x1="30" y1="30" x2="10" y2="50" stroke="red" stroke-width="3" /></g><use x="250" y="48" xlink:href="#f" filter="url(#b)" fill="',
                    toHSLString(snk.color),
                    '"/><use x="250" y="48" xlink:href="#f" filter="url(#d) url(#b)" fill="',
                    toHSLString(snk.color)
                    ));
    snakeParts[3] = 
                    string(
                    abi.encodePacked(               
                    '"/><path transform="rotate(45 89.216 337.812)" fill="',
                    toHSLString(snk.head_mark_color),
                    '" d="M0 0h',
                    Strings.toString(snk.head_mark),
                    'v',
                    Strings.toString(snk.head_mark),
                    'H0z"/></g>',
                    snk.bgIdx == 2 ? planet : "",
                    '<animate attributeName="stroke-dashoffset" fill="freeze" begin="0s;g.end+1s" from="0" dur="3s" xlink:href="#c" to="1000"/><animate attributeName="stroke-dashoffset" fill="freeze" begin="0s;g.end+1s" from="1000" id="i" dur="3s" xlink:href="#a" to="2000"/><animateMotion fill="freeze" begin="0s;g.end+1s" keyTimes="0 ; 1" dur="3s" xlink:href="#h" keyPoints="1 ; 0" rotate="auto" calcMode="linear"><mpath xlink:href="#a"/></animateMotion><animate attributeName="stroke-dashoffset" fill="freeze" begin="i.end" from="0" dur="3s" xlink:href="#a" to="1000"/><animate attributeName="stroke-dashoffset" fill="freeze" begin="i.end" from="1000" id="g" dur="3s" xlink:href="#c" to="2000"/><animateMotion fill="freeze" begin="i.end" keyTimes="0 ; 1" dur="3s" xlink:href="#h" keyPoints="1 ; 0" rotate="auto" calcMode="linear"><mpath xlink:href="#c"/></animateMotion><animate attributeName="opacity" fill="freeze" begin="g.end" from="0" dur="0.1s" xlink:href="#j" to="1"/><animate attributeName="opacity" fill="freeze" begin="g.end+1s" from="1" dur="0.1s" xlink:href="#j" to="0"/><defs><filter id="b" filterUnits="userSpaceOnUse"><feTurbulence baseFrequency=".35" type="fractalNoise"><animate attributeName="baseFrequency" begin="0s" dur="',
                    Strings.toString(snk.snakiness_s)
                    ));

    snakeParts[4] = 
                    string(
                    abi.encodePacked(   
                    's" values="0.0052;0.00753;0.0041;0.00924;0.0070;0.0052" repeatCount="indefinite"/></feTurbulence><feDisplacementMap in="SourceGraphic" scale="',
                    Strings.toString(snk.snakiness_d),
                    '"/></filter><filter id="e" width="200%" height="200%"><feTurbulence baseFrequency=".35" type="fractalNoise"><animate attributeName="baseFrequency" begin="0s" dur="0.1s" values="0.0052;0.00753;0.0041;0.00924;0.0070;0.004" repeatCount="indefinite"/></feTurbulence><feDisplacementMap in="SourceGraphic" scale="60"/></filter><filter id="d" filterUnits="userSpaceOnUse"><feTurbulence baseFrequency="',
                    snk.skin_pattern_freq,
                    '" type="fractalNoise" numOctaves="',
                    Strings.toString(snk.skin_pattern_octaves),
                    '"/><feDisplacementMap in="SourceGraphic" scale="',
                    Strings.toString(snk.skin_pattern_scale),
                    '"/><feComposite operator="in" in2="SourceGraphic"/></filter><filter id="S" width="200%" height="200%"><feGaussianBlur in="SourceGraphic" stdDeviation="4"/></filter></defs>'
                    ));

    string memory render = string(abi.encodePacked(
      '<svg xmlns="http://www.w3.org/2000/svg" version="1.2" xmlns:xlink="http://www.w3.org/1999/xlink" width="500" height="500" viewBox="0 0 500 500">',
        bg,
        snakeParts[0],
        snakeParts[1],
        snakeParts[2],
        snakeParts[3],
        snakeParts[4],
        '</svg>'
      ));

    return (snk, render);
  }

function toHSLString(Color memory color) public pure returns (string memory) {
    return
      string(
        abi.encodePacked(
          "hsl(",
          color.hue.toString(),
          ",",
          color.saturation.toString(),
          "%,",
          color.lightness.toString(),
          "%)"
        )
      );
  }

function randomColor(
      string memory seed,
      uint256 hMin,
      uint256 hMax,
      uint256 sMin,
      uint256 sMax,
      uint256 lMin,
      uint256 lMax
  ) internal pure returns (Color memory) {
      return
          Color(
              randomMaxMin(seed, "hue", hMin, hMax),
              randomMaxMin(seed, "saturation", sMin, sMax),
              randomMaxMin(seed, "lightness", lMin, lMax)
          );
  }

  function randomMaxMin(
      string memory seed,
      string memory key,
      uint256 min,
      uint256 max
  ) internal pure returns (uint256) {
      return
          (uint256(keccak256(abi.encodePacked("mainnet", seed, key))) % (max - min)) +
          min;
  }

  function random(string memory seed, string memory key)
      internal
      pure
      returns (uint256)
  {
      return uint256(keccak256(abi.encodePacked(key, seed)));
  }
}

// SPDX-License-Identifier: MIT

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);
    }
}

pragma solidity >=0.8.0 <0.9.0;
//SPDX-License-Identifier: MIT

//import "hardhat/console.sol";
import "@openzeppelin/contracts/token/ERC721/ERC721.sol";
import "@openzeppelin/contracts/token/ERC721/extensions/ERC721Enumerable.sol";
import "@openzeppelin/contracts/security/ReentrancyGuard.sol";
import "@openzeppelin/contracts/access/Ownable.sol";
import "@openzeppelin/contracts/utils/Counters.sol";
import "@openzeppelin/contracts/utils/Strings.sol";
import 'base64-sol/base64.sol';
import "./SnakerMaker.sol";
// import "@openzeppelin/contracts/access/Ownable.sol"; 
// https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/access/Ownable.sol

contract YourContract is ERC721, ERC721Enumerable, ReentrancyGuard, Ownable {
  constructor() ERC721("SNAKESONACHAIN", "SNKS") {}


  using Strings for uint256;
  using Counters for Counters.Counter;

  Counters.Counter private _tokenIds;

  uint256 public constant MAX_SUPPLY = 2000;
  uint256 public constant PRICE = 0.015 ether;

  function contractURI() public view returns (string memory) {
        return "https://snakesonachain.club/my-metadata";
    }
  

  function mintItem(uint256 numTokens)
      public
      payable
      virtual
  {     
      _mintItem(numTokens, _msgSender());
  }

    function mintForFriend(uint256 numTokens, address walletAddress) 
      public
      payable
      virtual
    {
      _mintItem(numTokens, walletAddress);
    }

  function _mintItem(uint256 numTokens, address destination) private {
      require(numTokens > 0, "Negative");
      require(PRICE * numTokens == msg.value, "amount wrong");
      require(totalSupply() < MAX_SUPPLY, "sold out");
      require(totalSupply() + numTokens <= MAX_SUPPLY, "Too many");
      require( numTokens < 21, "Too many");

      for (uint256 i = 0; i < numTokens; i++) {
          uint256 id = _tokenIds.current();
          _safeMint(destination, id);
          _tokenIds.increment();
      }
  }

  function getTotalSupply() public view returns (uint256) {
    return totalSupply();
  }

  function withdrawAll() public payable nonReentrant onlyOwner {
      require(payable(_msgSender()).send(address(this).balance));
  }

  function tokenURI(uint256 id) public view override returns (string memory) {
      require(_exists(id), "id does not exist");
      SnakerMaker.Snake memory snk;
      string memory svg;

      string[3] memory backgroundNames = [
            "WATER",
            "DESERT",
            "SPACE"
        ];

      string[5] memory thicknessNames = [
            "SKINNY",
            "WHIMSY",
            "BASIC",
            "NOICE", 
            "THICC"
        ];

       string memory name = string(abi.encodePacked('Snake on a chain #',id.toString()));
      string memory description = string(abi.encodePacked('Every snake follows its own path (in life)'));
      (snk, svg) = SnakerMaker.generateSVGofTokenById(id);
      string memory image = Base64.encode(bytes(svg));

      return
          string(
              abi.encodePacked(
                'data:application/json;base64,',
                Base64.encode(
                    bytes(
                          abi.encodePacked(
                              '{"name":"',
                              name,
                              '", "description":"',
                              description,
                              '", "attributes": [{"trait_type": "Color", "value": "',
                              //SnakerMaker.toHSLString(snk.color),
                              '"},{"trait_type": "Background", "value": "',
                              backgroundNames[snk.bgIdx],
                              '"},{"trait_type": "Thickness", "value": "',
                              thicknessNames[snk.thickIdx],
                              '"}], "image": "',
                              'data:image/svg+xml;base64,',
                              image,
                              '"}'
                          )
                        )
                    )
              )
          ); 
  }

  function _beforeTokenTransfer(
      address from,
      address to,
      uint256 tokenId
  ) internal override(ERC721, ERC721Enumerable) {
      super._beforeTokenTransfer(from, to, tokenId);
  }

  function supportsInterface(bytes4 interfaceId)
    public
    view
    override(ERC721, ERC721Enumerable)
    returns (bool)
  {
    return super.supportsInterface(interfaceId);
  }

}

// SPDX-License-Identifier: MIT

pragma solidity >=0.6.0;

/// @title Base64
/// @author Brecht Devos - <brecht@loopring.org>
/// @notice Provides functions for encoding/decoding base64
library Base64 {
    string internal constant TABLE_ENCODE = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/';
    bytes  internal constant TABLE_DECODE = hex"0000000000000000000000000000000000000000000000000000000000000000"
                                            hex"00000000000000000000003e0000003f3435363738393a3b3c3d000000000000"
                                            hex"00000102030405060708090a0b0c0d0e0f101112131415161718190000000000"
                                            hex"001a1b1c1d1e1f202122232425262728292a2b2c2d2e2f303132330000000000";

    function encode(bytes memory data) internal pure returns (string memory) {
        if (data.length == 0) return '';

        // load the table into memory
        string memory table = TABLE_ENCODE;

        // multiply by 4/3 rounded up
        uint256 encodedLen = 4 * ((data.length + 2) / 3);

        // add some extra buffer at the end required for the writing
        string memory result = new string(encodedLen + 32);

        assembly {
            // set the actual output length
            mstore(result, encodedLen)

            // prepare the lookup table
            let tablePtr := add(table, 1)

            // input ptr
            let dataPtr := data
            let endPtr := add(dataPtr, mload(data))

            // result ptr, jump over length
            let resultPtr := add(result, 32)

            // run over the input, 3 bytes at a time
            for {} lt(dataPtr, endPtr) {}
            {
                // read 3 bytes
                dataPtr := add(dataPtr, 3)
                let input := mload(dataPtr)

                // write 4 characters
                mstore8(resultPtr, mload(add(tablePtr, and(shr(18, input), 0x3F))))
                resultPtr := add(resultPtr, 1)
                mstore8(resultPtr, mload(add(tablePtr, and(shr(12, input), 0x3F))))
                resultPtr := add(resultPtr, 1)
                mstore8(resultPtr, mload(add(tablePtr, and(shr( 6, input), 0x3F))))
                resultPtr := add(resultPtr, 1)
                mstore8(resultPtr, mload(add(tablePtr, and(        input,  0x3F))))
                resultPtr := add(resultPtr, 1)
            }

            // padding with '='
            switch mod(mload(data), 3)
            case 1 { mstore(sub(resultPtr, 2), shl(240, 0x3d3d)) }
            case 2 { mstore(sub(resultPtr, 1), shl(248, 0x3d)) }
        }

        return result;
    }

    function decode(string memory _data) internal pure returns (bytes memory) {
        bytes memory data = bytes(_data);

        if (data.length == 0) return new bytes(0);
        require(data.length % 4 == 0, "invalid base64 decoder input");

        // load the table into memory
        bytes memory table = TABLE_DECODE;

        // every 4 characters represent 3 bytes
        uint256 decodedLen = (data.length / 4) * 3;

        // add some extra buffer at the end required for the writing
        bytes memory result = new bytes(decodedLen + 32);

        assembly {
            // padding with '='
            let lastBytes := mload(add(data, mload(data)))
            if eq(and(lastBytes, 0xFF), 0x3d) {
                decodedLen := sub(decodedLen, 1)
                if eq(and(lastBytes, 0xFFFF), 0x3d3d) {
                    decodedLen := sub(decodedLen, 1)
                }
            }

            // set the actual output length
            mstore(result, decodedLen)

            // prepare the lookup table
            let tablePtr := add(table, 1)

            // input ptr
            let dataPtr := data
            let endPtr := add(dataPtr, mload(data))

            // result ptr, jump over length
            let resultPtr := add(result, 32)

            // run over the input, 4 characters at a time
            for {} lt(dataPtr, endPtr) {}
            {
               // read 4 characters
               dataPtr := add(dataPtr, 4)
               let input := mload(dataPtr)

               // write 3 bytes
               let output := add(
                   add(
                       shl(18, and(mload(add(tablePtr, and(shr(24, input), 0xFF))), 0xFF)),
                       shl(12, and(mload(add(tablePtr, and(shr(16, input), 0xFF))), 0xFF))),
                   add(
                       shl( 6, and(mload(add(tablePtr, and(shr( 8, input), 0xFF))), 0xFF)),
                               and(mload(add(tablePtr, and(        input , 0xFF))), 0xFF)
                    )
                )
                mstore(resultPtr, shl(232, output))
                resultPtr := add(resultPtr, 3)
            }
        }

        return result;
    }
}

{
  "compilationTarget": {
    "contracts/YourContract.sol": "YourContract"
  },
  "evmVersion": "istanbul",
  "libraries": {},
  "metadata": {
    "bytecodeHash": "ipfs",
    "useLiteralContent": true
  },
  "optimizer": {
    "enabled": true,
    "runs": 200
  },
  "remappings": []
}