// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;


library Counters {
    struct Counter {        
        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;
    }
}



library SafeMath {
   
    function tryAdd(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            uint256 c = a + b;
            if (c < a) return (false, 0);
            return (true, c);
        }
    }

    
    function trySub(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b > a) return (false, 0);
            return (true, a - b);
        }
    }

    
    function tryMul(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
           
            if (a == 0) return (true, 0);
            uint256 c = a * b;
            if (c / a != b) return (false, 0);
            return (true, c);
        }
    }

   
    function tryDiv(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a / b);
        }
    }

   
    function tryMod(uint256 a, uint256 b) internal pure returns (bool, uint256) {
        unchecked {
            if (b == 0) return (false, 0);
            return (true, a % b);
        }
    }

   
    function add(uint256 a, uint256 b) internal pure returns (uint256) {
        return a + b;
    }

   
    function sub(uint256 a, uint256 b) internal pure returns (uint256) {
        return a - b;
    }

   
    function mul(uint256 a, uint256 b) internal pure returns (uint256) {
        return a * b;
    }

   
    function div(uint256 a, uint256 b) internal pure returns (uint256) {
        return a / b;
    }

    
    function mod(uint256 a, uint256 b) internal pure returns (uint256) {
        return a % b;
    }

    
    function sub(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b <= a, errorMessage);
            return a - b;
        }
    }

  
    function div(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a / b;
        }
    }

  
    function mod(
        uint256 a,
        uint256 b,
        string memory errorMessage
    ) internal pure returns (uint256) {
        unchecked {
            require(b > 0, errorMessage);
            return a % b;
        }
    }
}



library Strings {
    bytes16 private constant _HEX_SYMBOLS = "0123456789abcdef";

   
    function toString(uint256 value) internal pure returns (string memory) {
        
        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);
    }

   
    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);
    }

    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);
    }
}


abstract contract Context {
    function _msgSender() internal view virtual returns (address) {
        return msg.sender;
    }

    function _msgData() internal view virtual returns (bytes calldata) {
        return msg.data;
    }
}


abstract contract Ownable is Context {
    address private _owner;

    event OwnershipTransferred(address indexed previousOwner, address indexed newOwner);

    
    constructor() {
        _transferOwnership(_msgSender());
    }

    
    function owner() public view virtual returns (address) {
        return _owner;
    }

    modifier onlyOwner() {
        require(owner() == _msgSender(), "Ownable: caller is not the owner");
        _;
    }

   
    function renounceOwnership() public virtual onlyOwner {
        _transferOwnership(address(0));
    }

    
    function transferOwnership(address newOwner) public virtual onlyOwner {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        _transferOwnership(newOwner);
    }

    
    function _transferOwnership(address newOwner) internal virtual {
        address oldOwner = _owner;
        _owner = newOwner;
        emit OwnershipTransferred(oldOwner, newOwner);
    }
}


library Address {
    
    function isContract(address account) internal view returns (bool) {
        

        uint256 size;
        assembly {
            size := extcodesize(account)
        }
        return size > 0;
    }

    
    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");
    }

    
    function functionCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionCall(target, data, "Address: low-level call failed");
    }

    
    function functionCall(
        address target,
        bytes memory data,
        string memory errorMessage
    ) internal returns (bytes memory) {
        return functionCallWithValue(target, data, 0, errorMessage);
    }

   
    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");
    }

   
    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);
    }

   
    function functionStaticCall(address target, bytes memory data) internal view returns (bytes memory) {
        return functionStaticCall(target, data, "Address: low-level static call failed");
    }

   
    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);
    }

    
    function functionDelegateCall(address target, bytes memory data) internal returns (bytes memory) {
        return functionDelegateCall(target, data, "Address: low-level delegate call failed");
    }

    
    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);
    }

   
    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);
            }
        }
    }
}



interface IERC721Receiver {
    
    function onERC721Received(
        address operator,
        address from,
        uint256 tokenId,
        bytes calldata data
    ) external returns (bytes4);
}



interface IERC165 {
   
    function supportsInterface(bytes4 interfaceId) external view returns (bool);
}



abstract contract ERC165 is IERC165 {
    
    function supportsInterface(bytes4 interfaceId) public view virtual override returns (bool) {
        return interfaceId == type(IERC165).interfaceId;
    }
}


interface IERC721 is IERC165 {
    
    event Transfer(address indexed from, address indexed to, uint256 indexed tokenId);

    
    event Approval(address indexed owner, address indexed approved, uint256 indexed tokenId);

    
    event ApprovalForAll(address indexed owner, address indexed operator, bool approved);

    
    function balanceOf(address owner) external view returns (uint256 balance);

   
    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;
}


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);
}



interface IERC721Metadata is IERC721 {
   
    function name() external view returns (string memory);

    
    function symbol() external view returns (string memory);

    
    function tokenURI(uint256 tokenId) external view returns (string memory);
}



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;

    
    constructor(string memory name_, string memory symbol_) {
        _name = name_;
        _symbol = symbol_;
    }

   
    function supportsInterface(bytes4 interfaceId) public view virtual override(ERC165, IERC165) returns (bool) {
        return
            interfaceId == type(IERC721).interfaceId ||
            interfaceId == type(IERC721Metadata).interfaceId ||
            super.supportsInterface(interfaceId);
    }

   
    function balanceOf(address owner) public view virtual override returns (uint256) {
        require(owner != address(0), "ERC721: balance query for the zero address");
        return _balances[owner];
    }

   
    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;
    }

   
    function name() public view virtual override returns (string memory) {
        return _name;
    }

    
    function symbol() public view virtual override returns (string memory) {
        return _symbol;
    }

    
    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())) : "";
    }

    
    function _baseURI() internal view virtual returns (string memory) {
        return "";
    }

   
    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);
    }

   
    function getApproved(uint256 tokenId) public view virtual override returns (address) {
        require(_exists(tokenId), "ERC721: approved query for nonexistent token");

        return _tokenApprovals[tokenId];
    }

    
    function setApprovalForAll(address operator, bool approved) public virtual override {
        _setApprovalForAll(_msgSender(), operator, approved);
    }

    
    function isApprovedForAll(address owner, address operator) public view virtual override returns (bool) {
        return _operatorApprovals[owner][operator];
    }

    
    function transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) public virtual override {
        
        require(_isApprovedOrOwner(_msgSender(), tokenId), "ERC721: transfer caller is not owner nor approved");

        _transfer(from, to, tokenId);
    }

    
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId
    ) public virtual override {
        safeTransferFrom(from, to, tokenId, "");
    }

   
    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);
    }

   
    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");
    }

   
    function _exists(uint256 tokenId) internal view virtual returns (bool) {
        return _owners[tokenId] != address(0);
    }

    
    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));
    }

   
    function _safeMint(address to, uint256 tokenId) internal virtual {
        _safeMint(to, tokenId, "");
    }

    
    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"
        );
    }

   
    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);
    }

    
    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);
    }

   
    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);

        
        _approve(address(0), tokenId);

        _balances[from] -= 1;
        _balances[to] += 1;
        _owners[tokenId] = to;

        emit Transfer(from, to, tokenId);
    }

   
    function _approve(address to, uint256 tokenId) internal virtual {
        _tokenApprovals[tokenId] = to;
        emit Approval(ERC721.ownerOf(tokenId), to, tokenId);
    }

   
    function _setApprovalForAll(
        address owner,
        address operator,
        bool approved
    ) internal virtual {
        require(owner != operator, "ERC721: approve to caller");
        _operatorApprovals[owner][operator] = approved;
        emit ApprovalForAll(owner, operator, approved);
    }

   
    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;
        }
    }

   
    function _beforeTokenTransfer(
        address from,
        address to,
        uint256 tokenId
    ) internal virtual {}
}







abstract contract ERC721Enumerable is ERC721, IERC721Enumerable {
    
    mapping(address => mapping(uint256 => uint256)) private _ownedTokens;

 
    mapping(uint256 => uint256) private _ownedTokensIndex;

    
    uint256[] private _allTokens;

  
    mapping(uint256 => uint256) private _allTokensIndex;

   
     
    function supportsInterface(bytes4 interfaceId) public view virtual override(IERC165, ERC721) returns (bool) {
        return interfaceId == type(IERC721Enumerable).interfaceId || super.supportsInterface(interfaceId);
    }

    
    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];
    }

    
    function totalSupply() public view virtual override returns (uint256) {
        return _allTokens.length;
    }

    
    function tokenByIndex(uint256 index) public view virtual override returns (uint256) {
        require(index < ERC721Enumerable.totalSupply(), "ERC721Enumerable: global index out of bounds");
        return _allTokens[index];
    }

   
    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);
        }
    }

    
    function _addTokenToOwnerEnumeration(address to, uint256 tokenId) private {
        uint256 length = ERC721.balanceOf(to);
        _ownedTokens[to][length] = tokenId;
        _ownedTokensIndex[tokenId] = length;
    }

    
    function _addTokenToAllTokensEnumeration(uint256 tokenId) private {
        _allTokensIndex[tokenId] = _allTokens.length;
        _allTokens.push(tokenId);
    }

   
    function _removeTokenFromOwnerEnumeration(address from, uint256 tokenId) private {
        

        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
        }

        
        delete _ownedTokensIndex[tokenId];
        delete _ownedTokens[from][lastTokenIndex];
    }

   
    function _removeTokenFromAllTokensEnumeration(uint256 tokenId) private {
       
        uint256 lastTokenIndex = _allTokens.length - 1;
        uint256 tokenIndex = _allTokensIndex[tokenId];

        
        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

        
        delete _allTokensIndex[tokenId];
        _allTokens.pop();
    }
}




//MetaOtters
contract MetaOtters is ERC721Enumerable, Ownable {
    using SafeMath for uint256;
    using Strings for uint256;
    using Counters for Counters.Counter;

    Counters.Counter private _tokenIdTracker;

    uint256 public unitPrice = 8 * 10**16; // .08 eth
    uint256 public unitPrice_Presale = 3 * 10**16; //.03 eth
    uint256 public constant MAX_ELEMENTS = 8888;
    
    uint256 public constant MAX_PER_MINT = 10;
    uint256 public constant MAX_BY_MINT_WHITELIST = 3;
    uint256 public constant MAX_RESERVE_AMOUNT = 500;
    
    bool public isSaleOpen = false;
    bool public isPresaleOpen = false;
    bool public isOwnershipChangable =false;

    mapping(address => bool) private _whiteList;
    mapping(address => uint256) private _whiteListClaimed;
    uint256 public _reservedCount = 0;
    uint256 private _maxNumPerReserve = 100;

    string public baseTokenURI;
    string public uriExtension = ".json";
    event CreateOtters(uint256 indexed id);

    constructor(string memory NFTbaseURI) ERC721("MetaOtters", "MO") {
        setBaseURI(NFTbaseURI);
    }

   modifier onlySaleIsOpen {
        if (_msgSender() != owner()) {
            require(isSaleOpen, "Sale is not open");
        }
        _;
    }


//URI functions =>override view URI , set baseURI when contract is deployed.
    function _baseURI() internal view virtual override returns (string memory) {
        return baseTokenURI;
    }

    function setBaseURI(string memory inputbaseURI) public onlyOwner {
        baseTokenURI = inputbaseURI;
    }

    function tokenURI(uint256 _tokenId) public view virtual override returns (string memory) {
        require(_exists(_tokenId), "ERC721Metadata: URI query for nonexistent token");
        string memory currentBaseURI = _baseURI();
        return bytes(currentBaseURI).length > 0 
        ? string(abi.encodePacked(currentBaseURI, _tokenId.toString(), uriExtension)) : "";
  }

   
//saleopen functions => change sale open status, change presale open status;
 function setSaleOpen(bool _isSaleOpen) external onlyOwner {
        isSaleOpen = _isSaleOpen;
    }

    function setPresaleOpen(bool _isPresaleOpen) external onlyOwner {
        isPresaleOpen = _isPresaleOpen;
    }

//total supply functions => public check the current total amount of minted tokens;
    function _totalSupply() internal view returns (uint256) {
        return _tokenIdTracker.current();
    }

  

//reserve functions for owner => owner mint reserveNFTs, change max reserve mint amount per time;
    
    function reserveTokens(uint256 _Amount) public onlyOwner {
        uint256 reserveAmount = _Amount;
        require(reserveAmount > 0 && reserveAmount <= _maxNumPerReserve,"invalid amount");
        require(_reservedCount + reserveAmount <= MAX_RESERVE_AMOUNT, "Max reserve exceeded");       
        for (uint256 i = 0; i < reserveAmount; i++) {
            _reservedCount++;
            _mintAnOtter(msg.sender);
            
        }
    }

    function setMaxPerReserve(uint256 maxNum) public onlyOwner {
        _maxNumPerReserve = maxNum;
    }
    
/*
// mintpass function for public => check if current user has mintpass or not.
    function hasMintPass(address sender) public view returns (bool){
        if(sender==address(0)){
            return false;
        } 
        else if (isWhitelisted(sender)) {
            return true;                   
        }        
        return false;
    }
*/
// mint functions for public =>  mint after sale is open, presalemint for addresses has mintpass;
    function mint(address _to, uint256 _mintAmount) public payable onlySaleIsOpen {
        uint256 idcurrent= _tokenIdTracker.current();
        require( idcurrent < MAX_ELEMENTS, "All MetaOtters are sold out");
        require( idcurrent + _mintAmount <= MAX_ELEMENTS, "Max limit");      
        require(_mintAmount > 0 && _mintAmount<= MAX_PER_MINT, "Exceeds number");
        require(msg.value >= mintcost(_mintAmount), "Value below cost");

        for (uint256 i = 0; i < _mintAmount; i++) {
            _mintAnOtter(_to);
        }
    }

    function presaleMint(uint256 _mintAmount) public payable {
        require(isPresaleOpen, "Presale is not open"); //ensure presale is open;       
        require(isWhitelisted(msg.sender), "Must be whitelisted");
        require(_mintAmount > 0 && _mintAmount<= MAX_BY_MINT_WHITELIST, "Incorrect amount to claim"); //ensure mintAmount less than max limit of whitelist addresses;
        require(_whiteListClaimed[msg.sender] + _mintAmount <= MAX_BY_MINT_WHITELIST, "Purchase exceeds max allowed");//ensure total mint amount of whitelist addr not excceds max limit; 
        uint256 idcurrent= _tokenIdTracker.current();
        require(idcurrent < MAX_ELEMENTS, "All MettaOtters are sold out");
        require(idcurrent + _mintAmount <= MAX_ELEMENTS, "Max limit");    
        require(msg.value >= mintcost_Presale(_mintAmount), "Value below cost");

        for (uint256 i = 0; i < _mintAmount; i++) {
            _whiteListClaimed[msg.sender] += 1;
            _mintAnOtter(msg.sender);
        }
    }

//_tokenIdTracker =0 when initial. the first mint starts from 1.
    function _mintAnOtter(address _to) private {       
        _tokenIdTracker.increment();
        uint256 id = _tokenIdTracker.current();
        _safeMint(_to, id);
        emit CreateOtters(id);
    }

    function mintcost(uint256 _count) public view returns (uint256) {
        return unitPrice.mul(_count);
    }
    
    function mintcost_Presale(uint256 _count) public view returns (uint256) {
        return unitPrice_Presale.mul(_count);
    }

 
  
// price functions => public check price for each token, owner change unit price if needed.
    function setunitPrice(uint256 _price) public onlyOwner {
     unitPrice =_price;
  }
      function setunitPrice_Presale(uint256 _price) public onlyOwner {
     unitPrice_Presale =_price;
  }
	function getunitPrice() public view returns(uint256){
	return unitPrice;
	}

//whitelist functions => add, check, remove;
    function addToWhiteList(address[] calldata addresses) external onlyOwner {
        for (uint256 i = 0; i < addresses.length; i++) {
            require(addresses[i] != address(0), "Null address found");

            _whiteList[addresses[i]] = true;
            _whiteListClaimed[addresses[i]] > 0 ? _whiteListClaimed[addresses[i]] : 0;
        }
    }

    function isWhitelisted(address addr) public view returns (bool) {
        return _whiteList[addr];
    }

    function removeFromWhiteList(address[] calldata addresses) external onlyOwner {
        for (uint256 i = 0; i < addresses.length; i++) {
            require(addresses[i] != address(0), "Null address found");

            _whiteList[addresses[i]] = false;
        }
    }

// wallet of owner function for public =>  check the ownered ids for input address;
  function walletOfOwner(address ownerAddress) external view returns (uint256[] memory) {
        uint256 tokenCount = balanceOf(ownerAddress);

        uint256[] memory tokensId = new uint256[](tokenCount);
        for (uint256 i = 0; i < tokenCount; i++) {
            tokensId[i] = tokenOfOwnerByIndex(ownerAddress, i);
        }

        return tokensId;
    }

   
//withdraw functions for owner=> withdrawAll, withdraw certain amount;

    function withdrawAll() external onlyOwner {
        uint256 contractBalance = address(this).balance;
        require(contractBalance > 0,"insufficient balance.");     
        _withdraw(owner(), contractBalance);      
    }

    function withdraw(uint256 _withdrawAmount) external onlyOwner{
        uint256 contractBalance = address(this).balance;
        require(contractBalance > 0,"insufficient balance.");
        require(_withdrawAmount <= contractBalance, "withdraw amount exceeds current contract balance");
        _withdraw(owner(),_withdrawAmount);
    }
 
       function _withdraw(address _address, uint256 _amount) private {
        (bool success, ) = payable(_address).call{ value: _amount }("");
        require(success, "Failed to widthdraw Ether");
    }

 //set enable/disable switch for renounce or transfer ownership. In case irreparable loss caused by owner misoperation.
    function  flipOwnershipChangable() external onlyOwner {          
            isOwnershipChangable = !isOwnershipChangable;    
     }
          
    function renounceOwnership() public  onlyOwner override {           
    require(isOwnershipChangable,"Renounce ownership disabled. flip changlable state to enable. Be careful renounceownership will leave the contract with no owner!");
     _transferOwnership(address(0));
    } 
    
    function transferOwnership(address newOwner) public onlyOwner override {
        require(newOwner != address(0), "Ownable: new owner is the zero address");
        require(isOwnershipChangable,"Changing ownership disabled. flip changlable state to enable. Be careful you are trying to transfer contract ownership to somebody else!");
        require(newOwner != owner(),"The address is already the contract owner");

        _transferOwnership(newOwner);
    }

    //tokenByIndex is for all NFTs, index starts from 0 whereas token starts from 1.
    //tokenOfOwnerByIndex is for NFT owners, index starts from 0 whereas token starts from 1.
}