//SPDX-License-Identifier: MIT
pragma solidity 0.8.14;

/**
 * @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);
}

/**
 * @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;
    }
}

/**
 * @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;
}

/**
 * @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);
}


/**
 * @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);
}

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) {
        // According to EIP-1052, 0x0 is the value returned for not-yet created accounts
        // and 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470 is returned
        // for accounts without code, i.e. `keccak256('')`
        bytes32 codehash;
        bytes32 accountHash = 0xc5d2460186f7233c927e7db2dcc703c0e500b653ca82273b7bfad8045d85a470;
        // solhint-disable-next-line no-inline-assembly
        assembly { codehash := extcodehash(account) }
        return (codehash != accountHash && codehash != 0x0);
    }

}

/**
 * @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;
    }
}

interface IERC20 {

    function totalSupply() external view returns (uint256);
    
    function symbol() external view returns(string memory);
    
    function name() external view returns(string memory);

    /**
     * @dev Returns the amount of tokens owned by `account`.
     */
    function balanceOf(address account) external view returns (uint256);
    
    /**
     * @dev Returns the number of decimal places
     */
    function decimals() external view returns (uint8);

    /**
     * @dev Moves `amount` tokens from the caller's account to `recipient`.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transfer(address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Returns the remaining number of tokens that `spender` will be
     * allowed to spend on behalf of `owner` through {transferFrom}. This is
     * zero by default.
     *
     * This value changes when {approve} or {transferFrom} are called.
     */
    function allowance(address owner, address spender) external view returns (uint256);

    /**
     * @dev Sets `amount` as the allowance of `spender` over the caller's tokens.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * IMPORTANT: Beware that changing an allowance with this method brings the risk
     * that someone may use both the old and the new allowance by unfortunate
     * transaction ordering. One possible solution to mitigate this race
     * condition is to first reduce the spender's allowance to 0 and set the
     * desired value afterwards:
     * https://github.com/ethereum/EIPs/issues/20#issuecomment-263524729
     *
     * Emits an {Approval} event.
     */
    function approve(address spender, uint256 amount) external returns (bool);

    /**
     * @dev Moves `amount` tokens from `sender` to `recipient` using the
     * allowance mechanism. `amount` is then deducted from the caller's
     * allowance.
     *
     * Returns a boolean value indicating whether the operation succeeded.
     *
     * Emits a {Transfer} event.
     */
    function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);

    /**
     * @dev Emitted when `value` tokens are moved from one account (`from`) to
     * another (`to`).
     *
     * Note that `value` may be zero.
     */
    event Transfer(address indexed from, address indexed to, uint256 value);

    /**
     * @dev Emitted when the allowance of a `spender` for an `owner` is set by
     * a call to {approve}. `value` is the new allowance.
     */
    event Approval(address indexed owner, address indexed spender, uint256 value);
}

contract Ownable {

    address private owner;
    
    // event for EVM logging
    event OwnerSet(address indexed oldOwner, address indexed newOwner);
    
    // modifier to check if caller is owner
    modifier onlyOwner() {
        // If the first argument of 'require' evaluates to 'false', execution terminates and all
        // changes to the state and to Ether balances are reverted.
        // This used to consume all gas in old EVM versions, but not anymore.
        // It is often a good idea to use 'require' to check if functions are called correctly.
        // As a second argument, you can also provide an explanation about what went wrong.
        require(msg.sender == owner, "Caller is not owner");
        _;
    }
    
    /**
     * @dev Set contract deployer as owner
     */
    constructor() {
        owner = msg.sender; // 'msg.sender' is sender of current call, contract deployer for a constructor
        emit OwnerSet(address(0), owner);
    }

    /**
     * @dev Change owner
     * @param newOwner address of new owner
     */
    function changeOwner(address newOwner) public onlyOwner {
        emit OwnerSet(owner, newOwner);
        owner = newOwner;
    }

    /**
     * @dev Return owner address 
     * @return address of owner
     */
    function getOwner() external view returns (address) {
        return owner;
    }
}

contract HuslAppNow is Context, ERC165, IERC721, IERC721Metadata, Ownable {

    using Address for address;

    // Token name
    string private constant _name = "Husl App Now Collection";

    // Token symbol
    string private constant _symbol = "HSLAPPNOW";

    // Founder Card Token
    address private constant FCNFT = 0xBbeb904272FA9888C50DA37D16b9099FcaE78244;

    // total number of NFTs Minted
    uint256 private _totalSupply;

    // max supply cap
    uint256 public MAX_SUPPLY = 10_000;

    // 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;

    // max holdings per wallet post mint
    uint256 public MAX_MINT = 10**18; // default is set to no limit, more or less

    // cost for minting NFT
    uint256 public cost = 10**18;
    uint256 public discountedCost = 10**17;

    // base URI
    string private baseURI = "temp";
    string private ending = ".json";

    // Enable Trading
    bool public mintingEnabled = false;
    bool public whitelistEnabled = true;

    // Mint Info Struct
    struct MintInfo {
        bool isWhitelisted;
        uint256 discountsUsed;
        uint nMinted;
    }

    // White list
    mapping ( address => MintInfo ) public mintInfo;


    ////////////////////////////////////////////////
    ///////////   RESTRICTED FUNCTIONS   ///////////
    ////////////////////////////////////////////////

    function enableMinting() external onlyOwner {
        mintingEnabled = true;
    }

    function disableMinting() external onlyOwner {
        mintingEnabled = false;
    }

    function toggleWhitelist(bool whitelistEnabled_) external onlyOwner {
        whitelistEnabled = whitelistEnabled_;
    }

    function setWhitelist(address[] calldata users, bool isWhitelisted_) external onlyOwner {
        uint len = users.length;
        for (uint i = 0; i < len;) {
            mintInfo[users[i]].isWhitelisted = isWhitelisted_;
            unchecked { ++i; }
        }
    }

    function withdraw() external onlyOwner {
        (bool s,) = payable(msg.sender).call{value: address(this).balance}("");
        require(s);
    }

    function withdrawToken(address token_) external onlyOwner {
        require(token_ != address(0), 'Zero Address');
        IERC20(token_).transfer(msg.sender, IERC20(token_).balanceOf(address(this)));
    }

    function setCost(uint256 newCost) external onlyOwner {
        cost = newCost;
    }

    function setDiscount(uint256 newDiscount) external onlyOwner {
        discountedCost = newDiscount;
    }

    function setBaseURI(string calldata newURI) external onlyOwner {
        baseURI = newURI;
    }

    function setURIExtention(string calldata newExtention) external onlyOwner {
        ending = newExtention;
    }

    function setMaxMint(uint256 newMax) external onlyOwner {
        MAX_MINT = newMax;
    }

    function setMaxSupply(uint256 newMax) external onlyOwner {
        MAX_SUPPLY = newMax;
    }

    function ownerMint(address to, uint256 qty) external onlyOwner {
        for (uint i = 0; i < qty;) {
            _safeMint(to, _totalSupply);
            unchecked { ++i; }
        }
    }

    ////////////////////////////////////////////////
    ///////////     PUBLIC FUNCTIONS     ///////////
    ////////////////////////////////////////////////

    /** 
     * Mints `numberOfMints` NFTs To Caller
     */
    function mint(uint256 numberOfMints) external payable {
        require(
            mintingEnabled,
            'Minting Not Enabled'
        );
        if (whitelistEnabled) {
            require(
                mintInfo[msg.sender].isWhitelisted,
                'Sender Not Whitelisted'
            );
        }
        require(
            numberOfMints > 0, 
            'Invalid Input'
        );

        // get cost for mint
        (uint256 mintCost, uint nDiscounts) = estimateCost(msg.sender, numberOfMints);

        // if discounts were used
        if (nDiscounts > 0) {
            
            // increment number of discounts used
            unchecked {
                mintInfo[msg.sender].discountsUsed += nDiscounts;
            }
        }

        // enforce cost
        require(
            mintCost <= msg.value, 
            'Incorrect Value Sent'
        );

        // update number of NFTs minted for user to enforce maximum
        unchecked {
            mintInfo[msg.sender].nMinted += numberOfMints;
        }

        // mint `numberOfMints` NFTs to sender
        for (uint i = 0; i < numberOfMints;) {
            _safeMint(msg.sender, _totalSupply);
            unchecked { ++i; }
        }

        // enforce maximum mint per user
        require(
            mintInfo[msg.sender].nMinted <= MAX_MINT,
            'Max Holdings Exceeded'
        );
    }

    receive() external payable {}

    /**
     * @dev See {IERC721-approve}.
     */
    function approve(address to, uint256 tokenId) public override {
        address wpowner = ownerOf(tokenId);
        require(to != wpowner, "ERC721: approval to current owner");

        require(
            _msgSender() == wpowner || isApprovedForAll(wpowner, _msgSender()),
            "ERC721: not approved or owner"
        );

        _approve(to, tokenId);
    }

    /**
     * @dev See {IERC721-setApprovalForAll}.
     */
    function setApprovalForAll(address _operator, bool approved) public override {
        _setApprovalForAll(_msgSender(), _operator, approved);
    }

    /**
     * @dev See {IERC721-transferFrom}.
     */
    function transferFrom(
        address from,
        address to,
        uint256 tokenId
    ) public override {
        require(_isApprovedOrOwner(_msgSender(), tokenId), "caller not owner nor approved");
        _transfer(from, to, tokenId);
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId
    ) public override {
        safeTransferFrom(from, to, tokenId, "");
    }

    /**
     * @dev See {IERC721-safeTransferFrom}.
     */
    function safeTransferFrom(
        address from,
        address to,
        uint256 tokenId,
        bytes memory _data
    ) public override {
        require(_isApprovedOrOwner(_msgSender(), tokenId), "caller not owner nor approved");
        _safeTransfer(from, to, tokenId, _data);
    }


    ////////////////////////////////////////////////
    ///////////     READ FUNCTIONS       ///////////
    ////////////////////////////////////////////////

    function totalSupply() external view returns (uint256) {
        return _totalSupply;
    }

    function getIDsByOwner(address owner_) external view returns (uint256[] memory) {
        uint256[] memory ids = new uint256[](balanceOf(owner_));
        if (balanceOf(owner_) == 0) return ids;
        uint256 count = 0;
        for (uint i = 0; i < _totalSupply; i++) {
            if (_owners[i] == owner_) {
                ids[count] = i;
                count++;
            }
        }
        return ids;
    }

    /**
     * @dev See {IERC165-supportsInterface}.
     */
    function supportsInterface(bytes4 interfaceId) public view override(ERC165, IERC165) returns (bool) {
        return
            interfaceId == type(IERC721).interfaceId ||
            interfaceId == type(IERC721Metadata).interfaceId ||
            super.supportsInterface(interfaceId);
    }

    /**
     * @dev See {IERC721-balanceOf}.
     */
    function balanceOf(address wpowner) public view override returns (uint256) {
        require(wpowner != address(0), "query for the zero address");
        return _balances[wpowner];
    }

    /**
     * @dev See {IERC721-ownerOf}.
     */
    function ownerOf(uint256 tokenId) public view override returns (address) {
        address wpowner = _owners[tokenId];
        require(wpowner != address(0), "query for nonexistent token");
        return wpowner;
    }

    /**
     * @dev See {IERC721Metadata-name}.
     */
    function name() public pure override returns (string memory) {
        return _name;
    }

    /**
     * @dev See {IERC721Metadata-symbol}.
     */
    function symbol() public pure override returns (string memory) {
        return _symbol;
    }

    /**
     * @dev See {IERC721Metadata-tokenURI}.
     */
    function tokenURI(uint256 tokenId) public view override returns (string memory) {
        require(_exists(tokenId), "nonexistent token");

        string memory fHalf = string.concat(baseURI, uint2str(tokenId));
        return string.concat(fHalf, ending);
    }

    /**
        Converts A Uint Into a String
    */
    function uint2str(uint _i) internal pure returns (string memory _uintAsString) {
        if (_i == 0) {
            return "0";
        }
        uint j = _i;
        uint len;
        while (j != 0) {
            len++;
            j /= 10;
        }
        bytes memory bstr = new bytes(len);
        uint k = len;
        while (_i != 0) {
            k = k-1;
            uint8 temp = (48 + uint8(_i - _i / 10 * 10));
            bytes1 b1 = bytes1(temp);
            bstr[k] = b1;
            _i /= 10;
        }
        return string(bstr);
    }

    /**
     * @dev See {IERC721-getApproved}.
     */
    function getApproved(uint256 tokenId) public view override returns (address) {
        require(_exists(tokenId), "ERC721: query for nonexistent token");

        return _tokenApprovals[tokenId];
    }

    /**
     * @dev See {IERC721-isApprovedForAll}.
     */
    function isApprovedForAll(address wpowner, address _operator) public view override returns (bool) {
        return _operatorApprovals[wpowner][_operator];
    }

    /**
     * @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
     */
    function _exists(uint256 tokenId) internal view 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 returns (bool) {
        require(_exists(tokenId), "ERC721: nonexistent token");
        address wpowner = ownerOf(tokenId);
        return (spender == wpowner || getApproved(tokenId) == spender || isApprovedForAll(wpowner, spender));
    }

    ////////////////////////////////////////////////
    ///////////    INTERNAL FUNCTIONS    ///////////
    ////////////////////////////////////////////////


    /**
     * @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
    ) internal {
        _mint(to, tokenId);
        require(
            _checkOnERC721Received(address(0), to, tokenId, ""),
            "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 {
        require(!_exists(tokenId), "ERC721: token already minted");
        require(_totalSupply < MAX_SUPPLY, 'All NFTs Have Been Minted');

        _balances[to] += 1;
        _owners[tokenId] = to;
        _totalSupply++;

        emit Transfer(address(0), to, tokenId);
    }

    /**
     * @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 {
        _transfer(from, to, tokenId);
        require(_checkOnERC721Received(from, to, tokenId, _data), "ERC721: non ERC721Receiver implementer");
    }


    /**
     * @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 {
        require(ownerOf(tokenId) == from, "Incorrect owner");
        require(to != address(0), "zero address");
        require(balanceOf(from) > 0, 'Zero Balance');

        // Clear approvals from the previous owner
        _approve(address(0), tokenId);

        // Allocate balances
        _balances[from] -= 1;
        _balances[to] += 1;
        _owners[tokenId] = to;

        // emit transfer
        emit Transfer(from, to, tokenId);
    }

    /**
     * @dev Approve `to` to operate on `tokenId`
     *
     * Emits a {Approval} event.
     */
    function _approve(address to, uint256 tokenId) internal {
        _tokenApprovals[tokenId] = to;
        emit Approval(ownerOf(tokenId), to, tokenId);
    }

    /**
     * @dev Approve `operator` to operate on all of `owner` tokens
     *
     * Emits a {ApprovalForAll} event.
     */
    function _setApprovalForAll(
        address wpowner,
        address _operator,
        bool approved
    ) internal {
        require(wpowner != _operator, "ERC721: approve to caller");
        _operatorApprovals[wpowner][_operator] = approved;
        emit ApprovalForAll(wpowner, _operator, approved);
    }

    function onReceivedRetval() public pure returns (bytes4) {
        return IERC721Receiver.onERC721Received.selector;
    }

    function owner() external view returns (address) {
        return this.getOwner();
    }

    function estimateCost(address user, uint256 numberOfMints) public view returns (uint256, uint256) {
        uint256 balance = IERC721(FCNFT).balanceOf(user);
        uint256 nUsed = mintInfo[user].discountsUsed;
        uint256 nDiscounts = balance > nUsed ? balance - nUsed : 0;
        if (nDiscounts > numberOfMints) {
            nDiscounts = numberOfMints;
        }
        uint discount = discountedCost * nDiscounts;
        return (( numberOfMints * cost ) - discount, nDiscounts);
    }

    /**
     * @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: non ERC721Receiver implementer");
                } else {
                    assembly {
                        revert(add(32, reason), mload(reason))
                    }
                }
            }
        } else {
            return true;
        }
    }
}