n-lend smart contract

n-lend_flattened.sol

// Sources flattened with hardhat v2.6.3 https://hardhat.org

// File @openzeppelin/contracts/security/ReentrancyGuard.sol@v4.3.1

// 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;
    }
}


// File @openzeppelin/contracts/utils/Context.sol@v4.3.1

// 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;
    }
}


// File @openzeppelin/contracts/access/Ownable.sol@v4.3.1

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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);
    }
}


// File @openzeppelin/contracts/utils/introspection/IERC165.sol@v4.3.1

// 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);
}


// File @openzeppelin/contracts/token/ERC721/IERC721.sol@v4.3.1

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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;
}


// File @openzeppelin/contracts/token/ERC721/extensions/IERC721Enumerable.sol@v4.3.1

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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);
}


// File @openzeppelin/contracts/token/ERC721/extensions/IERC721Metadata.sol@v4.3.1

// SPDX-License-Identifier: MIT

pragma solidity ^0.8.0;

/**
 * @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);
}


// File contracts/interfaces/IN.sol

// SPDX-License-Identifier: MIT
pragma solidity 0.8.6;


interface IN is IERC721Enumerable, IERC721Metadata {
    function getFirst(uint256 tokenId) external view returns (uint256);

    function getSecond(uint256 tokenId) external view returns (uint256);

    function getThird(uint256 tokenId) external view returns (uint256);

    function getFourth(uint256 tokenId) external view returns (uint256);

    function getFifth(uint256 tokenId) external view returns (uint256);

    function getSixth(uint256 tokenId) external view returns (uint256);

    function getSeventh(uint256 tokenId) external view returns (uint256);

    function getEight(uint256 tokenId) external view returns (uint256);
}


// File contracts/core/NLend.sol

// SPDX-License-Identifier: MIT
pragma solidity >=0.8.4;



interface IReceiver {
    function receiveN(uint256 id, address owner, bytes calldata data) external payable;    
}

interface TokenOrNFT {
    function transferFrom(address from, address to, uint256 amountOrId) external;
}

contract nLend is ReentrancyGuard, Ownable {

    //State variables
    IN public immutable n;
    uint256 public adminFee;
    mapping(uint256 => address) public nOwner;
    mapping(uint256 => uint256) public borrowPrice;
    //Do I need arrays with the current NFTs? 
    //With it, we easily find which NFTs are available for loaning

    //Events
    event Deposit(address indexed _from, uint256 indexed _id, uint256 _value);
    event Withdraw(address indexed _from, uint256 indexed _id);
    event FlashBorrow(address indexed borrower,address indexed recipient, uint256 indexed _id, uint256 _value);
    event borrowFeeUpdated(uint256 indexed id, uint256 price);
    event adminFeeUpdated(uint256 indexed newAdminFee);

    constructor(
        IN _n,
        uint256 _adminFee
    )        
    {
        n = _n;
        adminFee = _adminFee;
    }

    /*
    * unprotected write functions
    * All functions should be protected with a reentrancy guard
    * None should have access control
    */

    /**
     * @notice Allow a n token holder to bulk mint tokens with id of their n tokens' id
     * @param id The n with ID id to deposit
     * @param price The price the owner wants to set to borrow their n, in wei
     * @notice Is checks-effects followed here? Yes
     */
    function deposit(uint256 id, uint256 price) external nonReentrant {
        //check if the msg.sender is the owner of id N
        require(n.ownerOf(id) == msg.sender, "nLend:INVALID_OWNER");
        
        //credit the owner with the ID in the nOwners mapping
        nOwner[id] = msg.sender;

        //assign the NFT the owner's price
        borrowPrice[id] = price;

        //transfer the NFT from the owner to this contract
        //NFT transfer does not return a bool so no need to require
        //we don't want safeTransferFrom since we don't want a callback
        n.transferFrom(msg.sender, address(this), id);

        //emit a deposit event
        emit Deposit(msg.sender, id, price);
    }
    
    /**
     * @notice Allow user's to withdraw their deposited n NFT with ID id
     * @param id The n with ID id to withdraw
     * @notice Is checks-effects followed here? Yes
     */
    function withdraw(uint256 id) external nonReentrant {
        //check if the msg.sender is the owner of id N
        require(nOwner[id] == msg.sender, "nLend:INVALID_OWNER");
        
        //clear the ownership
        nOwner[id] = address(0);

        //clear the price
        borrowPrice[id] = 0 ether;

        //transfer the NFT from this contract to the owner
        //NFT transfer does not return a bool so no need to require
        //we don't want safeTransferFrom since we don't want a callback
        n.transferFrom(address(this), msg.sender, id);

        //emit a deposit event
        emit Withdraw(msg.sender,id);
    }

    
    /**
     * @notice Flash borrow an n NFT with ID id
     * @param id The n NFT with ID id you want to borrow
     * @notice The receive contract needs to approve this contract in it's logic
     * @notice You can grief an unprotected receiver that has enough ETH in it + working logic  to execute
     */
    function flashBorrow(uint256 id, address receiver, bytes calldata data) external payable nonReentrant {
        
        //check that we have the NFT - this is to say that there is some owner in our mapping
        require(nOwner[id] != address(0));
        //check that the msg.value is enough incl fees
        uint amountReceived = msg.value;
        require(amountReceived >= borrowPrice[id] + (borrowPrice[id]*adminFee)/10000);
        
        //duduct admin fees and borrow fee from the amountReceived
        amountReceived -= borrowPrice[id] + (borrowPrice[id]*adminFee)/10000;

        //transfer the NFT
        //NFT transfer does not return a bool so no need to require
        //we don't want safeTransferFrom since we don't want a callback
        n.transferFrom(address(this), receiver, id);
        
        //send the rest of the msg.value to the receiver
        //Do the things
        IReceiver(receiver).receiveN{value: amountReceived}(id, nOwner[id], data);

        //transfer the NFT back
        //NFT transfer does not return a bool so no need to require
        //we don't want safeTransferFrom since we don't want a callback
        n.transferFrom(receiver, address(this), id);

        //send the borrower fees to the id owner
        payable(nOwner[id]).transfer(borrowPrice[id]);

        //emit an event - should we use the tracked msg.value?
        emit FlashBorrow(msg.sender, receiver, id, msg.value);
    }

    /**
     * @notice Allows the owner to withdraw all admin fees
     */
    function withdrawAll() external onlyOwner {
        payable(owner()).transfer(address(this).balance);
    }

    /**
     * @notice Allows the owner to withdraw all admin fees
     */
    function updateAdminFee(uint256 newAdminFee) external onlyOwner {
        require(newAdminFee <= 10000);
        adminFee = newAdminFee;
        emit adminFeeUpdated(newAdminFee);
    }

    /**
     * @notice Allows an owner to update their borrow fee
     */
    function updateBorrowFee(uint256 id, uint256 price) external nonReentrant {
        require(msg.sender == nOwner[id]);
        borrowPrice[id] = price;
        emit borrowFeeUpdated(id, price);
    }

    /**
     * @notice Allows an owner to recover any token or NFT other than n
     */
    function recovertokenOrNFT(address tokenOrNFT, uint256 amountOrAmount) external nonReentrant onlyOwner {
        require(tokenOrNFT != n.address);
        TokenOrNFT(token).transferFrom(address(this), owner(), amountOrAmount);
    }

}