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contracts...library.sol

pragma solidity ^0.8.4;

contract bookLibrary {
    address public contractOwner;

    constructor() public {
        contractOwner = msg.sender;
    }

    modifier onlyOwner() {
        require(msg.sender == contractOwner);
        _;
    }

    struct Book {
        uint256 id;
        string name;
        string author;
        uint256 price;
        bool exists;
    }

    mapping(uint256 => Book) public books;

    function addBook(
        uint256 _bookId,
        string memory _bookName,
        string memory _bookAuthor,
        uint256 _price
    ) public onlyOwner {
        require(_price > 0, "Book price can not be zero");
        books[_bookId].name = _bookName;
        books[_bookId].author = _bookAuthor;
        books[_bookId].price = _price;
        books[_bookId].exists = true;
    }

    function queryBookById(uint256 _bookId)
        public view returns (
            string memory name,
            string memory author,
            uint256 price
        )
    {
        require(books[_bookId].exists, "Book must be available to query");
        return (
            books[_bookId].name,
            books[_bookId].author,
            books[_bookId].price
        );
    }
}