instructions.md

Let's begin by writing our data structures

1. struct Book represents a Book that you may want to rent out

struct Book {
       string name;
       string description;
       bool valid; // false if been borrowed
       uint256 price; // TRX per day
       address owner; // owner of the book
   }

2. struct Tracking represents the details of a particular booking information

struct Tracking {
       uint256 bookId;
       uint256 startTime; // start time, in timestamp
       uint256 endTime; // end time, in timestamp
       address borrower; // borrower's address
   }

Functions

1. Put up your book on the library

  /**
    * @dev Add a Book with predefined `name`, `description` and `price`
    * to the library.
    *
    * Returns a boolean value indicating whether the operation succeeded.
    *
    * Emits a {NewBook} event.
    */
   function addBook(string memory name, string memory description, uint256 price) public returns (bool) {
       Book memory book = Book(name, description, true, price, _msgSender());

       books[bookId] = book;

       emit NewBook(bookId++);

       return true;
   }

   /**
    * @dev Emitted when a new book is added to the library.
    * Note bookId starts from 0.
    */
   event NewBook(uint256 bookId);

2. Borrow a book

 /**
    * @dev Borrow a book has `_bookId`. The rental period starts from
    * `startTime` ends with `endTime`.
    *
    * Returns a boolean value indicating whether the operation succeeded.
    *
    * Emits a `NewRental` event.
    */
   function borrowBook(uint256 _bookId, uint256 startTime, uint256 endTime) public payable returns(bool) {
       Book storage book = books[_bookId];

       require(book.valid == true, "The book is currently on loan");

       require(_msgValue() == book.price * _days(startTime, endTime), "Incorrect fund sent.");

       _sendTRX(book.owner, _msgValue());

       _createTracking(_bookId, startTime, endTime);

       emit NewRental(_bookId, trackingId++);
   }

3. delete book

/**
    * @dev Delete a book from the library. Only the book's owner or the
    * library's owner is authorised for this operation.
    *
    * Returns a boolean value indicating whether the operation succeeded.
    *
    * Emits a `DeleteBook` event.
    */
   function deleteBook(uint256 _bookId) public returns(bool) {
       require(_msgSender() == books[_bookId].owner || isOwner(),
               "You are not authorised to delete this book.");
      
       delete books[_bookId];

       emit DeleteBook(_bookId);

       return true;

4. Helper function to create a booking

/**
    * @dev Send TRX to the book's owner.
    */
   function _sendTRX(address receiver, uint256 value) internal {
       payable(address(uint160(receiver))).transfer(value);
   }

/**
    * @dev Create a new rental tracking.
    */
   function _createTracking(uint256 _bookId, uint256 startTime, uint256 endTime) internal {
         trackings[trackingId] = Tracking(_bookId, startTime, endTime, _msgSender());

         Book storage book = books[_bookId];

         book.valid = false;
   }