Instructions:

You have been provided with the skeleton of a simple project: Library management system written in PHP. Your task is to complete the implementation of the classes by fulfilling the requirements specified in the TODO comments. Below is a detailed breakdown of what you need to do for each class:

1. AbstractLibrary Class (Already Provided)

This abstract class defines the structure and methods for a library system. You do not need to modify this class. Instead, you will implement its methods in the Library class.

• Key Methods:
  • addAuthor: Adds an author to the library.
  • addBookForAuthor: Associates a book with an author.
  • getBooksForAuthor: Retrieves all books for a specific author.
  • search: Searches for a book by its title and returns its instance.
  • print: Prints the authors and their books in a formatted output.

---

2. Library Class

The Library class extends AbstractLibrary. Your job is to implement all the methods declared in the abstract class.

• Steps:
  • Implement the addAuthor method to add authors to the $authors array and return the newly created Author instance.
  • Implement the addBookForAuthor method to associate a Book instance with an existing author and set the book’s author property.
  • Implement the getBooksForAuthor method to retrieve all books for a given author.
  • Implement the search method to find and return a book by its title from the authors' books.
  • Implement the print method to display the authors and their books in the required format.

---

3. Book Class

The Book class represents a book and has the following attributes:

• title: The title of the book.

• price: The price of the book.

• author: The author of the book (optional during creation).

• Steps:

  • Generate getters and setters for all properties.
  • Create a constructor that accepts values for all attributes. The author parameter should be optional.

---

4. Author Class

The Author class represents an author and contains the following:

• name: The name of the author.

• books: An array of books written by the author.

• Steps:

  • Generate getters and setters for all properties.
  • Create a constructor that initializes the name and optionally the books array.
  • Implement the addBook method to create a new book, add it to the $books array, and return the Book instance.

---

5. Testing the Implementation

You are provided with a test script at the end of the file:

require_once "Book.php";
require_once "Library.php";

$library = new Library();
$author = $library->addAuthor('Jack London');
$author->addBook("Martin Eden", 55);
$author->addBook("The Game", 35);
$library->addBookForAuthor('Jack London', new Book("A Son of the Sun", 25));

$author2 = $library->addAuthor('Mark Twain');
$author2->addBook('The Adventures of Tom Sawyer', 65);
$author2->addBook('Luck', 12);

$book = $library->search('Martin Eden'); // This must return instance of the book
$author = $book->getAuthor(); // This must return instance of the Author class
echo $author->getName(); // This must print "Jack London"

$library->print();

• Run the Script:
  • After completing the implementation, run the test script to ensure all functionalities work as expected.
  • The output of the print method should match the format given in the comments.

---