LibraryApp.java

import java.util.List;
import java.util.Scanner;

public class LibraryApp {

    public static void main(String[] args) {
        
        // 1. Initialize the Library and Scanner for input
        Library library = new Library();
        Scanner scanner = new Scanner(System.in);
        
        // A few initial books for testing purposes (Optional)
        library.addBook(new Book("The Java Programming", "James Gosling", "978-0131489025"));
        library.addBook(new Book("Data Structures in Java", "Goodrich", "978-1119475501"));
        
        int choice = -1;

        // 2. Main application loop
        while (choice != 6) {
            displayMenu();
            
            // Handle non-integer input to prevent crash
            if (scanner.hasNextInt()) {
                choice = scanner.nextInt();
                scanner.nextLine(); // Consume the newline character
            } else {
                System.out.println("Invalid input. Please enter a number (1-6).");
                scanner.nextLine(); // Consume the invalid input
                continue; // Skip the rest of the loop and show menu again
            }

            // 3. Process the user's choice
            switch (choice) {
                case 1:
                    addBookUI(library, scanner);
                    break;
                case 2:
                    library.displayAllBooks();
                    break;
                case 3:
                    searchBookUI(library, scanner);
                    break;
                case 4:
                    issueBookUI(library, scanner, "Issue");
                    break;
                case 5:
                    issueBookUI(library, scanner, "Return");
                    break;
                case 6:
                    System.out.println("\nThank you for using the Library Management System. Exiting...");
                    break;
                default:
                    System.out.println("Invalid choice. Please select a number between 1 and 6.");
            }
        }
        
        scanner.close(); // Clean up the scanner resource
    }

    // --- Menu Display Method ---
    private static void displayMenu() {
        System.out.println("\n==================================");
        System.out.println("   Library Management System Menu   ");
        System.out.println("==================================");
        System.out.println("1. Add New Book");
        System.out.println("2. View All Books");
        System.out.println("3. Search Book (Title or ISBN)");
        System.out.println("4. Issue Book (Mark as Issued)");
        System.out.println("5. Return Book (Mark as Available)");
        System.out.println("6. Exit");
        System.out.print("Enter your choice: ");
    }

    // --- UI Helper Method: Add Book ---
    private static void addBookUI(Library library, Scanner scanner) {
        System.out.println("\n--- Add New Book ---");
        System.out.print("Enter Title: ");
        String title = scanner.nextLine();
        System.out.print("Enter Author: ");
        String author = scanner.nextLine();
        System.out.print("Enter ISBN (Unique ID): ");
        String isbn = scanner.nextLine();
        
        // Create the Book object and pass it to the Library
        Book newBook = new Book(title, author, isbn);
        library.addBook(newBook);
    }

    // --- UI Helper Method: Search Book ---
    private static void searchBookUI(Library library, Scanner scanner) {
        System.out.println("\n--- Search Book ---");
        System.out.print("Enter Title or ISBN to search: ");
        String query = scanner.nextLine();
        
        List<Book> results = library.searchBook(query);
        
        if (results.isEmpty()) {
            System.out.println("No books found matching '" + query + "'.");
        } else {
            System.out.println("\n--- Found " + results.size() + " Book(s) ---");
            for (Book book : results) {
                System.out.println(book);
            }
            System.out.println("------------------------------------");
        }
    }
    
    // --- UI Helper Method: Issue/Return Book ---
    private static void issueBookUI(Library library, Scanner scanner, String action) {
        System.out.println("\n--- " + action + " Book ---");
        System.out.print("Enter ISBN of the book to " + action.toLowerCase() + ": ");
        String isbn = scanner.nextLine();
        
        boolean success = false;
        
        if (action.equals("Issue")) {
            success = library.issueBook(isbn);
        } else if (action.equals("Return")) {
            success = library.returnBook(isbn);
        }
        
        if (success) {
            System.out.println("Success! Book with ISBN " + isbn + " has been " + action.toLowerCase() + "d.");
        } 
        // Note: Failure messages are handled inside the Library class methods
    }
}