Library.java

import java.io.*;
import java.util.*;

public class Library {
    private ArrayList<Book> books = new ArrayList<>();
    private static final String DATA_FILE = "library_data.json";

    public Library() {
        loadData();
    }

    // Add Book
    public void addBook(Scanner sc) {
        System.out.print("Enter book title: ");
        String title = sc.nextLine();
        System.out.print("Enter author name: ");
        String author = sc.nextLine();
        System.out.print("Enter ISBN: ");
        String isbn = sc.nextLine();

        if (findBookByISBN(isbn) != null) {
            System.out.println("Book with this ISBN already exists!");
            return;
        }

        books.add(new Book(title, author, isbn));
        System.out.println("Book added successfully!");
        saveData();
    }

    // Search Book
    public void searchBook(Scanner sc) {
        System.out.println("Search by: 1. Title  2. Author  3. ISBN");
        String choice = sc.nextLine();
        System.out.print("Enter search term: ");
        String query = sc.nextLine().toLowerCase();

        boolean found = false;
        for (Book book : books) {
            boolean match = switch (choice) {
                case "1" -> book.getTitle().toLowerCase().contains(query);
                case "2" -> book.getAuthor().toLowerCase().contains(query);
                case "3" -> book.getIsbn().equalsIgnoreCase(query);
                default -> false;
            };
            if (match) {
                System.out.println(book);
                found = true;
            }
        }
        if (!found) System.out.println("No matching book found.");
    }

    // Borrow Book
    public void borrowBook(Scanner sc) {
        System.out.print("Enter ISBN of book to borrow: ");
        String isbn = sc.nextLine();
        Book book = findBookByISBN(isbn);

        if (book == null) System.out.println("Book not found!");
        else if (book.borrowBook()) {
            System.out.println("Borrowed successfully!");
            saveData();
        } else System.out.println("Already borrowed!");
    }

    // Return Book
    public void returnBook(Scanner sc) {
        System.out.print("Enter ISBN of book to return: ");
        String isbn = sc.nextLine();
        Book book = findBookByISBN(isbn);

        if (book == null) System.out.println("Book not found!");
        else if (book.returnBook()) {
            System.out.println("Returned successfully!");
            saveData();
        } else System.out.println("Book wasn’t borrowed.");
    }

    // Remove Book
    public void removeBook(Scanner sc) {
        System.out.print("Enter ISBN of book to remove: ");
        String isbn = sc.nextLine();
        Book book = findBookByISBN(isbn);

        if (book == null) {
            System.out.println("Book not found!");
            return;
        }

        books.remove(book);
        System.out.println("Book removed successfully!");
        saveData();
    }

    // List All Books
    public void listAllBooks() {
        if (books.isEmpty()) {
            System.out.println("No books in library!");
            return;
        }

        System.out.println("\n=== All Books ===");
        for (Book book : books) System.out.println(book);
    }

    // Top Borrowed Books
    public void showTopBorrowed() {
        if (books.isEmpty()) {
            System.out.println("No books yet!");
            return;
        }

        books.sort((a, b) -> Integer.compare(b.getBorrowCount(), a.getBorrowCount()));

        System.out.println("\n=== Top Borrowed Books ===");
        for (int i = 0; i < Math.min(5, books.size()); i++) {
            System.out.println((i + 1) + ". " + books.get(i));
        }
    }

    private Book findBookByISBN(String isbn) {
        for (Book b : books)
            if (b.getIsbn().equalsIgnoreCase(isbn))
                return b;
        return null;
    }

    // Save data as JSON
    private void saveData() {
        try (PrintWriter pw = new PrintWriter(new FileWriter(DATA_FILE))) {
            pw.println("[");
            for (int i = 0; i < books.size(); i++) {
                pw.print("  " + books.get(i).toJson());
                if (i < books.size() - 1) pw.println(",");
                else pw.println();
            }
            pw.println("]");
        } catch (IOException e) {
            System.out.println("Error saving: " + e.getMessage());
        }
    }

    // Load data from JSON
    private void loadData() {
        File file = new File(DATA_FILE);
        if (!file.exists()) return;

        try (BufferedReader br = new BufferedReader(new FileReader(file))) {
            books.clear();
            String line;
            while ((line = br.readLine()) != null) {
                line = line.trim();
                if (line.startsWith("{")) {
                    if (line.endsWith(",")) line = line.substring(0, line.length() - 1);
                    books.add(Book.fromJson(line));
                }
            }
        } catch (IOException e) {
            System.out.println("Error loading: " + e.getMessage());
        }
    }
}