LibrarySystem.java

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

// Represents a Library Member
class Member implements Serializable {
    String id, name;
    public Member(String id, String name) { this.id = id; this.name = name; }
    @Override
    public String toString() { return "Member [ID=" + id + ", Name=" + name + "]"; }
}

// Represents a Book with tracking logic
class Book implements Serializable {
    String id, title, issuedToId;
    boolean isIssued;

    public Book(String id, String title) {
        this.id = id;
        this.title = title;
        this.isIssued = false;
        this.issuedToId = null;
    }

    @Override
    public String toString() {
        String status = isIssued ? "Issued to Member: " + issuedToId : "Available";
        return String.format("ID: %-5s | Title: %-20s | %s", id, title, status);
    }
}

public class LibrarySystem {
    private static final String DATA_FILE = "library_store.dat";
    private Map<String, Book> inventory = new HashMap<>();
    private Map<String, Member> members = new HashMap<>();
    private Scanner scanner = new Scanner(System.in);

    public LibrarySystem() { loadData(); }

    // --- Core Functionality ---

    public void addMember() {
        System.out.print("Enter Member ID: "); String id = scanner.nextLine();
        System.out.print("Enter Name: "); String name = scanner.nextLine();
        members.put(id, new Member(id, name));
        saveData();
        System.out.println("Member registered successfully.");
    }

    public void issueBook() {
        System.out.print("Enter Book ID: "); String bId = scanner.nextLine();
        System.out.print("Enter Member ID: "); String mId = scanner.nextLine();

        if (inventory.containsKey(bId) && members.containsKey(mId)) {
            Book b = inventory.get(bId);
            if (!b.isIssued) {
                b.isIssued = true;
                b.issuedToId = mId;
                saveData();
                System.out.println("Book '" + b.title + "' issued to " + members.get(mId).name);
            } else {
                System.out.println("Error: Book is already issued.");
            }
        } else {
            System.out.println("Error: Invalid Book or Member ID.");
        }
    }

    public void returnBook() {
        System.out.print("Enter Book ID to return: ");
        String id = scanner.nextLine();
        if (inventory.containsKey(id) && inventory.get(id).isIssued) {
            inventory.get(id).isIssued = false;
            inventory.get(id).issuedToId = null;
            saveData();
            System.out.println("Book returned and inventory updated.");
        } else {
            System.out.println("Error: Book was not issued or doesn't exist.");
        }
    }

    // --- Persistence Logic ---

    private void saveData() {
        try (ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream(DATA_FILE))) {
            oos.writeObject(inventory);
            oos.writeObject(members);
        } catch (IOException e) { System.out.println("Persistence Error: " + e.getMessage()); }
    }

    @SuppressWarnings("unchecked")
    private void loadData() {
        File file = new File(DATA_FILE);
        if (!file.exists()) return;
        try (ObjectInputStream ois = new ObjectInputStream(new FileInputStream(DATA_FILE))) {
            inventory = (Map<String, Book>) ois.readObject();
            members = (Map<String, Member>) ois.readObject();
        } catch (Exception e) { System.out.println("Welcome! Starting fresh session."); }
    }

    // --- UI/UX Console ---

    public void runMenu() {
        while (true) {
            System.out.println("\n--- Library Dashboard ---");
            System.out.println("1. Register Member");
            System.out.println("2. Add Book");
            System.out.println("3. Issue Book");
            System.out.println("4. Return Book");
            System.out.println("5. View All");
            System.out.println("6. Exit");
            System.out.print("Choice: ");
            String choice = scanner.nextLine();
            switch (choice) {
                case "1" -> addMember();
                case "2" -> {
                    System.out.print("ID: "); String id = scanner.nextLine();
                    System.out.print("Title: "); String t = scanner.nextLine();
                    inventory.put(id, new Book(id, t));
                    saveData();
                }
                case "3" -> issueBook();
                case "4" -> returnBook();
                case "5" -> {
                    System.out.println("\nINVENTORY:"); inventory.values().forEach(System.out::println);
                    System.out.println("\nMEMBERS:"); members.values().forEach(System.out::println);
                }
                case "6" -> System.exit(0);
                default -> System.out.println("Invalid entry.");
            }
        }
    }

    public static void main(String[] args) {
        new LibrarySystem().runMenu();
    }
}