Book.java

package models;

import java.io.Serializable;
import java.util.Objects;

/**
 * Book.java - Entity class representing a Library Book
 * 
 * OOP Principles Applied:
 * - Encapsulation: Private fields with public getters/setters
 * - Immutability options: Can make certain fields final
 * - Proper equals() and hashCode() for collections
 * 
 * Design: Follows JavaBean conventions for database mapping
 */
public class Book implements Serializable, Comparable<Book> {
    
    private static final long serialVersionUID = 1L;
    
    // Core book information
    private int bookId;              // Auto-generated primary key
    private String title;            // Book title (required)
    private String author;           // Author name (required)
    private String isbn;             // ISBN unique identifier (required)
    private String publisher;        // Publishing company
    private int publicationYear;     // Year of publication
    private String category;         // Category/Genre
    private double price;            // Book price
    
    // Inventory management
    private int totalCopies;         // Total copies in library
    private int availableCopies;     // Available for issue
    
    // Constructors
    
    /**
     * No-argument constructor for framework compatibility
     */
    public Book() {
        this.bookId = 0;
        this.totalCopies = 0;
        this.availableCopies = 0;
    }
    
    /**
     * Constructor for new book entry (bookId is auto-generated)
     */
    public Book(String title, String author, String isbn, String publisher, 
                int publicationYear, int totalCopies, String category, double price) {
        this.title = title;
        this.author = author;
        this.isbn = isbn;
        this.publisher = publisher;
        this.publicationYear = publicationYear;
        this.totalCopies = totalCopies;
        this.availableCopies = totalCopies;
        this.category = category;
        this.price = price;
    }
    
    /**
     * Full constructor with all fields (used when retrieving from DB)
     */
    public Book(int bookId, String title, String author, String isbn, 
                String publisher, int publicationYear, int totalCopies, 
                int availableCopies, String category, double price) {
        this.bookId = bookId;
        this.title = title;
        this.author = author;
        this.isbn = isbn;
        this.publisher = publisher;
        this.publicationYear = publicationYear;
        this.totalCopies = totalCopies;
        this.availableCopies = availableCopies;
        this.category = category;
        this.price = price;
    }
    
    // Getters and Setters (Encapsulation)
    
    public int getBookId() {
        return bookId;
    }
    
    public void setBookId(int bookId) {
        if (bookId < 0) {
            throw new IllegalArgumentException("Book ID must be positive");
        }
        this.bookId = bookId;
    }
    
    public String getTitle() {
        return title;
    }
    
    public void setTitle(String title) {
        if (title == null || title.trim().isEmpty()) {
            throw new IllegalArgumentException("Title cannot be empty");
        }
        this.title = title;
    }
    
    public String getAuthor() {
        return author;
    }
    
    public void setAuthor(String author) {
        if (author == null || author.trim().isEmpty()) {
            throw new IllegalArgumentException("Author name cannot be empty");
        }
        this.author = author;
    }
    
    public String getIsbn() {
        return isbn;
    }
    
    public void setIsbn(String isbn) {
        if (isbn == null || isbn.trim().isEmpty()) {
            throw new IllegalArgumentException("ISBN cannot be empty");
        }
        this.isbn = isbn;
    }
    
    public String getPublisher() {
        return publisher;
    }
    
    public void setPublisher(String publisher) {
        this.publisher = publisher != null ? publisher : "";
    }
    
    public int getPublicationYear() {
        return publicationYear;
    }
    
    public void setPublicationYear(int year) {
        int currentYear = java.time.Year.now().getValue();
        if (year < 1000 || year > currentYear) {
            throw new IllegalArgumentException("Publication year must be between 1000 and " + currentYear);
        }
        this.publicationYear = year;
    }
    
    public int getTotalCopies() {
        return totalCopies;
    }
    
    public void setTotalCopies(int totalCopies) {
        if (totalCopies < availableCopies) {
            throw new IllegalArgumentException("Total copies cannot be less than available copies");
        }
        this.totalCopies = totalCopies;
    }
    
    public int getAvailableCopies() {
        return availableCopies;
    }
    
    public void setAvailableCopies(int availableCopies) {
        if (availableCopies < 0 || availableCopies > totalCopies) {
            throw new IllegalArgumentException("Available copies must be between 0 and " + totalCopies);
        }
        this.availableCopies = availableCopies;
    }
    
    public String getCategory() {
        return category;
    }
    
    public void setCategory(String category) {
        this.category = category != null ? category : "General";
    }
    
    public double getPrice() {
        return price;
    }
    
    public void setPrice(double price) {
        if (price < 0) {
            throw new IllegalArgumentException("Price cannot be negative");
        }
        this.price = price;
    }
    
    // Business Logic Methods
    
    /**
     * Issues a book to a member (decrements available copies)
     * 
     * @throws IllegalStateException if no copies available
     */
    public void issueBook() {
        if (availableCopies <= 0) {
            throw new IllegalStateException("No copies available for '" + title + "'");
        }
        availableCopies--;
    }
    
    /**
     * Returns a book from a member (increments available copies)
     * 
     * @throws IllegalStateException if all copies already returned
     */
    public void returnBook() {
        if (availableCopies >= totalCopies) {
            throw new IllegalStateException("All copies of '" + title + "' already returned");
        }
        availableCopies++;
    }
    
    /**
     * Checks if book is available
     * 
     * @return true if at least one copy available
     */
    public boolean isAvailable() {
        return availableCopies > 0;
    }
    
    // Object Methods
    
    @Override
    public String toString() {
        return "Book{" +
                "bookId=" + bookId +
                ", title='" + title + '\'' +
                ", author='" + author + '\'' +
                ", isbn='" + isbn + '\'' +
                ", publisher='" + publisher + '\'' +
                ", publicationYear=" + publicationYear +
                ", totalCopies=" + totalCopies +
                ", availableCopies=" + availableCopies +
                ", category='" + category + '\'' +
                ", price=" + price +
                '}';
    }
    
    /**
     * ISBN-based equality check
     * Two books are equal if they have the same ISBN
     */
    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Book book = (Book) o;
        return Objects.equals(isbn, book.isbn);
    }
    
    @Override
    public int hashCode() {
        return Objects.hash(isbn);
    }
    
    /**
     * Comparable implementation for sorting by title
     */
    @Override
    public int compareTo(Book other) {
        return this.title.compareToIgnoreCase(other.title);
    }
}