Library.java

import java.sql.*;
import java.time.LocalDate;
import java.time.temporal.ChronoUnit;

public class Library{

    public String login(String userId,String password){
        try{
            Connection con=DBConnection.getConnection();

            PreparedStatement ps=con.prepareStatement("SELECT * FROM users WHERE user_id=? AND password=?");
            ps.setString(1,userId);
            ps.setString(2,password);

            ResultSet rs=ps.executeQuery();

            if(rs.next()){
                return rs.getString("role");
            }

        }catch(Exception e){
            System.out.println("Login failed");
        }
        return null;
    }

    public void registerUser(User user){
        try{
            Connection con=DBConnection.getConnection();

            PreparedStatement ps=con.prepareStatement("INSERT INTO users VALUES (?, ?, ?, ?)");
            ps.setString(1,user.getUserId());
            ps.setString(2,user.getName());
            ps.setString(3,user.getPassword());
            ps.setString(4,user.getRole());

            ps.executeUpdate();
            System.out.println("User registered successfully");

        }catch(Exception e){
            System.out.println("Error: "+e.getMessage());
        }
    }

    public void addBook(Book book){
        try{
            Connection con=DBConnection.getConnection();

            PreparedStatement ps=con.prepareStatement("INSERT INTO books VALUES (?, ?, ?, ?)");
            ps.setString(1,book.getBookId());
            ps.setString(2,book.getTitle());
            ps.setString(3,book.getAuthor());
            ps.setBoolean(4,false);

            ps.executeUpdate();
            System.out.println("Book added successfully");

        }catch(Exception e){
            System.out.println("Error: "+e.getMessage());
        }
    }

    public void issueBook(String bookId,String userId){
        try{
            Connection con=DBConnection.getConnection();

            PreparedStatement check=con.prepareStatement("SELECT is_issued FROM books WHERE book_id=?");
            check.setString(1,bookId);

            ResultSet rs=check.executeQuery();

            if(!rs.next()){
                System.out.println("Book not found");
                return;
            }

            if(rs.getBoolean("is_issued")){
                System.out.println("Book already issued");
                return;
            }

            LocalDate today=LocalDate.now();
            LocalDate due=today.plusDays(7);

            PreparedStatement ps1=con.prepareStatement("UPDATE books SET is_issued=true WHERE book_id=?");
            ps1.setString(1,bookId);
            ps1.executeUpdate();

            PreparedStatement ps2=con.prepareStatement("INSERT INTO transactions(book_id,user_id,issue_date,due_date) VALUES (?, ?, ?, ?)");
            ps2.setString(1,bookId);
            ps2.setString(2,userId);
            ps2.setDate(3,Date.valueOf(today));
            ps2.setDate(4,Date.valueOf(due));

            ps2.executeUpdate();

            System.out.println("Book issued. Due date: "+due);

        }catch(Exception e){
            System.out.println("Error: "+e.getMessage());
        }
    }

    public void returnBook(String bookId){
        try{
            Connection con=DBConnection.getConnection();

            PreparedStatement ps=con.prepareStatement("SELECT due_date FROM transactions WHERE book_id=? AND return_date IS NULL");
            ps.setString(1,bookId);

            ResultSet rs=ps.executeQuery();

            if(rs.next()){
                LocalDate due=rs.getDate("due_date").toLocalDate();
                LocalDate today=LocalDate.now();

                long delay=ChronoUnit.DAYS.between(due,today);

                if(delay>0){
                    System.out.println("Late by "+delay+" days. Fine: ₹"+(delay*10));
                }

                PreparedStatement ps1=con.prepareStatement("UPDATE books SET is_issued=false WHERE book_id=?");
                ps1.setString(1,bookId);
                ps1.executeUpdate();

                PreparedStatement ps2=con.prepareStatement("UPDATE transactions SET return_date=? WHERE book_id=? AND return_date IS NULL");
                ps2.setDate(1,Date.valueOf(today));
                ps2.setString(2,bookId);
                ps2.executeUpdate();

                System.out.println("Book returned");

            }else{
                System.out.println("No active transaction");
            }

        }catch(Exception e){
            System.out.println("Error: "+e.getMessage());
        }
    }

    public void showBooks(){
        try{
            Connection con=DBConnection.getConnection();

            ResultSet rs=con.createStatement().executeQuery("SELECT * FROM books");

            while(rs.next()){
                System.out.println(rs.getString("book_id")+" | "+rs.getString("title")+" | "+rs.getString("author")+" | Issued: "+rs.getBoolean("is_issued"));
            }

        }catch(Exception e){
            System.out.println("Error: "+e.getMessage());
        }
    }

    public void searchBook(String keyword){
        try{
            Connection con=DBConnection.getConnection();

            PreparedStatement ps=con.prepareStatement("SELECT * FROM books WHERE title LIKE ?");
            ps.setString(1,"%"+keyword+"%");

            ResultSet rs=ps.executeQuery();

            while(rs.next()){
                System.out.println(rs.getString("title")+" | "+rs.getString("author"));
            }

        }catch(Exception e){
            System.out.println("Error: "+e.getMessage());
        }
    }

    public void showTransactions(String userId){
        try{
            Connection con=DBConnection.getConnection();

            PreparedStatement ps=con.prepareStatement("SELECT * FROM transactions WHERE user_id=?");
            ps.setString(1,userId);

            ResultSet rs=ps.executeQuery();

            while(rs.next()){
                String bookId=rs.getString("book_id");
                LocalDate issue=rs.getDate("issue_date").toLocalDate();
                LocalDate due=rs.getDate("due_date").toLocalDate();
                Date returnDate=rs.getDate("return_date");

                int fine=0;

                if(returnDate!=null){
                    LocalDate returned=returnDate.toLocalDate();
                    long delay=ChronoUnit.DAYS.between(due,returned);

                    if(delay>0){
                        fine=(int)delay*10;
                    }

                    System.out.println("Book: "+bookId+" | Issued: "+issue+" | Due: "+due+" | Returned: "+returned+" | Fine: Rs."+fine);
                }else{
                    System.out.println("Book: "+bookId+" | Issued: "+issue+" | Due: "+due+" | Returned: Not yet");
                }
            }

        }catch(Exception e){
            System.out.println("Error: "+e.getMessage());
        }
    }
}