Main.java

import java.util.ArrayList;
import java.util.InputMismatchException;
import java.util.List;
import java.util.Optional;
import java.util.Scanner;

public class Main {
    private static EmployeeManager manager = new EmployeeManager();
    private static Scanner scanner = new Scanner(System.in);

    // ----------------------------------------------------------------
    // 1. Employee Model
    // ----------------------------------------------------------------
    private static class Employee {
        private int id;
        private String name;
        private String department;
        private double salary;

        public Employee(int id, String name, String department, double salary) {
            this.id = id;
            this.name = name;
            this.department = department;
            this.salary = salary;
        }

        public int getId() { return id; }
        public String getName() { return name; }
        public String getDepartment() { return department; }
        public double getSalary() { return salary; }

        public void setName(String name) { this.name = name; }
        public void setDepartment(String department) { this.department = department; }
        public void setSalary(double salary) { this.salary = salary; }

        @Override
        public String toString() {
            return String.format("| ID: %-5d | Name: %-20s | Dept: %-15s | Salary: ₹%,.2f |",
                                 id, name, department, salary);
        }
    }

    // ----------------------------------------------------------------
    // 2. Employee Manager (CRUD)
    // ----------------------------------------------------------------
    private static class EmployeeManager {
        private List<Employee> employees;

        public EmployeeManager() {
            this.employees = new ArrayList<>();
            // ✅ Removed the default employees (no pre-added data)
        }

        public void addEmployee(Employee employee) {
            employees.add(employee);
            System.out.println("-> Success: Employee " + employee.getName() + " added.");
        }

        public Optional<Employee> findEmployeeById(int id) {
            return employees.stream()
                    .filter(e -> e.getId() == id)
                    .findFirst();
        }

        public void viewAllEmployees() {
            if (employees.isEmpty()) {
                System.out.println("--- The employee list is currently empty. ---");
                return;
            }
            System.out.println("\n--- All Employees (Total: " + employees.size() + ") ---");
            System.out.println("----------------------------------------------------------------------------------");
            for (Employee e : employees) {
                System.out.println(e);
            }
            System.out.println("----------------------------------------------------------------------------------");
        }

        public boolean updateEmployee(int id, String newName, String newDept, double newSalary) {
            Optional<Employee> employeeOpt = findEmployeeById(id);
            if (employeeOpt.isPresent()) {
                Employee employee = employeeOpt.get();
                employee.setName(newName);
                employee.setDepartment(newDept);
                employee.setSalary(newSalary);
                System.out.println("-> Success: Employee ID " + id + " updated successfully.");
                return true;
            } else {
                System.out.println("-> Error: Employee ID " + id + " not found for update.");
                return false;
            }
        }

        public boolean deleteEmployee(int id) {
            Optional<Employee> employeeOpt = findEmployeeById(id);
            if (employeeOpt.isPresent()) {
                employees.remove(employeeOpt.get());
                System.out.println("-> Success: Employee ID " + id + " deleted.");
                return true;
            } else {
                System.out.println("-> Error: Employee ID " + id + " not found for deletion.");
                return false;
            }
        }
    }

    // ----------------------------------------------------------------
    // 3. Main Application Runner
    // ----------------------------------------------------------------
    public static void main(String[] args) {
        System.out.println("==================================================");
        System.out.println("  Welcome to the Employee Management System (EMS)");
        System.out.println("==================================================");

        boolean running = true;
        while (running) {
            displayMenu();
            try {
                int choice = scanner.nextInt();
                scanner.nextLine(); // Consume newline

                switch (choice) {
                    case 1:
                        addEmployee();
                        break;
                    case 2:
                        manager.viewAllEmployees();
                        break;
                    case 3:
                        viewEmployeeById();
                        break;
                    case 4:
                        updateEmployee();
                        break;
                    case 5:
                        deleteEmployee();
                        break;
                    case 6:
                        running = false;
                        System.out.println("Thank you for using the EMS. Goodbye!");
                        break;
                    default:
                        System.out.println("Invalid choice. Please enter a number between 1 and 6.");
                }
            } catch (InputMismatchException e) {
                System.out.println("\n!!! Invalid input. Please enter a number for your choice. !!!\n");
                scanner.nextLine();
            } catch (Exception e) {
                System.out.println("\n!!! An unexpected error occurred: " + e.getMessage() + " !!!\n");
            }
        }
        scanner.close();
    }

    private static void displayMenu() {
        System.out.println("\n--------------------------------------------------");
        System.out.println("Please select an option:");
        System.out.println("1. Add New Employee");
        System.out.println("2. View All Employees");
        System.out.println("3. View Employee by ID");
        System.out.println("4. Update Employee Details");
        System.out.println("5. Delete Employee by ID");
        System.out.println("6. Exit Application");
        System.out.print("Enter choice (1-6): ");
    }

    private static void addEmployee() {
        try {
            System.out.print("Enter Employee ID: ");
            int id = scanner.nextInt();
            scanner.nextLine();

            if (manager.findEmployeeById(id).isPresent()) {
                System.out.println("-> Error: Employee ID " + id + " already exists. Please use a unique ID.");
                return;
            }

            System.out.print("Enter Employee Name: ");
            String name = scanner.nextLine();

            System.out.print("Enter Employee Department: ");
            String department = scanner.nextLine();

            System.out.print("Enter Employee Salary (in ₹): ");
            double salary = scanner.nextDouble();
            scanner.nextLine();

            Employee newEmployee = new Employee(id, name, department, salary);
            manager.addEmployee(newEmployee);

        } catch (InputMismatchException e) {
            System.out.println("-> Input Error: ID and Salary must be numbers.");
            scanner.nextLine();
        }
    }

    private static void viewEmployeeById() {
        try {
            System.out.print("Enter Employee ID to view: ");
            int id = scanner.nextInt();
            scanner.nextLine();

            Optional<Employee> employeeOpt = manager.findEmployeeById(id);
            if (employeeOpt.isPresent()) {
                System.out.println("\n--- Employee Found ---");
                System.out.println(employeeOpt.get());
                System.out.println("----------------------");
            } else {
                System.out.println("-> Error: Employee ID " + id + " not found.");
            }
        } catch (InputMismatchException e) {
            System.out.println("-> Input Error: ID must be a number.");
            scanner.nextLine();
        }
    }

    private static void updateEmployee() {
        try {
            System.out.print("Enter Employee ID to update: ");
            int id = scanner.nextInt();
            scanner.nextLine();

            Optional<Employee> employeeOpt = manager.findEmployeeById(id);
            if (employeeOpt.isPresent()) {
                Employee employee = employeeOpt.get();
                System.out.println("\n--- Current Details ---");
                System.out.println(employee);
                System.out.println("-----------------------");

                System.out.print("Enter new Name (leave blank to keep '" + employee.getName() + "'): ");
                String newName = scanner.nextLine();
                if (newName.isEmpty()) newName = employee.getName();

                System.out.print("Enter new Department (leave blank to keep '" + employee.getDepartment() + "'): ");
                String newDept = scanner.nextLine();
                if (newDept.isEmpty()) newDept = employee.getDepartment();

                System.out.print("Enter new Salary (0 to skip): ");
                String salaryInput = scanner.nextLine();
                double newSalary = employee.getSalary();
                if (!salaryInput.trim().isEmpty() && Double.parseDouble(salaryInput) != 0) {
                    newSalary = Double.parseDouble(salaryInput);
                }

                manager.updateEmployee(id, newName, newDept, newSalary);

            } else {
                System.out.println("-> Error: Employee ID " + id + " not found.");
            }
        } catch (InputMismatchException | NumberFormatException e) {
            System.out.println("-> Input Error: Invalid number format for ID or Salary.");
            scanner.nextLine();
        }
    }

    private static void deleteEmployee() {
        try {
            System.out.print("Enter Employee ID to delete: ");
            int id = scanner.nextInt();
            scanner.nextLine();
            manager.deleteEmployee(id);
        } catch (InputMismatchException e) {
            System.out.println("-> Input Error: ID must be a number.");
            scanner.nextLine();
        }
    }
}