Main.java

import java.util.List;
import java.util.Scanner;

public class Main {
    private static final Scanner sc = new Scanner(System.in);

    public static void main(String[] args) {
        StudentStore store = new StudentStore("data/students.csv");
        List<Student> students = store.loadAll();

        while (true) {
            System.out.println("\n=== STUDENT MANAGEMENT SYSTEM ===");
            System.out.println("1) Add student");
            System.out.println("2) List students");
            System.out.println("3) Search by ID");
            System.out.println("4) Update student");
            System.out.println("5) Delete student");
            System.out.println("6) Exit");
            System.out.print("Choose: ");

            String choice = sc.nextLine().trim();

            switch (choice) {
                case "1":
                    addStudent(store, students);
                    break;
                case "2":
                    listStudents(students);
                    break;
                case "3":
                    searchById(store, students);
                    break;
                case "4":
                    updateStudent(store, students);
                    break;
                case "5":
                    deleteStudent(store, students);
                    break;
                case "6":
                    System.out.println("Bye!");
                    return;
                default:
                    System.out.println("Invalid choice. Try again.");
                    break;
            }
        }
    }

    private static void addStudent(StudentStore store, List<Student> students) {
        int id = store.nextId(students);

        System.out.print("Name: ");
        String name = mustNotEmpty(sc.nextLine(), "Name");

        int age = readInt("Age (10-80): ", 10, 80);

        System.out.print("Email: ");
        String email = mustContain(sc.nextLine(), "@", "Email must contain @");

        System.out.print("Program (e.g., Software Engineering): ");
        String program = mustNotEmpty(sc.nextLine(), "Program");

        double gpa = readDouble("GPA (0.0 - 4.0): ", 0.0, 4.0);

        Student s = new Student(id, name, age, email, program, gpa);
        students.add(s);
        store.saveAll(students);
        System.out.println("✅ Added: " + s);
    }

    private static void listStudents(List<Student> students) {
        if (students.isEmpty()) {
            System.out.println("No students found.");
            return;
        }
        System.out.println("\n--- Students ---");
        for (Student s : students) {
            System.out.println(s);
        }
        System.out.println("Total: " + students.size());
    }

    private static void searchById(StudentStore store, List<Student> students) {
        int id = readInt("Enter student ID: ", 1, 1000000);
        int idx = store.findIndexById(students, id);
        if (idx == -1) {
            System.out.println("Not found.");
            return;
        }
        System.out.println("✅ Found: " + students.get(idx));
    }

    private static void updateStudent(StudentStore store, List<Student> students) {
        int id = readInt("Enter student ID to update: ", 1, 1000000);
        int idx = store.findIndexById(students, id);
        if (idx == -1) {
            System.out.println("Not found.");
            return;
        }

        Student s = students.get(idx);
        System.out.println("Current: " + s);
        System.out.println("Leave blank to keep current value.");

        System.out.print("New name: ");
        String name = sc.nextLine().trim();
        if (!name.isEmpty()) s.setName(name);

        System.out.print("New age: ");
        String ageStr = sc.nextLine().trim();
        if (!ageStr.isEmpty()) s.setAge(parseIntRange(ageStr, 10, 80));

        System.out.print("New email: ");
        String email = sc.nextLine().trim();
        if (!email.isEmpty()) {
            if (!email.contains("@")) {
                System.out.println("Email must contain @ (skipped).");
            } else {
                s.setEmail(email);
            }
        }

        System.out.print("New program: ");
        String program = sc.nextLine().trim();
        if (!program.isEmpty()) s.setProgram(program);

        System.out.print("New GPA: ");
        String gpaStr = sc.nextLine().trim();
        if (!gpaStr.isEmpty()) s.setGpa(parseDoubleRange(gpaStr, 0.0, 4.0));

        store.saveAll(students);
        System.out.println("✅ Updated: " + s);
    }

    private static void deleteStudent(StudentStore store, List<Student> students) {
        int id = readInt("Enter student ID to delete: ", 1, 1000000);
        int idx = store.findIndexById(students, id);
        if (idx == -1) {
            System.out.println("Not found.");
            return;
        }
        Student removed = students.remove(idx);
        store.saveAll(students);
        System.out.println("🗑️ Deleted: " + removed);
    }

    // helpers
    private static String mustNotEmpty(String s, String fieldName) {
        s = s.trim();
        if (s.isEmpty()) throw new IllegalArgumentException(fieldName + " cannot be empty.");
        return s;
    }

    private static String mustContain(String s, String token, String msg) {
        s = s.trim();
        if (!s.contains(token)) throw new IllegalArgumentException(msg);
        return s;
    }

    private static int readInt(String prompt, int min, int max) {
        while (true) {
            System.out.print(prompt);
            String s = sc.nextLine().trim();
            try {
                return parseIntRange(s, min, max);
            } catch (Exception e) {
                System.out.println("❌ " + e.getMessage());
            }
        }
    }

    private static double readDouble(String prompt, double min, double max) {
        while (true) {
            System.out.print(prompt);
            String s = sc.nextLine().trim();
            try {
                return parseDoubleRange(s, min, max);
            } catch (Exception e) {
                System.out.println("❌ " + e.getMessage());
            }
        }
    }

    private static int parseIntRange(String s, int min, int max) {
        int v = Integer.parseInt(s);
        if (v < min || v > max) throw new IllegalArgumentException("Value must be between " + min + " and " + max);
        return v;
    }

    private static double parseDoubleRange(String s, double min, double max) {
        double v = Double.parseDouble(s);
        if (v < min || v > max) throw new IllegalArgumentException("Value must be between " + min + " and " + max);
        return v;
    }
}