import csv

def readStudentFile(file_path):
    """Reads student data from a file and returns a dictionary."""
    students = {}
    try:
        with open(file_path, 'r') as file:
            reader = csv.reader(file)
            for row in reader:
                student_id = row[0]
                first_name = row[1]
                last_name = row[2]
                courses = {row[i]: int(row[i + 1]) for i in range(3, len(row), 2)}
                students[student_id] = {
                    'first_name': first_name,
                    'last_name': last_name,
                    'courses': courses
                }
    except Exception as e:
        print(f"Error reading student file: {e}")
    return students

def saveStudentFile(file_path, students):
    """Saves student data to a file."""
    try:
        with open(file_path, 'w', newline='') as file:
            writer = csv.writer(file)
            for student_id, data in students.items():
                row = [
                    student_id,
                    data['first_name'],
                    data['last_name']
                ]
                for course, grade in data['courses'].items():
                    row.extend([course, grade])
                writer.writerow(row)
    except Exception as e:
        print(f"Error saving student file: {e}")

def menu():
    """Displays the menu and gets the user's choice."""
    print("\nMenu:")
    print("1. Add new student")
    print("2. Update grade")
    print("3. Load grade updates from file")
    print("4. Generate student report")
    print("5. Generate course report")
    print("6. Exit")
    
    while True:
        try:
            choice = int(input("Enter your choice: "))
            if 1 <= choice <= 6:
                return choice
            else:
                print("Invalid choice. Please choose between 1 and 6.")
        except ValueError:
            print("Invalid input. Please enter a number between 1 and 6.")

def add_new_student(students):
    """Adds a new student to the data."""
    student_id = input("Enter student ID: ")
    if student_id in students:
        print("Error: Student with this ID already exists.")
        return

    first_name = input("Enter first name: ")
    last_name = input("Enter last name: ")
    students[student_id] = {
        'first_name': first_name,
        'last_name': last_name,
        'courses': {}
    }
    print("Student added successfully.")

def updateGrade(students):
    """Updates a grade for a student."""
    student_id = input("Enter student ID: ")
    if student_id not in students:
        print("Error: Student not found.")
        return

    course = input("Enter course name: ").capitalize()
    try:
        grade = int(input("Enter grade (0-100): "))
        if 0 <= grade <= 100:
            students[student_id]['courses'][course] = grade
            print("Grade updated successfully.")
        else:
            print("Error: Grade must be between 0 and 100.")
    except ValueError:
        print("Error: Invalid grade format.")

def loadGrades(file_path, students):
    """Loads grade updates from a file."""
    try:
        with open(file_path, 'r') as file:
            reader = csv.reader(file)
            for row in reader:
                student_id, course, grade = row
                if student_id in students:
                    students[student_id]['courses'][course] = int(grade)
                else:
                    print(f"Warning: Student ID {student_id} not found.")
        print("Grade updates loaded successfully.")
    except Exception as e:
        print(f"Error loading grades: {e}")

def generateStudentReport(students):
    """Generates a report for a specific student."""
    student_id = input("Enter student ID: ")
    if student_id not in students:
        print("Error: Student not found.")
        return

    student = students[student_id]
    print(f"\nReport for {student['first_name']} {student['last_name']}:")
    total, count = 0, 0
    for course, grade in student['courses'].items():
        print(f"{course}: {grade}")
        total += grade
        count += 1
    if count > 0:
        print(f"Average grade: {total / count:.2f}")

def generateCourseReport(students):
    """Generates a report for a specific course."""
    course = input("Enter course name: ").capitalize()
    print(f"\nReport for course: {course}")
    total, count = 0, 0
    for student in students.values():
        if course in student['courses']:
            grade = student['courses'][course]
            print(f"{student['first_name']} {student['last_name']}: {grade}")
            total += grade
            count += 1
    if count > 0:
        print(f"Average grade: {total / count:.2f}")
    else:
        print("No students found for this course.")

def main():
    students = readStudentFile('students.csv')
    while True:
        choice = menu()
        if choice == 1:
            add_new_student(students)
        elif choice == 2:
            updateGrade(students)
        elif choice == 3:
            file_path = input("Enter grade updates file path: ")
            loadGrades(file_path, students)
        elif choice == 4:
            generateStudentReport(students)
        elif choice == 5:
            generateCourseReport(students)
        elif choice == 6:
            saveStudentFile('students.csv', students)
            print("Data saved. Exiting program.")
            break

if __name__ == "__main__":
    main()