def connect_db():
    conn = sqlite3.connect("school.db")
    return conn

def create_tables():
    conn = connect_db()
    cur = conn.cursor()

    cur.execute("""
        CREATE TABLE IF NOT EXISTS students (
            roll_no     INTEGER PRIMARY KEY,
            name        TEXT NOT NULL,
            class_name  TEXT,
            age         INTEGER,
            phone       TEXT
        )
    """)

    cur.execute("""
        CREATE TABLE IF NOT EXISTS attendance (
            id          INTEGER PRIMARY KEY AUTOINCREMENT,
            roll_no     INTEGER,
            date        TEXT,
            status      TEXT,
            FOREIGN KEY (roll_no) REFERENCES students (roll_no)
        )
    """)

    cur.execute("""
        CREATE TABLE IF NOT EXISTS grades (
            id          INTEGER PRIMARY KEY AUTOINCREMENT,
            roll_no     INTEGER,
            subject     TEXT,
            marks       INTEGER,
            FOREIGN KEY (roll_no) REFERENCES students (roll_no)
        )
    """)

    conn.commit()
    conn.close()