/// Process user authentication and validate credentials
/// This function handles user login by checking the provided credentials
/// against the database and returns an authentication token if successful
pub fn authenticate_user(username: &str, password: &str) -> Result<String, AuthError> {
    // Implementation details
    Ok("token123".to_string())
}

/// Fetch user profile data from the database
/// Retrieves comprehensive user information including preferences and settings
/// for the specified user identifier
pub fn get_user_profile(user_id: u32) -> Result<UserProfile, DatabaseError> {
    // Implementation details
    Ok(UserProfile::default())
}

/// Calculate order total with tax and shipping
/// Computes the final price including all applicable taxes and shipping costs
/// based on the user's location and selected shipping method
pub fn calculate_order_total(items: &[Item], location: &str) -> f64 {
    // Implementation details
    42.0
}

/// Send notification email to user
/// Dispatches an email notification to the user's registered email address
/// with the specified subject and message content
pub fn send_email_notification(email: &str, subject: &str, body: &str) -> bool {
    // Implementation details
    true
}

// Dummy types for compilation
pub struct AuthError;
pub struct UserProfile;
impl Default for UserProfile {
    fn default() -> Self {
        UserProfile
    }
}
pub struct DatabaseError;
pub struct Item;
