use serde::Deserialize; // Add `serde = { version = "1.0", features = ["derive"] }` and `serde_json = "1.0"` to Cargo.toml

#[derive(Debug, Deserialize)]
struct UserProfile {
    id: u32,
    username: String,
    // `Option<String>` safely represents data that might be missing or null from the API.
    // This prevents null pointer dereferences common in languages without explicit nullability.
    bio: Option<String>,
    last_login_ip: Option<String>,
}

fn process_user_profile(profile: UserProfile) {
    println!("
--- Processing User: {} (ID: {}) ---", profile.username, profile.id);

    // Method 1: Using a match statement for explicit handling of `Some` and `None` variants.
    match profile.bio {
        Some(bio_text) => println!("Bio: {}", bio_text),
        None => println!("Bio: Not provided."),
    }

    // Method 2: Using `if let` for concise handling of the `Some` variant.
    if let Some(ip) = profile.last_login_ip {
        println!("Last Login IP: {}", ip);
    } else {
        println!("Last Login IP: Unknown.");
    }

    // Method 3: Using `.map_or()` for default values or transformations.
    let bio_display = profile.bio.map_or("No bio available.".to_string(), |b| format!("\"{}\"", b));
    println!("Bio (concise): {}", bio_display);

    let ip_display = profile.last_login_ip.unwrap_or_else(|| "N/A".to_string());
    println!("Last Login IP (unwrap_or_else): {}", ip_display);

    // Attempting to directly unwrap a `None` value using `.unwrap()` would panic.
    // Rust forces you to explicitly handle the `None` case, preventing runtime errors.
    // Example (would panic if uncommented and `bio` is `None`):
    // let bio_content = profile.bio.unwrap();
}

fn main() {
    // Simulate a successful API response with all fields present.
    let json_full = r#"
        {
            "id": 101,
            "username": "alice_dev",
            "bio": "Rust developer and web enthusiast.",
            "last_login_ip": "192.168.1.100"
        }"#;
    let user_full: UserProfile = serde_json::from_str(json_full).unwrap();
    process_user_profile(user_full);

    // Simulate an API response where optional fields are missing.
    let json_partial = r#"
        {
            "id": 102,
            "username": "bob_tester"
        }"#;
    let user_partial: UserProfile = serde_json::from_str(json_partial).unwrap();
    process_user_profile(user_partial);

    // Simulate an API response where optional fields are explicitly null.
    let json_null = r#"
        {
            "id": 103,
            "username": "charlie_guest",
            "bio": null,
            "last_login_ip": null
        }"#;
    let user_null: UserProfile = serde_json::from_str(json_null).unwrap();
    process_user_profile(user_null);
}