/// # WatcherAgent
///
/// **WatcherAgent** is a cross-platform system monitoring agent written in Rust.
///
/// ## Overview
/// This agent collects real-time hardware metrics (CPU, GPU, RAM, disk, network) and communicates with a backend server for registration, reporting, and remote control. It is designed for deployment in environments where automated monitoring and remote management of system resources is required.
///
/// ## Features
/// - **Hardware Metrics:** Collects CPU, GPU, RAM, disk, and network statistics using platform-specific APIs.
/// - **Docker Integration:** Detects and manages its own Docker container, supports image updates and container restarts.
/// - **Server Communication:** Registers with a backend server, sends periodic heartbeats, and reports metrics securely.
/// - **Remote Commands:** Listens for and executes commands from the backend (e.g., update image, restart container, stop agent).
///
/// ## Modules
/// - [`api`]: Handles HTTP communication with the backend server (registration, heartbeat, metrics, commands).
/// - [`hardware`]: Collects hardware metrics from the host system (CPU, GPU, RAM, disk, network).
/// - [`metrics`]: Orchestrates metric collection and reporting.
/// - [`models`]: Defines data structures for server communication and metrics.
/// - [`docker`]: Integrates with Docker for container management and agent lifecycle.
///
/// ## Usage
/// Run the agent with the backend server URL as an argument:
/// ```sh
/// watcheragent <server-url>
/// ```
///
/// The agent will register itself, start collecting metrics, and listen for remote commands.
pub mod api;
pub mod docker;
pub mod hardware;
pub mod metrics;
pub mod models;

use bollard::Docker;
use std::env;
use std::error::Error;
use std::sync::Arc;
use tokio::task::JoinHandle;

/// Awaits a spawned asynchronous task and flattens its nested `Result` type.
///
/// This utility is used to handle the result of a `tokio::spawn`ed task that itself returns a `Result`,
/// propagating any errors from both the task and its execution.
///
/// # Type Parameters
/// * `T` - The type returned by the task on success.
///
/// # Arguments
/// * `handle` - The `JoinHandle` of the spawned task.
///
/// # Returns
/// * `Result<T, Box<dyn Error + Send + Sync>>` - The result of the task, or an error if the task failed or panicked.
async fn flatten<T>(
    handle: JoinHandle<Result<T, Box<dyn Error + Send + Sync>>>,
) -> Result<T, Box<dyn Error + Send + Sync>> {
    match handle.await {
        Ok(Ok(result)) => Ok(result),
        Ok(Err(err)) => Err(err),
        Err(_err) => Err("handling failed".into()),
    }
}

/// Main entry point for the WatcherAgent application.
///
/// This function performs the following steps:
/// 1. Initializes the Docker client for container management.
/// 2. Detects the current running image version.
/// 3. Parses command-line arguments to obtain the backend server URL.
/// 4. Registers the agent with the backend server and retrieves its server ID and IP address.
/// 5. Spawns background tasks for:
///     - Listening for remote commands from the server
///     - Sending periodic heartbeat signals
///     - Collecting and reporting hardware metrics
/// 6. Waits for all background tasks to complete and logs their results.
///
/// # Arguments
/// * `server-url` - The URL of the backend server to register and report metrics to (passed as a command-line argument).
///
/// # Errors
/// Returns an error if registration or any background task fails, or if required arguments are missing.
#[tokio::main]
async fn main() -> Result<(), Box<dyn Error + Send + Sync>> {
    // Parse command-line arguments
    let args: Vec<String> = env::args().collect();
    if args.len() < 2 {
        eprintln!("Usage: {} <server-url>", args[0]);
        return Err("Missing server URL argument".into());
    }
    let server_url = &args[1];
    println!("Server URL: {:?}", server_url);

    // Registration with backend server
    let (server_id, ip) = match api::register_with_server(&server_url).await {
        Ok((id, ip)) => {
            println!("Registered with server. ID: {}, IP: {}", id, ip);
            (id, ip)
        }
        Err(e) => {
            eprintln!("Fehler bei der Registrierung am Server: {e}");
            return Err(e);
        }
    };

    // Initialize Docker (optional - agent can run without Docker)
    let docker_manager = docker::DockerManager::new_optional();

    // Get current image version
    let client_version = if let Some(ref docker_manager) = docker_manager {
        docker_manager.get_client_version().await
    } else {
        "unknown".to_string()
    };
    println!("Client Version: {}", client_version);

    // Prepare Docker registration DTO
    let container_dto = if let Some(ref docker_manager) = docker_manager {
        docker_manager.create_registration_dto().await?
    } else {
        models::DockerRegistrationDto {
            server_id: 0,
            //container_count: 0, --- IGNORE ---
            containers: "[]".to_string(),
        }
    };
    let _ =
        api::broadcast_docker_containers(server_url, server_id, &mut container_dto.clone()).await?;

    // Start background tasks
    // Start server listening for commands (only if Docker is available)
    let listening_handle = if let Some(ref docker_manager) = docker_manager {
        tokio::spawn({
            let docker = docker_manager.docker.clone();
            let server_url = server_url.to_string();
            async move { api::listening_to_server(&docker, &server_url).await }
        })
    } else {
        println!("Docker not available, skipping server command listener.");
        tokio::spawn(async { Ok(()) }) // Dummy task
    };

    // Start heartbeat in background
    let heartbeat_handle = tokio::spawn({
        let ip = ip.clone();
        let server_url = server_url.to_string();
        async move { api::heartbeat_loop(&server_url, &ip).await }
    });

    // Main metrics loop
    println!("Starting metrics collection...");
    let metrics_handle = tokio::spawn({
        let ip = ip.clone();
        let server_url = server_url.to_string();
        let docker_manager = docker_manager.as_ref().cloned().unwrap();
        async move {
            let mut collector = metrics::Collector::new(server_id, ip, docker_manager);
            collector.run(&server_url).await
        }
    });

    // Wait for all tasks and check for errors
    let (listening_result, heartbeat_result, metrics_result) = tokio::try_join!(
        flatten(listening_handle),
        flatten(heartbeat_handle),
        flatten(metrics_handle)
    )?;

    println!(
        "All tasks completed: listening={:?}, heartbeat={:?}, metrics={:?}",
        listening_result, heartbeat_result, metrics_result
    );

    println!("All tasks completed successfully.");

    Ok(())
}