use futures::future::join_all;
use tokio::time::{sleep, Duration};

async fn download_file(url: &str) -> String {
    println!("Downloading {}...", url);
    // Simulate network latency
    sleep(Duration::from_millis(500)).await;
    format!("Content of {}", url)
}

#[tokio::main]
async fn main() {
    let urls = vec![
        "https://example.com/file1",
        "https://example.com/file2",
        "https://example.com/file3",
    ];

    println!("Starting downloads...");
    let start = std::time::Instant::now();

    // Create a vector of Futures
    // Note: This does NOT start the tasks yet if we just map them.
    // However, because we are calling an async fn, the futures are created.
    // To run them concurrently, we need to drive them all at once.
    let futures: Vec<_> = urls.into_iter()
                              .map(|url| download_file(url))
                              .collect();

    // join_all takes a collection of futures and returns a single future
    // that completes when ALL of them are complete.
    let results = join_all(futures).await;

    let duration = start.elapsed();
    println!("Downloaded {} files in {:?}", results.len(), duration);
    
    for res in results {
        println!(" - {}", res);
    }
}