//! This example demonstrates how to implement a clean shutdown
//! of a subsystem, through the example of a countdown that
//! gets cancelled on shutdown.
//!
//! There are two options to cancel tasks on shutdown:
//!   - with [tokio::select]
//!   - with [FutureExt::cancel_on_shutdown()]
//!
//! In this case we go with `cancel_on_shutdown()`, but `tokio::select` would be equally viable.

use miette::Result;
use tokio::time::{sleep, Duration};
use tokio_graceful_shutdown::{
    errors::CancelledByShutdown, FutureExt, SubsystemBuilder, SubsystemHandle, Toplevel,
};

struct CountdownSubsystem {}
impl CountdownSubsystem {
    fn new() -> Self {
        Self {}
    }

    async fn countdown(&self) {
        for i in (1..10).rev() {
            tracing::info!("Countdown: {}", i);
            sleep(Duration::from_millis(1000)).await;
        }
    }

    async fn run(self, subsys: SubsystemHandle) -> Result<()> {
        tracing::info!("Starting countdown ...");

        match self.countdown().cancel_on_shutdown(&subsys).await {
            Ok(()) => {
                tracing::info!("Countdown finished.");
            }
            Err(CancelledByShutdown) => {
                tracing::info!("Countdown cancelled.");
            }
        }

        Ok(())
    }
}

#[tokio::main]
async fn main() -> Result<()> {
    // Init logging
    tracing_subscriber::fmt()
        .with_max_level(tracing::Level::TRACE)
        .init();

    // Setup and execute subsystem tree
    Toplevel::new(|s| async move {
        s.start(SubsystemBuilder::new("Countdown", |h| {
            CountdownSubsystem::new().run(h)
        }));
    })
    .catch_signals()
    .handle_shutdown_requests(Duration::from_millis(1000))
    .await
    .map_err(Into::into)
}