use tokio::sync::watch;

/// Cooperative cancellation token for the copy loop and bounded I/O.
///
/// Cancel wakes waiters so in-flight operations bounded by
/// [`crate::copy_stream`] can return without waiting for their full
/// no-progress timeout.
///
/// A receiver is retained so `watch::Sender::send` always has a live
/// subscriber and the cancelled flag is stored.
#[derive(Clone, Debug)]
pub struct CancelToken {
    tx: watch::Sender<bool>,
    rx: watch::Receiver<bool>,
}

impl Default for CancelToken {
    fn default() -> Self {
        Self::new()
    }
}

impl CancelToken {
    #[must_use]
    pub fn new() -> Self {
        let (tx, rx) = watch::channel(false);
        Self { tx, rx }
    }

    pub fn cancel(&self) {
        let _ = self.tx.send(true);
    }

    #[must_use]
    pub fn is_cancelled(&self) -> bool {
        *self.rx.borrow()
    }

    /// Completes when [`Self::cancel`] has been called.
    pub async fn cancelled(&self) {
        let mut rx = self.rx.clone();
        if *rx.borrow_and_update() {
            return;
        }
        while rx.changed().await.is_ok() {
            if *rx.borrow_and_update() {
                return;
            }
        }
    }
}