use std::sync::atomic::{AtomicBool, Ordering};

#[cfg(feature = "client-runtime")]
use irtt_client::managed::{ManagedEvent, ManagedEventSubscription, ManagedEventTryRecvError};

#[cfg(feature = "client-runtime")]
pub(crate) const MANAGED_EVENT_WORK_BUDGET: usize = 128;

#[cfg(feature = "client-runtime")]
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub(crate) enum ManagedDrainState {
    Empty,
    Closed,
    BudgetExhausted,
}

/// Drain a bounded amount of lossy presentation work before returning to the
/// frontend control loop.
#[cfg(feature = "client-runtime")]
pub(crate) fn drain_managed_events<E>(
    events: &mut ManagedEventSubscription,
    dropped_events: &mut u64,
    mut process: impl FnMut(ManagedEvent) -> Result<(), E>,
) -> Result<ManagedDrainState, E> {
    for _ in 0..MANAGED_EVENT_WORK_BUDGET {
        match events.try_recv() {
            Ok(event) => process(event)?,
            Err(ManagedEventTryRecvError::Lagged(count)) => {
                *dropped_events = dropped_events.saturating_add(count);
            }
            Err(ManagedEventTryRecvError::Empty) => return Ok(ManagedDrainState::Empty),
            Err(ManagedEventTryRecvError::Closed) => return Ok(ManagedDrainState::Closed),
        }
    }
    Ok(ManagedDrainState::BudgetExhausted)
}

pub fn is_shutdown_requested(shutdown_requested: &AtomicBool) -> bool {
    shutdown_requested.load(Ordering::Relaxed)
}

pub fn should_print_final_summary(continuous: bool, interrupted: bool) -> bool {
    !continuous || interrupted
}

pub fn peer_close_run_error(
    continuous: bool,
    interrupted: bool,
    peer_closed_target_outcomes: u64,
) -> Option<String> {
    if !continuous || interrupted || peer_closed_target_outcomes == 0 {
        return None;
    }

    let sessions = if peer_closed_target_outcomes == 1 {
        "target session"
    } else {
        "target sessions"
    };
    Some(format!(
        "continuous run ended because of peer closure ({peer_closed_target_outcomes} {sessions})"
    ))
}

pub fn request_managed_stop_for_peer_close(
    continuous: bool,
    interrupted: bool,
    peer_closed_target_outcomes: u64,
    stop_requested: &mut bool,
) -> bool {
    if !continuous || interrupted || peer_closed_target_outcomes == 0 {
        return false;
    }
    request_managed_stop_once(stop_requested)
}

pub fn request_managed_stop_once(stop_requested: &mut bool) -> bool {
    if *stop_requested {
        return false;
    }
    *stop_requested = true;
    true
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn peer_close_run_error_is_run_mode_and_interruption_aware() {
        assert_eq!(peer_close_run_error(false, false, 1), None);
        assert_eq!(peer_close_run_error(true, false, 0), None);
        assert_eq!(peer_close_run_error(true, true, 1), None);
        assert_eq!(
            peer_close_run_error(true, false, 1).as_deref(),
            Some("continuous run ended because of peer closure (1 target session)")
        );
        assert_eq!(
            peer_close_run_error(true, false, 3).as_deref(),
            Some("continuous run ended because of peer closure (3 target sessions)")
        );
    }

    #[test]
    fn grouped_peer_close_stop_policy_is_run_mode_and_one_shot() {
        let mut stop_requested = false;
        assert!(!request_managed_stop_for_peer_close(
            false,
            false,
            1,
            &mut stop_requested,
        ));
        assert!(!request_managed_stop_for_peer_close(
            true,
            true,
            1,
            &mut stop_requested,
        ));
        assert!(!request_managed_stop_for_peer_close(
            true,
            false,
            0,
            &mut stop_requested,
        ));
        assert!(!stop_requested);

        assert!(request_managed_stop_for_peer_close(
            true,
            false,
            1,
            &mut stop_requested,
        ));
        assert!(stop_requested);
        assert!(!request_managed_stop_for_peer_close(
            true,
            false,
            1,
            &mut stop_requested,
        ));
    }
}