mecha10-behavior-runtime 0.7.0

//! Action node that hands control to the `instance-track` node while a target is live, and cedes
//! control back the moment there isn't one.
//!
//! For a `Watch`-wrapped instance-track interrupt layer to correctly claim control only while a
//! target is live and cede immediately when idle, *both* `InstanceTrackTaskNode` and
//! `SetInstanceTrackTargetNode` must independently resolve to `NodeStatus::Failure` when there's
//! no live target and `NodeStatus::Running` while there is one. Critically, **neither must ever
//! return `NodeStatus::Success`** for the "task complete, hand control back" case (the old
//! behavior here) - here's why:
//!
//! If the hand-back signal were `Success`, the `Watch` layer's aggregate status for that tick
//! would be `Success` too (`RequireOne`: any child succeeding wins), which `SubsumptionNode`
//! treats as a winning/claiming status (`Success | Running => return`) exactly like `Running` -
//! so the *whole tree's* tick for that cycle would resolve to `Success`, which the top-level
//! executor treats as "the tree finished" and resets *everything*, including the lower-priority
//! main layer (e.g. `patrol-simple`'s `Sequence`), wiping its progress and restarting from the
//! beginning instead of resuming where it was.
//!
//! Using `Failure` instead avoids this entirely: when the instance-track layer converges to
//! `Failure` that tick, `SubsumptionNode` immediately falls through *within that same tick* and
//! ticks the lower-priority layer right then - if that layer is `Running` (the normal case, e.g.
//! mid-patrol), `SubsumptionNode`'s own tick for that cycle returns `Running`, which the executor
//! does *not* reset on. The main layer's progress is therefore preserved with zero wasted ticks.
//!
//! To make that convergence happen on the *same* tick the underlying node gives up (rather than
//! racing a separate `clear` request), this node subscribes to the same target-request topic
//! `SetInstanceTrackTargetNode` does and tracks `has_target` locally, additionally forcing
//! `has_target = false` the instant a `task_complete` message arrives.

use crate::actions::set_instance_track_target::{default_request_topic, InstanceTrackTargetRequest};
use crate::{BehaviorNode, Context, NodeStatus};
use async_trait::async_trait;
use mecha10_core::Receiver;
use serde_json::Value;

const INSTANCE_TRACK_CAPABILITY: &str = "instance-track";

const TASK_COMPLETE_TOPIC: &str = "/instance-track/task_complete";

pub struct InstanceTrackTaskNode {
    complete_receiver: Option<Receiver<Value>>,
    target_receiver: Option<Receiver<Value>>,
    request_topic: String,
    has_target: bool,
}

impl std::fmt::Debug for InstanceTrackTaskNode {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("InstanceTrackTaskNode")
            .field("complete_subscribed", &self.complete_receiver.is_some())
            .field("target_subscribed", &self.target_receiver.is_some())
            .field("has_target", &self.has_target)
            .finish()
    }
}

impl InstanceTrackTaskNode {
    /// Construct a node. `_config` is ignored - this node takes none.
    pub fn from_json(_config: Value) -> anyhow::Result<Self> {
        Ok(Self {
            complete_receiver: None,
            target_receiver: None,
            request_topic: default_request_topic(),
            has_target: false,
        })
    }

    /// Construct a node with already-connected receivers, bypassing live subscription.
    ///
    /// Used by unit tests to exercise convergence without a real `Context`/Redis.
    #[cfg(test)]
    fn with_receivers(complete_receiver: Receiver<Value>, target_receiver: Receiver<Value>) -> Self {
        Self {
            complete_receiver: Some(complete_receiver),
            target_receiver: Some(target_receiver),
            request_topic: default_request_topic(),
            has_target: false,
        }
    }

    /// Drains every pending target request, updating `has_target` from the last one seen (if
    /// any) - mirrors `SetInstanceTrackTargetNode::poll_latest_request`'s "only the most recent
    /// request matters" semantics.
    fn poll_target(&mut self) {
        let Some(receiver) = self.target_receiver.as_mut() else {
            return;
        };

        let mut latest = None;
        while let Ok(value) = receiver.try_recv() {
            match serde_json::from_value::<InstanceTrackTargetRequest>(value) {
                Ok(request) => latest = Some(request.bbox.is_some()),
                Err(e) => tracing::warn!("InstanceTrackTaskNode: dropping malformed target request: {}", e),
            }
        }

        if let Some(has_target) = latest {
            self.has_target = has_target;
        }
    }

    /// Drain any pending completion messages - arrival of any message at all is the whole
    /// signal, same as `RlTaskNode::poll_complete`. Proactively clears `has_target` so this
    /// node and `SetInstanceTrackTargetNode` converge to "idle" on the same tick the underlying
    /// `instance-track` node gives up, rather than waiting for a separate `clear` request.
    fn poll_complete(&mut self) {
        let Some(receiver) = self.complete_receiver.as_mut() else {
            return;
        };

        if receiver.try_recv().is_ok() {
            self.has_target = false;
        }
    }
}

#[async_trait]
impl BehaviorNode for InstanceTrackTaskNode {
    async fn tick(&mut self, ctx: &Context) -> anyhow::Result<NodeStatus> {
        if self.complete_receiver.is_none() {
            self.complete_receiver = Some(ctx.subscribe_raw::<Value>(TASK_COMPLETE_TOPIC).await?);
        }
        if self.target_receiver.is_none() {
            self.target_receiver = Some(ctx.subscribe_raw::<Value>(&self.request_topic).await?);
        }

        self.poll_target();
        self.poll_complete();

        // `Failure` (never `Success`) when idle - see module doc for why.
        Ok(if self.has_target {
            NodeStatus::Running
        } else {
            NodeStatus::Failure
        })
    }

    fn name(&self) -> &str {
        "instance_track_task"
    }

    fn active_capability(&self) -> Option<&str> {
        Some(INSTANCE_TRACK_CAPABILITY)
    }

    fn reset_self(&mut self) {
        self.has_target = false;
    }
}

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

    fn node_with_channels() -> (
        InstanceTrackTaskNode,
        mpsc::UnboundedSender<Value>,
        mpsc::UnboundedSender<Value>,
    ) {
        let (complete_tx, complete_rx) = mpsc::unbounded_channel();
        let (target_tx, target_rx) = mpsc::unbounded_channel();
        (
            InstanceTrackTaskNode::with_receivers(Receiver::from(complete_rx), Receiver::from(target_rx)),
            complete_tx,
            target_tx,
        )
    }

    #[test]
    fn always_declares_the_instance_track_capability() {
        let (node, _complete_tx, _target_tx) = node_with_channels();
        assert_eq!(node.active_capability(), Some("instance-track"));
    }

    #[test]
    fn no_target_ever_set_stays_without_a_target() {
        let (mut node, _complete_tx, _target_tx) = node_with_channels();
        node.poll_target();
        node.poll_complete();
        assert!(!node.has_target);
    }

    #[test]
    fn a_live_target_request_sets_has_target() {
        let (mut node, _complete_tx, target_tx) = node_with_channels();
        target_tx
            .send(serde_json::json!({ "bbox": { "x": 0.1, "y": 0.2, "width": 0.3, "height": 0.4 } }))
            .unwrap();

        node.poll_target();

        assert!(node.has_target);
    }

    #[test]
    fn a_clear_request_unsets_has_target_even_with_no_task_complete() {
        let (mut node, _complete_tx, target_tx) = node_with_channels();
        target_tx
            .send(serde_json::json!({ "bbox": { "x": 0.1, "y": 0.2, "width": 0.3, "height": 0.4 } }))
            .unwrap();
        node.poll_target();
        assert!(node.has_target);

        target_tx.send(serde_json::json!({ "bbox": null })).unwrap();
        node.poll_target();

        assert!(!node.has_target);
    }

    #[test]
    fn task_complete_unsets_has_target_on_the_very_next_poll() {
        let (mut node, complete_tx, target_tx) = node_with_channels();
        target_tx
            .send(serde_json::json!({ "bbox": { "x": 0.1, "y": 0.2, "width": 0.3, "height": 0.4 } }))
            .unwrap();
        node.poll_target();
        assert!(node.has_target);

        complete_tx.send(serde_json::json!({})).unwrap();
        node.poll_complete();

        assert!(
            !node.has_target,
            "task_complete must converge has_target to false without waiting for a separate clear request"
        );
    }

    #[test]
    fn reset_self_clears_has_target_for_a_later_pass() {
        let (mut node, _complete_tx, target_tx) = node_with_channels();
        target_tx
            .send(serde_json::json!({ "bbox": { "x": 0.1, "y": 0.2, "width": 0.3, "height": 0.4 } }))
            .unwrap();
        node.poll_target();
        assert!(node.has_target);

        node.reset_self();

        assert!(!node.has_target);
    }

    #[test]
    fn from_json_ignores_any_input() {
        assert!(InstanceTrackTaskNode::from_json(Value::Null).is_ok());
        assert!(InstanceTrackTaskNode::from_json(serde_json::json!({"unexpected": "field"})).is_ok());
    }
}