bamboo-engine 2026.4.26

//! Sub-session spawn scheduler.
//!
//! Provides a background queue for spawning child sessions. Spawn is async
//! (tool returns immediately), but the UI can observe child progress via
//! events forwarded to the parent session stream.

use std::collections::HashMap;
use std::sync::Arc;
use std::time::Duration;

use chrono::Utc;
use tokio::sync::{broadcast, mpsc, RwLock};
use tokio_util::sync::CancellationToken;

use bamboo_agent_core::tools::ToolExecutor;
use bamboo_agent_core::{AgentEvent, Role, Session, SessionKind};

use crate::runtime::Agent;
use crate::runtime::ExecuteRequest;

use super::event_forwarder::create_event_forwarder;
use super::runner_lifecycle::{finalize_runner, try_reserve_runner};
use super::runner_state::AgentRunner;
use super::session_events::get_or_create_event_sender;

#[derive(Debug, Clone)]
pub struct SpawnJob {
    pub parent_session_id: String,
    pub child_session_id: String,
    pub model: String,
}

#[derive(Clone)]
pub struct SpawnContext {
    pub agent: Arc<Agent>,
    pub tools: Arc<dyn ToolExecutor>,
    pub sessions_cache: Arc<RwLock<HashMap<String, Session>>>,
    pub agent_runners: Arc<RwLock<HashMap<String, AgentRunner>>>,
    pub session_event_senders: Arc<RwLock<HashMap<String, broadcast::Sender<AgentEvent>>>>,
}

#[derive(Clone)]
pub struct SpawnScheduler {
    tx: mpsc::Sender<SpawnJob>,
}

impl SpawnScheduler {
    pub fn new(ctx: SpawnContext) -> Self {
        let (tx, mut rx) = mpsc::channel::<SpawnJob>(128);

        tokio::spawn(async move {
            while let Some(job) = rx.recv().await {
                if let Err(err) = run_spawn_job(ctx.clone(), job).await {
                    tracing::warn!("spawn job failed: {}", err);
                }
            }
        });

        Self { tx }
    }

    pub async fn enqueue(&self, job: SpawnJob) -> Result<(), String> {
        self.tx
            .send(job)
            .await
            .map_err(|_| "spawn scheduler is not running".to_string())
    }
}

async fn run_spawn_job(ctx: SpawnContext, job: SpawnJob) -> Result<(), String> {
    // Ensure both session event streams exist.
    let parent_tx =
        get_or_create_event_sender(&ctx.session_event_senders, &job.parent_session_id).await;
    let child_tx =
        get_or_create_event_sender(&ctx.session_event_senders, &job.child_session_id).await;

    let emit_error_completion = |error: String| {
        let _ = parent_tx.send(AgentEvent::SubSessionCompleted {
            parent_session_id: job.parent_session_id.clone(),
            child_session_id: job.child_session_id.clone(),
            status: "error".to_string(),
            error: Some(error.clone()),
        });
        error
    };

    // Load child session.
    let mut session = match ctx
        .agent
        .storage()
        .load_session(&job.child_session_id)
        .await
    {
        Ok(Some(s)) => s,
        Ok(None) => return Err(emit_error_completion("child session not found".to_string())),
        Err(e) => {
            return Err(emit_error_completion(format!(
                "failed to load child session: {e}"
            )))
        }
    };

    if session.kind != SessionKind::Child {
        return Err(emit_error_completion(
            "spawn job child session is not kind=child".to_string(),
        ));
    }

    // Ensure last message is user (otherwise nothing to do).
    let last_is_user = session
        .messages
        .last()
        .map(|m| matches!(m.role, Role::User))
        .unwrap_or(false);
    if !last_is_user {
        session
            .metadata
            .insert("last_run_status".to_string(), "skipped".to_string());
        session.metadata.insert(
            "last_run_error".to_string(),
            "No pending message to execute".to_string(),
        );
        let _ = ctx.agent.storage().save_session(&session).await;
        let _ = parent_tx.send(AgentEvent::SubSessionCompleted {
            parent_session_id: job.parent_session_id.clone(),
            child_session_id: job.child_session_id.clone(),
            status: "skipped".to_string(),
            error: Some("No pending message to execute".to_string()),
        });
        return Ok(());
    }

    // Persist a running marker early so list_sessions can reconstruct status.
    session
        .metadata
        .insert("last_run_status".to_string(), "running".to_string());
    session.metadata.remove("last_run_error");
    let _ = ctx.agent.storage().save_session(&session).await;

    // Insert runner status.
    let Some(cancel_token) =
        try_reserve_runner(&ctx.agent_runners, &job.child_session_id, &child_tx).await
    else {
        return Ok(());
    };

    // Forward ALL child events to parent.
    let forwarder_done = CancellationToken::new();
    {
        let mut rx = child_tx.subscribe();
        let parent_tx = parent_tx.clone();
        let job_clone = job.clone();
        let done = forwarder_done.clone();
        tokio::spawn(async move {
            loop {
                tokio::select! {
                    _ = done.cancelled() => break,
                    evt = rx.recv() => {
                        match evt {
                            Ok(event) => {
                                let _ = parent_tx.send(AgentEvent::SubSessionEvent {
                                    parent_session_id: job_clone.parent_session_id.clone(),
                                    child_session_id: job_clone.child_session_id.clone(),
                                    event: Box::new(event),
                                });
                            }
                            Err(broadcast::error::RecvError::Lagged(_)) => {
                                continue;
                            }
                            Err(_) => break,
                        }
                    }
                }
            }
        });
    }
    {
        let parent_tx = parent_tx.clone();
        let job_clone = job.clone();
        let done = forwarder_done.clone();
        tokio::spawn(async move {
            let mut ticker = tokio::time::interval(Duration::from_secs(5));
            loop {
                tokio::select! {
                    _ = done.cancelled() => break,
                    _ = ticker.tick() => {
                        let _ = parent_tx.send(AgentEvent::SubSessionHeartbeat {
                            parent_session_id: job_clone.parent_session_id.clone(),
                            child_session_id: job_clone.child_session_id.clone(),
                            timestamp: Utc::now(),
                        });
                    }
                }
            }
        });
    }

    // Create mpsc channel for agent loop → session events sender.
    let (mpsc_tx, _forwarder_handle) = create_event_forwarder(
        job.child_session_id.clone(),
        child_tx.clone(),
        ctx.agent_runners.clone(),
    );

    // Run child loop via unified spawn_session_execution.
    let model = job.model.clone();
    let session_id_clone = job.child_session_id.clone();
    let agent_runners_for_status = ctx.agent_runners.clone();
    let sessions_cache = ctx.sessions_cache.clone();
    let agent = ctx.agent.clone();
    let tools = ctx.tools.clone();
    let done = forwarder_done.clone();
    let parent_tx_for_done = parent_tx.clone();
    let parent_id_for_done = job.parent_session_id.clone();
    let child_id_for_done = job.child_session_id.clone();
    let session_event_senders = ctx.session_event_senders.clone();

    tokio::spawn(async move {
        session.model = model.clone();

        let result: crate::runtime::runner::Result<()> = agent
            .execute(
                &mut session,
                ExecuteRequest {
                    initial_message: String::new(), // handled by agent loop
                    event_tx: mpsc_tx,
                    cancel_token,
                    tools: Some(tools),
                    provider_override: None,
                    model: Some(model.clone()),
                    provider_name: None,
                    background_model: None,
                    background_model_provider: None,
                    reasoning_effort: None,
                    disabled_tools: None,
                    disabled_skill_ids: None,
                    selected_skill_ids: None,
                    selected_skill_mode: None,
                    image_fallback: None,
                },
            )
            .await;

        let (status, error) = match &result {
            Ok(_) => ("completed".to_string(), None),
            Err(e) if e.to_string().contains("cancelled") => {
                ("cancelled".to_string(), Some(e.to_string()))
            }
            Err(e) => ("error".to_string(), Some(e.to_string())),
        };

        finalize_runner(&agent_runners_for_status, &session_id_clone, &result).await;

        // Persist final session snapshot.
        session
            .metadata
            .insert("last_run_status".to_string(), status.clone());
        if let Some(err) = &error {
            session
                .metadata
                .insert("last_run_error".to_string(), err.clone());
        } else {
            session.metadata.remove("last_run_error");
        }
        let _ = agent.storage().save_session(&session).await;
        {
            let mut sessions = sessions_cache.write().await;
            sessions.insert(session_id_clone.clone(), session);
        }

        // Stop forwarding/heartbeats and emit terminal child status.
        done.cancel();
        let _ = parent_tx_for_done.send(AgentEvent::SubSessionCompleted {
            parent_session_id: parent_id_for_done,
            child_session_id: child_id_for_done,
            status,
            error,
        });

        // Allow dead code: session_event_senders keeps the sender alive during the task.
        drop(session_event_senders);
    });

    Ok(())
}