supercode-harness 0.4.3

//! Revisioned session-list subscriptions for latency-sensitive frontends.
//!
//! Native filesystem events are treated as invalidation hints, never as the
//! session record itself. Each hint causes a bounded re-read of the affected
//! Claude Code or Codex transcript; a slow periodic catalog reconciliation
//! repairs dropped/coalesced platform events and fills a page after removals.

use std::collections::{BTreeMap, BTreeSet};
use std::fs;
use std::path::{Path, PathBuf};
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::{mpsc, Arc};
use std::time::{Duration, Instant};

use notify::{Event, RecommendedWatcher, RecursiveMode, Watcher};
use serde::Serialize;

use crate::{
    DiscoveryQuery, HarnessCatalog, HarnessId, SessionDescriptor, SessionLocator, StorageLocator,
};

const RECONCILE_INTERVAL: Duration = Duration::from_secs(60);
const MAX_SUBSCRIPTION_ROWS: usize = 2_048;
const INVALIDATION_QUEUE_CAPACITY: usize = 1_024;

/// Stable public identity for a session-index change. Persistence paths remain
/// inside the trusted host and are sent only as part of complete descriptors.
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Serialize)]
pub struct SessionIndexKey {
    /// Owning harness id.
    pub harness: String,
    /// Harness-native durable session id.
    pub session_id: String,
}

impl SessionIndexKey {
    fn from_locator(locator: &SessionLocator) -> Self {
        Self {
            harness: locator.harness.as_str().to_string(),
            session_id: locator.session_id.clone(),
        }
    }
}

/// One complete replacement in a revisioned index delta.
#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
#[serde(tag = "kind", rename_all = "snake_case")]
pub enum SessionIndexChange {
    /// A session entered the bounded result page.
    Added {
        /// Complete current descriptor.
        descriptor: SessionDescriptor,
    },
    /// A visible session's descriptor changed.
    Updated {
        /// Complete replacement descriptor.
        descriptor: SessionDescriptor,
    },
    /// A session disappeared from the bounded result page.
    Removed {
        /// Stable identity of the removed descriptor.
        key: SessionIndexKey,
    },
}

/// One subscription poll result. Revisions start at one for the initial
/// snapshot and increase by exactly one for each non-empty delta batch.
#[derive(Debug, Clone, PartialEq, Eq, Serialize)]
pub struct SessionIndexDelta {
    /// Monotonic subscription-local revision.
    pub revision: u64,
    /// Complete replacement changes in deterministic identity order.
    pub changes: Vec<SessionIndexChange>,
}

/// Filesystem-backed index subscription. Dropping it drops the platform
/// watcher and callback channel, so unsubscribe has deterministic cleanup.
pub(crate) struct SessionIndexSubscription {
    query: DiscoveryQuery,
    current: BTreeMap<SessionIndexKey, SessionDescriptor>,
    revision: u64,
    receiver: mpsc::Receiver<notify::Result<Event>>,
    overflowed: Arc<AtomicBool>,
    _watcher: RecommendedWatcher,
    last_reconcile: Instant,
}

impl SessionIndexSubscription {
    pub(crate) fn homes(&self) -> &crate::HarnessHomes {
        &self.query.homes
    }

    pub(crate) fn open(
        mut query: DiscoveryQuery,
    ) -> Result<(Self, Vec<SessionDescriptor>), String> {
        validate_query(&query)?;
        query.cursor = None;
        query.limit = Some(query.limit.unwrap_or(100));

        let initial = HarnessCatalog::new()
            .discover_page(&query)
            .map_err(|error| error.to_string())?
            .sessions;
        let current = descriptor_map(initial.iter().cloned());
        let (sender, receiver) = mpsc::sync_channel(INVALIDATION_QUEUE_CAPACITY);
        let overflowed = Arc::new(AtomicBool::new(false));
        let callback_overflowed = Arc::clone(&overflowed);
        let mut watcher = notify::recommended_watcher(move |event| {
            if sender.try_send(event).is_err() {
                callback_overflowed.store(true, Ordering::Release);
            }
        })
        .map_err(|error| error.to_string())?;
        for root in watch_roots(&query) {
            if let Some(watched) = existing_watch_root(&root) {
                watcher
                    .watch(&watched, RecursiveMode::Recursive)
                    .map_err(|error| format!("cannot watch {}: {error}", watched.display()))?;
            }
        }

        Ok((
            Self {
                query,
                current,
                revision: 1,
                receiver,
                overflowed,
                _watcher: watcher,
                last_reconcile: Instant::now(),
            },
            initial,
        ))
    }

    /// Drain and coalesce native invalidations once. No events means no I/O
    /// until the minute-scale recovery reconciliation becomes due.
    pub(crate) fn poll(&mut self) -> Result<Option<SessionIndexDelta>, String> {
        let mut paths = BTreeSet::new();
        let mut reconcile = self.overflowed.swap(false, Ordering::AcqRel);
        while let Ok(event) = self.receiver.try_recv() {
            match event {
                Ok(event) => paths.extend(event.paths),
                Err(_) => reconcile = true,
            }
        }
        if self.last_reconcile.elapsed() >= RECONCILE_INTERVAL {
            reconcile = true;
        }
        if paths.is_empty() && !reconcile {
            return Ok(None);
        }

        let before = self.current.clone();
        if reconcile {
            self.reconcile()?;
        } else {
            let mut needs_fill = false;
            for path in paths {
                needs_fill |= self.refresh_path(&path)?;
            }
            if needs_fill {
                self.reconcile()?;
            } else {
                self.retain_page_limit();
            }
        }
        let changes = diff_descriptors(&before, &self.current);
        if changes.is_empty() {
            return Ok(None);
        }
        self.revision = self.revision.saturating_add(1);
        Ok(Some(SessionIndexDelta {
            revision: self.revision,
            changes,
        }))
    }

    fn reconcile(&mut self) -> Result<(), String> {
        // A temporarily unreadable native store must not turn the service's
        // 250 ms event pump into a hot full-catalog retry loop.
        self.last_reconcile = Instant::now();
        let sessions = HarnessCatalog::new()
            .discover_page(&self.query)
            .map_err(|error| error.to_string())?
            .sessions;
        self.current = descriptor_map(sessions);
        Ok(())
    }

    /// Returns true when a visible row disappeared and a complete page fill is
    /// required. Unknown/temporary paths are harmless invalidations.
    fn refresh_path(&mut self, path: &Path) -> Result<bool, String> {
        if path.extension().and_then(|value| value.to_str()) != Some("jsonl") {
            return Ok(false);
        }
        // macOS FSEvents reports canonical `/private/var/...` paths even when
        // the subscribed root was supplied through the `/var` symlink.
        let event_path = normalized_path(path);
        let known = self.current.iter().find_map(|(key, descriptor)| {
            (normalized_path(descriptor.locator.storage.path()) == event_path)
                .then(|| (key.clone(), descriptor.clone()))
        });
        let locator = match &known {
            Some((_, descriptor)) => descriptor.locator.clone(),
            None => match locator_for_path(&self.query, &event_path) {
                Some(locator) => locator,
                None => return Ok(false),
            },
        };
        let refreshed = HarnessCatalog::new()
            .refresh_file_descriptor(
                &locator,
                self.query.workspace.as_deref(),
                self.query.include_topic_candidates,
            )
            .map_err(|error| error.to_string())?;
        match (known, refreshed) {
            (Some((old_key, _)), None) => {
                self.current.remove(&old_key);
                Ok(true)
            }
            (Some((old_key, _)), Some(descriptor)) => {
                self.current.remove(&old_key);
                self.current.insert(
                    SessionIndexKey::from_locator(&descriptor.locator),
                    descriptor,
                );
                Ok(false)
            }
            (None, Some(descriptor)) => {
                self.current.insert(
                    SessionIndexKey::from_locator(&descriptor.locator),
                    descriptor,
                );
                Ok(false)
            }
            (None, None) => Ok(false),
        }
    }

    fn retain_page_limit(&mut self) {
        let limit = self.query.limit.unwrap_or(100);
        let mut sessions = self.current.values().cloned().collect::<Vec<_>>();
        sort_descriptors(&mut sessions);
        sessions.truncate(limit);
        self.current = descriptor_map(sessions);
    }
}

pub(crate) fn validate_query(query: &DiscoveryQuery) -> Result<(), String> {
    if query.cursor.is_some() {
        return Err("sessions.index.subscribe does not accept a cursor".into());
    }
    let limit = query.limit.unwrap_or(100);
    if limit == 0 || limit > MAX_SUBSCRIPTION_ROWS {
        return Err(format!(
            "sessions.index.subscribe limit must be between 1 and {MAX_SUBSCRIPTION_ROWS}"
        ));
    }
    if query.harnesses.is_empty()
        || query
            .harnesses
            .iter()
            .any(|harness| !matches!(harness.as_str(), HarnessId::CLAUDE_CODE | HarnessId::CODEX))
    {
        return Err(
            "sessions.index.subscribe currently requires explicit claude-code and/or codex harnesses"
                .into(),
        );
    }
    Ok(())
}

fn watch_roots(query: &DiscoveryQuery) -> BTreeSet<PathBuf> {
    query
        .harnesses
        .iter()
        .filter_map(|harness| match harness.as_str() {
            HarnessId::CLAUDE_CODE => Some(query.homes.claude_code.clone()),
            HarnessId::CODEX => Some(query.homes.codex.clone()),
            _ => None,
        })
        .collect()
}

fn existing_watch_root(root: &Path) -> Option<PathBuf> {
    if root.is_dir() {
        return Some(root.to_path_buf());
    }
    // Watching an entire home directory because a harness has never created
    // its store is disproportionate. One parent level catches the ordinary
    // first-run mkdir; the recovery reconciliation handles rarer deeper gaps.
    root.parent()
        .filter(|parent| parent.is_dir())
        .map(Path::to_path_buf)
}

fn locator_for_path(query: &DiscoveryQuery, path: &Path) -> Option<SessionLocator> {
    let claude_root = normalized_path(&query.homes.claude_code);
    let codex_root = normalized_path(&query.homes.codex);
    let harness = if query
        .harnesses
        .iter()
        .any(|harness| harness.as_str() == HarnessId::CLAUDE_CODE)
        && path.starts_with(&claude_root)
    {
        if path
            .components()
            .any(|component| component.as_os_str() == "subagents")
        {
            return None;
        }
        HarnessId::CLAUDE_CODE
    } else if query
        .harnesses
        .iter()
        .any(|harness| harness.as_str() == HarnessId::CODEX)
        && path.starts_with(&codex_root)
    {
        HarnessId::CODEX
    } else {
        return None;
    };
    Some(SessionLocator {
        harness: HarnessId::new(harness),
        session_id: path
            .file_stem()
            .and_then(|value| value.to_str())
            .unwrap_or("unknown")
            .to_string(),
        storage: StorageLocator::File {
            path: path.to_path_buf(),
        },
    })
}

fn normalized_path(path: &Path) -> PathBuf {
    fs::canonicalize(path).unwrap_or_else(|_| path.to_path_buf())
}

fn descriptor_map(
    descriptors: impl IntoIterator<Item = SessionDescriptor>,
) -> BTreeMap<SessionIndexKey, SessionDescriptor> {
    descriptors
        .into_iter()
        .map(|descriptor| {
            (
                SessionIndexKey::from_locator(&descriptor.locator),
                descriptor,
            )
        })
        .collect()
}

fn sort_descriptors(descriptors: &mut [SessionDescriptor]) {
    descriptors.sort_by(|left, right| {
        right
            .updated_at_ms
            .cmp(&left.updated_at_ms)
            .then_with(|| left.locator.harness.cmp(&right.locator.harness))
            .then_with(|| left.locator.session_id.cmp(&right.locator.session_id))
    });
}

fn diff_descriptors(
    before: &BTreeMap<SessionIndexKey, SessionDescriptor>,
    after: &BTreeMap<SessionIndexKey, SessionDescriptor>,
) -> Vec<SessionIndexChange> {
    let mut changes = Vec::new();
    for (key, descriptor) in after {
        match before.get(key) {
            None => changes.push(SessionIndexChange::Added {
                descriptor: descriptor.clone(),
            }),
            Some(previous) if previous != descriptor => {
                changes.push(SessionIndexChange::Updated {
                    descriptor: descriptor.clone(),
                });
            }
            Some(_) => {}
        }
    }
    for key in before.keys() {
        if !after.contains_key(key) {
            changes.push(SessionIndexChange::Removed { key: key.clone() });
        }
    }
    changes
}

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

    fn descriptor(id: &str, updated_at_ms: u64) -> SessionDescriptor {
        SessionDescriptor {
            locator: SessionLocator {
                harness: HarnessId::new(HarnessId::CODEX),
                session_id: id.into(),
                storage: StorageLocator::File {
                    path: PathBuf::from(format!("/{id}.jsonl")),
                },
            },
            cwd: None,
            title: None,
            preview_candidates: Vec::new(),
            latest_message_candidates: Vec::new(),
            updated_at_ms: Some(updated_at_ms),
            message_count: None,
            model: None,
        }
    }

    #[test]
    fn index_delta_is_a_complete_deterministic_replacement_set() {
        let before = descriptor_map([descriptor("removed", 1), descriptor("updated", 2)]);
        let after = descriptor_map([descriptor("updated", 3), descriptor("added", 4)]);
        let changes = diff_descriptors(&before, &after);
        assert!(matches!(
            &changes[0],
            SessionIndexChange::Added { descriptor } if descriptor.locator.session_id == "added"
        ));
        assert!(matches!(
            &changes[1],
            SessionIndexChange::Updated { descriptor } if descriptor.locator.session_id == "updated"
        ));
        assert!(matches!(
            &changes[2],
            SessionIndexChange::Removed { key } if key.session_id == "removed"
        ));
    }
}