sqlitegraph 2.2.3

//! SQLite backend implementation for GraphBackend trait.
//!
//! This module contains the SqliteGraphBackend implementation that wraps
//! SqliteGraph and provides the concrete implementation of all GraphBackend methods.

use parking_lot::RwLock;
use rusqlite::params;

use crate::{
    SqliteGraphError,
    backend::sqlite::types::{BackendDirection, EdgeSpec, NeighborQuery, NodeSpec},
    backend::{PubSubEvent, SubscriptionFilter},
    bfs::{bfs_neighbors, shortest_path},
    graph::{GraphEdge, GraphEntity, SqliteGraph},
    multi_hop,
    pattern::{self, PatternMatch, PatternQuery},
};

/// Simple in-memory publisher for SQLite backend pub/sub
///
/// Similar to V3's Publisher but simplified for SQLite backend use
struct Publisher {
    subscribers: RwLock<
        Vec<(
            u64,
            std::sync::mpsc::Sender<PubSubEvent>,
            SubscriptionFilter,
        )>,
    >,
    next_id: std::sync::atomic::AtomicU64,
}

impl Publisher {
    fn new() -> Self {
        Self {
            subscribers: RwLock::new(Vec::new()),
            next_id: std::sync::atomic::AtomicU64::new(1),
        }
    }

    fn subscribe(
        &self,
        filter: SubscriptionFilter,
    ) -> (u64, std::sync::mpsc::Receiver<PubSubEvent>) {
        let id = self
            .next_id
            .fetch_add(1, std::sync::atomic::Ordering::SeqCst);
        let (tx, rx) = std::sync::mpsc::channel();

        self.subscribers.write().push((id, tx, filter));
        (id, rx)
    }

    fn unsubscribe(&self, subscriber_id: u64) -> bool {
        let mut subs = self.subscribers.write();
        if let Some(pos) = subs.iter().position(|(id, _, _)| *id == subscriber_id) {
            subs.remove(pos);
            true
        } else {
            false
        }
    }

    fn emit(&self, event: PubSubEvent) {
        let subs = self.subscribers.read();
        for (_, sender, filter) in subs.iter() {
            if Self::should_send(&event, filter) {
                // Best-effort delivery - ignore send failures
                let _ = sender.send(event.clone());
            }
        }
    }

    fn should_send(event: &PubSubEvent, filter: &SubscriptionFilter) -> bool {
        match event {
            PubSubEvent::NodeChanged { .. } => filter.node_changes,
            PubSubEvent::EdgeChanged { .. } => filter.edge_changes,
            PubSubEvent::KvChanged { .. } => filter.kv_changes,
            PubSubEvent::SnapshotCommitted { .. } => filter.snapshot_commits,
        }
    }
}

/// Validate snapshot_id for SQLite backend
///
/// SQLite backend does not support historical snapshot isolation.
/// Only SnapshotId(0) is supported, which is returned by SnapshotId::current().
///
/// # Snapshot ID Contract
///
/// - `SnapshotId::current()` returns SnapshotId(0) - the "current" sentinel
/// - Any non-zero snapshot ID represents a historical snapshot (not supported)
///
/// Historical snapshot isolation would require:
/// - WAL-based versioning with timestamp/LSN indexing
/// - AS OF queries or point-in-time recovery mechanisms
/// - Multi-version concurrency control (MVCC) extensions
///
/// These are not implemented in the current SQLite backend.
fn validate_snapshot_for_sqlite(
    snapshot_id: crate::snapshot::SnapshotId,
) -> Result<(), SqliteGraphError> {
    if snapshot_id.as_lsn() == 0 {
        return Ok(());
    }
    Err(SqliteGraphError::query(format!(
        "SQLite backend does not support historical snapshots (requested: {}). \
        Only SnapshotId::current() (which returns SnapshotId(0)) is supported. \
        Historical snapshot isolation requires AS OF queries or MVCC which are not implemented.",
        snapshot_id.as_lsn()
    )))
}

/// SQLite-backed implementation of the GraphBackend trait.
///
/// This struct wraps a SqliteGraph instance and implements all GraphBackend methods
/// by delegating to the underlying SQLite-based graph operations.
pub struct SqliteGraphBackend {
    graph: SqliteGraph,
    /// In-memory publisher for pub/sub support (lazy initialized)
    publisher: RwLock<Option<Publisher>>,
}

impl SqliteGraphBackend {
    /// Create a new SQLite backend with an in-memory database.
    pub fn in_memory() -> Result<Self, SqliteGraphError> {
        Ok(Self {
            graph: SqliteGraph::open_in_memory()?,
            publisher: RwLock::new(None),
        })
    }

    /// Create a new SQLite backend from an existing SqliteGraph instance.
    pub fn from_graph(graph: SqliteGraph) -> Self {
        Self {
            graph,
            publisher: RwLock::new(None),
        }
    }

    /// Get a reference to the underlying SqliteGraph instance.
    pub fn graph(&self) -> &SqliteGraph {
        &self.graph
    }

    /// Create a new HNSW vector storage using this SQLite backend
    ///
    /// # Arguments
    ///
    /// * `index_name` - Name for the HNSW index (used for table naming)
    ///
    /// # Returns
    ///
    /// `Some(Box<dyn VectorStorage>)` containing a storage backed by SQLite
    ///
    /// # Example
    ///
    /// ```ignore
    /// let backend = SqliteGraphBackend::in_memory().unwrap();
    /// let storage = backend.create_hnsw_storage("my_index").unwrap();
    /// ```
    pub fn create_hnsw_storage(
        &self,
        _index_name: impl Into<String>,
    ) -> Option<Box<dyn crate::hnsw::storage::VectorStorage>> {
        // SQLiteVectorStorage requires an owned Connection, but we only have a reference
        // This is a limitation - we can't easily create a storage from &self
        // The caller should use SQLiteVectorStorage::new() directly with a connection
        None
    }

    /// Get all entity IDs from the graph.
    pub fn entity_ids(&self) -> Result<Vec<i64>, SqliteGraphError> {
        self.graph.all_entity_ids()
    }

    /// Ensure the kv_store table exists
    fn ensure_kv_table(&self) -> Result<(), SqliteGraphError> {
        let conn = self.graph.connection();

        conn.execute(
            "CREATE TABLE IF NOT EXISTS kv_store (
                key TEXT PRIMARY KEY,
                value_json TEXT NOT NULL,
                ttl_seconds INTEGER,
                version INTEGER NOT NULL DEFAULT 1,
                created_at INTEGER NOT NULL,
                updated_at INTEGER NOT NULL
            )",
            [],
        )
        .map_err(|e| {
            SqliteGraphError::connection(format!("Failed to create kv_store table: {}", e))
        })?;

        Ok(())
    }

    /// Execute optimized neighbor queries based on direction and edge type filtering.
    fn query_neighbors(
        &self,
        node: i64,
        direction: BackendDirection,
        edge_type: &Option<String>,
    ) -> Result<Vec<i64>, SqliteGraphError> {
        match (direction, edge_type) {
            (BackendDirection::Outgoing, None) => self.graph.fetch_outgoing(node),
            (BackendDirection::Incoming, None) => self.graph.fetch_incoming(node),
            (BackendDirection::Outgoing, Some(edge_type)) => {
                let conn = self.graph.connection();
                let mut stmt = conn
                    .prepare_cached(
                        "SELECT to_id FROM graph_edges WHERE from_id=?1 AND edge_type=?2 ORDER BY to_id, id",
                    )
                    .map_err(|e| SqliteGraphError::query(e.to_string()))?;
                let rows = stmt
                    .query_map(params![node, edge_type], |row| row.get(0))
                    .map_err(|e| SqliteGraphError::query(e.to_string()))?;
                let mut values = Vec::new();
                for value in rows {
                    values.push(value.map_err(|e| SqliteGraphError::query(e.to_string()))?);
                }
                Ok(values)
            }
            (BackendDirection::Incoming, Some(edge_type)) => {
                let conn = self.graph.connection();
                let mut stmt = conn
                    .prepare_cached(
                        "SELECT from_id FROM graph_edges WHERE to_id=?1 AND edge_type=?2 ORDER BY from_id, id",
                    )
                    .map_err(|e| SqliteGraphError::query(e.to_string()))?;
                let rows = stmt
                    .query_map(params![node, edge_type], |row| row.get(0))
                    .map_err(|e| SqliteGraphError::query(e.to_string()))?;
                let mut values = Vec::new();
                for value in rows {
                    values.push(value.map_err(|e| SqliteGraphError::query(e.to_string()))?);
                }
                Ok(values)
            }
        }
    }
}

impl crate::backend::GraphBackend for SqliteGraphBackend {
    fn insert_node(&self, node: NodeSpec) -> Result<i64, SqliteGraphError> {
        let id = self.graph.insert_entity(&GraphEntity {
            id: 0,
            kind: node.kind,
            name: node.name,
            file_path: node.file_path,
            data: node.data,
        })?;

        // Emit event if publisher is initialized
        let pub_guard = self.publisher.read();
        if let Some(ref publisher) = *pub_guard {
            publisher.emit(PubSubEvent::NodeChanged {
                node_id: id,
                snapshot_id: 0, // SQLite doesn't use snapshot IDs
            });
        }

        Ok(id)
    }

    fn get_node(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        id: i64,
    ) -> Result<GraphEntity, SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        self.graph.get_entity(id)
    }

    fn insert_edge(&self, edge: EdgeSpec) -> Result<i64, SqliteGraphError> {
        let id = self.graph.insert_edge(&GraphEdge {
            id: 0,
            from_id: edge.from,
            to_id: edge.to,
            edge_type: edge.edge_type,
            data: edge.data,
        })?;

        // Emit event if publisher is initialized
        let pub_guard = self.publisher.read();
        if let Some(ref publisher) = *pub_guard {
            publisher.emit(PubSubEvent::EdgeChanged {
                from_node: edge.from,
                to_node: edge.to,
                edge_id: id,
                snapshot_id: 0, // SQLite doesn't use snapshot IDs
            });
        }

        Ok(id)
    }

    fn delete_entity(&self, id: i64) -> Result<(), SqliteGraphError> {
        self.graph.delete_entity(id)
    }

    fn update_node(&self, node_id: i64, node: NodeSpec) -> Result<i64, SqliteGraphError> {
        // SQLite backend: Use UPDATE SQL query
        self.graph.update_entity(&GraphEntity {
            id: node_id,
            kind: node.kind,
            name: node.name,
            file_path: node.file_path,
            data: node.data,
        })?;
        Ok(node_id)
    }

    fn entity_ids(&self) -> Result<Vec<i64>, SqliteGraphError> {
        self.graph.all_entity_ids()
    }

    fn neighbors(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        node: i64,
        query: NeighborQuery,
    ) -> Result<Vec<i64>, SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        self.query_neighbors(node, query.direction, &query.edge_type)
    }

    fn bfs(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        start: i64,
        depth: u32,
    ) -> Result<Vec<i64>, SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        // Check query cache first
        if let Some(cached_result) = self.graph.query_cache.get_bfs(start, depth) {
            return Ok(cached_result);
        }

        // Cache miss - compute and cache the result
        let result = bfs_neighbors(&self.graph, start, depth)?;
        self.graph.query_cache.put_bfs(start, depth, result.clone());
        Ok(result)
    }

    fn shortest_path(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        start: i64,
        end: i64,
    ) -> Result<Option<Vec<i64>>, SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        // Check query cache first
        if let Some(cached_result) = self.graph.query_cache.get_shortest_path(start, end) {
            return Ok(cached_result);
        }

        // Cache miss - compute and cache the result
        let result = shortest_path(&self.graph, start, end)?;
        self.graph
            .query_cache
            .put_shortest_path(start, end, result.clone());
        Ok(result)
    }

    fn node_degree(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        node: i64,
    ) -> Result<(usize, usize), SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        let out = self.graph.fetch_outgoing(node)?.len();
        let incoming = self.graph.fetch_incoming(node)?.len();
        Ok((out, incoming))
    }

    fn k_hop(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        start: i64,
        depth: u32,
        direction: BackendDirection,
    ) -> Result<Vec<i64>, SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        // Check query cache first
        if let Some(cached_result) = self.graph.query_cache.get_k_hop(start, depth, direction) {
            return Ok(cached_result);
        }

        // Cache miss - compute and cache the result
        let result = multi_hop::k_hop(&self.graph, start, depth, direction)?;
        self.graph
            .query_cache
            .put_k_hop(start, depth, direction, result.clone());
        Ok(result)
    }

    fn k_hop_filtered(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        start: i64,
        depth: u32,
        direction: BackendDirection,
        allowed_edge_types: &[&str],
    ) -> Result<Vec<i64>, SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        // Check query cache first
        if let Some(cached_result) =
            self.graph
                .query_cache
                .get_k_hop_filtered(start, depth, direction, allowed_edge_types)
        {
            return Ok(cached_result);
        }

        // Cache miss - compute and cache the result
        let result =
            multi_hop::k_hop_filtered(&self.graph, start, depth, direction, allowed_edge_types)?;
        self.graph.query_cache.put_k_hop_filtered(
            start,
            depth,
            direction,
            allowed_edge_types,
            result.clone(),
        );
        Ok(result)
    }

    fn chain_query(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        start: i64,
        chain: &[crate::multi_hop::ChainStep],
    ) -> Result<Vec<i64>, SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        multi_hop::chain_query(&self.graph, start, chain)
    }

    fn pattern_search(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        start: i64,
        pattern: &PatternQuery,
    ) -> Result<Vec<PatternMatch>, SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        pattern::execute_pattern(&self.graph, start, pattern)
    }

    fn checkpoint(&self) -> Result<(), SqliteGraphError> {
        // Execute SQLite WAL checkpoint
        let conn = self.graph.connection();
        conn.query_row("PRAGMA wal_checkpoint(TRUNCATE)", [], |row| {
            // wal_checkpoint returns a row with 3 integers: (busy, log, checkpointed)
            // We don't need to use them, just execute the checkpoint
            let _busy: i32 = row.get(0)?;
            let _log: i32 = row.get(1)?;
            let _checkpointed: i32 = row.get(2)?;
            Ok(())
        })
        .map_err(|e| SqliteGraphError::connection(format!("WAL checkpoint failed: {}", e)))?;
        Ok(())
    }

    fn flush(&self) -> Result<(), SqliteGraphError> {
        // SQLite handles sync automatically; this is a no-op
        Ok(())
    }

    fn backup(
        &self,
        backup_dir: &std::path::Path,
    ) -> Result<crate::backend::BackupResult, SqliteGraphError> {
        use std::fs;

        // Ensure backup directory exists
        fs::create_dir_all(backup_dir).map_err(|e| {
            SqliteGraphError::connection(format!("Failed to create backup directory: {}", e))
        })?;

        // Generate backup filename with timestamp
        let timestamp = std::time::SystemTime::now()
            .duration_since(std::time::UNIX_EPOCH)
            .unwrap_or_default()
            .as_secs();
        let backup_path = backup_dir.join(format!("backup_{}.db", timestamp));
        let manifest_path = backup_dir.join(format!("backup_{}.json", timestamp));

        // Use SQLite's backup API via VACUUM INTO for a clean backup
        let conn = self.graph.connection();
        conn.execute(&format!("VACUUM INTO '{}'", backup_path.display()), [])
            .map_err(|e| SqliteGraphError::connection(format!("SQLite backup failed: {}", e)))?;

        // Get backup metadata
        let metadata = fs::metadata(&backup_path).map_err(|e| {
            SqliteGraphError::connection(format!("Failed to read backup metadata: {}", e))
        })?;

        // Get entity count
        let entity_ids = self
            .graph
            .all_entity_ids()
            .map_err(|e| SqliteGraphError::query(format!("Failed to get entity count: {}", e)))?;

        // Create a simple manifest
        let manifest = serde_json::json!({
            "timestamp": timestamp,
            "backup_file": backup_path.display().to_string(),
            "size_bytes": metadata.len(),
            "entity_count": entity_ids.len(),
        });
        fs::write(&manifest_path, manifest.to_string()).map_err(|e| {
            SqliteGraphError::connection(format!("Failed to write manifest: {}", e))
        })?;

        Ok(crate::backend::BackupResult {
            snapshot_path: backup_path,
            manifest_path,
            size_bytes: metadata.len() as u64,
            checksum: 0, // SQLite doesn't provide checksum
            record_count: entity_ids.len() as u64,
            duration_secs: 0.0, // Not tracked for SQLite backup
            timestamp,
            checkpoint_performed: false, // VACUUM INTO doesn't require explicit checkpoint
        })
    }

    fn snapshot_export(
        &self,
        export_dir: &std::path::Path,
    ) -> Result<crate::backend::SnapshotMetadata, SqliteGraphError> {
        use std::fs;

        // Ensure export directory exists
        fs::create_dir_all(export_dir).map_err(|e| {
            SqliteGraphError::connection(format!("Failed to create export directory: {}", e))
        })?;

        let snapshot_file = export_dir.join("snapshot.json");

        // Use existing dump_graph_to_path function
        crate::recovery::dump_graph_to_path(&self.graph, &snapshot_file)?;

        // Get metadata
        let metadata = fs::metadata(&snapshot_file).map_err(|e| {
            SqliteGraphError::connection(format!("Failed to read snapshot metadata: {}", e))
        })?;

        let entity_ids = self
            .graph
            .all_entity_ids()
            .map_err(|e| SqliteGraphError::query(format!("Failed to get entity count: {}", e)))?;

        Ok(crate::backend::SnapshotMetadata {
            snapshot_path: snapshot_file,
            size_bytes: metadata.len(),
            entity_count: entity_ids.len() as u64,
            edge_count: 0, // SQLite dump doesn't separate edge count easily
        })
    }

    fn snapshot_import(
        &self,
        import_dir: &std::path::Path,
    ) -> Result<crate::backend::ImportMetadata, SqliteGraphError> {
        let snapshot_file = import_dir.join("snapshot.json");

        if !snapshot_file.exists() {
            return Err(SqliteGraphError::connection(format!(
                "Snapshot file not found: {}",
                snapshot_file.display()
            )));
        }

        // Get entity count before import
        let before_count = self
            .graph
            .all_entity_ids()
            .map_err(|e| SqliteGraphError::query(format!("Failed to get entity count: {}", e)))?
            .len();

        // Use existing load_graph_from_path function
        crate::recovery::load_graph_from_path(&self.graph, &snapshot_file)?;

        // Get entity count after import
        let after_count = self
            .graph
            .all_entity_ids()
            .map_err(|e| SqliteGraphError::query(format!("Failed to get entity count: {}", e)))?
            .len();

        Ok(crate::backend::ImportMetadata {
            snapshot_path: snapshot_file,
            entities_imported: (after_count - before_count) as u64,
            edges_imported: 0, // SQLite load doesn't separate edge count easily
        })
    }

    fn kv_get(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        key: &[u8],
    ) -> Result<Option<crate::backend::native::types::KvValue>, crate::SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        use std::time::SystemTime;

        // Initialize KV table if needed
        self.ensure_kv_table()?;

        // Convert key to string for storage (comma-separated bytes)
        let key_str = bytes_to_string(key);

        let conn = self.graph.connection();

        // Query the kv_store table
        let result = conn.query_row(
            "SELECT value_json, ttl_seconds, created_at FROM kv_store WHERE key = ?1",
            params![key_str],
            |row| {
                let value_json: String = row.get(0)?;
                let ttl_seconds: Option<u64> = row.get(1)?;
                let created_at: u64 = row.get(2)?;

                Ok((value_json, ttl_seconds, created_at))
            },
        );

        match result {
            Ok((value_json, ttl_seconds, created_at)) => {
                // Check TTL expiration
                if let Some(ttl) = ttl_seconds {
                    let now = SystemTime::now()
                        .duration_since(SystemTime::UNIX_EPOCH)
                        .map(|d| d.as_secs())
                        .unwrap_or(0);

                    if now.saturating_sub(created_at) > ttl {
                        // Entry expired
                        return Ok(None);
                    }
                }

                // Parse JSON value back to KvValue
                let json_value: serde_json::Value =
                    serde_json::from_str(&value_json).map_err(|e| {
                        SqliteGraphError::connection(format!(
                            "Failed to parse KV value JSON: {}",
                            e
                        ))
                    })?;

                let kv_value = json_to_kv_value(json_value)?;
                Ok(Some(kv_value))
            }
            Err(rusqlite::Error::QueryReturnedNoRows) => Ok(None),
            Err(e) => Err(SqliteGraphError::query(format!(
                "Failed to query KV store: {}",
                e
            ))),
        }
    }

    fn kv_set(
        &self,
        key: Vec<u8>,
        value: crate::backend::native::types::KvValue,
        ttl_seconds: Option<u64>,
    ) -> Result<(), crate::SqliteGraphError> {
        use std::time::SystemTime;

        // Initialize KV table if needed
        self.ensure_kv_table()?;

        // Convert key to string for storage
        let key_str = bytes_to_string(&key);

        // Serialize KvValue to JSON
        let json_value = kv_value_to_json(&value);
        let value_json = serde_json::to_string(&json_value).map_err(|e| {
            SqliteGraphError::connection(format!("Failed to serialize KV value: {}", e))
        })?;

        let now = SystemTime::now()
            .duration_since(SystemTime::UNIX_EPOCH)
            .map(|d| d.as_secs())
            .unwrap_or(0);

        let conn = self.graph.connection();

        // Check if key exists
        let count: i64 = conn
            .query_row(
                "SELECT COUNT(*) FROM kv_store WHERE key = ?1",
                params![key_str],
                |row| row.get(0),
            )
            .unwrap_or(0);

        if count > 0 {
            // Update existing entry
            conn.execute(
                "UPDATE kv_store SET value_json = ?1, ttl_seconds = ?2, updated_at = ?3, version = version + 1 WHERE key = ?4",
                params![value_json, ttl_seconds, now, key_str],
            )
                .map_err(|e| SqliteGraphError::query(format!("Failed to update KV entry: {}", e)))?;
        } else {
            // Insert new entry
            conn.execute(
                "INSERT INTO kv_store (key, value_json, ttl_seconds, created_at, updated_at, version) VALUES (?1, ?2, ?3, ?4, ?4, 1)",
                params![key_str, value_json, ttl_seconds, now],
            )
                .map_err(|e| SqliteGraphError::query(format!("Failed to insert KV entry: {}", e)))?;
        }

        Ok(())
    }

    fn kv_delete(&self, key: &[u8]) -> Result<(), crate::SqliteGraphError> {
        // Initialize KV table if needed
        self.ensure_kv_table()?;

        // Convert key to string for storage
        let key_str = bytes_to_string(key);

        let conn = self.graph.connection();

        // Delete the entry (ignore if not found - idempotent)
        conn.execute("DELETE FROM kv_store WHERE key = ?1", params![key_str])
            .map_err(|e| SqliteGraphError::query(format!("Failed to delete KV entry: {}", e)))?;

        Ok(())
    }

    fn subscribe(
        &self,
        filter: crate::backend::SubscriptionFilter,
    ) -> Result<
        (u64, std::sync::mpsc::Receiver<crate::backend::PubSubEvent>),
        crate::SqliteGraphError,
    > {
        // Lazy initialize publisher
        let mut pub_guard = self.publisher.write();
        if pub_guard.is_none() {
            *pub_guard = Some(Publisher::new());
        }
        let (id, rx) = pub_guard.as_ref().unwrap().subscribe(filter);
        Ok((id, rx))
    }

    fn unsubscribe(&self, subscriber_id: u64) -> Result<bool, crate::SqliteGraphError> {
        let pub_guard = self.publisher.read();
        if let Some(ref publisher) = *pub_guard {
            Ok(publisher.unsubscribe(subscriber_id))
        } else {
            Ok(false) // Publisher not initialized, nothing to unsubscribe
        }
    }

    // ========== Pub/Sub Enhancement APIs (v1.4.0) ==========

    fn kv_prefix_scan(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        prefix: &[u8],
    ) -> Result<Vec<(Vec<u8>, crate::backend::native::types::KvValue)>, crate::SqliteGraphError>
    {
        validate_snapshot_for_sqlite(snapshot_id)?;
        self.ensure_kv_table()?;
        let conn = self.graph.connection();

        // Convert prefix to string pattern for LIKE query
        // Escape special LIKE characters: % and _
        let prefix_str = String::from_utf8_lossy(prefix);
        let pattern = prefix_str.replace('%', "\\%").replace('_', "\\_") + "%";

        let mut stmt = conn
            .prepare_cached("SELECT key, value_json FROM kv_store WHERE key LIKE ?1 ESCAPE '\\'")
            .map_err(|e| SqliteGraphError::query(e.to_string()))?;

        let mut results = Vec::new();
        let query_result = stmt.query_map([&pattern], |row| {
            let key: String = row.get(0)?;
            let value_json: String = row.get(1)?;
            Ok((key, value_json))
        });

        for row in query_result.map_err(|e| SqliteGraphError::query(e.to_string()))? {
            let (key, value_json) = row.map_err(|e| SqliteGraphError::query(e.to_string()))?;
            let json_value: serde_json::Value = serde_json::from_str(&value_json)
                .map_err(|e| SqliteGraphError::query(format!("Failed to parse JSON: {}", e)))?;
            let kv_value = json_to_kv_value(json_value)?;
            results.push((key.into_bytes(), kv_value));
        }

        // Sort by key for deterministic output
        results.sort_by(|a, b| a.0.cmp(&b.0));
        Ok(results)
    }

    fn query_nodes_by_kind(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        kind: &str,
    ) -> Result<Vec<i64>, crate::SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        let conn = self.graph.connection();
        let mut stmt = conn
            .prepare_cached("SELECT id FROM graph_entities WHERE kind = ?1")
            .map_err(|e| SqliteGraphError::query(e.to_string()))?;

        let node_ids: Vec<i64> = stmt
            .query_map([kind], |row| row.get(0))
            .map_err(|e| SqliteGraphError::query(e.to_string()))?
            .collect::<Result<_, _>>()
            .map_err(|e| SqliteGraphError::query(e.to_string()))?;

        Ok(node_ids)
    }

    fn query_nodes_by_name_pattern(
        &self,
        snapshot_id: crate::snapshot::SnapshotId,
        pattern: &str,
    ) -> Result<Vec<i64>, crate::SqliteGraphError> {
        validate_snapshot_for_sqlite(snapshot_id)?;
        let conn = self.graph.connection();
        let mut stmt = conn
            .prepare_cached("SELECT id FROM graph_entities WHERE name GLOB ?1")
            .map_err(|e| SqliteGraphError::query(e.to_string()))?;

        let node_ids: Vec<i64> = stmt
            .query_map([pattern], |row| row.get(0))
            .map_err(|e| SqliteGraphError::query(e.to_string()))?
            .collect::<Result<_, _>>()
            .map_err(|e| SqliteGraphError::query(e.to_string()))?;

        Ok(node_ids)
    }
}

/// Convert KvValue to serde_json::Value for serialization
fn kv_value_to_json(value: &crate::backend::native::types::KvValue) -> serde_json::Value {
    use crate::backend::native::types::KvValue;

    match value {
        KvValue::Null => serde_json::json!({"type": "null"}),
        KvValue::Bytes(bytes) => {
            serde_json::json!({
                "type": "bytes",
                "data": bytes_to_string(bytes),
            })
        }
        KvValue::String(s) => {
            serde_json::json!({
                "type": "string",
                "data": s,
            })
        }
        KvValue::Integer(n) => {
            serde_json::json!({
                "type": "integer",
                "data": n,
            })
        }
        KvValue::Float(f) => {
            serde_json::json!({
                "type": "float",
                "data": f,
            })
        }
        KvValue::Boolean(b) => {
            serde_json::json!({
                "type": "boolean",
                "data": b,
            })
        }
        KvValue::Json(j) => {
            serde_json::json!({
                "type": "json",
                "data": j,
            })
        }
    }
}

/// Convert bytes to comma-separated string for storage
fn bytes_to_string(bytes: &[u8]) -> String {
    use std::fmt::Write;
    let mut result = String::new();
    for (i, byte) in bytes.iter().enumerate() {
        if i > 0 {
            result.push(',');
        }
        write!(result, "{}", byte).unwrap();
    }
    result
}

/// Convert comma-separated string back to bytes
fn string_to_bytes(s: &str) -> Result<Vec<u8>, SqliteGraphError> {
    s.split(',')
        .map(|part| {
            part.trim()
                .parse::<u8>()
                .map_err(|_| SqliteGraphError::connection(format!("Invalid byte string: {}", s)))
        })
        .collect()
}

/// Convert serde_json::Value back to KvValue after deserialization
fn json_to_kv_value(
    json_value: serde_json::Value,
) -> Result<crate::backend::native::types::KvValue, SqliteGraphError> {
    use crate::backend::native::types::KvValue;

    let type_str = json_value
        .get("type")
        .and_then(|v| v.as_str())
        .ok_or_else(|| {
            SqliteGraphError::connection("Missing type field in KV value JSON".to_string())
        })?;

    let data = json_value.get("data").ok_or_else(|| {
        SqliteGraphError::connection("Missing data field in KV value JSON".to_string())
    })?;

    match type_str {
        "bytes" => {
            let bytes_str = data.as_str().ok_or_else(|| {
                SqliteGraphError::connection("Invalid bytes data in KV value".to_string())
            })?;
            let bytes = string_to_bytes(bytes_str)?;
            Ok(KvValue::Bytes(bytes))
        }
        "string" => {
            let s = data.as_str().ok_or_else(|| {
                SqliteGraphError::connection("Invalid string data in KV value".to_string())
            })?;
            Ok(KvValue::String(s.to_string()))
        }
        "integer" => {
            let n = data.as_i64().ok_or_else(|| {
                SqliteGraphError::connection("Invalid integer data in KV value".to_string())
            })?;
            Ok(KvValue::Integer(n))
        }
        "float" => {
            let f = data.as_f64().ok_or_else(|| {
                SqliteGraphError::connection("Invalid float data in KV value".to_string())
            })?;
            Ok(KvValue::Float(f))
        }
        "boolean" => {
            let b = data.as_bool().ok_or_else(|| {
                SqliteGraphError::connection("Invalid boolean data in KV value".to_string())
            })?;
            Ok(KvValue::Boolean(b))
        }
        "json" => Ok(KvValue::Json(data.clone())),
        _ => Err(SqliteGraphError::connection(format!(
            "Unknown KV value type: {}",
            type_str
        ))),
    }
}