hocuspocus-rs 0.1.3

//! Yjs Sync Protocol Implementation
//!
//! This module implements the y-websocket sync protocol for compatibility with
//! Hocuspocus/y-websocket clients. The protocol flow is:
//!
//! 1. Client connects and sends SyncStep1(client_state_vector)
//! 2. Server responds with SyncStep2(server_diff) + SyncStep1(server_state_vector)
//! 3. Client sends SyncStep2(client_diff)
//! 4. Ongoing: Both sides exchange Update messages
//!
//! Note: Awareness protocol (for cursors/presence) is handled by forwarding
//! messages between clients without server-side state.

#[cfg(feature = "sqlite")]
use std::sync::Arc;
use std::sync::Mutex as StdMutex;
use tokio::sync::broadcast;
#[cfg(feature = "sqlite")]
use tokio::sync::Mutex;
#[cfg(feature = "sqlite")]
use tokio::time::{Duration, Instant};
use yrs::encoding::read::Read;
use yrs::encoding::write::Write;
use yrs::updates::decoder::{Decode, DecoderV1};
use yrs::updates::encoder::{Encode, Encoder, EncoderV1};
use yrs::{Doc, ReadTxn, StateVector, Transact, Update};

#[cfg(feature = "sqlite")]
use crate::db::Database;

/// Message types for y-websocket protocol
/// The first byte of each message indicates its type
pub const MSG_SYNC: u8 = 0;
pub const MSG_AWARENESS: u8 = 1;
pub const MSG_AUTH: u8 = 2; // Hocuspocus-specific
pub const MSG_QUERY_AWARENESS: u8 = 3;

/// Debounce interval for persistence (milliseconds)
#[cfg(feature = "sqlite")]
const PERSIST_DEBOUNCE_MS: u64 = 500;

/// A handler for a single Yjs document/room
/// Manages the document state, persistence, and broadcasting
///
/// Note: We use std::sync::Mutex for the Doc because yrs::Doc operations are
/// synchronous and fast. tokio::sync::Mutex would cause unnecessary overhead.
pub struct DocHandler {
    pub doc_name: String,
    /// Thread-safe document access using std Mutex (Doc ops are sync & fast)
    doc: StdMutex<Doc>,
    /// Database for persistence
    #[cfg(feature = "sqlite")]
    db: Database,
    /// Broadcast channel for sending updates to other clients
    pub broadcast_tx: broadcast::Sender<Vec<u8>>,
    /// Track when persistence was last requested for debouncing
    #[cfg(feature = "sqlite")]
    last_persist_request: Arc<Mutex<Option<Instant>>>,
    /// Flag to indicate persistence is pending
    #[cfg(feature = "sqlite")]
    persist_pending: Arc<Mutex<bool>>,
}

// Explicitly mark DocHandler as Send + Sync since we use std::sync::Mutex
// and all fields are thread-safe
unsafe impl Send for DocHandler {}
unsafe impl Sync for DocHandler {}

impl DocHandler {
    #[cfg(feature = "sqlite")]
    pub async fn new(doc_name: String, db: Database) -> Self {
        let doc = Doc::new();
        let (broadcast_tx, _) = broadcast::channel(256);

        // Load existing state from DB
        tracing::info!("Loading document '{}' from database...", doc_name);
        if let Ok(Some(data)) = db.get_doc(&doc_name).await {
            tracing::info!(
                "Found existing data for '{}': {} bytes",
                doc_name,
                data.len()
            );
            let mut txn = doc.transact_mut();
            match Update::decode_v1(&data) {
                Ok(update) => {
                    txn.apply_update(update);
                    tracing::debug!("Applied stored state to document '{}'", doc_name);
                }
                Err(e) => {
                    tracing::error!("Failed to decode stored state for '{}': {:?}", doc_name, e);
                }
            }
        } else {
            tracing::info!("No existing data found for '{}', starting fresh", doc_name);
        }

        Self {
            doc_name,
            doc: StdMutex::new(doc),
            db,
            broadcast_tx,
            last_persist_request: Arc::new(Mutex::new(None)),
            persist_pending: Arc::new(Mutex::new(false)),
        }
    }

    #[cfg(not(feature = "sqlite"))]
    pub async fn new(doc_name: String) -> Self {
        let doc = Doc::new();
        let (broadcast_tx, _) = broadcast::channel(256);

        Self {
            doc_name,
            doc: StdMutex::new(doc),
            broadcast_tx,
        }
    }

    /// Generate the initial sync messages to send when a client connects
    /// Returns: [SyncStep1(server_state_vector)]
    pub fn generate_initial_sync(&self) -> Vec<Vec<u8>> {
        let doc = self.doc.lock().unwrap_or_else(|e| {
            tracing::warn!("Doc mutex was poisoned for '{}', recovering", self.doc_name);
            e.into_inner()
        });
        let txn = doc.transact();
        let state_vector = txn.state_vector();

        // Encode SyncStep1: [Tag 0] [Len] [SV]
        let mut encoder = EncoderV1::new();
        encoder.write_var(0u32); // Tag SyncStep1

        // Encode SV to bytes first
        let mut sv_encoder = EncoderV1::new();
        state_vector.encode(&mut sv_encoder);
        let sv_bytes = sv_encoder.to_vec();

        // Write as buffer (Length + Bytes)
        encoder.write_buf(&sv_bytes);

        let payload = encoder.to_vec();

        let encoded = self.encode_hocuspocus_message(MSG_SYNC, &payload);

        tracing::debug!(
            "Generated initial sync message ({} bytes): {:02x?}",
            encoded.len(),
            encoded
        );

        vec![encoded]
    }

    /// Process an incoming message from a client
    /// Returns a list of response messages to send back to this client
    /// Also broadcasts updates to other clients via the broadcast channel
    pub async fn handle_message(&self, msg_data: &[u8]) -> Vec<Vec<u8>> {
        let mut responses = Vec::new();

        if msg_data.is_empty() {
            return responses;
        }

        tracing::trace!("Received message ({} bytes)", msg_data.len());

        // Hocuspocus Protocol V2: [DocName (VarString)] [MessageType (VarUint)] [Payload]
        // We first need to skip the document name since we already know context from the room connection
        let (content_data, _doc_name) = match DocHandler::read_and_skip_doc_name(msg_data) {
            Some(res) => res,
            None => {
                tracing::warn!(
                    "Failed to parse document name from message: {:02x?}",
                    msg_data
                );
                return responses;
            }
        };

        if content_data.is_empty() {
            return responses;
        }

        let msg_type = content_data[0];
        let payload = &content_data[1..];

        match msg_type {
            MSG_SYNC => {
                self.handle_sync_message(payload, &mut responses).await;
            }
            MSG_AWARENESS => {
                // Awareness messages are forwarded to other clients
                // We re-wrap them with our doc_name to ensure clients route them correctly
                self.forward_awareness_message(payload);
            }
            MSG_QUERY_AWARENESS => {
                // Query awareness - we don't maintain server-side awareness state
                // Clients will receive awareness updates from other clients directly
                tracing::debug!("Received QUERY_AWARENESS (no server state maintained)");
            }
            MSG_AUTH => {
                // Auth messages are handled at the WebSocket layer
                // For now, we accept all connections
                tracing::debug!("Received AUTH message (accepted)");
            }
            _ => {
                tracing::warn!("Unknown message type: {}", msg_type);
            }
        }

        responses
    }

    /// Helper to read the VarString document name and return the rest of the buffer
    pub fn read_and_skip_doc_name(data: &[u8]) -> Option<(&[u8], String)> {
        let mut offset = 0;
        let mut len: usize = 0;
        let mut shift = 0;

        // Decode VarUint length
        loop {
            if offset >= data.len() {
                return None;
            }
            let b = data[offset];
            offset += 1;
            len |= ((b & 0x7F) as usize) << shift;
            if b & 0x80 == 0 {
                break;
            }
            shift += 7;
            if shift > 64 {
                return None;
            }
        }

        if offset + len > data.len() {
            return None;
        }

        // Decode string for debug/verification (optional but good for logging)
        let name_bytes = &data[offset..offset + len];
        let name = String::from_utf8_lossy(name_bytes).to_string();

        Some((&data[offset + len..], name))
    }

    /// Wraps a raw payload in the Hocuspocus V2 protocol structure:
    /// [DocName : VarString] [MsgType : VarUint] [Payload : Bytes]
    pub fn encode_hocuspocus_message(&self, msg_type: u8, payload: &[u8]) -> Vec<u8> {
        let mut encoder = EncoderV1::new();
        encoder.write_string(&self.doc_name);
        encoder.write_var(msg_type as u32);

        let mut encoded = encoder.to_vec();
        encoded.extend_from_slice(payload);
        encoded
    }

    /// Forward awareness message to other clients
    fn forward_awareness_message(&self, payload: &[u8]) {
        // Re-wrap the awareness message with the Hocuspocus protocol V2 prefix
        let broadcast_msg = self.encode_hocuspocus_message(MSG_AWARENESS, payload);
        let _ = self.broadcast_tx.send(broadcast_msg);
        tracing::trace!("Forwarded awareness message for '{}'", self.doc_name);
    }

    /// Handle sync protocol messages (SyncStep1, SyncStep2, Update)
    async fn handle_sync_message(&self, payload: &[u8], responses: &mut Vec<Vec<u8>>) {
        let mut decoder = DecoderV1::from(payload);

        // Loop over the payload to decode multiple messages (Hocuspocus/y-protocols stream)
        // We check loop by trying to read the next tag
        while let Ok(tag) = decoder.read_var::<u32>() {
            match tag {
                0 => {
                    // SyncStep1: [Tag 0] [Len] [StateVector]
                    // First read the length-prefixed buffer
                    match decoder.read_buf() {
                        Ok(sv_data) => {
                            // Then decode SV from the buffer
                            match StateVector::decode(&mut DecoderV1::from(sv_data)) {
                                Ok(client_sv) => {
                                    tracing::debug!(
                                        "Handling SyncStep1 (SV len: {})",
                                        client_sv.len()
                                    );
                                    let doc = self.doc.lock().unwrap_or_else(|e| {
                                        tracing::warn!(
                                            "Doc mutex was poisoned for '{}', recovering",
                                            self.doc_name
                                        );
                                        e.into_inner()
                                    });
                                    let txn = doc.transact();

                                    // Reply with SyncStep2 (updates client needs)
                                    // [Tag 1] [Len] [Bytes]
                                    let update = txn.encode_state_as_update_v1(&client_sv);
                                    let mut encoder = EncoderV1::new();
                                    encoder.write_var(1u32);
                                    encoder.write_buf(&update);
                                    responses.push(
                                        self.encode_hocuspocus_message(MSG_SYNC, &encoder.to_vec()),
                                    );

                                    // Also send our SyncStep1 (server SV) so client can sync vs us
                                    // [Tag 0] [Len] [StateVector]
                                    let server_sv = txn.state_vector();

                                    let mut sv_encoder = EncoderV1::new();
                                    server_sv.encode(&mut sv_encoder);
                                    let sv_bytes = sv_encoder.to_vec();

                                    let mut encoder_sv = EncoderV1::new();
                                    encoder_sv.write_var(0u32);
                                    encoder_sv.write_buf(&sv_bytes);

                                    responses.push(
                                        self.encode_hocuspocus_message(
                                            MSG_SYNC,
                                            &encoder_sv.to_vec(),
                                        ),
                                    );

                                    tracing::debug!(
                                        "Processed SyncStep1 for '{}', sent SyncStep2 + SyncStep1",
                                        self.doc_name
                                    );
                                }
                                Err(e) => {
                                    tracing::warn!(
                                        "Failed to decode StateVector in SyncStep1: {:?}",
                                        e
                                    );
                                    break;
                                }
                            }
                        }
                        Err(e) => {
                            tracing::warn!("Failed to read SyncStep1 payload: {:?}", e);
                            break;
                        }
                    }
                }
                1 => {
                    // SyncStep2: [Tag 1] [Len] [Bytes]
                    match decoder.read_buf() {
                        Ok(update_data) => {
                            tracing::debug!(
                                "Handling SyncStep2 (payload len: {})",
                                update_data.len()
                            );
                            if update_data.is_empty() {
                                tracing::debug!("Received empty SyncStep2 update, ignoring");
                                continue;
                            }

                            if let Err(e) = self.apply_update(update_data) {
                                tracing::error!(
                                    "Failed to apply SyncStep2 update: {:?}. Payload: {:02x?}",
                                    e,
                                    update_data
                                );
                            } else {
                                tracing::debug!("Applied SyncStep2 update for '{}'", self.doc_name);
                                self.request_persist().await;
                            }
                        }
                        Err(e) => {
                            tracing::warn!("Failed to read SyncStep2 payload: {:?}", e);
                            break;
                        }
                    }
                }
                2 => {
                    // Update: [Tag 2] [Len] [Bytes]
                    match decoder.read_buf() {
                        Ok(update_data) => {
                            if let Err(e) = self.apply_update(update_data) {
                                tracing::error!("Failed to apply incremental update: {:?}", e);
                            } else {
                                tracing::debug!(
                                    "Applied incremental update for '{}'",
                                    self.doc_name
                                );

                                // Broadcast to other clients - MUST include Hocuspocus prefix
                                // Broadcast format: [Tag 2] [Len] [Bytes]
                                let mut encoder = EncoderV1::new();
                                encoder.write_var(2u32);
                                encoder.write_buf(update_data);
                                let msg =
                                    self.encode_hocuspocus_message(MSG_SYNC, &encoder.to_vec());
                                let _ = self.broadcast_tx.send(msg);

                                self.request_persist().await;
                            }
                        }
                        Err(e) => {
                            tracing::warn!("Failed to read Update payload: {:?}", e);
                            break;
                        }
                    }
                }
                _ => {
                    tracing::warn!("Unknown sync message tag: {}", tag);
                    break;
                }
            }
        }
    }

    /// Apply a Yjs update to the document
    pub fn apply_update(
        &self,
        update_data: &[u8],
    ) -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
        let update = Update::decode_v1(update_data)?;
        let doc = self.doc.lock().unwrap_or_else(|e| {
            tracing::warn!("Doc mutex was poisoned for '{}', recovering", self.doc_name);
            e.into_inner()
        });
        let mut txn = doc.transact_mut();
        txn.apply_update(update);
        Ok(())
    }

    /// Request persistence with debouncing
    pub async fn request_persist(&self) {
        #[cfg(feature = "sqlite")]
        {
            let now = Instant::now();

            {
                let mut last_request = self.last_persist_request.lock().await;
                *last_request = Some(now);
            }

            // Check if persistence is already pending
            let already_pending = {
                let pending = self.persist_pending.lock().await;
                *pending
            };

            if !already_pending {
                // Mark as pending
                {
                    let mut pending = self.persist_pending.lock().await;
                    *pending = true;
                }

                // Clone what we need for the spawned task
                let doc_name = self.doc_name.clone();
                let db = self.db.clone();
                let last_persist_request = self.last_persist_request.clone();
                let persist_pending = self.persist_pending.clone();

                // Encode the state before spawning since Doc isn't Send
                let state = {
                    let doc = self.doc.lock().unwrap_or_else(|e| {
                        tracing::warn!(
                            "Doc mutex was poisoned for '{}', recovering",
                            self.doc_name
                        );
                        e.into_inner()
                    });
                    let txn = doc.transact();
                    txn.encode_state_as_update_v1(&StateVector::default())
                };

                tokio::spawn(async move {
                    // Wait for debounce interval
                    tokio::time::sleep(Duration::from_millis(PERSIST_DEBOUNCE_MS)).await;

                    // Check if there were more updates during the wait
                    let should_persist = {
                        let last_request = last_persist_request.lock().await;
                        if let Some(last) = *last_request {
                            last.elapsed() >= Duration::from_millis(PERSIST_DEBOUNCE_MS - 50)
                        } else {
                            true
                        }
                    };

                    if should_persist {
                        // Save to database
                        if let Err(e) = db.save_doc(&doc_name, state).await {
                            tracing::error!("Failed to persist document '{}': {:?}", doc_name, e);
                        } else {
                            tracing::debug!("Persisted document '{}'", doc_name);
                        }
                    }

                    // Clear pending flag
                    {
                        let mut pending = persist_pending.lock().await;
                        *pending = false;
                    }
                });
            }
        }
    }

    /// Force immediate persistence (for graceful shutdown)
    pub async fn force_persist(&self) {
        #[cfg(feature = "sqlite")]
        {
            let state = {
                let doc = self.doc.lock().unwrap_or_else(|e| {
                    tracing::warn!("Doc mutex was poisoned for '{}', recovering", self.doc_name);
                    e.into_inner()
                });
                let txn = doc.transact();
                txn.encode_state_as_update_v1(&StateVector::default())
            };

            if let Err(e) = self.db.save_doc(&self.doc_name, state).await {
                tracing::error!(
                    "Failed to persist document '{}' on shutdown: {:?}",
                    self.doc_name,
                    e
                );
            } else {
                tracing::info!("Persisted document '{}' on shutdown", self.doc_name);
            }
        }
    }

    /// Get a subscription to broadcast messages
    pub fn subscribe(&self) -> broadcast::Receiver<Vec<u8>> {
        self.broadcast_tx.subscribe()
    }
}

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

    #[cfg(feature = "sqlite")]
    use yrs::encoding::read::Read;
    #[cfg(feature = "sqlite")]
    use yrs::updates::decoder::DecoderV1;
    #[cfg(feature = "sqlite")]
    use yrs::updates::encoder::{Encoder, EncoderV1};
    #[cfg(feature = "sqlite")]
    use yrs::{GetString, Text, Transact};

    /// Creates an in-memory test database
    #[cfg(feature = "sqlite")]
    async fn create_test_db() -> Database {
        Database::init_in_memory().expect("Failed to create test database")
    }

    #[cfg(feature = "sqlite")]
    fn encode_test_msg(doc_name: &str, msg_type: u8, payload: &[u8]) -> Vec<u8> {
        let mut encoder = EncoderV1::new();
        encoder.write_string(doc_name);
        encoder.write_var(msg_type as u32);
        let mut v = encoder.to_vec();
        v.extend_from_slice(payload);
        v
    }

    #[cfg(feature = "sqlite")]
    fn encode_sync_step1(sv: &StateVector) -> Vec<u8> {
        let mut sv_encoder = EncoderV1::new();
        sv.encode(&mut sv_encoder);
        let sv_bytes = sv_encoder.to_vec();

        let mut encoder = EncoderV1::new();
        encoder.write_var(0u32); // Tag 0
        encoder.write_buf(&sv_bytes);
        encoder.to_vec()
    }

    #[cfg(feature = "sqlite")]
    fn encode_update(update: &[u8]) -> Vec<u8> {
        let mut encoder = EncoderV1::new();
        encoder.write_var(2u32); // Tag 2
        encoder.write_buf(update);
        encoder.to_vec()
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_doc_handler_creation() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db).await;
        assert_eq!(handler.doc_name, "test-room");
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_initial_sync_generation() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db).await;

        let messages = handler.generate_initial_sync();
        assert_eq!(messages.len(), 1);

        // Should start with doc name "test-room"
        let (rest, name) =
            DocHandler::read_and_skip_doc_name(&messages[0]).expect("Should parse doc name");
        assert_eq!(name, "test-room");

        // Next should be MSG_SYNC
        let mut decoder = DecoderV1::from(rest);
        let msg_type: u32 = decoder.read_var().expect("Should parse msg type");
        assert_eq!(msg_type as u8, MSG_SYNC);
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_sync_step1_response() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db).await;

        // Create a client state vector (empty = requesting all updates)
        let client_sv = StateVector::default();
        let payload = encode_sync_step1(&client_sv);

        let msg = encode_test_msg("test-room", MSG_SYNC, &payload);

        let responses = handler.handle_message(&msg).await;

        // Should get SyncStep2 + SyncStep1 back
        assert_eq!(responses.len(), 2);

        // Verify response structure
        for resp in responses {
            let (rest, name) = DocHandler::read_and_skip_doc_name(&resp).unwrap();
            assert_eq!(name, "test-room");
            let mut d = DecoderV1::from(rest);
            let t: u32 = d.read_var().unwrap();
            assert_eq!(t as u8, MSG_SYNC);
        }
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_update_application_and_broadcast() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db).await;

        // Subscribe to broadcasts
        let mut rx = handler.subscribe();

        // Create an update from a client doc
        let client_doc = Doc::new();
        let update = {
            let text = client_doc.get_or_insert_text("test");
            let mut txn = client_doc.transact_mut();
            text.push(&mut txn, "Hello, World!");
            txn.encode_update_v1()
        };

        // Send as SyncMessage::Update
        let payload = encode_update(&update);
        let msg = encode_test_msg("test-room", MSG_SYNC, &payload);

        let _responses = handler.handle_message(&msg).await;

        // Should have broadcast the update
        let broadcast = tokio::time::timeout(Duration::from_millis(100), rx.recv()).await;
        assert!(broadcast.is_ok());
        let broadcast_data = broadcast.unwrap().unwrap();

        // Verify broadcast format
        let (_, name) = DocHandler::read_and_skip_doc_name(&broadcast_data).unwrap();
        assert_eq!(name, "test-room");
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_persistence_after_update() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db.clone()).await;

        // Create an update
        let client_doc = Doc::new();
        let update = {
            let text = client_doc.get_or_insert_text("test");
            let mut txn = client_doc.transact_mut();
            text.push(&mut txn, "Persistent data");
            txn.encode_update_v1()
        };

        // Send update
        let payload = encode_update(&update);
        let msg = encode_test_msg("test-room", MSG_SYNC, &payload);

        let _responses = handler.handle_message(&msg).await;

        // Force persist (normally debounced)
        handler.force_persist().await;

        // Verify data was saved
        let saved = db.get_doc("test-room").await.unwrap();
        assert!(saved.is_some());
        assert!(!saved.unwrap().is_empty());
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_document_reload_from_db() {
        let db = create_test_db().await;

        // Create a handler and add some data
        let handler1 = DocHandler::new("reload-test".to_string(), db.clone()).await;

        let client_doc = Doc::new();
        let update = {
            let text = client_doc.get_or_insert_text("content");
            let mut txn = client_doc.transact_mut();
            text.push(&mut txn, "Test content for reload");
            txn.encode_update_v1()
        };

        let payload = encode_update(&update);
        let msg = encode_test_msg("reload-test", MSG_SYNC, &payload);

        handler1.handle_message(&msg).await;
        handler1.force_persist().await;

        // Drop the first handler
        drop(handler1);

        // Create a new handler for the same room - should load from DB
        let handler2 = DocHandler::new("reload-test".to_string(), db).await;

        // Verify the document has the content
        let doc = handler2.doc.lock().unwrap();
        let text = doc.get_or_insert_text("content");
        let txn = doc.transact();
        let content = text.get_string(&txn);

        assert_eq!(content, "Test content for reload");
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_awareness_forwarding() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db).await;

        // Subscribe to broadcasts
        let mut rx = handler.subscribe();

        // Create a fake awareness message
        let body = vec![1, 2, 3, 4];
        let awareness_msg = encode_test_msg("test-room", MSG_AWARENESS, &body);

        let _responses = handler.handle_message(&awareness_msg).await;

        // Should have broadcast the awareness message
        let broadcast = tokio::time::timeout(Duration::from_millis(100), rx.recv()).await;
        assert!(broadcast.is_ok());
        let received = broadcast.unwrap().unwrap();

        // Should effectively be identical to input since we re-wrap with same doc name
        assert_eq!(received, awareness_msg);
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_empty_message_handling() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db).await;

        // Empty message should return empty responses
        let responses = handler.handle_message(&[]).await;
        assert!(responses.is_empty());
    }

    #[tokio::test]
    #[cfg(not(feature = "sqlite"))]
    async fn test_doc_handler_no_sqlite() {
        let handler = DocHandler::new("test-room-no-db".to_string()).await;
        assert_eq!(handler.doc_name, "test-room-no-db");

        // Basic sync generation should still work
        let messages = handler.generate_initial_sync();
        assert_eq!(messages.len(), 1);

        let (_, name) = DocHandler::read_and_skip_doc_name(&messages[0]).unwrap();
        assert_eq!(name, "test-room-no-db");
    }

    // ---- Resilience tests: ensure no panics on malformed input ----

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_malformed_binary_message() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db).await;

        // Pure garbage bytes should not panic
        let garbage = vec![0xFF, 0xFE, 0xFD, 0xFC, 0xFB];
        let responses = handler.handle_message(&garbage).await;
        // Should gracefully return (possibly empty), not panic
        let _ = responses;
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_truncated_sync_message() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db).await;

        // Valid doc name header + MSG_SYNC + truncated payload (incomplete SyncStep1)
        let mut msg = Vec::new();
        // VarString "test-room" = len 9 + bytes
        msg.push(9);
        msg.extend_from_slice(b"test-room");
        msg.push(MSG_SYNC); // msg type
        msg.push(0); // SyncStep1 tag
        msg.push(99); // claims 99 bytes of SV data but provides none

        let responses = handler.handle_message(&msg).await;
        // Should return empty (decode failure logged), not panic
        assert!(responses.is_empty());
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_invalid_update_data() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db).await;

        // Valid envelope with Update tag (2) but invalid yrs data inside
        let garbage_update = vec![0xDE, 0xAD, 0xBE, 0xEF];
        let payload = encode_update(&garbage_update);
        let msg = encode_test_msg("test-room", MSG_SYNC, &payload);

        let responses = handler.handle_message(&msg).await;
        // apply_update should return Err (logged), not panic
        let _ = responses;
    }

    #[tokio::test]
    #[cfg(feature = "sqlite")]
    async fn test_empty_content_after_doc_name() {
        let db = create_test_db().await;
        let handler = DocHandler::new("test-room".to_string(), db).await;

        // Message with only doc name, no msg type or payload
        let mut msg = Vec::new();
        msg.push(9);
        msg.extend_from_slice(b"test-room");
        // Nothing after the doc name

        let responses = handler.handle_message(&msg).await;
        assert!(responses.is_empty());
    }
}