mq_bridge/endpoints/

memory.rs

//  mq-bridge
//  © Copyright 2025, by Marco Mengelkoch
//  Licensed under MIT License, see License file for more details
//  git clone https://github.com/marcomq/mq-bridge
use crate::canonical_message::tracing_support::LazyMessageIds;
use crate::event_store::{
    event_store_exists, get_or_create_event_store, EventStore, EventStoreConsumer,
};
use crate::models::MemoryConfig;
use crate::traits::{
    BatchCommitFunc, BoxFuture, ConsumerError, MessageConsumer, MessageDisposition,
    MessagePublisher, PublisherError, Received, ReceivedBatch, Sent, SentBatch,
};
use crate::CanonicalMessage;
use anyhow::anyhow;
use async_channel::{bounded, Receiver, Sender};
use async_trait::async_trait;
use once_cell::sync::Lazy;
use std::any::Any;
use std::collections::HashMap;
use std::sync::{Arc, Mutex};
use tokio::sync::oneshot;
use tracing::{info, trace};

/// A map to hold memory channels for the duration of the bridge setup.
/// This allows a consumer and publisher in different routes to connect to the same in-memory topic.
static RUNTIME_MEMORY_CHANNELS: Lazy<Mutex<HashMap<String, MemoryChannel>>> =
    Lazy::new(|| Mutex::new(HashMap::new()));

/// A map to hold memory response channels.
static RUNTIME_RESPONSE_CHANNELS: Lazy<Mutex<HashMap<String, MemoryResponseChannel>>> =
    Lazy::new(|| Mutex::new(HashMap::new()));

/// A shareable, thread-safe, in-memory channel for testing.
///
/// This struct holds the sender and receiver for an in-memory queue.
/// It can be cloned and shared between your test code and the bridge's endpoints. It transports batches of messages.
#[derive(Debug, Clone)]
pub struct MemoryChannel {
    pub sender: Sender<Vec<CanonicalMessage>>,
    pub receiver: Receiver<Vec<CanonicalMessage>>,
}

impl MemoryChannel {
    /// Creates a new batch channel with a specified capacity.
    pub fn new(capacity: usize) -> Self {
        let (sender, receiver) = bounded(capacity);
        Self { sender, receiver }
    }

    /// Helper function for tests to easily send a message to the channel.
    pub async fn send_message(&self, message: CanonicalMessage) -> anyhow::Result<()> {
        self.sender.send(vec![message]).await?;
        tracing::debug!("Message sent to memory {} channel", self.sender.len());
        Ok(())
    }

    /// Helper function for tests to easily fill in messages.
    pub async fn fill_messages(&self, messages: Vec<CanonicalMessage>) -> anyhow::Result<()> {
        // Send the entire vector as a single batch.
        self.sender
            .send(messages)
            .await
            .map_err(|e| anyhow!("Memory channel was closed while filling messages: {}", e))?;
        Ok(())
    }

    /// Closes the sender part of the channel.
    pub fn close(&self) {
        self.sender.close();
    }

    /// Helper function for tests to drain all messages from the channel.
    pub fn drain_messages(&self) -> Vec<CanonicalMessage> {
        let mut messages = Vec::new();
        // Drain all batches from the channel and flatten them into a single Vec.
        while let Ok(batch) = self.receiver.try_recv() {
            messages.extend(batch);
        }
        messages
    }

    /// Returns the number of bulk messages in the channel.
    pub fn len(&self) -> usize {
        self.receiver.len()
    }

    /// Returns the number of messages currently in the channel.
    pub fn is_empty(&self) -> bool {
        self.receiver.is_empty()
    }
}

/// A shareable, thread-safe, in-memory channel for responses.
#[derive(Debug, Clone)]
pub struct MemoryResponseChannel {
    pub sender: Sender<CanonicalMessage>,
    pub receiver: Receiver<CanonicalMessage>,
    waiters: Arc<tokio::sync::Mutex<HashMap<String, oneshot::Sender<CanonicalMessage>>>>,
}

impl MemoryResponseChannel {
    pub fn new(capacity: usize) -> Self {
        let (sender, receiver) = bounded(capacity);
        Self {
            sender,
            receiver,
            waiters: Arc::new(tokio::sync::Mutex::new(HashMap::new())),
        }
    }

    pub fn close(&self) {
        self.sender.close();
    }

    pub fn len(&self) -> usize {
        self.receiver.len()
    }

    pub fn is_empty(&self) -> bool {
        self.receiver.is_empty()
    }

    pub async fn wait_for_response(&self) -> anyhow::Result<CanonicalMessage> {
        self.receiver
            .recv()
            .await
            .map_err(|e| anyhow!("Error receiving response: {}", e))
    }

    pub async fn register_waiter(
        &self,
        correlation_id: &str,
        sender: oneshot::Sender<CanonicalMessage>,
    ) -> anyhow::Result<()> {
        let mut waiters = self.waiters.lock().await;
        if waiters.contains_key(correlation_id) {
            return Err(anyhow!(
                "Correlation ID {} already registered",
                correlation_id
            ));
        }
        waiters.insert(correlation_id.to_string(), sender);
        Ok(())
    }

    pub async fn remove_waiter(
        &self,
        correlation_id: &str,
    ) -> Option<oneshot::Sender<CanonicalMessage>> {
        self.waiters.lock().await.remove(correlation_id)
    }
}

/// Gets a shared `MemoryChannel` for a given topic, creating it if it doesn't exist.
pub fn get_or_create_channel(config: &MemoryConfig) -> MemoryChannel {
    let mut channels = RUNTIME_MEMORY_CHANNELS.lock().unwrap();
    channels
        .entry(config.topic.clone()) // Use the HashMap's entry API
        .or_insert_with(|| {
            info!(topic = %config.topic, "Creating new runtime memory channel");
            MemoryChannel::new(config.capacity.unwrap_or(100))
        })
        .clone()
}

/// Gets a shared `MemoryResponseChannel` for a given topic, creating it if it doesn't exist.
pub fn get_or_create_response_channel(topic: &str) -> MemoryResponseChannel {
    let mut channels = RUNTIME_RESPONSE_CHANNELS.lock().unwrap();
    channels
        .entry(topic.to_string())
        .or_insert_with(|| {
            info!(topic = %topic, "Creating new runtime memory response channel");
            MemoryResponseChannel::new(100)
        })
        .clone()
}

fn memory_channel_exists(topic: &str) -> bool {
    let channels = RUNTIME_MEMORY_CHANNELS.lock().unwrap();
    channels.contains_key(topic)
}

/// A sink that sends messages to an in-memory channel.
#[derive(Debug, Clone)]
pub struct MemoryPublisher {
    topic: String,
    backend: PublisherBackend,
    request_reply: bool,
    request_timeout: std::time::Duration,
}

#[derive(Debug, Clone)]
enum PublisherBackend {
    Queue(Sender<Vec<CanonicalMessage>>),
    Log(Arc<EventStore>),
}

impl MemoryPublisher {
    pub fn new(config: &MemoryConfig) -> anyhow::Result<Self> {
        let channel_exists = memory_channel_exists(&config.topic);
        let store_exists = event_store_exists(&config.topic);

        let backend = if config.subscribe_mode {
            if channel_exists {
                return Err(anyhow!("Topic '{}' is already active as a Queue (MemoryChannel), but Subscriber mode (EventStore) was requested.", config.topic));
            }
            let store = get_or_create_event_store(&config.topic);
            PublisherBackend::Log(store)
        } else if store_exists {
            // Adaptive behavior: If an EventStore already exists, we publish to it even if
            // subscribe_mode wasn't explicitly set. This prevents split-brain scenarios.
            tracing::debug!(topic = %config.topic, "Adapting publisher to Log mode due to existing EventStore");
            let store = get_or_create_event_store(&config.topic);
            PublisherBackend::Log(store)
        } else {
            let channel = get_or_create_channel(config);
            PublisherBackend::Queue(channel.sender)
        };

        Ok(Self {
            topic: config.topic.clone(),
            backend,
            request_reply: config.request_reply,
            request_timeout: std::time::Duration::from_millis(
                config.request_timeout_ms.unwrap_or(30000),
            ),
        })
    }

    /// Creates a new local memory publisher.
    ///
    /// This method creates a new in-memory publisher with the specified topic and capacity.
    /// The publisher will send messages to the in-memory channel for the specified topic.
    pub fn new_local(topic: &str, capacity: usize) -> Self {
        Self::new(&MemoryConfig {
            topic: topic.to_string(),
            capacity: Some(capacity),
            ..Default::default()
        })
        .expect("Failed to create local memory publisher")
    }

    /// Note: This helper is primarily for tests expecting a Queue.    
    /// If used on a broadcast publisher, it will create a separate Queue channel.
    pub fn channel(&self) -> MemoryChannel {
        get_or_create_channel(&MemoryConfig {
            topic: self.topic.clone(),
            capacity: None,
            ..Default::default()
        })
    }
}

#[async_trait]
impl MessagePublisher for MemoryPublisher {
    async fn send(&self, mut message: CanonicalMessage) -> Result<Sent, PublisherError> {
        match &self.backend {
            PublisherBackend::Log(store) => {
                store.append(message).await;
                Ok(Sent::Ack)
            }
            PublisherBackend::Queue(sender) => {
                if self.request_reply {
                    let cid = message
                        .metadata
                        .entry("correlation_id".to_string())
                        .or_insert_with(fast_uuid_v7::gen_id_string)
                        .clone();

                    let (tx, rx) = oneshot::channel();

                    // Register waiter before sending
                    let response_channel = get_or_create_response_channel(&self.topic);
                    response_channel
                        .register_waiter(&cid, tx)
                        .await
                        .map_err(PublisherError::NonRetryable)?;

                    // Send the message
                    // We use the internal sender directly to avoid recursion or cloning issues
                    if let Err(e) = sender.send(vec![message]).await {
                        response_channel.remove_waiter(&cid).await;
                        return Err(anyhow!("Failed to send to memory channel: {}", e).into());
                    }

                    // Wait for the response
                    let response = match tokio::time::timeout(self.request_timeout, rx).await {
                        Ok(Ok(resp)) => resp,
                        Ok(Err(e)) => {
                            response_channel.remove_waiter(&cid).await;
                            return Err(anyhow!(
                                "Failed to receive response for correlation_id {}: {}",
                                cid,
                                e
                            )
                            .into());
                        }
                        Err(_) => {
                            response_channel.remove_waiter(&cid).await;
                            return Err(PublisherError::Retryable(anyhow!(
                                "Request timed out waiting for response for correlation_id {}",
                                cid
                            )));
                        }
                    };

                    Ok(Sent::Response(response))
                } else {
                    self.send_batch(vec![message]).await?;
                    Ok(Sent::Ack)
                }
            }
        }
    }

    async fn send_batch(
        &self,
        messages: Vec<CanonicalMessage>,
    ) -> Result<SentBatch, PublisherError> {
        match &self.backend {
            PublisherBackend::Log(store) => {
                trace!(
                    topic = %self.topic,
                    message_ids = ?LazyMessageIds(&messages),
                    "Appending batch to event store"
                );
                store.append_batch(messages).await;
                Ok(SentBatch::Ack)
            }
            PublisherBackend::Queue(sender) => {
                trace!(
                    topic = %self.topic,
                    message_ids = ?LazyMessageIds(&messages),
                    "Sending batch to memory channel. Current batch count: {}",
                    sender.len()
                );
                sender
                    .send(messages)
                    .await
                    .map_err(|e| anyhow!("Failed to send to memory channel: {}", e))?;
                Ok(SentBatch::Ack)
            }
        }
    }

    fn as_any(&self) -> &dyn Any {
        self
    }
}

/// A queue-based consumer (legacy behavior).
#[derive(Debug)]
pub struct MemoryQueueConsumer {
    topic: String,
    receiver: Receiver<Vec<CanonicalMessage>>,
    // Internal buffer to hold messages from a received batch.
    buffer: Vec<CanonicalMessage>,
    enable_nack: bool,
}

/// A source that reads messages from an in-memory channel or event store.
#[derive(Debug)]
pub enum MemoryConsumer {
    Queue(MemoryQueueConsumer),
    Log {
        consumer: EventStoreConsumer,
        topic: String,
    },
}

impl MemoryConsumer {
    pub fn new(config: &MemoryConfig) -> anyhow::Result<Self> {
        let channel_exists = memory_channel_exists(&config.topic);
        let store_exists = event_store_exists(&config.topic);

        if config.subscribe_mode {
            if channel_exists {
                return Err(anyhow!("Topic '{}' is already active as a Queue (MemoryChannel), but Subscriber mode (EventStore) was requested.", config.topic));
            }
            let store = get_or_create_event_store(&config.topic);
            // For subscriber mode, we generate a unique ID if one isn't implicit in the usage.
            // However, MemorySubscriber struct usually handles the ID.
            // If MemoryConsumer is used directly with subscribe_mode=true, we assume a default ID or ephemeral.
            let subscriber_id = format!("{}-consumer", config.topic);
            info!(topic = %config.topic, subscriber_id = %subscriber_id, "Memory consumer (Log mode) connected");
            let consumer = store.consumer(subscriber_id);
            Ok(Self::Log {
                consumer,
                topic: config.topic.clone(),
            })
        } else {
            if store_exists {
                // Unlike the Publisher, we cannot silently adapt to Log mode here.
                // The EventStore implementation currently supports Pub/Sub (broadcast) only.
                // Adapting would result in this consumer receiving all messages, violating
                // the expected Queue (competing consumer) semantics requested by `subscribe_mode: false`.
                return Err(anyhow!("Topic '{}' is already active as a Subscriber Log (EventStore), but Queue mode (MemoryChannel) was requested.", config.topic));
            }
            let queue = MemoryQueueConsumer::new(config)?;
            Ok(Self::Queue(queue))
        }
    }
}

impl MemoryQueueConsumer {
    pub fn new(config: &MemoryConfig) -> anyhow::Result<Self> {
        let channel = get_or_create_channel(config);
        Ok(Self {
            topic: config.topic.clone(),
            receiver: channel.receiver.clone(),
            buffer: Vec::new(),
            enable_nack: config.enable_nack,
        })
    }

    async fn get_buffered_msgs(
        &mut self,
        max_messages: usize,
    ) -> Result<Vec<CanonicalMessage>, ConsumerError> {
        // If the internal buffer has messages, return them first.
        if self.buffer.is_empty() {
            // Buffer is empty. Wait for a new batch from the channel.
            self.buffer = match self.receiver.recv().await {
                Ok(batch) => batch,
                Err(_) => return Err(ConsumerError::EndOfStream),
            };
            // Reverse the buffer so we can efficiently pop from the end.
            self.buffer.reverse();
        }

        // Determine the number of messages to take from the buffer.
        let num_to_take = self.buffer.len().min(max_messages);
        let split_at = self.buffer.len() - num_to_take;

        // `split_off` is highly efficient. It splits the Vec in two at the given
        // index and returns the part after the index, leaving the first part.
        let mut messages = self.buffer.split_off(split_at);
        messages.reverse(); // Reverse back to original order.
        Ok(messages)
    }
}

#[async_trait]
impl MessageConsumer for MemoryQueueConsumer {
    async fn receive_batch(&mut self, max_messages: usize) -> Result<ReceivedBatch, ConsumerError> {
        // If the internal buffer has messages, return them first.

        let mut messages = self.get_buffered_msgs(max_messages).await?;
        while messages.len() < max_messages / 2 {
            if let Ok(mut next_batch) = self.receiver.try_recv() {
                if next_batch.len() + messages.len() > max_messages {
                    let needed = max_messages - messages.len();
                    let mut to_buffer = next_batch.split_off(needed);
                    messages.append(&mut next_batch);
                    self.buffer.append(&mut to_buffer);
                    self.buffer.reverse();
                    break;
                } else {
                    messages.append(&mut next_batch);
                }
            } else {
                break;
            }
        }
        trace!(count = messages.len(), topic = %self.topic, message_ids = ?LazyMessageIds(&messages), "Received batch of memory messages");
        if messages.is_empty() {
            return Ok(ReceivedBatch {
                messages: Vec::new(),
                commit: Box::new(|_| {
                    Box::pin(async move { Ok(()) }) as BoxFuture<'static, anyhow::Result<()>>
                }),
            });
        }

        let topic = self.topic.clone();
        let expected_count = messages.len();
        let correlation_ids: Vec<Option<String>> = messages
            .iter()
            .map(|m| m.metadata.get("correlation_id").cloned())
            .collect();

        // This clone is necessary to support NACKs. The commit function needs access
        // to the messages to re-queue them, but the `ReceivedBatch` must also return
        // ownership of the messages to the caller. Without changing the core traits,
        // cloning is the only way to satisfy both owners.
        let messages_for_retry = if self.enable_nack {
            Some(messages.clone())
        } else {
            None
        };
        let commit = Box::new(move |dispositions: Vec<MessageDisposition>| {
            Box::pin(async move {
                if dispositions.len() != expected_count {
                    return Err(anyhow::anyhow!(
                        "Memory batch commit received mismatched disposition count: expected {}, got {}",
                        expected_count,
                        dispositions.len()
                    ));
                }
                let response_channel = get_or_create_response_channel(&topic);
                let mut to_requeue = Vec::new();

                for (i, disposition) in dispositions.into_iter().enumerate() {
                    match disposition {
                        MessageDisposition::Reply(mut resp) => {
                            if !resp.metadata.contains_key("correlation_id") {
                                if let Some(Some(cid)) = correlation_ids.get(i) {
                                    resp.metadata
                                        .insert("correlation_id".to_string(), cid.clone());
                                }
                            }

                            // If the receiver is dropped, sending will fail. We can ignore it.
                            let mut handled = false;
                            if let Some(cid) = resp.metadata.get("correlation_id") {
                                if let Some(tx) = response_channel.remove_waiter(cid).await {
                                    let _ = tx.send(resp.clone());
                                    handled = true;
                                }
                            }
                            if !handled {
                                let _ = response_channel.sender.send(resp).await;
                            }
                        }
                        MessageDisposition::Nack => {
                            // Re-queue the message if Nacked
                            if let Some(msgs) = &messages_for_retry {
                                if let Some(msg) = msgs.get(i) {
                                    to_requeue.push(msg.clone());
                                }
                            }
                        }
                        MessageDisposition::Ack => {}
                    }
                }

                if !to_requeue.is_empty() {
                    let main_channel = get_or_create_channel(&MemoryConfig {
                        topic: topic.to_string(),
                        capacity: None,
                        ..Default::default()
                    });
                    if main_channel.sender.send(to_requeue).await.is_err() {
                        tracing::error!("Failed to re-queue NACKed messages to memory channel as it was closed.");
                    }
                }
                Ok(())
            }) as BoxFuture<'static, anyhow::Result<()>>
        }) as BatchCommitFunc;
        Ok(ReceivedBatch { messages, commit })
    }

    fn as_any(&self) -> &dyn Any {
        self
    }
}

#[async_trait]
impl MessageConsumer for MemoryConsumer {
    async fn receive_batch(&mut self, max_messages: usize) -> Result<ReceivedBatch, ConsumerError> {
        match self {
            Self::Queue(q) => q.receive_batch(max_messages).await,
            Self::Log { consumer, .. } => consumer.receive_batch(max_messages).await,
        }
    }

    fn as_any(&self) -> &dyn Any {
        self
    }
}

impl MemoryConsumer {
    pub fn new_local(topic: &str, capacity: usize) -> Self {
        Self::new(&MemoryConfig {
            topic: topic.to_string(),
            capacity: Some(capacity),
            ..Default::default()
        })
        .expect("Failed to create local memory consumer")
    }
    pub fn channel(&self) -> MemoryChannel {
        let topic = match self {
            Self::Queue(q) => &q.topic,
            Self::Log { topic, .. } => topic,
        };
        get_or_create_channel(&MemoryConfig {
            topic: topic.clone(),
            ..Default::default()
        })
    }
}

pub struct MemorySubscriber {
    consumer: MemoryConsumer,
}

impl MemorySubscriber {
    pub fn new(config: &MemoryConfig, id: &str) -> anyhow::Result<Self> {
        let mut sub_config = config.clone();
        // If subscribe_mode is true, we use EventStore with the original topic but unique subscriber ID.
        // If false (legacy), we use the suffixed topic queue.
        let consumer = if config.subscribe_mode {
            let store = get_or_create_event_store(&config.topic);
            MemoryConsumer::Log {
                consumer: store.consumer(id.to_string()),
                topic: config.topic.clone(),
            }
        } else {
            sub_config.topic = format!("{}-{}", config.topic, id);
            MemoryConsumer::new(&sub_config)?
        };
        Ok(Self { consumer })
    }
}

#[async_trait]
impl MessageConsumer for MemorySubscriber {
    async fn receive_batch(&mut self, max_messages: usize) -> Result<ReceivedBatch, ConsumerError> {
        self.consumer.receive_batch(max_messages).await
    }

    async fn receive(&mut self) -> Result<Received, ConsumerError> {
        self.consumer.receive().await
    }

    fn as_any(&self) -> &dyn Any {
        self
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::models::{Endpoint, Route};
    use crate::traits::Handled;
    use crate::{msg, CanonicalMessage};
    use serde_json::json;
    use tokio::time::sleep;

    #[tokio::test]
    async fn test_memory_channel_integration() {
        let mut consumer = MemoryConsumer::new_local("test-mem1", 10);
        let publisher = MemoryPublisher::new_local("test-mem1", 10);

        let msg = msg!(json!({"hello": "memory"}));

        // Send a message via the publisher
        publisher.send(msg.clone()).await.unwrap();

        sleep(std::time::Duration::from_millis(10)).await;
        // Receive it with the consumer
        let received = consumer.receive().await.unwrap();
        let _ = (received.commit)(MessageDisposition::Ack).await;
        assert_eq!(received.message.payload, msg.payload);
        assert_eq!(consumer.channel().len(), 0);
    }

    #[tokio::test]
    async fn test_memory_publisher_and_consumer_integration() {
        let mut consumer = MemoryConsumer::new_local("test-mem2", 10);
        let publisher = MemoryPublisher::new_local("test-mem2", 10);

        let msg1 = msg!(json!({"message": "one"}));
        let msg2 = msg!(json!({"message": "two"}));
        let msg3 = msg!(json!({"message": "three"}));

        // 3. Send messages via the publisher
        publisher
            .send_batch(vec![msg1.clone(), msg2.clone()])
            .await
            .unwrap();
        publisher.send(msg3.clone()).await.unwrap();

        // 4. Verify the channel has the messages
        assert_eq!(publisher.channel().len(), 2);

        // 5. Receive the messages and verify them
        let received1 = consumer.receive().await.unwrap();
        let _ = (received1.commit)(MessageDisposition::Ack).await;
        assert_eq!(received1.message.payload, msg1.payload);

        let batch2 = consumer.receive_batch(1).await.unwrap();
        let (received_msg2, commit2) = (batch2.messages, batch2.commit);
        let _ = commit2(vec![MessageDisposition::Ack; received_msg2.len()]).await;
        assert_eq!(received_msg2.len(), 1);
        assert_eq!(received_msg2.first().unwrap().payload, msg2.payload);
        let batch3 = consumer.receive_batch(2).await.unwrap();
        let (received_msg3, commit3) = (batch3.messages, batch3.commit);
        let _ = commit3(vec![MessageDisposition::Ack; received_msg3.len()]).await;
        assert_eq!(received_msg3.first().unwrap().payload, msg3.payload);

        // 6. Verify that the channel is now empty
        assert_eq!(publisher.channel().len(), 0);

        // 7. Verify that reading again results in an error because the channel is empty and we are not closing it
        // In a real scenario with a closed channel, this would error out. Here we can just check it's empty.
        // A `receive` call would just hang, waiting for a message.
    }

    #[tokio::test]
    async fn test_memory_subscriber_structure() {
        let cfg = MemoryConfig {
            topic: "base_topic".to_string(),
            capacity: Some(10),
            ..Default::default()
        };
        let subscriber_id = "sub1";
        let mut subscriber = MemorySubscriber::new(&cfg, subscriber_id).unwrap();

        // The subscriber should be listening on "base_topic-sub1"
        // We can verify this by creating a publisher for that specific topic.
        let pub_cfg = MemoryConfig {
            topic: format!("base_topic-{}", subscriber_id),
            capacity: Some(10),
            ..Default::default()
        };
        let publisher = MemoryPublisher::new(&pub_cfg).unwrap();

        publisher.send("hello subscriber".into()).await.unwrap();

        let received = subscriber.receive().await.unwrap();
        assert_eq!(received.message.get_payload_str(), "hello subscriber");
    }

    #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
    async fn test_memory_request_reply_mode() {
        let topic = format!("mem_rr_topic_{}", fast_uuid_v7::gen_id_str());
        let input_endpoint = Endpoint::new_memory(&topic, 10);
        let output_endpoint = Endpoint::new_response();
        let handler = |mut msg: CanonicalMessage| async move {
            let request_payload = msg.get_payload_str();
            let response_payload = format!("reply to {}", request_payload);
            msg.set_payload_str(response_payload);
            Ok(Handled::Publish(msg))
        };

        let route = Route::new(input_endpoint, output_endpoint).with_handler(handler);
        route.deploy("mem_rr_test").await.unwrap();

        // Create a publisher with request_reply = true
        let publisher = MemoryPublisher::new(&MemoryConfig {
            topic: topic.clone(),
            capacity: Some(10),
            request_reply: true,
            request_timeout_ms: Some(2000),
            ..Default::default()
        })
        .unwrap();

        let result = publisher.send("direct request".into()).await.unwrap();

        if let Sent::Response(response_msg) = result {
            assert_eq!(response_msg.get_payload_str(), "reply to direct request");
        } else {
            panic!("Expected Sent::Response, got {:?}", result);
        }

        // Clean up
        Route::stop("mem_rr_test").await;
    }

    #[tokio::test]
    async fn test_memory_nack_requeue() {
        let topic = format!("test_nack_requeue_{}", fast_uuid_v7::gen_id_str());
        let config = MemoryConfig {
            topic: topic.clone(),
            capacity: Some(10),
            enable_nack: true,
            ..Default::default()
        };
        let mut consumer = MemoryConsumer::new(&config).unwrap();
        let publisher = MemoryPublisher::new_local(&topic, 10);

        publisher.send("to_be_nacked".into()).await.unwrap();

        // 1. Receive and Nack
        let received1 = consumer.receive().await.unwrap();
        assert_eq!(received1.message.get_payload_str(), "to_be_nacked");
        (received1.commit)(crate::traits::MessageDisposition::Nack)
            .await
            .unwrap();

        // 2. Receive again (should be re-queued)
        let received2 = tokio::time::timeout(std::time::Duration::from_secs(1), consumer.receive())
            .await
            .expect("Timed out waiting for re-queued message")
            .unwrap();
        assert_eq!(received2.message.get_payload_str(), "to_be_nacked");

        // 3. Ack
        (received2.commit)(crate::traits::MessageDisposition::Ack)
            .await
            .unwrap();

        // 4. Verify empty
        let result =
            tokio::time::timeout(std::time::Duration::from_millis(100), consumer.receive()).await;
        assert!(result.is_err(), "Channel should be empty");
    }

    #[tokio::test]
    async fn test_memory_event_store_integration() {
        let topic = "event_store_test";
        // Publisher with subscribe_mode=true enables EventStore writing
        let pub_config = MemoryConfig {
            topic: topic.to_string(),
            subscribe_mode: true,
            ..Default::default()
        };
        let publisher = MemoryPublisher::new(&pub_config).unwrap();

        // Subscriber 1
        let mut sub1 = MemorySubscriber::new(&pub_config, "sub1").unwrap();
        // Subscriber 2
        let mut sub2 = MemorySubscriber::new(&pub_config, "sub2").unwrap();

        publisher.send("event1".into()).await.unwrap();

        let msg1 = sub1.receive().await.unwrap();
        assert_eq!(msg1.message.get_payload_str(), "event1");
        (msg1.commit)(MessageDisposition::Ack).await.unwrap();

        let msg2 = sub2.receive().await.unwrap();
        assert_eq!(msg2.message.get_payload_str(), "event1");
    }

    #[tokio::test]
    async fn test_memory_no_subscribers_persistence() {
        let topic = format!("no_subs_{}", fast_uuid_v7::gen_id_str());
        let pub_config = MemoryConfig {
            topic: topic.clone(),
            subscribe_mode: true,
            ..Default::default()
        };

        // 1. Create Publisher (Log mode)
        let publisher = MemoryPublisher::new(&pub_config).unwrap();

        // 2. Publish messages with no subscribers
        publisher.send("msg1".into()).await.unwrap();
        publisher.send("msg2".into()).await.unwrap();

        // 3. Create Subscriber (Late joiner)
        let sub_config = MemoryConfig {
            topic: topic.clone(),
            subscribe_mode: true,
            ..Default::default()
        };
        let mut subscriber = MemorySubscriber::new(&sub_config, "late_sub").unwrap();

        // 4. Verify messages are received
        let received1 = subscriber.receive().await.unwrap();
        assert_eq!(received1.message.get_payload_str(), "msg1");
        (received1.commit)(MessageDisposition::Ack).await.unwrap();

        let received2 = subscriber.receive().await.unwrap();
        assert_eq!(received2.message.get_payload_str(), "msg2");
        (received2.commit)(MessageDisposition::Ack).await.unwrap();
    }

    #[tokio::test]
    async fn test_memory_mixed_mode_error() {
        let topic_q = format!("mixed_q_{}", fast_uuid_v7::gen_id_str());
        let topic_l = format!("mixed_l_{}", fast_uuid_v7::gen_id_str());

        // Case 1: Active Queue, try to create Log Consumer
        let _pub_q = MemoryPublisher::new_local(&topic_q, 10); // Creates Queue backend

        let log_conf = MemoryConfig {
            topic: topic_q.clone(),
            subscribe_mode: true,
            ..Default::default()
        };
        let err = MemoryConsumer::new(&log_conf);
        assert!(err.is_err());
        assert!(err
            .unwrap_err()
            .to_string()
            .contains("already active as a Queue"));

        // Case 2: Active Log, try to create Queue Consumer
        let log_pub_conf = MemoryConfig {
            topic: topic_l.clone(),
            subscribe_mode: true,
            ..Default::default()
        };
        let _pub_l = MemoryPublisher::new(&log_pub_conf).unwrap(); // Creates Log backend

        let queue_conf = MemoryConfig {
            topic: topic_l.clone(),
            subscribe_mode: false,
            ..Default::default()
        };
        let err = MemoryConsumer::new(&queue_conf);
        assert!(err.is_err());
        assert!(err
            .unwrap_err()
            .to_string()
            .contains("already active as a Subscriber Log"));
    }

    #[tokio::test]
    async fn test_memory_publisher_mixed_mode_error() {
        let topic_q = format!("pub_mixed_q_{}", fast_uuid_v7::gen_id_str());

        // 1. Create a Queue Consumer to establish the channel
        let _cons_q = MemoryConsumer::new_local(&topic_q, 10);

        // 2. Try to create a Log Publisher on the same topic
        let log_conf = MemoryConfig {
            topic: topic_q.clone(),
            subscribe_mode: true,
            ..Default::default()
        };
        let err = MemoryPublisher::new(&log_conf);
        assert!(err.is_err());
        assert!(err
            .unwrap_err()
            .to_string()
            .contains("already active as a Queue"));
    }

    #[tokio::test]
    async fn test_memory_publisher_adaptive_behavior() {
        let topic = format!("adaptive_{}", fast_uuid_v7::gen_id_str());

        // 1. Create a Log Consumer (Subscriber) to establish the EventStore
        let sub_config = MemoryConfig {
            topic: topic.clone(),
            subscribe_mode: true,
            ..Default::default()
        };
        let mut subscriber = MemorySubscriber::new(&sub_config, "sub1").unwrap();

        // 2. Create a Publisher WITHOUT subscribe_mode explicitly set
        let pub_config = MemoryConfig {
            topic: topic.clone(),
            subscribe_mode: false, // Default is false
            ..Default::default()
        };
        // This should succeed and adapt to Log mode because the store exists
        let publisher = MemoryPublisher::new(&pub_config).unwrap();

        // 3. Verify it publishes to the store (subscriber receives it)
        publisher.send("adaptive_msg".into()).await.unwrap();

        let received = subscriber.receive().await.unwrap();
        assert_eq!(received.message.get_payload_str(), "adaptive_msg");
    }
}