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// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
#pragma once
#include "imessagehandler.h"
#include "ireplyhandler.h"
#include "message.h"
#include "reply.h"
#include "queue.h"
#include <mutex>
#include <map>
namespace mbus {
/**
* A Sequencer ensures correct sequencing of pending messages. When a Sequencer is created, it is given an
* object implementing the IMessageHandler API to use for sending messages. This class is used by the
* SourceSession class and is not intended for external use.
*/
class Sequencer : public IMessageHandler,
public IReplyHandler
{
private:
std::mutex _lock;
IMessageHandler &_sender;
using MessageQueue = Queue<Message*>;
using QueueMap = std::map<uint64_t, MessageQueue*>;
QueueMap _seqMap;
private:
/**
* Filter a message against the current sequencing state. If the message is returned back out again, it
* has been cleared for sending and its sequencing information has been added to the state. If the message
* is not returned it has been queued for later sending due to sequencing restrictions. This method also
* sets the sequence id as message context.
*
* @param msg The message to filter.
* @return The argument message if it passed the filter.
*/
Message::UP filter(Message::UP msg);
/**
* Internal method for forwarding a sequenced message to the underlying sender.
*
* @param msg The message to forward.
*/
void sequencedSend(Message::UP msg);
public:
/**
* Convenience typedef for an auto pointer to a Sequencer object.
*/
using UP = std::unique_ptr<Sequencer>;
/**
* Create a new Sequencer using the given sender to send messages.
*
* @param sender The underlying sender.
*/
Sequencer(IMessageHandler &sender);
/**
* Destruct. This will also destruct any Message objects held back due to sequencing collisions.
*/
virtual ~Sequencer();
/**
* All messages pass through this handler when being sent by the owning source session. In case the
* message has no sequencing-id, it is simply passed through to the next handler in the chain. Sequenced
* messages are sent only if there is no queue for their id, otherwise they are queued.
*
* @param msg The message to send.
*/
void handleMessage(Message::UP msg) override;
/**
* Lookup the sequencing id of an incoming reply to pop the front of the corresponding queue, and then
* send the next message in line, if any.
*
* @param reply The reply received.
*/
void handleReply(Reply::UP reply) override;
};
} // namespace mbus
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