#pragma once

#include <list>

#include "source/extensions/config_subscription/grpc/update_ack.h"

#include "absl/container/flat_hash_map.h"

namespace Envoy {

namespace Config {

// There is a head-of-line blocking issue resulting from the intersection of 1) ADS's need for

// subscription request ordering and 2) the ability to "pause" one of the resource types within ADS.

// We need a queue that understands ADS's resource type pausing. Specifically, we need front()/pop()

// to choose the first element whose type_url isn't paused.

class PausableAckQueue {

public:

  void push(UpdateAck x);

  size_t size() const;

  bool empty();

  const UpdateAck& front();

  UpdateAck popFront();

  void pause(const std::string& type_url);

  void resume(const std::string& type_url);

  bool paused(const std::string& type_url) const;

  void clear();

private:

  // It's ok for non-existent subs to be paused/resumed. The cleanest way to support that is to give

  // the pause state its own map. (Map key is type_url.)

  absl::flat_hash_map<std::string, uint32_t> pauses_;

  std::list<UpdateAck> storage_;

};

} // namespace Config

} // namespace Envoy