/*
 *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
 *
 *  Use of this source code is governed by a BSD-style license
 *  that can be found in the LICENSE file in the root of the source
 *  tree. An additional intellectual property rights grant can be found
 *  in the file PATENTS.  All contributing project authors may
 *  be found in the AUTHORS file in the root of the source tree.
 */

#ifndef MODULES_PACING_PACKET_QUEUE_H_
#define MODULES_PACING_PACKET_QUEUE_H_

#include <list>
#include <queue>
#include <vector>

#include "modules/rtp_rtcp/include/rtp_rtcp_defines.h"

namespace webrtc {

class PacketQueue {
 public:
  explicit PacketQueue(const Clock* clock);
  virtual ~PacketQueue();

  struct Packet {
    Packet(RtpPacketSender::Priority priority,
           uint32_t ssrc,
           uint16_t seq_number,
           int64_t capture_time_ms,
           int64_t enqueue_time_ms,
           size_t length_in_bytes,
           bool retransmission,
           uint64_t enqueue_order);

    virtual ~Packet();

    RtpPacketSender::Priority priority;
    uint32_t ssrc;
    uint16_t sequence_number;
    int64_t capture_time_ms;  // Absolute time of frame capture.
    int64_t enqueue_time_ms;  // Absolute time of pacer queue entry.
    int64_t sum_paused_ms;  // Sum of time spent in queue while pacer is paused.
    size_t bytes;
    bool retransmission;
    uint64_t enqueue_order;
    std::list<Packet>::iterator this_it;
  };

  void Push(const Packet& packet);
  const Packet& BeginPop();
  void CancelPop(const Packet& packet);
  void FinalizePop(const Packet& packet);
  bool Empty() const;
  size_t SizeInPackets() const;
  uint64_t SizeInBytes() const;
  int64_t OldestEnqueueTimeMs() const;
  void UpdateQueueTime(int64_t timestamp_ms);
  void SetPauseState(bool paused, int64_t timestamp_ms);
  int64_t AverageQueueTimeMs() const;

 private:
  // Try to add a packet to the set of ssrc/seqno identifiers currently in the
  // queue. Return true if inserted, false if this is a duplicate.
  bool AddToDupeSet(const Packet& packet);

  void RemoveFromDupeSet(const Packet& packet);

  // Used by priority queue to sort packets.
  struct Comparator {
    bool operator()(const Packet* first, const Packet* second) {
      // Highest prio = 0.
      if (first->priority != second->priority)
        return first->priority > second->priority;

      // Retransmissions go first.
      if (second->retransmission != first->retransmission)
        return second->retransmission;

      // Older frames have higher prio.
      if (first->capture_time_ms != second->capture_time_ms)
        return first->capture_time_ms > second->capture_time_ms;

      return first->enqueue_order > second->enqueue_order;
    }
  };

  // List of packets, in the order the were enqueued. Since dequeueing may
  // occur out of order, use list instead of vector.
  std::list<Packet> packet_list_;
  // Priority queue of the packets, sorted according to Comparator.
  // Use pointers into list, to avodi moving whole struct within heap.
  std::priority_queue<Packet*, std::vector<Packet*>, Comparator> prio_queue_;
  // Total number of bytes in the queue.
  uint64_t bytes_;
  const Clock* const clock_;
  int64_t queue_time_sum_;
  int64_t time_last_updated_;
  bool paused_;
};
}  // namespace webrtc

#endif  // MODULES_PACING_PACKET_QUEUE_H_