/*
 *  Copyright (c) 2014, Oculus VR, Inc.
 *  All rights reserved.
 *
 *  This source code is licensed under the BSD-style license found in the
 *  LICENSE file in the root directory of this source tree. An additional grant 
 *  of patent rights can be found in the PATENTS file in the same directory.
 *
 */

/*
http://www.ssfnet.org/Exchange/tcp/tcpTutorialNotes.html

cwnd=max bytes allowed on wire at once

Start:
cwnd=mtu
ssthresh=unlimited

Slow start:
On ack cwnd*=2

congestion avoidance:
On ack during new period
cwnd+=mtu*mtu/cwnd

on loss or duplicate ack during period:
sshtresh=cwnd/2
cwnd=MTU
This reenters slow start

If cwnd < ssthresh, then use slow start
else use congestion avoidance


*/

#include "RakNetDefines.h"

#if USE_SLIDING_WINDOW_CONGESTION_CONTROL==1

#ifndef __CONGESTION_CONTROL_SLIDING_WINDOW_H
#define __CONGESTION_CONTROL_SLIDING_WINDOW_H

#include "NativeTypes.h"
#include "RakNetTime.h"
#include "RakNetTypes.h"
#include "DS_Queue.h"

/// Sizeof an UDP header in byte
#define UDP_HEADER_SIZE 28

#define CC_DEBUG_PRINTF_1(x)
#define CC_DEBUG_PRINTF_2(x,y)
#define CC_DEBUG_PRINTF_3(x,y,z)
#define CC_DEBUG_PRINTF_4(x,y,z,a)
#define CC_DEBUG_PRINTF_5(x,y,z,a,b)
//#define CC_DEBUG_PRINTF_1(x) printf(x)
//#define CC_DEBUG_PRINTF_2(x,y) printf(x,y)
//#define CC_DEBUG_PRINTF_3(x,y,z) printf(x,y,z)
//#define CC_DEBUG_PRINTF_4(x,y,z,a) printf(x,y,z,a)
//#define CC_DEBUG_PRINTF_5(x,y,z,a,b) printf(x,y,z,a,b)

/// Set to 4 if you are using the iPod Touch TG. See http://www.jenkinssoftware.com/forum/index.php?topic=2717.0
#define CC_TIME_TYPE_BYTES 8

#if CC_TIME_TYPE_BYTES==8
typedef RakNet::TimeUS CCTimeType;
#else
typedef RakNet::TimeMS CCTimeType;
#endif

typedef RakNet::uint24_t DatagramSequenceNumberType;
typedef double BytesPerMicrosecond;
typedef double BytesPerSecond;
typedef double MicrosecondsPerByte;

namespace RakNet
{

class CCRakNetSlidingWindow
{
	public:
	
	CCRakNetSlidingWindow();
	~CCRakNetSlidingWindow();

	/// Reset all variables to their initial states, for a new connection
	void Init(CCTimeType curTime, uint32_t maxDatagramPayload);

	/// Update over time
	void Update(CCTimeType curTime, bool hasDataToSendOrResend);

	int GetRetransmissionBandwidth(CCTimeType curTime, CCTimeType timeSinceLastTick, uint32_t unacknowledgedBytes, bool isContinuousSend);
	int GetTransmissionBandwidth(CCTimeType curTime, CCTimeType timeSinceLastTick, uint32_t unacknowledgedBytes, bool isContinuousSend);

	/// Acks do not have to be sent immediately. Instead, they can be buffered up such that groups of acks are sent at a time
	/// This reduces overall bandwidth usage
	/// How long they can be buffered depends on the retransmit time of the sender
	/// Should call once per update tick, and send if needed
	bool ShouldSendACKs(CCTimeType curTime, CCTimeType estimatedTimeToNextTick);

	/// Every data packet sent must contain a sequence number
	/// Call this function to get it. The sequence number is passed into OnGotPacketPair()
	DatagramSequenceNumberType GetAndIncrementNextDatagramSequenceNumber(void);
	DatagramSequenceNumberType GetNextDatagramSequenceNumber(void);

	/// Call this when you send packets
	/// Every 15th and 16th packets should be sent as a packet pair if possible
	/// When packets marked as a packet pair arrive, pass to OnGotPacketPair()
	/// When any packets arrive, (additionally) pass to OnGotPacket
	/// Packets should contain our system time, so we can pass rtt to OnNonDuplicateAck()
	void OnSendBytes(CCTimeType curTime, uint32_t numBytes);

	/// Call this when you get a packet pair
	void OnGotPacketPair(DatagramSequenceNumberType datagramSequenceNumber, uint32_t sizeInBytes, CCTimeType curTime);

	/// Call this when you get a packet (including packet pairs)
	/// If the DatagramSequenceNumberType is out of order, skippedMessageCount will be non-zero
	/// In that case, send a NAK for every sequence number up to that count
	bool OnGotPacket(DatagramSequenceNumberType datagramSequenceNumber, bool isContinuousSend, CCTimeType curTime, uint32_t sizeInBytes, uint32_t *skippedMessageCount);

	/// Call when you get a NAK, with the sequence number of the lost message
	/// Affects the congestion control
	void OnResend(CCTimeType curTime, RakNet::TimeUS nextActionTime);
	void OnNAK(CCTimeType curTime, DatagramSequenceNumberType nakSequenceNumber);

	/// Call this when an ACK arrives.
	/// hasBAndAS are possibly written with the ack, see OnSendAck()
	/// B and AS are used in the calculations in UpdateWindowSizeAndAckOnAckPerSyn
	/// B and AS are updated at most once per SYN 
	void OnAck(CCTimeType curTime, CCTimeType rtt, bool hasBAndAS, BytesPerMicrosecond _B, BytesPerMicrosecond _AS, double totalUserDataBytesAcked, bool isContinuousSend, DatagramSequenceNumberType sequenceNumber );
	void OnDuplicateAck( CCTimeType curTime, DatagramSequenceNumberType sequenceNumber );
	
	/// Call when you send an ack, to see if the ack should have the B and AS parameters transmitted
	/// Call before calling OnSendAck()
	void OnSendAckGetBAndAS(CCTimeType curTime, bool *hasBAndAS, BytesPerMicrosecond *_B, BytesPerMicrosecond *_AS);

	/// Call when we send an ack, to write B and AS if needed
	/// B and AS are only written once per SYN, to prevent slow calculations
	/// Also updates SND, the period between sends, since data is written out
	/// Be sure to call OnSendAckGetBAndAS() before calling OnSendAck(), since whether you write it or not affects \a numBytes
	void OnSendAck(CCTimeType curTime, uint32_t numBytes);

	/// Call when we send a NACK
	/// Also updates SND, the period between sends, since data is written out
	void OnSendNACK(CCTimeType curTime, uint32_t numBytes);
	
	/// Retransmission time out for the sender
	/// If the time difference between when a message was last transmitted, and the current time is greater than RTO then packet is eligible for retransmission, pending congestion control
	/// RTO = (RTT + 4 * RTTVar) + SYN
	/// If we have been continuously sending for the last RTO, and no ACK or NAK at all, SND*=2;
	/// This is per message, which is different from UDT, but RakNet supports packetloss with continuing data where UDT is only RELIABLE_ORDERED
	/// Minimum value is 100 milliseconds
	CCTimeType GetRTOForRetransmission(unsigned char timesSent) const;

	/// Set the maximum amount of data that can be sent in one datagram
	/// Default to MAXIMUM_MTU_SIZE-UDP_HEADER_SIZE
	void SetMTU(uint32_t bytes);

	/// Return what was set by SetMTU()
	uint32_t GetMTU(void) const;

	/// Query for statistics
	BytesPerMicrosecond GetLocalSendRate(void) const {return 0;}
	BytesPerMicrosecond GetLocalReceiveRate(CCTimeType currentTime) const;
	BytesPerMicrosecond GetRemoveReceiveRate(void) const {return 0;}
	//BytesPerMicrosecond GetEstimatedBandwidth(void) const {return B;}
	BytesPerMicrosecond GetEstimatedBandwidth(void) const {return GetLinkCapacityBytesPerSecond()*1000000.0;}
	double GetLinkCapacityBytesPerSecond(void) const {return 0;}

	/// Query for statistics
	double GetRTT(void) const;

	bool GetIsInSlowStart(void) const {return IsInSlowStart();}
	uint32_t GetCWNDLimit(void) const {return (uint32_t) 0;}


	/// Is a > b, accounting for variable overflow?
	static bool GreaterThan(DatagramSequenceNumberType a, DatagramSequenceNumberType b);
	/// Is a < b, accounting for variable overflow?
	static bool LessThan(DatagramSequenceNumberType a, DatagramSequenceNumberType b);
//	void SetTimeBetweenSendsLimit(unsigned int bitsPerSecond);
	uint64_t GetBytesPerSecondLimitByCongestionControl(void) const;
	  
	protected:

	// Maximum amount of bytes that the user can send, e.g. the size of one full datagram
	uint32_t MAXIMUM_MTU_INCLUDING_UDP_HEADER;

	double cwnd; // max bytes on wire
	double ssThresh; // Threshhold between slow start and congestion avoidance

	/// When we get an ack, if oldestUnsentAck==0, set it to the current time
	/// When we send out acks, set oldestUnsentAck to 0
	CCTimeType oldestUnsentAck;

	CCTimeType GetSenderRTOForACK(void) const;

	/// Every outgoing datagram is assigned a sequence number, which increments by 1 every assignment
	DatagramSequenceNumberType nextDatagramSequenceNumber;
	DatagramSequenceNumberType nextCongestionControlBlock;
	bool backoffThisBlock, speedUpThisBlock;
	/// Track which datagram sequence numbers have arrived.
	/// If a sequence number is skipped, send a NAK for all skipped messages
	DatagramSequenceNumberType expectedNextSequenceNumber;

	bool _isContinuousSend;

	bool IsInSlowStart(void) const;

	double lastRtt, estimatedRTT, deviationRtt;

};

}

#endif

#endif