/*
* Copyright (c) 2022, The PurpleI2P Project
*
* This file is part of Purple i2pd project and licensed under BSD3
*
* See full license text in LICENSE file at top of project tree
*/

#ifndef SSU2_H__
#define SSU2_H__

#include <memory>
#include <map>
#include <set>
#include <unordered_map>
#include <boost/asio.hpp>
#include "Crypto.h"
#include "RouterInfo.h"
#include "TransportSession.h"

namespace i2p
{
namespace transport
{
	const int SSU2_CONNECT_TIMEOUT = 5; // 5 seconds
	const int SSU2_TERMINATION_TIMEOUT = 330; // 5.5 minutes
	const int SSU2_TERMINATION_CHECK_TIMEOUT = 30; // 30 seconds
	const int SSU2_TOKEN_EXPIRATION_TIMEOUT = 9; // in second
	const size_t SSU2_SOCKET_RECEIVE_BUFFER_SIZE = 0x1FFFF; // 128K
	const size_t SSU2_SOCKET_SEND_BUFFER_SIZE = 0x1FFFF; // 128K
	const size_t SSU2_MTU = 1488;
	const size_t SSU2_MAX_PAYLOAD_SIZE = SSU2_MTU - 32;
	const int SSU2_RESEND_INTERVAL = 3; // in seconds
	const int SSU2_MAX_NUM_RESENDS = 5;
	const int SSU2_INCOMPLETE_MESSAGES_CLEANUP_TIMEOUT = 30; // in seconds	
	
	enum SSU2MessageType
	{
		eSSU2SessionRequest = 0,
		eSSU2SessionCreated = 1,
		eSSU2SessionConfirmed = 2,
		eSSU2Data = 6,
		eSSU2Retry = 9,
		eSSU2TokenRequest = 10
	};

	enum SSU2BlockType
	{
		eSSU2BlkDateTime = 0,
		eSSU2BlkOptions, // 1
		eSSU2BlkRouterInfo, // 2
		eSSU2BlkI2NPMessage, // 3
		eSSU2BlkFirstFragment, // 4
		eSSU2BlkFollowOnFragment, // 5
		eSSU2BlkTermination, // 6
		eSSU2BlkRelayRequest, // 7
		eSSU2BlkRelayResponse, // 8
		eSSU2BlkRelayIntro, // 9
		eSSU2BlkPeerTest, // 10
		eSSU2BlkNextNonce, // 11
		eSSU2BlkAck, // 12
		eSSU2BlkAddress, // 13
		eSSU2BlkIntroKey, // 14
		eSSU2BlkRelayTagRequest, // 15
		eSSU2BlkRelayTag, // 16
		eSSU2BlkNewToken, // 17
		eSSU2BlkPathChallenge, // 18
		eSSU2BlkPathResponse, // 19
		eSSU2BlkFirstPacketNumber, // 20
		eSSU2BlkPadding = 254
	};

	enum SSU2SessionState
	{
		eSSU2SessionStateUnknown,
		eSSU2SessionStateEstablished,
		eSSU2SessionStateTerminated,
		eSSU2SessionStateFailed
	};

	struct SSU2IncompleteMessage
	{
		struct Fragment
		{
			uint8_t buf[SSU2_MTU];
			size_t len;
			bool isLast;
		};
		
		std::shared_ptr<I2NPMessage> msg;
		int nextFragmentNum;
		uint32_t lastFragmentInsertTime; // in seconds
		std::map<int, std::shared_ptr<Fragment> > outOfSequenceFragments; 
	};	
	
	// RouterInfo flags
	const uint8_t SSU2_ROUTER_INFO_FLAG_REQUEST_FLOOD = 0x01;
	const uint8_t SSU2_ROUTER_INFO_FLAG_GZIP = 0x02;	
	
	class SSU2Server;
	class SSU2Session: public TransportSession, public std::enable_shared_from_this<SSU2Session>
	{
		union Header
		{
			uint64_t ll[2];
			uint8_t buf[16];
			struct
			{
				uint64_t connID;
				uint32_t packetNum;
				uint8_t type;
				uint8_t flags[3];
			} h;
		};

		struct SentPacket
		{
			Header header;
			uint8_t payload[SSU2_MTU];
			size_t payloadLen;    
			uint32_t packetNum;
			uint32_t nextResendTime; // in seconds
			int numResends;
		};	
		
		public:

			SSU2Session (SSU2Server& server, std::shared_ptr<const i2p::data::RouterInfo> in_RemoteRouter = nullptr,
				std::shared_ptr<const i2p::data::RouterInfo::Address> addr = nullptr, bool peerTest = false);
			~SSU2Session ();

			void SetRemoteEndpoint (const boost::asio::ip::udp::endpoint& ep) { m_RemoteEndpoint = ep; };
			const boost::asio::ip::udp::endpoint& GetRemoteEndpoint () const { return m_RemoteEndpoint; };
			
			void Connect ();
			void Terminate ();
			void TerminateByTimeout ();
			void CleanUp (uint64_t ts);
			void Done () override;
			void SendI2NPMessages (const std::vector<std::shared_ptr<I2NPMessage> >& msgs) override;
			void Resend (uint64_t ts);
			bool IsEstablished () const { return m_State == eSSU2SessionStateEstablished; };
			uint64_t GetConnID () const { return m_SourceConnID; };
			
			void ProcessFirstIncomingMessage (uint64_t connID, uint8_t * buf, size_t len);
			bool ProcessSessionCreated (uint8_t * buf, size_t len);
			bool ProcessSessionConfirmed (uint8_t * buf, size_t len);
			bool ProcessRetry (uint8_t * buf, size_t len);
			void ProcessData (uint8_t * buf, size_t len);
			
		private:

			void Established ();
			void PostI2NPMessages (std::vector<std::shared_ptr<I2NPMessage> > msgs);
			void SendQueue ();
			void SendFragmentedMessage (std::shared_ptr<I2NPMessage> msg);
			
			void ProcessSessionRequest (Header& header, uint8_t * buf, size_t len);
			void ProcessTokenRequest (Header& header, uint8_t * buf, size_t len);
			
			void SendSessionRequest (uint64_t token = 0);
			void SendSessionCreated (const uint8_t * X);
			void SendSessionConfirmed (const uint8_t * Y);
			void KDFDataPhase (uint8_t * keydata_ab, uint8_t * keydata_ba);
			void SendTokenRequest ();
			void SendRetry ();
			std::shared_ptr<SentPacket> SendData (const uint8_t * buf, size_t len);
			void SendQuickAck ();
			void SendTermination ();
			
			bool HandlePayload (const uint8_t * buf, size_t len); // returns true is contains data
			void HandleAck (const uint8_t * buf, size_t len);
			void HandleAckRange (uint32_t firstPacketNum, uint32_t lastPacketNum);
			bool ExtractEndpoint (const uint8_t * buf, size_t size, boost::asio::ip::udp::endpoint& ep);
			std::shared_ptr<const i2p::data::RouterInfo> ExtractRouterInfo (const uint8_t * buf, size_t size);
			void CreateNonce (uint64_t seqn, uint8_t * nonce);
			bool UpdateReceivePacketNum (uint32_t packetNum); // for Ack, returns false if duplicate
			void HandleFirstFragment (const uint8_t * buf, size_t len);
			void HandleFollowOnFragment (const uint8_t * buf, size_t len);
			bool ConcatOutOfSequenceFragments (std::shared_ptr<SSU2IncompleteMessage> m); // true if message complete
			
			size_t CreateAddressBlock (const boost::asio::ip::udp::endpoint& ep, uint8_t * buf, size_t len);
			size_t CreateAckBlock (uint8_t * buf, size_t len);
			size_t CreatePaddingBlock (uint8_t * buf, size_t len, size_t minSize = 0);
			size_t CreateI2NPBlock (uint8_t * buf, size_t len, std::shared_ptr<I2NPMessage>&& msg);
			size_t CreateFirstFragmentBlock (uint8_t * buf, size_t len, std::shared_ptr<I2NPMessage> msg);
			size_t CreateFollowOnFragmentBlock (uint8_t * buf, size_t len, std::shared_ptr<I2NPMessage> msg, uint8_t& fragmentNum, uint32_t msgID);
			
		private:

			SSU2Server& m_Server;
			std::shared_ptr<i2p::crypto::X25519Keys> m_EphemeralKeys;
			std::unique_ptr<i2p::crypto::NoiseSymmetricState> m_NoiseState;
			std::unique_ptr<SentPacket> m_SessionConfirmedFragment1; // for Bob if applicable
			std::shared_ptr<const i2p::data::RouterInfo::Address> m_Address;
			boost::asio::ip::udp::endpoint m_RemoteEndpoint;
			uint64_t m_DestConnID, m_SourceConnID;
			SSU2SessionState m_State;
			uint8_t m_KeyDataSend[64], m_KeyDataReceive[64]; 
			uint32_t m_SendPacketNum, m_ReceivePacketNum;
			std::set<uint32_t> m_OutOfSequencePackets; // packet nums > receive packet num
			std::map<uint32_t, std::shared_ptr<SentPacket> > m_SentPackets; // packetNum -> packet
			std::map<uint32_t, std::shared_ptr<SSU2IncompleteMessage> > m_IncompleteMessages; // I2NP
			std::list<std::shared_ptr<I2NPMessage> > m_SendQueue;
			i2p::I2NPMessagesHandler m_Handler;
	};

	class SSU2Server:  private i2p::util::RunnableServiceWithWork
	{
		struct Packet
		{
			uint8_t buf[SSU2_MTU]; 
			size_t len;
			boost::asio::ip::udp::endpoint from;
		};	

		class ReceiveService: public i2p::util::RunnableService
		{
			public:

				ReceiveService (const std::string& name): RunnableService (name) {};
				boost::asio::io_service& GetService () { return GetIOService (); };
				void Start () { StartIOService (); };
				void Stop () { StopIOService (); };
		};	
		
		public:

			SSU2Server ();
			~SSU2Server () {};

			void Start ();
			void Stop ();
			boost::asio::io_service& GetService () { return GetIOService (); };
			
			void AddSession (std::shared_ptr<SSU2Session> session);
			void RemoveSession (uint64_t connID);
			void AddPendingOutgoingSession (std::shared_ptr<SSU2Session> session);

			void Send (const uint8_t * header, size_t headerLen, const uint8_t * payload, size_t payloadLen, 
				const boost::asio::ip::udp::endpoint& to);
			void Send (const uint8_t * header, size_t headerLen, const uint8_t * headerX, size_t headerXLen, 
				const uint8_t * payload, size_t payloadLen, const boost::asio::ip::udp::endpoint& to);

			bool CreateSession (std::shared_ptr<const i2p::data::RouterInfo> router,
				std::shared_ptr<const i2p::data::RouterInfo::Address> address);

			void UpdateOutgoingToken (const boost::asio::ip::udp::endpoint& ep, uint64_t token, uint32_t exp);
			uint64_t FindOutgoingToken (const boost::asio::ip::udp::endpoint& ep) const;
			uint64_t GetIncomingToken (const boost::asio::ip::udp::endpoint& ep);
			
		private:

			boost::asio::ip::udp::socket& OpenSocket (const boost::asio::ip::udp::endpoint& localEndpoint);
			void Receive (boost::asio::ip::udp::socket& socket);
			void HandleReceivedFrom (const boost::system::error_code& ecode, size_t bytes_transferred, 
				Packet * packet, boost::asio::ip::udp::socket& socket);
			void HandleReceivedPacket (Packet * packet);
			void ProcessNextPacket (uint8_t * buf, size_t len, const boost::asio::ip::udp::endpoint& senderEndpoint);

			void ScheduleTermination ();
			void HandleTerminationTimer (const boost::system::error_code& ecode);

			void ScheduleResend ();
			void HandleResendTimer (const boost::system::error_code& ecode);
			
		private:

			ReceiveService m_ReceiveService; 
			boost::asio::ip::udp::socket m_SocketV4, m_SocketV6;
			std::unordered_map<uint64_t, std::shared_ptr<SSU2Session> > m_Sessions;
			std::map<boost::asio::ip::udp::endpoint, std::shared_ptr<SSU2Session> > m_PendingOutgoingSessions;
			std::map<boost::asio::ip::udp::endpoint, std::pair<uint64_t, uint32_t> > m_IncomingTokens, m_OutgoingTokens; // remote endpoint -> (token, expires in seconds)
			i2p::util::MemoryPoolMt<Packet> m_PacketsPool;
			boost::asio::deadline_timer m_TerminationTimer, m_ResendTimer;
			std::shared_ptr<SSU2Session> m_LastSession;

		public:

			// for HTTP/I2PControl
			const decltype(m_Sessions)& GetSSU2Sessions () const { return m_Sessions; };	
	};	
}
}

#endif