/*
* Copyright (c) 2013-2026, 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 ECIES_X25519_AEAD_RATCHET_SESSION_H__
#define ECIES_X25519_AEAD_RATCHET_SESSION_H__

#include <string.h>
#include <inttypes.h>
#include <functional>
#include <memory>
#include <vector>
#include <array>
#include <list>
#include <unordered_map>
#include "Identity.h"
#include "Crypto.h"
#include "PostQuantum.h"
#include "Garlic.h"
#include "Tag.h"

namespace i2p
{
namespace garlic
{
	const int ECIESX25519_RESTART_TIMEOUT = 120; // number of second since session creation we can restart session after
	const int ECIESX25519_INACTIVITY_TIMEOUT = 90; // number of seconds we receive nothing and should restart if we can
	const int ECIESX25519_SEND_INACTIVITY_TIMEOUT = 5000; // number of milliseconds we can send empty(payload only) packet after
	const int ECIESX25519_SEND_EXPIRATION_TIMEOUT = 480; // in seconds
	const int ECIESX25519_RECEIVE_EXPIRATION_TIMEOUT = 600; // in seconds
	const int ECIESX25519_SESSION_CREATE_TIMEOUT = 3; // in seconds, NSR must be send after NS received
	const int ECIESX25519_SESSION_ESTABLISH_TIMEOUT = 15; // in seconds
	const int ECIESX25519_PREVIOUS_TAGSET_EXPIRATION_TIMEOUT = 180; // in seconds
	const int ECIESX25519_DEFAULT_ACK_REQUEST_INTERVAL = 33000; // in milliseconds
	const int ECIESX25519_ACK_REQUEST_MAX_NUM_ATTEMPTS = 3;
	const int ECIESX25519_TAGSET_MAX_NUM_TAGS = 8192; // number of tags we request new tagset after
	const int ECIESX25519_MIN_NUM_GENERATED_TAGS = 24;
	const int ECIESX25519_MAX_NUM_GENERATED_TAGS = 800;
	const int ECIESX25519_NSR_NUM_GENERATED_TAGS = 12;

	const size_t ECIESX25519_OPTIMAL_PAYLOAD_SIZE = 1912; // 1912 = 1956 /* to fit 2 tunnel messages */
	// - 16 /* I2NP header */ - 16 /* poly hash */ - 8 /* tag */ - 4 /* garlic length */

	class RatchetTagSet
	{
		public:

			RatchetTagSet () {};
			virtual ~RatchetTagSet () {};

			void DHInitialize (const uint8_t * rootKey, const uint8_t * k);
			void NextSessionTagRatchet ();
			uint64_t GetNextSessionTag (i2p::crypto::HKDFContext& hkdfCtx);
			const uint8_t * GetNextRootKey () const { return m_NextRootKey; };
			int GetNextIndex () const { return m_NextIndex; };
			void GetSymmKey (int index, uint8_t * key);
			void DeleteSymmKey (int index);

			int GetTagSetID () const { return m_TagSetID; };
			void SetTagSetID (int tagsetID) { m_TagSetID = tagsetID; };

			uint32_t GetMsgID () const { return (m_TagSetID << 16) + m_NextIndex; }; // (tagsetid << 16) + N

		private:

			i2p::data::Tag<64> m_SessionTagKeyData;
			uint8_t m_SessTagConstant[32], m_SymmKeyCK[32], m_CurrentSymmKeyCK[64], m_NextRootKey[32];
			int m_NextIndex = 0, m_NextSymmKeyIndex = 0;
			std::unordered_map<int, i2p::data::Tag<32> > m_ItermediateSymmKeys;

			int m_TagSetID = 0;
	};

	class ECIESX25519AEADRatchetSession;
	class ReceiveRatchetTagSet: public RatchetTagSet,
		public std::enable_shared_from_this<ReceiveRatchetTagSet>
	{
		public:

			ReceiveRatchetTagSet (std::shared_ptr<ECIESX25519AEADRatchetSession> session, bool isNS = false);
			~ReceiveRatchetTagSet () override;

			bool IsNS () const { return m_IsNS; };
			std::shared_ptr<ECIESX25519AEADRatchetSession> GetSession () { return m_Session; };
			void SetTrimBehind (int index) { if (index > m_TrimBehindIndex) m_TrimBehindIndex = index; };
			int GetTrimBehind () const { return m_TrimBehindIndex; };

			void Expire ();
			bool IsExpired (uint64_t ts) const;

			virtual bool IsIndexExpired (int index) const;
			virtual bool HandleNextMessage (uint8_t * buf, size_t len, int index);
			virtual bool IsSessionTerminated () const;

		private:

			int m_TrimBehindIndex = 0;
			std::shared_ptr<ECIESX25519AEADRatchetSession> m_Session;
			bool m_IsNS;
			uint64_t m_ExpirationTimestamp = 0;
	};

	class SymmetricKeyTagSet: public ReceiveRatchetTagSet
	{
		public:

			SymmetricKeyTagSet (GarlicDestination * destination, const uint8_t * key);

			bool IsIndexExpired (int index) const override { return false; };
			bool HandleNextMessage (uint8_t * buf, size_t len, int index) override;
			bool IsSessionTerminated () const override { return false; }

		private:

			GarlicDestination * m_Destination;
			uint8_t m_Key[32];
	};

	enum ECIESx25519BlockType
	{
		eECIESx25519BlkDateTime    = 0,
		eECIESx25519BlkSessionID   = 1,
		eECIESx25519BlkTermination = 4,
		eECIESx25519BlkOptions     = 5,
		eECIESx25519BlkNextKey     = 7,
		eECIESx25519BlkAck         = 8,
		eECIESx25519BlkAckRequest  = 9,
		eECIESx25519BlkGalicClove  = 11,
		eECIESx25519BlkPadding     = 254
	};

	const uint8_t ECIESX25519_NEXT_KEY_KEY_PRESENT_FLAG = 0x01;
	const uint8_t ECIESX25519_NEXT_KEY_REVERSE_KEY_FLAG = 0x02;
	const uint8_t ECIESX25519_NEXT_KEY_REQUEST_REVERSE_KEY_FLAG = 0x04;

	class ECIESX25519AEADRatchetSession: public GarlicRoutingSession,
		private i2p::crypto::NoiseSymmetricState,
		public std::enable_shared_from_this<ECIESX25519AEADRatchetSession>
	{
		enum SessionState
		{
			eSessionStateNew = 0,
			eSessionStateNewSessionReceived,
			eSessionStateNewSessionSent,
			eSessionStateNewSessionReplySent,
			eSessionStateEstablished,
			eSessionStateOneTime
		};

		struct DHRatchet
		{
			int keyID = 0;
			std::shared_ptr<i2p::crypto::X25519Keys> key;
			uint8_t remote[32]; // last remote public key
			bool newKey = true;
			int GetReceiveTagSetID () const { return newKey ? (2*keyID + 1) : 2*keyID; }
		};

		public:

			ECIESX25519AEADRatchetSession (GarlicDestination * owner, bool attachLeaseSetNS);
			~ECIESX25519AEADRatchetSession ();

			bool HandleNextMessage (uint8_t * buf, size_t len, std::shared_ptr<ReceiveRatchetTagSet> receiveTagset, int index = 0);
			std::shared_ptr<I2NPMessage> WrapSingleMessage (std::shared_ptr<const I2NPMessage> msg) override;
			std::vector<std::shared_ptr<I2NPMessage> > WrapMultipleMessages (const std::vector<std::shared_ptr<const I2NPMessage> >& msgs) override;
			std::shared_ptr<I2NPMessage> WrapOneTimeMessage (std::shared_ptr<const I2NPMessage> msg);

			const uint8_t * GetRemoteStaticKey () const { return m_RemoteStaticKey; }
			i2p::data::CryptoKeyType GetRemoteStaticKeyType () const { return m_RemoteStaticKeyType; }
			void SetRemoteStaticKey (i2p::data::CryptoKeyType keyType, const uint8_t * key)
			{
				m_RemoteStaticKeyType = keyType;
				memcpy (m_RemoteStaticKey, key, 32);
			}
			void Terminate () { m_IsTerminated = true; }
			void SetDestination (const i2p::data::IdentHash& dest)
			{
				if (!m_Destination) m_Destination.reset (new i2p::data::IdentHash (dest));
			}
			const i2p::data::IdentHash * GetDestinationPtr () const { return m_Destination ? m_Destination.get () : nullptr; }; // for pongs
			bool CheckExpired (uint64_t ts); // true is expired
			bool CanBeRestarted (uint64_t ts) const { return ts > m_SessionCreatedTimestamp + ECIESX25519_RESTART_TIMEOUT; }
			bool IsInactive (uint64_t ts) const override { return ts > m_LastActivityTimestamp + ECIESX25519_INACTIVITY_TIMEOUT && CanBeRestarted (ts); }
			void CleanupReceiveNSRKeys (); // called from ReceiveRatchetTagSet at Alice's side
			bool IsResponseRequired () const { return m_State == eSessionStateNewSessionReceived || m_SendReverseKey || !m_AckRequests.empty (); };

			bool IsRatchets () const override { return true; };
			bool IsReadyToSend () const override { return m_State != eSessionStateNewSessionSent; };
			bool IsTerminated () const override { return m_IsTerminated; }
			uint64_t GetLastActivityTimestamp () const override { return m_LastActivityTimestamp; };
			void SetAckRequestInterval (int interval) override { m_AckRequestInterval = interval; };
			bool CleanupUnconfirmedTags () override; // return true if unanswered Ack requests, called from I2CP

		protected:

			i2p::crypto::NoiseSymmetricState& GetNoiseState () { return *this; };
			void SetNoiseState (const i2p::crypto::NoiseSymmetricState& state) { GetNoiseState () = state; };
			void CreateNonce (uint64_t seqn, uint8_t * nonce);
			void HandlePayload (const uint8_t * buf, size_t len, const std::shared_ptr<ReceiveRatchetTagSet>& receiveTagset, int index);
			bool MessageConfirmed (uint32_t msgID) override;

		private:

			bool GenerateEphemeralKeysAndEncode (uint8_t * buf); // buf is 32 bytes
			void InitNewSessionTagset (std::shared_ptr<RatchetTagSet> tagsetNsr) const;

			bool HandleNewIncomingSession (const uint8_t * buf, size_t len);
			bool HandleNewOutgoingSessionReply (uint8_t * buf, size_t len);
			bool HandleExistingSessionMessage (uint8_t * buf, size_t len, std::shared_ptr<ReceiveRatchetTagSet> receiveTagset, int index);
			void HandleNextKey (const uint8_t * buf, size_t len, const std::shared_ptr<ReceiveRatchetTagSet>& receiveTagset);

			bool NewOutgoingSessionMessage (const uint8_t * payload, size_t len, uint8_t * out, size_t outLen, bool isStatic = true);
			bool NewSessionReplyMessage (const uint8_t * payload, size_t len, uint8_t * out, size_t outLen);
			bool NextNewSessionReplyMessage (const uint8_t * payload, size_t len, uint8_t * out, size_t outLen);
			bool NewExistingSessionMessage (const uint8_t * payload, size_t len, uint8_t * out, size_t outLen);

			size_t CreatePayload (std::shared_ptr<const I2NPMessage> msg, bool first, uint8_t * payload);
			size_t CreateGarlicClove (std::shared_ptr<const I2NPMessage> msg, uint8_t * buf, size_t len, bool alwaysLocal = false);
			size_t CreateLeaseSetClove (std::shared_ptr<const i2p::data::LocalLeaseSet> ls, uint64_t ts, uint8_t * buf, size_t len);
			size_t CreatePaddingClove (uint8_t paddingSize, uint8_t * buf, size_t len);

			void GenerateMoreReceiveTags (std::shared_ptr<ReceiveRatchetTagSet> receiveTagset, int numTags);
			void NewNextSendRatchet ();

			std::shared_ptr<I2NPMessage> WrapPayload (const uint8_t * payload, size_t len);
			uint8_t GetNextPaddingSize (size_t payloadLen);

		private:

			i2p::data::CryptoKeyType m_RemoteStaticKeyType;
			uint8_t m_RemoteStaticKey[32];
			uint8_t m_Aepk[32]; // Alice's ephemeral keys, for incoming only
			uint8_t m_NSREncodedKey[32], m_NSRH[32], m_NSRKey[32]; // new session reply, for incoming only
			std::shared_ptr<i2p::crypto::X25519Keys> m_EphemeralKeys;
#if OPENSSL_PQ
			std::unique_ptr<i2p::crypto::MLKEMKeys> m_PQKeys;
			std::unique_ptr<std::array<uint8_t, 64> > m_NSRCK; // before cipher text encryption
#endif
			SessionState m_State = eSessionStateNew;
			uint64_t m_SessionCreatedTimestamp = 0, m_LastActivityTimestamp = 0, // incoming (in seconds)
				m_LastSentTimestamp = 0; // in milliseconds
			std::shared_ptr<RatchetTagSet> m_SendTagset, m_NSRSendTagset;
			std::unique_ptr<i2p::data::IdentHash> m_Destination;// must be set for NS if outgoing and NSR if incoming
			std::list<std::pair<uint16_t, int> > m_AckRequests; // incoming (tagsetid, index)
			bool m_SendReverseKey = false, m_SendForwardKey = false, m_IsTerminated = false;
			std::unique_ptr<DHRatchet> m_NextReceiveRatchet, m_NextSendRatchet;

			uint64_t m_LastAckRequestSendTime = 0; // milliseconds
			uint32_t m_AckRequestMsgID = 0;
			int m_AckRequestNumAttempts = 0;
			int m_AckRequestInterval = ECIESX25519_DEFAULT_ACK_REQUEST_INTERVAL; // milliseconds

		public:

			// for HTTP only
			int GetState () const { return (int)m_State; }
			i2p::data::IdentHash GetDestination () const
			{
				return m_Destination ? *m_Destination : i2p::data::IdentHash ();
			}
	};

	// single session for all incoming messages
	class RouterIncomingRatchetSession: public ECIESX25519AEADRatchetSession
	{
		public:

			RouterIncomingRatchetSession (const i2p::crypto::NoiseSymmetricState& initState);
			bool HandleNextMessage (const uint8_t * buf, size_t len);
			i2p::crypto::NoiseSymmetricState& GetCurrentNoiseState () { return m_CurrentNoiseState; };

		private:

			i2p::crypto::NoiseSymmetricState m_CurrentNoiseState;
	};

	std::shared_ptr<I2NPMessage> WrapECIESX25519Message (std::shared_ptr<I2NPMessage> msg, const uint8_t * key, uint64_t tag);
	std::shared_ptr<I2NPMessage> WrapECIESX25519MessageForRouter (std::shared_ptr<I2NPMessage> msg, const uint8_t * routerPublicKey);
}
}

#endif

