/*******************************************************************************
 * libretroshare/src/gxs: gxsnettunnel.h                                       *
 *                                                                             *
 * libretroshare: retroshare core library                                      *
 *                                                                             *
 * Copyright (C) 2018  Cyril Soler <contact@retroshare.cc>              *
 * Copyright (C) 2021  Gioacchino Mazzurco <gio@eigenlab.org>                  *
 * Copyright (C) 2021  Asociación Civil Altermundi <info@altermundi.net>       *
 *                                                                             *
 * This program is free software: you can redistribute it and/or modify        *
 * it under the terms of the GNU Lesser General Public License as              *
 * published by the Free Software Foundation, either version 3 of the          *
 * License, or (at your option) any later version.                             *
 *                                                                             *
 * This program is distributed in the hope that it will be useful,             *
 * but WITHOUT ANY WARRANTY; without even the implied warranty of              *
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the                *
 * GNU Lesser General Public License for more details.                         *
 *                                                                             *
 * You should have received a copy of the GNU Lesser General Public License    *
 * along with this program. If not, see <https://www.gnu.org/licenses/>.       *
 *                                                                             *
 *******************************************************************************/

#pragma once

#include <map>
#include <system_error>

#include "turtle/p3turtle.h"
#include "retroshare/rsgxsdistsync.h"

/*!
 * \brief The RsGxsNetTunnelService class takes care of requesting tunnels to the turtle router, through which it is possible to sync
 *        a particular GXS group. For each group, a set of virtual peers, corresponding to active tunnels will be made available
 *        to RsGxsNetService.
 *
 *        It is the responsibility of RsGxsNetService to activate/desactivate tunnels for each particular group, depending on wether the group
 *        is already available at regular friends or not.
 *
 *        Tunnel management is done at the level of groups rather than services, because we would like to keep the possibility to not
 *        request tunnels for some groups which do not need it, and only request tunnels for specific groups that cannot be provided
 *        by direct connections.
 */

//   Protocol:
//      * request tunnels based on H(GroupId)
//      * encrypt tunnel data using chacha20+HMAC-SHA256 using AEAD( GroupId, 96bits IV, tunnel ID ) (similar to what FT does)
//      * when tunnel is established, exchange virtual peer names: vpid = H( GroupID | Random bias )
//      * when vpid is known, notify the client (GXS net service) which can use the virtual peer to sync
//      * only use a single tunnel per virtual peer ID
//                                                                                        -
//              Client  ------------------ TR(H(GroupId)) -------------->  Server         |
//                                                                                        |   Turtle
//              Client  <-------------------- T OK ----------------------  Server         |
//                                                                                        -
//                               Here, a turtle vpid is known                             |   [ addVirtualPeer() called by turtle ]
//                                                                                        -
//           [Encrypted traffic using H(GroupId | Tunnel ID, 96bits IV)]                  |
//                                                                                        |
//              Client  <--------- VPID = H( Random IV | GroupId ) ------  Server         |
//                 |                                                         |            |
//                 +--------------> Mark the virtual peer active <-----------+            |    Encrypted traffic decoded locally and sorted
//                                                                                        |
//                         Here, a consistent virtual peer ID is known                    |
//                                                                                        |
//              Client  <------------------- GXS Data ------------------>  Server         |
//                                                                                        -
//   Notes:
//      * tunnels are established symmetrically. If a distant peers wants to sync the same group, they'll have to open a single tunnel, with a different ID.
//        Groups therefore have two states:
//          - managed : the group can be used to answer tunnel requests. If server tunnels are established, the group will be synced with these peers
//          - tunneled: the group will actively request tunnels. If tunnels are established both ways, the same virtual peers will be used so the tunnels are "merged".
//                        * In practice, that means one of the two tunnels will not be used and therefore die.
//                        * If a tunneled group already has enough virtual peers, it will not request for tunnels itself.
//
//           Group policy      | Request tunnels   |    SyncWithPeers      |  Item receipt
//         --------------------+-------------------+-----------------------+----------------
//             Passive         |        no         |  If peers present     | If peers present
//             Active          |  yes, if no peers |  If peers present     | If peers present
//                             |                   |                       |
//
//      * when a service has the DistSync flag set, groups to sync are communicated passively to the GxsNetTunnel service when requesting distant peers.
//        However, a call should be made to set a particular group policy to "ACTIVE" for group that do not have peers and need some.
//
//      * services also need to retrieve GXS data items that come out of tunnels. These will be available as (data,len) type, since they are not de-serialized.
//
//      * GxsNetService stores data information (such as update maps) per peerId, so it makes sense to use the same PeerId for all groups of a given service
//        Therefore, virtual peers are stored separately from groups, because each one can sync multiple groups.
//
//      * virtual peers are also shared among services. This reduces the required amount of tunnels and tunnel requests to send.
//
//      * tunnels for a given service may also be used by the net service of p3IdService in order to explicitely request missing GxsIds.
//        So GxsNetTunnel somehow allows different services to use the same tunnel. However we make sure that this traffic is limited to only p3IdService.
//
//   How do we know that a group needs distant sync?
//		* look into GrpConfigMap for suppliers. Suppliers is cleared at load.
//		* last_update_TS in GrpConfigMap is randomised so it cannot be used
//      * we need a way to know that there's no suppliers for good reasons (not that we just started)
//
//   Security
//      * the question of sync-ing with distant anonymous peers is a bit tricky because these peers can try to generate fake requests or change which messages are available
//        and there is no way to prevent it. We therefore rely on GXS data integrity system to prevent this to happen.
//

struct RsGxsNetTunnelItem;
class RsNetworkExchangeService ;

class RsGxsNetTunnelService:
        public RsTurtleClientService, public RsTickingThread, public p3Config,
        public RsGxsDistSync
{
public:
	RsGxsNetTunnelService();
	~RsGxsNetTunnelService() override;

      /*!
       * \brief registerSearchableService
       * 			Adds the network exchange service as a possible search source. This is used to allow distant search on the corresponding
       * 			GXS service.
       * \return
       * 		always returns true.
       */
      bool registerSearchableService(RsNetworkExchangeService *) ;

	  /*!
	   * \brief Manage tunnels for this group
	   *	@param group_id group for which tunnels should be released
	   */
      bool requestDistantPeers(uint16_t service_id,const RsGxsGroupId&group_id) ;

	  /*!
	   * \brief Stop managing tunnels for this group
	   *	@param group_id group for which tunnels should be released
	   */
      bool releaseDistantPeers(uint16_t service_id, const RsGxsGroupId&group_id) ;

	  /*!
	   * \brief Get the list of active virtual peers for a given group. This implies that a tunnel is up and
	   *        alive. This function also "registers" the group which allows to handle tunnel requests in the server side.
	   */
      bool getVirtualPeers(std::list<RsGxsNetTunnelVirtualPeerId>& peers) ;	// returns the virtual peers for this service

      /*!
       * \brief serviceId
       * 			Overloads the method in RsTurtleClientService.
       * \return
       * 			The service id for RsGxsNetTunnel.
       */
      uint16_t serviceId() const override ;

	  /*!
	   * \brief sendData
	   *               send data to this virtual peer, and takes memory ownership (deletes the item)
	   * \param item           item to send
	   * \param virtual_peer   destination virtual peer
	   * \return
	   *               true if succeeded.
	   */
      bool sendTunnelData(uint16_t service_id,unsigned char *& data, uint32_t data_len, const RsGxsNetTunnelVirtualPeerId& virtual_peer) ;

	  /*!
	   * \brief receiveData
	   *                 returns the next piece of data received, and the virtual GXS peer that sended it.
	   * \param data              memory check containing the data. Memory ownership belongs to the client.
	   * \param data_len          length of memory chunk
	   * \param virtual_peer      peer who sent the data
	   * \return
	   *                          true if something is returned. If not, data is set to NULL, data_len to 0.
	   */
      bool receiveTunnelData(uint16_t service_id, unsigned char *& data, uint32_t& data_len, RsGxsNetTunnelVirtualPeerId& virtual_peer) ;

	  /*!
	   * \brief isDistantPeer
	   *                 returns wether the peer is in the list of available distant peers or not
	   * \param group_id          returned by the service to indicate which group this peer id is designed for.
	   * \return    true if the peer is a distant GXS peer.
	   */

	  bool isDistantPeer(const RsGxsNetTunnelVirtualPeerId& virtual_peer,RsGxsGroupId& group_id) ;

	  /*!
	   * \brief dumps all information about monitored groups.
	   */
	  void dump() const;

	/*!
	* Should be called after allocating a RsGxsNetTunnelService
	* \param tr turtle router object
	*/
	void connectToTurtleRouter(p3turtle *tr) override;

	/** Gxs services (channels, forums...) are supposed to use this to request
	 * searches on distant peers */
	std::error_condition turtleSearchRequest(
	        rs_owner_ptr<uint8_t> searchData, uint32_t dataSize,
	        RsServiceType serviceType, TurtleRequestId& requestId );

	///@see RsTurtleClientService
	bool receiveSearchRequest(
	        unsigned char* search_request_data,
	        uint32_t search_request_data_len,
	        unsigned char*& search_result_data,
	        uint32_t& search_result_data_len,
	        uint32_t& max_allowed_hits ) override;

	///@see RsTurtleClientService
	virtual void receiveSearchResult(
	        TurtleSearchRequestId request_id,
	        unsigned char* search_result_data,
	        uint32_t search_result_data_len ) override;

	TurtleRequestId turtleGroupRequest(
	        const RsGxsGroupId& group_id,
	        RsNetworkExchangeService* client_service );

	/// @see RsTickingThread
	void threadTick() override;

	  // Overloads p3Config

      RsSerialiser *setupSerialiser()override ;
      bool saveList(bool& cleanup, std::list<RsItem*>& save)override ;
      bool loadList(std::list<RsItem *> &load)override ;

      // Overloads RsGxsDistSync

	  void getStatistics(std::map<RsGxsGroupId,RsGxsNetTunnelGroupInfo>& groups,             // groups on the client and server side
	  		std::map<RsGxsNetTunnelVirtualPeerId, RsGxsNetTunnelVirtualPeerInfo>& virtual_peers,     // current virtual peers, which group they provide, and how to talk to them through turtle
            std::map<TurtleVirtualPeerId,RsGxsNetTunnelVirtualPeerId>& turtle_vpid_to_net_tunnel_vpid,
            Bias20Bytes& bias) const override ;

	RS_DEPRECATED
	TurtleRequestId turtleSearchRequest(
	        const std::string& match_string,
	        RsNetworkExchangeService* client_service );

protected:
	  // interaction with turtle router

      virtual bool handleTunnelRequest(const RsFileHash &hash,const RsPeerId& peer_id) override ;
      virtual void receiveTurtleData(const RsTurtleGenericTunnelItem *item,const RsFileHash& hash,const RsPeerId& virtual_peer_id,RsTurtleGenericTunnelItem::Direction direction) override ;
      void addVirtualPeer(const TurtleFileHash&, const TurtleVirtualPeerId&,RsTurtleGenericTunnelItem::Direction dir) override ;
      void removeVirtualPeer(const TurtleFileHash&, const TurtleVirtualPeerId&) override ;
	  const Bias20Bytes& locked_randomBias() ;

	  p3turtle 	*mTurtle ;

	  static const uint32_t RS_GXS_TUNNEL_CONST_RANDOM_BIAS_SIZE = 20 ;
	  static const uint32_t RS_GXS_TUNNEL_CONST_EKEY_SIZE        = 32 ;

	  mutable Bias20Bytes mRandomBias ; // constant accross reboots. Allows to disguise the real SSL id while providing a consistent value accross time.
private:
	  void autowash() ;
	  void sendKeepAlivePackets() ;
	  void handleIncoming(RsGxsNetTunnelItem *item) ;
	  void flush_pending_items();
	rs_view_ptr<RsNetworkExchangeService> retrievieSearchableServiceLocking(
	        uint16_t serviceType );

	  std::map<RsGxsGroupId,RsGxsNetTunnelGroupInfo> mGroups ;	// groups on the client and server side

	  std::map<RsGxsNetTunnelVirtualPeerId, RsGxsNetTunnelVirtualPeerInfo> mVirtualPeers ;	// current virtual peers, which group they provide, and how to talk to them through turtle
	  std::map<RsFileHash, RsGxsGroupId>                                   mHandledHashes ; // hashes asked to turtle. Used to answer tunnel requests
	  std::map<TurtleVirtualPeerId, RsGxsNetTunnelVirtualPeerId>           mTurtle2GxsPeer ; // convertion table to find GXS peer id from turtle

	  std::list<std::pair<TurtleVirtualPeerId,RsTurtleGenericDataItem*> >  mPendingTurtleItems ; // items that need to be sent off-turtle Mutex.

	  std::map<uint16_t, std::list<std::pair<RsGxsNetTunnelVirtualPeerId,RsTlvBinaryData *> > > mIncomingData; // list of incoming data items

      std::map<uint16_t,RsNetworkExchangeService *> mSearchableServices ;

	  /*!
	   * \brief Generates the hash to request tunnels for this group. This hash is only used by turtle, and is used to
	   * 		hide the real group id.
	   */

	  RsFileHash calculateGroupHash(const RsGxsGroupId&group_id) const ;

	  /*!
	   * \brief makeVirtualPeerIdForGroup creates a virtual peer id that can be used and that will be constant accross time, whatever the
	   * 		tunnel ID and turtle virtual peer id. This allows RsGxsNetService to keep sync-ing the data consistently.
	   */

	  RsGxsNetTunnelVirtualPeerId locked_makeVirtualPeerId(const RsGxsGroupId& group_id) ;

	  static void generateEncryptionKey(const RsGxsGroupId& group_id,const TurtleVirtualPeerId& vpid,unsigned char key[RS_GXS_TUNNEL_CONST_EKEY_SIZE]) ;

	  mutable RsMutex mGxsNetTunnelMtx;

	  friend class RsGxsTunnelRandomBiasItem ;
	  friend class StoreHere ;

	  rstime_t mLastKeepAlive ;
	  rstime_t mLastAutoWash ;
	  rstime_t mLastDump ;
};