/*
* TLS Session Manager
* (C) 2011 Jack Lloyd
*
* Botan is released under the Simplified BSD License (see license.txt)
*/

#ifndef BOTAN_TLS_SESSION_MANAGER_H_
#define BOTAN_TLS_SESSION_MANAGER_H_

#include <botan/tls_session.h>
#include <botan/mutex.h>
#include <chrono>
#include <map>

namespace Botan {

namespace TLS {

/**
* Session_Manager is an interface to systems which can save
* session parameters for supporting session resumption.
*
* Saving sessions is done on a best-effort basis; an implementation is
* allowed to drop sessions due to space constraints.
*
* Implementations should strive to be thread safe
*/
class BOTAN_PUBLIC_API(2,0) Session_Manager
   {
   public:
      /**
      * Try to load a saved session (using session ID)
      * @param session_id the session identifier we are trying to resume
      * @param session will be set to the saved session data (if found),
               or not modified if not found
      * @return true if session was modified
      */
      virtual bool load_from_session_id(const std::vector<uint8_t>& session_id,
                                        Session& session) = 0;

      /**
      * Try to load a saved session (using info about server)
      * @param info the information about the server
      * @param session will be set to the saved session data (if found),
               or not modified if not found
      * @return true if session was modified
      */
      virtual bool load_from_server_info(const Server_Information& info,
                                         Session& session) = 0;

      /**
      * Remove this session id from the cache, if it exists
      */
      virtual void remove_entry(const std::vector<uint8_t>& session_id) = 0;

      /**
      * Remove all sessions from the cache, return number of sessions deleted
      */
      virtual size_t remove_all() = 0;

      /**
      * Save a session on a best effort basis; the manager may not in
      * fact be able to save the session for whatever reason; this is
      * not an error. Caller cannot assume that calling save followed
      * immediately by load_from_* will result in a successful lookup.
      *
      * @param session to save
      */
      virtual void save(const Session& session) = 0;

      /**
      * Return the allowed lifetime of a session; beyond this time,
      * sessions are not resumed. Returns 0 if unknown/no explicit
      * expiration policy.
      */
      virtual std::chrono::seconds session_lifetime() const = 0;

      virtual ~Session_Manager() = default;
   };

/**
* An implementation of Session_Manager that does not save sessions at
* all, preventing session resumption.
*/
class BOTAN_PUBLIC_API(2,0) Session_Manager_Noop final : public Session_Manager
   {
   public:
      bool load_from_session_id(const std::vector<uint8_t>&, Session&) override
         { return false; }

      bool load_from_server_info(const Server_Information&, Session&) override
         { return false; }

      void remove_entry(const std::vector<uint8_t>&) override {}

      size_t remove_all() override { return 0; }

      void save(const Session&) override {}

      std::chrono::seconds session_lifetime() const override
         { return std::chrono::seconds(0); }
   };

/**
* An implementation of Session_Manager that saves values in memory.
*/
class BOTAN_PUBLIC_API(2,0) Session_Manager_In_Memory final : public Session_Manager
   {
   public:
      /**
      * @param rng a RNG used for generating session key and for
      *        session encryption
      * @param max_sessions a hint on the maximum number of sessions
      *        to keep in memory at any one time. (If zero, don't cap)
      * @param session_lifetime sessions are expired after this many
      *        seconds have elapsed from initial handshake.
      */
      Session_Manager_In_Memory(RandomNumberGenerator& rng,
                                size_t max_sessions = 1000,
                                std::chrono::seconds session_lifetime =
                                   std::chrono::seconds(7200));

      bool load_from_session_id(const std::vector<uint8_t>& session_id,
                                Session& session) override;

      bool load_from_server_info(const Server_Information& info,
                                 Session& session) override;

      void remove_entry(const std::vector<uint8_t>& session_id) override;

      size_t remove_all() override;

      void save(const Session& session_data) override;

      std::chrono::seconds session_lifetime() const override
         { return m_session_lifetime; }

   private:
      bool load_from_session_str(const std::string& session_str,
                                 Session& session);

      mutex_type m_mutex;

      size_t m_max_sessions;

      std::chrono::seconds m_session_lifetime;

      RandomNumberGenerator& m_rng;
      secure_vector<uint8_t> m_session_key;

      std::map<std::string, std::vector<uint8_t>> m_sessions; // hex(session_id) -> session
      std::map<Server_Information, std::string> m_info_sessions;
   };

}

}

#endif