////////////////////////////////////////////////////////////////////////////////
/// DISCLAIMER
///
/// Copyright 2014-2016 ArangoDB GmbH, Cologne, Germany
/// Copyright 2004-2014 triAGENS GmbH, Cologne, Germany
///
/// Licensed under the Apache License, Version 2.0 (the "License");
/// you may not use this file except in compliance with the License.
/// You may obtain a copy of the License at
///
///     http://www.apache.org/licenses/LICENSE-2.0
///
/// Unless required by applicable law or agreed to in writing, software
/// distributed under the License is distributed on an "AS IS" BASIS,
/// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
/// See the License for the specific language governing permissions and
/// limitations under the License.
///
/// Copyright holder is ArangoDB GmbH, Cologne, Germany
///
/// @author Kaveh Vahedipour
////////////////////////////////////////////////////////////////////////////////

#ifndef ARANGOD_CONSENSUS_AGENT_H
#define ARANGOD_CONSENSUS_AGENT_H 1

#include "Agency/AgencyCommon.h"
#include "Agency/AgentConfiguration.h"
#include "Agency/AgentCallback.h"
#include "Agency/Constituent.h"
#include "Agency/Supervision.h"
#include "Agency/State.h"
#include "Agency/Store.h"

struct TRI_server_t;
struct TRI_vocbase_t;

namespace arangodb {
namespace consensus {
class Agent : public arangodb::Thread {

public:
  /// @brief Construct with program options
  explicit Agent(config_t const&);

  /// @brief Clean up
  ~Agent();

  /// @brief Get current term
  term_t term() const;

  /// @brief Get current term
  arangodb::consensus::id_t id() const;

  /// @brief Vote request
  priv_rpc_ret_t requestVote(term_t, arangodb::consensus::id_t, index_t, index_t, query_t const&);

  /// @brief Provide configuration
  config_t const& config() const;

  /// @brief Start thread
  bool start();

  /// @brief Verbose print of myself
  ////
  void print(arangodb::LoggerStream&) const;

  /// @brief Are we fit to run?
  bool fitness() const;

  /// @brief Leader ID
  arangodb::consensus::id_t leaderID() const;

  /// @brief Are we leading?
  bool leading() const;

  /// @brief Pick up leadership tasks
  bool lead();

  /// @brief Load persistent state
  bool load();

  /// @brief Attempt write
  write_ret_t write(query_t const&);

  /// @brief Read from agency
  read_ret_t read(query_t const&) const;

  /// @brief Received by followers to replicate log entries ($5.3);
  ///        also used as heartbeat ($5.2).
  bool recvAppendEntriesRPC(term_t term, arangodb::consensus::id_t leaderId, index_t prevIndex,
                            term_t prevTerm, index_t lastCommitIndex,
                            query_t const& queries);

  /// @brief Invoked by leader to replicate log entries ($5.3);
  ///        also used as heartbeat ($5.2).
  append_entries_t sendAppendEntriesRPC(arangodb::consensus::id_t slave_id);

  /// @brief 1. Deal with appendEntries to slaves.
  ///        2. Report success of write processes.
  void run() override final;

  /// @brief Start orderly shutdown of threads
  void beginShutdown() override final;

  /// @brief Report appended entries from AgentCallback
  void reportIn(arangodb::consensus::id_t id, index_t idx);

  /// @brief Wait for slaves to confirm appended entries
  bool waitFor(index_t last_entry, double timeout = 2.0);

  /// @brief Convencience size of agency
  size_t size() const;

  /// @brief Rebuild DBs by applying state log to empty DB
  bool rebuildDBs();

  /// @brief Last log entry
  log_t const& lastLog() const;

  /// @brief Persist term
  void persist (term_t, arangodb::consensus::id_t);

  /// @brief State machine
  State const& state() const;

  /// @brief Get read store
  Store const& readDB() const;

  /// @brief Get spearhead store
  Store const& spearhead() const; 

 private:

  /// @brief This server (need endpoint)
  TRI_server_t*        _server;

  /// @brief Vocbase for agency persistence
  TRI_vocbase_t*       _vocbase; 

  /// @brief Query registry for agency persistence
  aql::QueryRegistry*  _queryRegistry;

  /// @brief Leader election delegate
  Constituent          _constituent;

  /// @brief Cluster supervision module
  Supervision          _supervision;

  /// @brief State machine
  State                _state;

  /// @brief Configuration of command line options
  config_t             _config;   

  /// @brief Last commit index (raft) 
  index_t _lastCommitIndex; 

  /// @brief Spearhead (write) kv-store
  Store                _spearhead;

  /// @brief Commited (read) kv-store
  Store                _readDB;

  /// @brief Condition variable for appendEntries 
  arangodb::basics::ConditionVariable _appendCV;

  /// @brief Condition variable for waitFor 
  arangodb::basics::ConditionVariable _waitForCV;

  /// @brief Confirmed indices of all members of agency
  std::vector<index_t> _confirmed;
  arangodb::Mutex _ioLock;          /**< @brief Read/Write lock */
};

}}

#endif