/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2020 The Stockfish developers (see AUTHORS file)

  Stockfish is free software: you can redistribute it and/or modify
  it under the terms of the GNU General Public License as published by
  the Free Software Foundation, either version 3 of the License, or
  (at your option) any later version.

  Stockfish 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 General Public License for more details.

  You should have received a copy of the GNU General Public License
  along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#ifndef CLUSTER_H_INCLUDED
#define CLUSTER_H_INCLUDED

#include <algorithm>
#include <array>
#include <istream>
#include <string>

#include "misc.h"
#include "tt.h"

namespace Stockfish {
class Thread;
class ThreadPool;

namespace Search {
class Worker;
}

/// The Distributed namespace contains functionality required to run on distributed
/// memory architectures using MPI as the message passing interface. On a high level,
/// a 'lazy SMP'-like scheme is implemented where TT saves of sufficient depth are
/// collected on each rank and distributed to, and used by, all other ranks,
/// which search essentially independently.  The root (MPI rank 0) of the cluster
/// is responsible for all I/O and time management, communicating this info to
/// the other ranks as needed. UCI options such as Threads and Hash specify these
/// quantities per MPI rank.  It is recommended to have one rank (MPI process) per node.
/// For the non-MPI case, wrappers that will be compiler-optimized away are provided.

namespace Distributed {

/// Basic info to find the cluster-wide bestMove
struct MoveInfo {
    int move;
    int ponder;
    int depth;
    int score;
    int rank;
};

#ifdef USE_MPI

// store the TTData with its (full) key, so it can be saved on the receiver side
using KeyedTTEntry                = std::pair<Key, TTData>;
constexpr std::size_t TTCacheSize = 16;

// Threads locally cache their high-depth TT entries till a batch can be send by MPI
template<std::size_t N>
class TTCache: public std::array<KeyedTTEntry, N> {

    struct Compare {
        inline bool operator()(const KeyedTTEntry& lhs, const KeyedTTEntry& rhs) {
            return lhs.second.depth > rhs.second.depth;
        }
    };
    Compare compare;

   public:
    // Keep a heap of entries replacing low depth with high depth entries
    bool replace(const KeyedTTEntry& value) {

        if (compare(value, this->front()))
        {
            std::pop_heap(this->begin(), this->end(), compare);
            this->back() = value;
            std::push_heap(this->begin(), this->end(), compare);
            return true;
        }
        return false;
    }
};

void        init();
void        finalize();
bool        getline(std::istream& input, std::string& str);
int         size();
int         rank();
inline bool is_root() { return rank() == 0; }
void        save(TranspositionTable&,
                 ThreadPool&,
                 Search::Worker* thread,
                 TTWriter        ttWriter,
                 Key             k,
                 Value           v,
                 bool            PvHit,
                 Bound           b,
                 Depth           d,
                 Move            m,
                 Value           ev,
                 uint8_t         generation8);
void        pick_moves(MoveInfo& mi, std::vector<std::vector<char>>& PVLine);
void        ttSendRecvBuff_resize(size_t nThreads);
uint64_t    nodes_searched(const ThreadPool&);
uint64_t    tb_hits(const ThreadPool&);
uint64_t    TT_saves(const ThreadPool&);
void        cluster_info(const ThreadPool&, Depth depth, TimePoint elapsed);
void        signals_init();
void        signals_poll(ThreadPool& threads);
void        signals_sync(ThreadPool& threads);

#else

inline void init() {}
inline void finalize() {}
inline bool getline(std::istream& input, std::string& str) {
    return static_cast<bool>(std::getline(input, str));
}
constexpr int  size() { return 1; }
constexpr int  rank() { return 0; }
constexpr bool is_root() { return true; }
inline void    save(TranspositionTable&,
                    ThreadPool&,
                    Search::Worker*,
                    TTWriter ttWriter,
                    Key      k,
                    Value    v,
                    bool     PvHit,
                    Bound    b,
                    Depth    d,
                    Move     m,
                    Value    ev,
                    uint8_t  generation8) {
    ttWriter.write(k, v, PvHit, b, d, m, ev, generation8);
}
inline void pick_moves(MoveInfo&, std::vector<std::vector<char>>&) {}
inline void ttSendRecvBuff_resize(size_t) {}
uint64_t    nodes_searched(const ThreadPool&);
uint64_t    tb_hits(const ThreadPool&);
uint64_t    TT_saves(const ThreadPool&);
inline void cluster_info(const ThreadPool&, Depth, TimePoint) {}
inline void signals_init() {}
inline void signals_poll(ThreadPool& threads) {}
inline void signals_sync(ThreadPool& threads) {}

#endif /* USE_MPI */

}
}

#endif  // #ifndef CLUSTER_H_INCLUDED