/*
  This file is part of ctak.

  This program 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.

  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
  General Public License for more details.

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

#ifndef TT_H
#define TT_H

#include <stdint.h>
#include <nn.h>
#include <actions.h>

// ===================================================================
// Types
// ===================================================================

enum TT_FLAG { TT_EXACT, TT_LOWERBOUND, TT_UPPERBOUND };

#ifdef RECORD_PV
#include <pv.h>
#endif

typedef struct tt_node_s {
  uint16_t gen;
  uint64_t key;
  nn_function eval;
  enum TT_FLAG flag;
  uint8_t depth;
  float value;
  action_t action;
#ifdef RECORD_PV
  // use for generating training data only
  pv_leaf_t leaf;
#endif
} tt_entry_t;

// ===================================================================
// Variables
// ===================================================================

// Direct-mapped hash table (no chaining); one slot per key.
#define TT_SIZE ((uint32_t)((1 << 19) - 1))

// ===================================================================
// Methods
// ===================================================================

// Bump the generation counter, invalidating all entries. Called from
// negamax_init when the board size (and hence the zobrist table) changes;
// entries are otherwise kept across plies on purpose (see negamax.c).
int tt_init(void);

tt_entry_t *tt_seek(const uint64_t key, const nn_function eval);

// Store a search result for `key', returning the entry it was written to, or
// NULL when the replacement policy keeps the current occupant instead.
//
// Replacement policy per slot:
//
//   - generation and key match: always update
//
//   - otherwise (empty slot, stale generation, or a different key): replace the
//     occupant unless it is a deeper search of a different position, which is
//     kept.
tt_entry_t *tt_store(const uint64_t key, const nn_function eval,
                     const enum TT_FLAG flag, const uint8_t depth,
                     const float value, const action_t action);

#endif