/*
  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/>.
*/

#include "tt.h"
#include <string.h>

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

static tt_entry_t table[TT_SIZE + 1];
static uint16_t tt_gen = 0;

// ===================================================================
// Exported functions
// ===================================================================

int tt_init(void) {
  tt_gen++;
  if (tt_gen == 0)
    memset(table, 0, sizeof(table));
  return EXIT_SUCCESS;
}

tt_entry_t *tt_seek(const uint64_t key, const nn_function eval) {
  tt_entry_t *e = &table[key & TT_SIZE];
  if (e->gen == tt_gen && e->key == key && e->eval == eval)
    return e;
  return NULL;
}

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) {
  tt_entry_t *e = &table[key & TT_SIZE];
  if (e->gen == tt_gen && e->key == key) {
    // The slot holds this very position: update it (gen and key are already
    // correct).
    e->eval = eval;
    e->flag = flag;
    e->value = value;
    e->depth = depth;
    e->action = action;
    return e;
  }
  // Empty slot, stale generation, or a different position: keep a deeper search
  // of a foreign position over this shallower one.
  if (e->gen == tt_gen && e->depth > depth)
    return NULL;
  e->key = key;
  e->eval = eval;
  e->value = value;
  e->action = action;
  e->gen = tt_gen;
  e->flag = flag;
  e->depth = depth;
  return e;
}