/*
  This file is part of ct.

  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 ct. If not, see <https://www.gnu.org/licenses/>.
*/

#include "zobrist.h"

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

static uint64_t *zobrist;

// ===================================================================
// Exported method implementations
// ===================================================================

int zobrist_init(const uint8_t board_size) {
  if (zobrist != NULL)
    return EXIT_FAILURE;

  zobrist = malloc(sizeof(uint64_t) * board_size * board_size * (15 * 2 * 3));
  // TODO: trap errno

  for (int k = 0; k < board_size * board_size * (15 * 2 * 3); k++) {
    XORSHIFT64;
    zobrist[k] = RANDOM64;
  }

  return EXIT_SUCCESS;
}

void zobrist_free(void) {
  if (zobrist != NULL) {
    free(zobrist);
    zobrist = NULL;
  }
}

uint64_t zobrist_compute(tak_state_p state) {
  uint64_t hash = 0;
  for (uint8_t l = 0; l < state->board_size * state->board_size; l++) {
    colour_stack_t c = state->colours[l];
    const uint8_t count = COUNT_AT(state, l);
    enum STONE_VARIANT s = STONE_AT(state, l);
    for (uint8_t h = 0; h < count; h++, c >>= 1)
      hash ^= zobrist[l * (15 * 2 * 3) + h * 2 * 3 + (c & 1) * 3 + s];
  }
  return hash;
}