/*
  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 "nn.h"
#include "tak.h"

/*
 * Encode a board position into the network's input vector:
 *   [0]       ply parity (-1 / +1)
 *   [1]       white flats remaining, as a fraction of the total
 *   [2]       black flats remaining, as a fraction of the total
 *   [3 ..]    one scalar per cell for the top stone:
 *             0 empty, +-0.25 standing, +-0.5 flat, +-1 capstone,
 *             + white, - black
 *
 * `cur_board' must have room for 3 + board_size*board_size floats.
 */

// The per-cell scalar depends only on the top stone's colour, variant
// and occupancy, so it's a table lookup keyed on those three bits.
static const float cell_scalar[16] = {
    0.0f,  -0.5f, 0.0f, -0.25f, 0.0f, -1.0f, 0.0f, 0.0f, // black
    0.0f,  +0.5f, 0.0f, +0.25f, 0.0f, +1.0f, 0.0f, 0.0f, // white
};

void nn_prepare_input(float *cur_board, tak_state_p state) {
  const float inv_max_flats =
      (state->board_size == 6) ? (1.0f / 30.0f) : (1.0f / 21.0f);
  const unsigned int n_cells = state->board_size * state->board_size;
  for (unsigned int loc = 0; loc < n_cells; loc++) {
    const uint8_t d = state->celldat[loc];
    cur_board[3 + loc] = cell_scalar[((state->colours[loc] & 1) << 3) |
                                     ((d & STONE_MASK) << 1) |
                                     ((d & NUM_MASK) != 0)];
  }
  // Add input of flat counts and ply parity
  cur_board[0] = (state->ply & 1) ? 1 : -1;
  cur_board[1] = (float)(state->white_count & 127) * inv_max_flats;
  cur_board[2] = (float)(state->black_count & 127) * inv_max_flats;
}