src/position.h

/*
  Stockfish, a UCI chess playing engine derived from Glaurung 2.1
  Copyright (C) 2004-2022 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 POSITION_H_INCLUDED
#define POSITION_H_INCLUDED

#include <cassert>
#include <deque>
#include <memory> // For std::unique_ptr
#include <string>

#include "bitboard.h"
#include "evaluate.h"
#include "psqt.h"
#include "types.h"

#include "nnue/nnue_accumulator.h"

namespace Stockfish {

/// StateInfo struct stores information needed to restore a Position object to
/// its previous state when we retract a move. Whenever a move is made on the
/// board (by calling Position::do_move), a StateInfo object must be passed.

struct StateInfo {

  // Copied when making a move
  Key    pawnKey;
  Key    materialKey;
  Value  nonPawnMaterial[COLOR_NB];
  int    castlingRights;
  int    rule50;
  int    pliesFromNull;
  Square epSquare;

  // Not copied when making a move (will be recomputed anyhow)
  Key        key;
  Bitboard   checkersBB;
  StateInfo* previous;
  Bitboard   blockersForKing[COLOR_NB];
  Bitboard   pinners[COLOR_NB];
  Bitboard   checkSquares[PIECE_TYPE_NB];
  Piece      capturedPiece;
  int        repetition;

  // Used by NNUE
  Eval::NNUE::Accumulator accumulator;
  DirtyPiece dirtyPiece;
};


/// A list to keep track of the position states along the setup moves (from the
/// start position to the position just before the search starts). Needed by
/// 'draw by repetition' detection. Use a std::deque because pointers to
/// elements are not invalidated upon list resizing.
typedef std::unique_ptr<std::deque<StateInfo>> StateListPtr;


/// Position class stores information regarding the board representation as
/// pieces, side to move, hash keys, castling info, etc. Important methods are
/// do_move() and undo_move(), used by the search to update node info when
/// traversing the search tree.
class Thread;

class Position {
public:
  static void init();

  Position() = default;
  Position(const Position&) = delete;
  Position& operator=(const Position&) = delete;

  // FEN string input/output
  Position& set(const std::string& fenStr, bool isChess960, StateInfo* si, Thread* th);
  Position& set(const std::string& code, Color c, StateInfo* si);
  std::string fen() const;

  // Position representation
  Bitboard pieces(PieceType pt) const;
  Bitboard pieces(PieceType pt1, PieceType pt2) const;
  Bitboard pieces(Color c) const;
  Bitboard pieces(Color c, PieceType pt) const;
  Bitboard pieces(Color c, PieceType pt1, PieceType pt2) const;
  Piece piece_on(Square s) const;
  Square ep_square() const;
  bool empty(Square s) const;
  template<PieceType Pt> int count(Color c) const;
  template<PieceType Pt> int count() const;
  template<PieceType Pt> Square square(Color c) const;
  bool is_on_semiopen_file(Color c, Square s) const;

  // Castling
  CastlingRights castling_rights(Color c) const;
  bool can_castle(CastlingRights cr) const;
  bool castling_impeded(CastlingRights cr) const;
  Square castling_rook_square(CastlingRights cr) const;

  // Checking
  Bitboard checkers() const;
  Bitboard blockers_for_king(Color c) const;
  Bitboard check_squares(PieceType pt) const;
  Bitboard pinners(Color c) const;

  // Attacks to/from a given square
  Bitboard attackers_to(Square s) const;
  Bitboard attackers_to(Square s, Bitboard occupied) const;
  Bitboard slider_blockers(Bitboard sliders, Square s, Bitboard& pinners) const;
  template<PieceType Pt> Bitboard attacks_by(Color c) const;

  // Properties of moves
  bool legal(Move m) const;
  bool pseudo_legal(const Move m) const;
  bool capture(Move m) const;
  bool gives_check(Move m) const;
  Piece moved_piece(Move m) const;
  Piece captured_piece() const;

  // Piece specific
  bool pawn_passed(Color c, Square s) const;
  bool opposite_bishops() const;
  int  pawns_on_same_color_squares(Color c, Square s) const;

  // Doing and undoing moves
  void do_move(Move m, StateInfo& newSt);
  void do_move(Move m, StateInfo& newSt, bool givesCheck);
  void undo_move(Move m);
  void do_null_move(StateInfo& newSt);
  void undo_null_move();

  // Static Exchange Evaluation
  bool see_ge(Move m, Value threshold = VALUE_ZERO) const;

  // Accessing hash keys
  Key key() const;
  Key key_after(Move m) const;
  Key material_key() const;
  Key pawn_key() const;

  // Other properties of the position
  Color side_to_move() const;
  int game_ply() const;
  bool is_chess960() const;
  Thread* this_thread() const;
  bool is_draw(int ply) const;
  bool has_game_cycle(int ply) const;
  bool has_repeated() const;
  int rule50_count() const;
  Score psq_score() const;
  Value psq_eg_stm() const;
  Value non_pawn_material(Color c) const;
  Value non_pawn_material() const;

  // Position consistency check, for debugging
  bool pos_is_ok() const;
  void flip();

  // Used by NNUE
  StateInfo* state() const;

  void put_piece(Piece pc, Square s);
  void remove_piece(Square s);

private:
  // Initialization helpers (used while setting up a position)
  void set_castling_right(Color c, Square rfrom);
  void set_state(StateInfo* si) const;
  void set_check_info(StateInfo* si) const;

  // Other helpers
  void move_piece(Square from, Square to);
  template<bool Do>
  void do_castling(Color us, Square from, Square& to, Square& rfrom, Square& rto);
  template<bool AfterMove>
  Key adjust_key50(Key k) const;

  // Data members
  Piece board[SQUARE_NB];
  Bitboard byTypeBB[PIECE_TYPE_NB];
  Bitboard byColorBB[COLOR_NB];
  int pieceCount[PIECE_NB];
  int castlingRightsMask[SQUARE_NB];
  Square castlingRookSquare[CASTLING_RIGHT_NB];
  Bitboard castlingPath[CASTLING_RIGHT_NB];
  Thread* thisThread;
  StateInfo* st;
  int gamePly;
  Color sideToMove;
  Score psq;
  bool chess960;
};

extern std::ostream& operator<<(std::ostream& os, const Position& pos);

inline Color Position::side_to_move() const {
  return sideToMove;
}

inline Piece Position::piece_on(Square s) const {
  assert(is_ok(s));
  return board[s];
}

inline bool Position::empty(Square s) const {
  return piece_on(s) == NO_PIECE;
}

inline Piece Position::moved_piece(Move m) const {
  return piece_on(from_sq(m));
}

inline Bitboard Position::pieces(PieceType pt = ALL_PIECES) const {
  return byTypeBB[pt];
}

inline Bitboard Position::pieces(PieceType pt1, PieceType pt2) const {
  return pieces(pt1) | pieces(pt2);
}

inline Bitboard Position::pieces(Color c) const {
  return byColorBB[c];
}

inline Bitboard Position::pieces(Color c, PieceType pt) const {
  return pieces(c) & pieces(pt);
}

inline Bitboard Position::pieces(Color c, PieceType pt1, PieceType pt2) const {
  return pieces(c) & (pieces(pt1) | pieces(pt2));
}

template<PieceType Pt> inline int Position::count(Color c) const {
  return pieceCount[make_piece(c, Pt)];
}

template<PieceType Pt> inline int Position::count() const {
  return count<Pt>(WHITE) + count<Pt>(BLACK);
}

template<PieceType Pt> inline Square Position::square(Color c) const {
  assert(count<Pt>(c) == 1);
  return lsb(pieces(c, Pt));
}

inline Square Position::ep_square() const {
  return st->epSquare;
}

inline bool Position::is_on_semiopen_file(Color c, Square s) const {
  return !(pieces(c, PAWN) & file_bb(s));
}

inline bool Position::can_castle(CastlingRights cr) const {
  return st->castlingRights & cr;
}

inline CastlingRights Position::castling_rights(Color c) const {
  return c & CastlingRights(st->castlingRights);
}

inline bool Position::castling_impeded(CastlingRights cr) const {
  assert(cr == WHITE_OO || cr == WHITE_OOO || cr == BLACK_OO || cr == BLACK_OOO);

  return pieces() & castlingPath[cr];
}

inline Square Position::castling_rook_square(CastlingRights cr) const {
  assert(cr == WHITE_OO || cr == WHITE_OOO || cr == BLACK_OO || cr == BLACK_OOO);

  return castlingRookSquare[cr];
}

inline Bitboard Position::attackers_to(Square s) const {
  return attackers_to(s, pieces());
}

template<PieceType Pt>
inline Bitboard Position::attacks_by(Color c) const {

  if constexpr (Pt == PAWN)
      return c == WHITE ? pawn_attacks_bb<WHITE>(pieces(WHITE, PAWN))
                        : pawn_attacks_bb<BLACK>(pieces(BLACK, PAWN));
  else
  {
      Bitboard threats = 0;
      Bitboard attackers = pieces(c, Pt);
      while (attackers)
          threats |= attacks_bb<Pt>(pop_lsb(attackers), pieces());
      return threats;
  }
}

inline Bitboard Position::checkers() const {
  return st->checkersBB;
}

inline Bitboard Position::blockers_for_king(Color c) const {
  return st->blockersForKing[c];
}

inline Bitboard Position::pinners(Color c) const {
  return st->pinners[c];
}

inline Bitboard Position::check_squares(PieceType pt) const {
  return st->checkSquares[pt];
}

inline bool Position::pawn_passed(Color c, Square s) const {
  return !(pieces(~c, PAWN) & passed_pawn_span(c, s));
}

inline int Position::pawns_on_same_color_squares(Color c, Square s) const {
  return popcount(pieces(c, PAWN) & ((DarkSquares & s) ? DarkSquares : ~DarkSquares));
}

inline Key Position::key() const {
  return adjust_key50<false>(st->key);
}

template<bool AfterMove>
inline Key Position::adjust_key50(Key k) const
{
  return st->rule50 < 14 - AfterMove
      ? k : k ^ make_key((st->rule50 - (14 - AfterMove)) / 8);
}

inline Key Position::pawn_key() const {
  return st->pawnKey;
}

inline Key Position::material_key() const {
  return st->materialKey;
}

inline Score Position::psq_score() const {
  return psq;
}

inline Value Position::psq_eg_stm() const {
  return (sideToMove == WHITE ? 1 : -1) * eg_value(psq);
}

inline Value Position::non_pawn_material(Color c) const {
  return st->nonPawnMaterial[c];
}

inline Value Position::non_pawn_material() const {
  return non_pawn_material(WHITE) + non_pawn_material(BLACK);
}

inline int Position::game_ply() const {
  return gamePly;
}

inline int Position::rule50_count() const {
  return st->rule50;
}

inline bool Position::opposite_bishops() const {
  return   count<BISHOP>(WHITE) == 1
        && count<BISHOP>(BLACK) == 1
        && opposite_colors(square<BISHOP>(WHITE), square<BISHOP>(BLACK));
}

inline bool Position::is_chess960() const {
  return chess960;
}

inline bool Position::capture(Move m) const {
  assert(is_ok(m));
  // Castling is encoded as "king captures rook"
  return (!empty(to_sq(m)) && type_of(m) != CASTLING) || type_of(m) == EN_PASSANT;
}

inline Piece Position::captured_piece() const {
  return st->capturedPiece;
}

inline Thread* Position::this_thread() const {
  return thisThread;
}

inline void Position::put_piece(Piece pc, Square s) {

  board[s] = pc;
  byTypeBB[ALL_PIECES] |= byTypeBB[type_of(pc)] |= s;
  byColorBB[color_of(pc)] |= s;
  pieceCount[pc]++;
  pieceCount[make_piece(color_of(pc), ALL_PIECES)]++;
  psq += PSQT::psq[pc][s];
}

inline void Position::remove_piece(Square s) {

  Piece pc = board[s];
  byTypeBB[ALL_PIECES] ^= s;
  byTypeBB[type_of(pc)] ^= s;
  byColorBB[color_of(pc)] ^= s;
  board[s] = NO_PIECE;
  pieceCount[pc]--;
  pieceCount[make_piece(color_of(pc), ALL_PIECES)]--;
  psq -= PSQT::psq[pc][s];
}

inline void Position::move_piece(Square from, Square to) {

  Piece pc = board[from];
  Bitboard fromTo = from | to;
  byTypeBB[ALL_PIECES] ^= fromTo;
  byTypeBB[type_of(pc)] ^= fromTo;
  byColorBB[color_of(pc)] ^= fromTo;
  board[from] = NO_PIECE;
  board[to] = pc;
  psq += PSQT::psq[pc][to] - PSQT::psq[pc][from];
}

inline void Position::do_move(Move m, StateInfo& newSt) {
  do_move(m, newSt, gives_check(m));
}

inline StateInfo* Position::state() const {

  return st;
}

} // namespace Stockfish

#endif // #ifndef POSITION_H_INCLUDED