text: // Copyright 2019 DeepMind Technologies Ltd. All rights reserved.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //     http://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  
  #ifndef OPEN_SPIEL_GAMES_OTHELLO_H_
  #define OPEN_SPIEL_GAMES_OTHELLO_H_
  
  #include <array>
  #include <map>
  #include <memory>
  #include <string>
  #include <vector>
  
  #include "open_spiel/abseil-cpp/absl/algorithm/container.h"  // for c_fill
  #include "open_spiel/spiel.h"
  
  // Simple game of Othello:
  // https://en.wikipedia.org/wiki/Reversi
  //
  // Parameters: none
  
  namespace open_spiel {
  namespace othello {
  
  // Constants.
  inline constexpr int kNumPlayers = 2;
  inline constexpr int kNumRows = 8;
  inline constexpr int kNumCols = 8;
  inline constexpr int kNumCells = kNumRows * kNumCols;
  inline constexpr int kCellStates = 1 + kNumPlayers;  // empty, 'x', and 'o'.
  inline constexpr int kPassMove = kNumCells;
  
  // State of a cell.
  enum class CellState {
    kEmpty,
    kBlack,
    kWhite,
  };
  
  enum Direction {
    kUp,
    kDown,
    kLeft,
    kRight,
    kUpLeft,
    kUpRight,
    kDownLeft,
    kDownRight,
  };
  
  inline constexpr std::array<Direction, 8> kDirections = {
      kUp, kDown, kLeft, kRight, kUpLeft, kUpRight, kDownLeft, kDownRight};
  
  class Move {
   public:
    Move(int move) : row_(move / kNumCols), col_(move % kNumCols) {
      SPIEL_CHECK_GE(move, 0);
      SPIEL_CHECK_LT(move, kNumCells);
    }
  
    Move(int row, int col) : row_(row), col_(col) {}
  
    inline int GetRow() const { return row_; }
    inline int GetColumn() const { return col_; }
    inline int GetAction() const { return row_ * kNumCols + col_; }
    inline bool OnBoard() const;
  
    Move Next(Direction dir) const;
    std::string ToString() const;
  
   private:
    int row_;
    int col_;
  };
  
  // State of an in-play game.
  class OthelloState : public State {
   public:
    OthelloState(std::shared_ptr<const Game> game);
  
    OthelloState(const OthelloState&) = default;
    OthelloState& operator=(const OthelloState&) = default;
  
    Player CurrentPlayer() const override { return current_player_; }
  
    std::string ActionToString(Player player, Action action_id) const override;
    std::string ToString() const override;
    bool IsTerminal() const override;
    std::vector<double> Returns() const override;
    std::string InformationStateString(Player player) const override;
    std::string ObservationString(Player player) const override;
    void ObservationTensor(Player player,
                           std::vector<double>* values) const override;
    std::unique_ptr<State> Clone() const override;
    std::vector<Action> LegalActions() const override;
  
   private:
    std::array<CellState, kNumCells> board_;
    void DoApplyAction(Action action) override;
  
    CellState BoardAt(int row, int col) const { return BoardAt(Move(row, col)); }
    CellState BoardAt(Move move) const { return board_[move.GetAction()]; }
  
    // Returns a list of regular (non-pass) actions.
    std::vector<Action> LegalRegularActions(Player p) const;
  
    // Returns true if the move would be valid for player if it were their turn.
    bool ValidAction(Player player, int move) const;
  
    // Returns true if there are no actions available for either player.
    bool NoValidActions() const;
  
    // Returns the number of pieces on the board for the given player.
    int DiskCount(Player player) const;
  
    // Returns true if the specified move would result in a capture.
    bool CanCapture(Player player, int move) const;
  
    // Returns the number of capturable disks of the opponent in the given
    // direction from the given starting location.
    int CountSteps(Player player, int action, Direction dir) const;
  
    // Updates the board to reflect a capture move.
    void Capture(Player player, int action, Direction dir, int steps);
  
    Player current_player_ = 0;  // Player zero goes first
    Player outcome_ = kInvalidPlayer;
  };
  
  // Game object.
  class OthelloGame : public Game {
   public:
    explicit OthelloGame(const GameParameters& params);
    int NumDistinctActions() const override { return kNumCells + 1; }  // can pass
    std::unique_ptr<State> NewInitialState() const override {
      return std::unique_ptr<State>(new OthelloState(shared_from_this()));
    }
    int NumPlayers() const override { return kNumPlayers; }
    double MinUtility() const override { return -1; }
    double UtilitySum() const override { return 0; }
    double MaxUtility() const override { return 1; }
    std::shared_ptr<const Game> Clone() const override {
      return std::shared_ptr<const Game>(new OthelloGame(*this));
    }
    std::vector<int> ObservationTensorShape() const override {
      return {kCellStates, kNumRows, kNumCols};
    }
    int MaxGameLength() const override { return kNumCells; }
  };
  
  }  // namespace othello
  }  // namespace open_spiel
  
  #endif  // OPEN_SPIEL_GAMES_OTHELLO_H_
  