backgammon/board.py

import numpy as np
import itertools

class Board:

    initial_state = ( 0,
                      2, 0, 0, 0, 0, -5,
                      0, -3, 0, 0, 0, 5,
                      -5, 0, 0, 0, 3, 0,
                      5, 0, 0, 0, 0, -2,
                      0 )
    
    @staticmethod
    def idxs_with_checkers_of_player(board, player):
        idxs = []
        for idx, checker_count in enumerate(board):
            if checker_count * player >= 1:
                idxs.append(idx)
        return idxs

    @staticmethod
    def is_move_valid(board, player, face_value, move):
        def sign(a):
            return (a > 0) - (a < 0)

        from_idx   = move[0]
        to_idx     = move[1]
        to_state   = None
        from_state = board[from_idx]
        delta      = to_idx - from_idx
        direction  = sign(delta)
        bearing_off = None

        # FIXME: Use get instead of array-like indexing
        if to_idx >= 1 and to_idx <= 24:
            to_state   = board[to_idx]
            bearing_off = False
        else:  # Bearing off
            to_state   = 0
            bearing_off = True

        # print("_"*20)
        # print("board:", board)
        # print("to_idx:", to_idx, "board[to_idx]:", board[to_idx], "to_state:", to_state)
        # print("+"*20)
        
        def is_forward_move():
            return direction == player

        def face_value_match_move_length():
            return abs(delta) == face_value

        def bear_in_if_checker_on_bar():
            if player == 1:
                bar = 0
            else:
                bar = 25

            bar_state = board[bar]

            if bar_state != 0:
                return from_idx == bar
            else:
                return True

        def checkers_at_from_idx():
            return sign(from_state) == player

        def no_block_at_to_idx():
            if -sign(to_state) == player:
                return abs(to_state) == 1
            else:
                return True

        def can_bear_off():
            checker_idxs = Board.idxs_with_checkers_of_player(board, player)
            def is_moving_backmost_checker():
                if player == 1:
                    return all([(idx >= from_idx) for idx in checker_idxs])
                else:
                    return all([(idx <= from_idx) for idx in checker_idxs])

            def all_checkers_in_last_quadrant():
                if player == 1:
                    return all([(idx >= 19) for idx in checker_idxs])
                else:
                    return all([(idx <= 6) for idx in checker_idxs])

            return all([ is_moving_backmost_checker(),
                         all_checkers_in_last_quadrant() ])
                
            # TODO: add switch here instead of wonky ternary in all        
            
        return all([ is_forward_move(),
                     face_value_match_move_length(),
                     bear_in_if_checker_on_bar(),
                     checkers_at_from_idx(),
                     no_block_at_to_idx(),
                     can_bear_off() if bearing_off else True ])

    @staticmethod
    def any_move_valid(board, player, roll):
        for die in roll:
            idxs = Board.idxs_with_checkers_of_player(board, player)
            for idx in idxs:
                if Board.is_move_valid(board, player, die,
                                       (idx, idx + (die * player))):
                    return True
        return False

    @staticmethod
    def num_of_checkers_for_player(board,player):
        return player * sum([board[idx] for idx in Board.idxs_with_checkers_of_player(board, player)])
    
    @staticmethod
    def outcome(board):
        def all_checkers_in_first_quadrant(player):
            checker_idxs = Board.idxs_with_checkers_of_player(board, player)
            if player == 1:
                return all([(idx <= 6) for idx in checker_idxs])
            else:
                return all([(idx >= 19) for idx in checker_idxs])
        winner = None
                
        for player in [1, -1]:
            if Board.idxs_with_checkers_of_player(board, player) == []:
                winner = player

        if winner == None:
            return None

        #backgammon = all_checkers_in_first_quadrant(-winner)
        gammon = Board.num_of_checkers_for_player(board, -winner) == 15
        score = 2 if gammon else 1
        return {winner: score, -winner: -score}


    @staticmethod
    def apply_moves_to_board(board, player, moves):
        for move in moves:
            from_idx, to_idx = move.split("/")
            board[int(from_idx)] -= int(player)
            board[int(to_idx)] += int(player)
        return board

    @staticmethod
    def calculate_legal_states(board, player, roll):
        # Find all points with checkers on them belonging to the player
        # Iterate through each index and check if it's a possible move given the roll

        # TODO: make sure that it is not possible to do nothing on first part of
        #       turn and then do something with the second die
        
        def calc_moves(board, face_value):
            idxs_with_checkers = Board.idxs_with_checkers_of_player(board, player)
            if len(idxs_with_checkers) == 0:
                return [board]
            boards = [(Board.do_move(board,
                               player,
                               (idx, idx + (face_value * player)))
                       if Board.is_move_valid(board,
                                              player,
                                              face_value,
                                              (idx, idx + (face_value * player)))
                       else None)
                      for idx in idxs_with_checkers]

            board_list = list(filter(None, boards))  # Remove None-values
            # if len(board_list) == 0:
            #     return [board]
            
            return board_list

        # Problem with cal_moves: Method can return empty list (should always contain at least same board).
        #               *Update*: Seems to be fixed.
            
        # ------------------
        # 1. Determine if dice have identical face value
        # 2. Iterate through remaining dice

        legal_moves = set()

        if not Board.any_move_valid(board, player, roll):
            return { board }
        
        dice_permutations = list(itertools.permutations(roll)) if roll[0] != roll[1] else [[roll[0]]*4]
        
        for roll in dice_permutations:
            # Calculate boards resulting from first move
            #print("initial board: ", board)
            #print("roll:", roll)
            boards = calc_moves(board, roll[0])
            #print("boards after first die: ", boards)

            for die in roll[1:]:
                # Calculate boards resulting from second move
                nested_boards = [calc_moves(board, die) for board in boards]
                #print("nested boards: ", nested_boards)
                boards = [board for boards in nested_boards for board in boards]

                # What the fuck
                #for board in boards:
                #    print(board)
                #    print("type__:",type(board))
                # Add resulting unique boards to set of legal boards resulting from roll

                #print("printing boards from calculate_legal_states: ", boards)
            legal_moves = legal_moves | set(boards)
            # print("legal moves: ", legal_moves)
        if len(legal_moves) == 0:
            legal_moves = { tuple(board) }
            
        return legal_moves 

    @staticmethod
    def pretty(board):
        def black(count):
            return "\033[0;30m\033[47m{}\033[0m\033[47m".format(count)
        def white(count):
            return "\033[0;31m\033[47m{}\033[0m\033[47m".format(count)
            
        temp = []
        for x in board:
            if x > 0:
                temp.append(" {}".format(x))
            elif x < 0:
                temp.append("{}".format(x))
            else: temp.append("  ")
                
        return """
  13  14  15  16  17  18               19  20  21  22  23  24
+--------------------------------------------------------------------------+
| {12}| {11}| {10}| {9}| {8}| {7}| bar -1: {0} | {6}| {5}| {4}| {3}| {2}| {1}| end -1: TODO|
|---|---|---|---|---|---|------------|---|---|---|---|---|---|             |
| {13}| {14}| {15}| {16}| {17}| {18}| bar  1: {25} | {19}| {20}| {21}| {22}| {23}| {24}| end  1: TODO|
+--------------------------------------------------------------------------+
  12  11  10   9   8   7                6   5   4   3   2   1 
 """.format(*temp)

    @staticmethod
    def do_move(board, player, move):
        # Implies that move is valid; make sure to check move validity before calling do_move(...)
        
        def move_to_bar(board, to_idx):
            board = list(board)
            if player == 1:
                board[25] -= player
            else:
                board[0] -= player
                
            board[to_idx] = 0
            return board

        # TODO: Moving in from bar is handled by the representation
        # TODONE: Handle bearing off

        from_idx = move[0]
        #print("from_idx: ", from_idx)
        to_idx = move[1]
        #print("to_idx: ", to_idx)
        # pdb.set_trace()
        board = list(board) # Make mutable copy of board

        # 'Lift' checker
        board[from_idx] -= player

        # Handle bearing off
        if to_idx < 1 or to_idx > 24:
            return tuple(board)
        
        # Handle hitting checkers
        if board[to_idx] * player == -1:
            board = move_to_bar(board, to_idx)

        # Put down checker
        board[to_idx] += player

        return tuple(board)

    @staticmethod
    def flip(board):
        return tuple((-x for x in reversed(board)))