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 ]
    
    # TODO: Remember to handle pushing other pieces to home
    # TODO: Also remember that a player can't move backwards and the one
    #  player goes from 1-47 while the other goes from 47-1

    # Remember to handle edge case when we're on the last moves and you may go
    # from position 22 -> 24 on a 6, if you have no pieces behind 22. Simply
    # check if any are behind if you're circle or if any are higher if you are
    # X, then it can be allowed.

    # Also, the check_move will also fail when you're attempting to leave a
    # bar. A fix of this is of course to check if the from_idx = bar and if so,
    # allow some extra stuff!

    # TODO: write tests
    # FIXME: make sure to disallow backwards movement
    # TODO: implement double roll feature (4 dice if dice are equal)
    # TODO: implement moving checkers into home (bearing off)
    # TODO: handle barring in a more elengant way
    # TODO: allow bearing off with non-exact die roll if this is only possible
    #       move
    # TODO: Allow not doing anything if and only if no alternatives
    @staticmethod
    def is_move_valid(board, player, face_value, move):
        board      = list(board)
        from_idx   = move[0]
        to_idx     = move[1]
        to_state   = board[to_idx]
        from_state = board[from_idx]
        
        if from_idx == 26:
            from_idx = 1
            face_value -= 1
        elif from_idx == 27:
            from_idx = 24
            face_value -= 1
            
        if not (1 <= from_idx <= 24 and
                1 <= to_idx   <= 24):
            return False
        elif ( abs( from_idx - to_idx ) != face_value ):
            return False
        elif (from_state *  player >= 1 and  # Is moving player's own checker?
              (to_state  *  player >= 0 or   # Is 'to' empty or has player's own checkers?
               to_state  * -player == 1)):   # Can opponent checker be hit?
            return True
    
    @staticmethod
    def is_winner(board, player):
        for i in range(1,25):
            if player * board[i] > 0:
                return False
        return True
        
    @staticmethod
    def calculate_legal_states(board, player, roll):
        # Find all pips with things on them belonging to the player
        # Iterate through each index and check if it's a possible move given the roll
        # If player is O, then check for idx + roll
        # If player is X, then check for idx - roll
        print("Find legal moves: ",roll,"-"*20)

        def idxs_with_checkers_of_current_player(board):
            idxs = []
            for idx, checker_count in enumerate(board):
                if checker_count * player >= 1:
                    idxs.append(idx)
                return idxs
        
        def calc_moves(board, face_value):
            idxs_with_checkers = idxs_with_checkers_of_current_player(board)
            boards = [(do_move(board,
                               player,
                               (idx, idx + (face_value * player))) if
                       is_move_valid(board,
                            player,
                            face_value,
                            (idx, idx + (face_value * player))) else None)
             for idx
             in idxs_with_checkers]

            # If no move can be made, make sure to include current board
            if is_move_valid(board, player, face_value, None):
                boards.append(board)
            
            return list(filter(None, boards)) # Remove None-values
            
        # ------------------
        # 1. Determine if dice have identical face value
        # 2. Iterate through remaining dice

        legal_moves = set()

        dice_permutations = list(itertools.permutations(roll)) if roll[0] != roll[1] else [[roll[0]]*4]
        
        for pair in dice_permutations:
            # Calculate boards resulting from first move
            boards = calc_moves(board, pair[0])

            for x in dice_permutations[1:None]:
                # Calculate boards resulting from second move
                nested_boards = [calc_moves(board, x) for board in boards]
                boards = [board for boards in nested_boards for board in boards]
                # Add resulting unique boards to set of legal boards resulting from roll
            legal_moves = legal_moves | set(boards)

        return legal_moves

    @staticmethod
    def pretty(board):
        temp = []
        for x in board:
            if x >= 0:
                temp.append(" {}".format(x))
            else:
                temp.append("{}".format(x))
                
        return """
  13  14  15  16  17  18               19  20  21  22  23  24
--------------------------------------------------------------------------
| {11}| {10}| {9}| {8}| {7}| {6}| bar  -1: {24} | {5}| {4}| {3}| {2}| {1}| {0}| end -1: TODO|
|---|---|---|---|---|---|-----------|---|---|---|---|---|---|
| {12}| {13}| {14}| {15}| {16}| {17}| bar 1: {25} | {18}| {19}| {20}| {21}| {22}| {23}| 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[0] += player
            else:
                board[25] += 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]
        to_idx = move[1]
        board = list(board) # Clone board

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

        # Handle bearing off
        if to_idx < 1 or to_idx > 24:
            return 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 board