import re
"""
Program that plays draughts (checkers) with user on 8x8 board using min-max with alpha-beta prunning
"""


class Game:
    """Game"""

    def __init__(self, size):
        self.board_size = size
        self.white_positions = self.initialize_white()
        self.black_positions = self.initialize_black()
        # print(self.white_positions)
        # print(self.black_positions)

    def initialize_white(self):
        """Initialize white pieces"""
        white_positions = []
        for y_coordinate in range(3):
            for x_coordinate in range(self.board_size):
                if y_coordinate % 2 == 0:
                    if x_coordinate % 2 == 1:
                        white_positions.append(
                            (x_coordinate, y_coordinate, False))
                else:
                    if x_coordinate % 2 == 0:
                        white_positions.append(
                            (x_coordinate, y_coordinate, False))
        return white_positions

    def initialize_black(self):
        """Initialize black pieces"""
        black_positions = []
        for y_coordinate in range(self.board_size - 3, self.board_size):
            for x_coordinate in range(self.board_size):
                if y_coordinate % 2 == 0:
                    if x_coordinate % 2 == 1:
                        black_positions.append(
                            (x_coordinate, y_coordinate, False))
                else:
                    if x_coordinate % 2 == 0:
                        black_positions.append(
                            (x_coordinate, y_coordinate, False))
        return black_positions

  def check_move_out_of_bounds(self, from_, to):
    """Check if the move destination is out of the bounds of the board"""
    if to[0] < 0 or to[0] >= self.board_size - 1:
      print(f"Illegal move! Final x coordinate must be between 0 and {self.board_size}!")
      return True
    if to[1] < 0 or to[1] >= self.board_size - 1:
      print(f"Illegal move! Final y coordinate must be between 0 and {self.board_size}!")
      return True
    return False

    def check_piece_exists(self, coords, color):
        """Check if a piece of given color exists at a given spot"""
        if color == "white":
            if any(piece in self.white_positions for piece in ((*coords, False), (*coords, False))):
                return True
        else:
            if any(piece in self.black_positions for piece in ((*coords, False), (*coords, False))):
                return True
        return False

    def check_piece_king(self, coords, color):
        """Check if a piece of in a given spot and of a given color is a king. Return false if no piece is found"""
        if color == "white":
            return (*coords, True) in self.white_positions
        else:
            return (*coords, True) in self.black_positions

    # https://stackoverflow.com/a/2191707
    def check_move_piece_capable(self, from_, to, color):
        """Check if the move is exactly one square diagonally"""
        if abs(to[0] - from_[0]) == 1:
            if self.check_piece_king(from_, color):
                return True
            else:
                if color == "white":
                    return to[1] == from_[1] + 1
                elif color == "black":
                    return to[1] == from_[1] - 1
        return False

    def check_capture(self, from_, to, color):
        """Check if a piece was captured for a given move. Return captured piece coordinates or None"""
        # captures can only happen if the player moved twice-diagonally
        if (abs(to[0]-from_[0]) != 2 or abs(to[1]-from_[1] != 2)):
            return None

        middle = (abs(to[0]-from_[0])//2, abs(to[1]-from_[1])//2)

        if color == "white" and self.check_piece_exists(middle, "black"):
            return middle
        elif color == "black" and self.check_piece_exists(middle, "white"):
            return middle
        return None

    def check_move_legal(self, from_, to, color):
        """Check if a move is legal. Return a boolean or coordinates of captured piece"""
        if self.check_move_out_of_bounds(from_, to):
            print("Illegal move! Final position is out of the bounds of the board")
            return False
        if not self.check_piece_exists(from_, color):
            print(
                "Illegal move! There is no piece on the starting position that belongs to the player")
            return False
        if self.check_piece_exists(to, "white") or self.check_piece_exists(to, "black"):
            print("Illegal move! Cannot move to position taken by another piece")
            return False
        capture = self.check_capture(from_, to, color)
        if capture == None:
            if self.check_move_piece_capable(from_, to, color):
                return True
            else:
                print('Illegal move!')
                return False
        return capture

    def make_move(self, from_, to, color):
        """Move a piece on the board and remove any captured pieces"""
        move_legal = self.check_move_legal(from_, to, color)
        if move_legal == False:
            return False
        capture = move_legal if type(move_legal) is tuple else None
        king = self.check_piece_king(from_, color)

        if (color == "white"):
            self.white_positions.remove((*from_, king))
            self.white_positions.append((*to, king))
            if (capture):
                captured_king = self.check_piece_king(capture, "black")
                self.black_positions.remove((*move_legal, captured_king))

        else:
            self.black_positions.remove((*from_, king))
            self.black_positions.append((*to, king))
            if (capture):
                captured_king = self.check_piece_king(capture, "white")
                self.white_positions.remove((*move_legal, captured_king))
        return True

    def print_board(self):
        """Print the board in the console"""
        print("   ", end="")
        for x in range(self.board_size):
            print(f"  {chr(ord('a')+x)} ", end="")
        print(" ")
        line = 0
        for y in range(self.board_size*4):
            for x in range(self.board_size):
                bg = "#" if x % 2 == (y//4) % 2 else " "
                checker = bg
                if ((x, y//4, False) in self.white_positions):
                    checker = "w"
                elif ((x, y//4, True) in self.white_positions):
                    checker = "W"
                elif ((x, y//4, False) in self.black_positions):
                    checker = "b"
                elif ((x, y//4, True) in self.black_positions):
                    checker = "B"

        if(x==0):
          if(line%4==2):
            print('{:3d}'.format(y//4), end="")
          else:
            print("   ", end="")
        
        match line%4:
          case 0:
            print("+---", end="")
          case 1 | 3:
            print(f"|{3*bg}", end="")
          case 2:
            print(f"|{bg}{checker}{bg}", end="")
      if(line%4==0):
        print("+")
      else:
        print(f"|{y//4}" if line%4==2 else "|")
      line+=1
    print("   ", end="")
    for x in range(self.board_size):
      print("+---", end="")
    print("+\n   ", end="")
    for x in range(self.board_size):
      print(f"  {chr(ord('a')+x)}", end=" ")
    print()
    
# Ran first in the code
  def get_possible_move_down(self, from_, color):
    # all moves "down":
    legal_moves = []
    move_down_left_two = (from_[0] + 2, from_[1] - 2)
    move_down_right_two = (from_[0] + 2, from_[1] + 2)
    move_down_left_one = (from_[0] + 1, from_[1] - 1)
    move_down_right_one = (from_[0] + 1, from_[1] + 1)
    if self.check_move_legal(from_, move_down_left_two, color) != False:
      legal_moves.append((from_, move_down_two))
    elif self.check_move_legal(from_, move_down_right_two, color) != False:
      legal_moves.append((from_, move_down_right_two))
    elif self.check_move_legal(from_, move_down_left_one, color) != False:
      legal_moves.append((from_, move_down_left_one))
    elif self.check_move_legal(from_, move_down_right_one, color) != False:
      legal_moves.append((from_, move_down_right_one))
    return legal_moves

  def get_possible_move(self, from_, color):
    # get all possible moves from the pawn in from_ position
    # "-" in first position -> move to the "left" 
    # "+" in first postiin -> move to the "right"
    # "-" in second postion -> move "up"
    # "+" in second position -> move "down"
    legal_moves = self.get_possible_move_up(from_, color)
    legal_moves.append(self.get_possible_move_down(from_, color))
    return legal_moves

  def get_possible_moves(self, color):
    # toDo: get possible moves for single piece, then iterate through all pieces
    legal_moves = []
    if color == "white":
      for white_position in self.white_positions:
        print((white_position[0], white_position[1]))
        legal_moves.append(self.get_possible_move((white_position[0], white_position[1]), color))
    elif color == "black":
      for black_position in self.black_positions:
        legal_moves.append(self.get_possible_move((black_position[0], black_position[1]), color))
    return legal_moves
  
  def alpha_beta(self, depth, alpha, beta, player):
    if depth == 0:
        return self.evaluate(), None
    
    if player == 'x':
        max_eval = float('-inf')
        best_move = None
        
        for move in self.get_possible_moves(player):
            new_state = copy.deepcopy(self)
            new_state.move(*move)
            eval, _ = alpha_beta(new_state, depth-1, alpha, beta, 'o')
            
            if eval > max_eval:
                max_eval = eval
                best_move = move
            
            alpha = max(alpha, eval)
            
            if alpha >= beta:
                break
        
        return max_eval, best_move
    
    else:
        min_eval = float('inf')
        best_move = None
        
        for move in state.get_possible_moves(player):
            new_state = copy.deepcopy(state)
            new_state.move(*move)
            eval, _ = alpha_beta(new_state, depth-1, alpha, beta, 'x')
            
            if eval < min_eval:
                min_eval = eval
                best_move = move
            
            beta = min(beta, eval)
            
            if beta <= alpha:
                break
        
        return min_eval, best_move
      
  def evaluate(self):
    white_score = 0
    black_score = 0
    
    for white_position in self.white_positions:
      if white_position[2]:
        white_score += 2
      else:
        white_score += 2
      
    for black_position in self.black_positions:
      if black_position[2]:
        black_score += 2
      else:
        black_score += 2
    
    return x_score - o_score

  def input_to_coordinates(self, input):
    pos_x = ord(input[0])-ord('a')
    pos_y = int(input[1::])
    return pos_x, pos_y

  def handle_player_move(self, color):
      has_moved = False
      while not has_moved:
          user_input = input('How do you want to move? (format: d6 e5)\n')
          regex = r"^[A-Za-z]\d+\s[A-Za-z]\d+$"
          match = re.search(regex, user_input)
          if not match:
              print('Invalid input, try again')
              continue
          [move_from, move_to] = user_input.split(' ')
          from_coordinates = self.input_to_coordinates(move_from)
          to_coordinates = self.input_to_coordinates(move_to)
          has_moved = self.make_move(
              from_coordinates, to_coordinates, color)
      self.print_board()



# Ran first in the code
if __name__ == "__main__":
    game = Game(8)
    game.print_board()
    game.handle_player_move('black')