module BookKeeping
  VERSION = 1
end
Position = Struct.new(:x, :y)
class Board
  DIRECTIONS = [[1, 0], [-1, 0], [0, 1], [0, -1], [-1, 1], [1, -1]].freeze
  BLACK = 'X'.freeze
  WHITE = 'O'.freeze

  def initialize(game)
    @height = game.size
    @width = cols(game[0]).size
    @fields = Array.new(@height) { Array.new(@width) }
    prepare_board(game)
    @history = {}
  end

  def cols(line)
    line.tr(' ', '').split('')
  end

  def prepare_board(game)
    game.each_with_index do |line, y|
      cols(line).each_with_index do |char, x|
        @fields[x][y] =
          if char == BLACK || char == WHITE
            char
          else nil
          end
      end
    end
  end

  def start_of(winner)
    case winner
    when BLACK then (0...@height).map { |y| Position.new(0, y) }
    when WHITE then (0...@width).map { |x| Position.new(x, 0) }
    end
  end

  def winner?(winner)
    start_of(winner).any? {|position| winner_on?(position, winner) }
  end

  def neighbours(pos)
    neighbours = []
    DIRECTIONS.each do |x, y|
      position = Position.new pos.x + x, pos.y + y
      neighbours << position if into_board? position
    end
    neighbours
  end

  def into_board?(position)
    position.x >= 0 && position.y >= 0 &&
      position.x < @width && position.y < @height
  end

  def reach_target?(winner, position)
    axis_position = winner == BLACK ? position.x : position.y
    axis_position == edge_of(winner)
  end

  def edge_of winner
    {
      BLACK  => @width - 1,
      WHITE => @height - 1
    }[winner]
  end

  def winner_on?(position, winner)
    x = position.x
    y = position.y
    if @fields[x][y] == winner
      return false if @history[[winner, x, y]]
      @history[[winner, x, y]] = true
      return true if reach_target? winner, position
      return neighbours(position).any?{|pos| winner_on? pos, winner}
    end
    false
  end

  def winner
    return BLACK if winner? BLACK
    return WHITE if winner? WHITE
    ''
  end

  def each_field
    (0...@height).each do |y|
      (0...@width).each do |x|
        yield @fields[x][y], x, y
      end
    end
  end

  def to_s
    s = ""
    each_field do |chr, x, y|
      s << ' ' * y if x == 0
      if chr == BLACK || chr == WHITE
        chr = chr.downcase if @history[[chr, x, y]]
        s << chr + ' '
      else
        s << '. '
      end
      s << ?\n if x == @width - 1
    end
    s
  end
end