Kanye's Game of Life

conway_spec.rb

class Point < Struct.new(:x,:y)
  def self.at(x,y)
    new x, y
  end

  def ==(other)
    other.x == x and other.y == y
  end

  def around
    -1.upto(1).map do |diff_x|
      -1.upto(1).map do |diff_y|
        next if diff_x == 0 and diff_y == 0
        self.class.at(x + diff_x,y + diff_y)
      end
    end.flatten.compact
  end
end

class Cell
  def self.at(x,y)
    AliveCell.new Point.at(x,y)
  end

  def initialize(position)
    @position = position
    @neighbors = 0
  end

  attr_reader :position, :neighbors

  def neighbored
    @neighbors += 1
  end

  def to_s
    "#{self.class.name} @ #{position.x},#{position.y} - Neighbors: #{neighbors}"
  end
end

class AliveCell < Cell
  def transform
    AliveCell.new(position) if neighbors == 2 || neighbors == 3
  end
end

class DeadCell < Cell
  def transform
    AliveCell.new(position) if neighbors == 3
  end
end

class Board

  def initialize(cells=[])
    cells.each {|cell| add cell }
  end

  def cells
    @cells ||= Hash.new {|hash,position| hash[position] = DeadCell.new(position)}
  end

  def alive_cells
    cells.values.find_all {|cell| cell.is_a? AliveCell }
  end

  def add(cell)
    cell.position.around.each do |position|
      found_cell = cells[position]
      found_cell.neighbored
      cell.neighbored if found_cell.is_a? AliveCell
    end

    cells[cell.position] = cell
  end

  def tick
    surviving_cells = cells.values.map {|cell| cell.transform }.compact
    self.class.new surviving_cells
  end
end

describe Board do

  describe '#tick' do
    context "when the board has one lonely cell" do
      #
      #  X => 0
      #
      it "generates a board with no alive cells" do
        cell1 = Cell.at 0, 0
        board = Board.new
        board.add cell1
        board = board.tick
        expect(board.alive_cells).to have(0).cells
      end
    end

    context "when the board has two lonely cells" do
      #
      #  XX => 00
      #
      it "generates a board with no alive cells" do
        cell1 = Cell.at 0, 0
        cell2 = Cell.at 1, 0
        board = Board.new
        board.add cell1
        board.add cell2
        board = board.tick
        expect(board.alive_cells).to have(0).cells
      end
    end

    context "when the board has three neighboring cells" do
      #
      #   X => XX => XX
      #  XX => XX => XX
      #
      it "generates the correct board" do
        cell1 = Cell.at 0, 0
        cell2 = Cell.at 1, 0
        cell3 = Cell.at 1, 1

        board = Board.new
        board.add cell1
        board.add cell2
        board.add cell3
        board = board.tick
        expect(board.alive_cells).to have(4).cells
        board = board.tick
        # Four cells next to each other are in perfect harmony
        expect(board.alive_cells).to have(4).cells
      end
    end


    context "when a board has five live cells" do
      #
      #  X  => XXX => XXX => XXX
      # XXX => X0X => X0X => X0X
      #  X  => XXX => XXX => XXX
      #
      it "generates the correct board" do
        cell1 = Cell.at 0, 0
        cell2 = Cell.at 1, 0
        cell3 = Cell.at 0, 1
        cell4 = Cell.at -1,0
        cell5 = Cell.at 0,-1

        board = Board.new
        board.add cell1
        board.add cell2
        board.add cell3
        board.add cell4
        board.add cell5
        board = board.tick
        expect(board.alive_cells).to have(8).cells
        board = board.tick
        expect(board.alive_cells).to have(8).cells
      end
    end
  end

end

cells.values.grep(AliveCell)