in_check.rb

in_check.rb

def in_check?(input_string)
  board = format_input_string(input_string)

  king_coords = king_location(board)
  king_x = king_coords[:x]
  king_y = king_coords[:y]

  # Pawns
  return true if piece_at_coords(board, relative_coords(king_coords, { x: 1, y: -1 })) == "P"
  return true if piece_at_coords(board, relative_coords(king_coords, { x: 1, y: 1 })) == "P"

  # Rook South
  ((king_y + 1)..7).each do |row|
    piece = piece_at_coords(board, { x: king_x, y: row })
    if piece == "R" || piece == "Q"
      return true
    elsif piece != "."
      break
    end
  end

  # Rook North
  (0..(king_y - 1)).each do |row|
    piece = piece_at_coords(board, { x: king_x, y: row })
    if piece == "R" || piece == "Q"
      return true
    elsif piece != "."
      break
    end
  end

  # Rook East
  ((king_x + 1)..7).each do |column|
    piece = piece_at_coords(board, { x: column, y: king_y })
    if piece == "R" || piece == "Q"
      return true
    elsif piece != "."
      break
    end
  end

  # Rook West
  (0..(king_x - 1)).each do |column|
    piece = piece_at_coords(board, { x: column, y: king_y })
    if piece == "R" || piece == "Q"
      return true
    elsif piece != "."
      break
    end
  end

  # Bishop Northeast
  distance_to_east_edge = 7 - king_coords[:x]
  distance_to_north_edge = king_coords[:y]

  diagonal_distance_to_edge = [distance_to_east_edge, distance_to_north_edge].min

  (1..diagonal_distance_to_edge).each do |step_number|
    piece = piece_at_coords(board, { x: king_x + step_number, y: king_y - step_number })
    if piece == "B" || piece == "Q"
      return true
    elsif piece != "."
      break
    end
  end

  # Bishop Southeast
  distance_to_east_edge = 7 - king_coords[:x]
  distance_to_south_edge = 7 - king_coords[:y]

  diagonal_distance_to_edge = [distance_to_east_edge, distance_to_south_edge].min

  (1..diagonal_distance_to_edge).each do |step_number|
    piece = piece_at_coords(board, { x: king_x + step_number, y: king_y + step_number })
    if piece == "B" || piece == "Q"
      return true
    elsif piece != "."
      break
    end
  end

  # Bishop Southwest
  distance_to_west_edge = king_coords[:x]
  distance_to_south_edge = 7 - king_coords[:y]

  diagonal_distance_to_edge = [distance_to_west_edge, distance_to_south_edge].min

  (1..diagonal_distance_to_edge).each do |step_number|
    piece = piece_at_coords(board, { x: king_x - step_number, y: king_y + step_number })
    if piece == "B" || piece == "Q"
      return true
    elsif piece != "."
      break
    end
  end

  # Bishop Northwest
  distance_to_west_edge = king_coords[:x]
  distance_to_north_edge = king_coords[:y]

  diagonal_distance_to_edge = [distance_to_west_edge, distance_to_north_edge].min

  (1..diagonal_distance_to_edge).each do |step_number|
    piece = piece_at_coords(board, { x: king_x - step_number, y: king_y - step_number })
    if piece == "B" || piece == "Q"
      return true
    elsif piece != "."
      break
    end
  end

  # Knight
  knight_relative_coords = [
    {x: 2, y: -1},
    {x: 1, y: -2},
    {x: 2, y: 1},
    {x: 1, y: 2},
    {x: -2, y: -1},
    {x: -1, y: -2},
    {x: -2, y: 1},
    {x: -1, y: 2},
  ].map { |kight_coords| relative_coords(king_coords, kight_coords) }
   .reject { |coords| out_of_bounds?(coords) }


  knight_relative_coords.each do |knight_coord|
    return true if piece_at_coords(board, knight_coord) == "N"
  end

  # King is safe ;)
  return false
end

def format_input_string(input_string)
  input_string.gsub(/\s/, "").chars
end


def king_location(board)
  index_to_coords(board.index("K"))
end

def index_to_coords(index)
  {
    x: index % 8,
    y: index / 8
  }
end

def relative_coords(coords, transform_coords)
  {
    x: coords[:x] + transform_coords[:x],
    y: coords[:y] + transform_coords[:y]
  }
end

def piece_at_coords(board, coords)
  board[coords_to_index(coords)]
end

def coords_to_index(coords)
  coords[:y] * 8 + coords[:x]
end

def out_of_bounds?(coords)
  coords[:y] > 7 || coords[:y] < 0 || coords[:x] > 7 || coords[:x] < 0
end