Class: PGN::Board

Inherits:
Object
  • Object
show all
Defined in:
lib/pgn/board.rb

Overview

Board represents the squares of a chess board and the pieces on each square. It is responsible for translating between a human readable format (white queen’s rook on the bottom left) and the obvious internal representation (white queen’s rook is position [0,0]). It takes care of converting square names (e4) to actual locations, and can convert to unicode chess pieces for display purposes.

Constant Summary collapse

START =

The starting, internal representation of a chess board

[
  ['R', 'P', nil, nil, nil, nil, 'p', 'r'],
  ['N', 'P', nil, nil, nil, nil, 'p', 'n'],
  ['B', 'P', nil, nil, nil, nil, 'p', 'b'],
  ['Q', 'P', nil, nil, nil, nil, 'p', 'q'],
  ['K', 'P', nil, nil, nil, nil, 'p', 'k'],
  ['B', 'P', nil, nil, nil, nil, 'p', 'b'],
  ['N', 'P', nil, nil, nil, nil, 'p', 'n'],
  ['R', 'P', nil, nil, nil, nil, 'p', 'r']
].freeze
FILE_TO_INDEX = 
('a'..'h').each_with_index.to_h
INDEX_TO_FILE = 
FILE_TO_INDEX.map(&:reverse).to_h
RANK_TO_INDEX = 
('1'..'8').each_with_index.to_h
INDEX_TO_RANK = 
RANK_TO_INDEX.map(&:reverse).to_h
UNICODE_PIECES =

algebraic to unicode piece lookup

{
  'k' => "\u{265A}",
  'q' => "\u{265B}",
  'r' => "\u{265C}",
  'b' => "\u{265D}",
  'n' => "\u{265E}",
  'p' => "\u{265F}",
  'K' => "\u{2654}",
  'Q' => "\u{2655}",
  'R' => "\u{2656}",
  'B' => "\u{2657}",
  'N' => "\u{2658}",
  'P' => "\u{2659}",
  nil => '_'
}.freeze

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(squares) ⇒ Board

Returns a new instance of Board.

Examples:

PGN::Board.new(
  [
    ["R", "P", nil, nil, nil, nil, "p", "r"],
    ["N", "P", nil, nil, nil, nil, "p", "n"],
    ["B", "P", nil, nil, nil, nil, "p", "b"],
    ["Q", "P", nil, nil, nil, nil, "p", "q"],
    ["K", "P", nil, nil, nil, nil, "p", "k"],
    ["B", "P", nil, nil, nil, nil, "p", "b"],
    ["N", "P", nil, nil, nil, nil, "p", "n"],
    ["R", "P", nil, nil, nil, nil, "p", "r"],
  ]
)



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# File 'lib/pgn/board.rb', line 74

def initialize(squares)
  self.squares = squares
end

Instance Attribute Details

#squares ⇒ Array<Array<String>> 



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# File 'lib/pgn/board.rb', line 13

class Board
  # The starting, internal representation of a chess board
  #
  START = [
    ['R', 'P', nil, nil, nil, nil, 'p', 'r'],
    ['N', 'P', nil, nil, nil, nil, 'p', 'n'],
    ['B', 'P', nil, nil, nil, nil, 'p', 'b'],
    ['Q', 'P', nil, nil, nil, nil, 'p', 'q'],
    ['K', 'P', nil, nil, nil, nil, 'p', 'k'],
    ['B', 'P', nil, nil, nil, nil, 'p', 'b'],
    ['N', 'P', nil, nil, nil, nil, 'p', 'n'],
    ['R', 'P', nil, nil, nil, nil, 'p', 'r']
  ].freeze

  FILE_TO_INDEX = ('a'..'h').each_with_index.to_h
  INDEX_TO_FILE = FILE_TO_INDEX.map(&:reverse).to_h

  RANK_TO_INDEX = ('1'..'8').each_with_index.to_h
  INDEX_TO_RANK = RANK_TO_INDEX.map(&:reverse).to_h

  # algebraic to unicode piece lookup
  #
  UNICODE_PIECES = {
    'k' => "\u{265A}",
    'q' => "\u{265B}",
    'r' => "\u{265C}",
    'b' => "\u{265D}",
    'n' => "\u{265E}",
    'p' => "\u{265F}",
    'K' => "\u{2654}",
    'Q' => "\u{2655}",
    'R' => "\u{2656}",
    'B' => "\u{2657}",
    'N' => "\u{2658}",
    'P' => "\u{2659}",
    nil => '_'
  }.freeze

  attr_accessor :squares

  # @return [PGN::Board] a board in the starting position
  #
  def self.start
    PGN::Board.new(START)
  end

  # @param squares [<Array<Array<String>>>] the squares of the board
  # @example
  #   PGN::Board.new(
  #     [
  #       ["R", "P", nil, nil, nil, nil, "p", "r"],
  #       ["N", "P", nil, nil, nil, nil, "p", "n"],
  #       ["B", "P", nil, nil, nil, nil, "p", "b"],
  #       ["Q", "P", nil, nil, nil, nil, "p", "q"],
  #       ["K", "P", nil, nil, nil, nil, "p", "k"],
  #       ["B", "P", nil, nil, nil, nil, "p", "b"],
  #       ["N", "P", nil, nil, nil, nil, "p", "n"],
  #       ["R", "P", nil, nil, nil, nil, "p", "r"],
  #     ]
  #   )
  #
  def initialize(squares)
    self.squares = squares
  end

  # @overload at(str)
  #   Looks up a piece based on the string representation of a square (e4)
  #   @param str [String] the square in algebraic notation
  # @overload at(file, rank)
  #   Looks up a piece based on zero-indexed coordinates (4, 3)
  #   @param file [Integer] the file the piece is on
  #   @param rank [Integer] the rank the piece is on
  # @return [String, nil] the piece on the square, or nil if it is
  #   empty
  # @example
  #   board.at(4,3)  #=> "P"
  #   board.at("e4") #=> "P"
  #
  def at(*args)
    case args.length
    when 1
      at(*coordinates_for(args.first))
    when 2
      squares[args[0]][args[1]]
    end
  end

  # @param changes [Hash<String, <String, nil>>] changes to make to the board
  # @return [self]
  # @example
  #   board.change!({"e2" => nil, "e4" => "P"})
  #
  def change!(changes)
    changes.each do |square, piece|
      update(square, piece)
    end
    self
  end

  # @param square [String] the square in algebraic notation
  # @param piece [String, nil] the piece to put on the square
  # @return [self]
  # @example
  #   board.update("e4", "P")
  #
  def update(square, piece)
    coords = coordinates_for(square)
    squares[coords[0]][coords[1]] = piece
    self
  end

  # @param position [String] the square in algebraic notation
  # @return [Array<Integer>] the coordinates of the square
  # @example
  #   board.coordinates_for("e4") #=> [4, 3]
  #
  def coordinates_for(position)
    file_chr, rank_chr = position.chars.to_a
    file = FILE_TO_INDEX[file_chr]
    rank = RANK_TO_INDEX[rank_chr]
    [file, rank]
  end

  # @param coordinates [Array<Integer>] the coordinates of the square
  # @return [String] the square in algebraic notation
  # @example
  #   board.position_for([4, 3]) #=> "e4"
  #
  def position_for(coordinates)
    file, rank = coordinates
    file_chr = INDEX_TO_FILE[file]
    rank_chr = INDEX_TO_RANK[rank]
    [file_chr, rank_chr].join('')
  end

  # @return [String] the board in human readable format with unicode
  #   pieces
  #
  def inspect
    squares.transpose.reverse.map do |row|
      row.map { |chr| UNICODE_PIECES[chr] }.join(' ')
    end.join("\n")
  end

  # @return [PGN::Board] a copy of self with duplicated squares
  #
  def dup
    PGN::Board.new(squares.map(&:dup))
  end
end

Class Method Details

.start ⇒ PGN::Board 



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# File 'lib/pgn/board.rb', line 55

def self.start
  PGN::Board.new(START)
end

Instance Method Details

#at(str) ⇒ String? #at(file, rank) ⇒ String?

Returns the piece on the square, or nil if it is empty.

Examples:

board.at(4,3)  #=> "P"
board.at("e4") #=> "P"

Overloads:

  • #at(str) ⇒ String?

    Looks up a piece based on the string representation of a square (e4)

  • #at(file, rank) ⇒ String?

    Looks up a piece based on zero-indexed coordinates (4, 3)



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# File 'lib/pgn/board.rb', line 91

def at(*args)
  case args.length
  when 1
    at(*coordinates_for(args.first))
  when 2
    squares[args[0]][args[1]]
  end
end

#change!(changes) ⇒ self

Examples:

board.change!({"e2" => nil, "e4" => "P"})



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# File 'lib/pgn/board.rb', line 105

def change!(changes)
  changes.each do |square, piece|
    update(square, piece)
  end
  self
end

#coordinates_for(position) ⇒ Array<Integer>

Returns the coordinates of the square.

Examples:

board.coordinates_for("e4") #=> [4, 3]



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# File 'lib/pgn/board.rb', line 129

def coordinates_for(position)
  file_chr, rank_chr = position.chars.to_a
  file = FILE_TO_INDEX[file_chr]
  rank = RANK_TO_INDEX[rank_chr]
  [file, rank]
end

#dup ⇒ PGN::Board 



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# File 'lib/pgn/board.rb', line 159

def dup
  PGN::Board.new(squares.map(&:dup))
end

#inspect ⇒ String 



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# File 'lib/pgn/board.rb', line 151

def inspect
  squares.transpose.reverse.map do |row|
    row.map { |chr| UNICODE_PIECES[chr] }.join(' ')
  end.join("\n")
end

#position_for(coordinates) ⇒ String

Returns the square in algebraic notation.

Examples:

board.position_for([4, 3]) #=> "e4"



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# File 'lib/pgn/board.rb', line 141

def position_for(coordinates)
  file, rank = coordinates
  file_chr = INDEX_TO_FILE[file]
  rank_chr = INDEX_TO_RANK[rank]
  [file_chr, rank_chr].join('')
end

#update(square, piece) ⇒ self

Examples:

board.update("e4", "P")



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# File 'lib/pgn/board.rb', line 118

def update(square, piece)
  coords = coordinates_for(square)
  squares[coords[0]][coords[1]] = piece
  self
end