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"],
  ]
)

Parameters:

  • squares (<Array<Array<String>>>) —

    the squares of the board



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# File 'lib/pgn/board.rb', line 76

def initialize(squares)
  self.squares = squares
  @owned = Array.new(8, false)
end

Instance Attribute Details

#squares ⇒ Array<Array<String>>

Returns the pieces on the board.

Returns:

  • (Array<Array<String>>) —

    the pieces on the board



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# File 'lib/pgn/board.rb', line 15

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
    @owned = Array.new(8, false)
  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"
  #
  # String squares are parsed with getbyte arithmetic (a=0x61, '1'=0x31)
  # so the common string lookup allocates nothing.
  def at(arg0, arg1 = nil)
    return squares[arg0][arg1] unless arg1.nil?

    squares[file_of(arg0)][rank_of(arg0)]
  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")
  #
  # Copy-on-write: clone only the column being mutated, and only once per
  # instance, so unchanged columns stay shared with any board this one was
  # duped from.
  def update(square, piece)
    file = file_of(square)
    unless @owned[file]
      squares[file] = squares[file].dup
      @owned[file] = true
    end
    squares[file][rank_of(square)] = 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_of(position), rank_of(position)]
  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. The outer array is copied; the
  # 8 column arrays are shared and cloned lazily by #update on first
  # mutation (copy-on-write).
  #
  def dup
    PGN::Board.new(squares.dup)
  end

  private

  def file_of(square)
    square.getbyte(0) - 97
  end

  def rank_of(square)
    square.getbyte(1) - 49
  end
end

Class Method Details

.start ⇒ PGN::Board

Returns a board in the starting position.

Returns:

  • (PGN::Board) —

    a board in the starting position



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# File 'lib/pgn/board.rb', line 57

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

Instance Method Details

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

String squares are parsed with getbyte arithmetic (a=0x61, '1'=0x31) so the common string lookup allocates nothing.

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)

    Parameters:

    • str (String) —

      the square in algebraic notation

  • #at(file, rank) ⇒ String?

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

    Parameters:

    • file (Integer) —

      the file the piece is on

    • rank (Integer) —

      the rank the piece is on

Returns:

  • (String, nil) —

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



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# File 'lib/pgn/board.rb', line 96

def at(arg0, arg1 = nil)
  return squares[arg0][arg1] unless arg1.nil?

  squares[file_of(arg0)][rank_of(arg0)]
end

#change!(changes) ⇒ self

Examples:

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

Parameters:

  • changes (Hash<String, <String, nil>>) —

    changes to make to the board

Returns:

  • (self) 


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# File 'lib/pgn/board.rb', line 107

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]

Parameters:

  • position (String) —

    the square in algebraic notation

Returns:

  • (Array<Integer>) —

    the coordinates of the square



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# File 'lib/pgn/board.rb', line 138

def coordinates_for(position)
  [file_of(position), rank_of(position)]
end

#dup ⇒ PGN::Board

8 column arrays are shared and cloned lazily by #update on first mutation (copy-on-write).

Returns:

  • (PGN::Board) —

    a copy of self. The outer array is copied; the



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# File 'lib/pgn/board.rb', line 167

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

#inspect ⇒ String

Returns the board in human readable format with unicode pieces.

Returns:

  • (String) —

    the board in human readable format with unicode pieces



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# File 'lib/pgn/board.rb', line 157

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"

Parameters:

  • coordinates (Array<Integer>) —

    the coordinates of the square

Returns:

  • (String) —

    the square in algebraic notation



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# File 'lib/pgn/board.rb', line 147

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

Copy-on-write: clone only the column being mutated, and only once per instance, so unchanged columns stay shared with any board this one was duped from.

Examples:

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

Parameters:

  • square (String) —

    the square in algebraic notation

  • piece (String, nil) —

    the piece to put on the square

Returns:

  • (self) 


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# File 'lib/pgn/board.rb', line 123

def update(square, piece)
  file = file_of(square)
  unless @owned[file]
    squares[file] = squares[file].dup
    @owned[file] = true
  end
  squares[file][rank_of(square)] = piece
  self
end