Class: PGN::Position

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

Overview

Position encapsulates all of the information necessary to completely understand a chess position. It can be turned into a FEN string or perform a move.

Constant Summary collapse

PLAYERS = 
%i[white black].freeze
CASTLING = 
%w[K Q k q].freeze

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(board, player, castling = CASTLING, en_passant = nil, halfmove = 0, fullmove = 1) ⇒ Position

Returns a new instance of Position.

Examples:

PGN::Position.new(
  PGN::Board.start,
  :white,
)

Parameters:

  • board (PGN::Board) —

    the board for the position

  • player (Symbol) —

    the player who moves next

  • castling (Array<String>) (defaults to: CASTLING) —

    the castling moves that are still available

  • en_passant (String, nil) (defaults to: nil) —

    the en passant square if applicable

  • halfmove (Integer) (defaults to: 0) —

    the number of halfmoves since the last pawn move or capture

  • fullmove (Integer) (defaults to: 1) —

    the number of fullmoves made so far



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# File 'lib/pgn/position.rb', line 65

def initialize(board, player, castling = CASTLING, en_passant = nil, halfmove = 0, fullmove = 1)
  self.board      = board
  self.player     = player
  self.castling   = castling
  self.en_passant = en_passant
  self.halfmove   = halfmove
  self.fullmove   = fullmove
end

Instance Attribute Details

#board ⇒ PGN::Board

Returns the board for the position.

Returns:



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# File 'lib/pgn/position.rb', line 30

class Position
  PLAYERS  = %i[white black].freeze
  CASTLING = %w[K Q k q].freeze

  attr_accessor :board
  attr_accessor :player
  attr_accessor :castling
  attr_accessor :en_passant
  attr_accessor :halfmove
  attr_accessor :fullmove

  # @return [PGN::Position] the starting position of a chess game
  #
  def self.start
    PGN::Position.new(
      PGN::Board.start,
      PLAYERS.first
    )
  end

  # @param board [PGN::Board] the board for the position
  # @param player [Symbol] the player who moves next
  # @param castling [Array<String>] the castling moves that are still
  #   available
  # @param en_passant [String, nil] the en passant square if applicable
  # @param halfmove [Integer] the number of halfmoves since the last pawn
  #   move or capture
  # @param fullmove [Integer] the number of fullmoves made so far
  #
  # @example
  #   PGN::Position.new(
  #     PGN::Board.start,
  #     :white,
  #   )
  #
  def initialize(board, player, castling = CASTLING, en_passant = nil, halfmove = 0, fullmove = 1)
    self.board      = board
    self.player     = player
    self.castling   = castling
    self.en_passant = en_passant
    self.halfmove   = halfmove
    self.fullmove   = fullmove
  end

  # @param str [String] the move to make in SAN
  # @return [PGN::Position] the resulting position
  #
  # @example
  #   queens_pawn = PGN::Position.start.move("d4")
  #
  def move(str)
    move       = PGN::Move.new(str, player)
    calculator = PGN::MoveCalculator.new(board, move)

    new_castling = castling - calculator.castling_restrictions
    new_halfmove = if calculator.increment_halfmove?
                     halfmove + 1
                   else
                     0
                   end
    new_fullmove = if calculator.increment_fullmove?
                     fullmove + 1
                   else
                     fullmove
                   end
    no_move = str == '--'
    PGN::Position.new(
      no_move ? board : calculator.result_board,
      next_player,
      new_castling,
      calculator.en_passant_square,
      new_halfmove,
      new_fullmove
    )
  end

  # @return [Symbol] the next player to move
  #
  def next_player
    (PLAYERS - [player]).first
  end

  def inspect
    "\n" + board.inspect
  end

  # @return [PGN::FEN] a {PGN::FEN} object representing the current position
  #
  def to_fen
    PGN::FEN.from_attributes(
      board: board,
      active: player == :white ? 'w' : 'b',
      castling: castling.join(''),
      en_passant: en_passant,
      halfmove: halfmove.to_s,
      fullmove: fullmove.to_s
    )
  end
end

#castling ⇒ Array<String>

Returns the castling moves that are still available.

Examples:

position.castling #=> ["K", "k", "q"]

Returns:

  • (Array<String>) —

    the castling moves that are still available



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# File 'lib/pgn/position.rb', line 30

class Position
  PLAYERS  = %i[white black].freeze
  CASTLING = %w[K Q k q].freeze

  attr_accessor :board
  attr_accessor :player
  attr_accessor :castling
  attr_accessor :en_passant
  attr_accessor :halfmove
  attr_accessor :fullmove

  # @return [PGN::Position] the starting position of a chess game
  #
  def self.start
    PGN::Position.new(
      PGN::Board.start,
      PLAYERS.first
    )
  end

  # @param board [PGN::Board] the board for the position
  # @param player [Symbol] the player who moves next
  # @param castling [Array<String>] the castling moves that are still
  #   available
  # @param en_passant [String, nil] the en passant square if applicable
  # @param halfmove [Integer] the number of halfmoves since the last pawn
  #   move or capture
  # @param fullmove [Integer] the number of fullmoves made so far
  #
  # @example
  #   PGN::Position.new(
  #     PGN::Board.start,
  #     :white,
  #   )
  #
  def initialize(board, player, castling = CASTLING, en_passant = nil, halfmove = 0, fullmove = 1)
    self.board      = board
    self.player     = player
    self.castling   = castling
    self.en_passant = en_passant
    self.halfmove   = halfmove
    self.fullmove   = fullmove
  end

  # @param str [String] the move to make in SAN
  # @return [PGN::Position] the resulting position
  #
  # @example
  #   queens_pawn = PGN::Position.start.move("d4")
  #
  def move(str)
    move       = PGN::Move.new(str, player)
    calculator = PGN::MoveCalculator.new(board, move)

    new_castling = castling - calculator.castling_restrictions
    new_halfmove = if calculator.increment_halfmove?
                     halfmove + 1
                   else
                     0
                   end
    new_fullmove = if calculator.increment_fullmove?
                     fullmove + 1
                   else
                     fullmove
                   end
    no_move = str == '--'
    PGN::Position.new(
      no_move ? board : calculator.result_board,
      next_player,
      new_castling,
      calculator.en_passant_square,
      new_halfmove,
      new_fullmove
    )
  end

  # @return [Symbol] the next player to move
  #
  def next_player
    (PLAYERS - [player]).first
  end

  def inspect
    "\n" + board.inspect
  end

  # @return [PGN::FEN] a {PGN::FEN} object representing the current position
  #
  def to_fen
    PGN::FEN.from_attributes(
      board: board,
      active: player == :white ? 'w' : 'b',
      castling: castling.join(''),
      en_passant: en_passant,
      halfmove: halfmove.to_s,
      fullmove: fullmove.to_s
    )
  end
end

#en_passant ⇒ String

Returns the en passant square if applicable.

Returns:

  • (String) —

    the en passant square if applicable



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# File 'lib/pgn/position.rb', line 30

class Position
  PLAYERS  = %i[white black].freeze
  CASTLING = %w[K Q k q].freeze

  attr_accessor :board
  attr_accessor :player
  attr_accessor :castling
  attr_accessor :en_passant
  attr_accessor :halfmove
  attr_accessor :fullmove

  # @return [PGN::Position] the starting position of a chess game
  #
  def self.start
    PGN::Position.new(
      PGN::Board.start,
      PLAYERS.first
    )
  end

  # @param board [PGN::Board] the board for the position
  # @param player [Symbol] the player who moves next
  # @param castling [Array<String>] the castling moves that are still
  #   available
  # @param en_passant [String, nil] the en passant square if applicable
  # @param halfmove [Integer] the number of halfmoves since the last pawn
  #   move or capture
  # @param fullmove [Integer] the number of fullmoves made so far
  #
  # @example
  #   PGN::Position.new(
  #     PGN::Board.start,
  #     :white,
  #   )
  #
  def initialize(board, player, castling = CASTLING, en_passant = nil, halfmove = 0, fullmove = 1)
    self.board      = board
    self.player     = player
    self.castling   = castling
    self.en_passant = en_passant
    self.halfmove   = halfmove
    self.fullmove   = fullmove
  end

  # @param str [String] the move to make in SAN
  # @return [PGN::Position] the resulting position
  #
  # @example
  #   queens_pawn = PGN::Position.start.move("d4")
  #
  def move(str)
    move       = PGN::Move.new(str, player)
    calculator = PGN::MoveCalculator.new(board, move)

    new_castling = castling - calculator.castling_restrictions
    new_halfmove = if calculator.increment_halfmove?
                     halfmove + 1
                   else
                     0
                   end
    new_fullmove = if calculator.increment_fullmove?
                     fullmove + 1
                   else
                     fullmove
                   end
    no_move = str == '--'
    PGN::Position.new(
      no_move ? board : calculator.result_board,
      next_player,
      new_castling,
      calculator.en_passant_square,
      new_halfmove,
      new_fullmove
    )
  end

  # @return [Symbol] the next player to move
  #
  def next_player
    (PLAYERS - [player]).first
  end

  def inspect
    "\n" + board.inspect
  end

  # @return [PGN::FEN] a {PGN::FEN} object representing the current position
  #
  def to_fen
    PGN::FEN.from_attributes(
      board: board,
      active: player == :white ? 'w' : 'b',
      castling: castling.join(''),
      en_passant: en_passant,
      halfmove: halfmove.to_s,
      fullmove: fullmove.to_s
    )
  end
end

#fullmove ⇒ Integer

Returns the number of fullmoves made so far.

Returns:

  • (Integer) —

    the number of fullmoves made so far



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# File 'lib/pgn/position.rb', line 30

class Position
  PLAYERS  = %i[white black].freeze
  CASTLING = %w[K Q k q].freeze

  attr_accessor :board
  attr_accessor :player
  attr_accessor :castling
  attr_accessor :en_passant
  attr_accessor :halfmove
  attr_accessor :fullmove

  # @return [PGN::Position] the starting position of a chess game
  #
  def self.start
    PGN::Position.new(
      PGN::Board.start,
      PLAYERS.first
    )
  end

  # @param board [PGN::Board] the board for the position
  # @param player [Symbol] the player who moves next
  # @param castling [Array<String>] the castling moves that are still
  #   available
  # @param en_passant [String, nil] the en passant square if applicable
  # @param halfmove [Integer] the number of halfmoves since the last pawn
  #   move or capture
  # @param fullmove [Integer] the number of fullmoves made so far
  #
  # @example
  #   PGN::Position.new(
  #     PGN::Board.start,
  #     :white,
  #   )
  #
  def initialize(board, player, castling = CASTLING, en_passant = nil, halfmove = 0, fullmove = 1)
    self.board      = board
    self.player     = player
    self.castling   = castling
    self.en_passant = en_passant
    self.halfmove   = halfmove
    self.fullmove   = fullmove
  end

  # @param str [String] the move to make in SAN
  # @return [PGN::Position] the resulting position
  #
  # @example
  #   queens_pawn = PGN::Position.start.move("d4")
  #
  def move(str)
    move       = PGN::Move.new(str, player)
    calculator = PGN::MoveCalculator.new(board, move)

    new_castling = castling - calculator.castling_restrictions
    new_halfmove = if calculator.increment_halfmove?
                     halfmove + 1
                   else
                     0
                   end
    new_fullmove = if calculator.increment_fullmove?
                     fullmove + 1
                   else
                     fullmove
                   end
    no_move = str == '--'
    PGN::Position.new(
      no_move ? board : calculator.result_board,
      next_player,
      new_castling,
      calculator.en_passant_square,
      new_halfmove,
      new_fullmove
    )
  end

  # @return [Symbol] the next player to move
  #
  def next_player
    (PLAYERS - [player]).first
  end

  def inspect
    "\n" + board.inspect
  end

  # @return [PGN::FEN] a {PGN::FEN} object representing the current position
  #
  def to_fen
    PGN::FEN.from_attributes(
      board: board,
      active: player == :white ? 'w' : 'b',
      castling: castling.join(''),
      en_passant: en_passant,
      halfmove: halfmove.to_s,
      fullmove: fullmove.to_s
    )
  end
end

#halfmove ⇒ Integer

Returns the number of halfmoves since the last pawn move or capture.

Returns:

  • (Integer) —

    the number of halfmoves since the last pawn move or capture



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# File 'lib/pgn/position.rb', line 30

class Position
  PLAYERS  = %i[white black].freeze
  CASTLING = %w[K Q k q].freeze

  attr_accessor :board
  attr_accessor :player
  attr_accessor :castling
  attr_accessor :en_passant
  attr_accessor :halfmove
  attr_accessor :fullmove

  # @return [PGN::Position] the starting position of a chess game
  #
  def self.start
    PGN::Position.new(
      PGN::Board.start,
      PLAYERS.first
    )
  end

  # @param board [PGN::Board] the board for the position
  # @param player [Symbol] the player who moves next
  # @param castling [Array<String>] the castling moves that are still
  #   available
  # @param en_passant [String, nil] the en passant square if applicable
  # @param halfmove [Integer] the number of halfmoves since the last pawn
  #   move or capture
  # @param fullmove [Integer] the number of fullmoves made so far
  #
  # @example
  #   PGN::Position.new(
  #     PGN::Board.start,
  #     :white,
  #   )
  #
  def initialize(board, player, castling = CASTLING, en_passant = nil, halfmove = 0, fullmove = 1)
    self.board      = board
    self.player     = player
    self.castling   = castling
    self.en_passant = en_passant
    self.halfmove   = halfmove
    self.fullmove   = fullmove
  end

  # @param str [String] the move to make in SAN
  # @return [PGN::Position] the resulting position
  #
  # @example
  #   queens_pawn = PGN::Position.start.move("d4")
  #
  def move(str)
    move       = PGN::Move.new(str, player)
    calculator = PGN::MoveCalculator.new(board, move)

    new_castling = castling - calculator.castling_restrictions
    new_halfmove = if calculator.increment_halfmove?
                     halfmove + 1
                   else
                     0
                   end
    new_fullmove = if calculator.increment_fullmove?
                     fullmove + 1
                   else
                     fullmove
                   end
    no_move = str == '--'
    PGN::Position.new(
      no_move ? board : calculator.result_board,
      next_player,
      new_castling,
      calculator.en_passant_square,
      new_halfmove,
      new_fullmove
    )
  end

  # @return [Symbol] the next player to move
  #
  def next_player
    (PLAYERS - [player]).first
  end

  def inspect
    "\n" + board.inspect
  end

  # @return [PGN::FEN] a {PGN::FEN} object representing the current position
  #
  def to_fen
    PGN::FEN.from_attributes(
      board: board,
      active: player == :white ? 'w' : 'b',
      castling: castling.join(''),
      en_passant: en_passant,
      halfmove: halfmove.to_s,
      fullmove: fullmove.to_s
    )
  end
end

#player ⇒ Symbol

Returns the player who moves next.

Examples:

position.player #=> :white

Returns:

  • (Symbol) —

    the player who moves next



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# File 'lib/pgn/position.rb', line 30

class Position
  PLAYERS  = %i[white black].freeze
  CASTLING = %w[K Q k q].freeze

  attr_accessor :board
  attr_accessor :player
  attr_accessor :castling
  attr_accessor :en_passant
  attr_accessor :halfmove
  attr_accessor :fullmove

  # @return [PGN::Position] the starting position of a chess game
  #
  def self.start
    PGN::Position.new(
      PGN::Board.start,
      PLAYERS.first
    )
  end

  # @param board [PGN::Board] the board for the position
  # @param player [Symbol] the player who moves next
  # @param castling [Array<String>] the castling moves that are still
  #   available
  # @param en_passant [String, nil] the en passant square if applicable
  # @param halfmove [Integer] the number of halfmoves since the last pawn
  #   move or capture
  # @param fullmove [Integer] the number of fullmoves made so far
  #
  # @example
  #   PGN::Position.new(
  #     PGN::Board.start,
  #     :white,
  #   )
  #
  def initialize(board, player, castling = CASTLING, en_passant = nil, halfmove = 0, fullmove = 1)
    self.board      = board
    self.player     = player
    self.castling   = castling
    self.en_passant = en_passant
    self.halfmove   = halfmove
    self.fullmove   = fullmove
  end

  # @param str [String] the move to make in SAN
  # @return [PGN::Position] the resulting position
  #
  # @example
  #   queens_pawn = PGN::Position.start.move("d4")
  #
  def move(str)
    move       = PGN::Move.new(str, player)
    calculator = PGN::MoveCalculator.new(board, move)

    new_castling = castling - calculator.castling_restrictions
    new_halfmove = if calculator.increment_halfmove?
                     halfmove + 1
                   else
                     0
                   end
    new_fullmove = if calculator.increment_fullmove?
                     fullmove + 1
                   else
                     fullmove
                   end
    no_move = str == '--'
    PGN::Position.new(
      no_move ? board : calculator.result_board,
      next_player,
      new_castling,
      calculator.en_passant_square,
      new_halfmove,
      new_fullmove
    )
  end

  # @return [Symbol] the next player to move
  #
  def next_player
    (PLAYERS - [player]).first
  end

  def inspect
    "\n" + board.inspect
  end

  # @return [PGN::FEN] a {PGN::FEN} object representing the current position
  #
  def to_fen
    PGN::FEN.from_attributes(
      board: board,
      active: player == :white ? 'w' : 'b',
      castling: castling.join(''),
      en_passant: en_passant,
      halfmove: halfmove.to_s,
      fullmove: fullmove.to_s
    )
  end
end

Class Method Details

.start ⇒ PGN::Position

Returns the starting position of a chess game.

Returns:



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# File 'lib/pgn/position.rb', line 43

def self.start
  PGN::Position.new(
    PGN::Board.start,
    PLAYERS.first
  )
end

Instance Method Details

#inspect ⇒ Object 



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# File 'lib/pgn/position.rb', line 112

def inspect
  "\n" + board.inspect
end

#move(str) ⇒ PGN::Position

Returns the resulting position.

Examples:

queens_pawn = PGN::Position.start.move("d4")

Parameters:

  • str (String) —

    the move to make in SAN

Returns:



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# File 'lib/pgn/position.rb', line 80

def move(str)
  move       = PGN::Move.new(str, player)
  calculator = PGN::MoveCalculator.new(board, move)

  new_castling = castling - calculator.castling_restrictions
  new_halfmove = if calculator.increment_halfmove?
                   halfmove + 1
                 else
                   0
                 end
  new_fullmove = if calculator.increment_fullmove?
                   fullmove + 1
                 else
                   fullmove
                 end
  no_move = str == '--'
  PGN::Position.new(
    no_move ? board : calculator.result_board,
    next_player,
    new_castling,
    calculator.en_passant_square,
    new_halfmove,
    new_fullmove
  )
end

#next_player ⇒ Symbol

Returns the next player to move.

Returns:

  • (Symbol) —

    the next player to move



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# File 'lib/pgn/position.rb', line 108

def next_player
  (PLAYERS - [player]).first
end

#to_fen ⇒ PGN::FEN

Returns a FEN object representing the current position.

Returns:

  • (PGN::FEN) —

    a FEN object representing the current position



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

def to_fen
  PGN::FEN.from_attributes(
    board: board,
    active: player == :white ? 'w' : 'b',
    castling: castling.join(''),
    en_passant: en_passant,
    halfmove: halfmove.to_s,
    fullmove: fullmove.to_s
  )
end