Class: JustChess::GameState

Inherits:
Object
  • Object
show all
Defined in:
lib/just_chess/game_state.rb

Overview

Game State

Represents a game of Chess in progress.

Constant Summary collapse

PROMOTABLE_PIECE_TYPES =

They piece types that a pawn can promote to.

['queen', 'knight', 'bishop', 'rook']

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(current_player_number:, squares: [], last_double_step_pawn_id: nil) ⇒ GameState

Returns a new instance of GameState.



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# File 'lib/just_chess/game_state.rb', line 18

def initialize(current_player_number: , squares: [], last_double_step_pawn_id: nil)
  @current_player_number = current_player_number
  @squares = if squares.is_a?(SquareSet)
    squares
  else
    SquareSet.new(squares: squares)
  end
  @last_double_step_pawn_id = last_double_step_pawn_id
  @last_change = {}
  @errors = []
end

Instance Attribute Details

#current_player_number ⇒ Object (readonly)

Returns the value of attribute current_player_number.



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# File 'lib/just_chess/game_state.rb', line 30

def current_player_number
  @current_player_number
end

#errors ⇒ Object (readonly)

Returns the value of attribute errors.



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# File 'lib/just_chess/game_state.rb', line 30

def errors
  @errors
end

#last_change ⇒ Object (readonly)

Returns the value of attribute last_change.



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# File 'lib/just_chess/game_state.rb', line 30

def last_change
  @last_change
end

#last_double_step_pawn_id ⇒ Object (readonly)

Returns the value of attribute last_double_step_pawn_id.



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# File 'lib/just_chess/game_state.rb', line 30

def last_double_step_pawn_id
  @last_double_step_pawn_id
end

#squares ⇒ Object (readonly)

Returns the value of attribute squares.



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# File 'lib/just_chess/game_state.rb', line 30

def squares
  @squares
end

Class Method Details

.default ⇒ GameState

Instantiates a new GameState object in the starting position

Returns:



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# File 'lib/just_chess/game_state.rb', line 35

def self.default
  new({
    current_player_number: 1,
    squares: [
      { id: 'a8', x: 0, y: 0, piece: { id: 1, player_number: 2, type: 'rook' } },
      { id: 'b8', x: 1, y: 0, piece: { id: 2, player_number: 2, type: 'knight' } },
      { id: 'c8', x: 2, y: 0, piece: { id: 3, player_number: 2, type: 'bishop' } },
      { id: 'd8', x: 3, y: 0, piece: { id: 4, player_number: 2, type: 'queen' } },
      { id: 'e8', x: 4, y: 0, piece: { id: 5, player_number: 2, type: 'king' } },
      { id: 'f8', x: 5, y: 0, piece: { id: 6, player_number: 2, type: 'bishop' } },
      { id: 'g8', x: 6, y: 0, piece: { id: 7, player_number: 2, type: 'knight' } },
      { id: 'h8', x: 7, y: 0, piece: { id: 8, player_number: 2, type: 'rook' } },

      { id: 'a7', x: 0, y: 1, piece: { id: 9, player_number: 2, type: 'pawn' } },
      { id: 'b7', x: 1, y: 1, piece: { id: 10, player_number: 2, type: 'pawn' } },
      { id: 'c7', x: 2, y: 1, piece: { id: 11, player_number: 2, type: 'pawn' } },
      { id: 'd7', x: 3, y: 1, piece: { id: 12, player_number: 2, type: 'pawn' } },
      { id: 'e7', x: 4, y: 1, piece: { id: 13, player_number: 2, type: 'pawn' } },
      { id: 'f7', x: 5, y: 1, piece: { id: 14, player_number: 2, type: 'pawn' } },
      { id: 'g7', x: 6, y: 1, piece: { id: 15, player_number: 2, type: 'pawn' } },
      { id: 'h7', x: 7, y: 1, piece: { id: 16, player_number: 2, type: 'pawn' } },

      { id: 'a6', x: 0, y: 2, piece: nil },
      { id: 'b6', x: 1, y: 2, piece: nil },
      { id: 'c6', x: 2, y: 2, piece: nil },
      { id: 'd6', x: 3, y: 2, piece: nil },
      { id: 'e6', x: 4, y: 2, piece: nil },
      { id: 'f6', x: 5, y: 2, piece: nil },
      { id: 'g6', x: 6, y: 2, piece: nil },
      { id: 'h6', x: 7, y: 2, piece: nil },

      { id: 'a5', x: 0, y: 3, piece: nil },
      { id: 'b5', x: 1, y: 3, piece: nil },
      { id: 'c5', x: 2, y: 3, piece: nil },
      { id: 'd5', x: 3, y: 3, piece: nil },
      { id: 'e5', x: 4, y: 3, piece: nil },
      { id: 'f5', x: 5, y: 3, piece: nil },
      { id: 'g5', x: 6, y: 3, piece: nil },
      { id: 'h5', x: 7, y: 3, piece: nil },

      { id: 'a4', x: 0, y: 4, piece: nil },
      { id: 'b4', x: 1, y: 4, piece: nil },
      { id: 'c4', x: 2, y: 4, piece: nil },
      { id: 'd4', x: 3, y: 4, piece: nil },
      { id: 'e4', x: 4, y: 4, piece: nil },
      { id: 'f4', x: 5, y: 4, piece: nil },
      { id: 'g4', x: 6, y: 4, piece: nil },
      { id: 'h4', x: 7, y: 4, piece: nil },

      { id: 'a3', x: 0, y: 5, piece: nil },
      { id: 'b3', x: 1, y: 5, piece: nil },
      { id: 'c3', x: 2, y: 5, piece: nil },
      { id: 'd3', x: 3, y: 5, piece: nil },
      { id: 'e3', x: 4, y: 5, piece: nil },
      { id: 'f3', x: 5, y: 5, piece: nil },
      { id: 'g3', x: 6, y: 5, piece: nil },
      { id: 'h3', x: 7, y: 5, piece: nil },

      { id: 'a2', x: 0, y: 6, piece: { id: 17, player_number: 1, type: 'pawn' } },
      { id: 'b2', x: 1, y: 6, piece: { id: 18, player_number: 1, type: 'pawn' } },
      { id: 'c2', x: 2, y: 6, piece: { id: 19, player_number: 1, type: 'pawn' } },
      { id: 'd2', x: 3, y: 6, piece: { id: 20, player_number: 1, type: 'pawn' } },
      { id: 'e2', x: 4, y: 6, piece: { id: 21, player_number: 1, type: 'pawn' } },
      { id: 'f2', x: 5, y: 6, piece: { id: 22, player_number: 1, type: 'pawn' } },
      { id: 'g2', x: 6, y: 6, piece: { id: 23, player_number: 1, type: 'pawn' } },
      { id: 'h2', x: 7, y: 6, piece: { id: 24, player_number: 1, type: 'pawn' } },

      { id: 'a1', x: 0, y: 7, piece: { id: 25, player_number: 1, type: 'rook' } },
      { id: 'b1', x: 1, y: 7, piece: { id: 26, player_number: 1, type: 'knight' } },
      { id: 'c1', x: 2, y: 7, piece: { id: 27, player_number: 1, type: 'bishop' } },
      { id: 'd1', x: 3, y: 7, piece: { id: 28, player_number: 1, type: 'queen' } },
      { id: 'e1', x: 4, y: 7, piece: { id: 29, player_number: 1, type: 'king' } },
      { id: 'f1', x: 5, y: 7, piece: { id: 30, player_number: 1, type: 'bishop' } },
      { id: 'g1', x: 6, y: 7, piece: { id: 31, player_number: 1, type: 'knight' } },
      { id: 'h1', x: 7, y: 7, piece: { id: 32, player_number: 1, type: 'rook' } },
    ]
  })
end

Instance Method Details

#as_json ⇒ Hash

serializes the game state as a hash

Returns:

  • (Hash) 


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# File 'lib/just_chess/game_state.rb', line 117

def as_json
  {
    current_player_number: current_player_number,
    squares: squares.as_json,
    last_double_step_pawn_id: last_double_step_pawn_id
  }
end

#clone ⇒ GameState

deep clone of the game state

Returns:



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# File 'lib/just_chess/game_state.rb', line 128

def clone
  self.class.new(as_json)
end

#in_check?(player_number) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/just_chess/game_state.rb', line 240

def in_check?(player_number)
  king_square = squares.find_king_for_player(player_number)
  threatened_by = squares.threatened_by(opposing_player_number(player_number), self)
  threatened_by.include?(king_square)
end

#in_checkmate?(player_number) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/just_chess/game_state.rb', line 246

def in_checkmate?(player_number)
  in_check?(player_number) && king_cannot_move?(player_number)
end

#king_cannot_move?(player_number) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/just_chess/game_state.rb', line 251

def king_cannot_move?(player_number)
  king_square = squares.find_king_for_player(player_number)
  threatened_by = squares.threatened_by(opposing_player_number(player_number), self)
  destinations = king_square.piece.destinations(king_square, self)
  remove_threats = destinations - threatened_by
  remove_threats.none?
end

#move(player_number, from_id, to_id, promote_to = nil) ⇒ Boolean

Moves a piece owned by the player, from one square, to another, with an optional promotion.

It moves the piece and returns true if the move is valid and it’s the player’s turn. It returns false otherwise.

Example:

# Moves a piece from a square to perform a move
game_state.move(1, 'h7', 'h6')

Parameters:

  • player_number (Fixnum) —

    the player number, 1 or 2.

  • from_id (String) —

    the id of the from square

  • to_id (String) —

    the id of the to square

  • [String] (Hash) —

    a customizable set of options

Returns:

  • (Boolean) 


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# File 'lib/just_chess/game_state.rb', line 154

def move(player_number, from_id, to_id, promote_to=nil)
  @errors = []

  from = squares.find_by_id(from_id)
  to = squares.find_by_id(to_id)

  if current_player_number != player_number
    @errors.push JustChess::NotPlayersTurnError.new
  elsif from.unoccupied?
    @errors.push JustChess::NoPieceError.new
  elsif !((0..7).include?(to.x) && (0..7).include?(to.y))
    @errors.push JustChess::OffBoardError.new
  elsif !promote_to.nil? && !PROMOTABLE_PIECE_TYPES.include?(promote_to)
    @errors.push JustChess::InvalidPromotion.new
  elsif from.piece.can_move?(from, to, self)

    duplicate = self.clone
    duplicate.perform_complete_move(player_number, from_id, to_id, promote_to)

    if duplicate.in_check?(current_player_number)
      @errors.push JustChess::MovedIntoCheckError.new
    else
      perform_complete_move(player_number, from_id, to_id, promote_to)
    end
  else
    @errors.push JustChess::InvalidMoveError.new
  end
  @errors.empty?
end

#perform_complete_move(player_number, from_id, to_id, promote_to = nil) ⇒ Boolean

Moves a piece owned by the player, from one square, to another, with an optional promotion without validation

It handles castling, en passant and promotion. It moves the piece and returns true if the move is valid and it’s the player’s turn. It returns false otherwise.

Example:

# Moves a piece from a square to perform a move
game_state.move(1, 'h7', 'h6')

Parameters:

  • player_number (Fixnum) —

    the player number, 1 or 2.

  • from_id (String) —

    the id of the from square

  • to_id (String) —

    the id of the to square

  • [String] (Hash) —

    a customizable set of options

Returns:

  • (Boolean) 


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# File 'lib/just_chess/game_state.rb', line 221

def perform_complete_move(player_number, from_id, to_id, promote_to=nil)
  from = squares.find_by_id(from_id)
  to = squares.find_by_id(to_id)

  captured = captured_square(from, to)
  double_step_pawn = from.piece.is_a?(JustChess::Pawn) && Vector.new(from,to).magnitude == 2
  @last_double_step_pawn_id = double_step_pawn ? from.piece.id : nil

  @last_change = { type: 'move', data: {player_number: player_number, from: from_id, to: to_id} }

  rook_castle = rook_castle_move(from, to)
  perform_move(rook_castle.from, rook_castle.to, nil) if rook_castle

  perform_move(from, to, captured)

  promote(to, promote_to) if pawn_moved_to_last_rank(to)
  pass_turn
end

#winner ⇒ Fixnum, NilClass

The player number of the winner. It returns nil if there is no winner.

Returns:

  • (Fixnum, NilClass) 


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# File 'lib/just_chess/game_state.rb', line 187

def winner
  case
  when in_checkmate?(1)
    2
  when in_checkmate?(2)
    1
  else
    nil
  end
end