Class: Chess::Pieces::Pawn

Inherits:
Piece
  • Object
show all
Defined in:
lib/chess/pieces/pawn.rb

Overview

Pawn

Instance Attribute Summary

Attributes inherited from Piece

#color, #pos, #valid_moves

Instance Method Summary collapse

Methods inherited from Piece

#black?, #initialize, #white?

Constructor Details

This class inherits a constructor from Chess::Pieces::Piece

Instance Method Details

#attack_en_passant(board, file, rank) ⇒ Array

moves for attacking an pawn which is a Board#possible_en_passant_target

Parameters:

Returns:

  • (Array) —

    moves



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# File 'lib/chess/pieces/pawn.rb', line 146

def attack_en_passant(board, file, rank) # rubocop:disable Metrics/AbcSize,Metrics/MethodLength
  moves = []
  if white?
    north_east = board.north_east_pos(file, rank)
    moves << north_east if (north_east.first + north_east.last.to_s) == board.possible_en_passant_target
    north_west = board.north_west_pos(file, rank)
    moves << north_west if (north_west.first + north_west.last.to_s) == board.possible_en_passant_target
  else
    south_east = board.south_east_pos(file, rank)
    moves << south_east if (south_east.first + south_east.last.to_s) == board.possible_en_passant_target
    south_west = board.south_west_pos(file, rank)
    moves << south_west if (south_west.first + south_west.last.to_s) == board.possible_en_passant_target
  end
  moves
end

#cross_side_attack(board, file, rank) ⇒ Array

cross attack moves of pawn

Parameters:

Returns:

  • (Array) —

    moves



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# File 'lib/chess/pieces/pawn.rb', line 104

def cross_side_attack(board, file, rank)
  moves = []
  moves += if white?
             north_attack(board, file, rank)
           else
             south_attack(board, file, rank)
           end
  moves
end

#first_move?(rank) ⇒ Boolean

checks if it’s first move of pawn

Parameters:

  • rank (Integer)

Returns:

  • (Boolean) 


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# File 'lib/chess/pieces/pawn.rb', line 22

def first_move?(rank)
  (rank == 1 && white?) || (rank == 6 && black?)
end

#north_attack(board, file, rank) ⇒ Array

helper method for #cross_side_attack

Parameters:

Returns:

  • (Array) —

    moves



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# File 'lib/chess/pieces/pawn.rb', line 117

def north_attack(board, file, rank)
  moves = []
  north_east = board.north_east_pos(file, rank)
  north_west = board.north_west_pos(file, rank)
  [north_east, north_west].each do |pos|
    moves << pos if !(board.empty_at?(*pos) || board.pos_nil?(pos)) && board.piece_at(*pos).black?
  end
  moves
end

#north_two_step(board, file, rank) ⇒ Array

helper method for #two_step_forward

Parameters:

Returns:

  • (Array) —

    moves



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# File 'lib/chess/pieces/pawn.rb', line 76

def north_two_step(board, file, rank)
  north_one_step = board.north_pos(file, rank)
  north_two_step = board.north_pos(*north_one_step)
  return [] unless board.empty_at?(*north_one_step) && board.empty_at?(*north_two_step)

  north_two_step
end

#one_step_forward(board, file, rank) ⇒ Array

one step move of pawn

Parameters:

Returns:

  • (Array) —

    moves



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# File 'lib/chess/pieces/pawn.rb', line 46

def one_step_forward(board, file, rank)
  moves = []
  if white?
    north = board.north_pos(file, rank)
    moves << north if board.empty_at?(*north)
  else
    south = board.south_pos(file, rank)
    moves << south if board.empty_at?(*south) && board.pos_in_range?(south)
  end
  moves
end

#pawn_moves_by_color(board, file, rank) ⇒ Array

creates all the possible first moves

Parameters:

Returns:

  • (Array) —

    moves



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# File 'lib/chess/pieces/pawn.rb', line 31

def pawn_moves_by_color(board, file, rank)
  moves = []
  moves += one_step_forward(board, file, rank)
  moves += two_step_forward(board, file, rank) if first_move?(rank)
  moves += attack_en_passant(board, file, rank) unless first_move?(rank)
  moves += cross_side_attack(board, file, rank)
  moves.reject!(&:empty?)
  moves
end

#possible_moves(board) ⇒ Array

possible_moves of the pawn

Parameters:

Returns:

  • (Array) —

    moves



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# File 'lib/chess/pieces/pawn.rb', line 12

def possible_moves(board)
  moves = []
  file = @pos[0]
  rank = @pos[1]
  moves += pawn_moves_by_color(board, file, rank)
  moves
end

#south_attack(board, file, rank) ⇒ Array

helper method for #cross_side_attack

Parameters:

Returns:

  • (Array) —

    moves



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# File 'lib/chess/pieces/pawn.rb', line 130

def south_attack(board, file, rank)
  moves = []
  south_east = board.south_east_pos(file, rank)
  south_west = board.south_west_pos(file, rank)
  [south_east, south_west].each do |pos|
    moves << pos if !(board.empty_at?(*pos) || board.pos_nil?(pos)) &&
                    board.piece_at(*pos).white? &&
                    board.pos_in_range?(pos)
  end
  moves
end

#south_two_step(board, file, rank) ⇒ Array

helper method for #two_step_forward

Parameters:

Returns:

  • (Array) —

    moves



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# File 'lib/chess/pieces/pawn.rb', line 87

def south_two_step(board, file, rank)
  south_one_step = board.south_pos(file, rank)
  south_two_step = board.south_pos(*south_one_step)
  unless board.empty_at?(*south_one_step) && board.empty_at?(*south_two_step) &&
         board.pos_in_range?(south_one_step) && board.pos_in_range?(south_two_step)

    return []
  end

  south_two_step
end

#two_step_forward(board, file, rank) ⇒ Array

two step move of pawn

Parameters:

Returns:

  • (Array) —

    moves



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# File 'lib/chess/pieces/pawn.rb', line 63

def two_step_forward(board, file, rank)
  moves = []
  moves << if white?
             north_two_step(board, file, rank)
           else
             south_two_step(board, file, rank)
           end
  moves
end