import board
from board import BLACK, WHITE, onBoard

def addPos((c,r),(dc,dr)):
	return (c+dc,r+dr)

class Piece (object):
	def isOpponent(self, otherPieceOrNone):
		if otherPieceOrNone == None:
			return False
		return otherPieceOrNone.color != self.color
			
	def isMyPiece(self, otherPieceOrNone):
		if otherPieceOrNone == None:
			return False
		return otherPieceOrNone.color == self.color

class Fog (Piece):
    def code(self):
        return "?"

class MoveablePiece (Piece):
	def __init__(self, board, color):
		self.board = board
		self.color = color
		
	def moves(self):
		possibleMoves = []
		return possibleMoves

	def attacks(self):
		"""Used to determine visibility. This is only different for pawns"""
		return self.moves()

	def openSquare(self,pos):
		return onBoard(pos) and not self.isMyPiece(self.board.pieceAt(pos))

	def neighbors(self, *offsets):
		src = self.board.whereIs(self)
		return filter(self.openSquare, [addPos(src,off) for off in offsets])

	def ray(self, src, offset):
		"""Generator for ranged piece movement"""
		pos = addPos(src,offset)
		while self.openSquare(pos):
			yield(pos)
			if self.isOpponent(self.board.pieceAt(pos)):
				break
			pos = addPos(pos,offset)

	def rays(self, *offsets):
		src = self.board.whereIs(self)
		return [p for off in offsets for p in self.ray(src,off)]

class Bishop(MoveablePiece):
	def code(self):
		if self.color == BLACK:
			return "b"
		else:
			return "B"

	def moves(self):
		return self.rays((1,1), (-1,1), (1,-1), (-1,-1))



class King(MoveablePiece):
	def code(self):
		if self.color == BLACK:
			return "k"
		else:
			return "K"

	def moves(self):
		return self.neighbors((1,0), (-1,0), (0,1), (0,-1),      (1,1), (-1,1), (1,-1), (-1,-1))

			
class Knight(MoveablePiece):
	def code(self):
		if self.color == BLACK:
			return "n"
		else:
			return "N"
			
	def moves(self):
		return self.neighbors((-1, 2) ,(-1, -2), (1,2),(1,-2),(2,1),(2,-1),(-2,1),(-2,-1))


class Pawn(MoveablePiece):
	def code(self):
		if self.color == BLACK:
			return "p"
		else:
			return "P"
			
	def forward(self):
	 	if self.color == WHITE:
			return 1
		else:
			return -1
			
	def unmovedPawnRank(self):
	 	if self.color == WHITE:
			return 1
		else:
			return 6
			
	def moves(self):
		possibleMoves = []
		(col, rank) = self.board.whereIs(self)
		spot = (col, rank + self.forward())        # straight forward
		if  onBoard(spot) and not self.board.pieceAt(spot):
			possibleMoves.append(spot)
			# Initial two-space pawn move.
			if rank == self.unmovedPawnRank():
				spot = (col, rank + 2*self.forward())
				if not self.board.pieceAt(spot):
					possibleMoves.append(spot)
		# pawn captures
		for delta in (-1, 1):
			spot = (col + delta, rank + self.forward())
			if  onBoard(spot) and self.isOpponent(self.board.pieceAt(spot)):
				possibleMoves.append(spot)

		# En passant capture.
		if rank == self.enPassantRank():
			start, stop = self.board.lastMove
			otherCol, otherRank = stop
			if (abs(otherCol - col) == 1 and
			    stop[1] == rank and
			    abs(start[1] - stop[1]) == 2 and
			    isinstance(self.board.pieceAt(stop), Pawn)):
				possibleMoves.append((otherCol,
				    (start[1] + stop[1]) // 2))
				
				
		return possibleMoves
		
	def attacks(self):
		possibleAttacks = []
		(col, rank) = self.board.whereIs(self)
		for delta in (-1, 1):  		# attacks
			spot = (col + delta, rank + self.forward())
			if onBoard(spot):
				possibleAttacks.append(spot)
		# En passant capture.
		if rank == self.enPassantRank():
			start, stop = self.board.lastMove
			otherCol, otherRank = stop
			if (abs(otherCol - col) == 1 and
			    stop[1] == rank and
			    abs(start[1] - stop[1]) == 2 and
			    isinstance(self.board.pieceAt(stop), Pawn)):
				possibleAttacks.append((otherCol,
				    (start[1] + stop[1]) // 2))
		return possibleAttacks

	def enPassantRank(self):
		if self.color == WHITE:
			return 4
		else:
			return 3
			
class Queen(MoveablePiece):
	def code(self):
		if self.color == BLACK:
			return "q"
		else:
			return "Q"


	def moves(self):
		return self.rays((1,0), (-1,0), (0,1), (0,-1), (1,1), (-1,1), (1,-1), (-1,-1))

		

class Rook(MoveablePiece):
	def code(self):
		if self.color == BLACK:
			return "r"
		else:
			return "R"
						
	def moves(self):
		return self.rays((1,0), (-1,0), (0,1), (0,-1))