def get_theoretical_ep_right(self, x):
"""Checks if a player could have an ep-move in theory from
looking just at the piece positions.
:param file:
The file to check as a letter between `"a"` and `"h"`.
:return:
A boolean indicating whether the player could theoretically
have that en-passant move.
"""
if x < 0 or x > 7:
raise ValueError(x)
'''
3 states of en-passant
p. pP ..
.. .. .p
.P .. ..
'''
# Check there is a pawn on the right rank for e.p.
y = 3 if self.fen._to_move == WHITE else 4
x88 = X88.from_x_and_y(x, y)
piece = self._pieces[x88]
if not piece:
return False
# If the square is not an opposite colored pawn then its not possible.
ocolor = Piece.opposite_color(self.fen._to_move)
if not Piece.is_klass_and_color(piece, PAWN, ocolor):
return False
# If the square below the pawn is not empty then it not possible.
y = 2 if self.turn == WHITE else 5
x88 = X88.from_x_and_y(x, y)
if self[x88]:
return False
# If there is not pawn of opposite color on a neighboring file then its not possible.
xs = [_x for _x in range(8) if _x>=0 and _x<8 and abs(x-_x) == 1]
for _x in xs:
x88 = X88.from_x_and_y(_x, y)
piece = self._pieces[x88]
if Piece.is_klass_color(piece, PAWN, Piece.opposite_color(self.fen._to_move)):
return True
# Else its just not possible.
return False
