engine/endgame.py

"""
Endgame Detection for Nexus-Core
Simplified endgame handling
"""

import chess


class EndgameDetector:
    """Basic endgame phase detection"""
    
    def __init__(self):
        self.phase = 'middlegame'
    
    def detect_phase(self, board: chess.Board) -> str:
        """Detect game phase"""
        
        # Count material
        total_material = 0
        piece_values = {
            chess.PAWN: 1,
            chess.KNIGHT: 3,
            chess.BISHOP: 3,
            chess.ROOK: 5,
            chess.QUEEN: 9
        }
        
        for piece_type in piece_values:
            count = len(board.pieces(piece_type, chess.WHITE))
            count += len(board.pieces(piece_type, chess.BLACK))
            total_material += count * piece_values[piece_type]
        
        # Phase detection
        if board.fullmove_number < 10:
            self.phase = 'opening'
        elif total_material <= 16:
            self.phase = 'endgame'
        else:
            self.phase = 'middlegame'
        
        return self.phase
    
    def is_known_draw(self, board: chess.Board) -> bool:
        """Check for known draws"""
        
        if board.is_insufficient_material():
            return True
        
        if board.halfmove_clock >= 100:
            return True
        
        return False
    
    def adjust_evaluation(self, board: chess.Board, eval_score: float) -> float:
        """Adjust evaluation for endgame"""
        
        phase = self.detect_phase(board)
        
        if self.is_known_draw(board):
            return 0.0
        
        # Endgame adjustments
        if phase == 'endgame':
            # King activity bonus
            king_activity = self._king_activity_bonus(board)
            eval_score += king_activity
        
        return eval_score
    
    def _king_activity_bonus(self, board: chess.Board) -> float:
        """King activity in endgame"""
        bonus = 0.0
        
        for color in [chess.WHITE, chess.BLACK]:
            king_sq = board.king(color)
            if king_sq is None:
                continue
            
            # Distance to center
            rank, file = divmod(king_sq, 8)
            center_distance = abs(rank - 3.5) + abs(file - 3.5)
            
            activity = (7 - center_distance) * 5
            
            if color == chess.WHITE:
                bonus += activity
            else:
                bonus -= activity
        
        return bonus