/***************************************************************************
 *   Copyright (C) 2009 by Stefan Bühler                                   *
 *   stbuehler@web.de                                                      *
 *                                                                         *
 *   This program is free software; you can redistribute it and/or modify  *
 *   it under the terms of the GNU General Public License as published by  *
 *   the Free Software Foundation; either version 2 of the License, or     *
 *   (at your option) any later version.                                   *
 *                                                                         *
 *   This program is distributed in the hope that it will be useful,       *
 *   but WITHOUT ANY WARRANTY; without even the implied warranty of        *
 *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
 *   GNU General Public License for more details.                          *
 *                                                                         *
 *   You should have received a copy of the GNU General Public License     *
 *   along with this program; if not, write to the                         *
 *   Free Software Foundation, Inc.,                                       *
 *   59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.             *
 ***************************************************************************/
#include "ai.h"

namespace toruschess {

// 	NOPIECE = 0, PAWN = 1, KNIGHT = 2, BISHOP = 3, ROOK = 4, QUEEN = 5, KING = 6
	static int piece_value[] = {
		0, 1, 3, 3, 5, 9, 10
	};
	static const int MAXVAL = 10000;
	static const int NOMOVE = -MAXVAL - 1;
	static const int DRAWVAL = -7;

	/* standard minimax search; saves the best move in *move if move != NULL;
	 * balance is the current "heuristic value" of a state (mult with curp to get the
	 * rating for a specifig player)
	 */
	static int minimax(Field &field, int bal, Player curp, unsigned int depth, Move *move) {
		if (depth == 0) return curp * bal;
		
		int mx = NOMOVE;
		for (int x = 0; x < 8; x++)
		for (int y = 0; y < 8; y++) {
			Pos p(x, y);
			if (field.player(p) != curp) continue;
			int cbal = bal;
			QList<Move> moves = field.validMoves(p);
			foreach(Move m, moves) {
				field.move_unchecked(m);
				cbal -= m.prevTo();
				int val = -minimax(field, cbal, Player(-curp), depth-1, NULL);
				if (val > mx) {
					mx = val;
					if (move) *move = m;
				}
				field.undo_unchecked(m);
				if (mx == MAXVAL) return mx;
			}
		}
		if (mx == NOMOVE) {
			if (field.inCheck(curp)) return -MAXVAL;
			return curp * DRAWVAL;
		}
		return mx;
	}
	
	Move ai::getMove(Field &field, Player curp, int depth) {
		int balance = 0;
		for (int x = 0; x < 8; x++)
		for (int y = 0; y < 8; y++) {
			Pos p(x,y);
			balance += field.player(p) * piece_value[field.piece(p)];
		}
		
		Move move;
		minimax(field, balance, curp, depth, &move);
		
		return move;
	}
	
}