/***
	This file is part of Let's play gomoku!
	Copyright (C) 2021 Aleksandr D. Goncharov (Joursoir) <chat@joursoir.net>

	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 3 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, see <https://www.gnu.org/licenses/>.
***/

#include <stdlib.h>
#include <time.h>

#include "ai.hpp"
#include "GameField.hpp"

enum scores {
	MIN_SCORE = -1000,
	MAX_SCORE = 1000,
	NONE_SCORE = 0,
	DRAW_SCORE = 2,
	WIN_SCORE = 10,
	LOSE_SCORE = -10
};

AI::AI(int p, int d) : player(p), max_depth(d), first_move(true)
{
	srand(time(NULL));
}

void AI::GetBestMove(int &my, int &mx, GameField field)
{
	int score = MIN_SCORE;
	int rows = field.GetRows();
	int cols = field.GetCols();

	// give chance to user :)
	if(first_move) {
		do {
			my = rand() % rows;
			mx = rand() % cols;
		} while( !field.CanMove(my, mx) );
		first_move = false;
		return;
	}

	int y, x;
	for(y = 0; y < rows; y++) {
		for(x = 0; x < cols; x++)
		{
			if(!field.CanMove(y, x))
				continue;
			field.Move(y, x);
			int result = MinMax(field, score, MAX_SCORE, 1);
			field.UndoMove(y, x);
			if(result > score) {
				score = result;
				my = y;
				mx = x;
			}
		}
	}
}

int AI::score(GameField field)
{
	int state = field.GetState();
	if(state == G_DRAW)
		return DRAW_SCORE;
	if(state == G_XPLAYER)
		return player == G_XPLAYER ? WIN_SCORE : LOSE_SCORE;
	if(state == G_OPLAYER)
		return player == G_OPLAYER ? WIN_SCORE : LOSE_SCORE;
	return NONE_SCORE;
}

//								MIN_SCORE, MAX_SCORE
int AI::MinMax(GameField field, int alpha, int beta, int depth)
{
	if(field.GetState() != G_NONE || depth >= max_depth) {
		return score(field);
	}

	int score = beta;
	int rows = field.GetRows();
	int cols = field.GetCols();

	int y, x;
	for(y = 0; y < rows; y++) {
		for(x = 0; x < cols; x++)
		{
			if(!field.CanMove(y, x))
				continue;
			field.Move(y, x);
			int result = MinMax(field, alpha, score, depth + 1);
			field.UndoMove(y, x);
			if(result < score)
				score = result;
			if(alpha >= score)
				return score;
		}
	}
	return score;
}