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#include "bot.hpp"
#include "board.hpp"
#include "moves.hpp"
#include <algorithm>
#include <cassert>
#include <cmath>
#include <iostream>
int PAWN_VALUE = 100;
int KNIGHT_VALUE = 200;
int BISHOP_VALUE = 300;
int ROOK_VALUE = 400;
int QUEEN_VALUE = 900;
int MATE = 10000;
const int SEARCH_DEPTH = 3;
int positions_consider = 0;
Move EngineGetBestMove(Game *b) {
auto moves = GetLegalMoves(b);
if (moves.size() == 0) {
assert(false && "Unhanled error zero legal moves for bot");
}
Move bestMove = moves[0];
float BestEval = (b->turn ? -INFINITY : INFINITY);
for (Move move : moves) {
Game TestBoard = *b;
PlayMove(move, &TestBoard);
float alpha = -INFINITY;
float beta = INFINITY;
float eval = minimax(SEARCH_DEPTH - 1, &TestBoard, alpha, beta);
if (b->turn) {
if (eval > BestEval) {
BestEval = eval;
bestMove = move;
}
} else {
if (eval < BestEval) {
BestEval = eval;
bestMove = move;
}
}
}
std::cout << "\nConsider: " << positions_consider << "\n";
return bestMove;
}
float minimax(int depth, Game *b, float alpha, float beta) {
if (depth == 0) {
return EvaluateBoardForWhite(b);
}
auto moves = GetLegalMoves(b);
if (moves.size() == 0) {
return EvaluateBoardForWhite(b);
}
if (b->turn) {
float bestEval = -INFINITY;
for (Move move : moves) {
Game next = *b;
PlayMove(move, &next);
float eval = minimax(depth - 1, &next, alpha, beta);
bestEval = std::max(bestEval, eval);
alpha = std::max(alpha, bestEval);
if (alpha >= beta) {
break;
}
}
return bestEval;
} else {
float BestEval = INFINITY;
for (Move move : moves) {
Game next = *b;
PlayMove(move, &next);
float eval = minimax(depth - 1, &next, alpha, beta);
BestEval = std::min(BestEval, eval);
beta = std::min(beta, BestEval);
if (alpha >= beta) {
break; // *snips*
}
}
return BestEval;
}
}
float EvaluateBoardForWhite(Game *b) {
positions_consider++;
float score = 0;
bool isStaleMate = false;
GetLegalMoves(b);
if (b->state == WHITE_WON) {
return MATE;
}
if (b->state == BLACK_WON) {
return -MATE;
}
if (b->state == STALEMATE || b->state == DRAW) {
isStaleMate = true;
}
for (Piece piece : b->pieces) {
if (piece.type == NONE)
continue;
int value = 0;
switch (piece.type) {
case PAWN:
value = PAWN_VALUE;
break;
case KNIGHT:
value = KNIGHT_VALUE;
break;
case BISHOP:
value = BISHOP_VALUE;
break;
case ROOK:
value = ROOK_VALUE;
break;
case QUEEN:
value = QUEEN_VALUE;
break;
default:
break;
}
if (piece.color)
score += value;
else
score -= value;
}
if (isStaleMate) {
return 0;
}
return score;
}
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