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#include "bot.hpp"
#include "board.hpp"
#include "moves.hpp"
#include "zobrist.hpp"
#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstdint>
#include <cstdlib>
#include <iostream>
#include <vector>
const int SEARCH_DEPTH = 5;
const int PAWN_VALUE = 100;
const int KNIGHT_VALUE = 320;
const int BISHOP_VALUE = 330;
const int ROOK_VALUE = 500;
const int QUEEN_VALUE = 900;
const int CHECK = 10;
const int MATE = 10000;
const int PAWN_TABLE[64] = {
0, 0, 0, 0, 0, 0, 0, 0, // last rank promotes to a quuen
50, 50, 50, 50, 50, 50, 50, 50, // comments to stop formating to ruin it
10, 10, 20, 30, 30, 20, 10, 10, //
5, 5, 10, 25, 25, 10, 5, 5, //
0, 0, 0, 20, 20, 0, 0, 0, //
5, -5, -10, 0, 0, -10, -5, 5, //
5, 10, 10, -20, -20, 10, 10, 5, //
0, 0, 0, 0, 0, 0, 0, 0 //
};
int KNIGHT_TABLE[64] = {
-50, -40, -30, -30, -30, -30, -40, -50, //
-40, -20, 0, 0, 0, 0, -20, -40, //
-30, 0, 10, 15, 15, 10, 0, -30, //
-30, 5, 15, 20, 20, 15, 5, -30, //
-30, 0, 15, 20, 20, 15, 0, -30, //
-30, 5, 10, 15, 15, 10, 5, -30, //
-40, -20, 0, 5, 5, 0, -20, -40, //
-50, -40, -30, -30, -30, -30, -40, -50, //
};
int BISHOP_TABLE[64] = {
-20, -10, -10, -10, -10, -10, -10, -20, //
-10, 5, 0, 0, 0, 0, 5, -10, //
-10, 10, 10, 10, 10, 10, 10, -10, //
-10, 0, 10, 15, 15, 10, 0, -10, //
-10, 5, 5, 10, 10, 5, 5, -10, //
-10, 0, 5, 10, 10, 5, 0, -10, //
-10, 0, 0, 0, 0, 0, 0, -10, //
-20, -10, -10, -10, -10, -10, -10, -20, //
};
int ROOK_TABLE[64] = {
0, 0, 5, 10, 10, 5, 0, 0, //
5, 10, 10, 10, 10, 10, 10, 5, //
-5, 0, 0, 0, 0, 0, 0, -5, //
-5, 0, 0, 5, 5, 0, 0, -5, //
-5, 0, 0, 5, 5, 0, 0, -5, //
-5, 0, 0, 0, 0, 0, 0, -5, //
5, 10, 10, 10, 10, 10, 10, 5, //
0, 0, 5, 10, 10, 5, 0, 0, //
};
int ScoreMove(const Game *board, const Move &move) {
int score = 0;
Piece moving = board->pieces[PositionToIndex(move.From)];
Piece captured = board->pieces[PositionToIndex(move.To)];
// Captures (MVV-LVA)
if (captured.type != NONEPIECE) {
static const int pieceValue[] = {
0, // NONE
20000, // KING (should never happen)
900, // QUEEN
500, // ROOK
330, // BISHOP
320, // KNIGHT
100 // PAWN
};
score += 10000;
score += pieceValue[captured.type] * 10;
score -= pieceValue[moving.type];
}
// Promotions
if (move.promotion != NONEPIECE) {
score += 8000;
}
return score;
}
Move EngineGetBestMove(Game *b) {
auto moves = GetLegalMoves(b);
if (moves.size() == 0) {
std::cout << "Expected a position with legal moves";
assert(false && "Unhanled error zero legal moves for bot");
exit(1);
}
// sort legal moves
std::sort(moves.begin(), moves.end(), [&](const Move &a, const Move &c) {
return ScoreMove(b, a) > ScoreMove(b, c);
});
Move bestMove = moves[0];
float BestEval = (b->turn ? -INFINITY : INFINITY);
for (Move move : moves) {
UndoMove undo = MakeMove(move, b);
float alpha = -INFINITY;
float beta = INFINITY;
float eval = minimax(SEARCH_DEPTH - 1, b, alpha, beta);
UnMakeMove(undo, b);
if (b->turn) {
if (eval > BestEval) {
BestEval = eval;
bestMove = move;
}
} else {
if (eval < BestEval) {
BestEval = eval;
bestMove = move;
}
}
}
return bestMove;
}
float minimax(int depth, Game *b, float alpha, float beta) {
uint64_t gameHash = GenerateZobristKey(b);
if (b->Transpositions->contains(gameHash)) {
TranspositionsEntry data = b->Transpositions->at(gameHash);
if (data.depth >= depth) {
return data.Eval;
}
}
auto moves = GetLegalMoves(b);
if (depth == 0 || moves.size() == 0) {
return EvaluateBoardForWhite(b, depth);
}
float bestEval = b->turn ? -INFINITY : INFINITY;
if (b->turn) {
for (Move move : moves) {
UndoMove undo = MakeMove(move, b);
float eval = minimax(depth - 1, b, alpha, beta);
UnMakeMove(undo, b);
bestEval = std::max(bestEval, eval);
alpha = std::max(alpha, bestEval);
if (alpha >= beta) {
break;
}
}
} else {
for (Move move : moves) {
UndoMove undo = MakeMove(move, b);
float eval = minimax(depth - 1, b, alpha, beta);
UnMakeMove(undo, b);
bestEval = std::min(bestEval, eval);
beta = std::min(beta, bestEval);
if (alpha >= beta) {
break; // *snips*
}
}
}
b->Transpositions->operator[](gameHash) = {depth, bestEval};
return bestEval;
}
int PSTIndex(int square, bool white) { return white ? square : (56 ^ square); }
float EvaluateBoardForWhite(Game *b, int depth) {
float score = 0;
bool isStaleMate = false;
if (b->state == WHITE_WON) {
return MATE + depth;
}
if (b->state == BLACK_WON) {
return -MATE - depth;
}
if (b->state == STALEMATE || b->state == DRAW) {
isStaleMate = true;
}
for (int i = 0; i < 64; i++) {
Piece piece = b->pieces[i];
if (piece.type == NONEPIECE)
continue;
int value = 0;
switch (piece.type) {
case PAWN:
value = PAWN_VALUE;
value += PAWN_TABLE[PSTIndex(i, piece.color)];
break;
case KNIGHT:
value = KNIGHT_VALUE;
value += KNIGHT_TABLE[PSTIndex(i, piece.color)];
break;
case BISHOP:
value = BISHOP_VALUE;
value += BISHOP_TABLE[PSTIndex(i, piece.color)];
break;
case ROOK:
value = ROOK_VALUE;
value += ROOK_TABLE[PSTIndex(i, piece.color)];
break;
case QUEEN:
value = QUEEN_VALUE;
break;
default:
break;
}
if (piece.color)
score += value;
else
score -= value;
}
if (IsPieceTypeAttacked(b, KING, true))
score -= CHECK; // white king attacked
if (IsPieceTypeAttacked(b, KING, false))
score += CHECK; // black king attacked
if (isStaleMate) {
return 0;
}
return score;
}
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