refactor(book): refactoring opening book code

5 files changed, 32 insertions, 37 deletions

diff --git a/src/book.cpp b/src/book.cpp
index e1cd127..abf9693 100644
--- a/src/book.cpp
+++ b/src/book.cpp
@@ -6,13 +6,12 @@
 #include <cstdlib>
 #include <fstream>
 #include <iostream>
+#include <optional>
 #include <random>
 #include <vector>
 
 #include "board/board.hpp"
 
-constexpr int BOOK_DEPTH = 16;
-
 struct BookEntry {
   uint64_t key;
   uint16_t move;
@@ -27,7 +26,7 @@ static std::mt19937 rng{std::random_device{}()};
 void InitBook(const std::string &path) {
   std::ifstream file(path, std::ios::binary);
   if (!file.is_open()) {
-    std::cerr << "info string Could not open book file: " << path << "\n";
+    std::cerr << "info string Failed to open: " << path << "\n";
     return;
   }
 
@@ -74,12 +73,9 @@ void InitBook(const std::string &path) {
                   ((l & 0x00FF0000U) >> 8) | ((l & 0xFF000000U) >> 24);
   }
 
-  std::cerr << "info string Book loaded: " << book.size() << " entries\n";
+  std::cerr << "info string " << path << ": " << book.size() << " entries\n";
 }
 
-// Convert Polyglot move to Mono internal move format.
-// Polyglot: bits 0-5=to, 6-11=from, 12-14=promo (0=N,1=B,2=R,3=Q)
-// Mono:     bits 0-1=promo (00=N,11=B,01=R,10=Q), 2-7=from, 8-13=to
 static uint16_t PolyglotToMono(uint16_t polyglotMove) {
   uint8_t to = polyglotMove & 63;
   uint8_t from = (polyglotMove >> 6) & 63;
@@ -106,9 +102,9 @@ static uint16_t PolyglotToMono(uint16_t polyglotMove) {
   return CreateMove(from, to, promotion);
 }
 
-uint16_t ProbeBook(uint64_t key) {
+std::optional<uint16_t> ProbeBook(uint64_t key) {
   if (book.empty()) {
-    return 0;
+    return {};
   }
 
   // Binary search for first matching entry
@@ -124,7 +120,7 @@ uint16_t ProbeBook(uint64_t key) {
   }
 
   if (matches.empty()) {
-    return 0;
+    return {};
   }
 
   // Weighted random selection
@@ -145,5 +141,3 @@ uint16_t ProbeBook(uint64_t key) {
 
   return PolyglotToMono(matches.back()->move);
 }
-
-int GetBookDepth() { return BOOK_DEPTH; }
diff --git a/src/book.hpp b/src/book.hpp
index 4382dc7..bc08782 100644
--- a/src/book.hpp
+++ b/src/book.hpp
@@ -1,7 +1,7 @@
 #pragma once
 #include <cstdint>
+#include <optional>
 #include <string>
 
 void InitBook(const std::string &path);
-uint16_t ProbeBook(uint64_t key);
-int GetBookDepth();
+std::optional<uint16_t> ProbeBook(uint64_t key);
\ No newline at end of file
diff --git a/src/bot.cpp b/src/bot.cpp
index 7b937bd..99f60aa 100644
--- a/src/bot.cpp
+++ b/src/bot.cpp
@@ -12,6 +12,7 @@
 #include <vector>
 
 #include "board/board.hpp"
+#include "book.hpp"
 #include "bot.hpp"
 #include "evaluate.hpp"
 #include "moves.hpp"
@@ -19,6 +20,7 @@
 
 constexpr int DEFAULT_TIME = 7;
 constexpr int Q_DEPTH_LIMIT = 4;
+constexpr int BOOK_DEPTH = 100;
 
 constexpr int MATE = 10000;
 
@@ -320,6 +322,15 @@ uint16_t GetBestMove(Game *b, int maxDepth, move_options options) {
   searchStopped = false;
   Nodes = 0;
 
+  uint64_t hash = GenerateZobristKey(b);
+
+  if (b->MoveClock <= BOOK_DEPTH) {
+    std::optional<uint16_t> bookMove = ProbeBook(hash);
+    if (bookMove.has_value()) {
+      return bookMove.value();
+    }
+  }
+
   // use depth INF if caller hasnt provided depth
   int actualDepth = maxDepth > 0 ? maxDepth : INF;
 
diff --git a/src/uci.cpp b/src/uci.cpp
index 23e8419..812a0cd 100644
--- a/src/uci.cpp
+++ b/src/uci.cpp
@@ -13,8 +13,8 @@
 
 #include "board/board.hpp"
 #include "board/fen.hpp"
-#include "bot.hpp"
 #include "book.hpp"
+#include "bot.hpp"
 #include "misc.hpp"
 #include "moves.hpp"
 #include "uci.hpp"
@@ -224,24 +224,13 @@ static void GoCommand(Game *game, std::string &cmd) {
     exit(1);
   }
 
-  // Try opening book first
-  uint16_t bookMove = 0;
-  if (game->MoveClock < GetBookDepth()) {
-    bookMove = ProbeBook(GenerateZobristKey(game));
-  }
-
-  uint16_t best;
-  if (bookMove != 0) {
-    best = bookMove;
-  } else {
-    move_options options = {
-        .wtime = wtime,
-        .btime = btime,
-        .wncr = wncr,
-        .bncr = bncr,
-    };
-    best = GetBestMove(game, depth, options);
-  }
+  move_options options = {
+      .wtime = wtime,
+      .btime = btime,
+      .wncr = wncr,
+      .bncr = bncr,
+  };
+  uint16_t best = GetBestMove(game, depth, options);
 
   Piece piece = game->pieces[getFromValueFromMove(best)];
 
diff --git a/src/zobrist.cpp b/src/zobrist.cpp
index 5250687..c06f1a2 100644
--- a/src/zobrist.cpp
+++ b/src/zobrist.cpp
@@ -312,9 +312,10 @@ static bool IsEnpassantLegal(Game *g) {
 // PolyglotRandom64 layout (standard Polyglot spec):
 //   [0..767]   piece keys, kind = (pieceType-1)*2 + color:
 //              [0-63] black pawn, [64-127] white pawn, [128-191] black knight,
-//              [192-255] white knight, [256-319] black bishop, [320-383] white bishop,
-//              [384-447] black rook, [448-511] white rook, [512-575] black queen,
-//              [576-639] white queen, [640-703] black king, [704-767] white king
+//              [192-255] white knight, [256-319] black bishop, [320-383] white
+//              bishop, [384-447] black rook, [448-511] white rook, [512-575]
+//              black queen, [576-639] white queen, [640-703] black king,
+//              [704-767] white king
 //   [768]      white kingside castling
 //   [769]      white queenside castling
 //   [770]      black kingside castling
@@ -326,7 +327,7 @@ void InitZobrist() {
 
   // Piece keys: interleaved by kind = (pieceType-1)*2 + color
   for (int kind = 0; kind < 12; ++kind) {
-    int color = kind % 2;          // 0=black, 1=white
+    int color = kind % 2;           // 0=black, 1=white
     int pieceType = (kind / 2) + 1; // PAWN=1..KING=6
     for (int square = 0; square < 64; ++square) {
       PieceKeys[color][pieceType][square] = PolyglotRandom64[idx++];