From 81b24d30828db06c058452798bc4ed9090f9c625 Mon Sep 17 00:00:00 2001
From: Karma Riuk <riukkarma@gmail.com>
Date: Sun, 2 Feb 2025 21:39:33 +0100
Subject: [PATCH] extended FEN support to include who's turn it is

---
 cpp/src/board.cpp | 15 +++++++++++++--
 cpp/tests/fen.cpp | 24 ++++++++++++------------
 2 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/cpp/src/board.cpp b/cpp/src/board.cpp
index 439b72e..1331409 100644
--- a/cpp/src/board.cpp
+++ b/cpp/src/board.cpp
@@ -19,6 +19,7 @@ Board Board::setup_fen_position(std::string fen) {
         {'q', Piece::Queen},
     };
 
+    // -- Pieces
     std::string fen_board = fen.substr(0, fen.find(' '));
     int rank = 7, file = 0;
     for (char symbol : fen_board) {
@@ -39,6 +40,11 @@ Board Board::setup_fen_position(std::string fen) {
             file++;
         }
     }
+
+    // -- Active colour
+    int index = fen.find(' ');
+    index++;
+    board.white_to_play = fen[index] == 'w';
     return board;
 }
 
@@ -53,15 +59,16 @@ std::string Board::to_fen() const {
     };
 
     std::string ret;
+    // -- Pieces
     for (int rank = 7; rank >= 0; rank--) {
         int empty_cell_counter = 0;
         for (int file = 0; file < 8; file++) {
-            if (this->squares[rank * 8 + file] == Piece::None) {
+            if (squares[rank * 8 + file] == Piece::None) {
                 empty_cell_counter++;
                 continue;
             }
 
-            int full_piece = this->squares[rank * 8 + file];
+            int full_piece = squares[rank * 8 + file];
             char piece = p2c[full_piece & 0b111];
             int8_t colour = colour_at({file, rank});
 
@@ -76,6 +83,10 @@ std::string Board::to_fen() const {
         if (rank > 0)
             ret += "/";
     }
+    ret += " ";
+
+    // -- Active colour
+    ret += white_to_play ? 'w' : 'b';
     return ret;
 }
 
diff --git a/cpp/tests/fen.cpp b/cpp/tests/fen.cpp
index e2f6675..9a5030f 100644
--- a/cpp/tests/fen.cpp
+++ b/cpp/tests/fen.cpp
@@ -2,21 +2,21 @@
 #include "lib.hpp"
 
 int main() {
-    std::string pos = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR";
-    ASSERT_EQUALS(pos, Board::setup_fen_position(pos)->to_fen());
+    std::string pos = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w";
+    ASSERT_EQUALS(pos, Board::setup_fen_position(pos).to_fen());
 
-    pos = "r1bk3r/p2pBpNp/n4n2/1p1NP2P/6P1/3P4/P1P1K3/q5b1";
-    ASSERT_EQUALS(pos, Board::setup_fen_position(pos)->to_fen());
+    pos = "r1bk3r/p2pBpNp/n4n2/1p1NP2P/6P1/3P4/P1P1K3/q5b1 b";
+    ASSERT_EQUALS(pos, Board::setup_fen_position(pos).to_fen());
 
-    pos = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR";
-    ASSERT_EQUALS(pos, Board::setup_fen_position(pos)->to_fen());
+    pos = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b";
+    ASSERT_EQUALS(pos, Board::setup_fen_position(pos).to_fen());
 
-    pos = "4k2r/6r1/8/8/8/8/3R4/R3K3";
-    ASSERT_EQUALS(pos, Board::setup_fen_position(pos)->to_fen());
+    pos = "4k2r/6r1/8/8/8/8/3R4/R3K3 w";
+    ASSERT_EQUALS(pos, Board::setup_fen_position(pos).to_fen());
 
-    pos = "8/8/8/4p1K1/2k1P3/8/8/8";
-    ASSERT_EQUALS(pos, Board::setup_fen_position(pos)->to_fen());
+    pos = "8/8/8/4p1K1/2k1P3/8/8/8 b";
+    ASSERT_EQUALS(pos, Board::setup_fen_position(pos).to_fen());
 
-    pos = "8/5k2/3p4/1p1Pp2p/pP2Pp1P/P4P1K/8/8";
-    ASSERT_EQUALS(pos, Board::setup_fen_position(pos)->to_fen());
+    pos = "8/5k2/3p4/1p1Pp2p/pP2Pp1P/P4P1K/8/8 b";
+    ASSERT_EQUALS(pos, Board::setup_fen_position(pos).to_fen());
 }