initFEN method

Implementation

void initFEN(String fen) {
  board = _emptyBoard;

  List<String> parts = fen.split(" ");
  List<String> rows = parts[0].split("/");

  // Determine turn from FEN.
  turn = (parts[1] == "w") ? PieceColor.white : PieceColor.black;

  // En-passant target square (if any).
  if (parts[3] != "-") {
    String targetSquare = parts[3];
    int col = targetSquare.codeUnitAt(0) - 'a'.codeUnitAt(0);
    int row = 8 - int.parse(targetSquare[1]);
    enPassantTarget = Position(row: row, col: col);
  } else {
    enPassantTarget = null;
  }

  halfMoveClock = int.tryParse(parts[4]) ?? 0; // Halfmove clock from FEN
  fullMoveNumber = int.tryParse(parts[5]) ?? 1; // Fullmove number from FEN

  // Here we assume the FEN rows correspond directly to board rows (0 to 7).
  for (int row = 0; row < 8; row++) {
    int col = 0;
    String fenRow = rows[row]; // no reversal
    for (int i = 0; i < fenRow.length; i++) {
      String charAt = fenRow[i];
      if (RegExp(r'[1-8]').hasMatch(charAt)) {
        col += int.parse(charAt);
      } else {
        board[row][col] = ChessBoardInterface.getPieceFromChar(charAt);
        col++;
      }
    }
  }
}