src/dev/kske/chess/board/FENString.java

@@ -0,0 +1,194 @@
+package dev.kske.chess.board;
+
+import java.util.LinkedHashMap;
+import java.util.Map;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import dev.kske.chess.board.Piece.Color;
+import dev.kske.chess.exception.ChessException;
+
+/**
+ * Project: <strong>Chess</strong><br>
+ * File: <strong>FENString.java</strong><br>
+ * Created: <strong>20 Oct 2019</strong><br>
+ * <br>
+ * Represents a FEN string and enables parsing an existing FEN string or
+ * serializing a {@link Board} to one.
+ * 
+ * @author Kai S. K. Engelbart
+ * @since Chess v0.4-alpha
+ */
+public class FENString {
+
+	private Board					board;
+	private Map<FENField, String>	fields	= new LinkedHashMap<>();
+
+	public static enum FENField {
+		PIECE_PLACEMENT, ACTIVE_COLOR, CASTLING_AVAILABILITY, EN_PASSANT_TARGET_SQUARE, HALFMOVE_CLOCK, FULLMOVE_NUMBER
+	}
+
+	/**
+	 * Constructs a {@link FENString} representing the starting position
+	 * {@code rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1}.
+	 */
+	public FENString() {
+		board = new Board();
+		fields.put(FENField.PIECE_PLACEMENT, "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR");
+		fields.put(FENField.ACTIVE_COLOR, "w");
+		fields.put(FENField.CASTLING_AVAILABILITY, "KQkq");
+		fields.put(FENField.EN_PASSANT_TARGET_SQUARE, "-");
+		fields.put(FENField.HALFMOVE_CLOCK, "0");
+		fields.put(FENField.FULLMOVE_NUMBER, "1");
+	}
+
+	/**
+	 * Constructs a {@link FENString} by parsing an existing string.
+	 * 
+	 * @param fen the FEN string to parse
+	 * @throws ChessException
+	 */
+	public FENString(String fen) throws ChessException {
+		// Check fen string against regex
+		Pattern	fenPattern	= Pattern.compile(
+				"^(?<PIECE_PLACEMENT>(?:[1-8nbrqkpNBRQKP]{1,8}\\/){7}[1-8nbrqkpNBRQKP]{1,8}) (?<ACTIVE_COLOR>[wb]) (?<CASTLING_AVAILABILITY>-|[KQkq]{1,4}) (?<EN_PASSANT_TARGET_SQUARE>-|[a-h][1-8]) (?<HALFMOVE_CLOCK>\\d) (?<FULLMOVE_NUMBER>\\d)$");
+		Matcher	matcher		= fenPattern.matcher(fen);
+		if (!matcher.find()) throw new ChessException("FEN string does not match pattern " + fenPattern.pattern());
+		for (FENField field : FENField.values())
+			fields.put(field, matcher.group(field.toString()));
+
+		// Initialize and clean board
+		board = new Board();
+		for (int i = 0; i < 8; i++)
+			for (int j = 0; j < 8; j++)
+				board.getBoardArr()[i][j] = null;
+
+		// Parse individual fields
+
+		// Piece placement
+		final String[] rows = fields.get(FENField.PIECE_PLACEMENT).split("/");
+		if (rows.length != 8) throw new ChessException("FEN string contains invalid piece placement");
+		for (int i = 0; i < 8; i++) {
+			final char[]	cols	= rows[i].toCharArray();
+			int				j		= 0;
+			for (char c : cols) {
+
+				// Empty space
+				if (Character.isDigit(c)) {
+					j += Character.getNumericValue(c);
+				} else {
+					Color color = Character.isUpperCase(c) ? Color.WHITE : Color.BLACK;
+					switch (Character.toUpperCase(c)) {
+						case 'K':
+							board.getBoardArr()[i][j] = new King(color, board);
+							break;
+						case 'Q':
+							board.getBoardArr()[i][j] = new Queen(color, board);
+							break;
+						case 'R':
+							board.getBoardArr()[i][j] = new Rook(color, board);
+							break;
+						case 'N':
+							board.getBoardArr()[i][j] = new Knight(color, board);
+							break;
+						case 'B':
+							board.getBoardArr()[i][j] = new Bishop(color, board);
+							break;
+						case 'P':
+							board.getBoardArr()[i][j] = new Pawn(color, board);
+							break;
+					}
+					++j;
+				}
+			}
+		}
+
+		// Active color
+		board.getLog().setActiveColor(Color.fromFirstChar(fields.get(FENField.ACTIVE_COLOR).charAt(0)));
+
+		// TODO: Castling availability
+
+		// En passant square
+		if (!fields.get(FENField.EN_PASSANT_TARGET_SQUARE).equals("-"))
+			board.getLog().setEnPassant(Position.fromLAN(fields.get(FENField.EN_PASSANT_TARGET_SQUARE)));
+
+		// Halfmove clock
+		board.getLog().setHalfmoveClock(Integer.parseInt(fields.get(FENField.HALFMOVE_CLOCK)));
+
+		// Fullmove number
+		board.getLog().setFullmoveNumber(Integer.parseInt(fields.get(FENField.FULLMOVE_NUMBER)));
+	}
+
+	/**
+	 * Constructs a {@link FENString} form a {@link Board} object.
+	 * 
+	 * @param board the {@link Board} object to encode in this {@link FENString}
+	 */
+	public FENString(Board board) {
+		this.board = board;
+
+		// Serialize individual fields
+
+		// Piece placement
+		StringBuilder sb = new StringBuilder();
+		for (int i = 0; i < 8; i++) {
+			int empty = 0;
+			for (int j = 0; j < 8; j++) {
+				final Piece piece = board.getBoardArr()[i][j];
+
+				if (piece == null) ++empty;
+				else {
+
+					// Write empty field count
+					if (empty > 0) {
+						sb.append(empty);
+						empty = 0;
+					}
+
+					// Write piece character
+					char p = piece.getType().firstChar();
+					sb.append(piece.getColor() == Color.WHITE ? Character.toUpperCase(p) : p);
+				}
+			}
+
+			// Write empty field count
+			if (empty > 0) {
+				sb.append(empty);
+				empty = 0;
+			}
+
+			if (i < 7) sb.append('/');
+		}
+		fields.put(FENField.PIECE_PLACEMENT, sb.toString());
+
+		// Active color
+		fields.put(FENField.ACTIVE_COLOR, String.valueOf(board.getLog().getActiveColor().firstChar()));
+
+		// TODO: Castling availability
+
+		// En passant availability
+		final Position enPassantPosition = board.getLog().getEnPassant();
+		fields.put(FENField.EN_PASSANT_TARGET_SQUARE, enPassantPosition == null ? "-" : enPassantPosition.toLAN());
+
+		// Halfmove clock
+		fields.put(FENField.HALFMOVE_CLOCK, String.valueOf(board.getLog().getHalfmoveClock()));
+
+		// Fullmove counter
+		fields.put(FENField.FULLMOVE_NUMBER, String.valueOf(board.getLog().getFullmoveNumber()));
+	}
+
+	/**
+	 * Exports this {@link FENString} object to a FEN string.
+	 * 
+	 * @return a FEN string representing the board
+	 */
+	@Override
+	public String toString() {
+		return String.join(" ", fields.values());
+	}
+
+	/**
+	 * @return a {@link Board} object corresponding to this {@link FENString}
+	 */
+	public Board getBoard() { return board; }
+}