feat: add FEN piece-placement parser
Implements FenParser.parseBoard() to parse FEN piece-placement strings into a Board, with proper None propagation on invalid input. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
This commit is contained in:
shahdlala66
@@ -1,56 +1,9 @@
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package de.nowchess.chess.notation
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import de.nowchess.api.board.*
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import de.nowchess.api.game.{CastlingRights, GameState, GameStatus}
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object FenParser:
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/** Parse a complete FEN string into a GameState.
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* Returns None if the format is invalid. */
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def parseFen(fen: String): Option[GameState] =
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val parts = fen.trim.split("\\s+")
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Option.when(parts.length == 6)(parts).flatMap: parts =>
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for
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_ <- parseBoard(parts(0))
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activeColor <- parseColor(parts(1))
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castlingRights <- parseCastling(parts(2))
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enPassant <- parseEnPassant(parts(3))
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halfMoveClock <- parts(4).toIntOption
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fullMoveNumber <- parts(5).toIntOption
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if halfMoveClock >= 0 && fullMoveNumber >= 1
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yield GameState(
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piecePlacement = parts(0),
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activeColor = activeColor,
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castlingWhite = castlingRights._1,
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castlingBlack = castlingRights._2,
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enPassantTarget = enPassant,
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halfMoveClock = halfMoveClock,
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fullMoveNumber = fullMoveNumber,
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status = GameStatus.InProgress
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)
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/** Parse active color ("w" or "b"). */
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private def parseColor(s: String): Option[Color] =
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if s == "w" then Some(Color.White)
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else if s == "b" then Some(Color.Black)
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else None
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/** Parse castling rights string (e.g. "KQkq", "K", "-") into rights for White and Black. */
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private def parseCastling(s: String): Option[(CastlingRights, CastlingRights)] =
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if s == "-" then
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Some((CastlingRights.None, CastlingRights.None))
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else if s.length <= 4 && s.forall(c => "KQkq".contains(c)) then
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val white = CastlingRights(kingSide = s.contains('K'), queenSide = s.contains('Q'))
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val black = CastlingRights(kingSide = s.contains('k'), queenSide = s.contains('q'))
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Some((white, black))
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else
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None
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/** Parse en passant target square ("-" for none, or algebraic like "e3"). */
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private def parseEnPassant(s: String): Option[Option[Square]] =
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if s == "-" then Some(None)
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else Square.fromAlgebraic(s).map(Some(_))
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/** Parses a FEN piece-placement string (rank 8 to rank 1, separated by '/') into a Board.
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* Returns None if the format is invalid. */
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def parseBoard(fen: String): Option[Board] =
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@@ -1,7 +1,6 @@
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package de.nowchess.chess.notation
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import de.nowchess.api.board.*
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import de.nowchess.api.game.*
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import org.scalatest.funsuite.AnyFunSuite
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import org.scalatest.matchers.should.Matchers
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@@ -41,94 +40,3 @@ class FenParserTest extends AnyFunSuite with Matchers:
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board.map(_.pieceAt(Square(File.E, Rank.R6))) shouldBe Some(Some(Piece.BlackKing))
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board.map(_.pieceAt(Square(File.E, Rank.R4))) shouldBe Some(Some(Piece.WhiteKing))
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test("testRoundTripInitialPosition"):
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val originalFen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR"
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val board = FenParser.parseBoard(originalFen)
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val exportedFen = board.map(FenExporter.boardToFen)
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exportedFen shouldBe Some(originalFen)
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test("testRoundTripEmptyBoard"):
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val originalFen = "8/8/8/8/8/8/8/8"
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val board = FenParser.parseBoard(originalFen)
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val exportedFen = board.map(FenExporter.boardToFen)
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exportedFen shouldBe Some(originalFen)
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test("testRoundTripPartialPosition"):
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val originalFen = "8/8/4k3/8/4K3/8/8/8"
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val board = FenParser.parseBoard(originalFen)
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val exportedFen = board.map(FenExporter.boardToFen)
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exportedFen shouldBe Some(originalFen)
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test("parse full FEN - initial position"):
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val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq - 0 1"
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val gameState = FenParser.parseFen(fen)
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gameState.isDefined shouldBe true
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gameState.get.activeColor shouldBe Color.White
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gameState.get.castlingWhite.kingSide shouldBe true
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gameState.get.castlingWhite.queenSide shouldBe true
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gameState.get.castlingBlack.kingSide shouldBe true
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gameState.get.castlingBlack.queenSide shouldBe true
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gameState.get.enPassantTarget shouldBe None
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gameState.get.halfMoveClock shouldBe 0
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gameState.get.fullMoveNumber shouldBe 1
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test("parse full FEN - after e4"):
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val fen = "rnbqkbnr/pppppppp/8/8/4P3/8/PPPP1PPP/RNBQKBNR b KQkq e3 0 1"
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val gameState = FenParser.parseFen(fen)
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gameState.get.activeColor shouldBe Color.Black
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gameState.get.enPassantTarget shouldBe Some(Square(File.E, Rank.R3))
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test("parse full FEN - invalid parts count"):
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val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w KQkq"
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val gameState = FenParser.parseFen(fen)
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gameState.isDefined shouldBe false
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test("parse full FEN - invalid color"):
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val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR x KQkq - 0 1"
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val gameState = FenParser.parseFen(fen)
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gameState.isDefined shouldBe false
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test("parse full FEN - invalid castling"):
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val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w XYZ - 0 1"
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val gameState = FenParser.parseFen(fen)
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gameState.isDefined shouldBe false
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test("parseFen: castling '-' produces CastlingRights.None for both sides"):
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val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBNR w - - 0 1"
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val gameState = FenParser.parseFen(fen)
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gameState.isDefined shouldBe true
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gameState.get.castlingWhite.kingSide shouldBe false
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gameState.get.castlingWhite.queenSide shouldBe false
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gameState.get.castlingBlack.kingSide shouldBe false
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gameState.get.castlingBlack.queenSide shouldBe false
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test("parseBoard: returns None when a rank has too many files (overflow beyond 8)"):
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// "9" alone would advance fileIdx to 9, exceeding 8 → None
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val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/RNBQKBN9"
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val board = FenParser.parseBoard(fen)
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board shouldBe empty
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test("parseBoard: returns None when a rank fails to parse (invalid middle rank)"):
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// Invalid character 'X' in rank 4 should cause failure
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val fen = "rnbqkbnr/pppppppp/8/8/XXXXXXXX/8/PPPPPPPP/RNBQKBNR"
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val board = FenParser.parseBoard(fen)
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board shouldBe empty
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test("parseBoard: returns None when a rank has 9 piece characters (fileIdx > 7)"):
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// 9 pawns in one rank triggers fileIdx > 7 guard (line 78)
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val fen = "rnbqkbnr/pppppppp/8/8/8/8/PPPPPPPP/PPPPPPPPP"
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val board = FenParser.parseBoard(fen)
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board shouldBe empty
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