Board(Grid) -> FEN

Sources/Engine/Board.swift

@@ -33,7 +33,7 @@ public class Board: CustomStringConvertible, EventDelegate {
 	}
 
 	private var squares = [Square]()
-	private var board: Grid {
+	internal var board: Grid {
 		var board = Grid()
 		var rank = -1
 		for i in 0...63 {
@@ -46,7 +46,7 @@ public class Board: CustomStringConvertible, EventDelegate {
 		return board
 	}
 
-	public private(set) var fen: Fen
+	public internal(set) var fen: Fen
 
 	public func setBoard() throws {
 		var file: Int8 = 1

Sources/Engine/FEN.swift

@@ -14,7 +14,7 @@ public struct Fen: CustomStringConvertible {
 		case All = "KQkq"
 	}
 	private var _fen: String = ""
-	private var value: String {
+	public private(set) var value: String {
 		get {
 			return _fen
 		}
@@ -63,14 +63,49 @@ public struct Fen: CustomStringConvertible {
 		self.value = value
 	}
 
+	internal mutating func set(
+		from board: Board.Grid, castiling ca: CastlingAvailibility,
+		enPassant: String
+	) {
+		#warning(
+			"Determine active color, halfMoveClock, fullMoveClock based on history SAN later passed in arguments"
+		)
+		var placement = ""
+		var rankNr = 0
+		for rank in board {
+			var count = 0
+			for i in 0..<rank.count {
+				let file = rank[i]
+				if let piece = file.piece {
+					if count > 0 {
+						placement += String(count)
+						count = 0
+					}
+					placement += piece.kind.fenRepresentation(with: piece.color)
+				} else {
+					count += 1
+				}
+			}
+			if count > 0 {
+				placement += String(count)
+			}
+			if rankNr != rank.count - 1 {
+				placement += "/"
+			}
+			rankNr += 1
+		}
+
+		value = placement + " w " + ca.rawValue + " " + enPassant + " 0 " + "1"
+	}
+
 	public enum FenError: Error {
 		case InvalidCharacter(c: String, column: Int8)
 		case NumberTooBig(n: Int8, column: Int8)
 		case NumberTooSmall(n: Int8, column: Int8)
-        case NotAppropriateLength(n: Int8, column: Int8)
+		case NotAppropriateLength(n: Int8, column: Int8)
 	}
 
 	public var description: String {
 		return value
 	}
-}
+}

Sources/Engine/Pieces/Piece.swift

@@ -12,6 +12,20 @@ public enum Kind: String, CaseIterable {
 		}
 	}
 
+	func fenRepresentation(with color: Color) -> String {
+		let str =
+			switch self {
+			case .Pawn: "P"
+			case .Bishop: "B"
+			case .Knight: "N"
+			case .Rook: "R"
+			case .Queen: "Q"
+			case .King: "K"
+			}
+
+		return color == .White ? str : str.lowercased()
+	}
+
 	static subscript(_ c: Character) -> (Self, Color)? {
 		let v = c.uppercased()
 

Tests/EngineTests/EngineTests.swift

@@ -105,6 +105,16 @@ final class EngineTests: XCTestCase {
 		XCTAssertEqual(result, pb.pseudoLegalPositions)
 	}
 
+	func testSetFenFromBoard() throws {
+		let board: Board = .init()
+		let fen = board.fen.value
+		board.fen.set(
+			from: board.board, castiling: board.fen.castlingAvailibility,
+			enPassant: board.fen.enPassant)
+		XCTAssertEqual(
+			fen, board.fen.value, "Expected \(fen) got \(board.fen.value)")
+	}
+
 	// func testBoard() throws {
 	// 	let board = Board()
 	// }