Board(Grid) -> FEN

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
 	}
-}
+}