public struct Fen: CustomStringConvertible {
	public enum CastlingAvailibility: String {
		case Neither = "-"
		case WhiteKingSide = "K"
		case WhiteQueenSide = "Q"
		case BlackKingSide = "k"
		case BlackQueenSide = "q"
		case WhiteSide = "KQ"
		case BlackSide = "kq"
		case Kings = "Kk"
		case Queens = "Qq"
		case WKingBQueen = "Kq"
		case WQueenBKing = "Qk"
		case All = "KQkq"
	}
	private var _fen: String = ""
	public private(set) var value: String {
		get {
			return _fen
		}
		set {
			_fen = newValue
			let splitted = _fen.split(separator: " ")
			guard splitted.count == 6 else {
				return
			}
			placement = String(splitted[0])
			activeColor =
				switch splitted[1] {
				case "w": .White
				case "b": .Black
				default: .White
				}
			castlingAvailibility =
				CastlingAvailibility(
					rawValue:
						String(splitted[2])) ?? .Neither
			enPassant = String(splitted[3])
			halfMoveClock =
				if let c = splitted[4].first, c.isWholeNumber {
					UInt8(String(c)) ?? 0
				} else {
					0
				}
			fullMoveClock =
				if let c = splitted[5].first, c.isWholeNumber {
					UInt8(String(c)) ?? 1
				} else {
					1
				}
		}
	}

	public private(set) var placement: String = ""  // 70 chars
	public private(set) var activeColor: Color = .White  // 1 char
	public private(set) var castlingAvailibility: CastlingAvailibility = .All
	// 1 to 4 chars
	public private(set) var enPassant: String = "-"  // 1 or 2 chars
	public private(set) var halfMoveClock: UInt8 = 0
	public package(set) var fullMoveClock: UInt8 = 1

	public init(fen value: String) {
		self.value = value
	}

	internal mutating func set(
		from board: Board.Grid, castling 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)
	}

	public var description: String {
		return value
	}
}