public struct Square: Equatable {

	public struct Position: Equatable {
		public let rank: Int8
		public let file: Int8

		public var index: Int? {
			guard (rank > 0 && rank < 9) && (file > 0 && file < 9) else {
				return nil
			}
			return Int(8*(8-rank)+file-1)
		}

		public static func == (lhs: Position, rhs: Position) -> Bool {
			return lhs.index == rhs.index
		}

		public static func + (lhs: Position, rhs: Position) -> Position {
			.init(rank: lhs.rank + rhs.rank, file: lhs.file + rhs.file)
		}

		public static func + (lhs: Position, rhs: (Int8, Int8)) -> Position {
			.init(rank: lhs.rank + rhs.0, file: lhs.file + rhs.1)
		}

		public static func += (lhs: inout Position, rhs: Position) {
			lhs = lhs + rhs
		}

		public static func += (lhs: inout Position, rhs: (Int8, Int8)) {
			lhs = lhs + rhs
		}
	}

	public let position: Position
	public let index: Int
	var piece: Piece? = nil
	public let color: Color

	public static func == (lhs: Square, rhs: Square) -> Bool {
		return lhs.position == rhs.position
	}
}