public enum Kind: String, CaseIterable {
	case Pawn, Knight, Bishop, Rook, Queen, King

	public var value: Int8 {
		switch self {
		case .Pawn: 1
		case .Bishop: 3
		case .Knight: 3
		case .Rook: 5
		case .Queen: 9
		case .King: -1
		}
	}

	public static subscript(_ c: Character) -> (Self, Color)? {
		let v = c.uppercased()

		guard
			v == "N"
				|| (Self.allCases.contains { String($0.rawValue.first!) == v })
		else {
			return nil
		}

		let kind: Self =
			switch v {
			case "P": .Pawn
			case "N": .Knight
			case "B": .Bishop
			case "R": .Rook
			case "Q": .Queen
			case "K": .King
			default: .Pawn
			}

		let color: Color = c.isUppercase ? .White : .Black

		return (kind, color)
	}
}

public protocol Piece {
	var board: Board? { get }
	var color: Color { get }
	var unicodeRepresentation: String { get }
	var kind: Kind { get }
	var position: Square.Position { get }
	var pseudoLegalPositions: [Square.Position] { get }
	var legalPositions: [Square.Position] { get }
	func move(dst: Square.Position) -> Bool
	func isLegal(pos: Square.Position) -> Bool
}