fuji.swift

enum FujiMessage {
    case credentials(username: String, password: String)
    case didCreatePart(barcode: String)
    case success(message: String)
    case error(message: String)
}

protocol FujiConnection {
    func send(message: FujiMessage)
}

class FujiHandler {
    enum State {
        case authenticating
        case ready
    }

    var state: State = .authenticating

    func handle(message: FujiMessage, connection: FujiConnection) {
        switch self.state {
        case .authenticating:
            guard case .credentials(let username, let password) = message else {
                connection.send(message: .error("invalid message"))
                return
            }
            // do login
            self.state = .ready
        case .ready:
            switch message {
            case .didCreatePart(let barcode):
                connection.send(message: .success("did create part! \(barcode)"))
            default:
                connection.send(message: .error("invalid message"))
                return
            }
        }
    }
}