ConnectionObserver.swift

import Network

protocol ConnectionAttribute: Equatable {
    init(path: NWPath)
}

class ConnectionObserver<T: ConnectionAttribute> {
    var handler: ((T) -> Void)?
    private var monitor: NWPathMonitor

    private(set) var attribute: T {
        didSet {
            guard oldValue != attribute else { return }
            handler?(attribute)
        }
    }

    deinit {
        cancel()
    }

    init(monitor: NWPathMonitor = NWPathMonitor(),
         queue: DispatchQueue = .main,
         handler: ((T) -> Void)? = nil) {
        self.monitor = monitor
        self.attribute = T(path: monitor.currentPath)
        self.handler = handler
        self.monitor.start(queue: queue)
        self.monitor.pathUpdateHandler = { [weak self] path in
            self?.attribute = T(path: path)
        }
    }

    func cancel() {
        monitor.cancel()
    }
}

struct BasicConnectionAttribute: Equatable, ConnectionAttribute {
    let isExpensive: Bool
    let hasConnection: Bool

    init(path: NWPath) {
        isExpensive = path.isExpensive
        hasConnection = path.status == .satisfied
    }
}