[Rx Network Loader] A network request performer with RxSwift

RxNetworkLoader.swift

// Source: https://gist.github.com/dtartaglia/6ebec424bc57d47ed133e9306b74b55f

struct LoadInput<T, U> {
    let trigger: Observable<T> /// will cause the network request to start passing the T to the request generator.
    let makeRequest: (T) -> URLRequest /// a function that knows how to create the URLRequest
    let download: (URLRequest) -> Observable<Data> /// the function that actually does the download. By default, it uses URLSession.shared
    let makeObject: (Data) -> U /// a function that knows how to convert the data into the needed resource.
}

extension LoadInput {
    init(trigger: Observable<T>, makeRequest: @escaping (T) -> URLRequest, makeObject: @escaping (Data) -> U) {
        self.trigger = trigger
        self.makeRequest = makeRequest
        self.download = URLSession.shared.rx.data(request:)
        self.makeObject = makeObject
    }
}

struct NetworkLoader<T, U> {
    let item: Observable<U>
    let error: Observable<Error>
    let refreshing: Observable<Bool>

    init(input: LoadInput<T, U>) {
        let trigger = input.trigger

        let networkData = input.trigger
            .map(input.makeRequest)
            .flatMap { input.download($0).materialize() }
            .share(replay: 1, scope: .whileConnected)

        item = networkData
            .map { $0.element }
            .filter { $0 != nil }
            .map { $0! }
            .map(input.makeObject)

        error = networkData
            .map { $0.error }
            .filter { $0 != nil }
            .map { $0! }

        // The delay is necessary because calling `endRefreshing()` on a
        // UIRefreshControl too quickly after beginning the refresh
        // will cause it to not work.
        refreshing = Observable.merge([
            trigger.map { _ in true },
            networkData.delay(0.125, scheduler: MainScheduler.instance)
                .map { _ in false }
        ])
    }
}