HNStoriesFeed-Combine.swift

class HNStoriesFeed : ObservableObject{

    @Published var storyItems = [StoryItem]()
    var urlBase = "https://hacker-news.firebaseio.com/v0/topstories.json?print=pretty"

    var cancellable : Set<AnyCancellable> = Set()
        
    private var topStoryIds = [Int]() {
        didSet {
            fetchStoryById(ids: topStoryIds.prefix(10))
        }
    }

    init() {
        fetchTopStories()
    }

    func fetchStoryById<S>(ids: S) where S: Sequence, S.Element == Int{

        Publishers.MergeMany(ids.map{FetchItem(id: $0)})
        .collect()
        .receive(on: DispatchQueue.main)
        .sink(receiveCompletion: {
            if case let .failure(error) = $0 {
                print(error)
            }
        }, receiveValue: {
            self.storyItems = self.storyItems + $0
        })
        .store(in: &cancellable)
        
    }
    
    func fetchTopStories(){

        URLSession.shared.dataTaskPublisher(for: URL(string: "\(urlBase)")!)
        .map{$0.data}
        .decode(type: [Int].self, decoder: JSONDecoder())
        .sink(receiveCompletion: { completion in
          switch completion {
          case .failure(let error):
            print("Something went wrong: \(error)")
          case .finished:
            print("Received Completion")
          }
        }, receiveValue: { value in
            self.topStoryIds = value
        })
        .store(in: &cancellable)

    }
}