RxSwift parallel downloading demo

download_events_parallel.swift

  func startDownload() {
    let eoCategories = EONET.categories
    let downloadedEvents = eoCategories.flatMap { categories in
        return Observable.from(categories.map { category in
            EONET.events(forLast: 360, category: category)
        })
    }
    .merge(maxConcurrent: 2)
    let updatedCategories = eoCategories.flatMap { categories in
        downloadedEvents.scan(categories, accumulator: { (updated, events) in
            return updated.map { category in
                let eventForCategory = EONET.filteredEvents(events: events, forCategory: category)
                if !eventForCategory.isEmpty {
                    var cat = category
                    cat.events = cat.events + eventForCategory
                    return cat
                } else {
                    return category
                }
            }
        })
    }

    eoCategories
        .concat(updatedCategories)
        .bindTo(categories)
        .addDisposableTo(disposeBag)
  }