Combine publishers to sequence result

publisher_sequence.swift

func fetchCoachingRoom(complete: @escaping (Error?) -> Void) {
    refreshCoachingRoomStatus = .working
    cancellableCoachingRoom?.cancel()
    cancellableCoachingRoom = apiService.stream(Api.getCoachingRoom())
        .map({ (res) -> [AClass] in
            return res.userClassList
        })
        .receive(on: DispatchQueue.main)
        .map { [weak self] list -> [Int] in
            self?.coachingRoomClasses = list
            return list.compactMap { $0._id }
        }
        .receive(on: DispatchQueue.global())
        .flatMap { (idList) -> AnyPublisher<[UserClassResponse], Error>  in
            let requests = idList.map { Webservice.shared.stream(Api.getUserClass(classId: $0)) }
            let publisherOfPublishers = Publishers.Sequence<[AnyPublisher<UserClassResponse, Error>], Error>(sequence: requests)
            HLog.d("getCoachingRoom--1")
            return publisherOfPublishers.flatMap { $0 }.collect().eraseToAnyPublisher()
        }
        .subscribe(on: DispatchQueue.global())
        .receive(on: DispatchQueue.main)
        .sink(receiveCompletion: { [weak self] (completion) in
            HLog.d("getCoachingRoom--2")
            switch completion {
                case .failure(let error):
                    self?.refreshCoachingRoomStatus = .notYet
                    complete(error)
                case .finished:
                    self?.refreshCoachingRoomStatus = .done
                    complete(nil)
            }
        }, receiveValue: { [weak self] (classes) in
            self?.handleAllUserClassResponseList(list: classes)
        })
}