UploadServiceImpl.swift

    enum TestError: Swift.Error {
        case uploadFailed
    }
    class Album {
        let pages: [Page] = []
    }
    class Page {}
    class UploadServiceImpl {
        private(set) lazy var addAction = Action<Album, Void, TestError>(execute:self.addActionBlock)
        private lazy var pageAction = Action<Page, Void, TestError>(execute:self.pageActionBlock)
        private lazy var completeAction = Action<Album, Void, TestError>(execute:self.completeActionBlock)
        private func addActionBlock(input: Album) -> SignalProducer<Void, TestError> {
            return SignalProducer<Page, TestError>(input.pages)
                .flatMap(.concat) { pageAction.apply($0) }
                .flatMap(.latest) { completeAction.apply(input) }
        }
        private func pageActionBlock(input: Page) -> SignalProducer<Void, TestError> {
            return SignalProducer.empty
        }
        private func completeActionBlock(input: Album) -> SignalProducer<Void, TestError> {
            return SignalProducer.empty
        }
    }