protocol PDFListViewModelInput {
  func storePDF(title: String, urlString: String) throws
  func deletePDF(at index: Int) throws
  func searchPDF(_ text: String)
}

protocol PDFListViewModelOutput {
  var pdfDatasPublisher: Published<[PDFData]>.Publisher { get }
  var searchPDFDatasPublisher: Published<[PDFData]>.Publisher { get }
}

typealias PDFListViewModel = PDFListViewModelInput & PDFListViewModelOutput

// MARK: - SearchResults Updating
extension PDFListViewController: UISearchResultsUpdating {
  func updateSearchResults(for searchController: UISearchController) {
    guard let text = searchController.searchBar.text?.lowercased() else {
      return
    }
    
    viewModel.searchPDF(text)
  }
}

// MARK: - Data Binding
extension PDFListViewController {
  // ...
  
  private func bindingSearchPDFData() {
    viewModel.searchPDFDatasPublisher.sink { pdfDatas in
      if !pdfDatas.isEmpty {
        self.loadCollectionView(pdfDatas)
      }
    }.store(in: &cancellables)
  }
}

final class PDFDetailViewController: UIViewController {
  
  // MARK: - Private Property
  private let pdfView: PDFView
    
  // MARK: - Configure UI Object
  private func configurePDFView(pdfDocument: PDFDocument?) {
    DispatchQueue.main.async {
      self.pdfView.document = pdfDocument
    }
  }
    
  // MARK: - Move PDF Page
  @objc private func tapNextButton() {
    pdfView.goToNextPage(nil)
  }
    
  // ...
}

final class RealmRepository: Repository {
  
  // MARK: - Static Property
  static let shared = RealmRepository()
  
  // MARK: - Private Property
  private var realm: Realm
    
  // ...
}

final class DefaultPDFListViewModel: PDFListViewModel {
  
  // MARK: - Private Property
  private let repository: Repository
  
  // ...
}