PDF collaboration using Swift for iOS

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//
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//  Copyright © 2017-2026 PSPDFKit GmbH. All rights reserved.
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//
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//  The Nutrient sample applications are licensed with a modified BSD license.
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//  Please see License for details. This notice may not be removed from this file.
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//
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import Instant
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import PSPDFKit
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import PSPDFKitUI
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/// This example connects to our public Nutrient Web SDK examples server and downloads documents using Nutrient Instant.
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/// You can then collaboratively annotate these documents using Instant.
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/// Each document on the Nutrient Web SDK examples server can be accessed via its URL.
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///
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/// The example lets you either create a new collaboration group then share the URL,
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/// or join an existing collaboration group by entering a URL.
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/// To speed this up, the URL can be read from a QR code.
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///
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/// Other supported clients include:
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///
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/// - Nutrient Web SDK examples: https://web-examples.our.services.nutrient-powered.io
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/// - PDF Viewer for iOS and Android: https://pdfviewer.io
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/// - Nutrient Catalog example app for Android
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///
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/// As is usually the case with Instant, most of the code here deals with communicating with the
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/// particular server backend (our Web examples server in this case), so is not particularly useful
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/// as example code. The same applies to the other files in this folder.
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///
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/// The code actually interacting with the Instant framework API is in `InstantDocumentViewController.swift`.
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class InstantExample: Example {
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    override init() {
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        super.init()
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        title = "Nutrient Instant"
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        contentDescription = "Downloads a document for collaborative editing."
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        category = .collaboration
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        targetDevice = [.vision, .phone, .pad]
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        priority = 1
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    }
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    weak var presentingViewController: UIViewController?
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController? {
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        let presentingViewController = delegate.currentViewController!
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        // We store the document info once the session is created.
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        // We will try to find the stored info matching the document identifier for this example if available.
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        if let docInfoDict = UserDefaults.standard.object(forKey: InstantExampleLastViewedDocumentInfoKey) as? [String: String],
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           let lastViewDocumentInfo = InstantDocumentInfo(from: docInfoDict) {
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            // Present the InstantViewController directly using the existing document info extracted from the cache.
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            presentInstantViewController(for: lastViewDocumentInfo, on: presentingViewController)
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        } else {
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            presentNewSession(on: presentingViewController)
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        }
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        // Hold a reference to the presentingViewController to handle authentication challenges.
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        self.presentingViewController = presentingViewController
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        return nil
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    }
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    /// Connects to the Example API Client to get the document info for the current example
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    /// and then displays that document in a `InstantViewController`.
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    func presentNewSession(on viewController: UIViewController) {
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        // Create a `WebExamplesAPIClient` instance using the URL of the client server
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        // that has the list of documents the particular user can access.
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        //
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        // `WebExamplesAPIClient` can make calls to the server to get the document info required
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        // to connect to a Nutrient Document Engine instance.
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        //
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        // For the purpose of this example we are using the Nutrient Web SDK Catalog server.
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        // In your app, this should be replaced by the URL of your that is interacting with your Nutrient Document Engine.
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        // See https://www.nutrient.io/guides/ios/instant-synchronization/ for more details.
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        let apiClient = WebExamplesAPIClient(baseURL: InstantWebExamplesServerURL, delegate: self)
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        let progressHUDItem = StatusHUDItem.indeterminateProgress(withText: "Creating")
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        progressHUDItem.setHUDStyle(.black)
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        progressHUDItem.push(animated: true, on: viewController.view.window) {
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            // Asking the Nutrient Web SDK Catalog example server to create a new session
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            // for the given user and the specified document identifier.
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            // It should ideally provide a signed JWT (and the Nutrient Document Engine if not already available)
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            // that can be used by the `InstantClient` to access and download the document for iOS.
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            apiClient.createNewSession(documentIdentifier: .demoDocument) { result in
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                DispatchQueue.main.async {
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                    progressHUDItem.pop(animated: true, completion: nil)
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                    switch result {
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                    case let .success(documentInfo):
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                        self.presentInstantViewController(for: documentInfo, on: viewController)
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                    case .failure(.cancelled):
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                        break // Do not show the alert if user cancelled the request themselves.
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                    case let .failure(otherError):
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                        viewController.showAlert(withTitle: "Couldn’t Get Instant Document Info", message: otherError.localizedDescription)
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                    }
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                }
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            }
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        }
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    }
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    private func presentInstantViewController(for instantDocumentInfo: InstantDocumentInfo, on viewController: UIViewController) {
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        let instantViewController = InstantDocumentViewController(documentInfo: instantDocumentInfo, lastViewedDocumentInfoKey: InstantExampleLastViewedDocumentInfoKey)
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        instantViewController.title = "Nutrient Instant Example"
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        let navigationController = UINavigationController(rootViewController: instantViewController)
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        navigationController.modalPresentationStyle = .fullScreen
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        viewController.present(navigationController, animated: true)
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    }
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}
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extension InstantExample: WebExamplesAPIClientDelegate {
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    func examplesAPIClient(_ apiClient: WebExamplesAPIClient, didReceiveBasicAuthenticationChallenge challenge: URLAuthenticationChallenge, completion: @escaping (URLCredential?) -> Void) {
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        presentingViewController?.presentBasicAuthPrompt(for: challenge) { username, password in
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            guard let user = username,
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                  let pass = password else {
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                completion(nil)
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                return
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            }
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            let urlCredential = URLCredential(user: user, password: pass, persistence: .permanent)
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            completion(urlCredential)
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        }
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    }
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}