Store PDF annotations for multiple users in Swift for iOS

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//
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//  Copyright © 2020-2026 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 PSPDFKit
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import PSPDFKitUI
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class MultipleUsersExample: Example {
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    override init() {
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        super.init()
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        title = "Store annotations in JSON files for multiple users"
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        contentDescription = "Shows how to store annotations in JSON files for multiple users"
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        category = .subclassing
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        priority = 50
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    }
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    override func invoke(with delegate: ExampleRunnerDelegate) -> UIViewController {
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        let document = AssetLoader.document(for: .annualReport)
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        let controller = MultipleUsersPDFViewController(document: document)
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        return controller
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    }
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}
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private class MultipleUsersPDFViewController: PDFViewController {
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    private func withFirstProvider<T>(of document: Document, perform: (PDFDocumentProvider) -> T ) -> T {
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        return perform(document.documentProviders.first!)
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    }
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    private(set) var currentUsername: String = "" {
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        didSet {
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            guard oldValue != currentUsername else { return }
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            let document = self.document!
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            // Forward to the document
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            document.defaultAnnotationUsername = currentUsername
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            guard let documentsUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first else { return }
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            let oldInstantJSONFile = documentsUrl.appendingPathComponent("\(oldValue).json", isDirectory: false)
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            let currentInstantJSONFile = documentsUrl.appendingPathComponent("\(currentUsername).json", isDirectory: false)
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            // Save the previous user's annotation into its own JSON file.
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            let oldJsonData = withFirstProvider(of: document) {
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                return try! document.generateInstantJSON(from: $0)
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            }
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            try? oldJsonData.write(to: oldInstantJSONFile, options: Data.WritingOptions.atomic)
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            // Then clear the document cache
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            document.clearCache()
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            // Load the annotations of the current users into the document.
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            guard let newJsonData = try? Data(contentsOf: currentInstantJSONFile) else { return }
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            let jsonContainer = DataContainerProvider(data: newJsonData)
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            withFirstProvider(of: document) {
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                try! document.applyInstantJSON(fromDataProvider: jsonContainer, to: $0, lenient: false)
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            }
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            // And finally - reload the PDF.
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            reloadData()
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        }
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    }
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    override func commonInit(with document: Document?, configuration: PDFConfiguration) {
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        super.commonInit(with: document, configuration: configuration)
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        // Set a test user.
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        self.currentUsername = "Testuser"
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        // Customize the toolbar.
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        // See https://www.nutrient.io/guides/ios/customizing-the-interface/customizing-the-toolbar/ for more details.
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        updateCustomToolbar()
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        documentInfoCoordinator.availableControllerOptions = [DocumentInfoOption.annotations]
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        navigationItem.rightBarButtonItems = [thumbnailsButtonItem, outlineButtonItem, annotationButtonItem]
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    }
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    // MARK: - Private
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    private func updateCustomToolbar() {
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        let switchUserButtonItem = UIBarButtonItem(title: "User: \(currentUsername)", style: .plain, target: self, action: #selector(switchUser(_:)))
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        navigationItem.leftBarButtonItems = [closeButtonItem, switchUserButtonItem]
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    }
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    @objc func switchUser(_ sender: UIBarButtonItem) {
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        // Dismiss any popovers.
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        dismissViewController(of: nil, animated: true)
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        let alertController = UIAlertController(title: "Switch User", message: "Enter username.", preferredStyle: .alert)
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        alertController.addTextField { textField in
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            textField.text = self.currentUsername
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        }
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        alertController.addAction(UIAlertAction(title: "Cancel", style: .cancel))
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        alertController.addAction(UIAlertAction(title: "Switch", style: .default, handler: { [unowned self] _ in
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            // In a real application you want to make the username unique and also check for characters that are trouble on file systems.
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            guard let username = alertController.textFields?.first?.text else { return }
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            // Set new username
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            self.currentUsername = username
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            // Update toolbar to show new name.
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            self.updateCustomToolbar()
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        }))
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        present(alertController, animated: true, completion: nil)
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    }
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}