SafariExtensionHandler.swift

import SafariServices
import SwiftUI

struct Popover: View {
    @State private var content = ""
    
    var body: some View {
        VStack(spacing: 16) {
            Text("URL")
                .font(.headline)
            Text(content)
        }
        .frame(minWidth: 300)
        .padding()
        .onAppear {
            SFSafariApplication.getActiveWindow { (window) in
                window?.getActiveTab { (tab) in
                    tab?.getActivePage(completionHandler: { (page) in
                        page?.getPropertiesWithCompletionHandler( { (properties) in
                            DispatchQueue.main.async {
                                if let url = properties?.url {
                                    content = url.absoluteString
                                }
                            }
                        })
                    })
                }
            }
        }
    }
}

final class PopoverViewController: SFSafariExtensionViewController {
    init() {
        super.init(nibName: nil, bundle: nil)
        let popover = Popover()
        self.view = NSHostingView(rootView: popover)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

class SafariExtensionHandler: SFSafariExtensionHandler {
    override func popoverViewController() -> SFSafariExtensionViewController {
        PopoverViewController()
    }
    
    override func validateToolbarItem(in window: SFSafariWindow, validationHandler: @escaping ((Bool, String) -> Void)) {
        window.getActiveTab { (tab) in
            tab?.getActivePage(completionHandler: { (page) in
                page?.getPropertiesWithCompletionHandler( { (properties) in
                    validationHandler(properties?.url != nil, "")
                })
            })
        }
    }
}