Issue #3: First implementation of a DoH configuration setting.

dns/ViewModel.swift

@@ -7,10 +7,89 @@
 
 import Foundation
 import Combine
+import NetworkExtension
+import OSLog
 
 class ViewModel: NSObject, ObservableObject {
 
+    // TODO: Store this in UserDefaults
     @Published
     var blocklist: BlocklistOption = .secure
 
+    // TODO: Store this in UserDefaults
+    @Published
+    var isDnsEnabled = false {
+        didSet {
+            if !isProgrammaticChange {
+                toggleDns()
+            }
+            else {
+                // Reset, so next one is recognized as coming from the user again.
+                isProgrammaticChange = false
+            }
+        }
+    }
+
+    private var isProgrammaticChange = false
+
+
+    private let manager = NEDNSSettingsManager.shared()
+
+    private let log = Logger(subsystem: String(describing: ViewModel.self), category: String(describing: ViewModel.self))
+
+
+    func toggleDns() {
+        Task {
+            if isDnsEnabled {
+                do {
+                    try await manager.loadFromPreferences()
+                }
+                catch {
+                    log.error("Error loading preferences: \(error)")
+
+                    delayedToggle(false)
+
+                    return
+                }
+
+                let settings = NEDNSOverHTTPSSettings(servers: [blocklist.ipv4, blocklist.ipv6])
+                settings.serverURL = URL(string: "https://\(blocklist.server)")
+                settings.matchDomains = [""]
+
+
+                manager.dnsSettings = settings
+                manager.localizedDescription = blocklist.description
+
+                do {
+                    try await manager.saveToPreferences()
+                }
+                catch {
+                    log.error("Error storing preferences: \(error)")
+
+                    delayedToggle(false)
+                }
+            }
+            else {
+                do {
+                    try await manager.removeFromPreferences()
+                }
+                catch {
+                    log.error("Error removing preferences: \(error)")
+
+                    delayedToggle(true)
+                }
+            }
+        }
+    }
+
+    private func delayedToggle(_ enabled: Bool) {
+        Task {
+            try? await Task.sleep(nanoseconds: 500_000_000)
+
+            await MainActor.run {
+                isProgrammaticChange = true
+                isDnsEnabled = enabled
+            }
+        }
+    }
 }