Implement preliminary app mode switch

Signal/src/Loki/View Controllers/SettingsVC.swift

@@ -128,6 +128,12 @@ final class SettingsVC : BaseVC, AvatarViewHelperDelegate {
         stackView.pin(to: scrollView)
         view.addSubview(scrollView)
         scrollView.pin(to: view)
+        // Register for notifications
+        NotificationCenter.default.addObserver(self, selector: #selector(handleAppModeSwitchedNotification(_:)), name: .appModeSwitched, object: nil)
+    }
+
+    deinit {
+        NotificationCenter.default.removeObserver(self)
     }
     
     private func getSettingButtons() -> [UIView] {
@@ -203,6 +209,11 @@ final class SettingsVC : BaseVC, AvatarViewHelperDelegate {
     }
     
     // MARK: Updating
+    @objc private func handleAppModeSwitchedNotification(_ notification: Notification) {
+        updateNavigationBarButtons()
+        // TODO: Redraw UI
+    }
+
     private func handleIsEditingDisplayNameChanged() {
         updateNavigationBarButtons()
         UIView.animate(withDuration: 0.25) {
@@ -228,9 +239,12 @@ final class SettingsVC : BaseVC, AvatarViewHelperDelegate {
             let closeButton = UIBarButtonItem(image: #imageLiteral(resourceName: "X"), style: .plain, target: self, action: #selector(close))
             closeButton.tintColor = Colors.text
             navigationItem.leftBarButtonItem = closeButton
+            let appModeIcon = UserDefaults.standard[.isUsingDarkMode] ? #imageLiteral(resourceName: "ic_dark_theme_on") : #imageLiteral(resourceName: "ic_dark_theme_off")
+            let appModeButton = UIBarButtonItem(image: appModeIcon, style: .plain, target: self, action: #selector(switchAppMode))
+            appModeButton.tintColor = Colors.text
             let qrCodeButton = UIBarButtonItem(image: #imageLiteral(resourceName: "QRCode"), style: .plain, target: self, action: #selector(showQRCode))
             qrCodeButton.tintColor = Colors.text
-            navigationItem.rightBarButtonItem = qrCodeButton
+            navigationItem.rightBarButtonItems = [ qrCodeButton/*, appModeButton*/ ]
         }
     }
     
@@ -281,7 +295,13 @@ final class SettingsVC : BaseVC, AvatarViewHelperDelegate {
     @objc private func close() {
         dismiss(animated: true, completion: nil)
     }
-    
+
+    @objc private func switchAppMode() {
+        let isUsingDarkMode = UserDefaults.standard[.isUsingDarkMode]
+        UserDefaults.standard[.isUsingDarkMode] = !isUsingDarkMode
+        NotificationCenter.default.post(name: .appModeSwitched, object: nil)
+    }
+
     @objc private func showQRCode() {
         let qrCodeVC = QRCodeVC()
         navigationController!.pushViewController(qrCodeVC, animated: true)

SignalMessaging/Loki/Redesign/Style Guide/AppMode.swift

@@ -3,6 +3,9 @@ public enum AppMode {
     case light, dark
     
     public static var current: AppMode = .dark
+//    public static var current: AppMode {
+//        return UserDefaults.standard[.isUsingDarkMode] ? .dark : .light
+//    }
 }
 
 public var isLightMode: Bool {

SignalServiceKit/src/Loki/Utilities/LKUserDefaults.swift

@@ -10,6 +10,7 @@ public enum LKUserDefaults {
         case hasViewedSeed
         /// Whether the device was unlinked as a slave device (used to notify the user on the landing screen).
         case wasUnlinked
+        case isUsingDarkMode
         case isUsingFullAPNs
     }
 

SignalServiceKit/src/Loki/Utilities/Notification+Loki.swift

@@ -2,6 +2,7 @@
 public extension Notification.Name {
 
     // State changes
+    public static let appModeSwitched = Notification.Name("appModeSwitched")
     public static let blockedContactsUpdated = Notification.Name("blockedContactsUpdated")
     public static let contactOnlineStatusChanged = Notification.Name("contactOnlineStatusChanged")
     public static let groupThreadUpdated = Notification.Name("groupThreadUpdated")
@@ -28,6 +29,7 @@ public extension Notification.Name {
 @objc public extension NSNotification {
 
     // State changes
+    @objc public static let appModeSwitched = Notification.Name.appModeSwitched.rawValue as NSString
     @objc public static let blockedContactsUpdated = Notification.Name.blockedContactsUpdated.rawValue as NSString
     @objc public static let contactOnlineStatusChanged = Notification.Name.contactOnlineStatusChanged.rawValue as NSString
     @objc public static let groupThreadUpdated = Notification.Name.groupThreadUpdated.rawValue as NSString