Add theme toggle separate from system appearance

Closes #67

Tusker/AppDelegate.swift

@@ -26,6 +26,9 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
         
         NotificationCenter.default.addObserver(self, selector: #selector(onUserLoggedOut), name: .userLoggedOut, object: nil)
         
+        NotificationCenter.default.addObserver(self, selector: #selector(themePrefChanged), name: .themePreferenceChanged, object: nil)
+        themePrefChanged()
+        
         window!.makeKeyAndVisible()
         
         if let shortcutItem = launchOptions?[.shortcutItem] as? UIApplicationShortcutItem {
@@ -110,6 +113,10 @@ class AppDelegate: UIResponder, UIApplicationDelegate {
         showOnboardingUI()
     }
     
+    @objc func themePrefChanged() {
+        window?.overrideUserInterfaceStyle = Preferences.shared.theme
+    }
+
 }
 
 extension AppDelegate: OnboardingViewControllerDelegate {

Tusker/Preferences/Preferences+Notification.swift

@@ -10,4 +10,5 @@ import Foundation
 
 extension Notification.Name {
     static let preferencesChanged = Notification.Name("Tusker.preferencesChanged")
+    static let themePreferenceChanged = Notification.Name("Tusker.themePreferenceChanged")
 }

Tusker/Preferences/Preferences.swift

@@ -37,6 +37,7 @@ class Preferences: Codable, ObservableObject {
     required init(from decoder: Decoder) throws {
         let container = try decoder.container(keyedBy: CodingKeys.self)
         
+        self.theme = try container.decode(UIUserInterfaceStyle.self, forKey: .theme)
         self.showRepliesInProfiles = try container.decode(Bool.self, forKey: .showRepliesInProfiles)
         self.avatarStyle = try container.decode(AvatarStyle.self, forKey: .avatarStyle)
         self.hideCustomEmojiInUsernames = try container.decode(Bool.self, forKey: .hideCustomEmojiInUsernames)
@@ -59,6 +60,7 @@ class Preferences: Codable, ObservableObject {
     func encode(to encoder: Encoder) throws {
         var container = encoder.container(keyedBy: CodingKeys.self)
         
+        try container.encode(theme, forKey: .theme)
         try container.encode(showRepliesInProfiles, forKey: .showRepliesInProfiles)
         try container.encode(avatarStyle, forKey: .avatarStyle)
         try container.encode(hideCustomEmojiInUsernames, forKey: .hideCustomEmojiInUsernames)
@@ -79,6 +81,7 @@ class Preferences: Codable, ObservableObject {
     }
     
     // MARK: - Appearance
+    @Published var theme = UIUserInterfaceStyle.unspecified
     @Published var showRepliesInProfiles = false
     @Published var avatarStyle = AvatarStyle.roundRect
     @Published var hideCustomEmojiInUsernames = false
@@ -101,6 +104,7 @@ class Preferences: Codable, ObservableObject {
     @Published var statusContentType: StatusContentType = .plain
 
     enum CodingKeys: String, CodingKey {
+        case theme
         case showRepliesInProfiles
         case avatarStyle
         case hideCustomEmojiInUsernames
@@ -127,3 +131,5 @@ extension Preferences {
         case undecided, accepted, rejected
     }
 }
+
+extension UIUserInterfaceStyle: Codable {}

Tusker/Screens/Preferences/AppearancePrefsView.swift

@@ -10,6 +10,13 @@ import SwiftUI
 struct AppearancePrefsView : View {
     @ObservedObject var preferences = Preferences.shared
 
+    var theme: Binding<UIUserInterfaceStyle> = Binding(get: {
+        Preferences.shared.theme
+    }, set: {
+        Preferences.shared.theme = $0
+        NotificationCenter.default.post(name: .themePreferenceChanged, object: nil)
+    })
+    
     var useCircularAvatars: Binding<Bool> = Binding(get: {
         Preferences.shared.avatarStyle == .circle
     }) {
@@ -18,6 +25,11 @@ struct AppearancePrefsView : View {
 
     var body: some View {
         List {
+            Picker(selection: theme, label: Text("Theme")) {
+                Text("Use System Theme").tag(UIUserInterfaceStyle.unspecified)
+                Text("Light").tag(UIUserInterfaceStyle.light)
+                Text("Dark").tag(UIUserInterfaceStyle.dark)
+            }
             Toggle(isOn: $preferences.showRepliesInProfiles) {
                 Text("Show Replies in Profiles")
             }