add color scheme setting

Features/Sources/AppFeature/AppView.swift

@@ -1,11 +1,14 @@
 import ComposableArchitecture
+import Models
 import Settings
 import SwiftUI
 import Today
 
 public struct AppView: View {
     var store: StoreOf<AppReducer>
 
+    @Shared(.appStorage("colorScheme")) var userColorScheme = UserColorScheme.light
+
     public init(store: StoreOf<AppReducer>) {
         self.store = store
     }
@@ -30,5 +33,6 @@ public struct AppView: View {
                     }
                 }
         }
+        .preferredColorScheme(userColorScheme.colorScheme)
     }
 }

Features/Sources/AppFeature/Views/UserColorScheme.swift

@@ -0,0 +1,16 @@
+import Models
+import SwiftUI
+
+extension UserColorScheme {
+    var colorScheme: ColorScheme? {
+        switch self {
+        case .dark:
+            .dark
+        case .light:
+            .light
+        case .system:
+            nil
+        }
+    }
+}
+

Features/Sources/Models/UserColorScheme.swift

@@ -0,0 +1,5 @@
+public enum UserColorScheme: String, Sendable {
+    case dark = "dark"
+    case light = "light"
+    case system = "system"
+}

Features/Sources/Settings/Appearance/AppearanceView.swift

@@ -0,0 +1,70 @@
+import Models
+import Sharing
+import SwiftUI
+
+struct AppearanceView: View {
+    @Shared(.appStorage("colorScheme")) var userColorScheme = UserColorScheme.system
+
+    var body: some View {
+        Form {
+            Button(
+                action: {
+                    $userColorScheme.withLock {
+                        $0 = .light
+                    }
+                }
+            ) {
+                HStack {
+                    Text("Light")
+                        .foregroundStyle(Color.primary)
+
+                    Spacer()
+
+                    if userColorScheme == .light {
+                        Image(systemName: "checkmark")
+                    }
+                }
+            }
+
+            Button(
+                action: {
+                    $userColorScheme.withLock {
+                        $0 = .dark
+                    }
+                }
+            ) {
+                HStack {
+                    Text("Dark")
+                        .foregroundStyle(Color.primary)
+
+                    Spacer()
+
+                    if userColorScheme == .dark {
+                        Image(systemName: "checkmark")
+                    }
+                }
+            }
+
+            Button(
+                action: {
+                    $userColorScheme.withLock {
+                        $0 = .system
+                    }
+                }
+            ) {
+                HStack {
+                    Text("System")
+                        .foregroundStyle(Color.primary)
+
+                    Spacer()
+
+                    if userColorScheme == .system {
+                        Image(systemName: "checkmark")
+                    }
+                }
+            }
+        }
+        .navigationTitle("Appearance")
+        .navigationBarTitleDisplayMode(.inline)
+    }
+}

Features/Sources/Settings/Settings/SettingsView.swift

@@ -46,7 +46,7 @@ public struct SettingsView: View {
                     }
 
                     NavigationLink {
-                        Text("Appearance")
+                        AppearanceView()
                     } label: {
                         NavigationLinkLabel(
                             color: .cyan,

Features/Tests/AppFeatureTests/UserColorSchemeTests.swift

@@ -0,0 +1,14 @@
+import Models
+import Testing
+
+@testable import AppFeature
+
+@MainActor
+struct UserColorSchemeTests {
+    @Test
+    func colorScheme() {
+        #expect(UserColorScheme.dark.colorScheme == .dark)
+        #expect(UserColorScheme.light.colorScheme == .light)
+        #expect(UserColorScheme.system.colorScheme == nil)
+    }
+}