add Sparkle

Cheetah/Sparkle.swift

@@ -0,0 +1,32 @@
+import SwiftUI
+import Sparkle
+
+// This view model class publishes when new updates can be checked by the user
+final class CheckForUpdatesViewModel: ObservableObject {
+    @Published var canCheckForUpdates = false
+
+    init(updater: SPUUpdater) {
+        updater.publisher(for: \.canCheckForUpdates)
+            .assign(to: &$canCheckForUpdates)
+    }
+}
+
+// This is the view for the Check for Updates menu item
+// Note this intermediate view is necessary for the disabled state on the menu item to work properly before Monterey.
+// See https://stackoverflow.com/questions/68553092/menu-not-updating-swiftui-bug for more info
+struct CheckForUpdatesView: View {
+    @ObservedObject private var checkForUpdatesViewModel: CheckForUpdatesViewModel
+    private let updater: SPUUpdater
+    
+    init(updater: SPUUpdater) {
+        self.updater = updater
+        
+        // Create our view model for our CheckForUpdatesView
+        self.checkForUpdatesViewModel = CheckForUpdatesViewModel(updater: updater)
+    }
+    
+    var body: some View {
+        Button("Check for Updates…", action: updater.checkForUpdates)
+            .disabled(!checkForUpdatesViewModel.canCheckForUpdates)
+    }
+}