add update notifications, only when new packages appear

Off by default. Enabling the checkbox requests notification permission
(UNUserNotificationCenter); if denied, the checkbox reverts — the auth
callback arrives on a background queue, so the UI update hops to main.

notifyIfNeeded remembers the last notified set and stays silent while
the outdated list is unchanged, so an hourly refresh doesn't re-ping
about the same packages. The set resets as packages get upgraded.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

BrewBar/BrewBarApp.swift

@@ -1,4 +1,5 @@
 import Cocoa
+import UserNotifications
 
 @main
 class AppDelegate: NSObject, NSApplicationDelegate {
@@ -40,6 +41,7 @@ class AppDelegate: NSObject, NSApplicationDelegate {
 
     /// last known outdated list, shown in the Upgrade All confirmation
     var cachedOutdated: [String] = []
+    var lastNotifiedOutdated: Set<String> = []
 
     // MARK: - Menu
 
@@ -266,6 +268,7 @@ class AppDelegate: NSObject, NSApplicationDelegate {
 
             self.updateOutdatedMenu(with: lines)
             self.updateStatus(count: lines.count)
+            self.notifyIfNeeded(outdated: lines)
             if lines.isEmpty {
                 self.setMenuBarIcon("brewbar-uptodate")
             } else {
@@ -274,6 +277,24 @@ class AppDelegate: NSObject, NSApplicationDelegate {
         }
     }
 
+    /// Notifies only when packages appear that weren't in the last notified
+    /// set — an unchanged list stays silent instead of pinging every refresh.
+    func notifyIfNeeded(outdated: [String]) {
+        let current = Set(outdated)
+        defer { lastNotifiedOutdated = current }
+
+        guard Settings.notifyOnNewUpdates,
+              !current.subtracting(lastNotifiedOutdated).isEmpty else { return }
+
+        let content = UNMutableNotificationContent()
+        content.title = "Homebrew updates available"
+        let shown = outdated.prefix(4).joined(separator: ", ")
+        content.body = outdated.count > 4 ? "\(shown) and \(outdated.count - 4) more" : shown
+
+        let request = UNNotificationRequest(identifier: UUID().uuidString, content: content, trigger: nil)
+        UNUserNotificationCenter.current().add(request)
+    }
+
     func runAutoUpgrade() {
         statusMenuItem.title = "Auto-upgrading..."
 

BrewBar/SettingsWindowController.swift

@@ -1,5 +1,6 @@
 import Cocoa
 import ServiceManagement
+import UserNotifications
 
 class SettingsWindowController: NSWindowController {
     weak var appDelegate: AppDelegate?
@@ -18,6 +19,7 @@ class SettingsWindowController: NSWindowController {
     var greedyCheckbox: NSButton!
     var autoUpgradeFormulaeCheckbox: NSButton!
     var autoUpgradeCasksCheckbox: NSButton!
+    var notifyCheckbox: NSButton!
 
     convenience init(appDelegate: AppDelegate) {
         let window = NSWindow(
@@ -108,6 +110,12 @@ class SettingsWindowController: NSWindowController {
         let caskWarningRow = NSStackView(views: [spacer, caskWarning])
         caskWarningRow.orientation = .horizontal
 
+        notifyCheckbox = NSButton(
+            checkboxWithTitle: "Notify when new updates are found",
+            target: self,
+            action: #selector(toggleNotify(_:))
+        )
+
         let stack = NSStackView(views: [
             frequencyRow,
             customRow,
@@ -117,6 +125,7 @@ class SettingsWindowController: NSWindowController {
             autoUpgradeCasksCheckbox,
             caskWarningRow,
             separator(),
+            notifyCheckbox,
             launchAtLoginCheckbox,
         ])
         stack.orientation = .vertical
@@ -155,6 +164,7 @@ class SettingsWindowController: NSWindowController {
         greedyCheckbox.state = Settings.includeGreedyCasks ? .on : .off
         autoUpgradeFormulaeCheckbox.state = Settings.autoUpgradeFormulae ? .on : .off
         autoUpgradeCasksCheckbox.state = Settings.autoUpgradeCasks ? .on : .off
+        notifyCheckbox.state = Settings.notifyOnNewUpdates ? .on : .off
     }
 
     func separator() -> NSBox {
@@ -200,6 +210,21 @@ class SettingsWindowController: NSWindowController {
         Settings.autoUpgradeCasks = sender.state == .on
     }
 
+    @objc func toggleNotify(_ sender: NSButton) {
+        guard sender.state == .on else {
+            Settings.notifyOnNewUpdates = false
+            return
+        }
+
+        UNUserNotificationCenter.current().requestAuthorization(options: [.alert]) { granted, _ in
+            // callback arrives on a background queue; UI needs main
+            DispatchQueue.main.async {
+                Settings.notifyOnNewUpdates = granted
+                sender.state = granted ? .on : .off
+            }
+        }
+    }
+
     @objc func toggleLaunchAtLogin(_ sender: NSButton) {
         do {
             if sender.state == .on {