feat: add alert grace period controls

Sources/Model/API/PingService.swift

@@ -50,7 +50,12 @@ enum PingService {
     }
 
     private static func handlePingFailure(for hostname: String, notificationsEnabled: Bool) async {
-        if let notification = await stateStore.recordFailure(for: hostname, notificationsEnabled: notificationsEnabled) {
+        let alertGracePeriod = UserDefaults.standard.integer(forKey: "alertGracePeriod")
+        if let notification = await stateStore.recordFailure(
+            for: hostname,
+            notificationsEnabled: notificationsEnabled,
+            gracePeriod: TimeInterval(alertGracePeriod)
+        ) {
             sendNotification(title: notification.title, body: notification.body)
         }
     }
@@ -69,10 +74,12 @@ enum PingService {
 private actor PingStateStore {
     private var previousPingStates: [String: Bool] = [:]
     private var suppressedUntil: [String: Date] = [:]
+    private var failureStartedAt: [String: Date] = [:]
 
     func suppressChecks(for hostname: String, duration: TimeInterval) {
         suppressedUntil[hostname] = Date().addingTimeInterval(duration)
         previousPingStates[hostname] = false
+        failureStartedAt.removeValue(forKey: hostname)
     }
 
     func shouldSkipPing(for hostname: String) -> Bool {
@@ -87,6 +94,7 @@ private actor PingStateStore {
     func recordSuccess(for hostname: String, notificationsEnabled: Bool) -> PingNotification? {
         let wasPreviouslyDown = previousPingStates[hostname] == false
         previousPingStates[hostname] = true
+        failureStartedAt.removeValue(forKey: hostname)
 
         guard wasPreviouslyDown, notificationsEnabled else {
             return nil
@@ -98,9 +106,20 @@ private actor PingStateStore {
         )
     }
 
-    func recordFailure(for hostname: String, notificationsEnabled: Bool) -> PingNotification? {
+    func recordFailure(for hostname: String, notificationsEnabled: Bool, gracePeriod: TimeInterval) -> PingNotification? {
+        let now = Date()
+        let startedAt = failureStartedAt[hostname] ?? now
+        if failureStartedAt[hostname] == nil {
+            failureStartedAt[hostname] = startedAt
+        }
+
+        guard now.timeIntervalSince(startedAt) >= gracePeriod else {
+            return nil
+        }
+
         let wasPreviouslyUp = previousPingStates[hostname] != false
         previousPingStates[hostname] = false
+        failureStartedAt.removeValue(forKey: hostname)
 
         guard wasPreviouslyUp, notificationsEnabled else {
             return nil