Rebuilt MetricKit with Swift-First API

−import UIKit
+import SwiftUI
 import MetricKit
 
−// MARK: - Old delegate-based approach (pre-iOS 27)
+// MARK: - Service (keep alive for app lifetime)
 
−class AppDelegate: UIResponder, UIApplicationDelegate, MXMetricManagerSubscriber {
−    let metricManager = MXMetricManager.shared
+actor MetricKitService {
+    static let shared = MetricKitService()
 
−    func application(_ application: UIApplication,
−                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
−        metricManager.add(self)
−        return true
+    func startMonitoring() async {
+        async let _ = receiveMetrics()
+        async let _ = receiveDiagnostics()
     }
 
−    // Called once per day with an array of MXMetricPayload
−    func didReceive(_ payloads: [MXMetricPayload]) {
−        for payload in payloads {
−            if let memory = payload.memoryMetrics {
−                print("Peak memory: \(memory.peakMemoryUsage)")
+    private func receiveMetrics() async {
+        let manager = MetricManager.shared
+        for await report in manager.metricReports {
+            for entry in report.intervalEntries {
+                let interval = entry.interval
+                print("Metric window: \(interval.start) – \(interval.end)")
+                let memoryMetrics = entry.metrics.filter { $0.group == .memory }
+                for metric in memoryMetrics {
+                    switch metric {
+                    case .peakMemory(let measurement):
+                        print("  Peak memory: \(measurement)")
+                    default:
+                        break
+                    }
+                }
             }
−            // Encode manually
−            if let json = try? JSONEncoder().encode(payload.jsonRepresentation()) {
−                print(String(data: json, encoding: .utf8) ?? "")
−            }
         }
     }
 
−    // Called immediately for crash/hang diagnostics
−    func didReceive(_ payloads: [MXDiagnosticPayload]) {
−        for payload in payloads {
−            if let crashes = payload.crashDiagnostics {
−                for crash in crashes {
−                    print("Exception type: \(crash.exceptionType ?? 0)")
−                    print("Backtrace:\n\(crash.callStackTree)")
−                    // No termination category available pre-iOS 27
+    private func receiveDiagnostics() async {
+        let manager = MetricManager.shared
+        for await report in manager.diagnosticReports {
+            for diagnostic in report.diagnostics {
+                switch diagnostic {
+                case .crash(let crash):
+                    print("Crash reason: \(crash.reason)")
+                    print("Termination category: \(crash.terminationCategory)")
+                    if let frames = crash.backtrace?.frames {
+                        print("Top frame: \(frames.first?.symbol ?? "unknown")")
+                    }
+                case .hang(let hang):
+                    print("Hang duration: \(hang.duration)")
+                default:
+                    break
                 }
             }
−            if let hangs = payload.hangDiagnostics {
−                for hang in hangs {
−                    print("Hang duration: \(hang.hangDuration)")
+        }
+    }
+}
+
+// MARK: - App Entry
+
+@main
+struct MetricKitDemoApp: App {
+    var body: some Scene {
+        WindowGroup {
+            ContentView()
+                .task {
+                    await MetricKitService.shared.startMonitoring()
                 }
−            }
         }
     }
+}
+
+// MARK: - Encode a full report to JSON for server upload
+
+func encodeReport(_ report: MetricReport) throws -> Data {
+    let encoder = JSONEncoder()
+    encoder.outputFormatting = .prettyPrinted
+    return try encoder.encode(report)
+}
+
+struct ContentView: View {
+    var body: some View {
+        Text("MetricKit monitoring active")
+            .padding()
+    }
 }