import UIKit
import BackgroundTasks

/// App delegate that schedules the background refresh task which drives the
/// push-equivalent notifications (polling the monitored repos).
///
/// iOS runs BGAppRefreshTask opportunistically (~every 15 min at best, often
/// slower), and only when the app has been used recently and isn't force-quit.
final class AppDelegate: NSObject, UIApplicationDelegate {
    static let taskIdentifier = "com.bueso.giteapr.refresh"

    func application(_ application: UIApplication,
                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]? = nil) -> Bool {
        registerBackgroundTask()
        return true
    }

    private func registerBackgroundTask() {
        BGTaskScheduler.shared.register(
            forTaskWithIdentifier: Self.taskIdentifier,
            using: nil
        ) { task in
            // Handle the background refresh.
            self.handle(task)
        }
    }

    private func handle(_ task: BGTask) {
        // Reschedule the next refresh so the chain continues.
        scheduleNextRefresh()

        let pollTask = Task { @MainActor in
            await NotificationService.shared.poll()
        }
        task.expirationHandler = {
            pollTask.cancel()
        }
        Task {
            await pollTask.value
            task.setTaskCompleted(success: true)
        }
    }

    /// Schedule the next background refresh (~15 min from now, earliest).
    func scheduleNextRefresh() {
        let request = BGAppRefreshTaskRequest(identifier: Self.taskIdentifier)
        request.earliestBeginDate = Date(timeIntervalSinceNow: 15 * 60)
        try? BGTaskScheduler.shared.submit(request)
    }
}