//
//  FTStoreAdminApp.swift
//  FTStore Admin
//
//  FTStore Admin as its own app. It used to be a second tab inside
//  FTStore Manager, gated behind a hidden developer mode; splitting it out means
//  someone who only wants to install FTStore never sees an operator surface at
//  all, and this app never has to carry the Manager's signing/install engine.
//
//  It ships no credential of any kind — the only baked-in value is the server's
//  base URL (see `AdminConfig`), and every screen sits behind `AdminSession`,
//  which is behind a server login the operator can revoke.
//

import BackgroundTasks
import SwiftUI

@main
struct FTStoreAdminApp: App {
	@StateObject private var session = AdminSession.shared
	@Environment(\.scenePhase) private var scenePhase

	/// The background refresh that lets FTStore Admin say anything while it is
	/// closed. Declared in `Info.plist` under the same string.
	private static let alertTaskId = "app.ftstore.admin.alerts"

	init() {
		Self._registerAlertTask()
	}

	var body: some Scene {
		WindowGroup {
			AdminRootView()
				.environmentObject(session)
				.tint(AdminTheme.brand)
				// Check on the way in as well as in the background. Somebody who
				// opens FTStore Admin after a day away should not have to wait for
				// iOS to decide it is time.
				.task { await AdminAlertWatcher.shared.check(session: session) }
				// Re-arm the optional biometric gate whenever FTStore Admin leaves
				// the screen: an unattended device is exactly the case it exists
				// for. `.background` rather than `.inactive`, so the Face ID sheet
				// and the share sheet don't lock FTStore Admin behind themselves.
				.onChange(of: scenePhase) { phase in
					guard phase == .background else { return }
					// Ask for a refresh on the way out, which is the only moment
					// iOS accepts one. Locking follows, since the lock is about
					// the screen and the refresh is not.
					Self._scheduleAlertTask()
					guard session.requireBiometrics else { return }
					session.lock()
				}
		}
	}

	// MARK: - Background refresh

	/// Register before the app finishes launching, which `init` guarantees and a
	/// `.task` does not: iOS rejects a handler registered any later.
	private static func _registerAlertTask() {
		BGTaskScheduler.shared.register(
			forTaskWithIdentifier: alertTaskId,
			using: nil
		) { task in
			// Queue the next one first. A run that returned without rescheduling
			// would be the last one this install ever gets.
			_scheduleAlertTask()

			let work = Task { @MainActor in
				let posted = await AdminAlertWatcher.shared.check()
				task.setTaskCompleted(success: posted)
			}
			// iOS reclaims the time whenever it likes; without this the task is
			// killed rather than ended, which counts against future scheduling.
			task.expirationHandler = { work.cancel() }
		}
	}

	private static func _scheduleAlertTask() {
		guard AdminAlertWatcher.shared.anyEnabled else { return }

		let request = BGAppRefreshTaskRequest(identifier: alertTaskId)
		// A floor, not a promise. The system decides the real cadence from how
		// often FTStore Admin is opened and what the battery is doing.
		request.earliestBeginDate = Date(timeIntervalSinceNow: 30 * 60)
		try? BGTaskScheduler.shared.submit(request)
	}
}