import Foundation
#if canImport(UIKit) && !os(watchOS)
import UIKit
#elseif canImport(AppKit)
import AppKit
#endif

/// Calls `onForeground` when the app returns to the foreground (iOS) or becomes
/// active (macOS), so rooms can reconnect immediately instead of waiting out a backoff.
final class AppLifecycleObserver: Sendable {
    private let task: Task<Void, Never>?

    init(onForeground: @escaping @Sendable () async -> Void) {
        #if canImport(UIKit) && !os(watchOS)
        let name = UIApplication.willEnterForegroundNotification
        #elseif canImport(AppKit)
        let name = NSApplication.didBecomeActiveNotification
        #else
        let name: Notification.Name? = nil
        #endif
        if let name = name as Notification.Name? {
            task = Task {
                for await _ in NotificationCenter.default.notifications(named: name) {
                    if Task.isCancelled { return }
                    await onForeground()
                }
            }
        } else {
            task = nil
        }
    }

    func cancel() { task?.cancel() }
}