import AppKit
import Combine
import Foundation

@MainActor
final class AppUsageManager {
    static let shared = AppUsageManager()

    static let didCompleteFirstSession = Notification.Name("AppUsageManager.didCompleteFirstSession")

    private static let hasCompletedFirstSessionKey = "AppUsageManager.hasCompletedFirstSession"

    private let defaults: UserDefaults
    private var cancellables = Set<AnyCancellable>()

    private init(defaults: UserDefaults = .standard) {
        self.defaults = defaults
    }

    /// `true` until the user has finished their first app session.
    var isFirstTimeUser: Bool {
        !defaults.bool(forKey: Self.hasCompletedFirstSessionKey)
    }

    func start() {
        guard cancellables.isEmpty else { return }

        NotificationCenter.default.publisher(for: NSApplication.willResignActiveNotification)
            .sink { [weak self] _ in
                self?.markFirstSessionCompleted()
            }
            .store(in: &cancellables)
    }

    func markFirstSessionCompleted() {
        guard isFirstTimeUser else { return }
        defaults.set(true, forKey: Self.hasCompletedFirstSessionKey)
        NotificationCenter.default.post(name: Self.didCompleteFirstSession, object: nil)
    }
}