//
//  RootViewController.swift
//  suixinkan
//

import SnapKit
import UIKit

@MainActor
/// 应用根 ViewController，根据登录阶段切换子页面并挂载全局 Overlay。
final class RootViewController: UIViewController {

    private let services: AppServices
    private var currentChild: UIViewController?
    private let restoringView = UIView()

    init(services: AppServices = .shared) {
        self.services = services
        super.init(nibName: nil, bundle: nil)
    }

    @available(*, unavailable)
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .systemBackground
        restoringView.backgroundColor = .systemBackground

        services.appSession.onChange = { [weak self] in
            self?.handleSessionPhaseChange()
        }

        mountChild(for: services.appSession.phase)
        bootstrapSession()
        configurePushNotifications()
    }

    override func viewDidAppear(_ animated: Bool) {
        super.viewDidAppear(animated)
        attachGlobalOverlays()
    }

    private func bootstrapSession() {
        Task {
            await services.globalLoading.withLoading {
                await services.sessionBootstrapper.restore(
                    appSession: services.appSession,
                    accountContext: services.accountContext,
                    permissionContext: services.permissionContext,
                    profileAPI: services.profileAPI,
                    accountContextAPI: services.accountContextAPI,
                    toastCenter: services.toastCenter
                )
            }

            if services.appSession.isLoggedIn, !AppUITestLaunchState.isRunningUITests {
                PushNotificationManager.shared.requestAuthorizationAndRegister()
            }
        }
    }

    private func configurePushNotifications() {
        services.configurePushNotifications()
    }

    private func attachGlobalOverlays() {
        guard let window = view.window else { return }
        services.toastCenter.attachToWindow(window)
        services.globalLoading.attachToWindow(window)
    }

    private func handleSessionPhaseChange() {
        mountChild(for: services.appSession.phase)

        switch services.appSession.phase {
        case .loggedIn:
            if !AppUITestLaunchState.isRunningUITests {
                PushNotificationManager.shared.requestAuthorizationAndRegister()
            }
            Task { await reloadScenicSpotContextIfNeeded() }
        case .loggedOut:
            services.accountContext.reset()
            services.permissionContext.reset()
            services.scenicSpotContext.reset()
            services.appRouter.reset()
            services.toastCenter.dismiss()
            services.scenicQueueRuntime.stop()
        case .restoring:
            break
        }
    }

    private func reloadScenicSpotContextIfNeeded() async {
        guard services.appSession.isLoggedIn else {
            services.scenicSpotContext.reset()
            return
        }
        await services.scenicSpotContext.reload(
            scenicId: services.accountContext.currentScenic?.id,
            api: services.accountContextAPI
        )
    }

    private func mountChild(for phase: AuthPhase) {
        let nextChild: UIViewController
        switch phase {
        case .loggedOut:
            nextChild = LoginViewController(services: services)
        case .restoring:
            nextChild = restoringViewController()
        case .loggedIn:
            nextChild = MainTabBarController(services: services)
        }

        guard currentChild !== nextChild else { return }

        currentChild?.willMove(toParent: nil)
        currentChild?.view.removeFromSuperview()
        currentChild?.removeFromParent()

        addChild(nextChild)
        view.addSubview(nextChild.view)
        nextChild.view.snp.makeConstraints { make in
            make.edges.equalToSuperview()
        }
        nextChild.didMove(toParent: self)
        currentChild = nextChild
    }

    private func restoringViewController() -> UIViewController {
        let controller = UIViewController()
        controller.view.backgroundColor = .systemBackground
        return controller
    }
}