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

import SnapKit
import UIKit

@MainActor
/// 应用根协调器，监听登录阶段并在 window 根层级切换登录页与 `MainTabBarController`。
final class RootViewController: UIViewController {

    private let services: AppServices
    private let lifecycleCoordinator: AppSessionLifecycleCoordinator
    private var currentAuthChild: UIViewController?

    /// 初始化实例。
    init(services: AppServices = .shared) {
        self.services = services
        lifecycleCoordinator = AppSessionLifecycleCoordinator(services: services)
        super.init(nibName: nil, bundle: nil)
    }

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

    /// 初始化视图、监听登录阶段变化并启动会话恢复。
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .systemBackground

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

        applyRoot(for: services.appSession.phase)
        lifecycleCoordinator.bootstrapSession()
        lifecycleCoordinator.configurePushNotifications()
    }

    /// 登录阶段变化时切换 window 根控制器，并在登出时清理各上下文状态。
    private func handleSessionPhaseChange() {
        applyRoot(for: services.appSession.phase)
        lifecycleCoordinator.handleSessionPhaseChange()
    }

    /// 按登录阶段切换 window 根控制器。
    private func applyRoot(for phase: AuthPhase) {
        switch phase {
        case .loggedIn:
            showMainTabBarAsWindowRoot()
        case .loggedOut:
            showAuthRoot(with: LoginViewController(services: services))
        case .restoring:
            showAuthRoot(with: restoringViewController())
        }
    }

    /// 登录后将 `MainTabBarController` 设为 window 根控制器。
    private func showMainTabBarAsWindowRoot() {
        removeCurrentAuthChild()

        guard let window = activeWindow else { return }

        let mainTabBarController = MainTabBarController(services: services)
        window.rootViewController = mainTabBarController
        attachGlobalOverlays(to: window)
    }

    /// 未登录或恢复阶段展示登录/占位页，由当前协调器承载。
    private func showAuthRoot(with child: UIViewController) {
        guard let window = activeWindow else {
            mountAuthChild(child)
            return
        }

        if window.rootViewController !== self {
            window.rootViewController = self
        }

        mountAuthChild(child)
        attachGlobalOverlays(to: window)
    }

    /// 将登录页或恢复占位页挂载为当前协调器的子控制器。
    private func mountAuthChild(_ child: UIViewController) {
        guard currentAuthChild !== child else { return }

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

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

    /// 移除当前认证阶段子控制器。
    private func removeCurrentAuthChild() {
        currentAuthChild?.willMove(toParent: nil)
        currentAuthChild?.view.removeFromSuperview()
        currentAuthChild?.removeFromParent()
        currentAuthChild = nil
    }

    /// 会话恢复阶段的空白占位页，避免闪烁登录页。
    private func restoringViewController() -> UIViewController {
        let controller = UIViewController()
        controller.view.backgroundColor = .systemBackground
        return controller
    }

    /// 将全局 Toast 与 Loading 视图附加到指定 window。
    private func attachGlobalOverlays(to window: UIWindow) {
        services.toastCenter.attachToWindow(window)
        services.globalLoading.attachToWindow(window)
    }

    /// 获取当前 key window。
    private var activeWindow: UIWindow? {
        view.window ?? UIApplication.shared.connectedScenes
            .compactMap { $0 as? UIWindowScene }
            .flatMap(\.windows)
            .first(where: \.isKeyWindow)
    }
}