//
//  MainTabBarController.swift
//  suixinkan
//

import UIKit

@MainActor
/// 主 Tab 容器，使用系统 TabBar 展示四个一级入口及中间扫码按钮。
final class MainTabBarController: UITabBarController {

    private let services: AppServices
    private let badgeViewModel = MainTabBadgeViewModel()
    private var tabNavigationControllers: [AppTab: TabNavigationController] = [:]
    private var isSyncingTabSelection = false

    /// 测试时可注入扫码点击处理，生产环境为空时执行真实扫码展示。
    var onScanTabSelected: (() -> Void)?

    /// 主 TabBar 固定槽位，扫码槽位只负责触发全局扫码，不参与业务路由。
    private enum TabSlot: CaseIterable {
        case home
        case orders
        case scan
        case statistics
        case profile

        /// 返回槽位对应的业务 Tab，扫码槽位无业务根页面。
        var appTab: AppTab? {
            switch self {
            case .home:
                return .home
            case .orders:
                return .orders
            case .scan:
                return nil
            case .statistics:
                return .statistics
            case .profile:
                return .profile
            }
        }

        /// 返回指定业务 Tab 在系统 TabBar 中的槽位索引。
        static func index(for tab: AppTab) -> Int? {
            allCases.firstIndex { $0.appTab == tab }
        }

        /// 返回扫码槽位在系统 TabBar 中的索引。
        static var scanIndex: Int? {
            allCases.firstIndex(of: .scan)
        }
    }

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

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

    /// 视图加载完成后的 UI 初始化与数据绑定。
    override func viewDidLoad() {
        super.viewDidLoad()
        configureTabBarAppearance()
        configureTabs()
        services.appNavigator.attach(host: self)
        bindBadgeViewModel()
        bindAccountContext()
        Task { await refreshOrderBadge() }
        #if DEBUG
        Task { await AppUITestRouteDriver.applyIfNeeded(services: services) }
        #endif
    }

    /// 配置 TabBar 外观，对齐参考工程 CustomMainTabBar 样式。
    private func configureTabBarAppearance() {
        tabBar.tintColor = AppDesign.primary
        tabBar.backgroundColor = .white
        tabBar.shadowImage = UIImage()

        let normalAttributes: [NSAttributedString.Key: Any] = [
            .foregroundColor: UIColor(hex: 0x7D8DA3),
            .font: UIFont.systemFont(ofSize: 12, weight: .regular)
        ]
        let selectedAttributes: [NSAttributedString.Key: Any] = [
            .foregroundColor: AppDesign.primary,
            .font: UIFont.systemFont(ofSize: 12, weight: .medium)
        ]

        let appearance = UITabBarAppearance()
        appearance.configureWithOpaqueBackground()
        appearance.backgroundColor = .white
        appearance.shadowColor = .clear
        appearance.stackedLayoutAppearance.normal.titleTextAttributes = normalAttributes
        appearance.stackedLayoutAppearance.selected.titleTextAttributes = selectedAttributes
        tabBar.standardAppearance = appearance
        tabBar.scrollEdgeAppearance = appearance
    }

    /// 为每个业务 Tab 创建独立导航栈，并在中间插入系统扫码槽位。
    private func configureTabs() {
        tabNavigationControllers.removeAll()
        viewControllers = TabSlot.allCases.map { slot in
            if let tab = slot.appTab {
                let navigationController = TabNavigationController(tab: tab, services: services)
                navigationController.tabBarItem = tab.makeTabBarItem()
                tabNavigationControllers[tab] = navigationController
                return navigationController
            }
            let scannerPlaceholder = UIViewController()
            scannerPlaceholder.tabBarItem = MainScanTabItem.makeTabBarItem()
            return scannerPlaceholder
        }
    }

    /// 绑定角标 ViewModel 回调。
    private func bindBadgeViewModel() {
        badgeViewModel.onChange = { [weak self] in
            self?.updateOrderBadge()
        }
    }

    /// 绑定账号上下文，景区或门店变化时刷新角标。
    private func bindAccountContext() {
        services.accountContext.onChange = { [weak self] in
            Task { await self?.refreshOrderBadge() }
        }
    }

    /// 更新订单 Tab 待核销角标。
    private func updateOrderBadge() {
        let badgeValue: String?
        if let count = badgeViewModel.pendingWriteOffCount, count > 0 {
            badgeValue = "\(count)"
        } else {
            badgeValue = nil
        }
        tabNavigationControllers[.orders]?.tabBarItem.badgeValue = badgeValue
    }

    /// 刷新订单 Tab 待核销角标数据。
    private func refreshOrderBadge() async {
        await badgeViewModel.refreshPendingWriteOffCount(
            api: services.ordersAPI,
            scenicId: services.accountContext.currentScenic?.id,
            storeId: services.accountContext.currentStore?.id
        )
    }

    /// 从 TabBar 中间按钮打开全局扫码页，成功后路由至订单核销入口。
    private func presentGlobalScanner() {
        guard presentedViewController == nil else { return }

        let scanner = OrderCodeScannerViewController()
        scanner.onScanResult = { [weak self, weak scanner] result in
            scanner?.dismiss(animated: true)
            guard let self else { return }
            switch result {
            case .success(let code):
                self.services.appNavigator.openOrdersEntry(.verificationOrders, scannedCode: code)
            case .failure(let error):
                self.services.toastCenter.show(error.localizedDescription)
            }
        }
        let navigationController = UINavigationController(rootViewController: scanner)
        navigationController.modalPresentationStyle = .fullScreen
        present(navigationController, animated: true)
    }
}

extension MainTabBarController: UITabBarControllerDelegate {
    /// 用户选择 TabBar 槽位前拦截扫码入口，使关闭扫码页后保留原页面。
    func tabBarController(_ tabBarController: UITabBarController, shouldSelect viewController: UIViewController) -> Bool {
        guard viewControllers?.firstIndex(of: viewController) == TabSlot.scanIndex else {
            return true
        }

        if let onScanTabSelected {
            onScanTabSelected()
        } else {
            presentGlobalScanner()
        }
        return false
    }

    /// 用户点击 TabBar 时刷新订单角标。
    func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        guard !isSyncingTabSelection,
              let navigationController = viewController as? TabNavigationController else { return }

        if navigationController.appTab == .orders {
            Task { await refreshOrderBadge() }
        }
    }
}

extension MainTabBarController: AppNavigationHost {
    /// 选中指定主 Tab。
    func selectTab(_ tab: AppTab) {
        guard let index = TabSlot.index(for: tab) else { return }
        guard selectedIndex != index else { return }
        isSyncingTabSelection = true
        selectedIndex = index
        isSyncingTabSelection = false
        if tab == .orders {
            Task { await refreshOrderBadge() }
        }
    }

    /// 返回指定 Tab 的导航控制器。
    func navigationController(for tab: AppTab) -> TabNavigationController? {
        tabNavigationControllers[tab]
    }

    /// 返回当前选中 Tab 的导航控制器。
    func selectedNavigationController() -> TabNavigationController? {
        selectedViewController as? TabNavigationController
    }

    /// 重置全部 Tab 的导航栈。
    func resetAllStacks() {
        for navigationController in tabNavigationControllers.values {
            navigationController.popToRootViewController(animated: false)
        }
        selectTab(.home)
    }

    /// 将订单入口和可选扫码结果应用到订单根页面。
    func applyOrdersEntry(_ entry: OrdersEntry, scannedCode: String?) {
        guard let ordersController = tabNavigationControllers[.orders]?.viewControllers.first as? OrdersViewController else {
            return
        }
        ordersController.applyOrdersEntry(entry, scannedCode: scannedCode)
    }
}