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

import UIKit

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

    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。
    var onScanTabSelected: (() -> Void)?

    private enum TabSlot: CaseIterable {
        case home
        case orders
        case scan
        case statistics
        case profile

        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
            }
        }

        static func index(for tab: AppTab) -> Int? {
            allCases.firstIndex { $0.appTab == tab }
        }

        static var scanIndex: Int? {
            allCases.firstIndex(of: .scan)
        }
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        delegate = self
        configureTabBarAppearance()
        configureTabs()
        bindBadgeViewModel()
        badgeViewModel.refreshPendingWriteOffCount()
    }

    /// 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 {
            badgeViewModel.refreshPendingWriteOffCount()
        }
    }

    private func configureTabBarAppearance() {
        tabBar.tintColor = AppColor.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: AppColor.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
    }

    private func configureTabs() {
        tabNavigationControllers.removeAll()
        viewControllers = TabSlot.allCases.map { slot in
            if let tab = slot.appTab {
                let navigationController = TabNavigationController(tab: tab)
                navigationController.tabBarItem = tab.makeTabBarItem()
                tabNavigationControllers[tab] = navigationController
                return navigationController
            }

            let scannerPlaceholder = UIViewController()
            scannerPlaceholder.tabBarItem = MainScanTabItem.makeTabBarItem()
            return scannerPlaceholder
        }
    }

    private func bindBadgeViewModel() {
        badgeViewModel.onChange = { [weak self] in
            self?.updateOrderBadge()
        }
    }

    private func updateOrderBadge() {
        let badgeValue: String?
        if let count = badgeViewModel.pendingWriteOffCount, count > 0 {
            badgeValue = "\(count)"
        } else {
            badgeValue = nil
        }
        tabNavigationControllers[.orders]?.tabBarItem.badgeValue = badgeValue
    }

    private func presentGlobalScanner() {
        guard presentedViewController == nil else { return }

        let scanner = ScanPlaceholderViewController()
        let navigationController = UINavigationController(rootViewController: scanner)
        navigationController.modalPresentationStyle = .fullScreen
        present(navigationController, animated: true)
    }
}

extension MainTabBarController: UITabBarControllerDelegate {

    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
    }

    func tabBarController(_ tabBarController: UITabBarController, didSelect viewController: UIViewController) {
        guard !isSyncingTabSelection,
              let navigationController = viewController as? TabNavigationController else { return }

        if navigationController.appTab == .orders {
            badgeViewModel.refreshPendingWriteOffCount()
        }
    }
}