//
//  MainTabsView.swift
//  suixinkan
//
//  Created by Codex on 2026/6/18.
//

import SwiftUI

/// 主 TabBar 样式，决定登录后首页使用系统 TabView 还是自定义底部栏。
enum MainTabBarStyle {
    case system
    case custom
}

/// 主 TabBar 配置，后续需要切回系统 TabView 时只修改 activeStyle。
enum MainTabBarConfiguration {
    static let activeStyle: MainTabBarStyle = .custom
}

/// 主 Tab 容器视图，根据配置选择系统 TabView 或自定义 TabBar 外壳。
struct MainTabsView: View {
    var body: some View {
        switch MainTabBarConfiguration.activeStyle {
        case .system:
            SystemMainTabsView()
        case .custom:
            CustomMainTabsView()
        }
    }
}

/// 系统 TabView 外壳，保留原生 TabBar 行为以便后续切换回系统实现。
private struct SystemMainTabsView: View {
    @Environment(AppRouter.self) private var appRouter

    var body: some View {
        @Bindable var appRouter = appRouter

        TabView(selection: $appRouter.selectedTab) {
            ForEach(AppTab.allCases) { tab in
                TabNavigationStackHost(tab: tab)
                .tabItem { tab.label }
                .tag(tab)
            }
        }
    }
}

/// 自定义 TabBar 外壳，复用每个 Tab 独立 NavigationStack 并保留已访问页面状态。
private struct CustomMainTabsView: View {
    @Environment(AccountContext.self) private var accountContext
    @Environment(AppRouter.self) private var appRouter
    @Environment(OrdersAPI.self) private var ordersAPI
    @Environment(ToastCenter.self) private var toastCenter

    @State private var badgeViewModel = MainTabBadgeViewModel()
    @State private var showScanner = false
    @State private var loadedTabs: Set<AppTab> = [.home]

    private var orderBadgeText: String? {
        guard let count = badgeViewModel.pendingWriteOffCount, count > 0 else {
            return nil
        }
        return "\(count)"
    }

    var body: some View {
        @Bindable var appRouter = appRouter

        ZStack {
            ForEach(AppTab.allCases) { tab in
                PreservedTabPage(
                    tab: tab,
                    selectedTab: appRouter.selectedTab,
                    isLoaded: loadedTabs.contains(tab)
                ) {
                    CustomTabNavigationStackHost(
                        tab: tab,
                        selectedTab: $appRouter.selectedTab,
                        orderBadgeText: orderBadgeText,
                        onScanTap: { showScanner = true }
                    )
                }
            }
        }
        .ignoresSafeArea(.keyboard, edges: .bottom)
        .fullScreenCover(isPresented: $showScanner) {
            OrderScannerPage(
                onClose: { showScanner = false },
                onSuccess: { rawCode in
                    showScanner = false
                    appRouter.routeToOrderVerification(scannedCode: rawCode)
                },
                onFailure: { error in
                    showScanner = false
                    toastCenter.show(error.localizedDescription)
                }
            )
        }
        .task {
            loadedTabs.insert(appRouter.selectedTab)
            await refreshOrderBadge()
        }
        .onChange(of: appRouter.selectedTab) { _, selectedTab in
            loadedTabs.insert(selectedTab)
            guard selectedTab == .orders else { return }
            Task { await refreshOrderBadge() }
        }
        .onChange(of: accountContext.currentScenic?.id) { _, _ in
            Task { await refreshOrderBadge() }
        }
        .onChange(of: accountContext.currentStore?.id) { _, _ in
            Task { await refreshOrderBadge() }
        }
    }

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

/// 自定义 TabBar 模式下的单个 Tab 导航栈，TabBar 只属于根页面内容。
private struct CustomTabNavigationStackHost: View {
    @Environment(AppRouter.self) private var appRouter

    let tab: AppTab
    @Binding var selectedTab: AppTab
    let orderBadgeText: String?
    let onScanTap: () -> Void

    var body: some View {
        NavigationStack(path: appRouter.binding(for: tab)) {
            VStack(spacing: 0) {
                tab.rootView
                    .frame(maxWidth: .infinity, maxHeight: .infinity)

                CustomMainTabBar(
                    selectedTab: $selectedTab,
                    orderBadgeText: orderBadgeText,
                    onScanTap: onScanTap
                )
            }
            .ignoresSafeArea(.keyboard, edges: .bottom)
            .navigationTitle(tab.title)
            .navigationDestination(for: AppRoute.self) { route in
                route.destinationView
                    .toolbar(route.hidesTabBarWhenPushed ? .hidden : .visible, for: .tabBar)
            }
        }
        .environment(appRouter.router(for: tab))
    }
}

/// 单个 Tab 对应的导航栈，供系统和自定义 TabBar 外壳共同复用。
private struct TabNavigationStackHost: View {
    @Environment(AppRouter.self) private var appRouter

    let tab: AppTab

    var body: some View {
        NavigationStack(path: appRouter.binding(for: tab)) {
            tab.rootView
                .navigationTitle(tab.title)
                .navigationDestination(for: AppRoute.self) { route in
                    route.destinationView
                        .toolbar(route.hidesTabBarWhenPushed ? .hidden : .visible, for: .tabBar)
                }
        }
        .environment(appRouter.router(for: tab))
    }
}

/// 自定义 TabBar 中保持已加载 Tab 页面存活的容器。
private struct PreservedTabPage<Content: View>: View {
    let tab: AppTab
    let selectedTab: AppTab
    let isLoaded: Bool
    @ViewBuilder let content: () -> Content

    var body: some View {
        if isLoaded {
            content()
                .frame(maxWidth: .infinity, maxHeight: .infinity)
                .opacity(selectedTab == tab ? 1 : 0)
                .zIndex(selectedTab == tab ? 1 : 0)
                .allowsHitTesting(selectedTab == tab)
                .accessibilityHidden(selectedTab != tab)
        }
    }
}

#Preview {
    MainTabsView()
        .environment(AppRouter())
        .environment(AccountContext())
        .environment(OrdersAPI(client: APIClient()))
        .environment(ToastCenter())
}