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

import Foundation
import UIKit

/// 应用内可导航目标，承载各 Tab 内部的路由目的地。
enum AppRoute: Hashable {
    case placeholder(title: String)
    case home(HomeRoute)
    case profile(ProfileRoute)
    case orders(OrdersRoute)

    /// 返回该路由通过 push 后是否隐藏底部 TabBar。
    var hidesTabBarWhenPushed: Bool {
        true
    }
}

@MainActor
/// UIKit 路由执行策略，描述全局入口应如何选择导航栈。
enum AppNavigationPolicy: Equatable {
    case currentStack
    case tabRoot(AppTab)
    case preserveTab(AppTab)
}

@MainActor
/// 主 Tab 导航宿主协议，由 `MainTabBarController` 提供 UIKit 栈能力。
protocol AppNavigationHost: AnyObject {
    /// 选中指定主 Tab。
    func selectTab(_ tab: AppTab)

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

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

    /// 重置全部 Tab 的导航栈。
    func resetAllStacks()

    /// 将指定订单入口应用到订单根页面。
    func applyOrdersEntry(_ entry: OrdersEntry, scannedCode: String?)
}

@MainActor
/// UIKit 主导航器，以 `UINavigationController.viewControllers` 作为唯一导航事实源。
final class AppNavigator {
    private weak var host: AppNavigationHost?
    private var pendingActions: [(@MainActor (AppNavigationHost) -> Void)] = []

    /// 绑定主 Tab 宿主，并按 FIFO 执行挂载前暂存的全局导航请求。
    func attach(host: AppNavigationHost) {
        self.host = host
        let actions = pendingActions
        pendingActions.removeAll()
        actions.forEach { $0(host) }
    }

    /// 解绑主 Tab 宿主并清理尚未执行的全局导航请求。
    func detach(host: AppNavigationHost? = nil) {
        if let host, self.host !== host {
            return
        }
        self.host = nil
        pendingActions.removeAll()
    }

    /// 切换到指定主 Tab，保留该 Tab 已有导航栈。
    func selectTab(_ tab: AppTab) {
        performOrEnqueue { host in
            host.selectTab(tab)
        }
    }

    /// 在当前或指定来源的导航栈中 push 应用路由。
    func push(_ route: AppRoute, from source: UIViewController?, animated: Bool = true) {
        if let navigationController = source?.navigationController as? TabNavigationController {
            navigationController.push(route: route, animated: animated)
            return
        }

        performOrEnqueue { host in
            guard let navigationController = source?.navigationController as? TabNavigationController
                ?? host.selectedNavigationController()
            else { return }
            navigationController.push(route: route, animated: animated)
        }
    }

    /// 打开首页路由。
    func openHome(_ route: HomeRoute, policy: AppNavigationPolicy = .currentStack, animated: Bool = true) {
        open(.home(route), defaultTab: .home, policy: policy, animated: animated)
    }

    /// 打开个人中心路由。
    func openProfile(_ route: ProfileRoute, policy: AppNavigationPolicy = .currentStack, animated: Bool = true) {
        open(.profile(route), defaultTab: .profile, policy: policy, animated: animated)
    }

    /// 切换到订单 Tab 并应用订单内部入口，可携带全局扫码结果。
    func openOrdersEntry(_ entry: OrdersEntry, scannedCode: String? = nil) {
        performOrEnqueue { host in
            host.selectTab(.orders)
            host.navigationController(for: .orders)?.popToRootViewController(animated: false)
            host.applyOrdersEntry(entry, scannedCode: scannedCode)
        }
    }

    /// 重置全部 Tab 导航栈并清空暂存请求。
    func resetAllStacks() {
        pendingActions.removeAll()
        host?.resetAllStacks()
    }

    /// 执行通用路由打开逻辑。
    private func open(
        _ route: AppRoute,
        defaultTab: AppTab,
        policy: AppNavigationPolicy,
        animated: Bool
    ) {
        performOrEnqueue { host in
            let targetTab: AppTab
            switch policy {
            case .currentStack:
                guard let navigationController = host.selectedNavigationController() else { return }
                navigationController.push(route: route, animated: animated)
                return
            case .tabRoot(let tab):
                targetTab = tab
                host.selectTab(tab)
                guard let navigationController = host.navigationController(for: tab) else { return }
                navigationController.popToRootViewController(animated: false)
                navigationController.push(route: route, animated: animated)
            case .preserveTab(let tab):
                targetTab = tab
                host.selectTab(tab)
                host.navigationController(for: tab)?.push(route: route, animated: animated)
            }

            if targetTab != defaultTab {
                assertionFailure("Route \(route) opened on unexpected tab \(targetTab)")
            }
        }
    }

    /// 主 Tab 已挂载时立即执行，否则暂存至登录后执行。
    private func performOrEnqueue(_ action: @escaping @MainActor (AppNavigationHost) -> Void) {
        if let host {
            action(host)
        } else {
            pendingActions.append(action)
        }
    }
}