import 'dart:async';

import 'package:flutter/material.dart';

import '../../../../core/constants/app_sizes.dart';
import '../../../../core/services/url_opener.dart';
import '../../../../core/theme/app_colors.dart';
import '../../../../core/theme/app_text_styles.dart';
import '../../data/home_repository.dart';
import '../../domain/models/home_data.dart';
import '../../domain/models/link_item.dart';
import '../../domain/models/link_section.dart';
import '../widgets/back_to_top_button.dart';
import '../widgets/link_section_view.dart';
import '../widgets/sidebar_nav.dart';
import '../widgets/top_bar.dart';

/// 首页：可折叠侧栏 + 顶部控制栏 + 分组卡片网格。
///
/// 数据来自后端 `GET /api/nav`，所以页面要表达三种状态：加载中、加载失败
/// （带重试）、加载完成。布局与交互仍然以项目根目录的 `index3.html` 为准。
class HomePage extends StatefulWidget {
  const HomePage({
    super.key,
    required this.repository,
    required this.urlOpener,
  });

  /// 数据来源（当前是 HTTP 实现，测试里注入 mock）。
  final HomeRepository repository;

  /// 打开链接的能力（当前是 Web 实现）。
  final UrlOpener urlOpener;

  @override
  State<HomePage> createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  HomeData? _data;
  String? _error;
  bool _loading = true;

  /// 有对应分区的分组，用于「点导航滚动过去」；数据到了之后才建。
  Map<String, GlobalKey> _sectionKeys = <String, GlobalKey>{};

  final ScrollController _scrollController = ScrollController();
  final TextEditingController _searchController = TextEditingController();

  /// 已展开的分组。原型初始全部收起。
  final Set<String> _openGroupIds = <String>{};

  /// 侧栏是否折叠。原型初始是展开的（body 上没有 sidebar-collapsed）。
  bool _collapsed = false;

  @override
  void initState() {
    super.initState();
    unawaited(_load());
  }

  @override
  void dispose() {
    _scrollController.dispose();
    _searchController.dispose();
    super.dispose();
  }

  /// 向后端取一次数据。失败时把说明留在 `_error` 里给用户看，并允许重试。
  ///
  /// [showLoading] 为 false 时是「静默刷新」：页面继续显示旧内容，
  /// 失败了只提示一句，不会把已经渲染好的页面换成错误页。
  Future<void> _load({bool showLoading = true}) async {
    if (showLoading) {
      setState(() {
        _loading = true;
        _error = null;
      });
    }
    try {
      final HomeData data = await widget.repository.fetchHomeData();
      if (!mounted) {
        return;
      }
      setState(() {
        _data = data;
        _loading = false;
        _error = null;
        _sectionKeys = <String, GlobalKey>{
          for (final LinkSection section in data.sections)
            section.id: GlobalKey(),
        };
      });
    } catch (error) {
      if (!mounted) {
        return;
      }
      if (showLoading) {
        setState(() {
          _loading = false;
          _error = error.toString();
        });
      } else {
        ScaffoldMessenger.of(
          context,
        ).showSnackBar(SnackBar(content: Text('刷新失败：$error')));
      }
    }
  }

  // ---- 交互 ----

  /// `#toggleBtn`：切换 `sidebar-collapsed`。
  void _toggleSidebar() {
    setState(() => _collapsed = !_collapsed);
  }

  /// `.has-sub` 的点击：折叠时先展开侧栏，再切换该分组的 open。
  void _toggleGroup(String groupId) {
    setState(() {
      if (_collapsed) {
        _collapsed = false;
        _openGroupIds.add(groupId);
        return;
      }
      if (!_openGroupIds.remove(groupId)) {
        _openGroupIds.add(groupId);
      }
    });
  }

  /// 点导航叶子：滚到对应分区。
  ///
  /// 后端允许存在没有网站的分组，这类分组在内容区没有对应元素，
  /// 点了不会有任何反应——和原型里那几个空锚点一致。
  void _goToSection(String sectionId) {
    final BuildContext? sectionContext = _sectionKeys[sectionId]?.currentContext;
    if (sectionContext == null) {
      return;
    }
    unawaited(
      Scrollable.ensureVisible(
        sectionContext,
        duration: const Duration(milliseconds: 300),
        curve: Curves.easeOutCubic,
      ),
    );
  }

  void _openItem(LinkItem item) => widget.urlOpener.open(item.url);

  /// 「提交网站」跳到后端配好的收集入口（Mattermost 之类）。
  ///
  /// 地址在 `data/nav.json` 的 `site.submitUrl`；没配就什么都不做。
  void _openSubmitUrl(HomeData data) {
    if (data.submitUrl.isEmpty) {
      return;
    }
    widget.urlOpener.open(data.submitUrl);
  }

  void _backToTop() {
    _scrollController.animateTo(
      0,
      duration: const Duration(milliseconds: 400),
      curve: Curves.easeOutCubic,
    );
  }

  // ---- 布局 ----

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: AppColors.background,
      body: _buildBody(),
    );
  }

  Widget _buildBody() {
    if (_loading) {
      return const _StatusView(message: '正在加载…', loading: true);
    }
    final String? error = _error;
    if (error != null) {
      return _StatusView(title: '加载失败', message: error, onRetry: _load);
    }
    return _buildLoaded(_data!);
  }

  Widget _buildLoaded(HomeData data) {
    return Stack(
      children: <Widget>[
        Row(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            SidebarNav(
              siteName: data.siteName,
              navNodes: data.navNodes,
              // 原型把 active 写死在第一个条目上。
              activeSectionId: data.activeSectionId,
              collapsed: _collapsed,
              openGroupIds: _openGroupIds,
              onToggleGroup: _toggleGroup,
              onSectionSelected: _goToSection,
              onSubmitSite: () => _openSubmitUrl(data),
              onToggleCollapse: _toggleSidebar,
            ),
            Expanded(child: _buildMain(data)),
          ],
        ),
        Positioned(
          right: AppSizes.backToTopOffset,
          bottom: AppSizes.backToTopOffset,
          child: BackToTopButton(onTap: _backToTop),
        ),
      ],
    );
  }

  Widget _buildMain(HomeData data) {
    return SingleChildScrollView(
      controller: _scrollController,
      padding: const EdgeInsets.fromLTRB(
        AppSizes.contentPaddingHorizontal,
        AppSizes.contentPaddingTop,
        AppSizes.contentPaddingHorizontal,
        AppSizes.contentPaddingBottom,
      ),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.start,
        children: <Widget>[
          TopBar(
            searchController: _searchController,
            searchHint: data.searchHint,
            sidebarCollapsed: _collapsed,
            onToggleSidebar: _toggleSidebar,
          ),
          for (final LinkSection section in data.sections)
            Padding(
              // 原型里每个 .grid 都带 margin-bottom: 36px。
              padding: const EdgeInsets.only(bottom: AppSizes.sectionGap),
              child: LinkSectionView(
                key: _sectionKeys[section.id],
                section: section,
                onOpen: _openItem,
              ),
            ),
        ],
      ),
    );
  }
}

/// 加载中 / 加载失败时占满内容区的提示。
class _StatusView extends StatelessWidget {
  const _StatusView({
    required this.message,
    this.title,
    this.loading = false,
    this.onRetry,
  });

  final String message;
  final String? title;
  final bool loading;
  final VoidCallback? onRetry;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Padding(
        padding: const EdgeInsets.all(AppSizes.contentPaddingHorizontal),
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            if (loading) ...<Widget>[
              const SizedBox(
                width: 20,
                height: 20,
                child: CircularProgressIndicator(strokeWidth: 2),
              ),
              const SizedBox(height: AppSizes.gridGap),
            ],
            if (title != null) ...<Widget>[
              Text(title!, style: AppTextStyles.emptyTitle),
              const SizedBox(height: 6),
            ],
            Text(
              message,
              style: AppTextStyles.emptyMessage,
              textAlign: TextAlign.center,
            ),
            if (onRetry != null) ...<Widget>[
              const SizedBox(height: AppSizes.gridGap),
              _RetryButton(onTap: onRetry!),
            ],
          ],
        ),
      ),
    );
  }
}

/// 「重试」按钮：跟前端其它次级按钮同一套描边样式。
class _RetryButton extends StatefulWidget {
  const _RetryButton({required this.onTap});

  final VoidCallback onTap;

  @override
  State<_RetryButton> createState() => _RetryButtonState();
}

class _RetryButtonState extends State<_RetryButton> {
  bool _hovered = false;

  @override
  Widget build(BuildContext context) {
    return MouseRegion(
      cursor: SystemMouseCursors.click,
      onEnter: (_) => setState(() => _hovered = true),
      onExit: (_) => setState(() => _hovered = false),
      child: GestureDetector(
        onTap: widget.onTap,
        child: AnimatedContainer(
          duration: AppSizes.transition,
          padding: const EdgeInsets.symmetric(horizontal: 16, vertical: 8),
          decoration: BoxDecoration(
            color: _hovered ? AppColors.primaryFaint : Colors.transparent,
            border: Border.all(color: AppColors.primary),
            borderRadius: BorderRadius.circular(AppSizes.navItemRadius),
          ),
          child: Text(
            '重试',
            style: AppTextStyles.navItem.copyWith(color: AppColors.primary),
          ),
        ),
      ),
    );
  }
}