import 'dart:convert';

import 'package:http/http.dart' as http;

import '../domain/models/home_data.dart';
import '../domain/models/link_item.dart';
import '../domain/models/link_section.dart';
import '../domain/models/nav_node.dart';
import '../domain/models/submit_site_draft.dart';
import 'home_repository.dart';

/// 后端地址。
///
/// 默认指向本机后端，打包时用 `--dart-define=NAVIUS_API_BASE=https://…` 覆盖：
/// `flutter build web --dart-define=NAVIUS_API_BASE=https://api.example.com`
const String _apiBase = String.fromEnvironment(
  'NAVIUS_API_BASE',
  defaultValue: 'http://127.0.0.1:8080',
);

/// 接口没给站点信息时的兜底值。正常情况下这两个值来自 `GET /api/nav` 的
/// `site` 字段（后端 `data/site.json`）。
const String _fallbackSiteName = 'Suxing Nav';
const String _fallbackSearchHint = '输入关键字搜索全网资源...';

/// 从后端读取首页数据。
class HttpHomeRepository implements HomeRepository {
  HttpHomeRepository({String? baseUrl, http.Client? client})
    : _baseUrl = baseUrl ?? _apiBase,
      _client = client ?? http.Client();

  final String _baseUrl;
  final http.Client _client;

  @override
  Future<HomeData> fetchHomeData() async {
    final Uri uri = Uri.parse('$_baseUrl/api/nav');
    final http.Response response;
    try {
      response = await _client.get(uri).timeout(const Duration(seconds: 10));
    } catch (error) {
      throw HomeFailure('连不上后端（$_baseUrl）：$error');
    }
    if (response.statusCode != 200) {
      throw HomeFailure(
        '后端返回 ${response.statusCode}：${_errorMessage(response)}',
      );
    }

    final Object? decoded;
    try {
      decoded = jsonDecode(utf8.decode(response.bodyBytes));
    } catch (error) {
      throw const HomeFailure('后端返回的不是合法 JSON');
    }
    if (decoded is! Map<String, dynamic>) {
      throw const HomeFailure('后端返回的结构不对：顶层不是对象');
    }
    final Object? groups = decoded['groups'];
    if (groups is! List) {
      throw const HomeFailure('后端返回的结构不对：缺少 groups 数组');
    }
    final Object? rawSite = decoded['site'];
    return _toHomeData(
      groups,
      rawSite is Map<String, dynamic> ? rawSite : const <String, dynamic>{},
    );
  }

  @override
  Future<void> submitSite(SubmitSiteDraft draft) async {
    final Uri uri = Uri.parse('$_baseUrl/api/sites');
    final http.Response response;
    try {
      response = await _client
          .post(
            uri,
            headers: const <String, String>{
              'content-type': 'application/json; charset=utf-8',
            },
            body: jsonEncode(draft.toJson()),
          )
          .timeout(const Duration(seconds: 10));
    } catch (error) {
      throw HomeFailure('连不上后端（$_baseUrl）：$error');
    }
    if (response.statusCode != 201) {
      throw HomeFailure(
        '提交失败（${response.statusCode}）：${_errorMessage(response)}',
      );
    }
  }

  @override
  Future<void> updateSite(String id, SubmitSiteDraft draft) async {
    final Uri uri = Uri.parse('$_baseUrl/api/sites/${Uri.encodeComponent(id)}');
    final http.Response response;
    try {
      response = await _client
          .patch(
            uri,
            headers: const <String, String>{
              'content-type': 'application/json; charset=utf-8',
            },
            body: jsonEncode(draft.toJson()),
          )
          .timeout(const Duration(seconds: 10));
    } catch (error) {
      throw HomeFailure('连不上后端（$_baseUrl）：$error');
    }
    if (response.statusCode != 200) {
      throw HomeFailure(
        '保存失败（${response.statusCode}）：${_errorMessage(response)}',
      );
    }
  }

  @override
  Future<void> deleteSite(String id) async {
    final Uri uri = Uri.parse('$_baseUrl/api/sites/${Uri.encodeComponent(id)}');
    final http.Response response;
    try {
      response = await _client.delete(uri).timeout(const Duration(seconds: 10));
    } catch (error) {
      throw HomeFailure('连不上后端（$_baseUrl）：$error');
    }
    if (response.statusCode != 204) {
      throw HomeFailure(
        '删除失败（${response.statusCode}）：${_errorMessage(response)}',
      );
    }
  }
}

/// 把 `/api/nav` 的响应映射成前端模型。
///
/// 分组直接变成侧栏的导航树；**只有挂着网站的组才会进入内容区**，
/// 空分组只在侧栏里当导航项——这与原型里那几个没有内容的锚点一致。
HomeData _toHomeData(List<Object?> groups, Map<String, dynamic> siteMeta) {
  final List<NavNode> navNodes = <NavNode>[];
  final List<LinkSection> sections = <LinkSection>[];
  for (final Object? group in groups) {
    if (group is Map<String, dynamic>) {
      navNodes.add(_navNode(group, parentTitle: '', sections: sections));
    }
  }
  return HomeData(
    siteName: siteMeta['name'] as String? ?? _fallbackSiteName,
    searchHint: siteMeta['searchHint'] as String? ?? _fallbackSearchHint,
    navNodes: navNodes,
    sections: sections,
    submitUrl: siteMeta['submitUrl'] as String? ?? '',
  );
}

NavNode _navNode(
  Map<String, dynamic> json, {
  required String parentTitle,
  required List<LinkSection> sections,
}) {
  final String id = json['id'] as String? ?? '';
  final String title = json['title'] as String? ?? '';

  // 子分组在内容区的标题带上父级（「素材资源 - UI 设计」），
  // 侧栏里仍然只显示「UI 设计」——和原型一致。
  final String sectionTitle = parentTitle.isEmpty
      ? title
      : '$parentTitle - $title';
  final List<LinkItem> sites = _sites(json);
  if (sites.isNotEmpty && id.isNotEmpty) {
    sections.add(LinkSection(id: id, title: sectionTitle, items: sites));
  }

  final List<NavNode> children = <NavNode>[];
  final Object? rawChildren = json['children'];
  if (rawChildren is List) {
    for (final Object? child in rawChildren) {
      if (child is Map<String, dynamic>) {
        children.add(
          _navNode(child, parentTitle: title, sections: sections),
        );
      }
    }
  }
  return NavNode(
    id: id,
    title: title,
    children: children,
    // 后端给了 editable；缺省按内置处理（内置不可选）。
    editable: json['editable'] as bool? ?? false,
  );
}

List<LinkItem> _sites(Map<String, dynamic> json) {
  final Object? raw = json['sites'];
  if (raw is! List) {
    return const <LinkItem>[];
  }
  final List<LinkItem> items = <LinkItem>[];
  for (final Object? site in raw) {
    if (site is! Map<String, dynamic>) {
      continue;
    }
    final String id = site['id'] as String? ?? '';
    final String title = site['title'] as String? ?? '';
    final String url = site['url'] as String? ?? '';
    if (id.isEmpty || title.isEmpty || url.isEmpty) {
      // 缺字段的条目直接跳过：后端已经校验过，这里只是不想让一条坏数据
      // 把整个页面打挂。
      continue;
    }
    items.add(
      LinkItem(
        id: id,
        title: title,
        url: url,
        categoryId: site['categoryId'] as String? ?? '',
        description: site['description'] as String? ?? '',
        editable: site['editable'] as bool? ?? false,
      ),
    );
  }
  return items;
}

/// 后端出错时统一返回 `{"error":"…"}`，能取到就显示那句话。
///
/// 用 `bodyBytes` 自己按 UTF-8 解，而不是 `response.body`：后者在响应没带
/// charset 时会退回 latin1，中文会变成乱码。
String _errorMessage(http.Response response) {
  final String body = utf8.decode(response.bodyBytes, allowMalformed: true);
  try {
    final Object? decoded = jsonDecode(body);
    if (decoded is Map<String, dynamic> && decoded['error'] is String) {
      return decoded['error'] as String;
    }
  } catch (_) {
    // 不是 JSON 就退回原文。
  }
  return body.isEmpty ? '没有返回内容' : body;
}